CONCEPTUAL ECOLOGY AND INVASION BIOLOGY: RECIPROCAL APPROACHES TO NATURE
INVADING NATURE SPRINGER SERIES IN INVASION ...
18 downloads
772 Views
5MB Size
Report
This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!
Report copyright / DMCA form
CONCEPTUAL ECOLOGY AND INVASION BIOLOGY: RECIPROCAL APPROACHES TO NATURE
INVADING NATURE SPRINGER SERIES IN INVASION ECOLOGY Volume 1 Series Editor: JAMES A. DRAKE University of Tennessee, Knoxville, TN, U.S.A.
Conceptual Ecology and Invasion Biology: Reciprocal Approaches to Nature Edited by
MARC WILLIAM CADOTTE University of Tennessee, Knoxville, U.S.A.
SEAN M. MCMAHON University of Tennessee, Knoxville, U.S.A. and
TADASHI FUKAMI University of Hawaii at Manoa, Honolulu, U.S.A.
A C.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN-10 ISBN-13 ISBN-10 ISBN-13 ISBN-10 ISBN-13
1-4020-4158-6 (PB) 978-1-4020-4158-7 (PB) 1-4020-4157-8 (HB) 978-1-4020-4157-0 (HB) 1-4020-4925-0 ( e-book) 978-1-4020-4925-5 (e-book)
Published by Springer, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. www.springer.com
Printed on acid-free paper
Cover design by Jeff McMahon All Rights Reserved © 2006 Springer No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed in the Netherlands.
#ONTENTS #ONTRIBUTORS &OREWORD 0REFACE
IX XV XVII
)NTRODUCTION HISTORY AND TERMINOLOGY
4RACKING THE TRACTABLE USING INVASIONS TO GUIDE THE EXPLORATION OF CONCEPTUAL ECOLOGY 3EAN - -C-AHON -ARC 7 #ADOTTE AND 4ADASHI &UKAMI
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES -ARC 7 #ADOTTE
)NVASION BIOLOGY THE PURSUIT OF SCIENCE AND CONSERVATION -ARK ! $AVIS
)NVASIVENESS IN EXOTIC PLANTS IMMIGRATION AND NATURALIZATION IN AN ECOLOGICAL CONTINUUM (ELEN 4 -URPHY *EREMY 6AN$ER7AL ,ESLEY ,OVETT $OUST AND *ON ,OVETT $OUST
0OPULATIONS AT PLAY
$ENSITY DEPENDENCE IN INVASIVE PLANTS DEMOGRAPHY HERBIVORY SPREAD AND EVOLUTION 9VONNE - "UCKLEY AND *ESSICA -ETCALF V
VI
#ONTENTS
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS 2OBERT 0 &RECKLETON 0ETER - $OWLING AND .ICHOLAS + $ULVY ,OCAL INTERACTIONS AND INVASION DYNAMICS POPULATION GROWTH IN SPACE AND TIME $AVID * -URRELL
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA -ARK ! ,EWIS -ICHAEL ' .EUBERT (AL #ASWELL *AMES 3 #LARK AND +ATRIONA 3HEA
4HE ROLE OF EVOLUTIONARY GENETICS IN STUDIES OF PLANT INVASIONS +RISTINA ! 3CHIERENBECK AND -ALIKA , !ÕNOUCHE
5NWELCOMED VISITOR SPECIES INTERACTIONS
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS AND THEIR COMMUNITY CONSEQUENCES A THEORETICAL CONSIDERATION ON THE ROLE OF ADAPTATION IN BIOLOGICAL INVASION -ICHIO +ONDOH 5SE OF BIOLOGICAL INVASIONS AND THEIR CONTROL TO STUDY THE DYNAMICS OF INTERACTING POPULATIONS &RANCK #OURCHAMP AND 3TEPHANE #AUT
)NVASIBILITY OF SEED PREDATORS ON SYNCHRONIZED AND INTERMITTENT SEED PRODUCTION OF HOST PLANTS !KIKO 3ATAKE /TTAR . "JRNSTAD AND 9OH )WASA
)NVASIONS AND THE REGULATION OF PLANT POPULATIONS BY PATHOGENS 'REGORY 3 'ILBERT AND )NGRID - 0ARKER %XPLORING THE RELATIONSHIP BETWEEN NICHE BREADTH AND INVASION SUCCESS $IEGO 0 6É ZQUEZ
#ONTENTS
)NTERACTIONS BETWEEN INVASIVE PLANTS AND SOIL ECOSYSTEMS POSITIVE FEEDBACKS AND THEIR POTENTIAL TO PERSIST !NDREA 3 4HORPE AND 2AGAN - #ALLAWAY
VII
)NVASION BIOLOGY AS A COMMUNITY PROCESS MESSAGES FROM MICROBIAL MICROCOSMS 0HILIP ( 7ARREN 2ICHARD ,AW AND !NITA * 7EATHERBY
,ARGE SCALE CONSEQUENCES AND PATTERNS OF INVASIONS
5NDERSTANDING INVASIONS IN PATCHY HABITATS THROUGH METAPOPULATION THEORY +ARIN # (ARDING *OHN - -C.AMARA AND 2OBERT $ (OLT
#OMPETITION AND THE ASSEMBLY OF INTRODUCED BIRD COMMUNITIES 2ICHARD 0 $UNCAN AND $AVID - &ORSYTH
2OOM FOR ONE MORE %VIDENCE FOR INVASIBILITY AND SATURATION IN ECOLOGICAL COMMUNITIES 3COTT ! 3MITH AND *ONATHAN " 3HURIN
4HE BIOGEOGRAPHY OF NATURALIZED SPECIES AND THE SPECIES AREA RELATIONSHIP RECIPROCAL INSIGHTS TO BIOGEOGRAPHY AND INVASION BIOLOGY $OV & 3AX AND 3TEVEN $ 'AINES
3YNTHESIS
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS -ARC 7 #ADOTTE 4ADASHI &UKAMI AND 3EAN - -C-AHON
)NDEX
#ONTRIBUTORS -ALIKA , !ÕNOUCHE $EPARTMENT OF %VOLUTIONARY %COLOGY 'ENOME %VOLUTION AND 3PECIATION LAB 5-2 #.23 5NIVERSITY OF 2ENNES #AMPUS DE "EAULIEU 2ENNES CEDEX &RANCE /TTAR . "JRNSTAD $EPARTMENT OF %NTOMOLOGY AND "IOLOGY 4HE 0ENNSYLVANIA 3TATE 5NIVERSITY 5NIVERSITY 0ARK 0! 53! 9VONNE - "UCKLEY 4HE %COLOGY #ENTRE (INES "UILDING 5NIVERSITY OF 1UEENSLAND 3T ,UCIA "RISBANE 1,$ !USTRALIA -ARC 7 #ADOTTE $EPARTMENT OF %COLOGY AND %VOLUTIONARY "IOLOGY $ABNEY (ALL 5NIVERSITY OF 4ENNESSEE +NOXVILLE 4. 53! 2AGAN - #ALLAWAY $IVISION OF "IOLOGICAL 3CIENCES 4HE 5NIVERSITY OF -ONTANA -ISSOULA -4 53! (AL #ASWELL 7OODS (OLE /CEANOGRAPHIC )NSTITUTION 7OODS (OLE -! 53! *AMES 3 #LARK .ICHOLAS 3CHOOL OF THE %NVIRONMENT AND %ARTH 3CIENCES ! ,32# "OX $UKE 5NIVERSITY $URHAM .# 53!
IX
X
#ONTRIBUTORS
3TEPHANE #AUT %COLOGIE 3YSTÏMATIQUE %VOLUTION "ÊT 5NIVERSITÏ 0ARIS 3UD 8) & /RSAY #EDEX &RANCE &RANCK #OURCHAMP %COLOGIE 3YSTÏMATIQUE %VOLUTION "ÊT 5NIVERSITÏ 0ARIS 3UD 8) & /RSAY #EDEX &RANCE -ARK ! $AVIS $EPARTMENT OF "IOLOGY -ACALESTER #OLLEGE 3AINT 0AUL -. 53! 0ETER - $OWLING .37 !GRICULTURE !USTRALIAN #ENTRE FOR 7EED 2ESEARCH AND #2# FOR 7EED -ANAGEMENT 3YSTEM !GRICULTURAL AND 6ETERINARY #ENTRE &OREST 2OAD /RANGE .37 .37 !USTRALIA .ICHOLAS + $ULVY %COSYSTEM 2ESEARCH 'ROUP #ENTRE FOR %NVIRONMENT &ISHERIES AND !QUACULTURE 3CIENCE 0AKElELD 2OAD ,OWESTOFT 3UFFOLK .2 /(4 5+ 2ICHARD 0 $UNCAN %COLOGY AND %NTOMOLOGY 'ROUP 0/ "OX ,INCOLN 5NIVERSITY #ANTERBURY .EW :EALAND AND ,ANDCARE 2ESEARCH 0/ "OX ,INCOLN .EW :EALAND $AVID - &ORSYTH !RTHUR 2YLAH )NSTITUTE FOR %NVIRONMENTAL 2ESEARCH $EPARTMENT OF 3USTAINABILITY AND %NVIRONMENT "ROWN 3TREET (EIDELBERG 6ICTORIA !USTRALIA 2OBERT 0 &RECKLETON $EPARTMENT OF :OOLOGY 5NIVERSITY OF /XFORD 3OUTH 0ARKS 2OAD /XFORD /8 03 5+ 4ADASHI &UKAMI $EPARTMENT OF :OOLOGY 5NIVERSITY OF (AWAII AT -ANOA -C#ARTHY -ALL %DMONDSON (ONOLULU () 53! 3TEVEN $ 'AINES $EPARTMENT OF %COLOGY %VOLUTION AND -ARINE "IOLOGY 5NIVERSITY OF #ALIFORNIA 3ANTA "ARBARA #! 53!
#ONTRIBUTORS
XI
'REGORY 3 'ILBERT %NVIRONMENTAL 3TUDIES 5NIVERSITY OF #ALIFORNIA 3ANTA #RUZ #! 53! +ARIN # (ARDING $EPARTMENT OF -ARINE %COLOGY 'ÚTEBORG 5NIVERSITY "OX 'ÚTEBORG 3WEDEN 2OBERT $ (OLT $EPARTMENT OF :OOLOGY 5NIVERSITY OF &LORIDA "ARTRAM (ALL 0/ "OX 'AINESVILLE &LORIDA 53! 9OH )WASA $EPARTMENT OF "IOLOGY &ACULTY OF 3CIENCES +YUSHU 5NIVERSITY &UKUOKA *APAN -ICHIO +ONDOH $EPARTMENT OF %NVIRONMENTAL 3OLUTION 4ECHNOLOGY &ACULTY OF 3CIENCE AND 4ECHNOLOGY 2YUKOKU 5NIVERSITY 9OKOYA 3ETA /E CHO /TSU *APAN AND #ENTER FOR %COLOGICAL 2ESEARCH +YOTO 5NIVERSITY +AMITANAKAMI /TSU *APAN 2ICHARD ,AW $EPARTMENT OF "IOLOGY 5NIVERSITY OF 9ORK 0/ "OX 9ORK 9/ 97 5+ -ARK ! ,EWIS $EPARTMENT OF -ATHEMATICAL AND 3TATISTICAL 3CIENCES 5NIVERSITY OF !LBERTA #ENTRAL !CADEMIC "UILDING %DMONTON !" 4' ' #ANADA *ON ,OVETT $OUST $EPARTMENT OF "IOLOGY 5NIVERSITY OF 7INDSOR 7INDSOR /NTARIO ." 0 #ANADA ,ESLEY ,OVETT $OUST $EPARTMENT OF "IOLOGY 5NIVERSITY OF 7INDSOR 7INDSOR /NTARIO ." 0 #ANADA 3EAN - -C-AHON $EPARTMENT OF %COLOGY AND %VOLUTIONARY "IOLOGY $ABNEY (ALL 5NIVERSITY OF 4ENNESSEE +NOXVILLE 4. 53!
XII
#ONTRIBUTORS
*OHN - -C.AMARA $EPARTMENT OF -ATHEMATICS 5NIVERSITY OF "RISTOL 5NIVERSITY 7ALK "RISTOL "3 47 5+ *ESSICA -ETCALF $EPARTMENT OF "IOLOGY )MPERIAL #OLLEGE ,ONDON 3ILWOOD 0ARK #AMPUS !SCOT "ERKSHIRE 3, 09 5+ (ELEN -URPHY $EPARTMENT OF "IOLOGY 5NIVERSITY OF 7INDSOR 7INDSOR /NTARIO ." 0 #ANADA 0RESENT ADDRESS #3)2/ 3USTAINABLE %COSYSTEMS 0/ "OX !THERTON 1,$ !USTRALIA $AVID *OHN -URRELL .%2# #ENTRE FOR 0OPULATION "IOLOGY )MPERIAL #OLLEGE ,ONDON 3ILWOOD 0ARK #AMPUS !SCOT "ERKSHIRE 3, 09 5+ -ICHAEL ' .EUBERT 7OODS (OLE /CEANOGRAPHIC )NSTITUTION 7OODS (OLE -! 53! )NGRID - 0ARKER %COLOGY AND %VOLUTIONARY "IOLOGY 5NIVERSITY OF #ALIFORNIA 3ANTA #RUZ #! 53! !KIKO 3ATAKE #ENTER FOR %COLOGICAL 2ESEARCH +YOTO 5NIVERSITY /TSU *APAN $OV & 3AX )NSTITUTE OF %COLOGY 5NIVERSITY OF 'EORGIA !THENS 'EORGIA 53! +RISTINA ! 3CHIERENBECK $EPARTMENT OF "IOLOGICAL 3CIENCES #ALIFORNIA 3TATE 5NIVERSITY #HICO #HICO #! 53! +ATRIONA 3HEA "IOLOGY $EPARTMENT 0ENNSYLVANIA 3TATE 5NIVERSITY -UELLER ,AB 5NIVERSITY 0ARK 0! 53!
#ONTRIBUTORS
XIII
*ONATHAN " 3HURIN $EPARTMENT OF :OOLOGY 5NIVERSITY OF "RITISH #OLUMBIA 5NIVERSITY "LVD 6ANCOUVER "# 64 : #ANADA 3COTT ! 3MITH $EPARTMENT OF "IOLOGY -C'ILL 5NIVERSITY !VENUE $R 0ENlELD -ONTREAL 1UEBEC (! " #ANADA !NDREA 3 4HORPE $IVISION OF "IOLOGICAL 3CIENCES 4HE 5NIVERSITY OF -ONTANA -ISSOULA -4 53! *EREMY 6AN$ER7AL $EPARTMENT OF "IOLOGY 5NIVERSITY OF 7INDSOR 7INDSOR /NTARIO ." 0 #ANADA $IEGO 0 6É ZQUEZ )NSTITUTO !RGENTINO DE )NVESTIGACIONES DE LAS :ONAS !RIDAS #ENTRO 2EGIONAL DE )NVESTIGACIONES #IENTIlCAS Y 4ECNOLOGICAS !V 2UIZ ,EAL SN -ENDOZA !RGENTINA 0HILIP ( 7ARREN $EPARTMENT OF !NIMAL AND 0LANT 3CIENCES 5NIVERSITY OF 3HEFlELD 3HEFlELD 3 4. 5+ !NITA 7EATHERBY 4HE 0ONDS #ONSERVATION 4RUST 0OLICY AND 2ESEARCH CO "-3 /XFORD "ROOKES 5NIVERSITY 'IPSY ,ANE (EADINGTON /XFORD /8 "0 5+
&OREWORD h7HEN ) TOOK THIS PLOT OF LAND lVE YEARS AGO v HE SAID h) WAS DISAPPOINTED TO lND THAT INSTEAD OF ITS BEING ONE WITH THE RICH SANDY SOIL OF THE DISTRICT IT WAS PRACTICALLY A POCKET OF CLAY WHICH HAD TO BE PUT UNDER TREATMENT BEFORE IT WOULD YIELD THE RESULT ) DESIRED ) HAVE BEEN FAIRLY SUC CESSFUL AND NOW HAVE MORE THAN TWO HUNDRED SUBTROPICAL SHRUBS mOURISHING OUT THERE IN THE GROUNDS )T HAS BEEN AN EXPERIMENT IN ACCLIMATISATION WITH WHICH ) AM WELL PLEASED -ANY OF THE PLANTS CAME FROM !USTRALIA AND .EW :EALAND )N MOST CASES ) HAVE BOUGHT THE SEED AND REARED THEM ENTIRELY BY MYSELFv !LFRED 2USSEL 7ALLACE FROM AN INTERVIEW BY % ( 2ANN
1 7HAT ARE THE CHARACTERISTICS OF A GOOD INVADER ! )T DEPENDS 1 $EPENDS ON WHAT ! 4HAT DEPENDS TOO "IOLOGICAL INVASION HAS BECOME ONE OF THOSE RARE THEMES SO PROFOUND IN ITS IMPLI CATIONS AND SCOPE THAT IT CUTS A BROAD PATH ACROSS THE ACADEMIC DISCIPLINES &ROM GENES TO ECOSYSTEMS AND ECONOMICS TO LAW SPECIES INCURSIONS HAVE CONFRONTED THE GLOBAL COMMUNITY WITH A MOST TRANSCENDENT 'ORDIAN KNOT /URS IS A PECULIAR KNOT HOWEVER AS INVADERS COLONIZE ECOLOGICAL SYSTEMS THAT HAVE BEEN FASHIONED FROM STRANDS OF COMPLEXITY WITH ORIGINS IN EVOLUTIONARY TIME ! HALF CENTURY HAS PASSED SINCE THE PUBLICATION OF %LTONS DELIGHTFUL IF NOT FOREBODING TREATISE /F COURSE %LTONS ASSESSMENT WAS CORRECT AND INDEED THE PROBLEM IS EVEN GREATER TODAY "IOLOGICAL INVASIONS HAVE BECOME A PIVOTAL FORCE IN DIRECTING THE FUTURE EXPRESSION OF NATURE 7HILE CONSIDERABLE PROGRESS HAS BEEN MADE GENERALITY REMAINS ELUSIVE PREDICTION HIT OR MISS AND INVASIONS ARE PROCEEDING LARGELY UNCHECKED XV
XVI
&OREWORD
!DOPTING AN INTEGRATIVE APPROACH #ONCEPTUAL %COLOGY AND )NVASIONS "IOLOGY 2ECIPROCAL !PPROACHES TO .ATURE OFFERS ESSENTIAL INSIGHTS INTO THE TOPOLOGY OF OUR ECOLOGICAL KNOT 4HE EDITORS HAVE BROUGHT TOGETHER A SUPERB CAST OF SCIENTISTS WITH A SINGULAR AIM ORCHESTRATING THE DIVERSITY OF APPROACHES TO BIOLOGICAL INVA SIONS INTO A MORE COHERENT AND SYNTHETIC WHOLE 7HAT EMERGES FROM THIS EFFORT IS COMPELLING FRAMEWORK THAT CAPTURES THE INTRICACY AND NUANCE OF THE PROCESSES DYNAMICS AND MECHANISMS AT PLAY WHEN SPECIES INVADE NATURE 7HILE NO ONE WOULD ARGUE THAT THIS FRAMEWORK IS COMPLETE IT IS CLEAR THAT ANY SOLUTION TO THE PROBLEM OF BIOLOGICAL INVASIONS IS FOUNDED HEREIN 4HIS BOOK IS THE INAUGURAL VOLUME IN 3PRINGERS )NVADING .ATURE SERIES AND ) AM PLEASED TO HAVE HAD THE OPPORTUNITY TO INTRODUCE BOTH
*AMES $RAKE 3ERIES %DITOR
0REFACE (UMAN ACTIVITIES AFFECT NATURAL SYSTEMS IN EVERY CORNER OF THE GLOBE AND ONE OF THE MOST WIDESPREAD AND POTENTIALLY DISRUPTIVE OF THESE IS THE INTRODUCTION OF NON INDIGENOUS SPECIES INTO NEW ENVIRONMENTS 4HESE INTRODUCTIONS CAN HAVE PROFOUND CONSEQUENCES FOR RESIDENT POPULATIONS COMMUNITY DYNAMICS AND ECO SYSTEM FUNCTION /VER AND ABOVE THE NEED TO UNDERSTAND HOW A NON INDIGENOUS SPECIES CAN AFFECT A NATIVE COMMUNITY INTRODUCTIONS OFFER ECOLOGISTS THE POTENTIAL TO LEARN ABOUT HOW COMMUNITIES ARE PUT TOGETHER HOW SPECIES CONTRIBUTE TO ECOSYSTEM FUNCTION OR HOW POPULATIONS EVOLVE IN THE FACE OF NOVEL ENVIRONMENTS AND NOVEL SPECIES *UST LIKE THE RAILROAD SPIKE THAT PIERCED 0HINEAS 'AGES SKULL TAUGHT PHYSICIANS MUCH ABOUT THE FUNCTION OF THE CEREBRAL CORTEX ENVIRONMENTAL PERTURBATIONS CAN TEACH US ABOUT NATURAL SYSTEMS )NVASIONS CAN INFORM ECOLOGI CAL THEORY BY SERVING AS NATURAL EXPERIMENTS /N THE OTHER HAND MODERN DAY ECOLOGISTS USE SOPHISTICATED CONCEPTUAL TOOLS TO AID IN THE UNDERSTANDING OF THE FUNCTIONING OF NATURAL SYSTEMS 4HESE TOOLS WE FEEL HAVE BEEN LARGELY UNDER UTILIZED IN UNDERSTANDING SPECIES INVASIONS 7E SEE HERE THE POTENTIAL FOR A RECIPROCAL APPROACH TO GAIN A DEEPER UNDERSTAND ING OF HOW ECOLOGICAL SYSTEMS ARE PUT TOGETHER 7E HAVE ASSEMBLED AN EXCELLENT GROUP OF AUTHORS THAT EACH IN THEIR OWN WAY ATTEMPT TO USE THEIR TOOLS TO EXPLORE THIS RECIPROCAL RELATIONSHIP 4HE AUTHORS IN THIS VOLUME WERE INVITED BECAUSE OF THEIR RECENT PUBLICATIONS WHICH SHOW THEIR USE OF NOVEL APPROACHES TO EITHER UNDERSTANDING THE CAUSES AND CONSEQUENCES OF SPECIES INVASIONS OR ELSE USE CONCEPTUAL TOOLS TO UNDERSTAND HOW NATURAL SYSTEMS FUNCTION 7E ASKED AUTHORS REGARDLESS OF THEIR INDIVIDUAL APPROACHES TO THINK ABOUT THIS RECIPROCAL RELATIONSHIP BETWEEN INVASIONS AND THEORY 4HE CHAPTERS HERE USE EXAMPLES FROM NUMEROUS ORGANISMS ECOLOGICAL SYSTEMS AND GEOGRAPHIC LOCATIONS AND ARE EVENLY SPLIT BETWEEN THEORY AND NATURAL EXAMPLES 4HIS VOLUME COULD NOT HAVE BEEN POSSIBLE WITHOUT THE INVOLVEMENT OF OTHERS 7E ARE GRATEFUL lRST AND FOREMOST TO THE AUTHORS FOR PRODUCING SUCH lNE WORK FOR US 7E WISH TO THANK THE CHAPTER REVIEWERS WHO AS PER USUAL IN SCIENCE SELmESSLY REVIEWED CHAPTERS AND GREATLY IMPROVED THE QUALITY OF THIS BOOK 7E OFFER A SPE CIAL THANKS TO THE SERIES EDITOR AND OUR MENTOR *IM $RAKE WHO ALLOWED US TO FOCUS OUR CREATIVE ENERGIES ON TO THIS PROJECT AND TO AGREE TO MAKE THIS THE PREMIERE XVII
XVIII
0REFACE
VOLUME OF THIS BOOK SERIES &INALLY 3UZANNE -EKKING AND -ARTINE VAN "EZOOIJEN AT 3PRINGER FORMED A SUPREMELY ENCOURAGING AND WELL ORGANIZED PUBLISHING TEAM INSTRUMENTAL IN MAKING THIS BOOK A REALITY
0:& 600 .QR[YLOOH7HQQHVVHH -XO\
7) /LQFROQ1HZ=HDODQG
#HAPTER ONE
4RACKING THE TRACTABLE USING INVASIONS TO GUIDE THE EXPLORATION OF CONCEPTUAL ECOLOGY 3 - -C-AHON - 7 #ADOTTE AND 4 &UKAMI
).42/$5#4)/. /UR UNDERSTANDING OF THE COMPLEX FUNCTIONING OF HUMAN PHYSIOLOGY NEUROLOGY AND BEHAVIOR HAS LONG BEEN GUIDED BY THE STUDY OF ANOMALIES IN THESE SYSTEMS 7HEN FACED WITH A SEEMINGLY INTRACTABLY COMPLEX SYSTEM IT IS AT TIMES EASIER TO FATHOM ITS MECHANISMS BY DISRUPTING OR DISTURBING IT RATHER THAN TRYING TO DELICATELY EXPLORE THE @NATURAL ENTITY )T HAS RECENTLY BECOME CLEAR TO ECOLOGISTS THIS TACT OF USING THE DISRUPTION OR DISTORTION OF A SYSTEM TO BETTER UNDERSTAND ITS NORMAL WORKINGS CAN BE APPLIED TO THE STUDY OF THE BEHAVIOR SPREAD AND IMPACT OF NON INDIGENOUS SPECIES .)3 ON NATURAL COMMUNITIES 3AX ET AL 4HE POWER OF THIS VIEW OF .)3 IS THAT SYSTEMS ARE INADVERTENTLY BEING PERTURBED ALL OVER THE GLOBE 7HAT WE CAN LEARN FROM THE PERTURBATIONS WILL NOT ONLY ADVANCE THE SCIENCE OF ECOLOGY BUT ALSO WILL ALLOW ECOLOGISTS TO RESTORE AND REBUILD THESE VERY SYSTEMS (OWEVER NOT ALL DISRUPTIONS OF A SYSTEM ARE NECESSARILY INFOR MATIVE &URTHER IF THE SYSTEM AS IT NORMALLY FUNCTIONS HOLDS SOME INTRINSIC VALUE -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
3- -C-AHON -7 #ADOTTE AND 4 &UKAMI
AS DO INVADED ECOLOGICAL SYSTEMS IT IS IN THE INTEREST OF THE RESEARCHER TO WORK TO BOTH UNDERSTAND INVASIONS BUT ALSO TO CORRECT OR MITIGATE THE DAMAGING IMPACT OF NON NATIVE POPULATIONS .)3 POSE A WIDE VARIETY OF THREATS TO THEIR NON NATIVE HABITATS THROUGH IMMEDI ATE AND LONG TERM INmUENCES ON SPECIES COMPOSITION AND ECOSYSTEM FUNCTIONING 0ARKER ET AL "ECAUSE THE NEGATIVE IMPACTS OF .)3 ARE lRST DIRECTLY AND PRIMARILY ECOLOGICAL ECOLOGISTS AND EVOLUTIONARY BIOLOGISTS CONSTITUTE THE FOR WARD LINE IN MEETING THE CHALLENGES POSED BY THE INTRODUCTION AND SPREAD OF .)3 4HE MANY PATHWAYS THROUGH WHICH AN INTRODUCED POPULATION CAN AFFECT NON NATIVE HABITATS AND COMMUNITIES HOWEVER ARE DIFlCULT TO DETERMINE AND PREDICT 7HICH TOOLS CAN THE ECOLOGIST APPLY TO THE PROBLEM OF .)3 !NY SOLUTION MUST DEVELOP FROM A SOLID UNDERSTANDING OF THE FOLLOWING HOW POPULATIONS INTRIN SICALLY BEHAVE HOW POPULATIONS INmUENCE THE BIOTIC AND ABIOTIC SYSTEMS OF WHICH THEY ARE COMPONENTS HOW CONVERSELY AN ENVIRONMENT CAN INmUENCE A NON INDIGENOUS POPULATION AND HOW .)3 POPULATIONS CAN CHANGE PHENO TYPICALLY AND GENOTYPICALLY IN NEW ENVIRONMENTS !LTHOUGH ALL OF THESE QUESTIONS FALL SOLIDLY WITHIN THE TRADITION OF ECOLOGICAL RESEARCH THEY DEMAND WITH A STARTLING IMMEDIACY CAPABLE ANSWERS CULLED FROM UNRESOLVED AMBIVALENT AND EVEN CONTENTIOUS ECOLOGICAL DEBATE 7HILE ECOLOGISTS ARE AT ONCE WELL POSITIONED TO ADDRESS THE KEY ELEMENTS THAT HAVE ARISEN FROM THE IMPORTANCE OF .)3 OUR ANSWERS ARE LIKELY TO CARRY WITH THEM SOME OF THE STRUGGLES BORN OF CLASSIC THEORET ICAL AND CONCEPTUAL DEBATES IN ECOLOGY AND EVOLUTIONARY BIOLOGY (ERE HOWEVER THE STUDY OF .)3 MAY NOT NECESSARILY SUFFER FOR THESE CHALLENGES 4HE STUDY OF .)3 WHEN APPROACHED FROM THE REALM OF CONCEPTUAL ECOLOGY CAN ACT AS INTERESTING TESTS OF COMPETING ECOLOGICAL THEORIES 4HIS POTENTIAL HAS LONG BEEN RECOGNIZED AND MORE RECENTLY BEEN PROMOTED ,ODGE $AVIS ET AL 9ET NOT ALL ECOLOGICAL THEORY IS APPLICABLE OR APPROPRIATE FOR THIS TYPE OF TEST .OR WILL THE ANSWERS GAINED FROM ALL APPLICATIONS OF ECOLOGICAL THEORY ASSIST IN IMPROVING OUR UNDERSTANDING INTERVENTION OR PREDICTION ABOUT ACTUAL COLONIZATIONS OF .)3 /NE OF THE KEY GOALS OF THIS BOOK IS TO BETTER RElNE WHAT ECOLOGISTS BELIEVE THE STUDY OF .)3 CAN DO FOR THE lELD OF ECOLOGY AND CONVERSELY HOW CONCEPTUAL ECOLOGY CAN ADVANCE OUR ABILITY TO EXPLAIN AND ADDRESS THE CHALLENGES POSED BY .)3 )N THIS CHAPTER WE WILL ORGANIZE SOME OF THE WAYS IN WHICH THE STUDY OF .)3 CAN ADVANCE CONCEPTUAL ECOLOGY AND VISE VERSA FOCUSING ON RECENT LITERATURE IN THE lELD AND THE WAYS IN WHICH THE CHAPTERS OF THIS BOOK lT INTO THAT SCHEME 4HIS CHAPTER WILL ALSO DISCUSS HOW THIS BOOK ESTABLISHES GUIDELINES NOT ONLY FOR WHAT WE MAY LEARN FROM .)3 BUT FOR WHAT WE ARE UNLIKELY TO LEARN !GAIN WITH IMMINENT CHALLENGES AND LIMITED RESOURCES UNDERSTANDING WHICH SCIENTIlC APPROACHES THEORETICAL AND APPLIED ARE INTRACTABLE OR IMPRACTI CAL IS AS IMPORTANT TO ADVANCING THIS lELD AS KNOWING WHICH APPROACHES SHOW PROMISE WHEN CONFRONTING THIS COMPLEX PROBLEM
4RACKING THE TRACTABLE
42!#4!",% ).42!#4!",% !.$ 02!#4)#!, 345$)%3 /& ")/,/')#!, ).6!3)/.3 !LTHOUGH STUDIES ON THE DYNAMICS OF INVASIVE ORGANISMS DEMONSTRATE MANY RESEARCH METHODOLOGIES THREE APPROACHES ARE CRUCIAL TO THE ADVANCEMENT OF OUR UNDERSTANDING OF INVASIONS THEY ARE MATHEMATICAL MODELS EXPERIMENTS EITHER MANIPULATIVE OR OBSERVATIONAL AND REVIEWS OR META ANALYSES 4HE STRENGTH DERIVED FROM EXPLORING INVASION DYNAMICS THROUGH MATHEMATICAL MODELING IS THAT SCIENTISTS WITH EXPERTISE IN A VARIETY OF THEORETICAL APPLICATIONS CAN TACKLE THE CHALLENGES OF UNDERSTANDING BIOLOGICAL INVASIONS THROUGH NOVEL TECHNIQUES 3HEA AND #HESSON -ODELING SUGGESTS BOTH POSSIBLE DYNAMICS PROB ABLE lNDINGS AND PERHAPS MORE IMPORTANTLY THE LIMITS TO CERTAIN CONCEPTUAL APPROACHES TO INVASIONS (ARDING ET AL #HAPTER )T IS BROADLY ACKNOWLEDGED THAT IN ORDER TO BETTER UNDERSTAND INVASIONS EXPERIMENTAL APPROACHES ARE CRUCIAL 4HERE HAS BEEN A GROWTH OF STRONG EXPERIMENTS IN INVASIONS RANGING FROM LABO RATORY MICROCOSMS $ICK AND 0LATVOET TO lELD MESOCOSMS $UKES TO LARGE SCALE MANIPULATIVE lELD EXPERIMENTS 4ILMAN -ANY OF THE STRENGTHS OF INFERENCES DERIVED FROM THESE STUDIES IN ORDER TO BE BROADLY APPRECI ATED NEED TO BE REINCORPORATED INTO MATHEMATICAL MODELS &INALLY META ANALYSES AND REVIEWS PROVIDE A GENERALIZED ASSESSMENT OF THE THEORETICAL AND EMPIRICAL WORK THAT HAS COLLECTED OVER SEVERAL YEARS 4HE SYNTHESIS DERIVED FROM THESE ANALYSES CAN AS WITH THE MODELS SERVE TO INFORM DIRECT OR DELIMIT THE QUESTIONS RESEARCHERS ASK ABOUT INVASIONS #ADOTTE ET AL 4HE DIALECTIC DERIVED FROM THE COMPLEMENTARY APPROACHES OF SUPPOSITION EXPERIMENTATION AND ASSESSMENT OFFERS THE MOST EFlCIENT WAY TO STUDY INVASIONS AND DRAW BROADER UNDERSTANDING OF ECOLOGICAL PROCESSES THROUGH THE STUDY OF INVASIONS !LL THREE OF THESE APPROACHES ARE FEATURED IN THIS BOOK AND IN THE FOLLOWING INTRODUCTION TO THE THEMES OF THIS BOOK WE PAY SPECIAL ATTENTION TO HOW THIS DIALECTIC CAN GUIDE IMPORTANT RESEARCH AND THINKING ON INVASIONS 4HE BEHAVIOR OF POPULATIONS
%VEN IN MODELS OF POPULATIONS THAT DO NOT INCLUDE ABIOTIC OR INTERSPECIlC ENVI RONMENTAL INTERACTIONS INTRASPECIlC POPULATION DYNAMICS CAN ILLUSTRATE IMPOR TANT PROPERTIES OF INVADING POPULATIONS THROUGH PATTERNS OF INTRINSIC POPULATION GROWTH AND SPREAD SEE #ADOTTE ET AL #HAPTER !LTHOUGH A NUMBER OF SCALES MAY ULTIMATELY PROVE IMPORTANT WHEN ASSESSING THE ARRIVAL ESTABLISHMENT GROWTH AND IMPACT OF AN .)3 ,LORET ET AL (AMILTON ET AL THE POPU LATION SCALE HAS LONG PROVIDED SOME OF THE CLEAREST INSIGHTS INTO THE BASIC QUESTIONS OF INVASION DYNAMICS 0ETROVSKII ET AL 4HOMSON !LL OF THE FEATURES THAT lGURE PROMINENTLY IN POPULATION BIOLOGY FROM THE ROLE OF CARRYING CAPACITY TO MORTALITY AND REPRODUCTION PROVIDE A BASELINE UNDERSTANDING OF HOW AN .)3 CAN BE EXPECTED TO BEHAVE WHEN COLONIZING A NEW AREA ! KEY DISTINCTION WHEN EXPLORING THESE INTRINSIC PROPERTIES LIES IN THE DIFFERENT EXPECTATIONS OF STOCHASTIC
3- -C-AHON -7 #ADOTTE AND 4 &UKAMI
VERSUS DETERMINISTIC PROCESSES 1UITE A FEW CHAPTERS IN THIS BOOK IMPLICITLY AND EXPLICITLY ADDRESS THIS IMPORTANT DISTINCTION "UCKLEY AND -ETCALF #HAPTER REVIEW THE ROLE OF DENSITY DEPENDENCE IN DETER MINING THE POPULATION DENSITIES THAT CAN BE REACHED BY AN INVASIVE POPULATION AND THE INmUENCES OF THOSE DENSITIES ON INVASIVE SUCCESS 4HEY SHOW HOW DENSITY DEPENDENCE CAN DELIMIT DEMOGRAPHIC PARAMETERS SUCH AS INTRINSIC RATE OF INCREASE AND DISPERSAL ABILITY 5SING MICROBIAL MICROCOSMS 7ARREN ET AL #HAPTER SHOW THAT CHANCE EVENTS PLAY A KEY ROLE IN THE ESTABLISHMENT OF AN INVADER )NITIAL DEMOGRAPHIC STOCHASTICITY PROPAGULE PRESSURE AND THE INITIAL RATE OF INCREASE ALL CONTRIBUTE TO WHETHER A POPULATION IS ABLE TO ESTABLISH IN A COMMUNITY BUT NOT NECESSARILY PERSIST IN THAT COMMUNITY 3PECIES SPECIlC EFFECTS WERE ALSO FOUND TO BE IMPORTANT IN BOTH ESTABLISHMENT AND PERSISTENCE WHICH INDICATES THAT CARE FUL CHARACTERIZATION OF THE DEMOGRAPHIC QUALITIES OF AN INVADING SPECIES MAY BE IMPORTANT TO UNDERSTANDING ITS POTENTIAL IMPACT 7HAT POPULATION SCALE PATTERNS DO LEAD TO PERSISTENCE OVER TIME -URREL #HAPTER TAKES A @PLANT EYE VIEW IN USING SIMULATIONS TO SHOW HOW THE DENSITY AND AGGREGATION OF A POPULATION CAN CREATE A @NEIGHBORHOOD EFFECT THAT DETER MINES ULTIMATE POPULATION GROWTH 4HIS APPROACH COULD BE QUITE IMPORTANT IN PLANT INVASIONS AS INTRA SPECIlC COMPETITION CAN DETERMINE ULTIMATE VIABILITY AND SPREAD OF A POPULATION !FTER THE POPULATION IS ESTABLISHED ITS DISPERSAL BECOMES A CRUCIAL ISSUE IN ANTICIPATING THE EXTENT AND IMPACT OF AN INVASION 0UTH AND 0OST ,EWIS ET AL #HAPTER DEMONSTRATE A NOVEL APPROACH TO MODELING DISPERSAL THROUGH TWO DIMENSIONS 5SING KERNEL METHODS TO INCORPORATE LONG DIS TANCE DISPERSAL INTO MODELS AND TWO DIMENSIONAL MODELS TO CORRECT FOR BIASES IN MORE COMMONLY USED ONE DIMENSIONAL MODELS A MORE ACCURATE PREDICTION OF THE DISPERSAL BEHAVIOR OF AN INVADING POPULATION CAN BE MADE -ETAPOPULATION THEORY ALSO EMPHASIZES THE ROLE OF DISPERSAL IN MAINTAINING .)3 PERSISTENCE OVER TIME (ARDING ET AL #HAPTER SHOW THAT FOR SINGLE .)3 COLONIZING PATCHY ENVIRONMENTS COLONIZATION SUCCESS INTO EMPTY PATCHES MUST BE GREATER THAN EXTINCTIONS 4HIS IMPLIES THAT SPECIES WITH STRONG DISPERSAL MAY BE PREDISPOSED TO COLONIZE #OMBINED WITH BUFFERING LIFE HISTORY TRAITS SUCH AS PLANTS THAT CAN SELF POLLINATE OR VEGETATIVELY REPRODUCE A GOOD DISPERSAL MECHANISM CAN LEAD TO SUCCESSFUL COLONIZATION OF A HETEROGENEOUS LANDSCAPE %NVIRONMENT INFLUENCING .)3 POPULATIONS
)NTRINSIC POPULATION BEHAVIORS ARE CLEARLY CRUCIAL TO ANY UNDERSTANDING OF THE ESTABLISHMENT AND SPREAD OF .)3 BUT AS WITH MANY ECOLOGICAL STUDIES OF POPU LATIONS THE BEHAVIORS OF THE POPULATION CAN DEPEND ON THE BIOTIC AND ABIOTIC COMPONENTS OF THE ENVIRONMENT ,ODGE $UKES AND -OONEY (OLWAY ET AL )NCORPORATING THE ADDITIONAL LEVEL OF COMMUNITY COMPLEXITY TO POPU LATION DYNAMICS HOWEVER CAN BE DAUNTING WHEN DETERMINING THE IMPACT OF .)3 $AVIS ET AL 4HE STUDY OF THE ESTABLISHMENT AND SPREAD OF .)3 CAN PROVIDE INSIGHT INTO HOW THESE MORE COMPLEX RELATIONSHIPS DEVELOP LENDING IMPORTANT
4RACKING THE TRACTABLE
CASE STUDIES TO THE ANALYSIS OF ECOLOGICAL COMMUNITIES 4HE COMPLEX AND COMPLICATED DYNAMICS OF THE ENVIRONMENT ALSO MEAN THAT THESE ADDITIONAL COMPONENTS CAN MOVE PROBLEMS FROM LESS REALISTIC BUT TRACTABLE PROBLEMS TO INTRACTABLE ONES 4HEREFORE IT IS IMPORTANT TO USE STUDIES OF ENVIRONMENTAL INmUENCES ON .)3 TO DETERMINE WHICH APPROACHES MAY BE APPROPRIATE AND WHICH AN INEFlCIENT USE OF TIME AND RESOURCES ! CLASSIC CONCEPT OF HOW AN ENVIRONMENT CAN DICTATE WHETHER OR NOT A SPE CIES CAN PERSIST IS THAT OF THE ECOLOGICAL NICHE 4HE IDEA THAT AN ENVIRONMENT IS PARSED INTO A lNITE SET OF NICHES HAS BEEN AN IMPORTANT ONE FOR THE DEVELOPMENT OF INVASIONS BIOLOGY #ADOTTE #HAPTER 6AZQUEZ #HAPTER USES A SERIES OF META ANALYSES TO EXPLORE HOW NICHE BREADTH AND INVASION SUCCESS RELATE 7HEN LOOKING AT FUNDAMENTAL NICHES WHERE SPECIES REQUIREMENTS ARE INDEPENDENT OF COMMUNITY INTERACTIONS VERSUS REALIZED NICHES WHERE THE SUITABILITY OF AN ENVIRONMENT TAKES INTO ACCOUNT COMPETITION THE REALIZED NICHE ULTIMATELY DETER MINES THE SUCCESS OF AN .)3 6AZQUEZ POINTS OUT THAT REALIZED NICHES HOWEVER ARE IMPOSSIBLE TO MEASURE AND WARNS AGAINST PURSUING STRAIGHTFORWARD INVESTIGA TION INTO NICHE BASED PREDICTIONS OF POTENTIAL .)3 SUCCESS 4HIS MARKS A POWERFUL RECOMMENDATION FOR INVASIONS BIOLOGY AS A TRADITIONAL LINE OF INQUIRY INTO PREDICT ING THE ESTABLISHMENT OF .)3 HAS BEEN THE SUSCEPTIBILITY OF DIFFERENT HABITATS TO INVASIONS (OLWAY ,EVINE AND $!NTONIO )N OTHER CIRCUMSTANCES INVASIONS CAN SHED LIGHT ON CONCEPTUAL TOPICS THAT ARE DIFlCULT TO ASSESS IN NATURAL COMMUNITIES $UNCAN AND &ORSYTH #HAPTER USE HISTORICAL RECORDS OF BIRD INVASIONS TO TEST CLASSIC HYPOTHESES OF COMPETITION AND COMMUNITY STRUCTURE )NVASION RECORDS OFFER A UNIQUE WAY OF DISCOVERING IF INVA SIONS OF BIRD SPECIES INTO CERTAIN TYPES OF ENVIRONMENTS ARE MORE LIKELY TO PERSIST 4HEY lND THAT PRIORITY EFFECTS DO OCCUR AND THAT DEPENDING ON CIRCUMSTANCES STO CHASTIC PROCESSES AND DETERMINISTIC PROCESSES SUCH AS COMPETITION CAN DETERMINE ULTIMATE COMMUNITY COMPOSITION 3AX AND 'AINES #HAPTER SUGGEST THAT SPE CIES RICH COMMUNITIES ARE LIKELY TO BE MORE SUSCEPTIBLE TO INVASIONS BECAUSE CON DITIONS ARE FAVORABLE FOR MANY SPECIES 4HEY ARGUE HOWEVER THAT THIS IS TRUE ONLY UP TO A CRITICAL THRESHOLD SUCH AS HIGHLY SPECIOSE TROPICAL RAIN FORESTS AT WHICH POINT %LTONS %LTON MODEL IN WHICH SPECIES RICH COMMUNITIES HAVE LESS AVAILABLE NICHE SPACE UNEXPLOITED BY THE BEST COMPETITOR BECOME APPLICABLE "OTH 3AX AND 'AINES #HAPTER AND 3MITH AND 3HURIN #HAPTER EXPLAIN THAT HETEROGENEITY WITHIN REGIONAL SCALES CAN MEAN THAT MULTIPLE PROCESSES STOCHASTIC AND DETERMINISTIC AND MULTIPLE OUTCOMES INVASION RESISTANCE AND SUSCEPTIBILITY CAN BE FOUND IN ANY ONE HABITAT 4HIS INDICATES THAT EVEN IN UNSATURATED COM MUNITIES WHERE PRESUMABLY THERE IS AMPLE NICHE SPACE FOR WELL DISPERSED INVAD ERS INVASION SUCCESS IS CONTINGENT ON OTHER FACTORS 4HIS ROLE OF CONTINGENCY AND COMPLEXITY IS BECOMING A COMMON THEME IN BOTH INVASIONS LITERATURE AND THE EMPIRICAL STUDIES OF COMMUNITY COMPOSITION AND ASSEMBLY AND THEREFORE POINTS TO AN IMPORTANT AREA OF RECIPROCAL RESEARCH !NOTHER EXAMPLE OF THE CHALLENGES INHERENT IN COMPLEX COMMUNITY DYNAMICS IS ILLUSTRATED IN (ARDING ET AL #HAPTER !LTHOUGH AS MENTIONED ABOVE THEY SHOW THAT METAPOPULATIONS WITHOUT COMPETITION RELY ON A SIMPLE STRATEGY OF
3- -C-AHON -7 #ADOTTE AND 4 &UKAMI
COLONIZATION AND BUFFERS FROM EXTINCTION ADDING EVEN ONE MORE SPECIES INTO THE MODEL CAN RADICALLY CHANGE THE NUMBER OF POPULATION PARAMETERS AND LIFE HISTORY TRAITS THAT MAY ULTIMATELY DICTATE THE SUCCESSFUL ESTABLISHMENT AND PERSISTENCE OF AN .)3 4HIS COMPLEXITY OF POTENTIAL OUTCOMES INDICATES THAT METAPOPULATION THEORY AS APPLIED TO MULTIPLE SPECIES LIVING IN SUBDIVIDED HABITATS MIGHT BE WELL APPLIED TO CASE STUDIES EXPERIMENTS AND MANAGEMENT PROBLEMS THAT OFFER SPECIFIC SPECIES CHARACTERISTICS AND ROBUST ESTIMATION OF POPULATION PARAMETERS 7ITH SUCH A META ANALYSIS IT MAY BE POSSIBLE TO DETERMINE WHETHER A METAPOPULATION MODEL CAN ACCURATELY DESCRIBE AND PREDICT CERTAIN TYPES OF INVASIONS 5SING MICROBIAL MICROCOSMS 7ARREN ET AL #HAPTER REINFORCE THIS CONCLU SION )N A SERIES OF AMBITIOUS EXPERIMENTS WHERE DIFFERENT SPECIES ARE INTRODUCED INTO ESTABLISHED COMMUNITIES THEY SHOW THAT PREDICTING INVASIONS CAN DEPEND ON A NUMBER OF CHARACTERISTICS OF THE SPECIES INVOLVED AS WELL AS THE COMMUNITY CHARACTERISTICS 3PECIlCALLY THE INTRINSIC RATE OF INCREASE A SIMPLE POPULATION PARAMETER SHOULD BE THOUGHT OF AS HAVING AS MUCH TO DO WITH THE INTERACTION CONTACT EXPERIENCE BETWEEN AN INVADER AND A COMMUNITY AS INTRINSIC PROPERTIES OF THE INVADING POPULATION $EMOGRAPHIC PARAMETERS LIKE THE INTRINSIC RATE OF INCREASE THEMSELVES ARE NOT CONSTANT 4HESE PARAMETERS CAN CHANGE STOCHASTICALLY DUE TO BOTH INTRINSIC DEMOGRAPHIC FACTORS SUCH AS RANDOM CHANGES IN BIRTH OR DEATH RATES 4HEY CAN ALSO CHANGE DUE TO ENVIRONMENTAL STOCHASTICITY &RECKLETON ET AL #HAPTER DISTINGUISH DEMOGRAPHIC VERSUS ENVIRONMENTAL STOCHASTICITY AT DIFFERENT STAGES OF AN INVASION ARRIVAL ESTABLISHMENT AND SPREAD 4HEY SHOW WITH MATHEMATICAL MODELS THAT STOCHASTIC PROCESSES INmUENCE THESE STAGES OF THE INVASION IN DIFFERENT WAYS AND WITH DIFFERENT CONSEQUENCES 3TOCHASTICITY MAY BE MORE IMPORTANT IN PHASES WITH LOW DENSITIES ARRIVAL AND ESTABLISHMENT WHILE DENSITY DEPENDENT BEHAVIORS MAY HOLD A GREATER INmUENCE ON THE SPREAD OF ALREADY ESTABLISHED POPU LATIONS !GAIN MODELS LIKE THIS CAN INDICATE WHEN AND HOW TO PROCEED WITH AN EXPERIMENTAL PROGRAM TO TEST STOCHASTIC AND DETERMINISTIC COMPONENTS OF INVA SION SUCCESS !LTHOUGH DIRECT AGONISTIC INTERACTIONS BETWEEN SPECIES SUCH AS COMPETITION AND PREDATION HAVE LONG BEEN HELD AS CENTRAL TO UNDERSTANDING THE POPULATION STRUCTURE OF COMMUNITIES INDIRECT EFFECTS AND MUTUALISMS HAVE RECENTLY BEEN THRUST INTO THE FOREFRONT OF THINKING ON A NUMBER OF CONCEPTUAL THEMES IN ECOLOGY 7OOTTON ,ORTIE ET AL SUCH AS RICHNESS PRODUCTIVITY POPULATION VIABILITY ANALYSIS AND INVASIONS ,ACH 6AZQUEZ #HAPTER SHOWS IN HIS META ANALYSES OF NICHE BREATH AND INVASIONS THAT THE PRESENCE OF MUTUALISTS AND OTHER NICHE CATEGORIES THAT MAY BE TRICKY TO MEASURE CAN HAVE AN IMPORTANT INmUENCE ON THE ULTIMATE VIABILITY OF A POPULATION IN A NEW HABITAT 4HORPE AND #ALLAWAY #HAPTER EXTEND THE DISCUSSION OF MUTUALISMS TO THE LEVEL OF INDI RECT MUTUALIST INTERACTIONS AND FEEDBACK LOOPS 'OOD EXPERIMENTAL EVIDENCE HAS SHOWN THAT PRESENCE OF SOIL PATHOGENS DECREASE .)3 PLANT SUCCESS IN NATIVE RANGE AND ABSENCE OF THOSE PATHOGENS INCREASES .)3 SUCCESS IN NEW RANGE &URTHER MUTUALIST INTERACTIONS CAN MORE EASILY CREATE POSITIVE FEEDBACKS IN A NEW RANGE
4RACKING THE TRACTABLE
ENHANCING PLANT SUCCESS 4HIS CONCEPTUAL APPROACH TO INVASIONS MIGHT BE WELL SUITED FOR A MATHEMATICAL STUDY AS FEEDBACKS ARE BOTH COMMON IN NATURE YET DIF lCULT TO TEASE APART FROM OTHER COMMUNITY EFFECTS )N ADDITION TO USING ANALYSES OF ENVIRONMENTAL CONTEXTS TO PREDICT WHETHER AN .)3 WILL SUCCESSFULLY ESTABLISH AND PERSIST IN A NOVEL ENVIRONMENT 'ILBERT AND 0ARKER #HAPTER AND 3ATAKE ET AL #HAPTER ADDRESS HOW THE ENVIRONMENT CAN PREVENT AN INVASION OR EVEN REVERSE AN ALREADY PERSISTENT .)3 'ILBERT AND 0ARKER ARGUE THAT THE UNDERSTUDIED ROLE THAT PATHOGENS PLAY IN PLANT POPULATION REGULATION CAN HAVE IMPORTANT CONSEQUENCES IN UNDERSTANDING PREDICTING AND MITIGATING OR REVERSING HIGH DENSITY PERSISTENCE OF .)3 3ATAKE ET AL #HAPTER MODEL @CLASSIC MAST SEEDING AND SHOW THAT WHEN SEED SET IS NEGATIVELY CORRELATED IN TIME BUT POSITIVELY CORRELATED ACROSS SPACE A SYSTEM IS MOST RESISTANT TO INVAD ING SEED PREDATORS 0HENOTYPIC AND GENOTYPIC CHANGE
! NEW AND EXCITING THEME IN INVASIONS BIOLOGY ADDRESSES HOW POPULATIONS OF .)3 MAY CHANGE IN PHENOTYPIC EXPRESSION 3CHWEITZER AND ,ARSON OR GENOTYPE 3AKAI ET AL DUE TO THE NOVEL ENVIRONMENTS THEY EXPERIENCE IN THEIR NEW RANGE THIS INCLUDES POPULATION CHANGES INHERENT IN A COLONIZING EVENT SUCH AS FOUNDER EFFECTS OR DRIFT 0ALUMBI #OX *UST AS MUTATIONS IN A VIRUS WITHIN HUMAN POPULATIONS CAN MEAN THE DIFFERENCE BETWEEN RARITY AND A PAN DEMIC SO TOO CHANGES IN .)3 POPULATIONS CAN TURN A RARE OR ISOLATED POPULATION INTO A PEST 4HIS CAN ALSO BE ONE OF THE MAJOR FACTORS IN CREATING CREATE TIME LAGS BETWEEN THE ARRIVAL PHASE OF AN .)3 AND AN OUTBREAK -ACK ET AL "YERS AND 'OLDWASSER -EMMOTT ET AL .EW METHODS IN GENETICS LIFE HISTORY EVOLUTION AND COEVOLUTIONARY THEORY CAN PROVIDE INSIGHT INTO AND DRAW INFERENCE FROM THE GROWING EXAMPLES OF .)3 POPULATIONS THAT HAVE CHANGED FUNDAMENTALLY SINCE THEIR ARRIVAL IN A NEW RANGE %VOLUTIONARY CHANGE IN .)3 POPULATIONS CAN FOLLOW MANY POSSIBLE PATHWAYS 3CHIERENBECK AND !ÕNOUCHE #HAPTER EMPHASIZE THAT PRE ADAPTED GENERALIST GENOTYPES WILL FACILITATE INVASION SUCCESS 3UBSTANTIAL GENETIC VARIATION CAN PRO VIDE THE REQUISITE GENETIC MATERIAL FOR RAPID EVOLUTIONARY RESPONSE TO THE NOVEL ENVIRONMENT AND 3HIERENBECK AND !ÕNOUCHE #HAPTER POINT OUT THAT THERE ARE MANY PATHWAYS TO THIS VARIATION HETEROZYGOSITY POLYPLOIDY AND PERHAPS NOW EVEN EXTRA GENOMIC GENETIC INFORMATION ,ALLE ET AL (OWEVER GENERAL GENETIC DIVERSITY MAY NOT ALONE BE ENOUGH TO INmUENCE INVASION SUCCESS (ERBEN ET AL -ORE IMPORTANTLY HOW LABILE LIFE HISTORY TRAITS ARE PHENOLOGY CLONAL OR VEGETATIVE REPRODUCTION IN PLANTS MATING BEHAVIORS ETC MAY MARK THE IMPORTANT GENETIC DISTINCTION "UCKLEY AND -ETCALF #HAPTER DESCRIBE HOW LIFE HISTORY EVOLUTION DUE TO UNIQUE FORCES AT WORK IN NOVEL ENVIRONMENTS DIFFER ENT LIFE HISTORY STRATEGIES MAY BENElT .)3 POPULATIONS 7HILE LIFE HISTORY EVOLUTION MAY BE RESPONSIBLE FOR RARE LARGE OUTBREAKS THIS WOULD BE DIFlCULT TO TEST 4HORPE AND #ALLAWAY #HAPTER EXPLAIN THAT
3- -C-AHON -7 #ADOTTE AND 4 &UKAMI
EVOLUTIONARY RESPONSE OF MICROBIAL COMMUNITIES CAN HAPPEN SO FAST THAT THIS MAY MUTE OR MITIGATE AN .)3 FROM LONG TERM DOMINANCE THROUGH POSITIVE SOIL FEEDBACK PATHWAYS "ECAUSE OF A POTENTIALLY RAPID RESPONSE AND THE SHORT GENERATION TIMES OF MICROBIAL COMMUNITIES IT MAY BE POSSIBLE TO TEST SOIL SYSTEMS FOR RAPID EVOLU TIONARY RESPONSE TO ENCOURAGING OR MITIGATING THE SUCCESSFUL ESTABLISHMENT OF AN .)3 .)3 COLONIZATION ADDITIONALLY MAY PROVIDE IDEAL SYSTEMS TO RESEARCH THE STABILITY OF MICROBIAL COMMUNITIES AS WELL AS THEIR RELATIONSHIP TO THE PLANTS WITH WHICH THEY INTERACT THROUGH BELOWGROUND PATHWAYS 7ARDLE 0ATHOGENS WOULD ALSO lT THIS MODEL AND 'ILBERT AND 0ARKER #HAPTER DESCRIBE THE COEVO LUTION OF PLANT PATHOGEN SYSTEMS AND MATERNALLY INHERITED INDUCED RESISTANCE 4HE EVOLUTIONARY RESPONSE OF AN .)3 TO THE BIOTIC COMMUNITY MAY BE CRUCIAL NOT ONLY IN THE ESTABLISHMENT BUT IN THE RESULTING EFFECT ON THE NATIVE BIOTA +ONDOH #HAPTER MODELS HOW CONTACT EXPERIENCE THE PREVIOUS EVOLUTIONARY lLTERING FROM PRIOR INTERACTIONS BETWEEN AN .)3 AND RELATED NOVEL COMPETITORS PREDATORS AND PREY CAN RESULT IN SUCCESSFUL INVASION (E DESCRIBES HOW THE CONTACT EXPERI ENCE IN MANY FORMS CAN INmUENCE THE SPECIlC COMPONENTS OF CONTACT BETWEEN THE .)3 AND NOVEL BIOTA AS INFORMATION RETRIEVAL DETECTING THE OTHER SPECIES PROCESSING RECOGNIZING CHARACTERISTICS OF THAT NOVEL SPECIES AND BEHAVIORAL RESPONSE BEING ABLE TO PREY UPON ESCAPE OR COMPETE WITH THAT SPECIES .)3 POPULATIONS INFLUENCING POPULATIONS AND ENVIRONMENT
)T SHOULD BE NOTED THAT EVEN IDENTIFYING AN INVASIVE SPECIES CAN BE PROBLEM ATIC #OLAUTTI AND -AC)SAAC -URPHY ET AL #HAPTER "UT REGARDLESS OF DElNITION THERE IS A GENERAL UNDERSTANDING AMONG BIOLOGISTS THAT ULTIMATELY ANY INVASIVE WILL IN SOME KEY WAY BE DElNED BY ITS INmUENCE ON THE BIOTIC AND ABIOTIC COMPONENTS OF ITS NEW RANGE 4HERE MAY BE MILLIONS OF .)3 PROPAGULES ENTERING COMPLEX ENVIRONMENTS BUT OUR CONCERN FOR THEIR RANGE EXPANSION IS ULTIMATELY A FUNCTION OF THEIR IMPACT ON OTHER SPECIES IN THEIR NEW RANGE THE WAYS IN WHICH THEY AFFECT ECOSYSTEM PROCESSES AND HOW THESE CHANGES MAY PERSIST OR INCREASE OVER TIME (ISTORICALLY DOCUMENTED INVASIONS CAN ALSO PROVIDE INSIGHTS INTO THE PATH WAYS THROUGH WHICH THE CONTEXT OF AND INVADING ORGANISMS CAN INmUENCE BOTH PERSISTENCE AND THE CONCOMITANT INmUENCE ON NATIVE BIOTA #OURCHAMP AND #AUT #HAPTER USED MODELS INCORPORATING DIRECT AND INDIRECT INTERACTIONS TO EXPLAIN INVASIONS AS WELL AS SHOW HOW THE INVASIONS THEMSELVES ILLUSTRATE THE COMPLEX AND SOMETIMES COUNTERINTUITIVE BEHAVIORS OF INTERACTING POPULATIONS #OMPLEX DYNAMICS BETWEEN POPULATIONS MAY ALSO MEAN THAT AFTER AN INVASION IT TAKES MANY GENERATIONS FOR THE EFFECTS OF THE NEW INTERACTIONS TO SHOW THEIR IMPACT &RECKLETON ET AL #HAPTER !LTHOUGH DOCUMENTED CHANGES IN NATIVE BIOTA OR ECOSYSTEM FUNCTION MAY BE CLEAR AFTER AN INVASIVE BECOMES A DAMAGING PEST PREDICTING THE ULTIMATE IMPACT OF AN .)3 ON NATIVE HABITATS IS DIFlCULT ! NUMBER OF FACTORS INTRINSIC TO THE INVADING POPULATION AND DUE TO THE NOVEL ENVIRONMENT CAN ELICIT COMPLEX
4RACKING THE TRACTABLE
RESPONSES TO THE NON NATIVE POPULATIONS )NDIRECT EFFECTS ON THE ENVIRONMENT ARE DIFlCULT TO DETECT LET ALONE PREDICT YET MAY BE AMONG THE MORE COMMON AND SERI OUS RESPONSES TO .)3 )NVASIVE PLANTS CAN ALTER THE SOIL NUTRIENT FEEDBACK LOOPS AND RENDER LONG TERM CHANGES TO THE SOIL ENVIRONMENT 4HORPE AND #ALLAWAY #HAPTER -UTUALISMS SUCH AS POLLINATION SERVICES CAN BE DISRUPTED BY INVA SIVES 4HOUGH THE CONVERSE MAY OCCUR .ON NATIVE BEES HAVE BEEN SHOWN TO INCREASE POLLINATION EFlCIENCY OF SOME PLANTS 2ICHARDSON ET AL ALTHOUGH THE EFFECT ON NATIVE POLLINATOR COMMUNITIES ADDS ADDITIONAL UNCERTAINTY TO THE DIAGNOSIS OF THESE EFFECTS 'ENERALISM VERSUS SPECIALISM CAN BE CRUCIAL TO THE EXTENT OF INmUENCE A NON NATIVE SPECIES MAY HAVE IN PATHOGEN HOST RELATIONSHIPS 'ILBERT AND 0ARKER #HAPTER POLLINATOR SYSTEMS 6AZQUEZ #HAPTER AND SOIL MUTUALISMS 4HORPE AND #ALLAWAY #HAPTER 4HE SYMMETRY OF THESE MUTU ALIST RELATIONSHIPS IS OF FURTHER CONSEQUENCE 6AZQUEZ #HAPTER WHEN INFERRING THE POTENTIAL IMPACT AN .)3 MAY HAVE ON NOVEL SYSTEMS 7HETHER DIRECT OR INDIRECT THE STOCHASTIC NATURE OF POPULATION INTERACTIONS CAN RADICALLY AFFECT THE ULTIMATE CONSEQUENCES OF A PERSISTENT .)3 &RECKLETON et al #HAPTER 7ARREN ET AL #HAPTER ESPECIALLY AS SYSTEMS MAY CONTAIN NON LINEAR DYNAMICS ! lNAL LEVEL OF COMPLEXITY RESULTS FROM THE MANY APPLICATIONS OF OUR INFERENCE TO POLITICAL SOCIAL AND ECONOMIC ISSUES )T IS BROADLY ACCEPTED THAT .)3 CAN AFFECT THE INHERENT RICHNESS OF NATIVE BIOTA SPECIlC ENDANGERED SPECIES THE ECOSYSTEM FUNCTION OF NATIVE HABITATS AS WELL AS BIOTA OF ECONOMIC IMPOR TANCE )N THEIR REVIEW OF HOW .)3 INmUENCE NOVEL COMMUNITIES -URPHY ET AL #HAPTER FOUND A CORRELATION BETWEEN LEVEL OF INVASIVE ON THE 3% SCALE AND COM MUNITY IMPACT THERE WAS NO CORRELATION WITH ECONOMIC IMPACT 4HIS MAY TROUBLE OUR ABILITY TO APPLY A LEVEL OF COMMUNITY CHANGE DUE TO AN INVASIVE TO SOME SYSTEM OF SOCIAL OR ECONOMIC @IMPORTANCE OF THE INVADER
#/.#,53)/. )NVASIONS BIOLOGY IS FACED WITH MANY OF THE SAME STRUGGLES THAT HAVE LONG FACED MAINSTREAM ECOLOGY /RGANISMS SHOW AN ARRAY OF INTRINSIC QUALITIES THAT ARE BOTH INDICATIVE OF THEIR POPULATION DYNAMICS AS WELL AS RESPONSIBLE FOR THOSE DYNAM ICS 9ET POPULATIONS OF ORGANISMS RESPOND AND INmUENCE THEIR BIOTIC AND ABIOTIC CONTEXTS AND THEY ADAPT PHENOTYPICALLY AND GENOTYPICALLY TO THEM 4HE PROBLEM OF lLTERING THAT WHICH IS BROADLY IMPORTANT TO POPULATIONS FROM THAT WHICH IS IDIOSYNCRATIC IS HIGHLIGHTED IN THE STUDY OF .)3 7E CERTAINLY NEED TO DEVELOP A GENERAL UNDERSTANDING OF THE QUALITIES OF POPULATIONS AND HABITATS THAT CAN LEAD TO INVASION PERSISTENCE AND IMPACT YET WE OFTEN lND THAT THE CAUSES OF ANY SPECIlC INVASION CAN BE UNIQUE TO THAT SPECIlC SPECIES OR HABITAT ! MAJOR GOAL OF THIS BOOK IS TO CAREFULLY ASSESS WHEN SIMPLICITY IS INFORMATIVE EG A POPULATION LEVEL ANALYSIS OF DENSITY DEPENDENCE WHEN COMPLEXITY IS INSTRUMENTAL SUCH AS WHEN ABIOTIC FACTORS INmUENCE .)3 PERSISTENCE AND WHEN GENERALIZATION IS NOT LIKELY POSSIBLE SUCH AS THE FACTORS THAT MAKE UP THE REALIZED NICHE OF AN .)3
3- -C-AHON -7 #ADOTTE AND 4 &UKAMI
/NE OF THE GREATEST CHALLENGES FACING THE STUDY OF INVASIONS BIOLOGY ARISES FROM SPECIES SPECIlC CHARACTERISTICS !S IS OFTEN SHOWN IN THIS BOOK A BETTER UNDERSTANDING OF THE INTERFACE BETWEEN INTRINSIC POPULATION PROPERTIES AND THE STOCHASTIC CONTEXT OF A POPULATION IS LIKELY TO PROVIDE IMPORTANT INSIGHTS INTO .)3 ESTABLISHMENT AND EXPANSION &RUSTRATING MANY STRAIGHTFORWARD PATHS TO INVA SION PREDICTION IS THE COMBINATION OF STOCHASTIC AND DETERMINISTIC PROCESSES THAT INmUENCE POPULATIONS BEHAVIORS $ENNIS ET AL -ATHEMATICAL MODELS MAY HELP INDICATE WHICH PARAMETERS UNDER WHICH ASSUMPTIONS CAN SHOW A DElNI TIVE INmUENCE ON POPULATION DYNAMICS 4HUS WHEN ENTERING AN OBSERVATIONAL OR MANIPULATIVE EXPERIMENTAL PROGRAM THE THEORETICAL LITERATURE CAN PROVE AN IMPORTANT GUIDE TO DEVELOPING HYPOTHESES AND TESTING THEM 2EmECTING RECENT CONCEPTUAL ADVANCES IN GENERAL ECOLOGICAL THEORY OFTEN IGNORED PROCESSES SUCH AS MUTUALISMS INTRA SPECIlC COMPETITION AND BELOW GROUND PROCESSES ARE ALSO LIKELY TO INmUENCE THE POTENTIAL IMPACT OF .)3 #ALLAWAY AND !SCHEHOUG 2ICHARDSON ET AL 0ARKER AND (AUBENSAK #ALLAWAY ET AL AND MARK POTENTIAL PATHWAYS TO BRIDGE WHAT APPEARS TO BE IDIOSYNCRATIC TO MORE GENERALIZABLE PATTERNS )N THESE AREAS THE STUDY OF .)3 MAY BE WELL SUITED TO INFORM OUR GREATER UNDERSTANDING OF SUCH COMPLEX AND OFTEN MASKED MECHANISMS IN GENERAL 4HUS NOT ONLY IS THERE A RECIPROCAL INTEREST IN UNDERSTANDING TRADITIONAL PROBLEMS IN ECOLOGY AND INVASIONS BIOLOGY THESE TWO APPROACHES TO NATURAL SYSTEMS SHOULD INTERACT AND INFORM EACH OTHER AS THEY ADVANCE IN TECHNIQUES CONCEPTS AND UNDERSTANDING
2%&%2%.#%3 "YERS * % AND , 'OLDWASSER %XPOSING THE MECHANISM AND TIMING OF IMPACT OF NONINDIGENOUS SPECIES ON NATIVE SPECIES %COLOGY #ADOTTE - 7 " -URRAY AND * ,OVETT $OUST 5SING DATABASE ANALYSES TO TEST WIDE SPREAD ECOLOGICAL GENERALITIES IN INVASIONS BIOLOGY "IOLOGICAL )NVASIONS IN PRESS #ALLAWAY 2 - AND % 4 !SCHEHOUG )NVASIVE PLANTS VERSUS THEIR NEW AND OLD NEIGHBORS ! MECHANISM FOR EXOTIC INVASION 3CIENCE #ALLAWAY 2 - ' # 4HELEN ! 2ODRIGUEZ AND 7 % (OLBEN 3OIL BIOTA AND EXOTIC PLANT INVASION .ATURE #OLAUTTI 2 ) AND ( * -AC)SAAC ! NEUTRAL TERMINOLOGY TO DElNE @INVASIVE SPECIES $IVERSITY AND $ISTRIBUTIONS $AVIS - ! * 0 'RIME AND + 4HOMPSON &LUCTUATING RESOURCES IN PLANT COMMUNI TIES A GENERAL THEORY OF INVASIBILITY *OURNAL OF %COLOGY $AVIS - ! + 4HOMPSON AND * 0 'RIME #HARLES 3 %LTON AND THE DISSOCIATION OF INVASION ECOLOGY FROM THE REST OF ECOLOGY $IVERSITY AND $ISTRIBUTIONS $ENNIS " 2 ! "ESHARNAIS * - #USHING 3 - (ENSON AND 2 & #ONSTANTINO #AN NOISE INDUCE CHAOS /)+/3 $ICK * 4 ! AND $ 0LATVOET )NVADING PREDATORY CRUSTACEAN $IKEROGAMMARUS VILLOSUS ELIMINATES BATH NATIVE AND EXOTIC SPECIES 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES
4RACKING THE TRACTABLE
$UKES * 3 3PECIES COMPOSITION AND DIVERSITY AFFECT GRASSLAND SUSCEPTIBILITY AND RESPONSE TO INVASION %COLOGICAL !PPLICATIONS $UKES * 3 AND ( ! -OONEY $OES GLOBAL CHANGE INCREASE THE SUCCESS OF BIOLOGICAL INVADERS 4RENDS IN %COLOGY %VOLUTION %LTON # 3 4HE ECOLOGY OF INVASIONS BY ANIMALS AND PLANTS -ETHUEN AND #O ,4$ ,ONDON 5+ (AMILTON - ! " 2 -URRAY - 7 #ADOTTE ' # -OSE ! # "AKER # * (ARRIS AND $ ,ICARI ,IFE HISTORY CORRELATES OF PLANT INVASIVENESS AT REGIONAL AND CONTINEN TAL SCALES %COLOGY ,ETTERS (ERBEN 4 " -ANDAK + "IMOVA AND : -UNZBERGOVA )NVASIBILITY AND SPECIES RICHNESS OF A COMMUNITY ! NEUTRAL MODEL AND A SURVEY OF PUBLISHED DATA %COLOGY (OLWAY $ ! &ACTORS GOVERNING RATE OF INVASION A NATURAL EXPERIMENT USING !RGENTINE ANTS /ECOLOGIA (OLWAY $ ! ! 6 3UAREZ AND 4 * #ASE 2OLE OF ABIOTIC FACTORS IN GOVERNING SUSCEPTIBILITY TO INVASION ! TEST WITH ARGENTINE ANTS %COLOGY ,ACH , )NVASIVE ANTS 5NWANTED PARTNERS IN ANT PLANT INTERACTIONS !NNALS OF THE -ISSOURI "OTANICAL 'ARDEN ,EVINE * - AND # - $!NTONIO %LTON REVISITED ! REVIEW OF EVIDENCE LINKING DIVER SITY AND INVASIBILITY /)+/3 ,LORET & & -EDAIL ' "RUNDU AND 0 % (ULME ,OCAL AND REGIONAL ABUNDANCE OF EXOTIC PLANT SPECIES ON -EDITERRANEAN ISLANDS ARE SPECIES TRAITS IMPORTANT 'LOBAL %COLOGY AND "IOGEOGRAPHY ,ODGE $ - "IOLOGICAL )NVASIONS – ,ESSONS FOR %COLOGY 4RENDS IN %COLOGY %VOLUTION ,ORTIE # * 2 7 "ROOKER 0 #HOLER : +IKVIDZE 2 -ICHALET & ) 0UGNAIRE AND 2 - #ALLAWAY 2ETHINKING PLANT COMMUNITY THEORY /IKOS -ACK 2 . $ 3IMBERLOFF 7 - ,ONSDALE ( %VANS - #LOUT AND & ! "AZZAZ "IOTIC INVASIONS #AUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COLOGICAL !PPLICATIONS -EMMOTT * . - 7ASER AND - 6 0RICE 4OLERANCE OF POLLINATION NETWORKS TO SPE CIES EXTINCTIONS 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES 0ARKER ) - AND + ! (AUBENSAK #OMPARATIVE POLLINATOR LIMITATION OF TWO NON NATIVE SHRUBS DO MUTUALISMS INmUENCE INVASIONS /ECOLOGIA 0ARKER ) - $ 3IMBERLOFF 7 - ,ONSDALE + 'OODELL - 7ONHAM 0 - +AREIVA - ( 7ILLIAMSON " 6ON (OLLE 0 " -OYLE * % "YERS AND , 'OLDWASSER )MPACT TOWARD A FRAMEWORK FOR UNDERSTANDING THE ECOLOGICAL EFFECTS OF INVADERS "IOLOGICAL )NVASIONS 0ETROVSKII 3 ! -OROZOV AND " , ,I 2EGIMES OF BIOLOGICAL INVASION IN A PREDATOR PREY SYSTEM WITH THE !LLEE EFFECT "ULLETIN OF -ATHEMATICAL "IOLOGY 0UTH , - AND $ - 0OST 3TUDYING INVASION HAVE WE MISSED THE BOAT %COLOGY ,ETTERS
3- -C-AHON -7 #ADOTTE AND 4 &UKAMI
2ICHARDSON $ - . !LLSOPP # - $!NTONIO 3 * -ILTON AND - 2EJMANEK 0LANT INVASIONS – THE ROLE OF MUTUALISMS "IOLOGICAL 2EVIEWS 3AKAI ! + & 7 !LLENDORF * 3 (OLT $ - ,ODGE * -OLOFSKY + ! 7ITH 3 "AUGHMAN 2 * #ABIN * % #OHEN . # %LLSTRAND $ % -C#AULEY 0 /.EIL ) - 0ARKER * . 4HOMPSON AND 3 ' 7ELLER 4HE POPULATION BIOLOGY OF INVASIVE SPECIES !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS 3AX $ & * * 3TACHOWICZ AND 3 $ 'AINES EDITORS 3PECIES )NVASIONS )NSIGHTS INTO %COLOGY %VOLUTION AND "IOGEOGRAPHY 3INAUER !SSOCIATES 3UNDERLAND -! 3CHWEITZER * ! AND + # ,ARSON 'REATER MORPHOLOGICAL PLASTICITY OF EXOTIC HONEY SUCKLE SPECIES MAY MAKE THEM BETTER INVADERS THAN NATIVE SPECIES *OURNAL OF THE 4ORREY "OTANICAL 3OCIETY 3HEA + AND 0 #HESSON #OMMUNITY ECOLOGY THEORY AS A FRAMEWORK FOR BIOLOGICAL INVASIONS 4RENDS IN %COLOGY %VOLUTION 4HOMSON $ - -ATRIX MODELS AS A TOOL FOR UNDERSTANDING INVASIVE PLANT AND NATIVE PLANT INTERACTIONS #ONSERVATION "IOLOGY 4ILMAN $ #OMMUNITY INVASIBILITY RECRUITMENT LIMITATION AND GRASSLAND BIODIVER SITY %COLOGY 7OOTTON * 4 4HE .ATURE AND #ONSEQUENCES OF )NDIRECT %FFECTS IN %COLOGICAL #OMMUNITIES !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS
#HAPTER TWO
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES - 7 #ADOTTE
).42/$5#4)/. ! NUMBER OF PROMINENT MODERN AUTHORS HAVE PERCEIVED A CHASM SEPARATING MAINSTREAM ECOLOGY AND INVASION BIOLOGY EG $AVIS ET AL )NTROSPECTION INTO THE NATURE OF INVASION BIOLOGY COULD BE SEEN AS PART OF A LARGER ENTERPRISE OF PRESCRIPTIVE PHILOSOPHY WITHIN ECOLOGY EG %GLER 0ETERS ,AWTON 4HESE TYPES OF INTROSPECTION ARE NOT SCIENCE PER SE THAT IS THEY ARE NOT TRY ING TO ANSWER QUESTIONS THROUGH DEDUCTION AND EMPIRICISM 2ATHER INTROSPECTION IS ABOUT THE EPISTEMOLOGY OF SCIENCE OR WHICH IDEAS AND CONCEPTS ARE VALUABLE AND WHAT KNOWLEDGE IS IMPORTANT BASICALLY (/7 SCIENCE IS DONE %PISTEMOLOGY IS NO TRIVIAL MATTER WHAT QUESTIONS WE ASK AND HOW WE COME TO CONCLUSIONS ARE UNDER THE PURVIEW OF EPISTEMOLOGY 4HIS CHAPTER IS ABOUT THE EPISTEMOLOGY OF ECOLOGICAL RESEARCH AND INVASION BIOLOGY 2ECENT CALLS FOR ECOLOGY AND INVASION BIOLOGY TO REINTEGRATE *OHNSTONE (USTON 4HOMPSON ET AL $AVIS ET AL ARE BASED UPON A PERCEIVED DISSOCIATION INSTIGATED BY %LTONS MAGISTERIAL BOOK ON INVASION BIOLOGY 4HESE CALLS ) BELIEVE RIGHTLY DRAW ATTENTION TO THE POTENTIAL FERTILE GROUND THAT LAY BETWEEN ECOLOGY AND INVASION BIOLOGY (OWEVER IF %LTON CAUSED THE DISSOCIATION -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
-7 #ADOTTE
$AVIS ET AL THEN WHAT WAS THE PRIOR STATE OF THE RELATIONSHIP BETWEEN ECOL OGY AND NON INDIGENOUS SPECIES .)3 ) WILL EXAMINE HOW EARLY ECOLOGISTS DEALT WITH NON NATIVE SPECIES IN THEIR WRITINGS ESPECIALLY AT THE TIME WHEN ECOLOGY BECAME ITS OWN lELD OF SCIENCE LATE S TO EARLY S
%#/,/')#!, 3#)%.#% !4 4(% "%')..).' %VEN THOUGH MANY GREAT THINKERS THOUGHT ABOUT WHY SPECIES OCCUR WHERE THEY DO EG !RISTOTLE 0ALEY !GASSIZ DE #ANDOLLE IT WASNT UNTIL THE MID S THAT THESE TYPES OF INVESTIGATIONS MOVED BEYOND METAPHYSICAL ACCOUNTS AND BEGAN TO USE WHAT COULD BE REFERRED TO AS MODERN SCIENTIlC EPISTEMOLOGY %ARLY @ECOLOGY WAS TYPIlED BY NATURAL HISTORY OBSERVATIONS %GERTON BUT THE CONTRIBUTION OF EARLY WORKERS CANNOT BE UNDERVALUED SIMPLY BECAUSE SCIENTIlC EPISTEMOLOGY WAS NOT AN INDEPENDENT BRANCH OF KNOWLEDGE 4HAT SAID THE NEW SCIENCE THAT WAS TO EMERGE IN THE MID TO LATE S WOULD ECLIPSE IN A MATTER OF DECADES THE PREVI OUS YEARS OF THOUGHT ON THE ORIGIN AND DISTRIBUTION OF SPECIES "EFORE THERE COULD BE A SCIENCE OF ECOLOGY THE ULTIMATE CAUSES OF SPECIES DIVERSITY AND DISTRIBU TIONS NEED TO BE ARTICULATED IN A WAY THAT WOULD REMOVE NON NATURALISTIC EXPLANA TIONS 7HAT FOLLOWS THROUGH THE REST OF THIS ESSAY IS NOT MEANT TO BE A EXHAUSTIVE SUMMARY OF EARLY ECOLOGY FOR THAT SEE %GERTON AND -C)NTOSH RATHER ) WILL USE SELECTED EXAMPLES TO EXAMINE HOW EARLY ECOLOGY DEALT WITH .)3 %ARLY PRE $ARWINIAN ECOLOGY WAS IMBUED WITH NOTIONS OF @BALANCE OF NATURE %GERTON AND SO CHANGES IN THE ABUNDANCE AND DISTRIBUTION OF SPECIES WERE NOT PROMINENT IN EARLY WRITINGS 4HE SCIENCE OF SPECIES DISTRIBUTIONS WAS LARGELY CONCEIVED IN THE TH AND TH CENTURIES IN THE WORK OF "UFFON DE #ANDOLLE AND $ARWIN AND STRONG EXPLANATORY SCIENCE DID NOT EMERGE UNTIL #HARLES $ARWINS 4HE /RIGIN OF THE 3PECIES IN 4HOUGH SOME OF $ARWINS CONTEMPORARIES DID NOT RECOGNIZE 4HE /RIGIN AS @SCIENTIlC ON THE GROUNDS THAT IT WAS NOT INDUCTIVE ENOUGH /WENS 3EDGWICK $ARWINS CONCEPTUAL LEAPS AND THE LINK ING OF FORMERLY DISPARATE PIECES OF INFORMATION RESEMBLE MODERN SCIENCE MORE THAN ANYTHING THAT PREDATES $ARWIN )N TRYING TO EXPLAIN PATTERNS OF SPECIES DISTRIBUTIONS AND ABUNDANCE $ARWIN WAS FACED WITH THE PROBLEM OF .)3 (OW DID $ARWIN ASSIMILATE SUCH AN APPAR ENT FACT THAT SPECIES READILY MOVE FROM THEIR NATIVE RANGE $ARWIN CLEVERLY USED NON INDIGENOUS SPECIES AS A DEVICE TO TEST OR ILLUSTRATE HIS THEORY OF NATURAL SELEC TION AND DESCENT WITH MODIlCATION .)3 ARE SPECIES LOCALLY COEXISTING WITH OTHER SPECIES YET INDEPENDENT OF THESE LOCAL ASSEMBLAGES WITH THEIR OWN EVOLUTIONARY HISTORIES 4HEREFORE $ARWIN SAW THE PRESENCE OF .)3 AS EFlCACIOUS EXAMPLES OF NATURAL SELECTION IN ALREADY DISTINCT FORMS $ARWIN NOTES THAT AN IMPORTANT ASPECT OF THE STRUGGLE FOR EXISTENCE IS THAT SPECIES NATURALLY HAVE A PROPENSITY TO INCREASE AT HIGH RATES SO THE STRUGGLE IS AN ISSUE OF POPULATION PROCESSES (E MENTIONS THAT WHEN DOMESTIC ANIMALS ARE RELEASED THEIR POPULATIONS OFTEN RAPIDLY INCREASE &URTHERMORE hSO IS IT WITH PLANTSv
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
THAT THERE ARE hINTRODUCED PLANTS WHICH HAVE BECOME COMMON THROUGHOUT WHOLE ISLANDS IN A PERIOD OF LESS THAN TEN YEARSv P 4HE EXPLANATION FOR THIS IS hTHAT THE CONDITIONS OF LIFE HAVE BEEN VERY FAVOURABLE AND THAT THERE HAS CONSE QUENTLY BEEN LESS DESTRUCTION OF THE YOUNG AND OLDv P %SSENTIALLY WHAT BETTER WAY TO SEE THE POTENTIAL HIGH RATES OF INCREASE THAN IN SPECIES ARRIVING IN PLACES WHERE THEY DIDNT EXIST BEFORE )SOLATION IS A FUNDAMENTAL PROCESS IN ECOLOGY AND EVOLUTIONARY BIOLOGY AND $ARWIN REMINDS THE READER OF THIS THAT ON ISOLATED ISLANDS hLET IT BE REMEMBERED HOW POWERFUL THE INmUENCE OF A SINGLE INTRODUCED TREE OR MAMMALv P !DAPTATION IS NOT ABSOLUTE IT IS RELATIVE TO SPECIES THAT EXIST TOGETHER AND THAT BARRIERS TO IMMIGRATION THAT ISOLATE HABITATS hINTO WHICH NEW AND BETTER ADAPTED FORMS COULD NOT FREELY ENTERv AND THAT hHAD THE AREA BEEN OPEN TO IMMIGRATION THESE SAME PLACES WOULD HENCE BEEN SEIZED ON BY INTRUDERSv P 4HERE IS THEN ALWAYS ROOM FOR IMPROVEMENT AND hWE MAY SAFELY CONCLUDED THAT THE NATIVES MIGHT HAVE BEEN MODIlED WITH ADVANTAGE SO AS TO HAVE BETTER RESISTED SUCH INTRUDERSv P &OR EXAMPLE h 4HE ENDEMIC PRODUCTIONS OF .EW :EALAND ARE PERFECT ONE COMPARED WITH ANOTHER BUT THEY ARE NOW RAPIDLY YIELDING BEFORE THE ADVANCING LEGIONS OF PLANTS AND ANIMALS INTRODUCED FROM %UROPEv P 7HEREAS SPECIES DIFFERENCES ARE SLIGHT COMPARED TO THOSE AMONG GENERA $ARWIN EXPECTED AS !LPHONSE DE #ANDOLLE SUGGESTED hTHAT mORAS GAIN BY NATURALISATION x PROPORTIONALLY x FAR MORE IN NEW GENERA THAN IN NEW SPECIESv $ARWIN P SEE $AEHLER
).6!3)6% 30%#)%3 !.$ %#/,/'9 "%&/2% 4(% 4( #%.4529 "Y THE EARLY TH CENTURY ECOLOGY WAS A SCIENCE AND EXOTIC SPECIES WERE A CON CERN BUT THESE TWO THINGS DID NOT SEEM TO INmUENCE ONE ANOTHER &OR ONE THING MODERN CALLS FOR ECOLOGISTS TO WORK TOWARDS SAVING THE NATURAL WORLD EG 0ETERS 3HRADER &RECHETTE %HRLICH SIMPLY DID NOT HAPPEN UNTIL THE MID TH CENTURY SEE $AVIS #HAPTER )NCIPIENT MODERNISM WAS SURFACING AND MODERN CIVILIZATION AND HER SCIENCE WAS QUICKLY BEING REGARDED AS THE ONLY VALID KNOWLEDGE ACQUIRING METHOD AND WAS NEUTRAL TO OR ABOVE MORALITY AND ETHICS )N !MERICA THIS PERIOD SAW UNPRECEDENTED CHANGE IN HIGHER EDUCATION AND THE PRE EXISTING EMPHASIS ON THEOLOGY AND PHILOSOPHY WAS BEING REPLACED WITH SCI ENCE AND PSYCHOLOGY CURRICULA WITH MANY INSTITUTIONS DEPARTMENTS AND ENDOW MENTS CREATED PROMOTING THE TRAINING OF PROFESSIONAL SCIENTISTS AT POSTSECONDARY INSTITUTIONS #ROKER -ENAND 4HIS WAS THE TIME PERIOD WHEN GREAT !MERICAN THINKERS SUCH AS 7ILLIAM *AMES AND *OHN $EWEY WOULD CULL OUT THE LAST REMAINING NOTIONS OF SUPERNATURAL EXPLANATION IN !MERICAN !CEDEMIA "UT ALL WAS NOT WELL PEOPLE WERE NOTICING THAT MODERN CIVILIZATION WAS HAV ING UNDESIRABLE IMPACTS ON THE NATURAL WORLD )N A DEVASTATING YELLOW FEVER OUTBREAK IN 0HILADELPHIA LIKELY IMPORTED FROM THE 7EST )NDIES HAD PEOPLE FEARING THE ACCEDENTAL IMPORTATION OF PATHOGENIC .)3 %GERTON 2ALPH
-7 #ADOTTE
7ALDO %MERSON HAD ALREADY BEEN PLEADING TO THE !MERICAN PUBLIC TO RETHINK ITS UNHEALTHY RELATIONSHIP WITH NATURE %MERSON 4HE IMPACT OF CERTAIN INVAD ERS WAS BECOMING APPARENT %IGHTEENTH CENTURY BOTANISTS SUCH AS *OHN "ARTRAM WERE STARTING TO COMMENT ON THE FACT THAT SOME INTRODUCED PLANTS WERE HAVING NEGATIVE IMPACTS AND WERE DIFlCULT TO CONTROL SEE -ACK (OOKER NOTICED THAT %UROPEAN SPECIES WERE QUICKLY REPLACING NATIVES IN .EW :EALAND 3OME OF THE EARLIEST CONCERNS ABOUT EXOTIC SPECIES WERE IN TERMS OF THE MAIN TENANCE OF THE @NATURAL BASED ON A MORALITY OF AESTHETICS EG /LMSTEAD 3ARGENT BOTH CITED AND DISCUSSED BY 3IMBERLOFF 3OON AFTER A MORE DISTINCTLY !MERICAN PRAGMATIC APPROACH RECOGNIZED THE ECONOMIC AGRICUL TURAL AND ECOLOGICAL EFFECTS BY NON INDIGENOUS SPECIES EG &ITCH (OWARD A )N HIS ADDRESS TO THE !MERICAN !SSOCIATION FOR THE !DVANCEMENT OF 3CIENCE ,ELAND (OWARD SAYS h0OTENTIALLY COSMOPOLITAN FORMS x HAVE BY HUMAN AGENCY BECOME DISPERSED OVER NEARLY ALL OF THE CIVILIZED PARTS OF THE GLOBE WHILE THOUSANDS OF OTHER SPECIES HAVE BEEN CARRIED THOUSANDS OF MILES FROM THEIR NATIVE HOMES AND HAVE ESTABLISHED THEMSELVES AND mOURISHED OFTEN WITH A NEW VIGOR IN A NEW SOIL AND WITH A NOVEL ENVIRONMENTv (OWARD A P (OWARD PUBLISHED MORE THAN ARTICLES ON NON NATIVE INSECT PESTS AND THE REALIZED OR POTENTIAL IMPACTS OF INTRODUCED SPECIES EG (OWARD A B (OWARDS PEER AND FRIEND 3TEPHEN &ORBES THE FATHER OF !MERICAN ECOLOGY ALSO BECAME PROFESSIONALLY DEDICATED TO THE EFFECTS THAT INSECT PESTS POSED FOR AGRICULTURE #ROKER &ORBES WROTE MANY ARTICLES ON THE BIOLOGY AND IMPACTS OF INSECT PESTS EG &ORBES A "Y THE TURN OF THE CENTURY WE HAVE LEGITIMATE NON AESTHETIC CONCERNS ABOUT THE IMPORTATION OF NOVEL SPECIES /F COURSE MUCH OF THIS CONCERN WAS IN TERMS OF AGRICULTURAL AND ECONOMIC COSTS $URING THIS TIME ECOLOGY WAS DEVELOP ING INTO ITS OWN SCIENCE %GERTON -C)NTOSH AND HOW DID THIS SCIENCE OF ECOLOGY ADDRESS THESE CONCERNS ABOUT INVASIVE SPECIES $URING THIS PERIOD THE DEVELOPMENT OF THE SCIENCE OF ECOLOGY WAS LARGELY A %UROPEAN PHENOMENON WITHOUT A UNIQUELY !MERICAN SCHOOL UNTIL SHORTLY AFTER THE TURN OF THE CENTURY -C)NTOSH /F COURSE THERE WAS &ORBES WHO WROTE SEVERAL PAPERS BEFORE THE TH CENTURY WHICH WE SHOULD CALL @ECOLOGICAL ESPECIALLY HIS FAMOUS ,AKE AS A -ICROCOSM TALK DELIVERED TO THE 0EORIA 3CIENTIlC !SSOCIATION &ORBES B (ERE HE STRESSED THE INTERACTION AMONG SPECIES AND A BALANCE OF NATURE VIEW BUT WE CANNOT CALL THIS A @SCHOOL AS LITTLE SUBSEQUENT WORK WAS DONE SPAWNING LITTLE RESEARCH AND NO TEXTBOOKS &ORBES AND HIS CONTEMPORARIES (ENRY #OWLES AND ,ELAND (OWARD COULD BE SAID TO HAVE STARTED APPLIED ECOLOGY )T IS CURIOUS THEN THAT ON THE ONE HAND &ORBES WORKED EXTENSIVELY WITH INSECT PESTS AND EXOTIC AGRICULTURAL DISEASES AND YET MAINTAINED A CLOSED SYSTEM BALANCE OF NATURE APPROACH IN HIS ECOLOGICAL WRITINGS 4HE FACT THAT A SINGLE INDIVIDUAL RECOGNIZING THE IMPORTANCE OF PESTS AND UNDERSTANDING ECOLOGICAL SYSTEMS WOULD KEEP THESE IDEAS DISSOCIATED IS PROPHETIC FOR THE REST OF EARLY ECOLOGY %COLOGY GREW OUT OF THE APPARENT NEED TO SEPARATE CAUSES IN WHOLE ORGANISM BIOLOGY 7HEREAS $ARWINS THEORY EXPLAINED THE ULTIMATE CAUSES AND PATTERNS
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
OF WHY WE lND SPECIES WHERE WE DO EG WHY CACTI ARE DIVERSE IN DESERT REGIONS AND THE PURPOSE OF THE PANDAS THUMB IT DID NOT INCLUDE A STRONG FRAMEWORK TO ACCOUNT FOR PROXIMATE CAUSES AND PATTERNS EG CYCLIC POPULATION DYNAMICS AND PATTERNS OF ABUNDANCES %ARLY FORAYS INTO THE ULTIMATE CAUSES OF SPECIES DISTRIBUTIONS FEATURED GEOGRAPHICAL AND GEOLOGICAL CAUSES OF SPECIES DISTRIBUTIONS EG 7ALLACE 7ALLACE OBSERVED THAT BIOTAS WERE LARGE REGIONAL ENTITIES OFTEN WITH FAIRLY DISCRETE BOUNDARIES #OMMON WAS THE IDEA OF BARRIERS TO MOVEMENT WITH ALL SPECIES BEING ABLE TO MOVE TO NEW LOCALS BUT RARELY DOING SO EG (EILPRIN 7RITINGS OF DE #ANDOLLE AND $ARWIN CERTAINLY ADDRESS ISSUES OF PROXIMATE PATTERNS BUT IT TOOK A SEPARATE lELD TO CREATE THEIR OWN PROXIMATE EXPLANATIONS 4HE BIOGEOGRAPHER /SCAR $RUDE WAS ABLE TO SEPARATE THESE CAUSES AND PAT TERNS IN HIS -ANUAL DE 'EOGRAPHIE "OTANIQUE (E NOTED THAT THERE WERE TWO FORCES OF CHANGE IN SPECIES RANGES AND ABUNDANCE GEOLOGICAL AND BIOLOGICAL $RUDE RIGHTLY THOUGHT THAT ALL ULTIMATE CHANGE HAPPENED IN hCOURS DE LÏVOLUTION GEOLOGIQUEv P THE COURSE OF GEOLOGICAL EVOLUTION 4HIS INCLUDED ADAPTA TION AS WELL AS CONSTANT CHANGE BUT HE ALSO SAW THE ROLES OF THE ORGANISM ENVIRONMENT INTERFACE DISPERSAL AND COMPETITION 4HE DISTINCTION BETWEEN GEOLOGICAL AND BIOLOGICAL CAUSES WAS IMPORTANT FOR $RUDES UNDERSTANDING OF RAPID CHANGES IN SPECIES DISTRIBUTIONS $RUDE CLASSIlES LIMITS TO SPECIES RANGES AS EITHER GEOGRAPHI CAL THAT IS MOUNTAINS OCEANS AND THE LIKE ARISING FROM GEOLOGICAL PROCESSES AND BIOLOGICAL BY WHICH HE MEANS CHANCE DISPERSAL AND THE AGENCY OF HUMANS h,ES LIMITS DES AIRES SONT PUREMENT GÏOGRAPHIQUES OU BIEN RÏSULTENT DE LACTION COMBINÏE DES CONDITIONS DE VIEv P $RUDE SAYS THAT WITHOUT THE AID OF HUMANS GEOGRAPHICAL BARRIERS LIMIT SPECIES SPREAD BUT THAT RARE CHANCE EVENTS STILL PLAY AN IMPORTANT ROLE FOR RANGE EXPANSION 7ITH HUMAN AID SPECIES WILL SPREAD AS FAR AS THE EXTERNAL ENVIRONMENT ALLOWS $RUDE TELLS THE READER THAT MOVING TO A NEW LOCATION WHICH MUST BE CLIMATICALLY SIMILAR TO THAT IN A SPECIES NATIVE RANGE IS ONLY HALF THE EQUATION AND ONCE A PLANT HAS ARRIVED hELLE LUTTE AVEC SUCCES CON TRE UNE PLANTE INDIGÒNE TOUT Ì FAIT ADAPTÏE AU CLIMATv P IT HAS TO BE SUC CESSFUL IN THE STRUGGLE AGAINST INDIGENOUS PLANTS PERFECTLY ADAPTED TO THE CLIMATE 'IVEN THIS LIMITATION PLANTS STILL COME TO hCOUVRIR DE GRANDES SURFACESv P AND IN COVERING THESE LARGE AREAS DISPLACE OTHER SPECIES (E GOES EVEN FURTHER TO SAY THAT SOME SPECIES DO NOT DOMINATE ONE ANOTHER AND COMPETITION IS INDETERMI NATE )N THESE SPECIES THE RANGES ARE SET UP BY WHOEVER ARRIVES THERE lRST $RUDES ACCOUNT SOUNDS VERY MODERN (IS BIOGEOGRAPHY INCORPORATES GEOGRA PHY CHANCE COMMUNITY ASSEMBLY AND LOCAL COMPETITION (E ALSO HAS A SYSTEM OF PROXIMATE CAUSES AND PATTERNS THAT READILY ACCOUNTS FOR THE DYNAMICS OF INVASIVE SPECIES (OWEVER IN READING THE CHAPTER ON RANGE EXPANSION IN $RUDE ONE GETS THE IMPRESSION THAT HE IS TRYING TO EXPLAIN THE FACT OF .)3 SPREAD IN LIGHT OF LATE NINETEENTH CENTURY KNOWLEDGE OF BIOGEOGRAPHY RATHER THAN TRYING TO UNDER STAND INVASIONS AND SPECIlC INVADERS 4HIS IS NOT A CRITICISM AS HE WAS DEVELOPING A SYSTEM OF KNOWLEDGE ABOUT THE NATURAL WORLD AND HIS EPISTEMOLOGY CALLED FOR EXPLAINING EXTANT PATTERNS WITHIN THE EXISTING FRAMEWORK
-7 #ADOTTE
!NOTHER %UROPEAN ECOLOGIST %UGENE 7ARMING WROTE AN INmUENTIAL ECOLOGY BOOK BEFORE THE TURN OF THE CENTURY 4HE %NGLISH TRANSLATION OF HIS /ECOLOGY OF 0LANTS WAS CONCERNED WITH POPULATION AND COMMUNITY ECOLOGY AND HE TRIED TO DEVELOP A SYSTEM OF ECOLOGICAL UNDERSTANDING 7ARMING WAS VERY MUCH INTERESTED IN THE PROCESS OF ECOLOGICAL CHANGE AND THIS CHANGE INCLUDED THE ARRIVAL OF NEW SPECIES (E BELIEVED THAT ECOLOGICAL PROCESSES INCLUDING CHANGE WERE REALIZED AT THE COMMUNITY LEVEL &OR EXAMPLE HE BELIEVED THAT SUCCESSIONAL CHANGE RESULTED FROM COMPETITION AMONG COMMUNITY TYPES AFFECTED BY CHANGES IN THE ENVIRONMENT %SSENTIALLY 7ARMINGS CHANGE IS ASSEMBLAGES OF SPECIES MOVING AMONG EQUILIBRIA BUT WHAT WAS HIS MECHANISM FOR THESE CHANGES 7ARMING SAYS THAT THERE ARE TWO TYPES OF COMMUNITY CHANGE lRST IS FROM @CHANGES IN SOIL AND THE OTHER IS CHANGE @WITHOUT NEW SOIL )N THE lRST TYPE OF CHANGE DISTURBANCES BOTH NATURAL AND HUMAN CAUSED ARE IMPORTANT AND ABRUPT 3LOWER TYPES OF CHANGE INCLUDE INCREASES OR DECREASES IN WATER CONTENT OR BY THE ACCUMULATION OF SOIL 4HE SECOND TYPE OF CHANGE HAPPENS THROUGH MIGRA TIONS AND STRUGGLES AMONG INDIVIDUAL SPECIES 4HIS SECOND TYPE OF COMMUNITY CHANGE 7ARMING SAYS IS ATYPICAL hTHE STRUG GLES IN QUESTION ARE RAREv AND THAT COUNTRIES hWHOSE VEGETATION IS NOT APPRECIABLY DISTURBED BY MAN OR ANIMALS AND WHICH HAS BEEN EXPOSED FOR LONG AGES PAST TO IMMIGRATION FROM ADJOINING COUNTRIES IN THIS CASE A CERTAIN EQUILIBRIUM MUST HAVE BEEN ATTAINEDv P 4HIS EQUILIBRIUM VIEW MEANS THAT THE PROBLEM OF INVASIVE SPECIES IS ONE PRIMARILY ASSOCIATED WITH DISTURBANCES WHICH IS LARGELY TRUE (OWEVER HIS VIEW MAY HAVE SOME DIFlCULTLY EXPLAINING WHY SOME SPE CIES INVADE INTACT COMMUNITIES (E CONCEDES THIS POINT ON THE NEXT PAGE hSOME CHANGES IN THE NATURE OF FORESTS MAY HAVE BEEN SIMPLY DUE TO THE ENTRY OF NEW SPECIESv P 7ARMING DOES MAKE AN EMOTIONAL PLEA TO BE WEARY OF IMPORTING NEW SPECIES BECAUSE OF THE COMPETITION TO WHICH THEY MAY SUBJECT NATIVE FORMS hA NEW x COM MUNITY WHICH DID NOT NATURALLY OCCUR BEFORE THE SOIL HAD BEEN DRAWN INTO THE SERVICE OF -AN AND THE SPECIES WHICH NOW OCCUR IN VAST NUMBERS AND FORM A COMMUNITY WITH ITS OWN SPECIAL STAMP AND ECONOMYv P 7ARMINGS SYSTEM MAKES PREDICTIONS AS TO WHAT TYPES OF COMMUNITIES OUGHT TO BE MORE INVADED AND OUR MODERN UNDERSTANDING OF THE INVASION PROCESS WOULD ALSO PREDICT THAT INTACT COMMUNITIES ARE LESS INVADABLE THAN DISTURBED ONES (OWEVER BOTH 7ARMING AND $RUDE WERE NOT EXPLICITLY TRYING TO UNDERSTAND INVASIONS RATHER THEY WERE TRYING TO lT THE FACT THAT WE SEE INVADERS INTO THEIR RESPECTIVE ECOLOGICAL SYSTEMS &OR THEM THERE WAS NO REAL ASSOCIATION BETWEEN DEVELOPING ECOLOGICAL UNDERSTANDING AND ADDRESSING THE PROBLEM OF INVASIVE SPECIES 4HEY FELT THAT IF THEIR RESEARCH PROGRAMMES EXPLAINED THE GENERAL PHENOMENON OF .)3 THEN THEIR ECOLOGY WAS ROBUST 4HE RELATIONSHIP BETWEEN ECOLOGY AND INVADERS WAS LIMITED AND ONE WAY !T MOST INVADERS WERE TESTS OF EARLY ECOLOGISTS IDEAS OR AT WORST PHENOMENA NEEDING EXPLANATION
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
4(% .!452% /& #(!.'% #,%-%.43 !.$ 4(% !-%2)#!. 3#(//, 3HORTLY AFTER THE TURN OF THE CENTURY AN !MERICAN SCHOOL EMBODIED IN &REDERIC #LEMENTS COME TO THE FORE -C)NTOSH ) SAY THAT #LEMENTS EMBODIED THE SCHOOL BECAUSE HE DID ALL THE THINGS THAT MAKE A SUCCESSFUL SCHOOL OF THOUGHT (E INTERACTED WITH A NUMBER OF STUDENTS AND COLLEAGUES HE WROTE NUMEROUS SUCCESSFUL TEXTBOOKS AND MOST IMPORTANTLY HE EMPHASIZED A STRONG HEURISTIC PARADIGM IN MUCH OF HIS WRITING NAMELY THE NATURE OF ECOLOGICAL CHANGE #LEMENTS lRST TWO BOOKS REALLY LAID THE GROUNDWORK FOR THIS NEW SCHOOL (IS lRST 2ESEARCH -ETHODS IN %COLOGY DETAILED HOW THE SCIENCE OF ECOLOGY SHOULD BE DONE WHAT TECHNIQUES AND RESEARCH TOPICS WERE MOST FRUITFUL 4HIS WAS SOON FOLLOWED BY A SECOND BOOK 0LANT 0HYSIOLOGY AND %COLOGY WHICH HAD MUCH OVERLAP WITH HIS BOOK BUT REINFORCED WHICH AREAS OF RESEARCH WERE MOST IMPORTANT AND THE PARADIGM OF PLANT ECOLOGY 3PECIlCALLY THESE BOOKS HAD AN UNPRECEDENTED FOCUS ON ECOLOGICAL CHANGE OR WHAT BECAME KNOWN AS SUCCES SION )NTUITIVELY SUCH A PARADIGM SEEMS LIKE .)3 WOULD BE OF CENTRAL CONCERN "OTH BOOKS DElNE INVASION ALMOST IDENTICALLY AS h4HE MOVEMENT OF ONE OR MORE PLANTS FROM ONE AREA INTO ANOTHER AND THEIR ESTABLISHMENT IN THE LATTER P ALSO A VERY SIMILAR QUOTE IN P (E NOTES h)NVASION IS A REGULAR OCCURRENCE BETWEEN ADJACENT FORMATIONS BUT IT ALSO TAKES PLACE INTO REMOTE ONES AS A RESULT OF LONG CARRIAGE BY WIND WATER BIRDS RAILROADS OR VESSELSv P (E TELLS US THAT DISPERSAL IS USUALLY CONSTRAINED BY BARRIERS BUT THAT HUMANS AS AN AGENT OF DISPERSAL ARE ABLE TO TRANSCEND THESE BARRIERS )NVASIONS ARE IMPORTANT FOR A NUMBER OF REASONS &IRST INVASIONS CAN SIGNIlCANTLY AFFECT SPECIES DISTRIBUTIONS 3ECONDLY ECOLOGICAL CHANGE DEPENDS ON INVASIONS #LEMENTS DElNES SUCCESSION AS A hSERIES OF INVASIONS xIN THE SAME SPOTv P P /F COURSE SEVERAL FACTORS WORK AGAINST THE SUCCESS OF AN INVASION &IRST OF ALL THERE ARE THE WELL KNOWN GEOGRAPHICAL BARRIERS TO MIGRATION MOUNTAINS OCEANS ETC BUT MORE IMPORTANTLY #LEMENTS DETAILS OTHER TYPES OF BARRIERS 4HERE IS AN ABIOTIC BARRIER THE SPECIES MUST lND ITSELF IN AN ENVIRONMENT IN WHICH IT CAN SURVIVE -ANY BIOLOGICAL FORCES WORK AGAINST SPECIES ESTABLISHMENT INCLUDING PREDATION DISEASE COMPETITION AND HUMANS TRYING TO CONTROL WEEDS !LSO #LEMENTS lNDS THAT WHETHER THE HABITAT IS FULL OR NOT IS OF PARAMOUNT IMPORTANCE TO INVASION SUCCESS AS COMPETITION FROM FULL COMMUNITIES WILL BE TOO SEVERE FOR THE COLONIZER TO SUCCEED 4HIS VIEW OF ECOLOGICAL SUCCESSION IS COMMON IN THE WRITINGS OF #LEMENTS COLLEAGUES AND COLLABORATORS 3HANTZ SAW INVASIONS AS THE PROCESS OF SUCCESSION AND SUCCESSION AS THE PROCESS OF CHANGING FORMATIONS OR COMMUNITY TYPES 4HE IDEA OF SPECIES INVASIONS AS THE FORCE BEHIND SUCCESSION IS ALSO DOMI NANT IN 7EAVER AND #LEMENTS (UMANITYS ROLE IS EXAMINED IN GREATER DETAIL AND THEY NOTICE THAT ANTHROPOGENIC EFFECTS ON COMMUNITY SUCCESSION CAN BE SEVERE AS WE BOTH DISTURB HABITATS AND BRING IN NEW INDIVIDUALS 4HEY NOTE THAT THE MOTOR OF SUCCESSION IS NOT DISTURBANCE BUT RATHER BIOTIC PROCESSES
-7 #ADOTTE
MIGRATION AND COMPETITION AND THAT CLIMAX COMMUNITIES OFTEN RESIST THESE BIOTIC FACTORS #LEMENTS AND 3HELFORD CLARIlED WHO ARE CALLED INVADERS 3PECIlCALLY INVADERS ARE THOSE SPECIES THAT DID NOT PREVIOUSLY EXIST IN THE HABITAT THEY ARE INVADING 0REVIOUSLY #LEMENTS DID NOT EXPLICITLY STIPULATE WHETHER THE INVADERS HAD TO BE SEPARATE SPECIES (ERE #LEMENTS AND 3HELFORD MAKE NO DISTINCTION ABOUT WHERE SPECIES COME FROM IN TERMS OF THEIR NATIVE OR INTRODUCED STATUS %ARLIER #LEMENTS DID CREATE TERMS TO REmECT SPECIES THAT MIGRATE FROM NEARBY VERSUS THOSE ORIGINATING FURTHER AWAY 9ET NONE OF THESE WORKS EXPLICITLY EXAMINES .)3 JUST ECOLOGICAL PROCESSES OF IDEALIZED SPECIES !GAIN LIKE THE OTHER EARLY ECOLOGISTS #LEMENTS AND COLLEAGUES WERE INTERESTED IN ESTABLISHING A STRONG PROGRAMME THAT COULD POTENTIALLY EXPLAIN THE OCCURRENCE OF .)3
%80,!).).' 30%#)%3 /##522%.#%3 7)4( 4(% .)#(% ) CONTINUE BY TAKING A BRIEF TOUR OF ECOLOGY UP TO THE S $URING THIS PERIOD PRIMARY PUBLICATIONS IE ACADEMIC JOURNAL ARTICLES WERE BECOMING INCREASINGLY IMPORTANT FOR THE DEVELOPMENT AND DISSEMINATION OF NEW IDEAS /NE OF THE MOST IMPORTANT CONCEPTUAL DEVELOPMENTS IN EARLY ECOLOGY WAS THE IDEA OF THE NICHE 4HROUGH UNDERSTANDING A SPECIES NICHE ONE COULD POTENTIALLY UNDERSTAND AND PREDICT WHERE AND WHEN SPECIES IS FOUND AND WHICH SPECIES ARE LIKELY TO REPLACE ONE ANOTHER 7E COULD PROBABLY TRACE THE NICHE CONCEPT ALL THE WAY BACK TO $ARWIN BUT THE IDEA OF EXAMINING THE DISTRIBUTION OF SPECIES THROUGH A SPECIES SUITE OF ENVIRON MENTAL NEEDS IS COMMONLY ATTRIBUTED TO 'RINNELL 'RINNELLS NICHE CONCEPT HAS BEEN AN IMPORTANT THEME IN THE DEVELOPMENT OF ECOLOGY (IS PREMISE WAS THAT PATTERNS OF SPECIES OCCURRENCE ARE BEST UNDERSTOOD THROUGH THEIR ABIOTIC AND BIOTIC REQUIREMENTS (UTCHINSON FAMOUSLY USED THIS NICHE CONCEPT TO ADVANCED THE NOTION OF A MULTIDIMENSIONAL NICHE SPACE DElNING WHERE EACH SPECIES COULD POTENTIALLY LIVE (UTCHINSONS CONCEPT COULD POTENTIALLY EXPLAIN WHERE SPECIES COULD LIVE AND THEREFORE WHERE THEY COULD INVADE AS EACH SPECIES POTENTIALLY OCCUPIES A UNIQUE REGION OF THE NTH DIMENSIONAL NICHE HYPERSPACE 4HE DElNI TION OF @NICHE HAS BEEN RECOGNIZED AS PROBLEMATIC 3IMBERLOFF #ONNER AND 3IMBERLOFF AND OPEN TO VARIOUS INTERPRETATIONS ,EIBOLD #HASE AND ,EIBOLD !N EARLY REINTERPRETATION WAS PROVIDED BY %LTON WHO SAW THE NICHE AS A SPECIES @STATUS IN THE COMMUNITY 4HIS INCLUDED THE ROLE AN ORGAN ISM PLAYED AND MOST IMPORTANTLY ITS RELATIONSHIP TO OTHER SPECIES AND ESPECIALLY THE TROPHIC STATUS OF A SPECIES %LTONS INVASIONS BOOK ACTUALLY USED BOTH CONCEPTS OF THE NICHE TO UNDERSTAND WHEN AND WHERE .)3 INVADE AND WHICH COM MUNITIES WERE MORE LIKELY TO BE INVADED /NLY RECENTLY HAD THERE BEEN AN ATTEMPT AT RECONCILING THESE TWO MAJOR CONCEPTUALIZATIONS OF THE NICHE CONCEPT ,EIBOLD #HASE AND ,EIBOLD 3INCE 'RINNELLS PAPER RESEARCH ON COMPETITION HAS BEEN INTIMATELY ASSOCIATED WITH THE NICHE CONCEPT %LTON LIKE 7ARMING THOUGHT
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
SPECIES RICH COMMUNITIES OUGHT TO BE LESS INVADABLE BECAUSE AVAILABLE NICHES SHOULD BE lLLED AND COMPETITION FOR NICHE SPACE MORE INTENSE #OMPETITION AS A MAJOR STRUCTURING FORCE SURFACED BEFORE %LTON EG 'AUSE $!NCONA WITH THE FOUNDATION IN WHAT 'AUSE CALLED THE @COMPETITIVE EXCLUSION PRINCIPLE SEE ALSO (ARDIN PROBABLY lRST ARTICULATED BY 'RINNELL 4HE CENTRAL PREMISE OF THIS PRINCIPLE IS THAT h.O TWO SPECIES OF IDENTICAL OR EVEN CLOSELY SIMILAR BIOLOGICAL PREDILECTIONS CAN LONG OCCUPY THE SAME NICHE x AT THE SAME TIMEv 'RINNELL P )N FACT 'RINNELL USED THIS REASON ING TO ARGUE AGAINST THE PURPOSEFUL INTRODUCTION BY THE STATE OF #LAIFORNIA OF THE (UNGARIAN PARTRIDGE FOR HUNTING 'RINNELLS CONCERN WAS THAT THE (UNGARIAN PARTRIDGE SHARED ITS NICHE WITH THE NATIVE #ALIFORNIA QUAIL AND THAT THE LATTER WOULD LIKELY BE COMPETITIVELY EXCLUDED 4HIS PREDICTION WAS BASED ON THE OBSER VATION THAT SPECIES HAVING LARGE NATIVE RANGES USUALLY EXCLUDE SMALLER RANGED COMPETITORS 'RINNELL APPLIED ECOLOGICAL REASONING TO PREDICTING THE OUTCOME OF A SPECIES INTRODUCTION 'AUSE SAW THE VALUE THAT INVASIONS HAVE FOR UNDERSTANDING GENERAL ECOLOGICAL PROCESSES 4O STUDY COMPETITION 'AUSE COMMENTED ON THE IMPORTANCE OF EXPERIMENTATION AND THAT IN NATURAL EXPERIMENTS hTHE MOST FREQUENT ONES CONSIST IN THE TRANSPORTATION OF ANIMALS INTO COUNTRIES NEW TO THEM WHICH COM MONLY LEADS TO A GREAT NUMBER OF HIGHLY INTERESTING PROCESSES OF THE STRUGGLE FOR EXISTENCEv P /NE EXAMPLE HIGHLIGHTED BY 'AUSE IS THE INTRODUCTION OF THE %UROPEAN CARP INTO EASTERN .ORTH !MERICA IN THE S AND HOW IT hHAS NOW IN MANY STREAMS AND LAKES MULTIPLIED TO SUCH AN EXTENT THAT SEVERAL NATIVE SPECIES ARE FOUND IN GREATLY DIMINISHED NUMBERv P -UCH UNDERSTANDING OF THE NATURE OF SPECIES INTERACTIONS AND ESPECIALLY THOSE THAT STIMULATED 'AUSE WAS ADVANCED BY THE THEORETICAL MODELS OF ,OTKA EG AND 6OLTERRA EG 4HE WORK OF ,OTKA AND 6OLTERRA NOT ONLY REVOLUTIONIZED HOW ECOLOGISTS THOUGHT ABOUT SPECIES INTERACTIONS BOTH COMPETI TION AND PREDATION BUT ALSO SHOWED HOW MODELS COULD BE USED TO UNDERSTAND APPLIED PROBLEMS 4HE FAMOUS INSTANCE IS THAT THE SON IN LAW 5MBERTO $!NCONA ASKED HIS FATHER IN LAW 6ITO 6OLTERRA IF IT WERE POSSIBLE TO EXPLAIN MATHEMATI CALLY WHY IT SHOULD BE THAT WITH THE CESSATION OF lSHING IN &IUME NEAR 4RIESTE DURING 77) PREDATORY SHARKS AND RAYS CAME TO CONSTITUTE A HIGHER MEAN PROPOR TION OF THE CATCH BIOMASS EG $!NCONA (ALLAM /F COURSE USING HIS PREDATOR PREY MODELS 6OLTERRA WAS ABLE TO EXPLAIN THIS INCREASE IN PREDATOR PROPORTION 6OLTERRA ASSUMED THAT THE HARVESTING PRIOR TO 77) WAS INDISCRIMI NANT AND RESULTED IN A lXED PROPORTION OF INDIVIDUALS REMOVED SO THAT THE PERIODIC EQUILIBRIUM BETWEEN PREDATOR AND PREY DENSITIES SHIFTED TO HAVE A CENTER WITH HIGHER PREY AND LOWER PREDATOR ABUNDANCE WHEN THERE IS DENSITY INDEPENDENT MORTALITY )N THE SAME VEIN $!NCONA SHOWED HOW ,OTKA 6OLTERRA TYPE FORMULA TIONS COULD BE USED TO UNDERSTAND THE DYNAMICS OF SPECIES INVASIONS 5SING THESE TYES OF EQUATIONS $!NCONA SHOWED THAT A NEW INVADER WILL EITHER MOVE TO AN EQUILIBRIUM OF ZERO DENSITY IE UNSUCCESSFUL OR CHANGE THE EQUILIBRIUM
-7 #ADOTTE
DYNAMICS OF THE EXTANT COMPETITORS WHICH ESSENTIALLY ALTERS THE DENSITIES OF THE OTHER SPECIES )T IS WORTH MENTIONING THAT THE ,OTKA 6OLTERRA EQUATIONS HAVE BEEN CRITICIZED WITH A NUMBER OF SHORTCOMINGS RECOGNIZED NAMELY THEY ARE DIFlCULT TO APPLY IN SPECIlC CIRCUMSTANCES AND THE INTERACTION COEFlCIENTS ARE PROBLEMATIC TO COMPUTE (ECK (ALLAM 4HAT SAID THEY DO OFFER GREAT USE AS HEURISTIC DEVICES AND AS A MECHANISM TO PRODUCE QUALITATIVE HYPOTHESES (ECK 4HESE TYPES OF MODELS HAVE FOUND USE IN UNDERSTANDING AND PREDICTING THE CONSEQUENCES OF INVASIONS EG #OURCHAMP ET AL #OURCHAMP AND #AUT #HAPTER 8
5.$%234!.$).' 30!4)!, 302%!$ /NE MAJOR DEVELOPMENT PRIOR TO %LTONS BOOK BRIDGING ECOLOGY AND INVASIONS BIOLOGY WAS 3KELLAMS USE OF SPATIAL SPREAD MODELS 4HE MAJOR THRUST OF THIS RESEARCH WAS THE APPLICATION OF MODELS DESCRIBING THE DIFFUSION OF PARTICLES IN A PHYSICAL SYSTEM TO THE SPREAD OF A REPRODUCING POPULATION OVER A TWO DIMENSIONAL landscape (Skellam 1951, Kiersteadt and Slobodkin 1953). Skellam (1951) APPLIED THESE PHYSICAL MODELS TO UNDERSTANDING AND POTENTIALLY PREDICTING POPULA TION SPREAD ACROSS A LANDSCAPE "Y THE S THE RAPID SPREAD OF .)3 FROM THEIR POINTS OF ORIGIN HAD BEEN DOCUMENTED AND TO 3KELLAM WERE IN NEED OF MECHANIS TIC EXPLANATION ,IKE $ARWIN 3KELLAM USED .)3 TO SHOW HOW HIS THEORY COULD BE USED TO EXPLAIN SPATIAL SPREAD OF A POPULATION 7HAT BETTER WAY TO STUDY THE DYNAMICS OF A SPREADING POPULATION THEN WITH NEWLY ARRIVING SPECIES 4HE INTRODUCTION AND SPREAD OF THE MUSKRAT /NDATRA ZIBETHICA IN CENTRAL %UROPE WAS AN ILLUSTRATIVE EXAMPLE FOR 3KELLAM 3KELLAM WAS ABLE TO ADD POPULATION GROWTH TERMS EITHER EXPONENTIAL OR LOGISTIC TO SPREAD MODELS !DDING EXPONEN TIAL GROWTH THE CHANGE IN DENSITY IS ,N , N RN $ ,T ,X WHERE N IS THE POPULATION DENSITY AND LOCATION X WITH GROWTH RATE R AND DIFFUSIVITY $ &OLLOWING +OT THE VELOCITY OF SPREAD IS
X R$ T
!DDING LOGISTIC GROWTH THE CHANGE IN DENSITY IS
,N N ,N RN £¤ n ¥¦ $ ,T + ,X
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
!GAIN FOLLOWING +OT THE VELOCITY OF SPREAD IS DX R$ DT Skellam’s spatial spread models have been used to understand the spread OF NATURAL POPULATIONS EG /VASKAINEN AND ESPECIALLY FOR THE SPREAD OF POPULATIONS OF INVASIVE SPECIES EG (ASTINGS +OT ET AL "UCHAN AND 0ADILLA
'%.%2!, 42%.$3 ). %#/,/'9 50 4/ %,4/. 3IMULTANEOUSLY WITH #LEMENTS EARLIER WORK ANOTHER PLANT ECOLOGIST 6OLNEY 3PALDING PUBLISHED A MONOGRAPH ON THE DISTRIBUTION OF DESERT PLANTS (E SHOWED THAT COMPETITION AND MIGRATION ARE THE MOST IMPORTANT FACTORS STRUCTURING DESERT COMMUNITIES (IS STUDIES SHOWED THAT CHANGE IS CONSTANTLY TAKING PLACE AND INVASION IS A CONSTANT PROCESS 4HIS INVASION PROCESS HE NOTED IS BY BOTH NATIVE AND EXOTIC SPECIES AND THE EXOTICS ARE NO DIFFERENT EXCEPT THAT THEY ARE JUST PART OF THE LOCAL mORA OWING TO hTHE HAND OF -ANv P 4HEREFORE THE SAME PROCESS SUCCESSION OCCURS REGARDLESS OF WHICH SPECIES AND WHERE THEY CAME FROM !NIMAL ECOLOGY HAD A LATER START THAN PLANT ECOLOGY AND SEEMS TO HAVE FOLLOWED ITS LEAD -C)NTOSH BUT A QUICK mURRY OF TEXTS MADE UP FOR PLANT ECOLOGYS HEAD START !RTHUR 0EARSES !NIMAL %COLOGY DElNITELY TOOK ITS LEAD FROM PLANT ECOLOGY ON THE NATURE OF CHANGE hSUCCESSION IS USUALLY DUE TO ONE OF TWO CAUSES THE ENVIRONMENT IS CHANGING OR THE INCREASING GROUP OF ANIMALS IS BETTER ABLE TO TAKE ADVANTAGE OF EXISTING CONDITIONSv P 4HERE IS NO MEN TION OF WHERE THE BETTER ADAPTED ANIMALS COME FROM MUCH LESS OF THE OVERARCHING IMPORTANCE OF DISPERSAL FOR SUCCESSION 3IMILARLY #HARLES %LTONS lRST BOOK !NIMAL %COLOGY NOTES THAT ANIMAL DISPERSAL IS IMPORTANT WITH SOME MOVING VOLUNTARILY AND OTHERS THROUGH CHANCE 9ET THERE IS NO MENTION OF .)3 OR THEIR IMPACTS -OREOVER 2OYAL #HAPMANS lTTINGLY TITLED !NIMAL %COLOGY WAS THE lRST TO EXAMINE EXPLICITLY THE EFFECTS OF MIGRATION ON ANIMAL COMMUNITIES AND THE CAUSES OF STABILITY (E EXPOUNDED ON TWO TYPES OF RESISTANCE TO INVASIONS AND POPULATION EXPLOSIONS 4HE lRST WAS PHYS ICAL RESISTANCE WHERE THE ABIOTIC ENVIRONMENT MUST BE OPTIMAL FOR THE POPULATION IN QUESTION 4HE SECOND HE CALLED BIOTIC RESISTANCE IN WHICH POPULATIONS ARE KEPT IN CHECK THROUGH COMPETITION PREDATION AND PARASITES -ORE DIVERSE COMMUNI TIES WOULD THEREFORE BE MORE RESISTANT TO INVADERS !S WITH THE OTHER AUTHORS THERE IS NO EXPLICIT DISCUSSION OF WHERE INVADERS COME FROM AND THEIR IMPACTS 4HERE WAS LITTLE ADVANCE IN THE lELD OF PLANT ECOLOGY LEADING UP TO %LTONS INVASION BOOK &OR EXAMPLE -C$OUGALLS 0LANT %COLOGY READS LIKE AN UPDATED VERSION OF #LEMENTS 4O -C$OUGALL SUCCESSION HAS BOTH ABIOTIC AND BIOTIC CAUSES AND THE BIOTIC MECHANISM IS INVASION WHICH hMEANS THE MOVEMENT
-7 #ADOTTE
OF PLANTS FROM ONE AREA INTO ANOTHER AND THEIR COLONIZATION IN THE LATTERv P 3OUNDS FAMILIAR )N 'OODS 4HE 'EOGRAPHY OF &LOWERING 0LANTS HE SAYS MORE ABOUT .)3 INVADERS THAN HIS PREDECESSORS (E NOTES THAT WHEREVER HUMANS HAVE GONE SO HAVE .)3 (E MAKES SOME PREDICTIONS AS TO WHY WE OUGHT NOT TO WORRY ABOUT .)3 7HEN IT COMES TO COMPETITION hTHE STRUGGLE OF ;EXOTIC= VERSUS NATIVE IS MUCH LESS IN FAVOUR OF THE FORMERv P &URTHERMORE .)3 ARE RELEGATED TO DISTURBED GROUND BECAUSE OF THIS COMPETITIVE INFERIORITY 7HERE .)3 DO SPREAD AND BECOME ABUNDANT AS DO A NUMBER OF FRESHWATER SPECIES THEY hTEND AFTER A TIME TO SETTLE DOWN TO A MORE REASONABLE SCALE OF EXISTENCEv P 'OODS VIEW IS INTERESTING AS HE DOES USE PREDICTION BASED ON ECOLOGICAL REASONING TO ADDRESS INVASIVE SPE CIES (OWEVER WE MUST QUESTION WHETHER HE WAS ACTUALLY ADDRESSING WHAT WAS BEING OBSERVED WITH INVASIVE .)3 OR IF HE WAS SIMPLY TRYING TO lT WHAT SHOULD HAPPEN INTO HIS ECOLOGICAL WORLDVIEW
).#)0)%.4 ).6!3)/.3 ")/,/'9 )T REALLY WASNT UNTIL THE MID S THAT STUDIES WHICH WE CAN REFER TO AS INVA SION BIOLOGY BEGAN TO SURFACE !S LATE AS 3TORER .)3 INVADERS WERE NOT CONSIDERED TO BE A MAJOR SOURCE OF CONCERN FOR MAINTAINING THE NATURAL ENVIRONMENT 4RACY 3TORER WRITING ABOUT FACTORS AFFECTING THE WILDLIFE OF #ALIFORNIA LISTED THE MAJOR FACTORS AS AGRICULTURE GRAZING BY CATTLE MANIPULA TION OF HYDROLOGY REMOVAL OF PREDATION DEFORESTATION AND THE CHANGING OF lRE REGIMES &URTHER HE NOTED THAT GOVERNMENT AND PROFESSIONAL ORGANIZATIONS WERE ACTIVELY MANAGING WILDLIFE BY REGULATING HUNTING MEANS AND SEASONS PROTECTING RESERVES AND REFUGES REMOVING PREDATORS AND PROPAGATING AND RELEASING YOUNG OF PARTICULAR SPECIES (E SHOWED NO CONCERN ABOUT .)3 OR THEIR CONTROL ( ( !LLEN GAVE SERIOUS AND ACADEMIC ATTENTION TO THE PROBLEM OF .)3 IN .EW :EALAND 7HEREAS AUTHORS LIKE (OOKER AND 4ANSLEY THOUGHT THAT INVADERS AS A GROUP CHANGE A mORA WITH UNIFORM SUCCESS !LLEN SHOWED THAT THE .)3 WERE NOT A HORDE OF COMPETITIVE INVADERS )N FACT RELATIVELY FEW .)3 OF SPECIES BECAME PROBLEM SPECIES AND THESE FEW PROBLEM SPECIES REPRESENTED A DIVERSE ARRAY OF ECOLOGIES &URTHER !LLEN THOUGHT THAT IF HUMANS WERE TO CEASE CLEARING AND GRAZING LAND NATIVE COMMUNITIES WOULD RETURN AND REPLACE THE NOVEL COMMUNITIES 3IMILARLY %GLER THOUGHT .)3 INVADERS WERE NOT A UNIFORM GROUP CHANGING THE ECOLOGY OF (AWAII 2ATHER HE SAW .)3 AS A DIVERSE GROUP WHICH MADE PREDICTING THE FUTURE OF COMMUNITY TYPES NEARLY IMPOSSIBLE (E SHOWED THAT MANY FACTORS AFFECT THE SUCCESS OF .)3 AND WHETHER THESE FACTORS WERE GRAZING ANTHROPOGENIC DISTURBANCES OR SPECIES INTERACTIONS THE FATE OF ANY ONE .)3 REMAINED FOGGY ,IKE !LLEN %GLER THOUGHT THAT AFTER GRAZING AND DISTURBANCES WERE REMOVED NATIVE COMMUNITIES WOULD BE MUCH BETTER SUITED TO COMPETE AGAINST .)3
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
4HE LATE S AND EARLY S HERALDED THE ARRIVAL OF STUDIES OF THE ECOLOGY OF INVASIONS 4HESE TYPES OF STUDIES SPANNED THE BIOLOGY OF .)3 IN THEIR NEW ENVI RONMENTS TO SPECIES INTERACTIONS TO CONTROL 3TEWART AND (ALL DEPICTED THE BIOLOGY OF THE .)3 CHEATGRASS AND HOW IT WAS AFFECTING THE NATIVE COMMUNITIES OF SOUTHERN )DAHO "AKER USED THE INVASIONS OF -ELANDRIUM ALBUM AND - DIOICUM IN 'REAT "RITAIN IN ORDER TO STUDY THE DYNAMICS OF INVASION AND RANGE EXPANSION AS WELL AS LARGE SCALE COMPETITION &INALLY THE CONTROL OF PROBLEMATIC .)3 WAS GAINING MOMENTUM BECAUSE OF FAMOUS EARLY INSTANCES OF SUCCESSFUL BIO LOGICAL CONTROL 4HESE EXAMPLES WOULD INCLUDE NOT ONLY THE CONTROL OF /PUNTIA CACTI IN !USTRALIA BY #ACTOBLASTIS CACTORUM BY 'ROVES BUT ALSO THE CONTROL OF (YPERICUM PERFORATUM BY #HRYSOMELA BEETLES IN WESTERN 5NITED 3TATES (UFFAKER AND (OLLOWAY (UFFAKER
7(!4 ()34/29 4%,,3 !"/54 %#/,/'9 !.$ ).6!3)/. ")/,/'9 ) AM PAINTING THE PICTURE THAT THE NEW SCIENCE OF ECOLOGY IN THE EARLY TH CEN TURY WAS DEVELOPING ITS EPISTEMOLOGICAL DOMAIN AND THE QUESTION IS DID THEY TRY TO USE THEIR NEW SCIENCE TO UNDERSTAND INVASIVE EXOTICS ) THINK THEY DID NOT 4HESE EARLY ECOLOGISTS SEEMED TO INCORPORATE .)3 BECAUSE THEY YIELDED REAL WORLD OBSERVATIONS WHICH OBEYED THE VERY NATURAL LAWS THESE AUTHORS WERE EXPLORING &URTHERMORE .)3 WERE IN SOME CASES USED TO SHOWCASE THEIR IDEAS ABOUT NATURAL LAWS OR AS NATURAL EXPERIMENTS "Y AND LARGE THE EARLY ECOLOGISTS DID NOT USE THEIR CONCEPTUAL IDEAS TO UNDERSTAND AND PREDICT THE PROBABLE OUTCOMES OF SPECIES INVA SIONS 4HEY DID NOT OFTEN IMPLEMENT 'AUSES SUGGESTION THAT INVASIONS CONSTITUTE NATURAL EXPERIMENTS TO UNDERSTAND ECOLOGY BETTER /F COURSE THIS REVIEW DOES NOT SCOUR THE LITERATURE FOR EVERY RECORDED IDEA OR EVERY DISCUSSION OF .)3 INVADER 2ATHER ) HAVE ATTEMPTED TO lND THE PROMINENT MODES OF THINKING IN ECOLOGY AND ESPECIALLY WITH RESPECT TO .)3 INVADERS ) HAVE RELIED EXTENSIVELY ON TEXTS AS RECORDS OF THESE TRENDS AND A VALID CRITICISM IS THAT GENERAL TEXTS DO NOT CAPTURE ALL THE DIVERSITY OF THINKING WITHIN A lELD OF STUDY BOTH SUBTLE AND STARK (OWEVER %GLER IN HIS CRITICISM OF THE EPISTEMOL OGY OF !MERICAN PLANT ECOLOGY DURING THE S FOUND THAT THE MAJOR TEXTS DID LARGELY REPRESENT THE SCHOOLS OF THOUGHT AND PHILOSOPHIES OF !MERICAN ECOLOGY $AVIS ET AL ASSOCIATE %LTONS INVASIONS BOOK WITH THE CAUSE OF THE DISSOCIATION BETWEEN ECOLOGY AND INVASIONS BIOLOGY )F WE THINK OF ECOLOGY AS A SCIENCE OF CASE STUDIES EG 3HRADER &RECHETTE AND -C#OY THEN PER HAPS THERE WOULD BE NO DISSOCIATION AND BY STUDYING INDIVIDUAL CASES OF SPECIES INVASIONS WE CAN THEN FORM LARGER PICTURES OF WHAT IS HAPPENING IN NATURE 3HRADER &RECHETTE 9ET MUCH OF ECOLOGY IS BASED ON THE PRECEPT THAT THERE ARE FUNDAMENTAL OPERATIONS IN NATURE 4HESE FUNDAMENTAL OPERATIONS ARE APPROXIMATED THROUGH THEORY CONSTRUCTION EXPERIMENTATION AND OBSERVATION 4HE DISSOCIATION SEEN BY $AVIS ET AL IS THAT THESE SCIENTIlC EXERCISES THEORY EXPERIMENT AND OBSERVATION ARE WHAT BOTH INVASIONS BIOLOGISTS AND
-7 #ADOTTE
ECOLOGISTS DO BUT THEY DO IT LARGELY IN ISOLATION FROM ONE ANOTHER !LSO THESE TWO SCIENTIlC ENTERPRISES THOUGH DRIVEN BY SOMETIMES SEPARATE GOALS COULD BENElT FROM USE OF EACH OTHERS IDEAS TECHNIQUES AND OBSERVATIONS (OWEVER AFTER REVIEWING MUCH OF THE EARLY ECOLOGY LITERATURE ) lND THIS DIS SOCIATION SEEMS TO HAVE A MUCH LONGER PEDIGREE LONG BEFORE %LTON -ANY EARLY ECOLOGISTS DO NOT SEEM TO APPLY THEIR SCIENCE TO APPLIED PROBLEMS 4HAT IS NOT TO SAY THAT MANY WERE NOT CONCERNED ABOUT HUMAN IMPACTS ON THE ENVIRONMENT BUT THAT THEY USED THEIR SCIENCE LITTLE IN THESE CONCERNS &OR ONE THING THERE WAS NO MORAL CALL FOR ECOLOGISTS TO SOLVE THE PROBLEMS OF THE NATURAL WORLD 4HE MODERN CONCERN FOR THE ENVIRONMENT APPEARED IN THE WORK OF NATURALISTS AND ECOLOGISTS IN THE LATER S AND EARLY S EG %LTON #ARSON IT IS NOW COMMONPLACE 4HE SOCIETAL IMPETUS WAS NOT THERE &UNDING AGENCIES SIMPLY DID NOT EXIST MUCH LESS SUPPORT RESEARCH PROGRAMMES PURPORTING TO ADDRESS APPLIED PROBLEMS -ORE FUNDAMENTALLY THE FOUNDATIONS OF ECOLOGY LIKE THE FOUNDATIONS OF ANY SCIENTIlC lELD SEEMED LAID BY THOSE SEEKING GENERAL EXPLANATIONS 4HAT IS NOT TO SAY THAT THERE WERE NOT AUTHORS LOOKING AT VERY SPECIlC PROBLEMS BUT ECOLOGY TEXTBOOKS RELAY THE GENERAL IDEAS THAT SEEM BEST SUITED TO EXPLAINING NATURAL PHENOMENA -ANY OF THESE EARLY AUTHORS ADDRESS ISSUES INTIMATELY LINKED TO UNDERSTANDING SPECIES INVASIONS EG DISPERSAL SUCCESSION CHANGE ETC 9ET THEIR CONSIDERATIONS OF NON NATIVE SPECIES INVOLVED USING THESE SPECIES AS EFlCA CIOUS TESTS OF THEIR IDEAS
#/.#,53)/. (ERE ) HAVE EVER SO BRIEmY REVIEWED SOME OF THE MAJOR WORKS OF THE SCIENCE OF ECOLOGY IN THE HUNDRED OR SO YEARS BEFORE %LTON PUBLISHED 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS IN )N REVIEWING THESE ) HAVE FOCUSED PARTICULARLY ON THE WAY IN WHICH THE DEVELOPMENT OF IDEAS IN ECOLOGY PERTAIN TO UNDERSTANDING THE PHENOMENON OF SPECIES INVASIONS #OUPLED WITH THIS HISTORICAL EXAMINATION ) HAVE CONSIDERED THE NOTION THAT %LTONS WORK CAUSED DISSOCIATION BETWEEN ECOLOGY AND INVASION BIOLOGY $AVIS ET AL 4O BE SURE THERE WAS NO INDE PENDENT lELD OF INVASION BIOLOGY IN THE EARLY YEARS OF ECOLOGY BEYOND AGRICULTURAL AND ECONOMIC CONCERNS POSED BY SOME NON INDIGENOUS SPECIES 4HE CURRENT lELD OF INVASION BIOLOGY OWES MUCH TO %LTONS BOOK 4HIS REVIEW SHOWS THAT EARLY ECOLOGISTS DID ADDRESS SPECIES INVASIONS BECAUSE THEY WE A REAL AND EVIDENT PHE NOMENA AND ANY GENERAL ACCOUNT ON THE FUNCTIONING OF BIOLOGICAL COMMUNITIES WOULD NEED TO BE ABLE TO EXPLAIN WHY SOME SPECIES REACH NEW LANDS AND SURVIVE AND GROW 3OME OF THESE EARLY ECOLOGISTS SAW INVADERS AS A WAY TO TEST THEORY 9ET THE CONCERN AND ENERGY DEVOTED TO UNDERSTANDING INVADERS WENT LITTLE BEYOND EXPLAINING AND USE AS EXAMPLE AND IT REALLY WASNT UNTIL THE MID TO LATE S THAT WE SEE ANYTHING RESEMBLING INVASION BIOLOGY
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
4HE CURRENT TREND TO UNIFY MAINSTREAM ECOLOGY AND INVASION BIOLOGY IS PRO CEEDING AS THE CURRENT VOLUME ATTESTS EXPLORING NEW GROUND AND PUSHING THE LIMITS OF WHAT HAS COME BEFORE 2ATHER THAN LOOK AT INVASION BIOLOGY AS A SEPARATE lELD IT MAY BE BETTER TO CONSIDER IT A NECESSARY CONDITION TO GENERATING AN ACCU RATE VIEW OF NATURE ONE THAT ECOLOGY MUST BE ABLE TO USE &URTHER THE PLETHORA OF CASE STUDIES OF INVADERS SHOULD BE INVALUABLE TO THE ENTERPRISE OF TRYING TO SYNTHE SIZE NATURAL PHENOMENA INTO A HOLISTIC FRAMEWORK 0ERHAPS CONCEPTS IN ECOLOGY ARE ADEQUATE IN THEIR CURRENT DEVELOPMENT BUT LEARNING FROM THE WAYS IN WHICH INVADERS RESPOND TO NEW ENVIRONMENTS AND CHANGE THE COMMUNITIES THEY ARE INVADING CAN TELL US MORE ABOUT NATURE THAN MOST OTHER EXERCISES
!#+./7,%$'%-%.43 ) AM TRULY STANDING ON THE SHOULDERS OF GIANTS AND ) HOPE THAT MY PERCEPTION OF THE HISTORY OF ECOLOGY AND INVASION BIOLOGY IS AN ACCURATE ONE LEST THOSE GIANTS TURN IN THEIR GRAVES ) AM INDEBTED TO *IM $RAKE $AN 3IMBERLOFF -ARK $AVIS 3EAN -C-AHON 4AD &UKAMI FOR READING AND EARLIER VERSION OF THIS CHAPTER /F COURSE ANY INACCURACIES ARE NO FAULT OF THEIRS
2%&%2%.#%3 !LLAN ( ( )NDIGENE VERSUS ALIEN IN THE .EW :EALAND PLANT WORLD %COLOGY "AKER ( ' 3TAGES IN INVASION AND REPLACEMENT DEMONSTRATED BY SPECIES OF -ELANDRIUM *OURNAL OF %COLOGY "UCHAN , ! * AND $ + 0ADILLA %STIMATING THE PROBABILITY OF LONG DISTANCE OVER LAND DISPERSAL OF INVADING AQUATIC SPECIES %COLOGICAL !PPLICATIONS #ANDOLLE DE ! , 0 'ÏOGRAPHIE "OTANIQUE RAISSONÏ 6 -ASSON 0ARIS #ARSON 2 3ILENT 3PRING (OUGHTON -IFmIN "OSTON -! #HAPMAN 2 . !NIMAL %COLOGY -C'RAW (ILL "OOK #OMPANY )NC .EW 9ORK .9 #HASE * - AND - ! ,EIBOLD %COLOGICAL .ICHES 4HE 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), #LEMENTS & % 2ESEARCH -ETHODS IN %COLOGY 5NIVERSITY 0UBLISHING #O ,INCOLN .% #LEMENTS & % 0LANT 0HYSIOLOGY AND %COLOGY (ENRY (OLT AND #OMPANY .EW 9ORK .9 #LEMENTS & % AND 6 % 3HELFORD "IO ECOLOGY *OHN 7ILEY 3ONS )NC .EW 9ORK .9 #ONNER % & AND $ 3 3IMBERLOFF 4HE ASSEMBLY OF SPECIES COMMUNITIES #HANCE OR COMPETITION %COLOGY #OURCHAMP & - ,ANGLAIS AND ' 3UGIHARA #ATS PROTECTING BIRDS MODELING THE MESOPREDATOR RELEASE EFFECT *OURNAL OF !NIMAL %COLOGY
-7 #ADOTTE
#ROKER 2 ! 3TEPHEN &ORBES AND THE 2ISE OF !MERICAN %COLOGY 3MITHSONIAN )NSTITUTION 0RESS 7ASHINGTON $# $AEHLER # # $ARWINS NATURALIZATION HYPOTHESIS REVISITED !MERICAN .ATURALIST $!NCONA 5 4HE 3TRUGGLE FOR %XISTENCE % * "RILL ,EIDEN 4HE .ETHERLANDS $ARWIN # 4HE /RIGIN OF THE 3PECIES * -URRAY ,ONDON $AVIS - ! + 4HOMPSON AND * 0 'RIME #HARLES 3 %LTON AND THE DISSOCIATION OF INVASION ECOLOGY FROM THE REST OF ECOLOGY $IVERSITY AND $ISTRIBUTIONS $RUDE / -ANUEL DE 'EOGRAPHIE "OTANIQUE ,IBRAIRIE $ES 3CIENCES .ATURELLES 0ARIS %GERTON & . %COLOGICAL STUDIES AND OBSERVATIONS BEFORE 0AGES IN " * 4AYLOR AND 4 * 7HITE EDITORS )SSUES AND )DEAS IN !MERICA 5NIVERSITY OF /KLAHOMA 0RESS /KLAHOMA /+ %GLER & % )NDIGENE VERSUS ALIEN IN THE DEVELOPMENT OF ARID (AWAIIAN VEGETATION %COLOGY %GLER & % ! COMMENTARY ON !MERICAN PLANT ECOLOGY BASED ON THE TEXTBOOKS OF %COLOGY %HRLICH 0 2 (UMAN NATURES NATURE CONSERVATION AND ENVIRONMENTAL ETHICS "IOSCIENCE %LTON # 3 !NIMAL %COLOGY 4HE -AC-ILLAN #OMPANY .EW 9ORK .9 %LTON # 3 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS -ETHUEN ,ONDON %MERSON 2 7 4HE %ARLY ,ECTURES EDITED BY 3 % 7HICHER AND 2 % 3PILLER (ARVARD 5NIVERSITY 0RESS #AMBRIDGE -! &ITCH ! 3IXTH REPORT ON THE NOXIOUS AND OTHER INSECTS OF THE STATE OF .EW 9ORK .EW 9ORK 3TATE !GRICULTURAL 3OCIETY 4RANSACTIONS &ORBES 3 ! )NSECTS AFFECTING CORN )LLINOIS 3TATE %NTOMOLOGY /FlCE #IRCULATION &ORBES 3 ! 4HE CLINCH BUG IN )LLINOIS )LLINOIS 3TATE %NTOMOLOGY /FlCE #IRCULATION PP 3EPTEMBER &ORBES 3 ! A !RSENICAL POISONS FOR THE CODLING MOTH RECORD AND DISCUSSION OF EXPERIMENTS FOR AND 4RANSACTIONS OF THE )LLINOIS 3TATE (ORTICULTURAL 3OCIETY &ORBES 3 ! B 4HE LAKE AS A MICROCOSM "ULLETIN OF THE 3CIENTIlC !SSOCIATION 0EORIA ), &ORBES 3 ! /N THE PRINCIPLE CORN INSECTS AND METHODS OF COLLECTING THEM )LLINOIS !GRICULTURALIST PP &ORBES 3 ! 4HE SEASONS CAMPAIGN AGAINST THE 3AN *OSÏ AND OTHER SCALE INSECTS IN )LLINOIS 4RANSACTIONS OF THE )LLINOIS 3TATE (ORTICULTURAL 3OCIETY 'AUSE ' & 4HE 3TRUGGLE FOR %XISTENCE (AFNER 0UBLISHING #OMPANY .EW 9ORK .9 'OOD 2 4HE 'EOGRAPHY OF THE &LOWERING 0LANTS ,ONGMANS 'REEN AND #O .EW 9ORK .9 'RINNELL * 4HE NICHE RELATIONSHIPS OF THE #ALIFORNIA THRASHER !UK 'RINNELL * 2ISKS INCURRED IN THE INTRODUCTION OF ALIEN GAME BIRDS 3CIENCE
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
'ROVES 2 ( %COLOGICAL CONTROL OF INVASIVE TERRESTRIAL PLANTS 0AGES IN * ! $RAKE ( ! -OONEY & DI #ASTRI 2 ( 'ROVES & * +RUGER - 2EJMANEK AND - 7ILLIAMSON EDITORS "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE *OHN 7ILEY AND 3ONS .EW 9ORK .9 (ALLAM 4 ' #OMMUNITY DYNAMICS IN A HOMOGENEOUS ENVIRONMENT 0AGES IN 4 ' (ALLAM AND 3 ! ,EVIN EDITORS -ATHEMATICAL %COLOGY 3PRINGER 6ERLAG "ERLIN (ARDIN ' 4HE COMPETITIVE EXCLUSION PRINCIPLE 3CIENCE (ASTINGS ! -ODELS OF SPATIAL SPREAD IS THE THEORY COMPLETE %COLOGY (ECK + , 3OME CRITICAL CONSIDERATIONS OF THE THEORY OF SPECIES PACKING %VOLUTIONARY 4HEORY (EILPRIN ! 4HE 'EOGRAPHICAL AND 'EOLOGICAL DISTRIBUTION OF !NIMALS $ !PPLETON #O .EW 9ORK .9 (OOKER * $ (ANDBOOK OF THE .EW :EALAND &LORA 6OLUME 3IR *OSEPH $ALTON (OOKER ,ONDON (OWARD , / )NSECTS AFFECTING THE COTTON PLANT "ULLETIN OF THE /FlCE OF %XPERIMENTAL 3TATIONS (OWARD , / 4HE mY WEEVIL !DDRESS AT THE &ARMERS )NSTITUTE -ANASSAS 6A (OWARD , / 4HE SHADE TREE INSECT PROBLEM IN THE EASTERN 5NITED 3TATES 9EARBOOK OF THE 5 3 $EPARTMENT OF !GRICULTURE (OWARD , / A 4HE SPREAD OF LAND SPECIES BY THE AGENCY OF -AN WITH ESPECIAL REFERENCE TO INSECTS 0ROCEEDINGS OF THE !MERICAN !SSOCIATION FOR THE !DVANCEMENT OF 3CIENCE (OWARD , / B $ANGER OF IMPORTING INSECT PESTS 9EARBOOK OF $EPARTMENT OF !GRICULTURE (OWARD , / 4HE PRINCIPAL INSECTS AFFECTING THE TOBACCO PLANT 9EARBOOK OF $EPARTMENT OF !GRICULTURE (OWARD , / 4HREE INSECT ENEMIES OF SHADE TREES 5 3 $EPARTMENT OF !GRICULTURE &ARMERS "ULLETIN (UFFAKER # " 4HE RETURN OF NATIVE PERENNIAL BUNCHGRASS FOLLOWING THE REMOVAL OF +LAMATH WEED (YPERICUM PERFORATUM , BY IMPORTED BEETLES %COLOGY (UFFAKER # " AND * + (OLLOWAY #HANGES IN RANGE PLANT POPULATION STRUCTURE ASSOCIATED WITH FEEDING OF IMPORTED ENEMIES OF +LAMATH WEED Hypericum perforatum , %COLOGY (USTON - ! "IOLOGICAL $IVERSITY #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE (UTCHINSON ' % #ONCLUDING REMARKS #OLD 3PRING (ARBOR 3YMPOSIA ON 1UANTITATIVE "IOLOGY *OHNSTONE ) - 0LANT INVASIONS WINDOWS A TIME BASED CLASSIlCATION OF INVASION POTENTIAL "IOLOGICAL 2EVIEW +IERSTEAD 3 % AND , " 3LOBODKIN 4HE SIZE OF WATER MASSES CONTAINING PLANKTON BLOOMS *OURNAL OF -ARINE 2ESEARCH +OT - %LEMENTS OF -ATHEMATICAL %COLOGY #AMBRIDGE 5NIVERSITY 0RESS .EW 9ORK .9
-7 #ADOTTE
+OT - - ! ,EWIS AND 0 VAN DEN $RIESSCH $ISPERSAL DATA AND THE SPREAD OF INVAD ING ORGANISMS %COLOGY ,AWTON * ( !RE THERE GENERAL LAWS IN ECOLOGY /IKOS ,EIBOLD - ! 4HE NICHE CONCEPT REVISITED MECHANISTIC MODELS AND COMMUNITY CONTEXT %COLOGY ,OTKA ! * %LEMENTS OF 0HYSICAL "IOLOGY 7ILLIAMS AND 7ILKINS "ALTIMORE -$ -ACK 2 . 0LANT NATURALIZATIONS AND INVASIONS IN THE EASTERN 5NITED 3TATES !NNALS OF THE -ISSOURI "OTANICAL 'ARDEN -C$OUGALL 7 " 0LANT %COLOGY ,EA AND &EBIGER 0HILADELPHIA 0! -C)NTOSH 2 0 %COLOGY SINCE 0AGES IN " * 4AYLOR AND 4 * 7HITE EDITORS )SSUES AND )DEAS IN !MERICA 5NIVERSITY OF /KLAHOMA 0RESS /KLAHOMA /+ -ENAND , 4HE -ETAPHYSICAL #LUB ! 3TORY OF )DEAS IN !MERICA &ARRAR 3TRAUS 'IROUX .EW 9ORK .9 /LMSTED & , ,ETTER TO THE EDITOR &OREIGN PLANTS AND !MERICAN SCENERY 'ARDEN AND &OREST /WENS 2 $ARWIN ON THE ORIGIN OF SPECIES 0AGES IN 0 !PPLEMAN EDITOR $ARWIN ! .ORTON #RITICAL %DITION THIRD EDITION 7 7 .ORTON #OMPANY .EW 9ORK .9 0EARSE ! 3 !NIMAL %COLOGY -C'RAW (ILL "OOK #OMPANY )NC .EW 9ORK .9 0ETERS 2 ( ! #RITIQUE FOR %COLOGY #AMBRIDGE 5NIVERSITY 0RESS .EW 9ORK .9 3ARGENT # 3 %DITORIAL 'ARDEN AND &OREST 3EDGWICK ! /BJECTIONS TO -R $ARWINS THEORY OF THE ORIGIN OF SPECIES 0AGES IN 0 !PPLEMAN EDITOR $ARWIN ! .ORTON #RITICAL %DITION THIRD EDITION 7 7 .ORTON #OMPANY .EW 9ORK .9 3HANTZ ( , ! STUDY OF THE VEGETATION OF THE -ESA REGION EAST OF 0IKES 0EAK "OTANICAL 'AZETTE 3HRADER &RECHETTE + .ON INDIGENOUS SPECIES AND ECOLOGICAL EXPLANATION "IOLOGY AND 0HILOSOPHY 3HRADER &RECHETTE + AND % $ -C#OY !PPLIED ECOLOGY AND THE LOGIC OF CASE STUDIES 0HILOSOPHY OF 3CIENCE 3IMBERLOFF $ 3 5SING ISLAND BIOGEOGRAPHIC DISTRIBUTIONS TO DETERMINE IF COLONIZA TION IS STOCHASTIC !MERICAN .ATURALIST 3IMBERLOFF $ #ONFRONTING INTRODUCED SPECIES A FORM OF XENOPHOBIA "IOLOGICAL )NVASIONS 3KELLAM * ' 2ANDOM DISPERSAL IN THEORETICAL POPULATIONS "IOMETRIKA 3PALDING 6 - $ISTRIBUTION AND -OVEMENTS OF $ESERT 0LANTS #ARNEGIE )NSTITUTE OF 7ASHINGTON 7ASHINGTON $# 3TEWART ' AND ! # (ULL #HEATGRASS "ROMUS TECTORUM , AN ECOLOGICAL INTRUDER IN SOUTHERN )DAHO %COLOGY 3TORER 4 ) &ACTORS INmUENCING WILD LIFE IN #ALIFORNIA PAST AND PRESENT %COLOGY 4ANSLEY ! ' 4HE USE AND ABUSE OF VEGETATIONAL CONCEPTS AND TERMS %COLOGY
$ARWIN TO %LTON EARLY ECOLOGY AND THE PROBLEM OF INVASIVE SPECIES
4HOMPSON + * ' (ODGSON AND 4 # ' 2ICH .ATIVE AND ALIEN PLANT INVASIVE PLANTS MORE OF THE SAME %COGRAPHY 6OLTERRA 6 6ARIATIONS AND mUCTUATIONS IN THE NUMBERS OF COEXISTING ANIMAL SPECIES 0AGES IN & - 3CUDO AND * 2 :IEGLER EDITORS 4HE 'OLDEN !GE OF 4HEORETICAL %COLOGY 3PRINGER 6ERLAG .EW 9ORK .9 7ALLACE ! 2 4HE 'EOGRAPHICAL $ISTRIBUTION OF !NIMALS (AFNER 0UBLISHING #OMPANY .EW 9ORK .9 7ARMING % /ECOLOGY OF 0LANTS !N )NTRODUCTION TO THE 3TUDY OF 0LANT #OMMUNITIES #LARENDON 0RESS /XFORD 5+ 7EAVER * % AND & % #LEMENTS 0LANT %COLOGY -C'RAW (ILL BOOK #OMPANY .EW 9ORK .9
#HAPTER THREE
)NVASION BIOLOGY THE PURSUIT OF SCIENCE AND CONSERVATION - ! $AVIS
).42/$5#4)/. 4HE HISTORY OF INVASION BIOLOGY WOULD BE A DREAM DISSERTATION TOPIC FOR SOME HIS TORY OF SCIENCE GRADUATE STUDENT 4HE LIST OF RESEARCHERS WHO HAVE WEIGHED IN ON THE TOPIC AT ONE TIME OR ANOTHER READS LIKE A 7HOS 7HO OF LATE TH CENTURY ECOL OGY #ONTROVERSY AND DISAGREEMENTS OCCASIONALLY RESULTING IN LIVELY EXCHANGES AMONG RESEARCHERS HAVE CREATED AN INTELLECTUALLY DYNAMIC AND SOMETIMES EMOTIONALLY CHARGED ATMOSPHERE IN RECENT YEARS !UTHORS OF BOTH TECHNICAL AND POPULAR ARTICLES HAVE OFTEN USED EVOCATIVE LANGUAGE AND IMAGERY IN THEIR WRITING 3OME OF THE ISSUES HAVE ATTRACTED THE INTERESTS OF SCHOLARS OUTSIDE THE BIOLOGICAL SCIENCES PARTICULARLY PHILOSOPHERS !ND FOR THE PAST SEVERAL DECADES INVASION ECOLOGY RESEARCH HAS BEEN CONDUCTED WITHIN A LARGER SOCIAL MILIEU OF CONTENTIOUS ENVIRONMENTAL VALUES AND POLITICS .O DOUBT FOR ALL THESE REASONS INVASION ECOLO GY HAS CAPTURED THE ATTENTION OF NATIONAL AND INTERNATIONAL MEDIA OUTLETS WHICH HAVING THEIR OWN AGENDAS HAVE EMPHASIZED AND PRESENTED PARTICULAR RESEARCH lNDINGS AND PERSPECTIVES FOR THEIR AUDIENCES (OWEVER AN EXAMINATION OF THE lELDS HISTORY SHOULD BE OF INTEREST NOT JUST TO HISTORIANS OF SCIENCE BUT TO ECOLOGISTS AS WELL !FTER ALL A LOOK BACKWARDS IS -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
-! $AVIS
ALMOST ALWAYS A GOOD IDEA BEFORE CHARTING NEW PATHS (OW HAVE RESEARCH QUES TIONS CHANGED OVER TIME 7HAT HAVE WE LEARNED 7HAT CONTINUES TO CHALLENGE OUR UNDERSTANDING )F WE CAN ANSWER THESE QUESTIONS WE CAN MORE EFFECTIVELY FORMULATE FUTURE PRIORITIES ! HISTORICAL REVIEW CANNOT GUARANTEE ANSWERS TO THESE QUESTIONS BUT NEITHER CAN THE ANSWERS BE OBTAINED WITHOUT SUCH A REVIEW )N RESEARCHING AND WRITING THIS CHAPTER ) HAVE STRIVED TO PROVIDE A HISTORICAL REVIEW OF INVASION BIOLOGY SINCE THE PUBLICATION DATE #HARLES %LTONS INVASION CLASSIC 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS IN ORDER TO ANSWER THE ABOVE QUESTIONS AND BASED ON WHATEVER INSIGHTS COULD BE GAINED FROM THESE EFFORTS TO OFFER A FEW SUGGESTIONS AS TO HOW INVASION BIOLOGY MIGHT PROlTABLY PROCEED FROM THIS POINT FORWARD
4(% 3 )N 4HE )NTERNATIONAL 5NION OF "IOLOGICAL 3CIENCES HELD ITS lRST "IOLOGICAL 3CIENCES 3YMPOSIUM PART OF WHAT WAS TO BE A SERIES OF SUCH MEETINGS DESIGNED TO FOCUS ATTENTION ON BIOLOGICAL TOPICS HAVING INTERNATIONAL SIGNIlCANCE 4HE OBJEC TIVE OF THE lRST SYMPOSIUM HELD IN !SILOMAR #ALIFORNIA WAS TO BRING TOGETHER GENETICISTS ECOLOGISTS TAXONOMISTS AND APPLIED SCIENTISTS WORKING IN THE AREA OF PEST CONTROL AND TO PRESENT AND DISCUSS FACTS AND IDEAS hABOUT THE KINDS OF EVOLUTIONARY CHANGE WHICH TAKE PLACE WHEN ORGANISMS ARE INTRODUCED INTO NEW TERRITORIESv 7ADDINGTON 4HE PROCEEDINGS WERE PUBLISHED IN A 4HE 'ENETICS OF #OLONIZING 3PECIES "AKER AND 3TEBBINS NOW REGARDED AS A CLASSIC !S WOULD BE EXPECTED GIVEN THE ORGANIZING GROUP THE BOOK REPRESENTED A DISTINCTLY INTERNATIONAL INITIATIVE CONSISTING OF AUTHORS REPRESENTING COUNTRIES 4HE RANGE OF TOPICS CONSIDERED IN THIS VOLUME WAS BROADER THAN THE TITLE SUG GESTS AND INCLUDED DISCUSSIONS ON THE NATURE OF THE COLONIZED ENVIRONMENTS AS WELL AS THE ATTRIBUTES AND GENETICS OF COLONIZING SPECIES #HAPTERS ADDRESSED A BROAD RANGE OF TAXA INCLUDING PLANTS INSECTS BIRDS MAMMALS AND MICROBES 4HE SYMPOSIUM AND THE BOOK WERE DElNED BY A STRONG EVOLUTIONARY EMPHASIS AND PARTICIPANTS INCLUDED MANY OF THE PROMINENT EVOLUTIONARY BIOLOGISTS OF THE TIME INCLUDING -AYR 3TEBBINS $OBZHANSKY 7ILSON % / #ARSON ,EWONTIN AND 7ADDINGTON 3IGNIlCANTLY AUTHORS CONSIDERED COLONISTS BROADLY DISCUSSING COLONIZATIONS THAT OCCURRED DURING SUCCESSION COLONIZATIONS OF WIDESPREAD SPE CIES THAT HAD OCCURRED WITHOUT HUMAN ASSISTANCE COLONIZATIONS OF NATIVE WEEDS AS WELL AS COLONIZATIONS OF SPECIES INTO NEW REGIONS OCCURRING AS A DIRECT RESULT OF HUMAN ACTIVITY !LTHOUGH THE LATTER GROUP DID RECEIVE THE MOST ATTENTION PARTICI PANTS RECOGNIZED THAT COMMON ECOLOGICAL AND EVOLUTIONARY PROCESSES UNDERLAY THE DIFFERENT TYPES OF COLONIZATIONS /NE NOTEWORTHY ASPECT OF THE BOOK IS THE STRIKING CONTRAST BETWEEN THE LAN GUAGE USED BY THE AUTHORS AND THAT COMMONLY USED BY INVASION ECOLOGISTS TODAY ! CAREFUL SEARCH OF THE BOOKS TEXT IS NECESSARY TO lND TERMS SUCH AS @ALIEN @EXOTIC @INVADER AND @INVASION -OST AUTHORS NEVER USED THESE WORDS ! FEW
)NVASION BIOLOGY
SUCH AS 7ILSON % / -AYR AND 7ODZICKI USED THEM OCCASIONALLY BUT THE ARTI CLES AND DISCUSSIONS WERE OVERWHELMINGLY GUIDED BY NOUNS VERBS AND ADJECTIVES SUCH AS @COLONIZERS @FOUNDING POPULATIONS @INTRODUCED @NON NATIVE @NEW ARRIVALS @MIGRATION @SPREAD @GEOGRAPHICALLY WIDESPREAD 4HUS PARTICIPANTS DID NOT ADOPT THE EFFUSIVE STYLE USED BY %LTON IN HIS BOOK CHARACTERIZED BY THE FREQUENT USE OF METAPHOR AND ANALOGY OFTEN WITH EXPLICIT MILITARISTIC REFERENCES 4HE ONE EXCEPTION WAS %LTONS COLLEAGUE *OHN (ARPER WHO USUALLY DID REFER TO THE NEW SPECIES AS @ALIENS AND @INVADERS AND WHOSE CHAPTER %STABLISHMENT !GGRESSION AND #OHABITATION IN 7EEDY 3PECIES EXHIBITED SOME OF THE SAME EVOCATIVE LANGUAGE THAT %LTON USED IN HIS BOOK 4HE OPENING SENTENCE OF (ARPERS CHAPTER IS SO REMINISCENT OF THE LANGUAGE USED BY %LTON THAT THE LATTERS INmUENCE ON (ARPER CAN HARDLY BE DENIED (ARPER BEGAN h4HE MOVEMENTS OF MAN AND HIS GOODS HAVE RESULTED IN A BOMBARDMENT OF AREAS OF LAND AND SEA BY ALIEN SPECIES BOTH BY CHANCE AND BY THE DELIBERATE INTRODUCTION OF CULTIVATED PLANTS OF THE FARM AND GARDENv )N THE PREFACE TO HIS BOOK %LTON SAID HIS GOAL WAS TO BRING TOGETHER THREE STREAMS OF THOUGHT FAUNAL HISTORY ECOLOGY PARTICULARLY POPULATION ECOLOGY AND CONSERVATION "UT THE CONSERVATION THEME DOMINATED THE BOOK (E OPENED HIS BOOK WITH GRAPHIC BATTLElELD EXAMPLES OF INVASIONS AND ENDED THE BOOK WITH TWO CHAPTERS ON THE NEED FOR CONSERVATION )N CONTRAST THE !SILOMAR PARTICIPANTS DID NOT CONSIDER CONSERVATION IMPLICATIONS OF SPECIES COLONIZATIONS WHATSOEVER % / 7ILSON PERSONAL COMMUNICATION 4HE CLEARLY DElNED AGENDA OF THE !SILOMAR SYMPOSIUM WAS THE SEARCH FOR GENERALIZATIONS REGARDING THE EVOLUTION ARY AND ECOLOGICAL PROCESSES INVOLVED IN SPECIES COLONIZATIONS )N THE CHAPTERS AND PAGES OF THE SYMPOSIUM PROCEEDINGS %LTONS INVASION CLASSIC WAS CITED ONLY THREE TIMES ONCE EACH BY "IRCH -AYR AND 7ILSON % / !S A PUBLICATION FOCUSING ON INTRODUCED SPECIES 4HE 'ENETICS OF #OLONIZING 3PECIES STANDS STARKLY ALONE DURING THIS TIME PERIOD 0ERHAPS IT WAS BECAUSE THE BOOK FOCUSED MORE ON EVOLUTIONARY ISSUES THAN ECOLOGICAL THEORY BUT THE SYM POSIUM AND COMPANION VOLUME ELICITED ALMOST NO RESPONSE FROM THE ECOLOGICAL COMMUNITY $ESPITE THE PUBLICATION OF THIS VOLUME AND %LTONS BOOK SEVEN YEARS EARLIER BIOLOGICAL INVASIONS DID NOT ATTRACT THE INTEREST OF MANY ECOLOGISTS DUR ING THE S AT LEAST FROM ECOLOGISTS WHOSE PRIMARY INTERESTS AND OBJECTIVES INVOLVED THE DEVELOPMENT OF THEORY AND GENERALIZATIONS THAT TRANSCEND PARTICULAR ORGANISMS AND HABITATS )T IS CERTAINLY TRUE THAT WITH THE DEVELOPMENT AND DIS SEMINATION OF ISLAND BIOGEOGRAPHY THEORY -AC!RTHUR AND 7ILSON 3IMBERLOFF AND 7ILSON CONSIDERABLE ATTENTION WAS GIVEN TO HOW ARRIVING SPECIES WOULD lT INTO RESIDENT COMMUNITIES (OWEVER FEW ECOLOGISTS AT THIS TIME CONNECTED THEIR RESEARCH WITH THE SORT OF INVASION LITERATURE AND ISSUES SUMMA RIZED AND PRESENTED BY %LTON 3IMBERLOFF PERSONAL COMMUNICATION )T MUST BE POINTED OUT THAT DURING THIS TIME SOME ECOLOGISTS OUTSIDE OF .ORTH !MERICA WERE ACTIVELY RESEARCHING AND PUBLISHING IN THE AREA OF INTRODUCED SPECIES 3UKOPP ADDRESSED BOTH THEORY AND TERMINOLOGY IN HIS REPORT ON INTRODUCED SPECIES IN THE NATURAL PLANT ASSOCIATIONS OF CENTRAL %UROPE (OLUB
-! $AVIS
AND *IRÉSEK AND 3CHROEDER PRESENTED CLASSIlCATION SCHEMES FOR NON NATIVE SPECIES BASED ON THE MODE OF INTRODUCTION TIME OF INTRODUCTION AND DEGREE OF NATURALIZATION &ALINÇSKI WROTE HIS DISSERTATION ON THE DISTRIBU TION OF INTRODUCED SPECIES IN 0OLANDS "IALOWIEZA 0RIMEVAL &OREST AND &ALINÇSKI AND +ORNAS A B PUBLISHED A NUMBER OF SUBSEQUENT ARTICLES DURING THE S ON THE ECOLOGY OF INTRODUCED SPECIES IN NATURAL AND SEMI NATURAL COMMUNITIES IN 0OLAND (UNGARIAN ECOLOGIST 0AL *UHASZ .AGY CONDUCTED lELD EXPERIMENTS IN HIS STUDIES OF @ECESIS RESISTANCE INVASIBIL ITY AND USED THE TERM @ECOLOGICAL HOMEOSTASIS TO DESCRIBE COMMUNITIES THAT WERE RESISTANT TO INVASION (EJNâ AND ,HOTSKÉ AND *EHLÓK AND 3LAVÓK DESCRIBED THE ECOLOGY AND DISTRIBUTION AND SPREAD IN NATURAL ENVIRONMENTS OF SEV ERAL INTRODUCED SPECIES IN THE #ZECH 2EPUBLIC +OHLER AND 3UKOPP STUDIED THE ECOLOGY OF INTRODUCED SPECIES IN CITIES PART OF A LONG STANDING INTEREST AMONG %UROPEAN PLANT ECOLOGISTS /NE OF THE MORE MEMORABLE lNDINGS OF +OHLER AND 3UKOPP WAS THAT 2OBINIA PSEUDOACACIA HAD SPREAD SPONTANEOUSLY ON THE RUBBLE OF CITIES BOMBED DURING 77)) %XCEPT FOR THE ABSTRACTS NONE OF THE ABOVE ARTICLES WAS PUBLISHED IN %NGLISH AND MOST %NGLISH SPEAKING ECOLOGISTS WERE PROBABLY NOT WELL AWARE OF THIS RESEARCH DURING THE SIXTIES !LTHOUGH BIOLOGICAL INVASIONS RECEIVED LITTLE ATTENTION FROM ECOLOGISTS DURING THE S PARTICULARLY IN .ORTH !MERICA THIS DOES NOT MEAN THAT RESEARCH WAS NOT BEING CONDUCTED ON INTRODUCED SPECIES AND THEIR IMPACTS )N FACT CONSIDER ABLE RESEARCH ON THIS TOPIC WAS BEING CONDUCTED IN !USTRALIA .EW :EALAND 3OUTH !FRICA %UROPE AS WELL AS .ORTH !MERICA )T WAS SIMPLY BEING CONDUCTED BY BIOLOGISTS WHOSE INTERESTS AND PRIORITIES WERE MORE APPLIED IN NATURE INVOLVING lSHERIES EG !LBRECT WILDLIFE EG "UMP AND "OHL 4#7& 7ARNER FORESTRY EG .ICHOLS 4AYLOR AND AGRICULTURE EG 3ALISBURY -ETCALF ET AL $E"ACH 4HE APPLIED AND PEST CONTROL RESEARCH CONDUCTED IN DURING THE S DID NOT REPRESENT ANY NEW INITIATIVE AND VERY LITTLE IF ANY OF IT WAS INSPIRED BY %LTONS BOOK 2ATHER IT WAS A CONTINUATION OF EXTENSIVE APPLIED RESEARCH IN THIS AREA EXTENDING BACK TO THE BEGINNING OF THE TH CENTURY EG ,ITTLE "AILEY "RYANT 3IM 7ICHT AND EVEN EARLIER EG -ERRIAM 0ALMER &ROM AN HISTORICAL PERSPECTIVE A BOOK BY 'EORGE ,AYCOCK WAS A NOTEWOR THY PUBLICATION DURING THIS TIME 4ITLED 4HE !LIEN !NIMALS 4HE 3TORY OF )MPORTED 7ILDLIFE THE BOOK WAS PUBLISHED BY 4HE !MERICAN -USEUM OF .ATURAL (ISTORY 7ELL RESEARCHED IT CONTAINED NEARLY REFERENCES FROM THE SCIENTIlC LITERA TURE ,IKE %LTONS CLASSIC THIS BOOK WAS WRITTEN FROM A CONSERVATION AND DISTINCTLY VALUE BASED PERSPECTIVE AS WELL AS FOR A LARGER PUBLIC AUDIENCE /N THE OPENING PAGE ,AYCOCK REFERS TO hMANv AS hTHE SUPREME MEDDLERv ON THE BOOKS lNAL PAGE HE WARNS OF NATURAL COMMUNITIES BEING hPOLLUTEDv BY ALIEN SPECIES AND TITLES OF HIS CHAPTERS INCLUDED 3TANGERS IN THE 3OUTHWEST (OW THE 'RAY 3QUIRRELS )NVADED %NGLAND AND 4HE #ONQUERING -ONGOOSE )N THE BOOK ,AYCOCK PRESENTS TWENTY CASE STUDIES OF ANIMAL INTRODUCTIONS AROUND THE WORLD THAT HAD CAUSED GREAT ECONOMIC AND CONSERVATION HARM 4HE BOOKS LANGUAGE TONE AND
)NVASION BIOLOGY
SERIES OF CASE STUDIES IS VERY SIMILAR TO %LTONS BOOK ALTHOUGH RATHER INEX PLICABLY %LTON WAS NOT ONE OF THE NEARLY REFERENCES LISTED IN THE BIBLIOGRAPHY (OWEVER UNLIKE %LTON ,AYCOCK WAS NOT A SCIENTIST (E WAS A FREELANCE WRITER WHO DURING HIS CAREER AUTHORED MORE THAN TWENTY BOOKS ON ANIMALS AND NATURE MANY OF THEM WRITTEN FOR CHILDREN AND YOUNG ADULTS .EVERTHELESS ,AYCOCKS CHARACTERIZATION OF INTRODUCED SPECIES SEEMS TO HAVE PORTENDED THE PERSPECTIVE ADOPTED IN A LARGE NUMBER OF INVASION ECOLOGY LITERATURE BOTH POPULAR AND SCIEN TIlC LATER IN THE CENTURY MORE SO THAN HAS THE !SILOMAR PUBLICATION 4HE 'ENETICS OF #OLONIZING 3PECIES
4(% 3 /N !PRIL HUNDREDS OF THOUSANDS OF STUDENTS AND OTHERS ACROSS THE 5NITED 3TATES CELEBRATED THE lRST %ARTH $AY AN EVENT CONCEIVED AND ORGANIZED BY 'AYLORD .ELSON THEN 3ENATOR OF 7ISCONSIN !LTHOUGH .ELSON 2ACHEL #ARSON AND OTHERS HAD BEEN TRYING TO RAISE ENVIRONMENTAL CONSCIOUSNESS WITHIN THE 5NITED 3TATES DURING THE SIXTIES THE S IS WHEN THE ENVIRONMENTAL MOVE MENT lNALLY CAPTURED THE PUBLICS ATTENTION IN THE 53 AND THROUGHOUT THE WORLD 3#/0% 3CIENTIlC #OMMITTEE ON 0ROBLEMS OF THE %NVIRONMENT A COMMITTEE ESTABLISHED BY THE )NTERNATIONAL #OUNCIL OF 3CIENTIlC 5NIONS PUBLISHED THE lRST OF ITS 3#/0% 3ERIES TITLES NOW NUMBERING MORE THAN SIXTY IN 4HE S IS WHEN CONSERVATION BIOLOGY BEGAN TO EMERGE AS A DISCIPLINE AND ECOLOGISTS WORLD WIDE BEGAN TO STUDY INTRODUCED SPECIES FROM A CONSERVATION PERSPECTIVE )N THE EARLY S THE NEW JOURNAL "IOLOGICAL #ONSERVATION BEGAN PUBLISHING ARTICLES DESCRIBING THE THREATS POSED BY INTRODUCED SPECIES EG #AMPBELL AND /RMOND 3CHOlELD !PPLIED ECOLOGISTS WHO HAD BEEN STUDYING INTRODUCED SPECIES AND THEIR ECOLOGI CAL EFFECTS IN THE SIXTIES AND EARLIER CONTINUED TO DO SO IN THE SEVENTIES PUBLISHING PRIMARILY IN TAXONOMIC SPECIlC JOURNALS AS THEY HAD PREVIOUSLY &OR EXAMPLE /WRE DESCRIBED THE EXTENT OF INTRODUCED AVIFAUNA IN SOUTHEASTERN &LORIDA AND RAISED THE POSSIBILITY OF COMPETITION BETWEEN THE NATIVE AND NEW SPECIES IN THE CONSERVATION SECTION OF 4HE 7ILSON "ULLETIN #HRISTIE DESCRIBED THE EFFECTS OF SPECIES INTRODUCTIONS ON SALMONID COMMUNITIES *OURNAL OF THE &ISHERIES "OARD OF #ANADA AND -OYLE REPORTED ON THE EFFECTS ON THE NATIVE FROGS OF THE INTRODUCED BULLFROGS IN #ALIFORNIA #OPEIA )N A "IOSCIENCE REVIEW PAPER #OURTENAY AND 2OBINS SUMMARIZED THE CONSERVATION PROBLEMS PRIMAR ILY IN .ORTH !MERICA CREATED BY THE INTRODUCTION OF hEXOTICv ANIMALS BY lSH AND GAME AGENCIES AND THE PET TRADE 4HE %UROPEAN ECOLOGISTS WHO HAD BEEN STUDY ING INTRODUCED SPECIES AND THEIR ECOLOGICAL EFFECTS IN THE SIXTIES ALSO CONTINUED THEIR RESEARCH IN THE SEVENTIES PUBLISHING HUNDREDS OF PAPERS ON THIS TOPIC &OR EXAMPLE &ALINÇSKI AND 3UKOPP CONTINUED THEIR WORK ON THE URBAN INTRODUCED AND ADVENTITIOUS mORA AND *EHLÓK AND (EJNâ CONTINUED THEIR RESEARCH IN THE #ZECH 2EPUBLIC DESCRIBING MIGRATION ROUTES OF INTRODUCED SPECIES
-! $AVIS
AND MAKING WHAT PERHAPS WERE THE lRST PREDICTIONS OF WHEN PLANT INVASIONS WOULD OCCUR IN PARTICULAR LOCATIONS (EJNâ ET AL !LTHOUGH THIS mORISTIC APPROACH TO INTRODUCED SPECIES WAS NOT AS COMMON IN THE 5NITED 3TATES AT THIS TIME OCCA SIONAL STUDIES OF THIS TYPE WERE UNDERTAKEN EG -UEHLENBACHS DETAILED ACCOUNT THE ADVENTIVE mORA ALONG RAILROADS AROUND 3AINT ,OUIS -ISSOURI /CCASIONAL PAPERS ON BIOLOGICAL INVASIONS CAN BE FOUND IN THE ECOLOGICAL LITERA TURE WELL BEFORE THE S EG %GLER (OWEVER THE SEVENTIES WAS THE lRST TIME SINCE %LTON THAT BIOLOGICAL INVASIONS BEGAN TO APPEAR IN MAINSTREAM ECOLOGY LITERATURE WITH ANY FREQUENCY )N HIS REVIEW OF THE ECOLOGY OF WEEDS PUBLISHED IN !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "AKER EXPLICITLY EXTENDED THE DISCUSSION OF WEEDS BEYOND THE DISCIPLINARY BOUNDARIES OF HORTICULTURE AND AGRI CULTURE TO INCLUDE ECOLOGY /THER EXAMPLES INCLUDE "URDON AND #HILVERS /ECOLOGIA ARTICLE ON THE IMPACT OF INTRODUCED PINE SPECIES ON !USTRALIAS EUCALYP TUS FORESTS AND %MBREES CHAPTER ON THE ECOLOGY OF ANIMAL INVADERS IN THE BOOK !N !NALYSIS OF %COLOGICAL 3YSTEMS (ORN ET AL !LTHOUGH SOME ECOLOGISTS WERE BEGINNING TO THINK ABOUT BIOLOGICAL INVA SIONS DURING THE SEVENTIES THERE WAS STILL LITTLE COORDINATION AND COMMUNICATION AMONG INVESTIGATORS !ND THERE WAS NO FORMAL INFRASTRUCTURE TO SUPPORT EFFORTS TO DEVELOP A THEORY OF BIOLOGICAL INVASIONS %COLOGY MEETINGS AT THAT TIME DID NOT DEVOTE SPECIAL SYMPOSIA OR PAPER SECTIONS TO BIOLOGICAL INVASIONS WHICH WOULD HAVE SERVED AS IMPORTANT COMMUNICATION HUBS FOR THIS TOPIC 4HUS ALTHOUGH SCATTERED PAPERS ON BIOLOGICAL INVASIONS WERE APPEARING IN THE ECOLOGICAL LITERA TURE INVASION ECOLOGY HAD NOT YET EMERGED AS ITS OWN RESEARCH SPECIALTY AREA
4HE NUMBER OF PUBLISHED STUDIES ON BIOLOGICAL INVASIONS INCREASED DRAMATICALLY DURING THE S ESPECIALLY IN PARTICULAR TAXA SUCH AS PLANTS SEE REVIEW BY 0YÝEK 4HE EMPHASIS ON mORISTICS THAT CHARACTERIZED MUCH OF THE WORK IN PREVIOUS DECADES BEGAN TO GIVE WAY TO THE INCREASING INTEREST ON SPECIES BIOLOGY AND ECOLOGICAL INTERACTIONS 0YÝEK $UE TO THE PROLIFERATION OF INVASION PUBLICATIONS DURING THIS TIME THE HISTORICAL ACCOUNT OF THIS DECADE HAS BEEN SPLIT INTO TWO PERIODS -ANY OF THE %UROPEAN ECOLOGISTS WHO HAD BEEN STUDYING INTRODUCED AND ADVENTIVE mORA IN PRIOR DECADES CONTINUED TO DO SO IN THE EIGHTIES PARTICULARLY FOCUSING ON THE ECOLOGY OF URBAN mORA EG 3UKOPP AND 7ERNER +OWARIK )N THE 5NITED 3TATES 2ICHARD -ACK PUBLISHED HIS lRST ARTICLE ON BIOLOGICAL INVASIONS IN REPORTING ON THE ECOLOGICAL IMPACT IN WESTERN .ORTH !MERICA OF "ROMUS TECTORUM -ACK TOOK A CONSERVATION APPROACH IN HIS ARTICLE QUOTING %LTON AND EMPHASIZING THE DECLINE OF NATIVE GRASS SPECIES (E CHOSE TO SUBMIT HIS ARTICLE TO THE MORE APPLIED JOURNAL !GROECOSYSTEMS BECAUSE ITS SCOPE ENCOMPASSED THE ECOSYSTEMS THAT CHEATGRASS HAD INVADED )N THE SAME YEAR $AN 3IMBERLOFF CONTRIBUTED A CHAPTER TO THE BOOK "IOTIC #RISES IN %COLOGICAL AND %VOLUTIONARY 4IME
)NVASION BIOLOGY
.ITECKI 4HE TITLE OF THE BOOK SUGGESTS THAT 3IMBERLOFF MIGHT ALSO HAVE EMPHASIZED THE CONSERVATION ASPECTS OF BIOLOGICAL INVASIONS )N FACT HE DID NOT DO THIS BUT RATHER USED BIOLOGICAL INVASIONS AS A WAY TO TEST ECOLOGICAL THEORY EG ISLAND BIOGEOGRAPHY THEORY AND MODELS OF LIMITING SIMILARITY 4HUS WHEREAS -ACKS ARTICLE WAS MORE IN THE CONSERVATION TRADITION OF %LTONS BOOK 3IMBERLOFFS CHAPTER WAS MORE IN KEEPING WITH THE EMPHASIS ON ECOLOGI CAL AND EVOLUTIONARY THEORY THAT DISTINGUISHED 4HE 'ENETICS OF #OLONIZING 3PECIES )N THE SAME YEAR "ROWN AND -ARSHALL PUBLISHED AN ARTICLE EVEN MORE REMINISCENT OF THE !SILOMAR PROCEEDINGS EMPHASIZING THE EVOLUTIONARY CHANGES ACCOMPANYING THE COLONIZATION OF PLANTS 4WO YEARS LATER -OULTON AND 0IMM EXAMINED THE IMPACTS OF THE INTRODUCED (AWAIIAN AVIFAUNA AS A WAY TO ASSESS THE IMPORTANCE OF COMPETITION IN COMMUNITY ASSEMBLY ,IKE 3IMBERLOFF AND "ROWN AND -ARSHALL THEY ALSO EMPHASIZED THEORY AS EVIDENCED BY THEIR CHOICE OF JOURNAL !MERICAN .ATURALIST 4HE TONE AND STYLE USED BY 3IMBERLOFF "ROWN AND -ARSHALL AND -OULTON AND 0IMM WAS CONSISTENT TO THAT USED BY THE CONTRIBUTORS TO 4HE 'ENETICS OF #OLONIZING 3PECIES OTHER THAN (ARPER 4HE CONNECTION BETWEEN INTRODUCED SPECIES AND CONSERVATION CONTINUED TO GROW DURING THE )MMIGRANT +ILLERS +ING DESCRIBED THE IMPACT OF INTRODUCED PREDATORS ON NATIVE BIRDS IN .EW :EALAND !LTHOUGH WRITTEN FOR A POPULAR AUDIENCE +INGS BOOK WAS WELL RESEARCHED AND REFERENCED AND IT REPRE SENTED AN IMPORTANT SCIENTIlC CONTRIBUTION AS WELL )N 7ILLIAM *ORDAN ))) AND THE 5NIVERSITY OF 7ISCONSIN !RBORETUM PUB LISHED THE lRST ISSUE OF 2ESTORATION AND -ANAGEMENT .OTES NOW PUBLISHED UNDER THE NAME OF %COLOGICAL 2ESTORATION AN EVENT THAT SIGNIlED THE BEGINNING OF AN ORGANIZED INTEREST IN HABITAT RESTORATION IN .ORTH !MERICA ,AND MANAGERS HAD BEEN THINKING ABOUT RESTORATION IN THE S &OR EXAMPLE .!4/ SPONSORED A CONFERENCE IN 2EYKJAVIK )CELAND THAT RESULTED IN THE PUBLICATION OF 4HE "REAKDOWN AND 2ESTORATION OF %COSYSTEMS (OLDGATE AND 7OODMAN %UROPEANS CONSTITUTED THE MAJORITY OF PARTICIPANTS AT THE 2EYKJAVIK CONFERENCE AND THE INTEREST AT THE MEETING WAS MORE IN hREHABILITATINGv THE LANDSCAPE RATHER THAN TRYING TO RESTORE THE HABITAT TO SOME PRIOR NATIVE CONDITION AS ILLUSTRATED BY A STATEMENT BY "RADSHAW ET AL hFROM THE POINT OF VIEW OF NATURE CONSERVA TION REHABILITATION SHOULD NOT NECESSARILY MEAN RESTORATION OF THE ORIGINAL OFTEN UNINTERESTING ECOSYSTEMv 4HIS PERSPECTIVE CONTRASTED GREATLY WITH THE EMERGING INTEREST IN ECOLOGICAL RESTORATION IN THE 5NITED 3TATES )N HIS OPENING EDITORIAL OF THE lRST VOLUME OF 2ESTORATION AND -ANAGEMENT .OTES 7ILLIAM *ORDAN ))) STATED THAT THE NEW JOURNAL hWILL DEAL ONLY WITH THE DEVELOPMENT AND MANAGE MENT OF COMMUNITIES THAT ARE NATIVE OR AT LEAST ECOLOGICALLY APPROPRIATE TO THEIR SITEv 4HE STATED FOCUS OF THE JOURNAL WAS TO BE THE RESTORATION AND MANAGEMENT OF ECOLOGICAL COMMUNITIES FOR SCIENTIlC AND AESTHETIC PURPOSES EG PRAIRIES WETLANDS AND FORESTS BUT NOT FOR RANGE OR TIMBER MANAGEMENT AND NOT FOR hREC LAMATION EFFORTS AIMED SOLELY AT LAND STABILIZATIONv 4HE SUBSEQUENT DEVELOPMENT OF THE lELD OF RESTORATION ECOLOGY IN FUTURE YEARS WAS TO HAVE A MAJOR IMPACT ON
-! $AVIS
INVASION ECOLOGY PARTICULARLY IN .ORTH !MERICA THROUGH ITS EMPHASIS ON NATIVE ENVIRONMENTS AND NATIVE SPECIES "Y THE MID S MORE AND MORE ECOLOGISTS WERE BEGINNING TO THINK ABOUT INVASIONS FROM AN ECOLOGICAL PERSPECTIVE (OWEVER WHAT WAS STILL LACKING WAS A SYNTHESIS OF THIS THINKING THAT WOULD HELP DElNE A lELD OF INVASION ECOLOGY )N FACT THE GROUNDWORK FOR SUCH AN EFFORT WAS ALREADY UNDERWAY )N THE 4HIRD )NTERNATIONAL #ONFERENCE ON -EDITERRANEAN %COSYSTEMS WAS HELD IN 3TELLENBOSCH 3OUTH !FRICA AND INTEREST IN BIOLOGICAL INVASIONS AT THE MEETING LED TO A PROPOSAL TO THE 3#/0% GENERAL ASSEMBLY IN /TTAWA IN 4HIS PROPOSAL RESULTED IN THE CREATION IN OF A SCIENTIlC ADVISORY COMMITTEE THAT WAS TO ENCOURAGE AND FACILITATE FOCUS ON THE IMPACTS OF BIOLOGICAL INVASIONS ON NATURAL ECOSYSTEMS 4HE ADVISORY COMMITTEE ARTICULATED THREE QUESTIONS TO GUIDE THE 3#/0% INVASION PRO GRAM WHAT FACTORS DETERMINE WHETHER A SPECIES WILL BE AN INVADER OR NOT WHAT ARE THE CHARACTERISTICS OF THE ENVIRONMENT THAT MAKE IT EITHER VULNERABLE TO OR RESISTANT TO INVASIONS HOW CAN THE KNOWLEDGE GAINED FROM ANSWERING THE lRST TWO QUESTIONS BE USED TO DEVELOP EFFECTIVE MANAGEMENT STRATEGIES $EVELOPED WITH THE INTENT OF hBUILDING ON THE CONSIDERABLE KNOWLEDGE BASE AVAILABLE ON INVADERS OF AGRICULTURAL SYSTEMSv THE 3#/0% PROGRAM ON BIOLOGICAL INVASIONS WAS CLEARLY CONCEIVED IN THE CONSERVATION TRADITION OF %LTON )T IS NO COINCIDENCE THAT SCIENTISTS FROM 3OUTH !FRICA !USTRALIA .EW :EALAND AND THE 5NITED 3TATES CONTRIBUTED SO SIGNIlCANTLY TO THE 3#/0% INITIATIVE 4HE NATURAL ENVIRONMENTS IN THESE COUNTRIES HAD BEEN EXPERIENCING RECENT AND SUBSTANTIAL INTRODUCTIONS OF NEW SPECIES FROM OTHER REGIONS OF THE WORLD AND CONSIDERABLE CONSERVATION CON CERNS WERE BEING RAISED IN THESE COUNTRIES REGARDING THE IMPACTS OF THESE SPECIES
3OUTH !FRICAN SCIENTISTS HAD BEEN AMONG THE LEADERS IN RECOGNIZING THE CONSER VATION IMPLICATIONS OF INTRODUCED SPECIES EG 7ICHT 4AYLOR AND THEY PUBLISHED THE lRST 3#/0% VOLUME IN -ACDONALD AND *ARMAN (OWEVER IT WAS NOT UNTIL THE LATTER HALF OF THE DECADE THAT MOST OF THE 3#/0% REGIONAL WORKSHOPS BEGAN PUBLISHING THEIR PROCEEDINGS 4HE .ORTH !MERICAN CONTINGENT PUBLISHED %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII -OONEY AND $RAKE 4HE BOOK WAS ORGANIZED AROUND VARIOUS PATTERNS OF INVASIONS INCLUDING ASSOCIATIONS WITH DIFFERENT TAXONOMIC GROUPS ATTRIBUTES OF INVADERS AND SITE CHARACTERISTICS PROMOTING INVASIONS )N ADDITION A VARIETY OF CASE STUDIES WERE PROVIDED 4HIS PUBLICATION WAS ENTIRELY A 5NITED 3TATES INITIATIVE WITH BOTH EDITORS AND ALL THE CONTRIBUTORS BEING FROM 53 UNIVERSITIES 4HAT BIO LOGICAL INVASIONS HAD lNALLY CAPTURED THE INTEREST OF PROMINENT .ORTH !MERICAN ECOLOGISTS IS EVIDENCED BY THE CONTRIBUTORS TO THE BOOK EG 3IMBERLOFF %HRLICH "AZAZZ 2EGAL /RIANS 6ITOUSEK 2OUGHGARDEN %WEL 0IMM AND -OONEY #OINCIDENTALLY THE SYMPOSIUM THAT LED TO THIS VOLUME TOOK PLACE IN !SILOMAR #ALIFORNIA THE SAME SITE OF THE SYMPOSIUM ON THE GENETICS OF COLONIZING SPECIES
)NVASION BIOLOGY
HELD TWENTY YEARS EARLIER 4HE VOLUME CONTAINS AN INTERESTING MIXTURE OF CHAPTERS -OST WERE CLEARLY CONCEIVED AND WRITTEN WITH A CONSERVATION AND ENVIRONMENTAL PERSPECTIVE AS WOULD BE EXPECTED GIVEN THE NATURE OF THE 3#/0% PROGRAM (OWEVER SOME CHAPTERS WERE WRITTEN MORE IN THE SPIRIT OF THE !SILOMAR SYMPOSIUM AND FOCUSED MORE ON ECOLOGICAL THEORY 3IMBERLOFFS CHAPTER ON THE BIOGEOGRAPHY OF INSECT INTRODUCTIONS EXAMINED TOPICS SUCH AS ISLAND MAINLAND PATTERNS AND ISSUES OF BIOTIC RESISTANCE PRIMARILY FROM A THEO RETICAL PERSPECTIVE !LTHOUGH HE DID CITE %LTON 3IMBERLOFF DID NOT TAKE A STRONGLY CONSERVATION APPROACH IN HIS CHAPTER REFERRING PRIMARILY TO @INTRODUCED SPE CIES AND @COLONIZERS RATHER THAN @INVADERS AND @EXOTICS AND SPECIlCALLY RECOM MENDED THE hRElNEMENT OF THE APPROACH OF MANY OF THE PAPERS IN 4HE 'ENETICS OF #OLONIZING 3PECIES "AZZAZ ORGANIZED HIS CHAPTER ON LIFE HISTORIES AROUND THE CONCEPT OF @COLONIZING SPECIES AND ALSO MADE EXPLICIT REFERENCES TO THE BOOK -OULTON AND 0IMM EXPANDED ON THEIR PAPER AND SHOWED HOW BIOLOGICAL INVASIONS CAN BE USED TO TEST ECOLOGICAL THEORY !DDITIONAL PROCEEDINGS WERE PUBLISHED FROM 3#/0% WORKSHOPS HELD IN 3OUTH !FRICA !USTRALIA AND 'REAT "RITAIN EG -ACDONALD ET AL 'ROVES AND "URDON +ORNBERG AND 7ILLIAMSON "EING 3#/0% INITIATIVES THESE PUBLICATIONS WERE ALSO WRITTEN FROM A CONSERVATION PERSPECTIVE (OWEVER COM MENTS BY THE EDITORS OF THE !USTRALIAN PROCEEDINGS INDICATE THAT THEY RECOGNIZED AN EMERGING TENSION THAT WAS DEVELOPING IN INVASION ECOLOGY AS SOME ECOLOGISTS EMBRACED THE CONSERVATION AND STRONG ENVIRONMENTAL EMPHASIS ARTICULATED BY %LTON WHILE OTHERS EXPRESSED CONCERN OVER THE STRONG NORMATIVE NATURE OF THIS APPROACH )N THE &OREWORD TO THE PUBLICATION 'ROVES AND "URDON THE EDITORS STATED THAT hTHE TERMINOLOGY ASSOCIATED WITH @INVASIONS GENERALLY IS UNSATISFACTORY WITH ITS CONNOTATIONS OF A MILITARY OPERATION x 7HEREVER POSSIBLE WE HAVE TRIED TO ELIMINATE EMOTIVE TERMS SUCH AS @WEEDS @PESTS @EXOTICS AND @ALIENSv )NSTEAD THE EDITORS STRIVED TO UTILIZE THE WORD @INTRODUCED AS MUCH AS POSSIBLE THROUGHOUT THE BOOK !NOTHER IMPORTANT DEVELOPMENT THAT OCCURRED DURING THIS TIME PERIOD WAS THE FOUNDING IN OF THE 3OCIETY FOR %COLOGICAL 2ESTORATION 3%2 NOW KNOWN AS 3OCIETY FOR %COLOGICAL 2ESTORATION )NTERNATIONAL 3%2 EMERGED OUT OF THE RAPIDLY DEVELOPING INTEREST IN RESTORATION BY INDIVIDUALS AND CONSERVATION GROUPS INTER ESTED IN MANAGING NATURAL ENVIRONMENTS 5PON ITS FOUNDING 3%2 WAS PRIMAR ILY A .ORTH !MERICAN INITIATIVE AND THE RESTORATION ECOLOGY MOVEMENT THAT IT REPRESENTED AND INSPIRED SHARPLY DISTINGUISHED BETWEEN SPECIES BASED ON THEIR GEOGRAPHY OF ORIGIN WITH NATIVE SPECIES BEING DESIRABLE AND NON NATIVES BEING UNDESIRABLE IN NATURAL ENVIRONMENTS 4HE STARK DICHOTOMY BETWEEN NATIVE AND NON NATIVE SPECIES PARTICULARLY CHARACTERIZED CONSERVATION AND RESTORATION EFFORTS IN REGIONS LIKE .ORTH !MERICA (AWAII AND .EW :EALAND WHICH HAD EXPERIENCED RELATIVELY FEW SPECIES INTRODUCTIONS UNTIL THE PAST FEW CENTURIES 4HIS DISTINCTION SEEMED TO BE LESS CRUCIAL AMONG CONSERVATIONISTS AND RESTORATIONISTS IN %UROPE WHERE AS 5SHER B ACKNOWLEDGED DISTINGUISHING BETWEEN NATIVE AND INTRO DUCED SPECIES IS OFTEN PROBLEMATIC DUE TO THE MILLENNIA OF HUMAN MOVEMENTS AND
-! $AVIS
SPECIES INTRODUCTIONS ACROSS THE CONTINENT 2ESTORATION ECOLOGY AND INVASION ECOL OGY EMERGED AT ABOUT THE SAME TIME AND IN .ORTH !MERICA THEY DEVELOPED AS SISTER DISCIPLINES DURING THE LATTERS AND CONTINUED TO REINFORCE ONE ANOTHER IN SUBSEQUENT YEARS 4HE GROWING RELATIONSHIP BETWEEN INVASION ECOLOGY AND CONSERVATION ECOLOGY DURING THIS TIME WAS ILLUSTRATED BY THE DECISION OF THE EDITORS OF THE JOURNAL "IOLOGICAL #ONSERVATION TO DEVOTE A SPECIAL ISSUE TO THIS TOPIC 4ITLED "IOLOGICAL )NVASIONS OF .ATURE 2ESERVES THIS PUBLICATION 5SHER A REPRESENTED ANOTHER 3#/0% PROD UCT !LTHOUGH IT WAS BECOMING INCREASINGLY COMMON FOR ECOLOGISTS TO ADOPT THE MORE EXPLICIT CONSERVATION PERSPECTIVE EMPHASIZED BY THE 3#/0% PROGRAM NOT ALL ECOLOGISTS WERE DOING SO &OR EXAMPLE IN HIS ARTICLE ON INVASION WINDOWS *OHNSTONE EXAMINED HABITAT INVASIBILITY MOSTLY FROM A THEORETICAL PERSPECTIVE AND HE DID NOT LINK HIS ARTICLE TO CONSERVATION CONCERNS REGARDING INVASIONS 4HE DECADE ENDED WITH THE PUBLICATION OF "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE $RAKE ET AL THE SYNTHESIS REPORT OF THE VARIOUS REGIONAL 3#/0% SYMPOSIA AND WORKSHOPS 4HIS PUBLICATION REPRESENTED THE TH PUBLICATION IN THE 3#/0% SERIES 4WENTY NINE ECOLOGISTS REPRESENTING SEVEN COUNTRIES 53! 5+ !USTRALIA 3OUTH !FRICA &RANCE $ENMARK )NDIA MANY OF WHOM HAD CONTRIBUTED TO THE VOLUME AUTHORED CHAPTERS FOR THIS PUBLICATION 3OME OF THE PROMI NENT NON !MERICAN CONTRIBUTORS MANY OF WHOM HAVE CONTINUED TO FOCUS MUCH OF THEIR RESEARCH ON BIOLOGICAL INVASIONS UP TO THE PRESENT INCLUDED &RANCESCO DI #ASTRI 0ETER !SHTON $AVID 2ICHARDSON )AN -ACDONALD -ICHAEL 5SHER -ARK 7ILLIAMSON 2ICHARD (OBBS -ICHAEL #RAWLEY 2ICHARD 'ROVES AND -ARCEL 2EJMANEK 2EJMANEK HAD MOVED FROM #ZECHOSLOVAKIA TO THE 5NITED 3TATES BY THE TIME THE BOOK WAS PUBLISHED )NDIVIDUALLY FOCUSING ON DIFFERENT TAXA OR REGIONS OF THE WORLD CONTRIBUTORS TRIED TO ANSWER THE THREE QUESTIONS THAT HAD BEEN POSED BY THE 3#/0% ADVISORY COMMITTEE IN )N THE BOOKS lNAL CHAPTER -OONEY AND $RAKE CONCLUDED THAT ALTHOUGH KNOWLEDGE PERMITTED hGENERIC GUIDELINESv FOR ASSESSING THE LIKELIHOOD OF BIOLOGICAL INVASIONS EG DISTURBANCES NORMALLY INCREASED INVASIBILITY THEY CONCURRED WITH THE CONCLUSIONS REACHED BY MOST OF THE AUTHORS THAT IT WAS NOT POSSIBLE AT THAT TIME TO MAKE ACCURATE PREDICTIONS ABOUT INDIVIDUAL CASES !LTHOUGH SOME OF THE .ORTH !MERICAN ECOLOGISTS CONTINUED TO USE THE TERMS @INTRODUCTION AND @INTRODUCED SPECIES RATHER THAN @INVASIONS AND @INVADERS IN THE VOLUME EG 3IMBERLOFF AND 0IMM POSSIBLY INDICATING SOME RESISTANCE TO ADOPTING THE MORE VALUE BASED CONSERVATION APPROACH IT IS INTERESTING THAT THE FREQUENCY WITH WHICH !MERICAN ECOLOGISTS CITED %LTONS BOOK CONTINUED TO INCREASE )N ONLY THREE OF THE ELEVEN 53 CONTRIBUTORS TO THE 'ENETICS OF #OLONIZING 3PECIES CITED 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS )N THE .ORTH !MERICAN 3#/0% VOLUME WHICH WAS AUTHORED ENTIRELY BY 53 ECOLO GISTS OF THE CHAPTERS CITED %LTONS BOOK !ND IN THE 3#/0% SYNTHESIS VOLUME OF THE 53 AUTHORED CHAPTERS CITED %LTONS BOOK "Y CONTRAST ONLY OF OF THE CHAPTERS IN THE 3#/0% VOLUME AUTHORED ENTIRELY BY NON 53 ECOLOGISTS CITED %LTON 4WO OF THE CHAPTERS WERE AUTHORED BY AT LEAST
)NVASION BIOLOGY
ONE 53 AND ONE NON 53 AUTHOR ONE OF THESE CITED %LTON AND THE OTHER DID NOT )N THE BOOKS lNAL CHAPTER (AL -OONEY AND *AMES $RAKE BOTH 53 ECOLOGISTS SPECIl CALLY ENCOURAGED THE READERS TO CONSULT %LTONS BOOK h4HOSE WISHING AN IN DEPTH TREATMENT OF THE DYNAMICS OF BIOLOGICAL INVASIONS ARE REFERRED TO %LTONS CLASSIC WORK AND TO THE PUBLICATIONS WHICH AROSE OUT OF THE PROGRAMv ;IE THE 3#/0% PROGRAM= 4HE SCATTERED IDEAS CONCERNING BIOLOGICAL INVASIONS PUT FORTH BY ECOLOGISTS IN THE SEVENTIES AND EARLY EIGHTIES lNALLY COALESCED IN THE MID TO LATE EIGHTIES RESULT ING IN THE PUBLICATION OF A NUMBER OF IMPORTANT PAPERS AND EDITED VOLUMES FROM 4HESE PUBLICATIONS REVIEWED KNOWLEDGE AND THEORY TO THAT POINT IDENTIlED QUESTIONS TO BE ANSWERED AND SET MUCH OF THE DIRECTION FOR FUTURE RESEARCH OF BIOLOGICAL INVASIONS )N SHORT INVASION ECOLOGY EMERGED AS A RESEARCH SPECIALTY AREA DURING THIS TIME PERIOD AS A DIRECT RESULT OF THESE PUBLICATIONS !LTHOUGH SOME INVESTIGATORS CONTINUED TO PURSUE INVASION ECOLOGY MORE IN THE TRADITION OF THE !SILOMAR SYMPOSIUM ON COLONIZATION IE FOCUSING PRIMAR ILY ON ECOLOGICAL AND EVOLUTIONARY THEORY MORE AND MORE ECOLOGISTS PARTICULARLY .ORTH !MERICAN ECOLOGISTS WERE PRESENTING THEIR WRITINGS IN AN EXPLICITLY ENVI RONMENTAL CONTEXT THE PATH SET FORTH BY %LTON IN
)NVASION ECOLOGY TOOK THE SPOTLIGHT FOLLOWING THE SERIES OF INVASION BOOKS AND ARTICLES PUBLISHED BETWEEN AND "IOLOGICAL INVASIONS BECAME A POPU LAR AREA OF RESEARCH AND AN INCREASINGLY CONTROVERSIAL TOPIC OF DEBATE DURING THE S RESULTING IN A mOOD OF PUBLICATIONS BOTH SCHOLARLY AND POPULAR THAT CON TINUES TO THIS DAY .ATIONAL AND INTERNATIONAL ECOLOGY MEETINGS AND SOME GENERAL SCIENCE MEETINGS EG !!!3 BEGAN TO REGULARLY SCHEDULE SYMPOSIA AND PAPER SESSIONS DEVOTED TO BIOLOGICAL INVASIONS AND INTRODUCED SPECIES DURING THE NINE TIES 4HE lRST OF SEVEN INTERNATIONAL CONFERENCES ON THE ECOLOGY OF ALIEN PLANT INVA SIONS WAS HELD IN ,OUGHBOROUGH 5+ IN AND THE TH CONFERENCE WAS HELD IN &ORT ,AUDERDALE &LORIDA 53! IN AND SEVERAL OF THESE CONFERENCES RESULTED IN PUBLICATIONS OF THE PROCEEDINGS EG 0YÝEK ET AL 3TARlNGER ET AL #HILD ET AL 7ITH THE EXCEPTION OF THE SECOND AND SEVENTH CONFERENCES HELD IN 4EMPE !RIZONA AND &ORT ,AUDERDALE &LORIDA THE CONFERENCES TOOK PLACE IN %UROPE WITH %UROPEAN ECOLOGISTS REPRESENTING THE MAJORITY OF PARTICIPANTS 4HUS THIS SERIES PROVIDES AN EXCELLENT OVERVIEW OF THE RESEARCH AND IDEAS COMING FROM %UROPE AT THIS TIME PARTICULARLY FROM EASTERN %UROPEAN COUNTRIES SUCH AS THE #ZECH 2EPUBLIC WHICH AS STATED ABOVE HAVE HAD A LONG TRADITION OF STUDY ING INVASIONS 3OME OF THE PROMINENT ECOLOGISTS WHO PLAYED A SIGNIlCANT ROLE IN THESE CONFERENCES AND PUBLICATIONS INCLUDE 0ETR 0YÝEK AND +AREL 0RACH #ZECH 2EPUBLIC )NGO +OWARIK AND 5WE 3TARlNGER 'ERMANY -ARK 7ILLIAMSON -AX 7ADE AND ,OIS #HILD 5+ 'IUSEPPI "RUNDU )TALY AND *OHN "ROCK AND -ARCEL 2EJMANEK 53!
-! $AVIS
5NLIKE THE TIME PERIODS DESCRIBED ABOVE THE YEARS DO NOT OFFER AN OBVIOUS LIST OF IMPORTANT PUBLICATIONS DUE TO THE SHEER NUMBER OF BOOKS AND ARTICLES PRODUCED DURING THIS TIME 4HUS THE PUBLICATIONS BRIEmY MENTIONED BELOW CONSTITUTE A VERY SMALL REPRESENTATIVE SUBSET OF THE LARGE NUMBER OF SIGNIlCANT PUBLICATIONS ONE COULD HAVE INCLUDED ,ODGE’S 42%% ARTICLE PROVIDED A COMPREHENSIVE OVERVIEW AND ASSESSMENT OF THE lELD OF INVASION ECOLOGY TO THAT POINT #ONSISTENT WITH PRIOR ASSESS MENTS ,ODGE CONCLUDED THAT IT WAS NOT YET POSSIBLE TO ACCURATELY PREDICT THE CONSEQUENCES OF A SINGLE INVASION EVENT AND THAT ANY HOPE OF USEFUL PREDICTIONS COULD ONLY EMERGE FROM FOCUSED STUDIES ON PARTICULAR SPECIES AND ENVIRONMENTS ,ODGES PAPER WAS DISTINCTIVE BECAUSE IT CONTAINED WELL DEVELOPED ASPECTS OF BOTH THE CONCEPTUAL APPROACHES TO BIOLOGICAL INVASIONS THAT HAD DEVELOPED DUR ING THE PRECEDING THREE DECADES 7HILE ,ODGE BEGAN HIS PAPER EMPHASIZING THE ENVIRONMENTAL IMPACTS OF @EXOTIC SPECIES WHICH HAVE hSERIOUS CONSEQUENCES FOR BOTH MAN AND NATUREv HE ALSO STRESSED THE SCIENTIlC OPPORTUNITY THAT INVASIONS PROVIDE hBECAUSE THE CHARACTERISTICS AND ECOLOGICAL IMPACT OF EXOTIC SPECIES MAY PROVIDE CLUES TO LONGSTANDING ISSUES IN THE STUDY OF COMMUNITY ASSEMBLYv #ONSISTENT WITH THIS DUAL EMPHASIS ,ODGE CITED BOTH %LTON AND "AKER AND 3TEBBINS IN THE SAME SENTENCE REFERRING TO THEM BOTH AS @CLASSICS 7ILLIAMSONS BOOK "IOLOGICAL )NVASIONS WHICH REVIEWED AND SYNTHESIZED INVASION RESEARCH AND THEORY CONDUCTED AND DEVELOPED DURING THE PRIOR SEV ERAL DECADES MADE A VERY IMPORTANT CONTRIBUTION BY PROVIDING INVESTIGATORS A COMPREHENSIVE AND UP TO DATE OVERVIEW OF THE NEW AND RAPIDLY EVOLVING lELD 7ILLIAMSONS BOOK PRIMARILY FOCUSED ON THE SCIENTIlC ASPECTS OF SPECIES INVA SIONS HOWEVER HE DID SET THE BOOK IN A CLEAR CONSERVATION CONTEXT EMPHASIZING THE MANAGEMENT VALUE OF BETTER SCIENTIlC UNDERSTANDING OF INVASIONS *AMES #ARLTONS NUMEROUS PUBLICATIONS ON THE IMPACTS OF INVASIONS ON MARINE ECO SYSTEMS EG #ARLTON A B PROMPTED MORE MARINE ECOLOGISTS TO CONSIDER THE IMPORTANCE OF BIOLOGICAL INVASIONS 4HE PUBLICATION OF "IOLOGICAL )NVASIONS 4HEORY AND 0RACTICE BY *APANESE ECOLOGISTS 3HIGESADA AND +AWASAKI WHICH REVIEWED MATHEMATICAL MODELS OF SPECIES SPREAD ILLUSTRATED THE EXTENT TO WHICH BIOLOGICAL INVASIONS HAD ATTRACTED THE INTERESTS OF ECOLOGISTS FROM AROUND THE WORLD 4HE IMPORTANCE OF UNDERSTANDING INTERACTIONS WITH SOIL MICROBES POSITIVE AND NEGATIVE AS PART OF THE INVASION PROCESS IN PLANTS WAS EMPHASIZED BY +LIRONOMOS AND 2ICHARDSON ET AL EMPHASIZED THE ROLE THAT MUTUALISMS CAN PLAY IN THE INVASION PROCESS 4HE ENEMY RELEASE HYPOTHESIS RECEIVED CONSIDERABLE ATTENTION DURING THIS TIME ALTHOUGH STUDIES PRODUCED CONmICTING RESULTS +EANE AND #RAWLEY 7ILLIAMSON PROPOSED THE SINCE OFT CITED @TENS RULE OF BIOLOGICAL INVASIONS WHICH STATES THAT APPROXIMATELY OF IMPORTED SPECIES EXIST IN SOME SENSE OUTSIDE OF CAPTIVITY OF THESE ESTABLISHED SELF SUSTAINING POPULATIONS AND OF THESE BECOME PESTS 2EVIVING THE EMPHASIS ON GENETICS OF COLONIZING SPECIES THAT CHARACTERIZED THE !SILOMAR SYMPOSIUM MANY ECOLOGISTS BEGAN FOCUSING ON THE GENETICS OF INTRODUCED SPECIES RECOGNIZING
)NVASION BIOLOGY
THE IMPORTANCE THAT NEW GENOTYPES MIGHT PLAY IN SPECIES SPREAD %LLSTRAND AND 3CHIERENBECK 6ILA ET AL $AEHLER AND #ARINO 0YSEËK ET AL %WEL ET AL REVIEWED THE BENElTS AND RISKS ASSOCIATED WITH DELIBER ATE SPECIES INTRODUCTIONS AND OUTLINED THE RESEARCH NEEDED TO PROVIDE THE INFOR MATION REQUIRED TO INCREASE THE FORMER AND LOWER THE LATTER !S INVASION ECOLOGY CONTINUED TO DEVELOP DURING THIS PERIOD SEVERAL SCIENTISTS EXPRESSED CONCERN THAT THE lELD WAS NOT WELL CONNECTED WITH OTHER DISCIPLINES AND THAT INVASION ECOL OGY WAS NOT BEING INFORMED BY NOR INFORMING DISCIPLINES SUCH AS BIOGEOGRAPHY EVOLUTIONARY BIOLOGY AND ECOLOGICAL SUBDISCIPLINES SUCH AS SUCCESSION ECOLOGY AND WEED ECOLOGY 6ERMEIJ $AVIS ET AL $AVIS ET AL !T THE SAME TIME SOME CONSCIOUS EFFORTS WERE BEING MADE TO BRIDGE THESE GAPS EG "OOTH ET AL $URING THE NINETIES ECOLOGISTS CONTINUED THE SEVERAL DECADES LONG EFFORT TO DETERMINE WHETHER INVADERS POSSESSED DISTINCTIVE TRAITS -ANY RESEARCHERS CON CLUDED THAT THERE WAS LITTLE DIFFERENCE BETWEEN THE TRAITS OF INVASIVE AND NON INVASIVE SPECIES EG 4HOMPSON ET AL 'OODWIN ET AL 7ILLIAMSON ALTHOUGH SOME TAXONOMICALLY BASED COMPARATIVE STUDIES DID SHOW DISTINCT DIFFERENCES BETWEEN RESIDENT AND SPREADING INTRODUCED SPECIES EG 2EJMANEK AND 2ICHARDSON +OLAR AND ,ODGE WERE MORE OPTIMISTIC THAT TRAITS COULD BE USED AS PREDICTORS OF INVASIONS CONCLUDING THAT QUANTITATIVE APPROACHES (e.g., Daehler and Carino 2000) were making progress and that these approACHES SHOULD “ALLOW US TO PREDICT PATTERNS OF INVADING SPECIES MORE SUCCESSFULLY” 5NLIKE ,ODGE’S PAPER WHICH EMPHASIZED BOTH THE CONSERVATION AND SCIENTIFIC IMPLICATIONS OF BIOLOGICAL INVASIONS THE 42%% PAPER BY +OLAR AND ,ODGE WAS MUCH MORE STRONGLY ORGANIZED AROUND THE CONSERVATION AND ENVIRONMENTAL CONCERNS ABOUT SPECIES INVASIONS &ACTORS THAT CONTRIBUTE TO AN ENVIRONMENTS SUSCEPTIBILITY TO INVASION INVASI BILITY ONE OF THE OTHER ORGANIZING THEMES OF THE 3#/0% INITIATIVES IN THE S ALSO CONTINUED TO BE A CENTRAL FOCUS OF RESEARCH AND DISCUSSION DURING THE S AND THE EARLY YEARS OF THE NEW CENTURY )N HIS BOOK "IOLOGICAL $IVERSITY (USTON ADDRESSED INVASIBILITY AND EMPHASIZED THE COMBINED IMPORTANCE OF DISTURBANCE AND PRODUCTIVITY ,ONSDALE PRESENTED HIS lNDINGS OF A COMPREHENSIVE REVIEW OF GLOBAL PATTERNS OF PLANT INVASIONS AND FOUND A POSITIVE CORRELATION BETWEEN NATIVE AND EXOTIC SPECIES AT A SITE ALTHOUGH HE CONCLUDED THAT IT WAS DIFl CULT TO DISCRIMINATE BETWEEN THE RELATIVE IMPORTANCE OF INVASIBILITY AND PROPAGULE PRESSURE $AVIS ET AL ARGUED FOR A THEORY OF INVASIBILITY BASED ON RESOURCE AVAILABILITY EMPHASIZING THAT INVASIBILITY IS NOT A CONSTANT CHARACTERISTIC OF AN ENVIRONMENT BUT IS AN ATTRIBUTE THAT VARIES OVER TIME AS RESOURCE AVAILABILITY mUCTUATES $AVIS AND 0ELSOR TESTED THIS THEORY IN A lELD EXPERIMENT BASED ON THE INTRODUCTION OF NATIVE SPECIES PRAIRIE FORBS INTO A PLANT COMMUNITY DOMI NATED BY INTRODUCED SPECIES .ORTH !MERICAN OLD lELD SHOWING THAT IT IS THE ECO LOGICAL PROCESSES THAT MATTER NOT THE GEOGRAPHIC ORIGIN OF THE SPECIES INVOLVED !LTHOUGH MUCH OF THE PROGRESS IN INVASION ECOLOGY DURING THE EIGHTIES AND NINETIES INVOLVED MOVING BEYOND PURELY mORISTIC STUDIES OF NATIVE AND INTRODUCED
-! $AVIS
mORA MORE COMPREHENSIVE EFFORTS TO DESCRIBE AND CATALOG mORA WERE ALSO UNDER TAKEN DURING THIS TIME PROVIDING VALUABLE DATA BASES FOR ONGOING AND FUTURE STUD IES EG 0YSEËK ET AL 4HE MOST COMPREHENSIVE NATIONAL OR REGIONAL PLANT DATA BASES AT THE CURRENT TIME ARE LIKELY THOSE OF THE 5NITED +INGDOM #LEMENT AND &OSTER 2YVES ET AL THE #ZECH 2EPUBLIC 0YSEËK ET AL AND !USTRIA %SSL AND 2ABITSCH /THER EXCELLENT PLANT DATA BASES INCLUDE THOSE IN 'ERMANY +LOTZ ET AL AND .ORTH !MERICA +ARTESZ AND -EACHAM 7ITH THE DEVELOPMENT OF INVASION ECOLOGY AS A RECOGNIZED RESEARCH SPECIALTY AREA TWO INVASION RELATED JOURNALS WERE ESTABLISHED IN THE LATE NINETIES $IVERSITY AND $ISTRIBUTIONS "LACKWELL 0UBLISHING WAS FOUNDED IN SUCCEEDING THE JOURNAL "IODIVERSITY ,ETTERS WITH AN EMPHASIS ON BIOLOGICAL INVASIONS AND BIO DIVERSITY $AVID 2ICHARDSON HAS SERVED AS THE JOURNALS EDITOR IN CHIEF FROM ITS OUTSET "IOLOGICAL )NVASIONS +LUWER WAS FOUNDED IN WITH *AMES 4 #ARLETON AS THE EDITOR IN CHIEF A POSITION CURRENTLY HELD BY *AMES ! $RAKE 4HE STATED AIMS AND SCOPES OF BOTH JOURNALS EMPHASIZE THE SCIENCE RATHER THAN THE CONSERVATION ASPECTS OF BIOLOGICAL INVASIONS (OWEVER IT IS NOT UNCOMMON FOR AUTHORS TO INVOKE CONSERVATION CONCERNS IN THEIR ARTICLES PARTICULARLY IN "IOLOGICAL )NVASIONS 4WO DEVELOPMENTS IN ECOLOGY DURING THE S PARTICULARLY IMPACTED INVA SION ECOLOGY A RENEWED EMPHASIS ON THE ECOLOGICAL EFFECTS OF BIODIVERSITY AND THE INCREASING EMPHASIS ON GLOBAL CHANGE 2ESEARCH ON THE ECOLOGICAL IMPACTS OF BIODIVERSITY FOCUSED ATTENTION ON %LTONS HYPOTHESIS THAT SPECIES RICH COM MUNITIES SHOULD BE MORE RESISTANT TO INVASIONS THAN SPECIES POOR COMMUNITIES ! NUMBER OF SMALL PLOT EXPERIMENTAL STUDIES INVOLVING CONSTRUCTED PLANT COM MUNITIES YIELDED RESULTS THAT SUPPORTED %LTONS DIVERSITY INVASIBILITY HYPOTHESIS 4ILMAN +NOPS ET AL (OWEVER THESE EXPERIMENTS WERE CHALLENGED ON METHODOLOGICAL GROUNDS 7ARDLE AND THEIR RELEVANCY WAS QUESTIONED SINCE STUDIES IN NATURAL COMMUNITIES OFTEN FOUND THAT THE MOST DIVERSE ENVIRON MENTS WERE THE MOST HEAVILY INVADED ,ONSDALE 3TOHLGREN ET AL %FFORTS HAVE BEEN MADE TO RESOLVE THIS DEBATE EG EMPHASIZING THE ROLE THAT SPATIAL SCALE PLAYS IN INTERPRETING THE RESULTS AND THE FACT THAT CORRELATED ENVIRON MENTAL FACTORS MAY AFFECT BOTH DIVERSITY AND INVASIBITY ,EVINE AND $!NTONIO ,EVINE 3HEA AND #HESSON (OWEVER TO DATE THESE EFFORTS HAVE NOT QUELLED THE CONTROVERSY 2EJMANEK 2ENNE AND 4RACY 3TOHLGREN 4HE INTEREST IN GLOBAL CHANGE THAT DEVELOPED IN ECOLOGY IN THE NINETIES WENT BEYOND CONCERNS INVOLVING INCREASES IN ATMOSPHERIC #/ AND CLIMATE CHANGE $UKES AND -OONEY EMPHASIZED THE GLOBAL DIMENSIONS OF BIOLOGICAL INVA SIONS AND RESEARCHERS EMPHASIZED THE CAUSE AND EFFECT RELATIONSHIP THAT EXISTED BETWEEN BIOLOGICAL INVASIONS AND OTHER TYPES OF GLOBAL CHANGE +OWARIK !S A RESULT OF CONNECTIONS MADE BETWEEN BIOLOGICAL INVASIONS AND GLOBAL CHANGE THE TOPIC OF BIOLOGICAL INVASION HISTORICALLY A RATHER NARROW AND SPECIALIZED AREA OF RESEARCH HAS BECOME PART OF A MUCH LARGER AND MORE PROMINENT ENVIRONMEN TAL AGENDA
)NVASION BIOLOGY
! NUMBER OF BOOKS PUBLISHED DURING THE S AND EARLY S AND LIKE %LTONS BOOK WERE WRITTEN FROM AN EXPLICIT CONSERVATION AND ENVIRONMEN TAL PERSPECTIVE AND AIMED AT THE GENERAL PUBLIC -ANY OF THESE BOOKS UTILIZED SIMILAR EVOCATIVE IMAGERY TO CAPTURE THE PUBLICS ATTENTION %XAMPLES OF SUCH BOOKS WRITTEN OR EDITED BY ECOLOGISTS OR SCIENCE JOURNALISTS INCLUDE ,IFE /UT OF "OUNDS "IOINVASIONS IN A "ORDERLESS 7ORLD "RIGHT AND +ILLER !LGAE -EINESZ .ATURE /UT OF 0LACE "IOLOGICAL )NVASIONS IN THE 'LOBAL !GE 6AN $RIESCHE AND 6AN $RIESCHE 4INKERING WITH %DEN ! .ATURAL (ISTORY OF %XOTICS IN !MERICA 4ODD AND 0LAGUES OF 2ATS AND 2UBBERVINES "ASKIN 7ITH THEIR LAMENTATION OVER THE LOSS OF NATIVE ENVIRONMENTS AND DECLINE OF NATIVE SPECIES THE ABOVE BOOKS ILLUSTRATE THE INCREASINGLY STRONG SYNERGY THAT HAD DEVELOPED BETWEEN RESTORATION ECOLOGY AND INVASION ECOLOGY PARTICULARLY IN .ORTH !MERICA DURING THE NINETIES WITH THE OBJECTIVES OF EACH REINFORCING THOSE OF THE OTHER 2ESTORATION ECOLOGYS EMPHASIS ON RESTORING ENVIRONMENTS WITH NATIVE SPECIES AFlRMED THE IMPORTANCE OF INVASION ECOLOGY AND INVASION ECOLO GYS EMPHASIS ON THE HARM CAUSED BY A SMALL PROPORTION OF INTRODUCED SPECIES PROVIDED IMPORTANT JUSTIlCATION FOR RESTORATION ECOLOGYS PREFERENCE FOR NATIVE SPECIES (OWEVER BY THE END OF THE NINETIES AND BEGINNING OF THIS CENTURY MORE SCIENTISTS WERE QUESTIONING THE DICHOTOMOUS AND NORMATIVE NATURE OF A PERSPEC TIVE THAT PREFERS SOME SPECIES OVER OTHERS ON THE BASIS OF THEIR GEOGRAPHY OF ORIGIN 'OULD 3LOBODKIN EMPHASIZING THE USEFUL CONTRIBUTIONS THAT SOME INTRODUCED SPECIES MIGHT BE ABLE TO MAKE IN RESTORATION PROJECTS $!NTONIO AND -EYERSON 3UCH OBJECTIONS WERE NOT NEW )N THE 3#/0% SYNTHESIS REPORT $RAKE ET AL *AMES "ROWN MADE THE SAME ARGUMENTS REGARDING THE POTENTIALLY POSITIVE VALUE OF SOME INTRODUCED SPECIES AND EXPRESSED CONCERN OVER hA KIND OF IRRATIONAL XENOPHOBIA ABOUT INVADING ANIMALS AND PLANTS THAT RESEMBLES THE INHERENT FEAR AND INTOLERANCE OF FOREIGN RACES CULTURES AND RELI GIONSv AN hATTITUDEv HE SAID HE hDETECTEDv AT THE 3#/0% CONFERENCE !CTUALLY %GLER RAISED THESE SAME CONCERNS FORTY SEVEN YEARS EARLIER )N HIS ARTICLE IN %COLOGY HE CRITICIZED THE COMMON RESORT TO HYPERBOLE AND MILITARY IMAGERY IN DISCUSSIONS OF ALIEN SPECIES AND WARNED AGAINST hANTHROPOMORPHIC SENTIMEN TALISM THAT BREEDS A SPIRIT OF DEFEATv $URING THE NINETIES WRITINGS OF INVASION BIOLOGISTS ALSO ATTRACTED THE ATTENTION OF PHILOSOPHERS %SER 3AGOFF WHO EXPRESSED SIMILAR CONCERNS OVER THE LANGUAGE AND VALUES THEY SAID PERME ATED THE WRITINGS OF INVASION ECOLOGY &INALLY ALTHOUGH NO ECOLOGISTS QUESTIONED THE FACT THAT THE EARTHS BIOTA WAS BECOMING INCREASINGLY HOMOGENIZED DUE TO WIDESPREAD SPECIES INTRODUCTIONS THE COMMON CONTENTION THAT SPECIES INTRODUC TIONS LEAD TO DECLINES IN REGIONAL AND LOCAL BIODIVERSITY WAS CHALLENGED BY SEVERAL INVESTIGATORS 2OSENZWEIG $AVIS 3AX AND 'AINES A POINT THAT HAD ACTUALLY BEEN MADE MUCH EARLIER BY (ARPER "Y THE END OF THE NINETIES INVASION BIOLOGY WAS BECOMING INCREASINGLY INSTI TUTIONALIZED WITH THE ESTABLISHMENT OF MORE NATIONAL AND INTERNATIONAL CONSER VATION AND BIODIVERSITY INITIATIVES RELATING TO BIOLOGICAL INVASIONS 4HE 5NITED .ATIONS SPONSORED CONFERENCE ON hINVASIVE ALIEN SPECIESv IN 4RONDHEIM .ORWAY
-! $AVIS
IN 3ANDLUND ET AL LED TO THE FORMATION IN THE FOLLOWING YEAR OF THE 'LOBAL )NVASIVE 3PECIES 0ROGRAMME ')30 ')30 WAS DEVELOPED EXPLICITLY AS A CONSERVATION AND ENVIRONMENTAL INITIATIVE AS EVIDENCED BY ITS MISSION STATEMENT @TO CONSERVE BIODIVERSITY AND SUSTAIN HUMAN LIVELIHOODS BY MINIMIZING THE SPREAD AND IMPACT OF INVASIVE ALIEN SPECIES 4O DATE THE ')30 PROGRAM HAS RESULTED IN PUBLICATIONS )N THE %UROPEAN %NVIRONMENT !GENCY %%! HIGHLIGHTED THE INTRO DUCTION OF ALIEN SPECIES AS ONE OF THE PRINCIPAL THREATS TO %UROPES BIODIVERSITY IN ITS YEAR END REPORT ON THE STATUS OF THE %UROPEAN ENVIRONMENT %%! )N 0RESIDENT #LINTON SIGNED %XECUTIVE /RDER WHICH AUTHORIZED 53 FEDERAL AGENCIES TO PREVENT THE INTRODUCTION OF ALIEN INVASIVE SPECIES CONTROL THE SPREAD OF ALIEN INVASIVE SPECIES IN THE 5NITED 3TATES AND RESTORE NATIVE SPECIES AND HABITATS THAT HAD BEEN INVADED )N )5#. 4HE 7ORLD #ONSERVATION 5NION PASSED @'UIDELINES FOR THE 0REVENTION OF "IODIVERSITY ,OSS #AUSED BY !LIEN )NVASIVE 3PECIES AND PUBLISHED THE GUIDELINES ON ITS WEBSITE IN )N THE #OMMITTEE ON THE 3CIENTIlC "ASIS FOR 0REDICTING THE )NVASIVE 0OTENTIAL OF .ONINDIGENOUS 0LANTS AND 0LANT 0ESTS IN THE 5NITED 3TATES PUBLISHED ITS lNAL REPORT .ATIONAL 2ESEARCH #OUNCIL 4HE lNAL REPORT OF ')30S lRST PHASE WAS PUBLISHED IN -OONEY ET AL AND BIOLOGICAL INVASIONS WAS THE THEME OF THE ANNUAL MEETING OF !)"3 !MERICAN )NSTITUTE FOR "IOLOGICAL 3CIENCES )T IS CLEAR THAT FORTY SIX YEARS FOLLOWING THE PUBLICATION OF %LTONS CLASSIC INTEREST IN BIOLOGICAL INVASIONS WAS STRONGER THAN EVER BOTH WITHIN AND OUTSIDE THE SCIENTIlC COMMUNITY PARTICULARLY WITH RESPECT TO THE CONSERVATION AND MANAGEMENT ASPECTS OF INTRODUCED SPECIES
,//+).' !(%!$ !.9 ,%33/.3 !.$ ).3)'(43 &2/- 4(% 0!34 !RE THERE ANY LESSONS WE CAN LEARN FROM THIS BRIEF LOOK OVER OUR SHOULDER #AN WE GAIN ANY INSIGHTS THAT MIGHT HELP US CHART A PRODUCTIVE PATH FOR THE FUTURE ) THINK SO /F COURSE EXACTLY WHAT ARE THOSE LESSONS AND INSIGHTS WILL LIKELY BE A MATTER OF LIVELY DEBATE 4HUS THE THOUGHTS THAT FOLLOW ARE NOT INTENDED TO BE PRESCRIPTIVE BUT RATHER TO FOCUS DISCUSSION ON HOW ECOLOGISTS INTERESTED IN BIOLOGICAL INVASIONS MIGHT BEST PROCEED FROM THIS POINT FORWARD 4WO ROADS ONE LESS TRAVELED THAN THE OTHER
!FTER THE !SILOMAR CONFERENCE IN THOSE INTERESTED IN STUDYING SPECIES INTRO DUCTIONS WERE PRESENTED WITH TWO DISTINCT PATHS 4HEY COULD TAKE THE STRONGLY CON SERVATION AND ENVIRONMENTAL APPROACH ADVANCED BY %LTON OR THEY COULD ADOPT THE MORE VALUE NEUTRAL AND MORE STRICTLY SCIENTIlC APPROACH EXHIBITED BY 4HE 'ENETICS OF #OLONIZING 3PECIES 4HE %LTONIAN PATH COULD BE DESCRIBED AS A TOP DOWN DEDUCTIVE APPROACH IN WHICH AN EFFORT WAS MADE TO APPLY GENERAL ECOLOGICAL THEORY AND PRIN CIPLES TO BIOLOGICAL INVASIONS IN ORDER TO HELP DEVELOP CONTROL MANAGEMENT PROGRAMS
)NVASION BIOLOGY
FOR SPECIlC INVASIONS #ONVERSELY THE !SILOMAR PATH COULD BE CONSIDERED MORE OF A BOTTOM UP INDUCTIVE APPROACH IN WHICH INDIVIDUAL COLONIZATIONSINVASIONS ARE EXAMINED IN AN EFFORT TO BETTER INFORM GENERAL ECOLOGICAL THEORY AND UNDERSTANDING OF COMMUNITIES AND POPULATIONS !NOTHER WAY TO CONTRAST THE TWO PATHS MIGHT BE TO CHARACTERIZE THE %LTONIAN PATH AS A 0LATONIC APPROACH AND THE !SILOMAR PATH AS AN !RISTOTELIAN APPROACH SENSU 3AGOFF !LTHOUGH THERE HAVE BEEN SOME EXCEPTIONS AND OCCASIONAL RESISTANCE BY SOME ECOLOGISTS OVER THE YEARS INVASION ECOLOGY HAS BECOME INCREASINGLY MORE ALLIED WITH THE %LTONIAN APPROACH PARTICULARLY IN THE 5NITED 3TATES DURING PAST FEW DECADES 4HERE ARE PROBABLY MANY EXPLANATIONS FOR THIS %COLOGISTS SUCH AS !LDO ,EOPOLD 2ACHEL #ARSON AND 0AUL %HRLICH WERE INSTRUMENTAL IN RAISING THE PUBLIC CONSCIOUSNESS ON ENVIRONMENTAL ISSUES WHICH RESULTED IN THE EMERGENCE OF THE ENVIRONMENTAL MOVEMENT DURING THE S 4HIS MOVEMENT ATTRACTED THE ATTENTION NOT ONLY OF THE GENERAL PUBLIC BUT ALSO OF MANY OTHER ECOLOGISTS 7HEREAS MUCH OF THE FOCUS IN ECOLOGY IN THE S AND S HAD BEEN ON THEORETI CAL ISSUES INVOLVING POPULATION DYNAMICS AND COMMUNITY ASSEMBLY DESIRE EVEN PRESSURE TO APPLY ECOLOGICAL KNOWLEDGE TO ENVIRONMENTAL PROBLEMS BEGAN TO BE EXPRESSED BOTH FROM WITHIN THE DISCIPLINE AND FROM SOCIETY AT LARGE 3OCIETY IN THE 53 AND ELSEWHERE HAD LONG APPLIED AN ECOLOGICAL APPROACH TO INTRODUCED PESTS OF lSHERIES FORESTS AND AGRICULTURAL SYSTEMS 4HE %LTONIAN PATH EXTENDED THIS APPROACH TO NATURAL SYSTEMS THAT WERE NOT NECESSARILY PROVIDING DIRECT ECONOMIC BENElTS 7ITHOUT QUESTION THE FOUNDING OF THE 3#/0% INITIATIVE ON INVASIONS IN THE EARLY S PLAYED A MAJOR ROLE IN DElNING THE CONSERVATION FOCUS OF INVA SION BIOLOGY FROM THAT POINT ONWARD $URING THE S AND S %3! BEGAN TO ADVOCATE A MORE ACTIVE PUBLIC ROLE IN GENERAL FOR ECOLOGISTS AND FOR ITSELF AS AN ORGANIZATION )N MANY WAYS WHAT HAD BEEN A FAIRLY CLEAR DISTINCTION BETWEEN hPUREv ECOLOGY AND hAPPLIEDv ECOLOGY IN THE S AND S DISSOLVED DURING THE LATTER DECADES OF THE TWENTIETH CENTURY $URING THE EIGHTIES AND NINETIES IN THE 5NITED 3TATES THERE WAS INCREASING PRES SURE FOR ECOLOGISTS TO JUSTIFY THEIR RESEARCH IN A LARGER SOCIAL CONTEXT 4HIS WAS FELT AT ALL LEVELS 4O JUSTIFY ITS BUDGET TO #ONGRESS 4HE .ATIONAL 3CIENCE &OUNDATION NEEDED TO MORE CLEARLY ARTICULATE HOW THE RESEARCH IT FUNDED BENElTED THE PUBLIC GOOD )N TURN IN ORDER TO GET FUNDED BY .3& INDIVIDUAL RESEARCHERS NEEDED TO PROVIDE INCREASING EVIDENCE NOT ONLY OF THE SCIENTIlC VALUE OF THEIR RESEARCH BUT ALSO OF ITS BROADER IMPACTS INCLUDING BENElTS TO SOCIETY )N ADDITION IRRESPECTIVE OF THESE INFRASTRUCTURE PRESSURES SOME ECOLOGISTS MAY HAVE WANTED TO SEEK A MORE PUBLIC FORUM FOR PERSONAL REASONS WHETHER OUT OF A SENSE OF SOCIAL RESPONSIBILITY OR SIMPLY AN INTEREST IN PARTICIPATING IN POLICY MAKING AND POLICY DISCUSSIONS 0ROBABLY ALL THESE FACTORS IN VARYING DEGREES PLAYED A ROLE IN THE DEVELOPMENT OF THE STRONG ENVIRONMENTAL EMPHASIS THAT NOW CHARACTERIZES INVASION ECOLOGY 4ODAY INVASION ECOLOGY HAS BECOME NEARLY AN EQUAL SIBLING AT LEAST A CLOSE COUS IN TO THE EXPLICITLY APPLIED lELDS OF CONSERVATION ECOLOGY AND RESTORATION ECOLOGY /NE MIGHT CONSIDER THE THREE lELDS AS CONSTITUTING A KIND OF TRIUMVIRATE LEADING THE EFFORTS TO PRESERVE THE EARTHS BIODIVERSITY
-! $AVIS
-OST MAJOR INVASION PUBLICATIONS AND CONFERENCES WHETHER TARGETED TO THE GENERAL PUBLIC OR TO A MORE STRICTLY SCIENTIlC AUDIENCE ARE NOW EXPLICITLY FRAMED FROM A CONSERVATION PERSPECTIVE USUALLY EMPHASIZING CURRENT BIODIVERSITY THREATS AND POTENTIAL IMPENDING ECOLOGICAL CRISES OFTEN USING LANGUAGE AND IMAGERY SIMILAR TO THAT USED BY %LTON IN %LTON WAS NOT THE FATHER OF INVASION ECOL OGY BUT HE MIGHT BE CONSIDERED THE FOUNDER OF ONE PATH OF INVASION ECOLOGY 4HIS PATH THE CONSERVATION AND ENVIRONMENTAL PATH HAS BEEN WELL TRAVELED AND MAINTAINED DURING PAST SEVERAL DECADES (OWEVER THE ALTERNATIVE PATH EMBOD IED BY THE !SILOMAR CONFERENCE WHILE CERTAINLY NOT WHOLLY REJECTED HAS NOT BEEN AS WELL TRAVELED 6ERMEIJ 4HE DIFFERENCE HAS PROBABLY BEEN MOST APPARENT DURING THE PAST YEARS AND PARTICULARLY IN THE 5NITED 3TATES .O DOUBT PART OF THE EXPLANATION FOR THIS DIFFERENCE IS THAT A LARGE NUMBER OF ECOLOGISTS ARE EMPLOYED BY CONSERVATION GROUPS AND GOVERNMENTAL AGENCIES WHERE THEY WORK PRIMARILY ON APPLIED PROBLEMS 0ROGRESS V S. EFFORT
)F ONE TAKES THE TIME TO GO BACK AND READ THE INVASION AND COLONIZATION LITERATURE FROM TWENTY THIRTY AND FORTY YEARS AGO ONE IS STRUCK BY HOW LITTLE THE QUES TIONS AND UNFORTUNATELY OFTEN THE ANSWERS SEEM TO HAVE CHANGED OVER TIME )T IS NOT EASY TO lND EITHER QUESTIONS OR ANSWERS GENERALIZATIONS AND THEORY MADE IN RECENT YEARS THAT ARE NOT IN THE LITERATURE OF THIRTY OR FORTY YEARS AGO OR EVEN EARLIER THAN THAT 4HE MISSION OF THE 3#/0% INVASION PROGRAM WAS TO TRY TO ANSWER THREE QUESTIONS WHAT FACTORS DETERMINE WHETHER OR NOT A SPECIES WILL BE AN INVADER WHAT PROPERTIES DETERMINE WHETHER OR NOT A PARTICULAR ENVIRONMENT WILL PRONE TO INVASION AND HOW CAN THE KNOWLEDGE GAINED FROM ANSWERING THESE QUESTIONS HELP MANAGEMENT EFFORTS 4HE lRST QUESTION WAS ACTUALLY THE ORGANIZ ING QUESTION OF THE !SIMOLAR SYMPOSIUM AND THE SECOND WAS ARTICULATED BY %LTON HIMSELF 4HERE IS NO QUESTION THAT OUR UNDERSTANDING OF THE PROCESS OF BIOLOGICAL INVA SIONS HAS INCREASED CONSIDERABLY DURING THE PAST FORTY SIX YEARS PARTICULARLY OUR KNOWLEDGE OF THE DETAILS INVOLVED IN PARTICULAR BIOLOGICAL INVASIONS (OWEVER THE EXTENT TO WHICH THIS UNDERSTANDING HAS ENHANCED OUR ABILITY TO DEVELOP EFFECTIVE MANAGEMENT STRATEGIES THE RD 3#/0% OBJECTIVE IS LESS CLEAR AND DEPENDS ON WHOM YOU ASK 3OME ECOLOGISTS MAINTAIN THAT GOOD PROGRESS IS BEING MADE AND THAT WITH THE APPLICATION OF NEW ANALYSIS TOOLS AND APPROACHES SUCH AS SPECIES SCREENING $AEHLER ET AL AND THE USE OF CLIMATIC ENVELOPES 0ETERSON THERE IS GOOD REASON TO BE OPTIMISTIC ABOUT INVASION ECOLOGISTS ABILITY TO EFFEC TIVELY INFORM LAND MANAGERS /THERS ARE NOT SO SANGUINE ARGUING THAT THE TYPE OF KNOWLEDGE AND UNDERSTANDING GAINED SO FAR ARE SELDOM USEFUL IN SPECIlC MANAGE MENT EFFORTS -OYLE AND ,IGHT 3IMBERLOFF AND 3TILING MEANING THAT EFFORTS BY INVASION ECOLOGISTS TO EFFECTIVELY INFORM LAND MANAGERS CONTINUE TO BE FRUSTRATED 7ILLIAMSON (ULME
)NVASION BIOLOGY
#/.#,53)/. 7)4( ! &%7 35''%34)/.3 4/ #/.3)$%2 )NVASION ECOLOGY AND CONSERVATION
!LL THE EVIDENCE TO DATE INDICATES THAT IT IS UNLIKELY THAT ECOLOGISTS WILL BE ABLE TO DEVELOP A GENERAL THEORY OF BIOLOGICAL INVASIONS THAT CAN BE OF SIGNIlCANT PRACTI CAL VALUE TO LAND MANAGERS -UCH RESEARCH SEEMS TO HAVE AFlRMED !SA 'RAYS OBSERVATIONS OF WEEDS MORE THAN A CENTURY AGO 4RYING TO DETERMINE SPECIlC CHARACTERISTICS THAT MAKE SOME PLANTS WEEDS 'RAY CONCLUDED THAT HE hCOULD DISCERN NOTHING IN THE PLANT ITSELF THAT WOULD GIVE IT AN ADVANTAGEv #ONTINUING HE WROTE hTHE REASONS FOR PREDOMINANCE MAY BE ALMOST AS DIVERSE AS THE WEEDS THEMSELVESv 7ITH RESPECT TO ITS GOAL OF ASSISTING LAND MANAGERS IN THE CONTROL AND MANAGE MENT OF INTRODUCED SPECIES INVASION ECOLOGY MIGHT CONSIDER EMPHASIZING LESS THE DEVELOPMENT OF GENERAL THEORY AND MORE THE ACQUISITION OF SYSTEM SPECIlC KNOWL EDGE 4HE FACT THAT INVASION ECOLOGY HAS CONSISTED PRIMARILY AS A SERIES OF CASE STUDIES HAS GENERALLY BEEN VIEWED AS A WEAKNESS OF THE lELD 7ILLIAMSON "UT IN REALITY IT MAY BE VERY DIFlCULTY PERHAPS EVEN IMPOSSIBLE FOR THE lELD TO MOVE MUCH BEYOND THIS AT LEAST AT THE LEVEL OF PROVIDING USEFUL MANAGEMENT INFORMATION )N THIS CASE INVASION ECOLOGISTS MIGHT BE BETTER OFF VIEWING THE hSYS TEM SPECIlCv NATURE OF THE lELDS KNOWLEDGE AS A STRENGTH 2ATHER THAN LAMENTING THE CASE STUDY NATURE OF THE lELD ECOLOGISTS MIGHT TRY TO MAKE INCREASING SYSTEM SPECIlC KNOWLEDGE A PRIMARY OBJECTIVE EG 2EJMANEK AND 2ICHARDSON 7HILE A LAND MANAGER TRYING TO MANAGE THE SPECIES COMPOSITION OF A GRASSLAND MAY NOT lND INVASION THEORY PARTICULARLY HELPFUL THE MORE SYSTEM SPECIlC KNOWL EDGE THAT IS AVAILABLE IN HISHER TOOLBOX THE MORE SUCCESSFUL THE MANAGEMENT EFFORTS WILL BE 4O THE EXTENT THAT INVASION ECOLOGY WANTS TO INFORM CONSERVATION EFFORTS IT MAY ALSO MAKE SENSE TO FOR INVASION ECOLOGISTS TO BECOME MORE INVOLVED IN DEVELOPING FORMALIZED AND COMPREHENSIVE MONITORING PROGRAMS WHICH HAVE THE POTENTIAL OF GREATLY ENHANCING THE EFFECTIVENESS OF MANAGEMENT AND CONTROL EFFORTS ,ONSDALE AND -ILTON )NVASION ECOLOGY AND SCIENCE
4HE CONSERVATION AND ENVIRONMENTAL EMPHASIS IN INVASION ECOLOGY DESCRIBED ABOVE HAS BEEN MOTIVATED BY THE CONVICTION THAT ECOLOGICAL KNOWLEDGE AND THEORY CAN BE USED TO BETTER UNDERSTAND AND PREDICT BIOLOGICAL INVASIONS 4HE !SILOMAR APPROACH WAS MOTIVATED BY THE OPPOSITE CONVICTION THAT BIOLOGICAL COLONIZA TIONSINVASIONS CAN BE VIEWED AS NATURAL EXPERIMENTS AND USED TO INFORM MORE GENERAL ECOLOGICAL THEORY AND UNDERSTANDING !LTHOUGH THERE WAS SOME INTER EST AMONG ECOLOGISTS IN THE EARLY EIGHTIES TO CONTINUE THIS EMPHASIS "ROWN AND -ARSHALL 3IMBERLOFF -OULTON AND 0IMM THIS APPROACH HAS NOT BEEN AS WELL NURTURED OVER THE YEARS BY INVASION ECOLOGY COMPARED TO THE
-! $AVIS
%LTONIAN CONSERVATION APPROACH 4HE REINVIGORATION OF A SCIENCE OF COLONIZATION AND SPECIES SPREAD AS A WAY TO STUDY CORE CONCEPTS AND THEORIES OF EVOLUTION AND ECOLOGY WOULD SEEM TO BE AN EXCITING OPTION FOR INVASION ECOLOGY 2OBERT &ROSTS TRAVELER COULD ONLY CHOOSE ONE ROAD BUT THERE IS NO REASON THAT INVASION ECOLOGY COULDNT EMBRACE BOTH A CONSERVATION AND A MORE STRICTLY SCIENTIlC PATH )T HAS BEEN FORTY YEARS SINCE THE HISTORIC !SILOMAR SYMPOSIUM ON COLONIZATION BIOLOGY PERHAPS IT IS TIME TO ORGANIZE ANOTHER ONE )NVASION ECOLOGY AND LANGUAGE
(IGH RATES OF SPECIES SPREAD AND INTRODUCTIONS ARE HERE TO STAY )N SOME RESPECTS ONE MIGHT QUESTION THE SENSE OF DElNING AN ECOLOGICAL SUBDISCIPLINE AREA AROUND SPECIES INTRODUCTIONS $UE TO THE ABUNDANCE OF INTRODUCED SPECIES IN ENVIRON MENTS THROUGHOUT THE WORLD WHICH IS ONLY GOING TO INCREASE IN THE FUTURE IT IS BECOMING INCREASINGLY DIFlCULT TO UNDERTAKE ANY ECOLOGICAL STUDY IN WHICH INTRODUCED SPECIES CAN BE IGNORED 4HAT BIOTIC GLOBALIZATION IS NOW THE WORLD IN WHICH WE NOW LIVE CERTAINLY DOES NOT MEAN WE SHOULD CEASE EFFORTS TO CONTROL AND MANAGE THE SMALL NUMBER OF INTRODUCED SPECIES THAT DO CAUSE GREAT HEALTH ECO NOMIC AND ECOLOGICAL HARM %WEL ET AL (OWEVER IT DOES RAISE QUESTIONS AS TO THE LOGIC OF DICHOTOMOUSLY SPLITTING SPECIES INTO NATIVES AND EXOTICS AND EVEN OF USING ANY TERMINOLOGY THAT SINGLES OUT RECENTLY INTRODUCED SPECIES AS A GROUP EG INDIGENOUS AND NON INDIGENOUS GIVEN THAT SO FEW OF THESE SPECIES ARE PROBLEMATIC !T THE SAME TIME PARTICULAR RESEARCH EFFORTS WILL NEED TO DISTINGUISH SPECIES THAT HAVE BEEN PRESENT IN A REGION FOR A LONG TIME FROM THOSE THAT HAVE RECENTLY ARRIVED THROUGH ONE MEANS OR ANOTHER 4HUS FROM A PRACTICAL PERSPEC TIVE CATEGORIZING SPECIES ON THEIR BASIS OF GEOGRAPHIC ORIGIN WILL BE NECESSARY IN SOME CASES 7EBB 2ICHARDSON ET AL #OLAUTTI AND -AC)SAAC 0YÝEK ET AL &ROM A STRICTLY SCIENTIlC POINT OF VIEW IT WOULD SEEM DIFlCULT TO ARGUE AGAINST THE VALUE OF RETURNING TO THE MORE VALUE NEUTRAL TERMINOLOGY USED AT THE !SILOMAR SYMPOSIUM )F ONE IS STUDYING SPECIES INTRODUCTIONS AS A WAY ILLUMI NATE BASIC ECOLOGICAL IDEAS AND THEORY THEN TERMS SUCH AS hINTRODUCED SPECIESv hCOLONIZERSv hNEW SPECIESv hNEW RESIDENTSv AND hGEOGRAPHIC SPREADv SEEM MORE APT THAN THE LANGUAGE OFTEN ASSOCIATED WITH THE %LTONIAN PATH EG hEXOTICSv hALIENSv AND hINVASIONSv 7HETHER OR NOT ECOLOGISTS SHOULD MODIFY THEIR LANGUAGE WHEN ADVOCATING ENVIRONMENTAL CONCERNS WILL LIKELY BE A MATTER OF DISAGREEMENT WITHIN THE lELD 3OME WILL BE CONCERNED THAT DESPITE THE BEST OF INTENTIONS THE lELDS CREDIBILITY AND STATURE AS A SCIENTIlC DISCIPLINE ARE BEING COMPROMISED WHEN ECOLOGISTS MAKE THEIR CASE TO THE PUBLIC AND TO ONE ANOTHER USING VALUE LADEN TERMINOLOGY AN APPROACH MORE TYPICALLY ASSOCIATED WITH ENVIRONMENTAL ACTION GROUPS 4HOSE WITH THIS CONCERN WOULD PROBABLY BE MORE COMFORTABLE IF THE lELD DROPPED THE INVASIONALIEN TERMINOLOGY ALTOGETHER AND REPLACED IT WITH A TERMI NOLOGY IN WHICH VALUES WERE ARTICULATED MORE EXPLICITLY THAN IMPLICITLY 5SING THIS APPROACH ECOLOGISTS MIGHT REFER TO PROBLEM SPECIES SUCH AS ZEBRA MUSSELS
)NVASION BIOLOGY
AND *APANESE KNOTWEED AS @HARMFUL NEW SPECIES OR @HARMFUL INTRODUCED SPECIES AS OPPOSED TO USING A TERMINOLOGY IN WHICH VALUES ARE MORE SUBTLY IMPLICATED EG @INVASIVE ALIEN SPECIES /THERS WILL ARGUE THAT METAPHORIC AND EVEN AT TIMES HYPERBOLIC LANGUAGE IS NEEDED TO CAPTURE THE ATTENTION OF POLICY MAKERS AND THE GENERAL PUBLIC AND TO PERSUADE THEM OF THE NEED TO ACT JUST AS %LTON DID WHEN HE CHARACTERIZED THE GLOBAL SPREAD OF SPECIES AS A hCONVULSION IN THE WORLDS mORA AND FAUNAv AND FRAMED THE CHALLENGE CONFRONTING US AS A hBATTLEv TO hDETERMINE THE FATE OF THE WORLDv THE LATTER A QUOTE FROM #ONAN $OYLES BOOK 4HE ,OST 7ORLD ,OOKING AHEAD
4HE PAST TWENTY YEARS HAVE SEEN EXTRAORDINARY DEVELOPMENT IN THE lELD OF INVA SION ECOLOGY 7ITH NUMEROUS NATIONAL AND INTERNATIONAL INITIATIVES THE CREATION OF TWO NEW JOURNALS AND THE COUNTLESS NUMBER OF SYMPOSIA CONFERENCES AND WORKSHOPS DEVOTED TO BIOLOGICAL INVASIONS NOT TO MENTION THE THOUSANDS OF INVA SION PAPERS PUBLISHED THERE HAS BEEN LITTLE TIME FOR PARTICIPANTS TO STEP BACK AND REmECT ON THE WAY THAT THE lELD HAS DEVELOPED 0ERHAPS NOW WOULD BE A GOOD TIME TO DO THIS BEFORE MOVING AHEAD 4O WHAT EXTENT IS INVASION ECOLOGY BECOMING LARGELY AN APPLIED DISCIPLINE LIKE CONSERVATION BIOLOGY AND RESTORATION ECOLOGY 4O WHAT EXTENT SHOULD THE lELD TRY TO REVITALIZE EFFORTS TO STUDY SPECIES INTRO DUCTIONS AS A WAY TO ILLUMINATE MORE GENERAL ECOLOGICAL THEORY A LA THE !SILOMAR SYMPOSIUM APPROACH 4HE CURRENT BOOK AND ONE SIMILAR TO IT 3AX ET AL IN PRESS APPEAR TO ILLUSTRATE A REVIVED INTEREST IN THIS APPROACH )S IT POS SIBLE FOR INVASION ECOLOGY AND INDIVIDUAL ECOLOGISTS TO EMBRACE BOTH A STRONGLY VALUE BASED ENVIRONMENTAL PATH AND A MORE VALUE NEUTRAL SCIENTIlC APPROACH TO SPECIES INTRODUCTIONS 3HOULD AN EFFORT BE MADE TO KEEP THE PATHS SEPARATE IN THE WAY THAT THE NEWS PAGES AND EDITORIAL PAGES ARE KEPT SEPARATE IN A NEWSPAPER OR SHOULD THE TWO PATHS BE INTEGRATED 7HAT LANGUAGE AND IMAGERY SHOULD ECOLOGISTS UTILIZE IN THEIR DISCOURSE AMONG THEMSELVES AND WITH THE PUBLIC 4HESE ARE SOME OF THE QUESTIONS THAT THE lELD OF INVASION ECOLOGY MIGHT WANT TO ADDRESS WAY BEFORE MOVING AHEAD
!#+./7,%$'-%.43 7RITING A HISTORICAL REVIEW OF A SCIENTIlC DISCIPLINE IS A CHALLENGE UNDER ANY CIR CUMSTANCES $OING SO WHILE MOST OF THE PARTICIPANTS ARE STILL ALIVE AND ACTIVE IN THE lELD IS A PARTICULARLY DAUNTING SOME MIGHT SAY FOOLISH ENDEAVOR ) THANK THE MANY COLLEAGUES WHO READ EARLIER DRAFTS AND PROVIDED THOUGHTFUL AND OFTEN DETAILED COMMENTS AND SUGGESTIONS PARTICULARLY #URT $AEHLER $ICK -ACK 0ETER 0YÝEK $AVE 2ICHARDSON -ARK 7ILLIAMSON -ARCEL 2EJMÉNEK AND $AN 3IMBERLOFF 4HE THOROUGHNESS OF THIS CHAPTER WOULD NOT HAVE BEEN POSSIBLE WITHOUT THEIR INPUT ) ALSO THANK %D 7ILSON FOR SHARING HIS MEMORIES OF THE !SILOMAR
-! $AVIS
SYMPOSIUM 4HERE IS NO SINGLE CORRECT CHARACTERIZATION OF THE PAST AND MY COL LEAGUES HAVE NOT ALWAYS FULLY AGREED WITH THE ONE ) PRESENTED .EVERTHELESS THEY WERE ALWAYS BEEN GENEROUS AND GRACIOUS IN THEIR ADVICE DURING THE WRITING OF THIS CHAPTER FOR WHICH ) AM INDEBTED 2ESEARCH AND WRITING OF THIS CHAPTER WAS PAR TIALLY SUPPORTED BY THE .ATIONAL 3CIENCE &OUNDATION UNDER 'RANT .O
2%&%2%.#%3 !LBRECT ! " 3OME OBSERVATIONS ON FACTORS ASSOCIATED WITH SURVIVAL OF STRIPED BASS EGGS AND LARVAE #ALIFORNIA &ISH AND 'AME "AILEY ( ( 4HE ARMADILLO IN &LORIDA AND HOW IT REACHED THERE *OURNAL OF -AMMOLOGY "AKER ( ' 4HE EVOLUTION OF WEEDS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "AKER ( ' AND ' , 3TEBBINS EDS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9 "ASKIN 9 ! 0LAGUE OF 2ATS AND 2UBBERVINES 4HE 'ROWING 4HREAT OF 3PECIES )NVASIONS 3HEARWATER "OOKS)SLAND 0RESS 7ASHINGTON $ # "AZZAZ & ! ,IFE HISTORY OF COLONIZING PLANTS SOME DEMOGRAPHIC GENETIC AND PHYSI OLOGICAL FEATURES 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK .9 "INGGELI 0 -ISUSE OF TERMINOLOGY AND ANTHROPOMORPHIC CONCEPTS IN THE DESCRIPTION OF INTRODUCED SPECIES "ULLETIN OF THE "RITISH %COLOGICAL 3OCIETY "IRCH , # %VOLUTIONARY OPPORTUNITY FOR INSECTS AND MAMMALS IN !USTRALIA 0AGES IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9 "OOTH " $ 3 $ -URPHY AND # * 3WANSON 7EED %COLOGY IN .ATURAL AND !GRICULTURAL 3YSTEMS #!") 0UBLISHING 7ALLINGORD /XON 5+ "RADSHAW ! $ 2 . (UMPHRIES - 3 *OHNSON AND 2 $ 2OBERTS 4HE RESTORATION OF VEGETATION ON DERELICT LAND PRODUCED BY INDUSTRIAL ACTIVITY 0AGES IN - 7 (OLDGATE AND - * 7OODMAN EDITORS 4HE "REAKDOWN AND 2ESTORATION OF %COSYSTEMS 0ROCEEDINGS #ONFERENCE 2EHABILITATION OF 3EVERELY $AMAGED ,AND AND &RESHWATER %COSYSTEMS IN 4EMPERATE :ONES 2EYKJAVIK )CELAND *ULY 0LENUM 0RESS .EW 9ORK 53! "RIGHT # ,IFE /UT OF "OUNDS "IOINVASION IN A "ORDERLESS 7ORLD .EW 9ORK 7 7 "ROWN ! ( $ AND $ 2 -ARSHALL %VOLUTIONARY CHANGES ACCOMPANYING COLONIZA TION IN PLANTS 0AGES IN ' ' % 3CUDDER AND * , 2EVEAL EDITORS %VOLUTION 4ODAY #ARNEGIE -ELLON 5NIVERSITY 0RESS 0ITTSBURGH 0! "RYANT ( # 4HE OPOSSUM REACHES 3AN $IEGO #OUNTY #ALIFORNIA &ISH AND 'AME "UMP ' AND 7 ( "OHL 3UMMARY OF FOREIGN GAME BIRD PROPAGATION AND LIBERA TIONS 3PECIAL 3CIENTIlC 2EPORT 7ILDLIFE .O "UREAU OF 3PORT &ISHERIES AND 7ILDLIFE
)NVASION BIOLOGY
"URDON * * AND ' ! #HILVERS 0RELIMINARY STUDIES ON A NATIVE !USTRALIAN EUCALYPT FOREST INVADED BY EXOTIC PINES /ECOLOGIA #AMPBELL A # AND 2 & ' /RMOND 4HE THREAT OF THE h#ROWN OF THORNSv STARlSH !CANTHASTER PLANCI TO CORAL REEFS IN THE )NDO 0ACIlC AREA /BSERVATIONS ON A NORMAL POPULATION IN THE 2ED 3EA "IOLOGICAL #ONSERVATION #ARLTON * 4 -ARINE BIOINVASIONS THE ALTERATION OF MARINE ECOSYSTEMS BY NONINDIG ENOUS SPECIES /CEANOGRAPHY #ARLTON * 4 "IOLOGICAL INVASIONS AND CRYPTOGENIC SPECIES %COLOGY #ARLTON * 4 -OLLUSCAN INVASIONS IN MARINE AND ESTUARINE COMMUNITIES -ALACOLOGIA #HILD , * ( "ROCK ' "RUNDU + 0RACH 0 0YÝEK 0 - 7ADE AND - 7ILLIAMSON EDITORS 0LANT )NVASIONS %COLOGICAL 4HREATS AND -ANAGEMENT 3OLUTIONS "ACKUYS 0UBLISHERS ,EIDEN 4HE .ETHERLANDS #HRISTIE 7 * ,AKE /NTARIO EFFECTS OF EXPLOITATION INTRODUCTIONS AND EUTROPHICA TION ON THE SALMONID COMMUNITY *OURNAL OF THE &ISHERIES 2ESEARCH "OARD OF #ANADA #LEMENT % * AND - # &OSTER !LIEN 0LANTS OF THE "RITISH )SLES ! 0ROVISIONAL #ATALOGUE OF 6ASCULAR 0LANTS EXCLUDING GRASSES "OTANICAL 3OCIETY OF THE "RITISH )SLES ,ONDON #OLAUTTI 2 ) AND ( * -AC)SAAC ! NEUTRAL TERMINOLOGY TO DElNE @INVASIVE SPECIES $IVERSITY AND $ISTRIBUTIONS #OURTENAY 7 2 *R AND # 2 2OBINS %XOTIC ORGANISMS !N UNSOLVED COMPLEX PROBLEM "IOSCIENCE #RAWLEY - * 4HE POPULATION BIOLOGY OF INVADERS 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY " #RAWLEY - * 7HAT MAKES A COMMUNITY INVASIBLE 3YMPOSIA OF THE "RITISH %COLOGICAL 3OCIETY $AEHLER # # AND $ #ARINO $ (YBRIDIZATION BETWEEN NATIVE AND ALIEN PLANTS AND ITS CONSEQUENCES 0AGES IN * , ,OCKWOOD * , AND - -C+INNEY EDITORS "IOTIC (OMOGENIZATION +LUWER!CADEMIC0LENUM 0UBLISHERS .EW 9ORK $AEHLER # # AND $ ! #ARINO 0REDICTING INVASIVE PLANTS 0ROSPECTS FOR A GENERAL SCREENING SYSTEM BASED ON CURRENT REGIONAL MODELS "IOLOGICAL )NVASIONS $AEHLER # # * 3 $ENSLOW 3 !NSARI AND ( +UO ! RISK ASSESSMENT SYSTEM FOR SCREENING OUT INVASIVE PEST PLANTS FROM (AWAII AND OTHER 0ACIlC )SLANDS #ONSERVATION "IOLOGY $AUGHERTY ( % 4HE IMPACT OF MAN ON THE ZOOGEOGRAPHY OF %L 3ALVADOR "IOLOGICAL #ONSERVATION $!NTONIO # AND , ! -EYERSON %XOTIC PLANT SPECIES AS PROBLEMS AND SOLUTIONS IN ECOLOGICAL RESTORATION A SYNTHESIS 2ESTORATION %COLOGY $AVIS - ! "IOTIC GLOBALIZATION DOES COMPETITION FROM INTRODUCED SPECIES THREATEN BIODIVERSITY "IOSCIENCE $AVIS - ! * 0 'RIME AND + 4HOMPSON &LUCTUATING RESOURCES IN PLANT COMMUNI TIES A GENERAL THEORY OF INVASIBILITY *OURNAL OF %COLOGY
-! $AVIS
$AVIS - ! * 0 'RIME AND + 4HOMPSON #HARLES 3 %LTON AND THE DISSOCIATION OF INVASION ECOLOGY FROM THE REST OF ECOLOGY $IVERSITY AND $ISTRIBUTIONS $AVIS - ! AND - 0ELSOR %XPERIMENTAL SUPPORT FOR A RESOURCE BASED MECHANISTIC MODEL OF INVASIBLITY %COLOGY ,ETTERS $AVIS - ! ET AL COAUTHORS 6EGETATION CHANGE A REUNIFYING CONCEPT IN PLANT ECOLOGY 0ERSPECTIVES IN 0LANT %COLOGY %VOLUTION AND 3YSTEMATICS $E"ACH 0 ED "IOLOGICAL #ONTROL OF )NSECT 0ESTS AND 7EEDS 2EINHOLD .EW 9ORK .9 $RAKE * ! ( ! -OONEY & DI #ASTRI 2 ( 'ROVES & * +RUGER - 2EJMANEK AND - 7ILLIAMSON "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE 3#/0% *OHN 7ILEY 3ONS #HICHESTER 5+ $UKES * 3 AND ( ! -OONEY $OES GLOBAL CHANGE INCREASE THE SUCCESS OF BIOLOGICAL INVADERS 4RENDS IN %COLOGY AND %VOLUTION %%! %UROPEAN %NVIRONMENTAL !GENCY %NVIRONMENT IN THE %UROPEAN 5NION AT THE TURN OF THE CENTURY %GLER & % )NDIGENE VERSUS ALIEN IN THE DEVELOPMENT OF ARID (AWAIIAN VEGETATION %COLOGY %LLSTRAND . # AND + ! 3CHIERENBECK (YBRIDIZATION AS A STIMULUS FOR THE EVOLU TION OF INVASIVENESS IN PLANTS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES %LTON # 3 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS -ETHUEN ,ONDON %MBREE $ ' 4HE ECOLOGY OF COLONIZING SPECIES WITH SPECIAL EMPHASIS ON ANIMAL INVADERS 0AGES IN $ * (ORN ' 2 3TAIRS AND 2 $ -ITCHELL EDITORS !NALYSIS OF %COLOGICAL 3YSTEMS /HIO 3TATE 5NIVERSITY 0RESS #OLUMBUS /( %SER 5 !SSESSMENT OF PLANT INVASIONS THEORETICAL AND PHILOSOPHICAL FUNDAMEN TALS 0AGES IN 5 3TARlNGER + %DWARDS ) +OWARIK AND - 7ILLIAMSON 0LANT )NVASIONS %COLOGICAL -ECHANISMS AND (UMAN 2ESPONSES "ACKHUYS 0UBLISHERS ,EIDEN 4HE .ETHERLANDS %SSL & AND 7 2ABITSCH EDITORS .EOBIOTA IN ¾STERREICH 5MWELTBUNDESAMT 'MB( 7IEN %WEL * * ET AL $ELIBERATE INTRODUCTIONS OF SPECIES RESEARCH NEEDS "IOSCIENCE &ALINÇSKI * " !NTROPOGENICZNA ROSLINNOSC 0USCZY "IALOWIESKIEJ JAKO WYNIK SYNANTROPIZACJI NATURALNEGO KOMPLEKSU LESNEGO 6EGETATION ANTHROPOGENE DE LA 'RANDE &ORET DE "IALOWIEZA COMME UN RESULTAT DE LA SYNANTHROPISATION DU TERROTOIRE SILVESTRE NATUREL $ISSERATATIONES 5NIVERSITATIS 6ARSOVIENSIS &ALINÇSKI * " 3TADIA NEOlTYZMU ) STOSUNEK NEOlTOW DO INNYCH KOMPONENTOW ZBIOROWISKA 3TAGES OF NEOPHYTISM AND THE REACTION OF NEOPHYTES TO OTHER COMPONENTS OF THE COMMUNITY )N * " &ALINÇSKI EDITOR 3YNANTROPIZACJA SZATY ROSLINNEJ ) .EOlTYZM I APOlTYZM W SZACIE ROSLINNEJ 0OLSKI -ATERIALY 3YMPOZJUM W .OWOGRODZIE -ATER :AKL &ITOSOC 3TOS 57 &ALINÇSKI * " .EOlTY I NEOlTYZM $YSKUSJE lTOSOCJOLOGICZNE .EOPHYTES ET NEOPHYTISME $ISCUSSION PHYTOSOCIOLOGIQUES %KOL POL " &ALINÇSKI * " ED 3YNANTHROPISATION OF PLANT COVER )) 3YNANTHROPIC mORA AND VEGETATION OF TOWNS CONNECTED WITH THEIR NATURAL CONDITIONS HISTORY AND FUNCTION
)NVASION BIOLOGY
-ATER :AKL &ITOSOC 3TOS 5NIV 7ARSZ 'OODWIN " * ! * -C!LLISTER AND , &AHRIG , 0REDICTING INVASIVENESS OF PLANT SPECIES BASED ON BIOLOGICAL INFORMATION #ONSERVATION "IOLOGY 'OULD 3 * !N EVOLUTIONARY PERSPECTIVE ON STRENGTHS FALLACIES AND CONFUSIONS IN THE CONCEPT OF NATIVE PLANTS !RNOLDIA 'RAY ! 4HE PERTINACITY AND PREDOMINANCE OF WEEDS 4HE !MERICAN *OURNAL OF 3CIENCE AND !RTS 6OL 86))) 'ROVES 2 ( AND * * "URDON EDITORS %COLOGY OF "IOLOGICAL )NVASIONS !N !USTRALIAN 0ERSPECTIVE !USTRALIAN !CADEMY OF 3CIENCE #ANBERRA PP (ARPER * , %STABLISHMENT AGGRESSION AND COHABITATION IN WEEDY SPECIES 0AGES IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9 (EJNâ 3 6 AND - ,HOTSKÉ (EJNâ 3 6 *EHLÓK + +OPECKâ : +ROPÉĆ : AND - ,HOTSKÉ +ARANTÏNNÓ PLEVELE ąESKOSLOVENSKA 3TUDIE ąS !KAD 6ĕD SER MATH NATUR (OLDGATE - 7 AND - * 7OODMAN EDITORS 4HE "REAKDOWN AND 2ESTORATION OF %COSYSTEMS 0ROCEEDINGS #ONFERENCE 2EHABILITATION OF 3EVERELY $AMAGED ,AND AND &RESHWATER %COSYSTEMS IN 4EMPERATE :ONES 2EYKJAVIK )CELAND *ULY 0LENUM 0RESS .EW 9ORK 53! (OLUB * AND 6 *IRÉSEK :UR 6EREINHEITLICHUNG DER 4ERMINOLOGIE IN DER 0HYTOGEO GRAPHIE &OLIA 'EOBOT 0HYTOTAX (ORN $ * ' 2 3TAIRS AND 2 $ -ITCHELL EDITORS !NALYSIS OF %COLOGICAL 3YSTEMS /HIO 3TATE 5NIVERSITY 0RESS #OLUMBUS /( (ULME 0 % "IOLOGICAL INVASIONS WINNING THE SCIENCE BATTLES BUT LOSING THE CONSER VATION WAR /RYX (USTON - ! "IOLOGICAL $IVERSITY 4HE #OEXISTENCE OF 3PECIES ON #HANGING ,ANDSCAPES #AMBRIDGE 5NIV 0RESS #AMBRIDGE 5+ *EHLIK 6 AND " 3LAVIK "EITRAG ZUM %RKENNEN DES 6ERBREITUNGSCHARAKTERS DER !RT "UNIAS ORIENTALIS , IN DER 4SCHECHOSLOWAKEI 0RESLIA *EHLÓK 6 AND 3 (EJNâ -AIN MIGRATION ROUTES OF ADVENTITIOUS PLANTS IN #ZECHOSLOVAKIA &OLIA 'EOBOT 0HYTOTAX *OHNSTONE ) - 0LANT INVASION WINDOWS A TIME BASED CLASSIlCATION OF INVASION POTENTIAL "IOLOGICAL 2EVIEWS *ORDAN 7ILLIAM 2 ))) 2ESTORATION AND -ANAGEMENT .OTES A BEGINNING 2ESTORATION AND -ANAGEMENT .OTES *UHASZ .AGY 0 )NVESTIGATIONS CONCERNING ECOLOGICAL HOMEOSTASIS !BSTRACT 0ROCEEDINGS OF THE 4ENTH )NTERNATIONAL "OTANICAL #ONGRESS %DINBURGH +ARTESZ * 4 AND # ! -EACHAM 3YNTHESIS OF THE .ORTH !MERICAN &LORA 6ERSION .ORTH #AROLINA "OTANICAL 'ARDEN #HAPEL (ILL .ORTH #AROLINA +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY AND %VOLUTION +ING # )MMIGRANT +ILLERS /XFORD 5NIVERSITY 0RESS !UCKLAND .: +LIRONOMOS * . &EEDBACK WITH SOIL BIOTA CONTRIBUTES TO PLANT RARITY AND INVASIVE NESS IN COMMUNITIES .ATURE
-! $AVIS
+LOTZ 3 ) +àHN AND 7 $ URKA ")/,&,/2 %INE $ATENBANK ZU BIOLOGISCH ÚKO LOGISCHEN -ERKMALEN DER 'EFËPmANZEN IN $EUTSCHLAND "UNDESAMT FàR .ATURSCHUTZ "ONN +LIRONOMOZ +NOPS * - ( $ 4ILMAN . - (ADDAD 3 .AEEM # % -ITCHELL * (AARSTAD - % 2ITCHIE + - (OWE 0 " 2EICH % 3IEMANN AND * 'ROTH %FFECTS OF PLANT SPECIES RICHNESS ON INVASION DYNAMICS DISEASE OUTBREAKS INSECT ABUNDANCES AND DIVERSITY %COLOGY ,ETTERS +OHLER ! AND ( 3UKOPP ÄBER DIE 'EHÚLZENTWICKLUNG AUF "ERLINER 4RàMMERSTAN DORTEN :UGLEICH EIN "EITRAG ZUM 3TUDIUM NEOPHYTISCHER (OLZARTEN "ERICHTE DER $EUTSCHEN "OTANISCHEN 'ESELLSCHAFT +OLAR # AND $ - ,ODGE 0ROGRESS IN INVASION BIOLOGY PREDICTING INVADERS 4RENDS IN %COLOGY AND %VOLUTION +ORNÉS * A 3TADIA NEOlTYZMU I STOSUNEK NEOlTOW DO INNYCH KOMPONENTOW ZBIOROW ISKA 3TAGES OF NEOPHYTISM AND THE RELATION OF NEOPHYTES TO OTHER COMPONENTS OF THE COMMUNITY )N * " &ALINÇSKI EDITOR 3YNANTROPIZACJA SZATY ROSLINNEJ ) .EOlTYZM I APOlTYZM W SZACIE ROSLINNEJ 0OLSKI -ATERIALY 3YMPOZJUM W .OWOGRODZIE -ATER :AKL &ITOSOC 3TOS 57 +ORNÉS * B 'EOGRAlCZNO HISTORYCZNA KLASYlKACJA ROSLIN SYNANTROPIJNYCH ! GEO GRAPHICAL HISTORICAL CLASSIlCATION OF SYNANTHROPIC PLANTS )N * " &ALINÇSKI EDITOR 3YNANTROPIZACJA SZATY ROSLINNEJ ) .EOlTYZM I APOlTYZM W SZACIE ROSLINNEJ 0OLSKI -ATERIALY 3YMPOZJUM W .OWOGRODZIE -ATER :AKL &ITOSOC 3TOS 57 +ORNBERG ( AND - ( 7ILLIAMSON EDS 1UANTITATIVE !SPECTS OF THE %COLOGY OF "IOLOGICAL )NVASIONS 4HE 2OYAL 3OCIETY ,ONDON +OWARIK ) 0LATANUS HYBRIDA "ROT UND ANDERE ADVENTIVE 'EHÚLZE AUF STËDTISCHEN 3TANDORTEN IN "ERLIN 7EST 'ÚTTINGER &LORISTISCHE 2UNDBRIEFE +OWARIK ) "IOLOGICAL )NVASIONS AS RESULT AND VECTOR OF GLOBAL CHANGE 0AGES IN #ONTRIBUTIONS TO 'LOBAL #HANGE 2ESEARCH ! 2EPORT BY THE 'ERMAN .ATIONAL #OMMITTEE ON 'LOBAL #HANGE 2ESEARCH "ONN ,AYCOCK ' 4HE !LIEN !NIMALS 4HE .ATURAL (ISTORY 0RESS 'ARDEN #ITY .* ,EVINE * - 3PECIES DIVERSITY AND BIOLOGICAL INVASIONS RELATING LOCAL PROCESS TO COMMUNITY PATTERN 3CIENCE ,EVINE * - AND # - $!NTONIO %LTON REVISITED ! REVIEW OF EVIDENCE LINKING DIVER SITY AND INVASIBILITY /IKOS ,ITTLE % 6 4HE OPOSSUM IN ,OS !NGELES #OUNTY #ALIFORNIA &ISH AND 'AME ,ODGE $ - "IOLOGICAL INVASIONS LESSONS FROM ECOLOGY 4RENDS IN %COLOGY AND %VOLUTION ,ONSDALE 7 - 'LOBAL PATTERNS OF PLANT INVASIONS AND THE CONCEPT OF INVASIBILITY %COLOGY ,ONSDALE 7 - AND 3 -ILTON 0EOPLE AND PLANT INVASIONS OF THE RANGELANDS 0AGES IN ! # 'RICE AND + # (ODGKINSON EDITORS 'LOBAL 2ANGELANDS 0ROGRESS AND 0ROSPECTS #!" )NTERNATIONAL 7ALLINGFORD 5+ -ACDONALD ) ! 7 AND - , *ARNUM EDITORS )NVASIVE !LIEN /RGANISMS IN THE 4ERRESTRIAL %COSYSTEMS OF THE &YNBOS "IOME 3OUTH !FRICA 3OUTH !FRICAN .ATIONAL 3CIENTIlC 0ROGRAMMES 2EPORT .O #3)2/ 0RETORIA
)NVASION BIOLOGY
-ACDONALD ) ! 7 & * +RUGER AND ! ! &ERRAR 4HE %COLOGY AND -ANAGEMENT OF "IOLOGICAL )NVASIONS IN 3OUTHERN !FRICA /XFORD 5NIVERSITY 0RESS #APE 4OWN -ACK 2 . )NVASION OF "ROMUS TECTORUM INTO WESTERN .ORTH !MERICA AN ECOLOGICAL CHRONICLE !GROECOSYSTEMS -AC!RTHUR 2 ( AND % / 7ILSON !N EQUILIBRIUM THEORY OF INSULAR ZOOGEOGRAPHY %VOLUTION -AC!RTHUR 2 ( AND % / 7ILSON 4HE 4HEORY OF )SLAND "IOGEOGRAPHY 0RINCETON 5NIVERSITY 0RESS 0RINCETON -AYR % 4HE NATURE OF COLONIZATIONS IN BIRDS 0AGES IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9 -EINEZ ! TRANSLATED BY $ 3IMBERLOFF +ILLER !LGAE 5NIVERSITY OF #HICAGO 0RESS #HICAGO )LLINOIS -ETCALF # , 7 0 &LINT AND 2 , -ETCALF $ESTRUCTIVE AND 5SEFUL )NSECTS TH EDI TION -C'RAW (ILL .EW 9ORK .9 -ERRIAM # ( 4HE %NGLISH SPARROW IN .ORTH !MERICA 53 $EPARTMENT OF !GRICULTURE "ULLETIN -OONEY ( ! AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK .9 -OONEY ( ! AND * ! $RAKE "IOLOGICAL INVASIONS A 3#/0% PROGRAM OVERVIEW 0AGES IN * ! $RAKE ( ! -OONEY & DI #ASTRI 2 ( 'ROVES & * +RUGER - 2EJMANEK AND - 7ILLIAMSON "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE 3#/0% *OHN 7ILEY 3ONS #HICHESTER 5+ -OONEY ( ! 2 . -ACK * ! -C.EELY , % .EVILLE 0 * 3CHEI AND * + 7AAGE EDITORS )NVASIVE !LIEN 3PECIES ! .EW 3YNTHESIS )SLAND 0RESS 7ASHINGTON $ # -OULTON - 0 AND 3 , 0IMM 4HE INTRODUCED (AWAIIAN AVIFAUNA BIOGEOGRAPHIC EVIDENCE FOR COMPETITION !MERICAN .ATURALIST -OULTON - 0 AND 3 , 0IMM 3PECIES INTRODUCTIONS TO (AWAII 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK .9 -OYLE 0 " %FFECTS OF INTRODUCED BULLFROGS 2ANA CATESBEIANA ON THE NATIVE FROGS OF THE 3AN *OAQUIN 6ALLEY #ALIFORNIA #OPEIA -OYLE 0 " AND 4 ,IGHT "IOLOGICAL INVASIONS OF FRESHWATER EMPIRICAL RULES AND ASSEMBLY THEORY "IOLOGICAL )NVASIONS -UHLENBACH 6 #ONTRIBUTIONS TO THE SYNANTHROPIC ADVENTIVE mORA OF THE RAILROADS IN 3T ,OUIS -ISSOURI 5 3 ! !NNALS OF THE -ISSOURI "OTANICAL 'ARDEN .ATIONAL 2ESEARCH #OUNCIL 0REDICTING )NVASIONS OF .ONINDIGENOUS 0LANTS AND 0LANT 0ESTS .ATIONAL !CADEMY OF 3CIENCES 7ASHINGTON $ # PP .ICHOLS * / 4HE GYPSY MOTH IN 0ENNSYLVANIA ITS HISTORY AND ERADICATION 0ENNSYLVANIA $EPARTMENT OF !GRICULTURE -ISCELLANEOUS "ULLETIN .O .ITECKI ( EDITOR "IOTIC #RISES IN %COLOGICAL AND %VOLUTIONARY 4IME !CADEMIC 0RESS .EW 9ORK .9 /WRE / 4 ! CONSIDERATION OF THE EXOTIC AVIFAUNA OF SOUTHEASTERN &LORIDA 7ILSON "ULLETIN
-! $AVIS
0ALMER 4 3 4HE DANGER OF INTRODUCING NOXIOUS ANIMALS AND BIRDS 53 $EPARTMENT OF !GRICULTURE 9EARBOOK FOR 0ETERSON ! 4 0REDICTING THE GEOGRAPHY OF SPECIES INVASIONS VIA ECOLOGICAL NICHE MODELING 1UARTERLY 2EVIEW OF "IOLOGY 0IMM 3 , 4HEORIES OF PREDICTING SUCCESS AND IMPACT OF INTRODUCED SPECIES 0AGES IN * ! $RAKE ( ! -OONEY & DI #ASTRI 2 ( 'ROVES & * +RUGER - 2EJMANEK AND - 7ILLIAMSON EDITORS "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE 3#/0% *OHN 7ILEY 3ONS #HICHESTER 5+ 0YÝEK 0 /N THE TERMINOLOGY USED IN PLANT INVASION STUDIES 0AGES IN 0 0YÝEK + 0RACH - 2EJMÉNEK AND - 7ADE EDITORS 0LANT )NVASIONS 'ENERAL !SPECTS AND 3PECIAL 0ROBLEMS 30" !CADEMIC 0UBLISHING !MSTERDAM 0YÝEK 0 * ( "ROCK + "ÓMOVÉ " -ANDÉK 6 *AROÝÓK ) +OUKOLÓKOVÉ * 0ERGL AND * ÁTĕPÉNEK 6EGETATIVE REGENERATION IN INVASIVE 2EYNOUTRIA 0OLYGONACEAE TAXA THE DETERMINANT OF INVASIBILITY AT THE GENOTYPE LEVEL !MERICAN *OURNAL OF "OTANY 0YÝEK 0 $ - 2ICHARDSON - 2EJMÉNEK ' 7EBSTER - 7ILLIAMSON AND * +IRSCHNER !LIEN PLANTS IN CHECKLISTS AND mORAS TOWARDS BETTER COMMUNICATION BETWEEN TAXONOMISTS AND ECOLOGISTS 4AXON 2EJMÉNEK - 4HE RICH GET RICHER n RESPONSES &RONTIERS IN %COLOGY AND THE %NVIRONMENT 2EJMÉNEK - AND $ - 2ICHARDSON 7HAT ATTRIBUTES MAKE SOME PLANT SPECIES MORE INVASIVE %COLOGY 2ICHARDSON $ - . !LLSOPP # - $!NTONIO 3 * -ILTON AND - 2EJMÉNEK 0LANT INVASIONS THE ROLE OF MUTUALISMS "IOLOGICAL 2EVIEWS 2ICHARDSON $ - 0 0YÝEK - 2EJMÉNEK - ' "ARBOUR & $ 0ANETTA AND # * 7EST .ATURALIZATION AND INVASION OF ALIEN PLANTS CONCEPTS AND DElNITIONS $IVERSITY $ISTRIBUTIONS 2ENNE ) * AND " & 4RACY 4HE RICH GET RICHER n RESPONSES &RONTIERS IN %COLOGY AND THE %NVIRONMENT 2OSENZWEIG - , 4HE FOUR QUESTIONS 7HAT DOES THE INTRODUCTION OF EXOTIC SPECIES DO TO DIVERSITY %VOLUTIONARY %COLOGY 2ESEARCH 3AGOFF - "IODIVERSITY AND THE #ULTURE OF %COLOGY "ULLETIN OF THE %COLOGICAL 3OCIETY OF !MERICA 3AGOFF - 7HATS WRONG WITH ALIEN SPECIES 2EPORT OF THE )NSTITUTE FOR 0HILOSOPHY AND 0UBLIC POLICY 5NIVERSITY OF -ARYLAND #OLLEGE 0ARK -ARYLAND 3ANDLUND / 4 0 * 3CHEI AND ! 6IKEN EDITORS 0ROCEEDINGS OF THE .ORWAY5. #ONFERENCE ON !LIEN 3PECIES $IRECTORATE FOR .ATURE -ANAGEMENT AND .ORWEGIAN )NSTITUTE FOR .ATURE 2ESEARCH 4RONDHEIM .ORWAY 3ALISBURY % 7EEDS AND !LIENS #OLLINS 0UBLISHING ,ONDON 3AX $ & AND 3 $ 'AINES 3PECIES DIVERSITY FROM GLOBAL DECREASES TO LOCAL INCREASES 4RENDS IN %COLOGY AND %VOLUTION 3AX $ & * * 3TACHOWICZ AND 3 $ 'AINES EDITORS 3PECIES )NVASIONS )NSIGHTS INTO %COLOGY %VOLUTION AND "IOGEOGRAPHY 3INAUER !SSOCIATES 3UNDERLAND -! 3CHROEDER & ' :UR +LASSIlZIERUNG DER !NTHROPOCHOREN 6EGETATIO
)NVASION BIOLOGY
3CHOlELD % + 'ALAPAGOS mORA THE THREAT OF INTRODUCED PLANTS "IOLOGICAL #ONSERVATION 3HEA + AND 0 #HESSON #OMMUNITY ECOLOGY THEORY AS A FRAMEWORK FOR BIOLOGICAL INVASIONS 4RENDS IN %COLOGY AND %VOLUTION 3HIGESADA . AND + +AWASAKI "IOLOGICAL )NVASIONS THEORY AND PRACTICE /XFORD 3ERIES IN %COLOGY AND %VOLUTION /XFORD 5NIVERSITY 0RESS /XFORD 5+ 3IM 4 2 3OME EFFECTS OF MANS INmUENCE ON THE 3OUTH !FRICAN mORA 3OUTH !FRICAN *OURNAL OF 3CIENCE 3IMBERLOFF $ #OMMUNITY EFFECTS OF INTRODUCED SPECIES 0AGES IN ( .ITECKI EDITOR "IOTIC #RISES IN %COLOGICAL AND %VOLUTIONARY 4IME !CADEMIC 0RESS .EW 9ORK .9 3IMBERLOFF $ )NTRODUCED INSECTS A BIOGEOGRAPHIC AND SYSTEMATIC PERSPECTIVE 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK .9 3IMBERLOFF $ 7HICH INSECT INTRODUCTIONS SUCCEED AND WHICH FAIL 0AGES IN * ! $RAKE ( ! -OONEY & DI #ASTRI 2 ( 'ROVES & * +RUGER - 2EJMANEK AND - 7ILLIAMSON "IOLOGICAL )NVASIONS ! 'LOBAL 0ERSPECTIVE 3#/0% *OHN 7ILEY 3ONS #HICHESTER 5+ 3IMBERLOFF $ AND 0 3TILING 2ISKS OF SPECIES INTRODUCED FOR BIOLOGICAL CONTROL "IOLOGICAL #ONSERVATION 3IMBERLOFF $ 3 AND % / 7ILSON %XPERIMENTAL ZOOGEOGRAPHY OF ISLANDS THE COLONIZATION OF EMPTY ISLANDS %COLOGY 3LOBODKIN , " 4HE GOOD THE BAD AND THE REIlED %VOLUTIONARY %COLOGY 2ESEARCH n 3TARlNGER 5 + %DWARDS ) +OWARIK AND - 7ILLIAMSON 0LANT )NVASIONS %COLOGICAL -ECHANISMS AND (UMAN 2ESPONSES "ACKHUYS 0UBLISHERS ,EIDEN 4HE .ETHERLANDS 3TOHLGREN 4 * $ "INKLEY ' 7 #HONG - ! +ALKHAN , $ 3CHELL + ! "ULL 9 /TSUKI ' .EWMAN - "ASHKIN AND 9 3ON %XOTIC PLANT SPECIES INVADE HOT SPOTS OF NATIVE PLANT DIVERSITY %COLOGICAL -ONOGRAPHS 3TOHLGREN 4 * $ 4 "ARNETT AND * 4 +ARTESZ 4HE RICH GET RICHERPATTERNS OF PLANT INVASIONS IN THE 5NITED 3TATES &RONTIERS IN %COLOGY AND THE %NVIRONMENT 3UKOPP ( .EOPHYTEN IN NATURLICHEN 0mANZENGESELLSCHAFTEN -ITTELEUROPAS "ER $EUTSCH "OT 'ES 3UKOPP ( "EITRËGE ZUR ¾KOLOGIE VON #HENOPODIUM BOTRYS , ) 6ERBREITUNG UND 'ESCHICHTE 6ERHANDLUNGEN DES "OTANISCHEN 6EREINS DER 0ROVINZ "RANDENBURG 3UKOPP ( AND 0 7ERNER 5RBAN ENVIRONMENTS AND VEGETATION )N 7 (OLZNER - * ! 7ERGER AND ) )KUSIMA EDITORS -ANS )MPACT ON 6EGETATION 'EOBOTANY *UNK $EN (AAG "OSTON ,ONDON 4AYLOR ( # 0EST PLANTS AND NATURE CONSERVATION IN THE WINTER RAINFALL REGION *OURNAL OF THE "OTANICAL 3OCIETY OF 3OUTH !FRICA 4#7& 4EXAS #HAPTER OF THE 7ILDLIFE 3OCIETY )NTRODUCTION OF %XOTIC !NIMALS %COLOGICAL AND 3OCIOLOGICAL #ONSIDERATIONS #AESAR +LEBERG 2ESEARCH 0ROGRAM IN 7ILDLIFE %COLOGY 4EXAS ! - 5NIVERSITY #OLLEGE 3TATION 4EXAS
-! $AVIS
4HOMPSON + * ' (ODGSON AND 4 # ' 2ICH .ATIVE AND ALIEN INVASIVE PLANTS MORE OF THE SAME %COGRAPHY 4ILMAN $ #OMMUNITY INVASIBILITY RECRUITMENT LIMITATION AND GRASSLAND BIODIVER SITY %COLOGY 4ODD + 4INKERING WITH %DEN ! .ATURAL (ISTORY OF %XOTICS IN !MERICA 7 7 .ORTON #OMPANY .EW 9ORK .9 5SHER - " A "IOLOGICAL INVASIONS OF NATURE RESERVES "IOLOGICAL #ONSERVATION 5SHER - " B "IOLOGICAL INVASIONS OF NATURE RESERVES A SEARCH FOR GENERALISATIONS "IOLOGICAL #ONSERVATION 6AN $RIESCHE * AND 2 6AN $RIESCHE .ATURE /UT OF 0LACE "IOLOGICAL )NVASIONS IN THE 'LOBAL !GE )SLAND 0RESS 7ASHINGTON $ # 6ERMEIJ ' * !N AGENDA FOR INVASION BIOLOGY "IOLOGICAL #ONSERVATION 6ILA - AND # $!NTONIO (YBRID VIGOR FOR CLONAL GROWTH IN #ARPOBROTUS !IZOACEAE IN COASTAL #ALIFORNIA %COLOGICAL !PPLICATIONS 7ADDINGTON # ( )NTRODUCTION TO THE SYMPOSIUM 0AGES IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9 7ARDLE $ ! %XPERIMENTAL DEMONSTRATION THAT PLANT DIVERSITY REDUCES INVASIBILITY EVIDENCE OF A BIOLOGICAL MECHANISM OR A CONSEQUENCE OF SAMPLING EFFECT /IKOS 7ARNER 2 % 4HE ROLE OF INTRODUCED DISEASES IN THE EXTINCTION OF THE ENDEMIC (AWAIIAN AVIFAUNA #ONDOR 7EBB $ ! 7HAT ARE THE CRITERIA FOR PRESUMING NATIVE STATUS 7ATSONIA 7ILSON % / 4HE CHALLENGE FROM RELATED JB 0AGES IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9 7ICHT # , 0RESERVATION OF THE VEGETATION OF THE 3OUTH WESTERN #APE 3PECIAL 0UBLICATION OF THE 2OYAL 3OCIETY OF 3OUTH !FRICA #APE 4OWN 7ILLIAMSON - )NVADERS WEEDS AND THE RISK FROM GENETICALLY MODIlED ORGANISMS %CPERIENTIA 7ILLIAMSON - "IOLOGICAL )NVASIONS #HAPMAN (ALL ,ONDON 7ILLIAMSON - )NVASIONS %COGRAPHY 7ODZICKI + 4HE STATUS OF SOME EXOTIC VERTEBRATES IN THE ECOLOGY OF .EW :EALAND 0AGES IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE %VOLUTION OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK .9
#HAPTER FOUR
)NVASIVENESS IN EXOTIC PLANTS IMMIGRATION AND NATURALIZATION IN AN ECOLOGICAL CONTINUUM ( 4 -URPHY * 6AN$ER7AL , ,OVETT $OUST AND * ,OVETT $OUST
).42/$5#4)/. ! MAJOR GOAL OF INVASIONS ECOLOGY IS TO EXPLAIN WHY SOME SPECIES ARE MORE SUCCESS FUL AS INVADERS THAN OTHERS AND ULTIMATELY TO BE ABLE TO PREDICT TRAITS PREDISPOSING A SPECIES TO SUCCESS IN ADVENTIVE ENVIRONMENTS 5NFORTUNATELY TO DATE FEW CLEAR GENERALITIES EXIST AND BIOLOGISTS ARE FAR FROM BEING ABLE TO PREDICT FUTURE INVASIONS 2ECENTLY SEVERAL GROUPS HAVE SHOWN HOW THE LACK OF CONSENSUS ON BASIC TERMI NOLOGY HAS SERIOUSLY LIMITED PROGRESS IN AND APPLICATION OF INVASIONS ECOLOGY AS WELL AS ITS CAPACITY TO DRAW SYSTEMATICALLY ON THEORY FROM ECOLOGICAL DISCIPLINES $AVIS AND 4HOMPSON 2ICHARDSON ET AL A $AEHLER A $AVIS AND 4HOMPSON 2EJMÉNEK ET AL #OLAUTTI AND -AC)SAAC 7ITHIN THE LITERATURE IN REGARD TO VERY SIMILAR ECOLOGICAL SITUATIONS A PARTICU LAR SPECIES MAY BE REGARDED AS ALIEN EXOTIC INVASIVE COLONIZING WEEDY INTRO DUCED NON INDIGENOUS IMPORTED OR NON NATIVE -OREOVER A WEEDY SPECIES MAY -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
(4 -URPHY ET AL
ALSO BE REFERRED TO AS A NATURALIZED TRANSFORMER SLEEPER ESTABLISHED CASUAL PERSISTENT NOXIOUS NATIVE ENVIRONMENTAL OR AGRICULTURAL WEED -ANY OF THESE TERMS CONNOTE ONLY THAT A SPECIES IS NOVEL TO A PARTICULAR AREA /THERS CARRY IMPLICATIONS ABOUT ACTUAL OR POTENTIAL IMPACT IN NOVEL HABITATS SEE $AVIS AND 4HOMPSON ;= AND #OLAUTTI AND -AC)SAAC ;= FOR A TREATMENT OF OTHER TERMS (ERE WE ARE CONCERNED PRIMARILY WITH SPECIES THAT ARE TERMED @INVASIVE OR @INVADERS 4HE SCOPE OF THIS NOTION ALONE COVERS MUCH GROUND AND IN RECENT YEARS DEBATE OVER THE CRITERIA FOR REGARDING A SPECIES AS INVASIVE HAS RECEIVED MUCH ATTENTION EG $AVIS AND 4HOMPSON 2ICHARDSON ET AL A $AVIS AND 4HOMPSON 2EJMÉNEK ET AL 0YÝEK ET AL AND THE TERM CONTINUES TO BE USED INCONSISTENTLY 4HE DEBATE ON TERMINOLOGY IS MORE THAN SIMPLE SEMAN TICS BECAUSE THE USE OF INCONSISTENT TERMS IMPAIRS UNDERSTANDING OF THE PROCESSES THEY ARE MEANT TO DESCRIBE #OLAUTTI AND -AC)SAAC #OMPARATIVE ANALYSIS OF ALIEN SPECIES IN REGIONAL mORAS HAS BEEN USED TO CHARACTERIZE BOTH INVASIVE SPECIES AND INVADED ECOSYSTEMS EG $AEHLER 0YÝEK ,ONSDALE (OWEVER SUCH COMPARISONS ARE mAWED IF THE ALIEN SPECIES IN THESE mORAS HAVE NOT BEEN CLASSIlED IN THE SAME WAYS 2ESEARCHERS ARE FREQUENTLY UNABLE TO DISTINGUISH CLEARLY THE PARTICULAR CHARACTERISTICS OF ALIEN INVADERS 4HOMPSON ET AL DISCREPANCIES IN TERMINOLOGY MAY CONTRIBUTE TO THIS PROBLEM AND CONFOUND META ANALYSES 4O BE MOST USEFUL IT IS LOGICAL THAT THE TERMINOLOGY USED TO DESCRIBE SPECIES AT VARIOUS STAGES OF INVASION SHOULD CLOSELY REmECT THE PROCESS BY WHICH INVA SIONS OCCUR AND THE VARIOUS CHARACTERISTICS OF THOSE STAGES 4HE lRST PART OF THIS CHAPTER IS A REVIEW OF THE STAGES IN THE PROCESS OF INVASION ,ATER WE TEST WHETHER TWO RECENT CLASSIlCATION SCHEMES PROPOSED BY 2ICHARDSON ET AL A AND SEE 0YÝEK ET AL AND $AVIS AND 4HOMPSON ARE OPERATIONAL GIVEN A RELA TIVELY RICH SPECIES DATASET AND WHETHER THEY SUCCEED IN IDENTIFYING THE SAME SETS OF SPECIES 7E CLASSIFY A SAMPLE OF THE EXOTIC mORA OF /NTARIO USING THE TWO SCHEMES 7E IDENTIFY LIMITS TO INFORMATION AVAILABLE IN THIS SPECIES DATASET AND SHOW HOW THE TWO CLASSIlCATION SYSTEMS CAN LEAD TO DIFFERENT CONCLUSIONS )T IS NECESSARY THAT FOR THE PURPOSES OF CLARITY WE PROVIDE PRELIMINARY DElNI TIONS OF CERTAIN TERMS WE WILL USE IN ORDER TO REVIEW THE INVASION PROCESS BEFORE LOOKING IN MORE DEPTH AT THE DIFFERENT APPROACHES TO CLASSIFYING SPECIES AT DIFFERENT STAGES OF THE PROCESS (ERE WE PRESENT SOME OF THE MOST COMMON TERMS TO DESCRIBE GENERALLY THE DIFFERENT STAGES OF INVASION THOUGH WE REALIZE THAT THESE TERMS ARE OFTEN USED INTERCHANGEABLY OR AS SYNONYMS FOR OTHER TERMS 4ERMS INCLUDE hINTRODUCTIONv INTRODUCED SPECIES ARE THOSE THAT APPEAR OUTSIDE THEIR NATIVE RANGE hESTABLISHMENTv ESTABLISHED SPECIES PERSIST OVER RELATIVELY LONG PERIODS OUTSIDE THEIR NATIVE RANGE hNATURALIZATIONv NATURALIZED SPECIES REPRODUCE AND SUSTAIN POPULATIONS OVER RELATIVELY LONG PERIODS AND hINVASIONv INVASIVE SPECIES ARE WIDESPREAD AND ABUNDANT OUTSIDE THEIR NATIVE RANGE )N THE lNAL SECTION OF THE CHAPTER WE DESCRIBE A WAY TO VISUALIZE AND MODEL THE INVASIONS PROCESS BASED ON THE STATUS OF POPULATIONS OF NON NATIVE SPECIES AT A SPECIlC SPATIAL AND TEMPORAL SCALE 7E DRAW ON THE @BLINKING LIGHTS METAPHOR
)NVASIVENESS IN EXOTIC PLANTS
OF METAPOPULATION ECOLOGY AND SHOW HOW THIS MAY BE USEFUL IN DESCRIBING THE INVASIONS PROCESS h"LINKING LIGHTSv DESCRIBES THE COLONIZATION LIGHT ON AND EXTINCTION LIGHT OFF OF POPULATIONS IN PATCHES OF HABITAT OVER TIME ACROSS A REGIONAL LANDSCAPE 4HUS WHEN POPULATION TURNOVER IS HIGH HIGH COLONIZATION AND HIGH EXTINCTION POPULATIONS ARE RAPIDLY BLINKING ON AND OFF WHEREAS WHERE TURNOVER IS SLOWER HIGH COLONIZATION LOW EXTINCTION POPULATIONS BLINK ON AND REMAIN ON FOR EXTENDED PERIODS )T IS POSSIBLE TO ENVISION THIS BLINKING ON OF POPU LATIONS DURING THE INVASION PROCESS lRST AS THE NON NATIVE SPECIES IS INTRODUCED THEN ESTABLISHES NATURALIZES AND lNALLY AS IT BECOMES INVASIVE 4HE PROBABILITY OF THE POPULATION BLINKING OFF WOULD DECREASE WITH TIME AND WITH PROGRESS THROUGH THE PROCESS 7E ATTEMPT TO SHOW HOW THIS PROCESS MAY USEFULLY BE MODELED THROUGH THE USE OF POPULATION VIABILITY ANALYSIS 06! A TOOL FROM CONSERVATION BIOLOGY FOR TRACKING POPULATIONS OF IMPERILED SPECIES )NDEED POPULATIONS OF NON NATIVE SPECIES ARE CHARACTERIZED BY THE SAME LARGE SCALE PROCESSES IMMIGRATION EMIGRATION COLONIZATION AND EXTINCTION AS NATIVE POPULATIONS AND SO IT MAKES SENSE TO UTILIZE THE TERMINOLOGY AND WELL TESTED TOOLS AVAILABLE TO UNDERSTAND REGIONAL DYNAMICS OF NATIVE POPULATIONS 7E PROPOSE A MODIlCATION TO THE 2ICHARDSON ET AL A FRAMEWORK FOR THE INVASION PROCESS PROMOTING A FOCUS ON DEMOGRAPHIC ELEMENTS OF CASUAL NATURALIZED SPREADING AND INVASIVE POPULA TIONS RATHER THAN CHARACTERIZING THE SPECIES THEMSELVES WITH THIS TERMINOLOGY
4(% ).6!3)/. 02/#%33 ).42/$5#4)/. %34!",)3(-%.4 !.$ .!452!,):!4)/. @)NVASION IS CONSIDERED TO BE THE LEAST LIKELY OUTCOME OF A MULTISTAGE PROCESS THAT BEGINS WHEN ORGANISMS ARE TRANSPORTED OUTSIDE THEIR NATIVE RANGE -ACK ET AL -OREOVER IT IS COMMONLY NOTED THAT MANY IF NOT MOST INTRODUCTIONS FAIL AND THAT EVEN WHEN A SPECIES BECOMES INVASIVE IN A NEW LOCATION THERE MAY HAVE BEEN NUMEROUS PREVIOUS UNSUCCESSFUL INTRODUCTIONS EG +OWARIK 4HIS IS WELL ILLUSTRATED IN BIRDS BY THE CLASSIC EXAMPLE OF THE %UROPEAN STARLING 3TURNUS VULGARIS WHICH SUCCESSFULLY COLONIZED .EW 9ORKS #ENTRAL 0ARK IN AND THEN MOST OF .ORTH !MERICA BUT ONLY AFTER MANY FAILED INTRODUCTIONS +REBS !NDERSON ET AL ARGUE THAT MOST OF THE IMPORTANT INFECTIOUS DISEASES OF PLANTS SIMILARLY DEPEND UPON MULTIPLE INTRODUCTIONS FOR THEIR SUCCESS 7ILLIAMSON AND &ITTERS @TENS RULE HOLDS THAT JUST ONE IN TEN OF THOSE INDIVIDUALS TRANS PORTED TO A NEW LOCATION WILL APPEAR IN THE WILD IE BECOME INTRODUCED AND ONLY ONE IN TEN OF THOSE INTRODUCED WILL BECOME ESTABLISHED AND ONE IN TEN OF THOSE ESTABLISHED WILL SPREAD AND BECOME INVASIVE 4HOSE INDIVIDUALS THAT DO SURVIVE THE INITIAL TRANSIT ARE UNLIKELY TO PERSIST FOR LONG IN THE NEW ENVIRONMENT DUE TO A RANGE OF PHYSICAL AND BIOTIC ELEMENTS ASSO CIATED WITH THE INVADING SPECIES ITSELF THE RECIPIENT COMMUNITY AND THE REST OF THE ENVIRONMENT &OR EXAMPLE ,ODGE DESCRIBED @ECOLOGICAL RESISTANCE AS COMPOSED OF DEMOGRAPHIC BIOTIC AND ENVIRONMENTAL FACTORS LIMITING THE SUCCESS
(4 -URPHY ET AL
OF INVADERS /THER OFTEN CITED EXPLANATIONS FOR THE SUCCESS OR FAILURE OF INTRODUC TIONS ARE THE @ENEMY RELEASE HYPOTHESIS GENETIC FACTORS AND DEMOGRAPHIC AND ENVIRONMENTAL STOCHASTICITY SEE BELOW @$EMOGRAPHIC RESISTANCE INVOLVES PARTICULAR LIFE HISTORY PARAMETERS OF THE INVADING SPECIES INmUENCING TYPICALLY PROPAGULE PRESSURE TO THE SYSTEM 6ON (OLLE ET AL 3UCCESSFUL INTRODUCTION AND ESTABLISHMENT IS OFTEN REPORTED TO BE STRONGLY RELATED TO PROPAGULE PRESSURE +OLAR AND ,ODGE 4HE EFFECTIVE NESS OF DIFFERENT BARRIERS LIMITING THE INVASION PROCESS MAY DEPEND ON THE NUMBER OF PROPAGULES THE GREATER THE NUMBER OF PROPAGULES THE GREATER THE CHANCE OF A BARRIER BEING OVERCOME AND INVASION PROCEEDING 2OUGET AND 2ICHARDSON 4HUS FACTORS INmUENCING THE NUMBER AND DISPERSAL POTENTIAL OF PROPAGULES ARE LIKELY TO BE CRITICAL IN REGULATING THE ESTABLISHMENT AND FUTURE SPREAD OF INTRODUCED SPECIES &OR EXAMPLE 2EJMÉNEK AND 2ICHARDSON FOUND THAT INVASIVE PINE SPECIES HAD SMALLER SEED MASS A SHORTER JUVENILE PERIOD AND SHORTER INTERVALS BETWEEN SEED CROPS COMPARED WITH INTRODUCED BUT NON INVASIVE PINES )N BOTH NATURAL AND HUMAN FACILITATED INTRODUCTIONS VARYING INOCULUM NUM BERS MAY BIAS OBSERVED PATTERNS OF INVASION AND LEAD TO ERRONEOUS CONCLUSIONS ABOUT THE IMPORTANCE OF OTHER DEMOGRAPHIC OR BIOTIC PARAMETERS IN INVASION SUCCESS &OR EXAMPLE A SPECIES COULD HAVE A HIGH RATE OF INTRODUCTION SUCCESS EITHER BECAUSE IT WAS INHERENTLY A GOOD INVADER OR BECAUSE IT WAS CONSISTENTLY INTRODUCED TO LOCATIONS THAT WERE EASY TO INVADE OR BECAUSE IT WAS INTRODUCED MORE FREQUENTLY AT DIFlCULT LOCATIONS 0ROPAGULE PRESSURE HAS BEEN IMPLICATED IN THE INTRODUCTION SUCCESS OF PLANTS &OXCROFT ET AL 2OUGET AND 2ICHARDSON BIRDS "LACKBURN AND $UNCAN AND MAMMALS &ORSYTH AND $UNCAN 3TUDIES OF PLANTS HAVE SHOWN THAT MODELS INCORPORATING PROPAGULE PRES SURE ARE SUPERIOR TO THOSE INVOKING ONLY ENVIRONMENTAL PARAMETERS IN EXPLAINING DISTRIBUTION AND ABUNDANCE OF NON NATIVE SPECIES &OXCROFT ET AL 2OUGET AND 2ICHARDSON )N AN ANALYSIS OF INTRODUCTION EVENTS FOR BIRD SPECIES ACROSS THE WORLD "LACKBURN AND $UNCAN FOUND THE BROAD PATTERN OF INTRODUCTION REmECTED PATTERNS OF %UROPEAN SETTLEMENT THE PROXIMITY OF SPE CIES TO INTRODUCTION LOCATIONS AND THE DESIRABILITY OF SPECIES IN CERTAIN TAXONOMIC FAMILIES @"IOTIC RESISTANCE REFERS TO FEATURES SHAPING THE INVADED COMMUNITY AND AFFECTING ITS @INVASIBILITY WHICH IS OFTEN SAID TO DECREASE WITH INCREASING SPE CIES RICHNESS OF THE INVADED COMMUNITY %LTON #ASE 4ILMAN 4HE IDEA THAT A COMMUNITYS RESIDENT BIOTIC RICHNESS IS INVERSELY RELATED TO INVASIBILITY ASSUMES THAT COMPETITION IS A MAJOR FORCE CONTROLLING COMMUNITY COMPOSITION AND THAT DIVERSE COMMUNITIES SHOULD USE RESOURCES MORE FULLY LEAVING LITTLE NICHE SPACE FOR POTENTIAL INVADERS "RUNO ET AL BUT SEE 3TOHLGREN ET AL "ESIDES COMPETITION FACTORS CONSIDERED TO BE THE MAJOR COMPONENTS OF BIOTIC RESISTANCE TO EXOTICS INCLUDE PREDATION HERBIVORY AND DIS EASEPARASITE PRESSURES ,EVINE ET AL 2ECENTLY ATTENTION HAS BEEN GIVEN TO THE ROLE OF FACILITATIVE INTERACTIONS IN PROMOTING COMMUNITY COEXISTENCE OF INVASIVE SPECIES WITH NATIVE SPECIES AS WELL
)NVASIVENESS IN EXOTIC PLANTS
AS WITH OTHER INVASIVE SPECIES 2ICHARDSON ET AL B 4HERE IS SOME EVIDENCE SUGGESTING THAT INVASIONS MAY DEPEND ON OR BE ENHANCED BY THE ESTABLISHMENT OF MUTUALISMS OR FACILITATIVE INTERACTIONS BETWEEN THE INVASIVE PLANT AND OTHER ORGANISMS EITHER INTRODUCED OR NATIVE 2ICHARDSON ET AL B 4HERE ARE MANY EXAMPLES OF INVASIVE WEED SPECIES THAT ARE OBLIGATE OUTCROSSERS AND REQUIRE A POLLINATOR MUTUALIST TO REPRODUCE EG PURPLE LOOSESTRIFE ,YTHRUM SALICARIA ;-AL ET AL = AND #ENTAUREA DIFFUSA AND # MACULOSA ;(ARROD AND 4AYLOR = #ARR REPORTED THAT THE INVASIVE mORA OF 6ICTORIA !USTRALIA IS POLLINATED BY A VARIETY OF BOTH NATIVE AND INTRODUCED INSECTS MAINLY HONEYBEES !PIS MELLIFERA )NTRODUCED PLANT SPECIES WHICH ALTER SOIL NUTRIENT AVAILABILITY CAN FACILITATE THE INVASION OF OTHER NON INDIGENOUS SPECIES &OR EXAMPLE THE !TLANTIC NITROGEN lXING SHRUB -YRICA FAYA HAS INVADED NITROGEN POOR VOLCANIC SOILS IN (AWAII AND PROBABLY FACILITATES FURTHER PLANT INVASIONS 6ITOUSEK AND 7ALKER AND SEE 3IMBERLOFF AND 6ON (OLLE FOR OTHER EXAMPLES 4HE INTERACTION BETWEEN PLANTS AND THEIR SOIL COMMUNITY CAN RESULT IN DYNAMIC FEEDBACK %MPIRICAL EVIDENCE SUGGESTS A NET POSITIVE FEEDBACK BETWEEN PLANTS AND THEIR SOIL COMMUNI TY IN COMMUNITIES OUTSIDE THEIR NATIVE RANGE 2EINHART ET AL FOUND THAT THE INVASION OF BLACK CHERRY 0RUNUS SEROTINA INTO NORTH WESTERN %UROPE WAS FACILITAT ED BY FEATURES OF THE SOIL COMMUNITY )N ITS NATIVE RANGE THE SOIL COMMUNITY THAT DEVELOPS AROUND BLACK CHERRY INHIBITS THE GROWTH OF NEARBY CONSPECIlCS WHEREAS THE OPPOSITE OCCURS IN THE NON NATIVE RANGE #ENTAUREA DIFFUSA HAS MUCH STRONGER NEGATIVE EFFECTS ON GRASS SPECIES IN ITS NON NATIVE .ORTH !MERICAN RANGE THAN IN ITS NATIVE %UROPEAN RANGE DUE TO DIFFERENCES IN THE EFFECTS OF ITS ROOT EXUDATES AND HOW THESE AFFECT COMPETITION FOR RESOURCES #ALLAWAY AND !SCHEHOUG %NVIRONMENTAL RESISTANCE MAY INVOLVE ABIOTIC RESOURCE AVAILABILITY SUITABLE CLIMATIC FACTORS OR LIGHT INTENSITIES FOR EXAMPLE AND MAY PRECLUDE A SPECIES ALTO GETHER OR MAY INDUCE A SIGNIlCANT TIME LAG BETWEEN ARRIVAL AND ESTABLISHMENT OF A SPECIES 6ON (OLLE ET AL "LACKBURN AND $UNCAN FOUND USING A GLOBAL DATASET THAT THE SUCCESS OF INTRODUCED BIRDS DEPENDS ON THE SUITABILITY OF THE ABIOTIC ENVIRONMENT FOR THE SPECIES AT THE INTRODUCTION SITE &OR EXAMPLE INTRODUCTION SUCCESS WAS SIGNIlCANTLY GREATER WHEN THE DIFFERENCE BETWEEN A SPE CIES LATITUDE OF ORIGIN AND THE LATITUDE OF INTRODUCTION WAS SMALL 4HE @ENEMY RELEASE HYPOTHESIS HAS BEEN USED TO EXPLAIN THE SUCCESS OF SOME SPECIES IN COMMUNITIES OUTSIDE THEIR NATIVE RANGE AND STATES THAT OUTSIDE OF THEIR NATIVE RANGE PLANT SPECIES SHOULD EXPERIENCE A DECREASE IN REGULATION BY HERBIVORES AND OTHER NATURAL ENEMIES RESULTING IN AN INCREASE IN ABUNDANCE AND DISTRIBUTION 4HE SUCCESS OF BIOLOGICAL CONTROL HAS BEEN USED AS SUPPORT FOR THE ENEMY RELEASE HYPOTHESIS +EANE AND #RAWLEY %MPIRICAL EVIDENCE IN SUPPORT OF THE HYPOTHESIS IS EQUIVOCAL +EANE AND #RAWLEY -ARON AND 6ILÉ HOWEVER IN AN ANALYSIS OF PLANT SPECIES NATURALIZED IN THE 53 -ITCHELL AND 0OWER FOUND SPECIES IN THEIR NON NATIVE RANGES HAD ON AVERAGE FEWER FUNGI AND FEWER VIRUS SPECIES THAN IN THE RESPECTIVE NATIVE RANGES
(4 -URPHY ET AL
$EMOGRAPHIC AND ENVIRONMENTAL STOCHASTICITIES PROBABLY PROMOTE LOCAL EXTINC TION IN MANY SMALL POPULATIONS OF SPECIES BEGINNING TO ESTABLISH IN NEW LOCATIONS 3AX AND "ROWN PROPOSED TWO FURTHER PHENOMENA THAT MAY ACCOUNT FOR THE LARGE FRACTION OF FAILED INTRODUCTIONS 4HEY NOTED THAT SPECIES WHICH ARE ABUN DANT AND WIDESPREAD TEND TO BE RARE OR ABSENT FROM MOST LOCATIONS WITHIN THEIR GEOGRAPHIC RANGE DUE TO SPATIAL ENVIRONMENTAL VARIATION 4HIS SUGGESTS THAT MOST LOCAL INTRODUCTIONS SHOULD FAIL BECAUSE PROPAGULES WOULD TEND BY CHANCE TO BE INTRODUCED TO MARGINAL OR UNSUITABLE SITES 3ECONDLY MANY ESTABLISHED POPULA TIONS ARE SUSTAINED BY THE POSITIVE FEEDBACK EFFECTS OF DISPERSAL EVENTS ON LOCAL POPULATION DYNAMICS 3INGLE SMALL AND NEWLY ESTABLISHED POPULATIONS ALL LACK OPPORTUNITIES FOR RESCUE BY OTHER POPULATIONS AND THUS ARE MORE SUSCEPTIBLE TO EXTINCTION 3AX AND "ROWN 4HERE ARE ALSO GENETIC OBSTACLES TO THE PERSISTENCE OF POPULATIONS OF INTRODUCED ORGANISMS 'ENETIC DIVERSITY AND PHENOTYPIC PLASTICITY THAT CAN BRING THE LINEAGE INTO ACCORD WITH ITS NEW PHYSICAL AND BIOLOGICAL ENVIRONMENT MAY BE DIFlCULT TO ACHIEVE IN FAR mUNG POPULATIONS ,EVIN BECAUSE THEY ARE SUBJECT TO GENETIC DRIFT AND FOUNDER EFFECTS %CKERT ET AL 'ENETIC VARIATION IN FOUNDER POPULA TIONS IS LIKELY TO BE LACKING IF THE NUMBER OF INDIVIDUALS INTRODUCED IS NOT LARGE OR POPULATION GROWTH RATE IS NOT SUBSTANTIAL .OVAK AND -ACK +OLBE ET AL RECENTLY DEMONSTRATED THAT INVASION SUCCESS WAS ENHANCED WHEN MULTIPLE INTRODUCTIONS OF THE #ARIBBEAN BROWN ANOLE !NOLIS SAGREI TO &LORIDA CAME FROM DIFFERENT SOURCE POPULATIONS IN THE LIZARDS GEOGRAPHIC RANGE 0OPULATIONS IN THE ADVENTIVE RANGE CONTAINED MORE GENETIC VARIATION THAN NATIVE POPULATIONS
).6!3)6%.%33 !MONG NATURALIZED SPECIES PERSISTING AT NEW LOCATIONS DESPITE THE SERIES OF SEVERE CONSTRAINTS DESCRIBED ABOVE A FEW MAY GO ON TO BECOME INVADERS 7ILLIAMSON AND &ITTER -ACK ET AL $ARWIN P WAS THE lRST TO PROPOSE A THEORY FOR INVASION SUCCESS IN PLANT SPECIES 5SING OBSERVATIONS BY !LPHONSE DE #ANDOLLE $ARWIN NOTED THAT hmORAS GAIN BY NATURALIZATION PROPORTIONALLY WITH THE NUMBER OF NATIVE GENERA AND SPECIES FAR MORE IN NEW GENERA THAN IN NEW SPECIESv $ARWIN GIVES THE EXAMPLE THAT h)N THE LAST EDITION OF $R !SA 'RAYS @-ANUAL OF THE mORA OF THE 5NITED 3TATES NATURALIZED SPECIES ARE ENUMERATED AND THESE BELONG TO GENERA OUT OF THE GENERA NO LESS THAN GENERA ARE NOT THERE INDIGENOUSv $ARWIN REASONED THAT BECAUSE DIFFERENCES IN STRUCTURE AND FUNCTIONING ARE GREATER BETWEEN GENERA THAN BETWEEN SPECIES COMPETITION IS LIKELY TO BE GREATER BETWEEN CONGENERS 2ESULTS BOTH SUPPORT EG -ACK 2EJMÉNEK AND ARGUE AGAINST $AEHLER B $ARWINS HYPOTHESIS $AEHLERS CONTRADICTORY RESULT FOR THE (AWAIIAN mORA INDEED SUPPORTS $ARWINS ORIGINAL LINE OF THINKING h)T MIGHT HAVE BEEN EXPECTED THAT THE PLANTS WHICH WOULD SUCCEED IN BECOMING NATURALIZED IN ANY LAND WOULD GENERALLY HAVE BEEN CLOSELY ALLIED TO INDIGENES FOR THESE ARE COMMONLY LOOKED AT AS SPECIALLY ADAPTED FOR THEIR OWN COUNTRYv
)NVASIVENESS IN EXOTIC PLANTS
.UMEROUS OFTEN DISPARATE LIFE HISTORY FACTORS HAVE BEEN SUGGESTED TO EXPLAIN THE INVASION SUCCESS OF PARTICULAR PLANT SPECIES "AKER DISCUSSED SEVERAL TRAITS ASSOCIATED WITH INVASIVE PLANT SPECIES AND PROPOSED THAT SPECIES HAVING MORE OF THESE TRAITS WOULD BE MORE @WEEDY THAN SPECIES WITH FEWER OF THESE TRAITS 4HUS THE @IDEAL WEED WOULD HAVE THE ABILITY TO REPRODUCE SEXUALLY AND GROW CLONALLY SHOW RAPID GROWTH PHENOTYPIC PLASTICITY AND HIGH TOLERANCE OF ENVIRONMENTAL HETEROGENEITY #ADOTTE AND ,OVETT $OUST EXPLICITLY TESTED "AKERS NOTION OF A WEED IN THE EXOTIC mORA OF /NTARIO AND FOUND GENERAL CONCORDANCE WITH THE TRAITS "AKER DESCRIBED /THER TRAITS HAVE ALSO BEEN SHOWN TO CORRELATE WITH INVASION SUCCESS 2EJMÉNEK FOUND THAT INVASIVENESS OF HERB SPECIES WAS BEST PREDICTED BY NATIVE LATITUDINAL RANGE 3IMILARLY #ADOTTE ET AL FOUND THAT SUCCESSFUL INVADERS IN /NTARIO WERE SIGNIlCANTLY OVER REPRESENTED BY SPECIES ORIGINATING IN %UROPE AND %URASIA ,IFE HISTORY ATTRIBUTES PARTICULARLY ASSOCIATED WITH INVASION SUCCESS IN THE /NTARIO mORA WERE THE PRES ENCE OF A CLONAL ORGAN AND A LONGER mOWERING SEASON
(/7 4/ #,!33)&9 ).6!3)6%3 !N IDEAL CLASSIlCATION SCHEME SHOULD TO HAVE UTILITY BE CAPABLE OF GENERAL APPLICATION 2ICHARDSON ET AL A OFFERED OPERATIONAL DElNITIONS FOR TERMS SUCH AS @ALIEN @CASUAL ALIEN @NATURALIZED @INVASIVE AND @TRANSFORMER WITH RESPECT TO PLANT SPECIES )N THEIR SCHEME INVASION OF A NEW REGION BY AN INTRO DUCED SPECIES WAS ENVISIONED AS SURMOUNTING A SERIES OF @BARRIERS SEE &IG 4HUS @CASUAL ALIEN SPECIES HAVE OVERCOME GEOGRAPHIC AND LOCAL ENVIRONMENTAL BARRIERS ENABLING THEM TO SURVIVE IN A NEW LOCATION BUT HAVE NOT OVERCOME BARRIERS TO SUCCESSFUL REPRODUCTION AND POPULATION GROWTH OR EXPANSION IN THE NEW LOCALE .ATURALIZATION IN 2ICHARDSON ET ALS SCHEME BEGINS WHEN VARIOUS BARRIERS TO REGULAR REPRODUCTION ARE OVERCOME AND POPULATION GROWTH AND SUR VIVAL PERSISTENCE IS MAINTAINED OVER THE LONG TERM FUNCTIONALLY LONG TERM HAS BEEN REGARDED AS C YEARS ;EG 4UTIN ET AL = OR YEARS ;0YÝEK ET AL = @)NVASION IS CONSIDERED TO HAVE OCCURRED WHEN THE SPECIES HAS OVERCOME THE BARRIERS TO DISPERSAL WITHIN THE NEW REGION AND NEW POPULATIONS ARE BEING FOUNDED AWAY FROM THE IMMEDIATE AREA OF INTRODUCTION $AVIS AND 4HOMPSON PROPOSED A CLASSIlCATION SCHEME MODELED AFTER 2ABINOWITZS TRIPARTITE SCHEME FOR RARITY TO DElNE @INVADERS AS DISTINCT FROM @SUCCESSIONAL COLONIZERS AND @NONINVASIVE COLONIZERS $AVIS AND 4HOMPSON USED A TAXONOMY OF INVASION THAT RAISES THREE DICHOTOMOUS QUESTIONS IS THE SPECIES A LONG DISTANCE OR SHORT DISTANCE DISPERSER IS THE SPECIES COMMON OR NOVEL TO THE REGION AND DOES IT HAVE A SMALL OR LARGE @IMPACT ON THE NEW ENVIRONMENT 4HIS SCHEME GENERATES EIGHT POTENTIAL CONDITIONS 4HE MAJOR OPERA TIONAL DIFFERENCE BETWEEN THE SYSTEM OF $AVIS AND 4HOMPSON AND OF 2ICHARDSON ET AL A LIES IN THE EMPHASIS IN $AVIS AND 4HOMPSON UPON @IMPACT IN THE NEW ENVIRONMENT WHEREAS 2ICHARDSON ET AL RELY ON MEASURES OF NATURAL
(4 -URPHY ET AL
&IG ! SCHEMATIC REPRESENTATION OF MAJOR BARRIERS !n' LIMITING THE SPREAD OF INTRODUCED PLANTS -ODIlED FROM 2ICHARDSON ET AL ;A=
REPRODUCTION AND RATES OF SPREAD IN THE NEW ENVIRONMENT AS MAJOR CRITERIA DETER MINING INVASIVENESS $AEHLER A HAS ARGUED AGAINST THE UTILITY OF $AVIS AND 4HOMPSONS SCHEME INSOFAR AS IT HINGED ON A SUBJECTIVE CRITERION @IMPACT WHEREAS THE @SPREAD CRITERION OF 2ICHARDSON ET AL CAN BE MEASURED RELATIVELY MORE OBJECTIVELY $AEHLER NOTED THAT BOTH SCHEMES PROBABLY EMBRACE SIMILAR SETS OF SPECIES SINCE THE CONCORDANCE BETWEEN INVADERS DElNED BY THE SPREAD CRITERION AND THOSE THAT HAVE A GREAT IMPACT IS LIKELY CLOSE TO A HUNDRED PERCENT
-%4(/$3 /VER THE PAST THREE DECADES THE #ANADIAN *OURNAL OF 0LANT 3CIENCE HAS PUBLISHED ACCOUNTS OF THE BIOLOGY OF PLANTS THAT ARE WEEDY IN #ANADA %ACH ACCOUNT FOL LOWS A PRESCRIBED LAYOUT AND PROVIDES A DETAILED DESCRIPTION OF A SINGLE SPECIES OF WEED OR CLOSELY RELATED GROUP OF SPECIES THE HISTORY OF ITS INTRODUCTION TO .ORTH !MERICA AND #ANADA DETAILS OF ITS ECONOMIC IMPORTANCE A #ANADIAN DIS TRIBUTION MAP AND DETAILS OF ITS DISTRIBUTION ELSEWHERE IN THE WORLD !DDITIONALLY
)NVASIVENESS IN EXOTIC PLANTS
INFORMATION ON HABITATS OCCUPIED MEANS OF SEED AND VEGETATIVE REPRODUCTION AND DISPERSAL AND DETAILS OF GROWTH AND DEVELOPMENT ARE PROVIDED AS WELL AS RESPONSE TO WEED CONTROL MEASURES !RTICLES IN THE SERIES BRING TOGETHER PUBLISHED AND UNPUBLISHED INFORMATION ON THE BIOLOGY ECOLOGY AND CONTROL OF THESE WEEDS 4HUS THE INFORMATION IS RELATIVELY COMPREHENSIVE AND CONSISTENTLY PRESENTED )NDEPENDENTLY AN EXOTIC SPECIES LIST FOR /NTARIO WAS GENERATED FROM THE /NTARIO -INISTRY OF .ATURAL 2ESOURCES .ATURAL (ERITAGE )NFORMATION #ENTRES DATA BASE OF VASCULAR PLANTS .()# HTTPWWWMNRGOVONCA-.2NHICNHICCFM &OR THE PRESENT ANALYSIS WE USED THE SPECIES OCCURRING ON THE .()# LIST OF /NTARIOS EXOTIC mORA FOR WHICH THERE WAS A "IOLOGY OF #ANADIAN 7EEDS ARTICLE . SEE !PPENDIX FOR LIST AND REFERENCES 7E ATTEMPTED lRST TO EXTRACT SPECIlC DATA REQUIRED TO MEET THE CRITERIA FOR EACH CATEGORY IN THE CLASSIlCATIONS OF 2ICHARDSON ET AL A AND $AVIS AND 4HOMPSON 4HIS WE TERM THE @IDEAL CRITERIA 4HAT IS IF AVAILABLE THE IDEAL CRITERIA WOULD BEST SATISFY THE DElNITION OF EACH CATEGORY IN THE CLASSIlCATION AND WOULD DIVIDE SPECIES INTO THE VARIOUS CATEGORIES DESCRIBED BY THE TWO SCHEMES 4HEN USING THE INFORMATION GIVEN IN THE "IOLOGY OF #ANADIAN 7EEDS REVIEWS AND THE REGIONAL ABUNDANCE RANKING VALUES DETERMINED BY THE .()# WE DEVELOPED @REALIZED CRITERIA FOR EACH CATEGORY IN THE TWO CLASSIlCATIONS 2EALIZED CRITERIA ARE THE BEST lT TO THE IDEAL CRITERIA USING INFORMATION THAT IS ACTUALLY AVAILABLE 4ABLE SHOWS IDEAL AND REALIZED CRITERIA FOR EACH CATEGORY IN THE TWO SCHEMES )N ORDER TO ADDRESS EACH CRITERION DATA WERE TABULATED FOR EACH OF THE WEED SPECIES SEE 4ABLE #ERTAIN LIMITATIONS OF BOTH SCHEMES BECAME EVIDENT EARLY $AVIS AND 4HOMPSON CALL FOR AN ASSESSMENT OF @DISPERSAL DISTANCE )N MANY CASES AN INITIAL LONG DISTANCE DISPERSAL EVENT BY ONE AGENT MAY LEAD TO AN INTRODUCTION IN A NEW REGION WHILE ANOTHER KIND OF AGENT IS RESPONSIBLE FOR SUBSEQUENT SHORT MEDIUM OR LONG DISTANCE DISPERSAL IN THE NEW LOCATION IE A FORM OF DIPLOCHORY SENSU 6ANDER 7ALL AND ,ONGLAND ;= )T SEEMS UNLIKELY THAT AN INITIAL LONG DISTANCE DISPERSAL EVENT FROM A WIDELY DISTANT ENVIRONMENT WOULD HAVE MUCH EFFECT IN THE NEW ENVIRONMENT OR RELEVANCE TO SUBSEQUENT SPREAD IF THE SPECIES DID NOT THEN SUCCESSFULLY DISPERSE FROM ITS INITIAL POINT OF ESTABLISHMENT 4HEREFORE IN OUR ANALYSIS THE DISPERSAL CRITERION IS BASED ON HOW THE SPECIES IS MOVED FOLLOWING ITS INITIAL INTRODUCTION TO THE ADVENTIVE REGION 4HIS IS NOT ALWAYS STRAIGHTFOR WARD SINCE EVEN APPROXIMATE KNOWLEDGE ABOUT DISPERSAL DISTANCE PARTICULARLY LONG DISTANCE DISPERSAL IS TYPICALLY SCARCE FOR EVEN THE BEST STUDIED SPECIES 7E DETERMINED THE PRINCIPAL MODES OF DISPERSAL AND ASSIGNED THEM TO EITHER A SHORT OR LONG DISTANCE CATEGORY BEARING IN MIND THAT THE OVERALL SCALE OF THE ANALYSIS WAS THE ENTIRE PROVINCE OF /NTARIO TOTAL AREA KM ;3TATISTICS #ANADA WWWSTATCANCA= 4HUS ANY SPECIES THAT DID NOT HAVE A KNOWN HUMAN FACILITATED MODE OF DISPERSAL WAS CONSIDERED A SHORT DISTANCE DISPERSER )N ADDITION SOME CATEGORIES OF HUMAN FACILITATED DISPERSAL THAT GENERALLY RESULT IN LIMITED DISPERSAL SUCH AS WITHIN A CROP lELD OR FARM PROPERTY WERE ALSO CONSIDERED SHORT DISTANCE EG THOSE ASSOCIATED WITH MOWING CULTIVATION FARM MACHINERY DOMESTIC ANIMALS
'REAT IMPACT IN THE NEW ENVIRONMENT
3HORT OR LONG DISTANCE DISPERSERS
3UCCESSIONAL COLONIZERS
.OVEL IN THE NEW ENVIRONMENT
4HE SPECIES IS NOTED TO REGULARLY OCCUR IN NATURAL OR SEMI NATURAL NATURAL DISTURBED COMMUNITIES !.$/2 4HE SPECIES IS NOTED TO SUBSTANTIALLY IMPACT ECOSYSTEM PROCESSES !.$/2 4HE SPECIES IS NOTED TO HAVE SUBSTANTIAL ECONOMIC IMPACT
/NTARIO IS NOT WITHIN THE NATIVE GEOGRAPHIC RANGE OF THE SPECIES
$ISPERSAL HAS OCCURRED GRADUALLY TO NEARBY OR $ISPERSAL IS BY VEGETATIVE OR SEED ADJACENT ENVIRONMENTS WITHOUT SIGNIlCANT DISPERSAL ANDOR IS OFTEN FACILITATED HUMAN ASSISTANCE /2 $ISPERSAL HAS OCCURRED BY HUMANS OVER LARGER DISTANCES BETWEEN WIDELY DISTANT ENVIRONMENTS AND MAY BE FACILITATED BY HUMANS
#OMMUNITY IMPACTS THE SPECIES IS NOTED TO HAVE A SUBSTANTIAL IMPACT ON NATIVE COMMUNITIES !.$/2 %COSYSTEM IMPACTS THE SPECIES IS NOTED TO HAVE A SUBSTANTIAL IMPACT ON ECOSYSTEM PROCESSES !.$/2 %CONOMIC IMPACTS THE SPECIES IS NOTED TO HAVE A SUBSTANTIAL ECONOMIC IMPACT
4HE SPECIES HAS EXPANDED ITS RANGE TO OCCUR IN THE REGION
4ABLE #RITERIA USED IN CLASSIFYING SPECIES ACCORDING TO THE SCHEMES OF $AVIS AND 4HOMPSON AND 2ICHARDSON ET AL A @)DEAL CRITERIA ARE THOSE THAT IF KNOWN WOULD BEST SATISFY THE CRITERIA PROPOSED BY THE AUTHORS OF THE TWO SCHEMES @2EALIZED CRITERIA ARE THE BEST lT TO THE IDEAL CRITERIA USING INFORMATION THAT IS ACTUALLY AVAILABLE 0ARAMETER )DEAL CRITERIA 2EALIZED #RITERIA $AVIS AND 4HOMPSON )NVADERS 3HORT OR LONG DISTANCE DISPERSERS $ISPERSAL HAS OCCURRED GRADUALLY TO NEARBY OR $ISPERSAL IS BY VEGETATIVE OR SEED ADJACENT ENVIRONMENTS WITHOUT SIGNIlCANT DISPERSAL ANDOR IS OFTEN HUMAN ASSISTANCE /2 $ISPERSAL HAS OCCURRED FACILITATED BY HUMANS OVER LARGER DISTANCES BETWEEN WIDELY DISTANT ENVIRONMENTS AND MAY BE FACILITATED BY HUMANS
(4 -URPHY ET AL
3MALL OR GREAT IMPACT IN THE NEW ENVIRONMENT
3UCCESSIONAL #OMMON IN THE NEW COLONIZERS ENVIRONMENT
/NTARIO IS WITHIN THE NATIVE GEOGRAPHIC RANGE OF THE SPECIES
#OMMUNITY IMPACTS THE SPECIES IS NOT NOTED 4HE SPECIES DOES NOT GENERALLY TO HAVE A SUBSTANTIAL IMPACT ON NATIVE OCCUR IN NATURAL OR SEMI NATURAL COMMUNITIES !.$ %COSYSTEM IMPACTS COMMUNITIES )T PRIMARILY INVADES THE SPECIES IS NOT NOTED TO HAVE A SUBSTANTIAL DISTURBED @UNNATURAL AREAS !.$ IMPACT ON ECOSYSTEM PROCESSES THE SPECIES 4HE SPECIES IS NOT NOTED TO DOES NOT PLAY A KEYSTONE ROLE IN THE NEW SUBSTANTIALLY IMPACT ECOSYSTEM COMMUNITY OR ECOSYSTEM !.$ %CONOMIC IMPACTS PROCESS !.$ ECONOMIC IMPACTS THE SPECIES IS NOT NOTED TO HAVE A SUBSTANTIAL ASSOCIATED WITH THE SPECIES ARE ECONOMIC IMPACT /2 #OMMUNITY IMPACTS LIMITED IN NATURE OR SCALE /2 THE SPECIES IS NOTED TO HAVE A SUBSTANTIAL IMPACT 4HE SPECIES IS NOTED REGULARLY TO ON NATIVE COMMUNITIES !.$/2 %COSYSTEM OCCUR IN NATURAL OR SEMI NATURAL IMPACTS THE SPECIES IS NOTED TO HAVE A NATURAL DISTURBED COMMUNITIES SUBSTANTIAL IMPACT ON ECOSYSTEM PROCESSES !.$/2 4HE SPECIES IS NOTED TO !.$/2 %CONOMIC IMPACTS THE SPECIES IS SUBSTANTIALLY IMPACT ECOSYSTEM NOTED TO HAVE A SUBSTANTIAL ECONOMIC IMPACT PROCESSES !.$/2 4HE SPECIES IS NOTED TO HAVE SUBSTANTIAL ECONOMIC IMPACT
4HE SPECIES IS NATIVE TO THE REGION ITS OCCURRENCE IN THE REGION INVOLVES NO RANGE EXPANSION
)NVASIVENESS IN EXOTIC PLANTS
)DEAL CRITERIA
2EALIZED #RITERIA
3MALL IMPACT IN THE NEW ENVIRONMENT
/NTARIO IS NOT WITHIN THE NATIVE GEOGRAPHIC RANGE OF THE SPECIES
#OMMUNITY IMPACTS THE SPECIES IS NOT NOTED 4HE SPECIES DOES NOT GENERALLY OCCUR IN NATURAL TO HAVE A SUBSTANTIAL IMPACT ON NATIVE OR SEMI NATURAL COMMUNITIES )T PRIMARILY COMMUNITIES !.$ %COSYSTEM IMPACTS INVADES DISTURBED @UNNATURAL AREAS !.$ 4HE THE SPECIES IS NOT NOTED TO HAVE A SUBSTANTIAL SPECIES IS NOT NOTED TO SUBSTANTIALLY IMPACT IMPACT ON ECOSYSTEM PROCESSES THE SPECIES DOES ECOSYSTEM PROCESS !.$ ECONOMIC IMPACTS NOT PLAY A KEYSTONE ROLE IN THE NEW COMMUNITY ASSOCIATED WITH THE SPECIES ARE LIMITED IN NATURE OR ECOSYSTEM !.$ %CONOMIC IMPACTS OR SCALE THE SPECIES IS NOT NOTED TO HAVE A SUBSTANTIAL ECONOMIC IMPACT
.OVEL IN THE NEW 4HE SPECIES HAS EXPANDED ITS RANGE TO OCCUR ENVIRONMENT IN THE REGION
$ISPERSAL HAS OCCURRED GRADUALLY TO NEARBY $ISPERSAL IS BY VEGETATIVE MEANS OR SEED ANDOR OR ADJACENT ENVIRONMENTS WITHOUT SIGNIlCANT IS OFTEN FACILITATED BY HUMANS HUMAN ASSISTANCE /2 $ISPERSAL HAS OCCURRED OVER LARGER DISTANCES BETWEEN WIDELY DISTANT ENVIRONMENTS AND MAY BE FACILITATED BY HUMANS
4ABLE #ONTINUED 0ARAMETER $AVIS AND 4HOMPSON .OVEL 3HORT OR LONG NON INVASIVE DISTANCE COLONIZERS DISPERSERS
(4 -URPHY ET AL
2ELIES ON REPEATED INTRODUCTIONS FOR ITS PERSISTENCE
5NCOMMON TO COMMON EXTINCTION PROBABILITY MEDIUM TO LOW 3% 3%
3% 2ANKING IN /NTARIO
(UMAN AIDED DISPERSAL COMMON !.$ OCCURRENCE ONLY IN HUMAN DISTURBED AREAS
%XTREMELY RARE TO VERY RARE HIGH EXTINCTION PROBABILITY 3% 3%
3% 2ANKING IN /NTARIO
!LL 3%S NOT NATIVE TO /NTARIO
(AS NOT SPREAD INTO NEW ENVIRONMENTS BEYOND /CCURRENCE ONLY IN HUMAN DISTURBED AREAS THE POINT OF INTRODUCTION HAVE NOT DISPERSED TO NATURAL OR SEMI NATURAL COMMUNITIES
2EPRODUCES CONSISTENTLY AND SUSTAINS POPULATIONS OVER MANY LIFECYLES
!N ALIEN PLANT
.ATURALIZED PLANTS
4HESE SPECIES DO NOT SPREAD NATURALLY PAST THEIR POINT OF INTRODUCTION
!N ALIEN PLANT
#ASUAL ALIEN PLANTS
4HE SPECIES OCCURS IN AN AREA KM FROM THE NEAREST @NATURAL POPULATION DUE TO INTRODUCTION AS A RESULT OF HUMAN ACTIVITY
2ICHARDSON ET AL A !LIEN PLANTS
)NVASIVENESS IN EXOTIC PLANTS
#HANGES THE CHARACTER CONDITION FORM OR NATURE OF ECOSYSTEMS OVER A SUBSTANTIAL AREA
!N INVASIVE PLANT
/CCUR IN HUMAN DISTURBED AREAS AND HAVE SPREAD TO OCCUR IN DISTURBED NATURAL AND SEMI NATURAL COMMUNITIES
/PERATIONALLY OUR DElNITION OF NATURALIZED THUS LIMITS SPECIES TO OCCURRENCE IN MAINLY HUMAN MODIlED COMMUNITIES THIS IS NOT NECESSARILY THE INTENT OF 2ICHARDSON ET ALS DElNITION SEE TEXT ON THIS
4RANSFORMERS
(AS SPREAD TO AREAS DISTANT TO THE POINT OF INTRODUCTION
0RODUCES REPRODUCTIVE OFFSPRING IN LARGE NUMBERS #OMMON AND WIDESPREAD LOW EXTINCTION AT CONSIDERABLE DISTANCE FROM PARENT PLANT PROBABILITY 3% 3% FOR SPECIES PRIMARILY DISPERSED BY SEED M IN YEARS FOR SPECIES SPREADING PRIMARILY VEGETATIVELY MYEARS OR ANY SPECIES PRIMARILY SPREAD BY HUMANS
3% 2ANKING IN /NTARIO
!N ALIEN PLANT
2EALIZED #RITERIA
)DEAL CRITERIA
4ABLE #ONTINUED 0ARAMETER 2ICHARDSON ET AL A )NVASIVE PLANTS
(4 -URPHY ET AL
)NVASIVENESS IN EXOTIC PLANTS
,ONG DISTANCE DISPERSAL VECTORS INCLUDED WEED CONTAMINATED CROP SEED SOIL OR OTHER AGRICULTURAL PRODUCTS BOATS CARS AND OTHER VEHICLES WATERFOWL FISH AND IRRIGATION WATER 2ATES OF SPREAD AS REQUIRED BY 2ICHARDSON ET ALS SCHEME PROVE TO BE ONLY RARELY AVAILABLE ONLY SEVEN OF THE ARTICLES WE SURVEYED REPORTED ANY RATE OF SPREAD &IVE OF THESE WERE FOR SPECIES THAT SPREAD PRIMARILY BY VEGETATIVE MEANS AND NONE HAD BEEN MEASURED OR ESTIMATED IN THE ADVENTIVE /NTARIO ENVIRONMENT 7HERE DISPERSAL OF PROPAGULES IS PROMOTED BY ANTHROPOGENIC ACTIVITIES OR OTHER NON STANDARD MEANS RATES OF SPREAD CANNOT REASONABLY BE ESTIMATED BY SEED OR VEGETATIVE PROPAGULE CHARACTERISTICS (IGGINS ET AL !LTHOUGH IN THEORY SPREAD COULD BE MEASURED RELATIVELY OBJECTIVELY USING POPULATION GROWTH AND DISTANCE FROM THE SOURCE UNLESS SUBSTANTIAL HISTORICAL INFORMATION IS AVAILABLE REAL RATES OF SPREAD ARE QUITE DIFlCULT TO DETERMINE &URTHERMORE FOR MANY OF THE SPECIES IN OUR DATASET WHICH ARE PRIMARILY AGRICULTURAL WEEDS LONG DISTANCE DISPERSAL MAY OCCUR RELATIVELY REGULARLY THROUGH TRANSPORT IN CONTAMINATED SEED STOCKS OR INFESTED HAY 4HESE METHODS HAVE BEEN CONSIDERED A MAJOR CON TRIBUTOR TO SPREAD FOR MANY SPECIES EG 3ILENE ALBA -C.EILL -ELILOTUS SPP 4URKINGTON ET AL 3ORGHUM HALEPENSE 7ARWICK AND "LACK 4HE .()# DATABASE INCLUDES ESTIMATES OF ABUNDANCE OF EXOTIC PLANTS USING A PROVINCIAL RANKING SYSTEM 3% RANK ;3UB NATIONAL EXOTIC= 7E USED THE PROVIN CIAL 3% RANKING AS A SURROGATE FOR THE AMOUNT OF @SPREAD THAT HAD BEEN ACHIEVED 4HE 3% RANKING IS ESSENTIALLY A DISTRIBUTION AND ABUNDANCE INDICATOR AND SO CARRIES IMPLICATIONS OF EXTINCTION RISK 4HUS 3% AND 3% RANKED SPECIES ARE CON SIDERED VULNERABLE TO EXTINCTION 3% SPECIES HAVE A MEDIUM RISK OF EXTINCTION AND 3% AND 3% HAVE GENERALLY A LOW RISK OF EXTINCTION SEE -ASTER 4HUS s 3% %XTREMELY RARE IN /NTARIO USUALLY OR FEWER OCCURRENCES IN THE PROV INCE OR VERY FEW REMAINING INDIVIDUALS OFTEN ESPECIALLY VULNERABLE TO EXTIRPATION s 3% 6ERY RARE IN /NTARIO USUALLY BETWEEN AND OCCURRENCES IN THE PROV INCE OR WITH MANY INDIVIDUALS IN FEWER OCCURRENCES OFTEN SUSCEPTIBLE TO EXTIRPATION s 3% 2ARE TO UNCOMMON IN /NTARIO USUALLY BETWEEN AND OCCURRENCES IN THE PROVINCE MAY HAVE FEWER OCCURRENCES BUT WITH A LARGE NUMBER OF INDIVIDUALS IN SOME POPULATIONS MAY BE SUSCEPTIBLE TO LARGE SCALE DISTURBANCES -OST SPECIES WITH AN 3% RANK ARE ASSIGNED TO THE WATCH LIST UNLESS THEY HAVE A RELATIVELY HIGH GLOBAL RANK s 3% #OMMON AND APPARENTLY SECURE IN /NTARIO USUALLY WITH MORE THAN OCCURRENCES IN THE PROVINCE s 3% 6ERY COMMON AND DEMONSTRABLY SECURE IN /NTARIO #OMMUNITY ECOSYSTEM AND ECONOMIC @IMPACTS AS PER $AVIS AND 4HOMPSONS SCHEME WERE QUANTIlED AS FOLLOWS AND SEE 4ABLE &OR COMMUNITY IMPACT SPECIES OCCURRENCE IN ONLY COMMUNITY TYPES ANDOR BOTH GENERALLY HIGHLY HUMAN MODIlED COMMUNITIES WAS SCORED AS POINT OCCURRENCE IN ANY OTHER
&ROM HERBARIUM SPECIMEN OR IF NO DATE GIVEN DATE IS NOTED AS IF THE SPECIES IS LISTED IN 'LEASON )S /NTARIO WITHIN THE NATIVE RANGE OF THE SPECIES 6EGETATIVE OR SEED
$ATE OF lRST DOCUMENTED OCCURRENCE IN /NTARIO
.ATIVITY TO /NTARIO
0RIMARY MEANS OF RECRUITMENT
VEGETATIVE SEED
YES NO
$ATE
4ABLE $ATA EXTRACTED FROM THE "IOLOGY OF #ANADIAN 7EEDS SERIES AND .()# DATABASE TO ADDRESS CRITERIA OUTLINED IN 4ABLE !TTRIBUTE $ESCRIPTION 6ARIABLE !BUNDANCE 2ANK 3% 2ANKING 3% %XTREMELY RARE IN /NTARIO USUALLY OR FEWER OCCURRENCES IN THE PROVINCE OR VERY FEW REMAINING INDIVIDUALS OFTEN ESPECIALLY VULNERABLE TO EXTIRPATION 3% 6ERY RARE IN /NTARIO USUALLY BETWEEN AND OCCURRENCES IN THE PROVINCE OR WITH MANY INDIVIDUALS IN FEWER OCCURRENCES OFTEN SUSCEPTIBLE TO EXTIRPATION 3% 2ARE TO UNCOMMON IN /NTARIO USUALLY BETWEEN AND OCCURRENCES IN THE PROVINCE MAY HAVE FEWER OCCURRENCES BUT WITH A LARGE NUMBER OF INDIVIDUALS IN SOME POPULATIONS MAY BE SUSCEPTIBLE TO LARGE SCALE DISTURBANCES 3% #OMMON AND APPARENTLY SECURE IN /NTARIO USUALLY WITH MORE THAN OCCURRENCES IN THE PROVINCE 3% 6ERY COMMON AND DEMONSTRABLY SECURE IN /NTARIO
(4 -URPHY ET AL
WIND WATER BIRD ANIMAL GRAVITY OR BALLISTIC
0RIMARY MODE OF NATURAL DISPERSAL USUALLY BASED ON ADAPTATIONS OF THE SEED OR FRUIT /THER DOCUMENTED USUALLY HUMAN FACILITATED MEANS OF DISPERSAL $OCUMENTED OCCURRENCE IN VARIOUS COMMUNITY TYPES $OCUMENTED ECONOMIC IMPACTS
3ECONDARY DISPERSAL MODE
#OMMUNITIES IN WHICH SPECIES OCCURS
%CONOMIC IMPACTS
%COSYSTEM IMPACTS $OCUMENTED ECOSYSTEM IMPACTS FORMS MONOCULTURES DOMINATES AQUATIC ECOSYSTEMS WITH MAJOR EFFECTS ON mOW OXYGEN LIGHT ETC SIGNIlCANT NITROGEN lXER %CONOMIC IMPACTS OTHER THAN THOSE LISTED HERE WERE OCCASIONALLY REPORTED EG MAKES HARVESTING DIFlCULT CHEMICALLY INHIBITS CROP SPECIES HOWEVER THESE IMPACTS ARE CLOSELY RELATED TO AND ALWAYS OCCURRED WITH AND THEREFORE WERE CONSIDERED REDUNDANT AND NOT INCLUDED AS SEPARATE IMPACTS
COMPETES WITH CROP OR PASTURE SPECIES IS TOXIC OR IRRITANT TO FARM ANIMALS OR HUMANS DESTROYS APPEARANCE OF LAWNS OR GARDENS HARBOURS INSECTS OR DISEASE ORGANISMS THAT ATTACK OTHER PLANT SPECIES INTERFERES WITH WATER INFRASTRUCTURE IMPACTS RECREATIONAL AREAS BEACHES LAKES ETC CONTAMI NATES SEED STOCKS INFESTS HAY ETC
ROADSIDES GARDENS WASTELANDS OTHER DISTURBED URBAN AREAS GRAZED PASTURE CULTIVATED lELDS CROPS DISTURBED NATURAL COMMUNITIES OPEN WOODLAND FOREST MARGINS OR CLEARINGS STREAM BANKS SHORELINES AQUATIC LAKE STREAM POND RIVER ETC
CONTAMINATED CROP SEEDS OR INFESTED HAY FARM MACHINERY OR VEHICLES IN SOIL OR MANURE LIVESTOCK OR DOMESTIC ANIMALS BOATS IRRIGATION WATER HUMAN CLOTHING OR FOOTWEAR
6ARIABLE
$ESCRIPTION
4ABLE #ONTINUED !TTRIBUTE 0RIMARY DISPERSAL MODE
)NVASIVENESS IN EXOTIC PLANTS
(4 -URPHY ET AL
MORE @NATURAL COMMUNITY TYPES BROUGHT AN ADDITIONAL POINT 4HUS IF THE SPECIES OCCURRED IN COMMUNITY TYPES AND SEE 4ABLE THE TOTAL SCORE WOULD BE POINTS 4HE TOTAL NUMBER OF POINTS SCORED WAS THEN MULTIPLIED BY THE 3% RANK VALUE &OR EXAMPLE IF THE ABOVE SPECIES WAS RANKED AS 3% THE #OMMUNITY )MPACT 3CORE #)3 WOULD BE ! SIMILAR SYSTEM WAS APPLIED TO ECOSYSTEM IMPACTS %COSYSTEM )MPACT 3CORE %)3 &OR ECONOMIC IMPACT A SPE CIES SCORED POINTS IF IT WAS NOTED TO HAVE IMPACTS RELATED TO DESCRIPTORS AND SEE 4ABLE WHICH IN GENERAL INVOLVE BOTH CROP PRODUCTION LOSSES AND CONTROL COSTS AND POINT IF IT WAS NOTED TO HAVE IMPACT IN ANY OTHER CATEGORY WHICH PRIMARILY INVOLVE CONTROL COSTS ONLY 4HAT TOTAL SCORE WAS THEN MULTIPLIED BY THE 3% RANK VALUE AS ABOVE %CONOMIC )MPACT 3CORE %CON)3 #RITERIA FOR DETERMINING WHETHER THE SCORE CORRESPONDED TO A @GREAT OR @SMALL IMPACT ARE SHOWN IN 4ABLE @$4 )F A SPECIES WAS DETERMINED TO HAVE A GREAT IMPACT IN ANY OF THE THREE IMPACT CATEGORIES THE OVERALL IMPACT WAS DETERMINED AS @GREAT IN THE LANGUAGE OF $4 )T IS DIFlCULT TO REMOVE SUBJECTIVITY FROM THE SCOR ING OF IMPACT 7E TRIED SEVERAL ALTERNATIVES TO THE ABOVE SCHEMES AND PRESENT ONE OF THEM HERE 7E APPLIED AN ALTERNATIVE METHOD TO CALCULATING #)3 IF THE SPECIES OCCURRED ONLY IN MEDIUM TO HIGHLY HUMAN MODIlED COMMUNITIES IE OR A SCORE OF WAS APPLIED AND A SCORE OF WAS APPLIED TO A SPECIES THAT OCCURRED IN ANY NATURAL OR SEMI NATURAL COMMUNITY 4HE SCORE WAS THEN MULTIPLIED BY THE 3% RANK VALUE 7E ALSO MODIlED THE CRITERIA FOR DETERMINING WHETHER THE IMPACT WAS SMALL OR GREAT 4HESE TWO MODIlCATIONS COMBINED RESULT IN THE ALTERNATIVE $AVIS AND 4HOMPSON CLASSIlCATION $4 IN 4ABLE AND IN 4ABLE IN RESULTS 4ABLE #RITERIA TO BE SATISlED FOR DETERMINATION OF IMPACT AS @SMALL OR @GREAT IN TWO ALTERNATIVE SCORING SCHEMES APPLIED TO $AVIS AND 4HOMPSONS CLASSIlCATION SCHEME )MPACT $4 $4 3MALL 'REAT 3MALL 'REAT
#OMMUNITY #)3 %COSYSTEM %)3 %CONOMIC %CON)3
) )
) )
)N OUR APPLICATION OF 2ICHARDSON ET ALS SCHEME THE 3% RANK VALUE IS THE PRI MARY FACTOR DRIVING THE DISTINCTION BETWEEN INVASIVE AND OTHER ALIEN SPECIES 3% RANK IS ALSO A KEY FACTOR IN OUR APPLICATION OF $AVIS AND 4HOMPSONS SCHEME IN THE DIVISION BETWEEN GREAT AND SMALL IMPACTS ! CLOSE ASSOCIATION BETWEEN 3% RANK AND THE RAW IMPACT FACTOR IE IMPACT SCORES PRIOR TO MULTIPLICATION BY 3% RANK VALUE SHOULD RESULT IN A GREATER OVERLAP BETWEEN THE TWO SCHEMES 7E USED
)NVASIVENESS IN EXOTIC PLANTS
CORRELATION ANALYSIS TO DETERMINE HOW THE 3% RANK VALUE WAS RELATED TO THE RAW IMPACT SCORES FOR COMMUNITY AND ECONOMIC IMPACTS ONLY SEVEN SPECIES SCORED ABOVE IN THE ECOSYSTEM IMPACT CATEGORY SO %)3 WAS NOT TESTED FOR ASSOCIATION 4O EXAMINE DIFFERENCES BETWEEN GREAT AND SMALL IMPACT SPECIES IN LIFE HISTORY TRAITS WE USED CHI SQUARED CONTINGENCY ANALYSIS WITH 9ATES CORRECTION )F TWO WAY CONTINGENCY TABLES SHOWED NON INDEPENDENCE 0 THE &REEMAN 4UKEY DEVIATE WAS USED TO DETERMINE IF ANY INDIVIDUAL CELL WAS EITHER UNDER OR OVER REPRESENTED COMPARED TO THE EXPECTED VALUE ,IFE HISTORY VARIABLES FOR WHICH DATA WERE COLLECTED ARE SHOWN IN 4ABLE 4ABLE ,IFE HISTORY TRAITS RECORDED FOR EACH SPECIES ,IFE HISTORY TRAIT 0ARAMETERS 3EED DORMANCY ,ONG YEARS 3HORT YEARS .ONE KNOWN 0RIMARY POLLINATION MODE )NSECT WIND SELF VARIOUS UNKNOWN #LONAL ORGAN PRESENCE 0RESENT ABSENT &LOWERING SEASON %ARLY MID LATE ALL SEASON &LOWERING DURATION .UMBER OF MONTHS 3OIL MOISTURE PREFERENCE -OIST DRY VARIABLE 3EX HABIT (ERMAPHRODITE MONOECIOUS DIOECIOUS POLYGAMOUS ,IFE CYCLE !NNUAL AND BIENNIAL PERENNIAL VARIABLE $OMINANT RECRUITMENT MODE 6EGETATIVE SEED VARIABLE
!S WITH MOST MACROECOLOGICAL DATASETS #ADOTTE ET AL OURS HAS ITS LIMITATIONS 4HE TERM @WEED IN THE "IOLOGY OF #ANADIAN 7EEDS SERIES REFERS TO ANY VASCULAR PLANT THAT PERPETUATES ITSELF IN HABITATS WHERE IT IS hNOT WANTEDv #AVERS AND 7ARWICK A MEANING DIFFERENT FROM THAT COMMONLY USED FOR @WEEDS IN THE ECOLOGICAL LITERATURE AND WHICH USUALLY INCLUDES THAT THE SPECIES HAS DETECT ABLE ECONOMIC OR ENVIRONMENTAL IMPACTS EG 0YÝEK ET AL 2ICHARDSON ET AL A 4HUS THESE SPECIES SHOULD NOT BE CONSIDERED TO HAVE BEEN ALREADY CLASSIlED AS @WEEDS IN THE TRADITIONAL ECOLOGICAL SENSE RATHER THEY STILL VALIDLY REPRESENT SPECIES IN THE RANGE OF CATEGORIES DElNED BY THE TWO SCHEMES 4HE SPE CIES IN OUR LIST ARE BIASED TOWARDS SPECIES OCCURRING IN AGRICULTURAL AREAS SINCE THE ORIGINAL PURPOSE OF THE SERIES WAS TO PROVIDE A BASIS FOR EFFECTIVE CONTROL METHODS AND TO MEET THE NEEDS OF REGULATORY AGENCIES IN #ANADA #AVERS AND 7ARWICK (OWEVER THE DATASET DOES INCLUDE A RANGE OF SPECIES OCCURRING IN BOTH NATURAL AND AGRICULTURAL HABITATS AND INCLUDES BOTH ABUNDANT 3% AND 3% AND RARE 3% SPECIES )T IS IMPORTANT TO NOTE THAT WE ARE NOT ATTEMPTING TO TEST THE ACCURACY OF EITHER SCHEME IN CLASSIFYING SPECIES INTO CATEGORIES SINCE THERE IS NO @RIGHT ANSWER 2ATHER WE AIM TO DETERMINE IF EITHER SCHEME IS MORE FUNCTIONAL OR OPERATIONAL BASED ON THE DATA AVAILABLE IN A TYPICAL SPECIES DATASET 4HUS ANY
(4 -URPHY ET AL
CONCLUSIONS WE MAKE AS TO WHICH CLASSIlCATION WAS @BETTER REFER ONLY TO WHICH MODEL COULD BE APPLIED MORE USEFULLY GIVEN THE DATA AVAILABLE TO EVALUATE EACH CRITERION FOR CATEGORIZATION
2%35,43 ! TOTAL OF FAMILIES WAS REPRESENTED IN THE DATASET OF SPECIES 4ABLE 4HE !STERACEAE WAS THE ONLY FAMILY REPRESENTED IN ALL 3% RANKS WITH A TOTAL OF SPECIES 0OACEAE WAS NEXT WITH A TOTAL OF SPECIES AND ONLY 3% SPECIES EXTREMELY RARE WERE NOT REPRESENTED &ABACEAE WAS NEXT WITH NINE SPECIES ALL RANKED 3% 4HERE WERE EIGHT "RASSICACEAE IN 3% 3% AND 3% RANKS 4WENTY TWO OF THE FAMILIES HAD ONLY OR SPECIES REPRESENT ED IN THE DATASET !STERACEAE &ABACEAE AND "RASSICACEAE ARE ALL OVER REPRESENTED IN OUR DATASET COMPARED WITH THEIR REPRESENTATION IN THE EXOTIC mORA OF /NTARIO AND AMONG NATIVE /NTARIO SPECIES SEE 4ABLE !PPLICATION OF THE 2ICHARDSON ET AL SCHEME CLASSIlED OF THE TOTAL SPECIES AS INVASIVE AS OPPOSED TO $AVIS AND 4HOMPSON WHERE APPROXIMATELY OF SPECIES WERE CLASSIlED AS INVADERS USING OUR lRST CRITERIA $4 AND USING THE ALTERNATIVE CRITERIA $4 4ABLE !LL BUT ONE OF THE SPECIES CLASSIlED AS INVASIVE BY 2ICHARDSON ET AL WERE ALSO CLASSIlED AS INVASIVE BY BOTH $AVIS AND 4HOMPSON SCHEMES 4HE EXCEPTION WAS (ELIANTHUS TUBEROSUS WHICH WAS CLASSIlED AS A SUCCESSIONAL COLONIZER IN BOTH $4 AND $4 DUE TO ITS ACTUALLY BEING CONSID ERED NATIVE TO /NTARIO 4HE DISTINCTION DEPENDS UPON CONmICTING CONCLUSIONS BY EXPERTS !LTHOUGH CONSIDERED NON NATIVE TO /NTARIO BY SEVERAL AUTHORS -ORTON AND 6ENN ;= .EWMASTER ET AL ;= AND 3COGGAN ;= MOST REGIONAL mORAS AND mORAS FROM NEARBY AREAS CONSIDER THE SPECIES NATIVE EG 'LEASON AND #RONQUIST )T IS LIKELY THAT AT SOME TIME IN THE FUTURE THE 3 RANK OF THIS SPECIES WILL BE CHANGED FROM 3% TO 3 INDICATING A NATIVE STATUS RATHER THAN EXOTIC IN THE PROVINCE .()# !LL SPECIES RANKED AS 3% WERE CLASSIlED BY 2ICHARDSON ET AL AS CASUAL AND BY $4 AND $4 AS NOVEL NON INVASIVE COLONIZERS 4ABLE )N OUR APPLICATION OF BOTH CLASSIlCATIONS IT WAS NOT POSSIBLE FOR AN 3% SPECIES TO BE REGARDED AS INVASIVE /F THE 3% SPECIES 2ICHARDSON ET ALS SCHEME CLASSIlED AS INVADERS COMPARED WITH $4 AND $4 4ABLE 3% RANK VALUE WAS SIGNIlCANTLY CORRELATED WITH RAW COMMUNITY IMPACT SCORES $4 R P N $4 R P N HOW EVER THERE WAS NO CORRELATION BETWEEN 3% RANK VALUE AND ECONOMIC IMPACT SCORE $4 R – P N 4HUS SPECIES WITH GREATER ABUNDANCE TENDED TO OCCUR IN MORE OF THE DElNED COMMUNITY TYPES INCLUDING NATURAL AND SEMI NATURAL COMMUNITIES THAN LESS ABUNDANT SPECIES BUT DID NOT NECESSARILY FALL INTO MORE ECONOMIC IMPACT CATEGORIES )N $4 ALL 3% SPECIES HAD AN OVERALL IMPACT OF @GREAT WHEREAS IN $4 THREE 3% SPECIES HAD ONLY @SMALL IMPACT 'REAT AND SMALL IMPACT SPECIES DIFFERED ONLY IN THEIR PROPORTIONS IN THE SEED DOR MANCY LIFE HISTORY PARAMETER LONG SHORT OR NONE $4 r P
)NVASIVENESS IN EXOTIC PLANTS
4ABLE &AMILY REPRESENTATION IN 3% RANK AND TOTAL NUMBER OF FAMILY MEMBERS IN THE DATABASE COMPARED WITH PROPORTION OF FAMILY IN ALL SPECIES LISTED AS @EXOTIC IN /NTARIO AND IN ALL NATIVE SPECIES OF /NTARIO &AMILY !MARANTHACEAE !PIACEAE !STERACEAE "ORAGINACEAE "RASSICACEAE #ANNABACEAE #ARYOPHYLLACEAE #HENOPODIACEAE #LUSIACEAE #ONVOLVULACEAE $IPSACACEAE %UPHORBIACEAE &ABACEAE (ALORAGACEAE ,AMIACEAE ,YTHRACEAE -ALVACEAE /XALIDACEAE 0LANTAGINACEAE 0OACEAE 0OLYGONACEAE 0ORTULACACEAE 0OTAMOGETONACEAE 2ANUNCULACEAE 2OSACEAE 2UBIACEAE 3CROPHULARIACEAE 3OLANACEAE 6IOLACEAE 4OTAL
3% 2ANK
4OTAL OF TOTAL DATASET
OF OF FAMILY FAMILY IN ALL IN NATIVES EXOTICS OF OF /NTARIO /NTARIO N N
(4 -URPHY ET AL
4ABLE 3UMMARY OF RESULTS OF CLASSIlCATION SCHEMES FOR SPECIES IN EACH 3% RANK REGIONAL DISTRIBUTION AND ABUNDANCE $4 $AVIS AND 4HOMPSON 4OTAL IN 3% CATEGORY
3%
3%
3%
3%
3%
4OTAL
2ICHARDSON ET AL s #ASUAL s .ATURALIZED s )NVASIVE
$4 s 3UCCESSIONAL COLONIZER s .OVEL NON INVASIVE COLONIZER s )NVADER
$4 s 3UCCESSIONAL COLONIZER s .OVEL NON INVASIVE COLONIZER s )NVADER
$4 GREAT IMPACT $4 SMALL IMPACT $4 GREAT IMPACT $4 SMALL IMPACT
$4 r P 2ESULTS OF THE &REEMAN 4UKEY DEVIATE TEST INDI CATED THAT SPECIES WITH A SMALL IMPACT WERE SIGNIlCANTLY UNDER REPRESENTED BY THE PRESENCE OF A LONG DORMANCY PERIOD AND SPECIES WITH A GREAT IMPACT WERE UNDER REPRESENTED BY PRESENCE OF SHORT ANDOR NO DORMANCY PERIOD !DDITIONALLY GREAT AND SMALL IMPACT SPECIES DIFFERED IN THEIR GEOGRAPHIC ORIGIN $4 r P $4 r P 3PECIES HAVING A SMALL IMPACT WERE UNDER REPRESENTED IN ORIGINATING FROM %URASIA AND WERE OVER REPRESENTED IN ORIGINATING FROM !SIA PROPER AND THE -EDITERRANEAN AREA OF %UROPE 3PECIES WITH A GREAT IMPACT WERE OVER REPRESENTED IN ORIGINATING FROM %URASIA
)NVASIVENESS IN EXOTIC PLANTS
$)3#533)/. $AVIS AND 4HOMPSONS CLASSIlCATION SCHEME WAS CLEARLY LESS DISCRIMINATING IN DETERMINING INVASIVE SPECIES IN THIS DATASET 4HIS COULD BE AMELIORATED SOMEWHAT BY INCREASING THE SCORE RANGE FOR @SMALL IMPACTS (OWEVER THE ORIGINAL SCORE RANGE FOR %CON)3 ) TAKES INTO ACCOUNT THE FACT THAT AN 3% SPECIES WITH AN IMPACT IN ONE ECONOMIC CATEGORY SUCH AS THE MOST COMMON CATEGORY n WOULD SCORE A )T MAKES LITTLE SENSE TO CALL THIS A @SMALL IMPACT (OWEVER EVEN WITH THE EXPANDED RANGE FOR SMALL ECONOMIC IMPACTS $4 THERE ARE ONLY SEVEN SPE CIES THAT WOULD BE REASSIGNED FROM THE @INVASIVE CATEGORY TO THE @NON INVA SIVE COLONIZER CATEGORY )T IS NOTEWORTHY THAT 3% RANK AND THE ECONOMIC IMPACT SCORE BEFORE ADJUSTING FOR ABUNDANCE WERE NOT CORRELATED 3% SPECIES WERE JUST AS LIKELY TO HAVE A NUMBER OF DIFFERENT TYPES OF ECONOMIC IMPACTS AS 3% SPECIES (OWEVER MORE ABUNDANT SPECIES WERE MORE LIKELY TO HAVE SPREAD TO NATURAL OR SEMI NATURAL HABITATS THAN LESS ABUNDANT SPECIES /N A CASE BY CASE BASIS 2ICHARDSON ET ALS SCHEME WOULD SEEM TO BE MORE PRACTICALLY USEFUL SINCE IT IS IN THEORY LESS SUBJECTIVE 9ET WHEN ATTEMPTING TO CLASSIFY EVEN A RELATIVELY DETAILED AND CONSISTENT DATASET AS WE HAVE DONE THE @SPREAD CRITERION PRESENTS ALMOST AS MANY PROBLEMS AND IS PERHAPS JUST AS SUBJEC TIVE AS $AVIS AND 4HOMPSONS IMPACT CRITERION 7E ARE FORTUNATE WITH THE /NTARIO DATASET TO HAVE THE DISTRIBUTION AND ABUNDANCE RANKING INFORMATION THAT CAN BE USED AS A SURROGATE FOR THE @SPREAD CRITERION (OWEVER THE 3% RANKING SYSTEM HAS SEVERAL LIMITATIONS IN ITS USE AS A SPREAD SURROGATE &IRST IT IS BASED ON CURRENT ABUNDANCE IN THE PROVINCE 3% RANKED SPECIES ARE AT THE LIMIT OF THE ABUNDANCE RANKING BUT SOME MAY HAVE EXHAUSTED THE POTENTIAL RANGE OF SUITABLE HABITATS AND BE NO LONGER CAPABLE OF FURTHER SPREAD WHILE OTHERS MAY NOT 3% SPECIES ALTHOUGH NOT CURRENTLY ABUNDANT MAY BE SPREADING AT A MORE RAPID RATE THAN 3% AND 3% SPECIES AND THIS REMAINING POTENTIAL FOR RAPID SPREAD IS NOT CAPTURED IN THE 3% RANKING 4HUS THE SPREAD CRITERION IS COMPLICATED BY THE TEMPORAL @SNAP SHOT NATURE OF THE ASSESSMENT ! RELATED PROBLEM IS THAT THE 3% RANKING GIVES NO INDICATION AS TO WHERE THE POPULATIONS ARE LOCATED RELATIVE TO EACH OTHER )N FACT VIRTUALLY ALL OF THE 3% SPE CIES IN OUR DATASET HAVE BEEN RECORDED FROM POPULATIONS WIDELY DISTANT FROM ONE ANOTHER IE KM DETERMINED THROUGH A VISUAL INSPECTION OF THE DISTRIBU TION MAPS )F WE WERE TO BASE THE RATE OF SPREAD CRITERION ON THE TIME SINCE INTRODUCTION OF THE SPECIES AND THE AVERAGE DISTANCE BETWEEN PERSISTENT POPULATIONS IN /NTARIO WE WOULD MOST LIKELY PLACE ALL THE SPECIES ON OUR LIST !PPENDIX IN 2ICHARDSON ET ALS @INVASIVE CATEGORY 4HE SPREAD CRITERION FOR INVASIVES IE FOR SEED DISPERSED SPECIES M FROM PARENTAL PLANTS IN YEARS BEGINS TO MAKE LITTLE SENSE ON REGIONAL AND LANDSCAPE SCALES ESPECIALLY WHEN MOST SPECIES HAVE MODES OF DISPERSAL WITH A POTENTIAL TO CARRY PROPAGULES GREAT DISTANCES FROM PARENTAL INDIVIDUALS 2ICHARDSON ET AL A ESTIMATED THAT OF @INVADERS AS DElNED BY THEIR CLASSIlCATION WOULD HAVE @HARMFUL DETECTABLE ENVIRONMENTAL OR ECONOMIC
(4 -URPHY ET AL
EFFECTS AND THAT THE REST ARE @BENIGN INVADERS WHOSE ENVIRONMENTAL OR ECONOMIC IMPACTS ARE BEYOND ANY PRACTICAL DETECTION LIMITS "Y OUR ANALYSIS OF THE SPECIES CLASSIlED AS INVASIVE BY 2ICHARDSON ET ALS SCHEME HAVE LARGE ENVIRONMENTAL OR ECONOMIC IMPACTS AND MOREOVER BETWEEN AND OF SPECIES DElNED AS NATURALIZED ALSO HAVE HARMFUL EFFECTS 4HIS IS PERHAPS NOT SURPRISING SINCE OUR CRITERIA FOR NATURALIZATION IN 2ICHARDSON ET ALS SCHEME INCLUDED A REQUIREMENT THAT THE SPECIES HAD NOT YET SPREAD TO NATURAL OR SEMI NATURAL HABITATS 4HUS WHILE COMMUNITY IMPACTS WERE MINIMIZED OCCURRENCE IN FEWER COMMUNITY TYPES ECONOMIC IMPACTS FOR THESE SPECIES MAY STILL HAVE BEEN LARGE ENOUGH TO GENERATE AN OVERALL GREAT IMPACT &OR EXAMPLE 3% SPECIES THAT ONLY OCCUR IN CULTIVATED lELDS IE 2ICHARDSON ET ALS @NATURALIZED SPECIES IN OUR ANALYSIS WOULD STILL HAVE SCORED A GREAT IMPACT IF THEY COMPETE WITH AGRICULTURAL SPECIES IN THOSE lELDS AND THEREFORE WOULD HAVE BEEN CLASSIlED AS INVADERS IN $ 4S SCHEME )T SHOULD BE NOTED THAT THE DISTINCTION BETWEEN NATURALIZED AND INVASIVE SPECIES WE USED HERE MAY NOT STRICTLY REPRESENT THE INTENTION OF 2ICHARDSON ET AL 3INCE 2ICHARDSON ET AL SUGGEST NATURALIZED PLANTS HAVE NOT OVERCOME BARRIERS TO DISPERSAL WE LIMITED NATURALIZED SPECIES TO OCCURRENCE ONLY IN HUMAN MODIlED COMMUNITIES 2ICHARDSON ET ALS DElNITION IS UNCLEAR IN THIS RESPECT THEY NOTED h.ATURALIZED PLANTSxDO NOT NECESSARILY INVADE NATURAL SEMI NATURAL OR HUMAN MADE ECOSYSTEMSv #ADOTTE ET AL HAVE STUDIED THE RELATIONSHIP BETWEEN 3% RANKS AND LIFE HISTORY ATTRIBUTES IN /NTARIOS EXOTIC mORA N 4HEIR RESULTS SHOWED THAT COMMON EXOTICS WERE MORE LIKELY TO HAVE A CLONAL ORGAN A LONGER mOWERING PERIOD AND A %URASIAN ORIGIN 7E FOUND THAT IN TERMS OF LIFE HISTORY TRAITS LARGE IMPACT SPECIES DIFFERED FROM SMALL IMPACT ONES IN THE LIKELIHOOD OF HAVING A LENGTHY SEED DORMANCY PERIOD #ADOTTE ET AL FOUND THE VARIABLE MOST STRONGLY ASSOCIATED WITH INVASIVENESS AND HIGHER 3% RANK WAS ORIGIN IN %URASIA AND %UROPE 3IMILARLY IN OUR ANALYSIS SPECIES HAVING GREAT IMPACT CAME DISPROPORTIONATELY OFTEN FROM %URASIA 4HIS SUPPORTS #ADOTTE ET AL IN THAT SPECIES NATIVE ELSEWHERE IN .ORTH !MERICA WERE NOT MORE LIKELY TO HAVE A GREAT IMPACT IN /NTARIO HOWEVER OUR SAMPLE SIZE IN THIS CATEGORY ; SPECIES= WAS SMALL #ADOTTE ET AL SUGGEST SEVERAL REASONS WHY %URASIAN SPECIES MAY BE MORE SUCCESSFUL IN /NTARIO 3PECIES FROM %URASIA MAY BE LESS PHYLOGENETICALLY RELATED TO SPECIES FROM .ORTH !MERICA AND MAY BE MORE LIKELY TO HAVE EVOLVED ECOLOGICAL NOVELTIES IN LINE WITH $ARWINS NATURALIZATION HYPOTHESIS ;$ARWIN = !LTERNATIVELY THE ENEMY RELEASE HYPOTHESIS MAY BE RESPONSIBLE OR THE MATCHING OF PROVENANCE IE COMING FROM A COMPARABLE CLIMATIC ZONE COULD BE ANOTHER POSSIBLE FACTOR 7E CONCLUDE THAT NEITHER FRAMEWORK IS ESPECIALLY USEFUL IN THEIR PRESENT FOR MULATIONS FOR CLASSIFYING REGIONAL OR LARGER EXOTIC mORAS IE LISTS OF KNOWN NON NATIVE SPECIES 4HE SEARCH FOR OPERATIONAL DElNITIONS OF TERMINOLOGY IN INVASIONS ECOLOGY REMAINS ELUSIVE 2ELEVANT INFORMATION IS SIMPLY NOT AVAILABLE AND THE USE OF SURROGATES FOR CRITERIA SUCH AS @SPREAD AND @IMPACT ARE LIKELY TO INTRODUCE JUST AS MUCH SUBJECTIVITY INCONSISTENCY AND CONFUSION IN THE LITERATURE AS ALREADY EXISTS &AILURE TO OPERATIONALISE DElNITIONS USED IN CLASSIFYING EXOTIC mORA DATASETS
)NVASIVENESS IN EXOTIC PLANTS
WILL LIKELY CONTINUE TO LEAD TO AMBIGUOUS GENERALIZATIONS AND PREDICTIONS .OTWITHSTANDING THIS AMBIGUITY COMPARATIVE STUDIES OF INVASIVE mORAS HAVE PRO VIDED NEW INSIGHTS IN THE UNDERSTANDING OF GENERAL PATTERNS OF PLANT INVASION AND THE VALUE OF THESE STUDIES IS NOT TO BE DIMINISHED 2ATHER WHEN CLASSIFYING LISTS OF mORA THE CRITERIA USED TO ASSIGN EACH SPECIES TO A CATEGORY SHOULD BE EXPLICITLY STATED SO THAT RESEARCHERS CAN COMPARE SPECIES BASED ON LIKE CRITERIA RATHER THAN THE CATEGORY ITSELF WHICH MAY HAVE BEEN DERIVED FROM UNLIKE DATA !S 0YÝEK ET AL CONCLUDE IN THEIR RECENT PAPER ON THE TREATMENT OF INVASIONS TERMINOLOGY IN REGIONAL mORAS STATEMENTS PRECEDED BY @PROBABLY OR @POSSIBLY MAY BE TEMPO RARILY THE MOST HONEST WAY OF CLASSIFYING SOME TAXA #OLAUTTI AND -AC)SAAC RECENTLY PROPOSED A SUPPLEMENTARY LEXICON TO CURRENT TERMINOLOGY IN INVASIONS ECOLOGY 4HEIR FRAMEWORK ATTEMPTED TO ELIMI NATE THE NEED FOR UNIVERSAL DElNITIONS OF CURRENT TERMS BY USING OPERATIONAL TERMS WITH NO A PRIORI MEANING IE AS STAGES IN A PROCESS BASED MODEL 4HE FRAMEWORK IS BASED ON CURRENT MODELS THAT ENVISION PROCESSES IN IMMIGRATION AND NATURALIZA TION AS A SERIES OF CONSECUTIVE STAGES 4HE GOAL OF THE FRAMEWORK IS TO SUPPLEMENT AMBIGUOUS TERMS WITH THE STAGE BASED TERMINOLOGY 3UCH A FRAMEWORK IS LOGICAL AND INTUITIVELY APPEALING AND WOULD LIKELY LEAD TO SOME CONSISTENCY IN INDIVIDUAL POPULATION BASED STUDIES OF INVASIVE SPECIES AS WOULD THAT OF 2ICHARDSON ET AL ;A= (OWEVER IT IS ALSO UNLIKELY TO BE USEFUL FOR CLASSIFYING LISTS OF ALIEN SPE CIES FOR COMPARATIVE PURPOSES SINCE THE SAME DATA LIMITATIONS WOULD APPLY AS DESCRIBED ABOVE FOR 2ICHARDSON ET AL AND $AVIS AND 4HOMPSONS SCHEMES
! 02/0/3%$ -/$)&)#!4)/. 4/ #522%.4 #/.#%045!, &2!-%7/2+3 &/2 4(% ).6!3)/.3 02/#%33 #OLAUTTI AND -AC)SAAC NOTED THAT TERMINOLOGY USED TO DESCRIBE INTRODUCED SPECIES ARE MISNOMERS IN THE SENSE THAT INTRODUCED NATURALIZED OR INVASIVE SPECIES ETC ARE OF COURSE INTRODUCED NATURALIZED OR INVASIVE POPULATIONS ! FOCUS ON INVA SIONS AT A POPULATION LEVEL RATHER THAN A SPECIES LEVEL HAS IMPORTANT IMPLICATIONS FOR THE DEVELOPMENT OF INVASIONS ECOLOGY )NDEED IT MAKES LITTLE SENSE TO ASSIGN CATEGORICAL PROPERTIES TO A @SPECIES 2ATHER DEMOGRAPHIC ATTRIBUTES OF THE ADVEN TIVE POPULATION AND OF ANY METAPOPULATION OR OTHER REGIONALLY CONNECTED GROUP SEE -URPHY AND ,OVETT $OUST NEED TO BE CHARACTERIZED AS THE ATTRIBUTES OF LONGEVITY FECUNDITY AND MORTALITY RATES ARE THE KEY DETERMINANTS OF AN INVADERS STATUS WITHIN THE ECOLOGICAL CONTINUUM REPRESENTING THE INVASION PROCESS AND EXTENDING ACROSS THE ARC FROM IMMIGRATION TO NATURALIZATION &URTHERMORE WHEN IT DOES HAPPEN CLASSIlCATION SHOULD OCCUR AT A DElNED TEMPORAL OR SPATIAL SCALE AS POPULATIONS OF SPECIES WILL APPEAR TO BE IN DIFFERENT PLACES ON THE CONTINUUM DEPENDING ON THE SCALE OF THE ASSESSMENT 4HE @BLINKING LIGHTS METAPHOR OF METAPOPULATION EXTINCTION AND COLONIZATIONS MAY BE USEFUL IN THE INVASIONS PROCESS TOO ! METAPOPULATION DESCRIBES A @POPU LATION CONSISTING OF A NUMBER OF LOCAL POPULATIONS IN THE SAME SENSE IN WHICH
(4 -URPHY ET AL
A LOCAL POPULATION IS A POPULATION CONSISTING OF MANY INDIVIDUALS !CCORDING TO THE ,EVINS CLASSICAL METAPOPULATION CONCEPT ALL LOCAL POPULATIONS HAVE A SUBSTANTIAL PROBABILITY OF EXTINCTION AND THEREFORE LONG TERM PERSISTENCE OF A SPECIES IS REGULATED AT THE REGIONAL OR METAPOPULATION LEVEL (ANSKI -ETAPOPULATION THEORY PROPOSES THAT THE REGIONAL POPULATION PERSISTS AS THE RESULT OF A BALANCE BETWEEN LOCAL POPULATION EXTINCTION IN PATCHES AND PATCH MIGRATIONS LEADING TO COLONIZATION 4HE KEY TO POPULATION PROCESSES LIES IN UNDERSTANDING THE SHIFTING MOSAIC OF PATCH OCCUPANCY AS OPPOSED TO DETAILS OF WITHIN PATCH EVENTS +AREIVA AND 7ENNERGREN &RECKLETON AND 7ATKINSON DESCRIBE OTHER REGIONAL ENSEMBLES OF PLANT POPULATION DYNAMICS AT LARGE SCALES )N THE FOLLOWING WE VISUALIZE 2ICHARDSON ET ALS CATEGORIES OF ALIEN SPECIES PLUS AN ADDITIONAL CATEGORY @SPREADING POPULATIONS BETWEEN NATURALIZED AND INVASIVE STAGES AND THE BARRIERS THEY SURMOUNT THROUGH THE INVASIONS PROCESS IN A POPULATION BASED CONTEXT 4HE FOUR CATEGORIES OF POPULATIONS CAN BE DESCRIBED IN TERMS OF THE METAPOPULATION PARAMETERS OF EXTINCTION AND COLONIZATION AS SHOWN IN 4ABLE 4ABLE -ETAPOPULATION CONDITIONS FOR POPULATION THROUGH THE INVASION PROCESS E EXTINCTION C COLONIZATION #ATEGORY3TAGE -ETAPOPULATION DYNAMICS #ASUAL E C .ATURALIZED E C 3PREADING E C )NVASIVE E C
#ASUAL
!DVENTIVE INDIVIDUALS APPEAR AND MAY BE INTRODUCED ON MULTIPLE OCCASIONS BEFORE A POPULATION @TAKES OR ESTABLISHES 4HE RECURRENT BUT EPHEMERAL INTRODUC TIONS GENERATE THE STATUS OF @CASUAL i.e., the iNTRODUCED SPECIES IS AT THE EARLY STAGE OF BEING AN INTERMITTENT MEMBER OF THE NEW mORA 4HE POPULATION MAY @BLINK OFF AND ON AGAIN AS IT FAILS TO SUSTAIN ITSELF OVER LONGER PERIODS BUT OCCASIONALLY PERSISTS OR BECOMES RE ESTABLISHED BECAUSE OF REPEATED INTRODUCTIONS FROM SOURCE POPULATIONS OUTSIDE THE ADVENTIVE AREA 4HESE POPULATIONS ESTABLISH BECAUSE SOME INDIVIDUALS OF THE SPECIES HAVE SURMOUNTED A MAJOR GEOGRAPHICAL BARRIER LONG DISTANCE BARRIER ! OF &IG .ATURALIZED
%VENTUALLY A CASUAL POPULATION MAY BLINK ON AND REMAIN ON FOR AN EXTENDED PERIOD 4HE lRST LOCAL POPULATION MEETS CRITERIA SET FOR STEADY STATE MAINTENANCE
)NVASIVENESS IN EXOTIC PLANTS
A SUSTAINABLE POPULATION 4HIS CORRESPONDS TO THE CONCEPT IN 0OPULATION 6IABILITY !NALYSIS OF AN -60 MINIMUM VIABLE POPULATION THE NUMBER OF INDIVIDUALS THAT ENSURES A POPULATIONS PERSISTENCE ;3HAFFER = )N THE VOCABULARY OF INVA SIONS THIS CAN BE TERMED @NATURALIZATION !T THAT POINT THE FOUNDER POPULATION HAS BECOME RESILIENT TO ENVIRONMENTAL AND DEMOGRAPHIC STOCHASTICITIES AND THE PROBABILITY OF CHANCE EXTINCTION HAS DECREASED $EMOGRAPHIC ATTRIBUTES OF THIS POPULATION INCLUDE A SIGNIlCANT BREEDING POPULATION FOR PLANTS AN ESTABLISHED SEED BANK IS A BENElT SO THAT YEAR TO YEAR VARIATIONS IN FECUNDITY ARE NOT DIRECTLY EVIDENT IN RECRUITMENT )N ADDITION INDIVIDUALS LIKELY DEVELOP FACILITATIVE ASSOCIA TIONS SUCH AS POLLINATION SEED DISPERSAL AND PERHAPS MYCORRHIZAL ASSOCIATIONS )NDIVIDUALS IN THESE POPULATIONS HAVE OVERCOME BARRIERS TO SURVIVAL IN ENVIRON MENTAL CONDITIONS BARRIER " IN &IG AT THE SITE OF INTRODUCTION SOIL AND CLIMATE FOR EXAMPLE AS WELL AS BARRIERS TO THE PREVENTION OF CONSISTENT AND LONG TERM GENERATION OF RECRUITS TO THE POPULATION MATING SYSTEM COMPATIBILITY FERTILITY FECUNDITY AND OTHER REPRODUCTIVE BARRIERS BARRIER # IN &IG 3PREADING METAPOPULATION OR OTHER REGIONAL ENTITY
@3PREADING POPULATIONS CAN BE VISUALIZED AS INCLUDING A POPULATION WITH A LIGHT PERMANENTLY ON THE NATURALIZED POPULATION SURROUNDED BY ADJACENT POPULA TIONS THAT MAY BLINK ON AND OFF LIKE CASUAL POPULATIONS BUT THE NATURALIZED POPULATION IS THE SOURCE RATHER THAN THE SOURCE BEING FROM BEYOND THE ADVENTIVE AREA 4HIS STAGE INVOLVES THE RELATIVELY SHORT DISTANCE DISPERSAL OF PROPAGULES TO ADJACENT SUITABLE SITES THEREBY OVERCOMING BARRIER $ IN &IG 3PREAD FROM THE INITIAL NATURALIZED POPULATION TO OTHER SUITABLE SITES REQUIRES SUFlCIENT DISPERSAL BY PROPAGULES ANDOR SUFlCIENT LANDSCAPE CONNECTIVITY BETWEEN SUITABLE SITES SUCH THAT LOCAL EXTINCTIONS MAY BE REPLACED BY RECOLONIZATIONS FROM NEARBY NATURAL IZED POPULATIONS IF NOT FROM THEIR OWN SEED BANK 4HE DISCOVERY OF CONTIGUOUS POPULATIONS OF DIFFERING SIZE AROUND AN OLDER ONE IS WELL DOCUMENTED IN THE HER BARIUM COLLECTIONS USED TO DEVELOP THE DISTRIBUTION MAPS OF THE SPECIES STUDIED IN THE "IOLOGY OF #ANADIAN 7EEDS SERIES 4HIS OCCURS WHEN INITIAL LONG DISTANCE DISPERSAL EG INTO A NEW PART OF THE PROVINCE OR WATERSHED IS FOLLOWED BY SUB SEQUENT OUTBREAKS OF POPULATIONS IN THE GENERAL AREA AS SUITABLE HABITAT BECOMES OCCUPIED 4HIS CORRESPONDS TO THE STAGE WE TERM LANDSCAPE @SPREADING &IG 4HESE POPULATIONS HAVE OVERCOME BARRIERS TO RELATIVELY SHORT DISTANCE DISPERSAL IN THE IMMEDIATE AREA BARRIER $ IN &IG AND ENVIRONMENTAL CONDITIONS AT ADJA CENT HUMAN MODIlED AREAS BARRIER % IN &IG ASSUMING AVAILABILITY OF SUITABLE DISTURBED SITES 3PREADING POPULATIONS ARE SELF SUSTAINING WITHOUT INPUT FROM SOURCES OUTSIDE THE ADVENTIVE REGION BUT MAY BE RECOLONIZED FROM NEARBY SITES IF LOCAL EXTINCTION OCCURS
(4 -URPHY ET AL
)NVASIVE METAPOPULATION OR OTHER REGIONAL ENTITY
4HE IMAGE OF THE SPREADING POPULATIONS AT LEAST ONE PERMANENTLY @ON LIGHT SUR ROUNDED BY NUMEROUS BLINKING LIGHTS IS REPEATED IN MANY PARTS OF THE ADVENTIVE RANGE 3PREADING POPULATIONS BECOME THEMSELVES THE PRIMARY SOURCE FOR NEW CASUAL NATURALIZED AND SPREADING POPULATIONS THOUGH SOME MAY ALSO CONTINUE TO BECOME ESTABLISHED THROUGH SEPARATE DISPERSAL EVENTS FROM THE ORIGINAL SOURCE REGION 4HESE POPULATIONS HAVE OVERCOME BARRIERS TO LONG DISTANCE DISPERSAL IN THE ADVENTIVE ENVIRONMENT 3OME RESEARCHERS ALSO CONSIDER THAT ABIOTIC AND BIOTIC BARRIERS TO ESTABLISHMENT IN NATURAL HABITATS NEEDS TO BE OVERCOME AT THIS STAGE OF THE INVASIONS PROCESS OTH ERS CONSIDER THAT THIS BARRIER MAY BE OVERCOME BY NATURALIZED POPULATIONS SEE 2ICHARDSON ET AL ;A= &ROM AN ECOLOGICAL STANDPOINT THE MORE IMPORTANT DEVELOPMENT OCCURS WHERE INVASIVE POPULATIONS SPREAD TO NATURAL ENVIRONMENTS (OWEVER FROM A MANAGEMENT AND ECONOMIC POINT OF VIEW INVASIVE POPULATIONS THAT ONLY OCCUR IN FOR EXAMPLE AGRICULTURAL SETTINGS ARE EQUALLY AS IMPORTANT 4HUS METAPOPULATIONS OF THE INTRODUCED SPECIES SHOULD NOT HAVE TO OCCUR IN NATU RAL HABITAT TO BE REGARDED AS INVASIVE 7E DO THINK IT IS USEFUL IN OUR FRAMEWORK HOWEVER TO DISTINGUISH ECOLOGICALLY INVASIVE POPULATIONS FROM INVASIVE POPULA TIONS IN DISTURBED HABITATS )N TERMS OF THE MAJOR ECOLOGICAL IMPACTS OF INVASIVE SPECIES ON BIODIVERSITY IT MAY BE IMPORTANT TO UNDERSTAND HOW SPECIES THAT ARE CAPABLE OF INVADING NATURAL HABITATS DIFFER FROM THOSE THAT REMAIN IN DISTURBED OR AGRICULTURAL COMMUNITIES AND HAVE PRIMARILY ECONOMIC IMPACTS
0/05,!4)/. 6)!"),)49 !.!,93)3 06! 4/ 42!#+ 0/05,!4)/.3 /& ./. .!4)6% 30%#)%3 0OPULATION VIABILITY ANALYSIS HAS BEEN USED TRADITIONALLY TO ESTIMATE THE RISK OR TIME TO EXTINCTION FOR AN ENDANGERED SPECIES AND COULD EQUALLY BE APPLIED TO PREDICT THE POTENTIAL FOR ESTABLISHMENT GROWTH OR PERSISTENCE IN NON NATIVE SPECIES 06! EVALUATES THE LIKELIHOOD THAT A GIVEN SPECIES WILL PERSIST FOR A GIVEN TIME INTO THE FUTURE 4HE GOAL OF 06! IS OFTEN CONSERVATION OR MANAGE MENT OF RARE OR ENDANGERED SPECIES THIS INCLUDES IDENTIFYING THREATS TO SPECIES PERSISTENCE AND APPLYING THEORETICAL CONCEPTS OF POPULATION AND METAPOPULA TION ECOLOGY TO IMPROVE SURVIVORSHIP SEE EG "ROOK ET AL !K AKAYA AND 3JÚGREN 'ULVE -ORRIS AND $OAK SUMMARIZED THREE GENERAL LEVELS OF COMPLEXITY AVAIL ABLE FOR 06! THAT INCORPORATE MULTI SITE DATA !LL RELY ON USE OF MATRICES TO CHARACTERIZE POPULATION STATUS OVER TIME 4HE SIMPLEST APPROACH IS TO TRACK THE NUMBER OF POPULATIONS SENSU METAPOPULATION AND OTHER REGIONAL ENTITIES THAT IS TO ESTIMATE THE PRESENCE OR ABSENCE OF POPULATIONS IN LOCAL SITES OF SUITABLE HABITAT )T IS RELATIVELY EASY TO ENUMERATE SITES WHERE AN INTRODUCED SPECIES IS REPORTED ! SECOND COUNT BASED CENSUS APPROACH IS A MORE USEFUL FORM OF 06!
)NVASIVENESS IN EXOTIC PLANTS
BUT ESTIMATES OF MIGRATION RATES AND MEAN VARIANCE AND COVARIANCE IN POPULA TION GROWTH RATES ARE NECESSARY TO DEVELOP SUCH MODELS -OST USEFUL OF ALL BUT ALSO MORE DATA DEMANDING IS A 06! MODEL INCLUDING DEMOGRAPHIC ANALYSIS AT EACH SITE BASED ON FOR EXAMPLE KNOWLEDGE OF BIRTH AND DEATH RATES AND RATES OF INDIVIDUAL TRANSITIONS THROUGH SIZE OR AGE CLASSES THAT GOVERN FECUNDITY RATES 3UCH INFORMATION WOULD ALLOW CONSTRUCTION OF A MULTI SITE MATRIX MODEL WHICH COULD MORE ACCURATELY PREDICT THE FATE OF THE INTRODUCED SPECIES 7HILE COUNT BASED AND DEMOGRAPHY BASED 06! PROVIDE MORE ROBUST RESULTS OUR ANALYSIS HERE HAS SHOWN THAT THIS LEVEL OF SPECIES SPECIlC INFORMATION IS OFTEN UNAVAILABLE AND MAY BE INSUFlCIENT TO ESTIMATE THE PARAMETERS OF THE MODEL (OWEVER TRACKING PRESENCE OR ABSENCE OF A NON NATIVE SPECIES IN SUITABLE HABI TAT IS SUFlCIENT TO ESTIMATE THE PARAMETERS OF THE SIMPLEST 06! MODELS 0ATCH /CCUPANCY -ODELS 0/- !K AKAYA AND 3JÚGREN 'ULVE 3UCH MODELS AS WITH ALL @PATCH MODELS OF METAPOPULATION DYNAMICS (ANSKI ASSUME THAT LOCAL DYNAMICS OCCUR RAPIDLY IN COMPARISON TO METAPOPULATION DYNAMICS IE CHANGES IN POPULATION SIZES OF LOCAL POPULATIONS TAKE PLACE MORE RAPIDLY THAN COLONIZATIONS OF CURRENTLY EMPTY HABITAT PATCHES 7ITH THIS ASSUMPTION IT IS REASONABLE TO FOCUS ENTIRELY ON THE PRESENCE OR ABSENCE OF THE SPECIES OF INTEREST IN THE AVAILABLE HABITAT PATCHES 'IVEN THIS THE PERSISTENCE OF THE SPECIES CAN BE MODELED BY EXAMINING THE PROBABILITY OF EXTINCTION OF AN OCCUPIED PATCH AND THE PROBABILITY OF COLONIZATION OF AN EMPTY PATCH 3IMPLE 0/-S ARE BASED ON CLASSICAL METAPOPULATION MODELS SENSU ,EVINS AND THUS TREAT HABITAT PATCHES AS IF THEY WERE IDENTICAL AND MOVEMENT BETWEEN ALL PAIRS OF PATCHES IS EQUALLY LIKELY (ANSKI AND 'YLLENBERG (ANSKI 2ECENTLY MORE DATA INTENSIVE AND SPATIALLY EXPLICIT MODELS HAVE BEEN CREATED SEE EG (ANSKI -OILANEN 7E CONSTRUCTED A SIMPLE 0/- BASED SOFTWARE MODULE THAT DEMONSTRATES THE USEFULNESS OF 06! FOR MODELING CONTRASTING LEVELS OF INVASIVENESS IN EXOTIC SPECIES 4HE MODEL USES TWO INPUTS THE PROBABILITY THAT AN OCCUPIED PATCH WILL BECOME VACANT DUE TO LOCAL EXTINCTION AND THE PROBABILITY OF AN UNOCCUPIED PATCH BECOMING OCCUPIED BY MIGRANTS FROM AN OCCUPIED PATCH IN EACH TIME STEP OR ITERATION 3UCH VALUES MAY BE ESTIMATED FROM A SERIES OF @SNAPSHOTS OF THE PRESENCE OR ABSENCE OF A SPECIES THROUGH TIME AND WITH PARTICULAR LIFE HISTORY CHARACTERISTICS INmUENCING COLONIZATION ABILITY 'OTELLI AND 4AYLOR A B ESTIMATED SUCH PROBABILITIES FOR lSH ASSEMBLAGES USING THE PROBABILITY OF COLONIZATION AS THE NUMBER OF UNOCCUPIED SITES IN YEAR T THAT WERE OCCUPIED IN YEAR T DIVIDED BY THE NUMBER OF SITES THAT WERE CENSUSED IN YEAR T 3IMILARLY THE PROBABILITY OF EXTINCTION CAN BE ESTIMATED AS THE NUMBER OF SITES OCCUPIED IN YEAR T THAT WERE UNOCCUPIED IN YEAR T DIVIDED BY THE NUMBER OF SITES OCCUPIED IN YEAR T 5SING A COMBINATION OF PROBABILITY LEVELS FOR EXTINCTION HIGH MEDIUM AND LOW 0EXT VALUES OF AND RESPECTIVELY AND THREE FOR THE PROB ABILITY OF COLONIZATION HIGH MEDIUM AND LOW 0COL VALUES OF AND RESPECTIVELY CLEAR CONSISTENT OUTCOMES EMERGED %ACH WAS PLOTTED FOR RAN DOM ITERATIONS TO GENERATE PLOTS THAT CORRESPOND TO THE FOUR CATEGORIES OF NON NATIVE
(4 -URPHY ET AL
POPULATIONS OF SPECIES 4HE VALUES USED TO PARAMETERIZE THIS MODEL WERE BASED ON A RANGE OF EXTINCTION AND COLONIZATION ESTIMATES GIVEN FOR A VARIETY OF ORGANISMS SEE EG 7AHLBERG ET AL -OILANEN ET AL -OILANEN 'OTELLI AND 4AYLOR A B 3IMULATIONS WERE RUN IN A RANDOM LANDSCAPE WITH AVAIL ABLE PATCHES INITIALLY WITH A SINGLE PATCH OCCUPIED REPRESENTING AN INTRODUCTION )N EACH CASE THERE WERE ITERATIONS IE SEPARATE INTRODUCTIONS 4ABLE SUMMARIZES THE SIMULATION OUTPUT AND &IG DEPICTS THE CHANGE IN PROPORTION OF PATCHES OCCUPIED OVER TIME FOR EACH SCENARIO 4HE MODELS PROVIDE AN EFFECTIVE FRAMEWORK FOR GENERALIZATION WE CAN STATE THAT WHERE 0COL ) 0EXT THE SPECIES IS CASUAL TO NATURALIZED 7HERE 0COL 0EXT THE SPECIES IS SPREADING IT IS ONLY WHERE 0COL 0EXT THAT THE SPECIES IS LIKELY TO BECOME INVASIVE 4HIS GEN ERALIZATION SUGGESTS THAT MOST INTRODUCTIONS SHOULD RESULT IN CASUAL OR NATURALIZED POPULATIONS OF SPECIES OF THE OUTCOMES WITH ONLY BEING SPREADING AND INVASIVE )NDEPENDENT OF 0COL IF 0EXT IS HIGH THEN THE SPECIES IS MERELY CASUAL %VEN IF THE SPECIES HAS LOW 0COL AND A MEDIUM 0EXT IT WILL OCCUR AS A CASUAL 0OPULATIONS MAY BLINK OFF AND ON AGAIN BUT FAIL TO SUSTAIN THEMSELVES OVER LONGER PERIODS ONLY OCCASIONALLY PERSISTING 3IMULATIONS SHOWED THAT ON AVERAGE WITH LOW COLONIZA TION RATE AND MEDIUM EXTINCTION RATE ALL POPULATIONS BLINKED OFF AFTER ITERA TIONS HOWEVER TWO OUTLIER POPULATIONS PERSISTED FOR THE FULL RUNS .ATURALIZED SPECIES WERE THOSE WITH AN EQUIVALENT EQUALLY WEAK OR STRONG 0COL AND 0EXT THAT IS HAVING LOW 0COL AND 0EXT LOW LOW OR MEDIUM 0COL AND 0EXT MEDIUM MEDIUM 7HILE MOST OF THE INTRODUCTIONS ENDED IN EXTINCTION LOW LOW AND MEDIUM MEDIUM PERSISTED FOR ALL ITERATIONS 3PREADING SPECIES WOULD HAVE A PROPORTIONATELY GREATER PROBABILITY OF 0COL AND 0EXT HIGH MEDIUM OR MEDIUM LOW )NVASIVE SPECIES ARE DISTINGUISHED BY HAVING A HIGH 0COL AND A LOW 0EXT 7E NOTE THESE EXEMPLARS REPRESENT AN ECOLOGICAL CON TINUUM FROM CASUAL TO INVASIVE )T IS INTERESTING THAT THE CURVES HAVE DISTINCTIVE SHAPES &OR EXAMPLE ALTHOUGH SPREADING SPECIES MAY REACH COMPARABLE LEVELS OF OCCUPANCY AS INVASIVES SEE &IGS B AND F SPREADING SPECIES SHOW A TIME LAG ASSOCIATED WITH PROLONGED LOW SITE OCCUPANCY RESULTING IN A GREATER RISK OF hINVA SION FAILUREv !NY INTRODUCTION HAD THE POSSIBILITY OF FAILURE %VEN THE INVASIVE SPECIES IN OUR SIMULATION FAILED TO ESTABLISH SIX PERCENT OF THE TIME FOLLOWING INTRODUCTION )NDEED AS NOTED EARLIER THE LITERATURE SUGGESTS THAT MOST INTRODUCTIONS FAIL TO ESTABLISH AND EVEN THOSE THAT SUCCESSFULLY ESTABLISH AND PERSIST MAY HAVE HAD MANY PREVIOUS FAILED ATTEMPTS )T IS IMPORTANT TO NOTE THAT EVEN WHEN POPULATIONS HAVE BECOME INVASIVE THE PROCESS IS NOT STATIC 2ATHER POPULATIONS MAY STILL BE VULNERABLE TO DEMOGRAPHIC AND ENVIRONMENTAL FACTORS ACTING TO INCREASE EXTINC TION AND DECREASE COLONIZATION RATES 7E HAVE OBSERVED DRAMATIC CHANGES OVER THE PAST lFTEEN YEARS IN SOUTHWESTERN /NTARIO POPULATIONS OF PURPLE LOOSESTRIFE ,YTHRUM SALICARIA SEE TOO -AL ET AL &OLLOWING A SURGE OF COLONIZATIONS OVER THE PAST DECADES AND ABUNDANT LARGE LOCAL POPULATIONS MANY OF THESE HAVE GONE EXTINCT OR BECOME EXTREMELY DIMINISHED IN RECENT YEARS
-EAN ¢ SE PATCH OCCUPANCY
-EAN ¢ SE TIME TO PATCHES GOING EXTINCT ITERATIONS
HIGH
%XTINCTION PROBABILITY
0ROPORTION OF INTRODUCTIONS ENDING IN EXTINCTION
MED
HIGH
HIGH
D
A
G
HIGH
LOW
CASUAL
MED
LOW
H
MED
MED
E
LOW
LOW
I
NATURALIZED
MED
HIGH
B
LOW
MED
F
SPREADING
2ESULTS OF POPULATION VIABILITY ANALYSIS FOR POPULATIONS WITH DIFFERING EXTINCTION AND COLONIZATION PROBABILITIES
2EFERENCE &IG #OLONIZATION PROBABILITY
4ABLE
LOW
HIGH
C
INVASIVE
)NVASIVENESS IN EXOTIC PLANTS
(4 -URPHY ET AL
&IG 2ESULTS OF 0OPULATION 6IABILITY !NALYSIS FOR POPULATIONS WITH DIFFERING EXTINCTION AND COLONIZATION RATES SEE 4ABLE A CASUAL B SPREADING C INVASIVE D CASUAL E NATURALIZED F SPREADING G CASUAL H CASUAL I NATURALIZED
4HE POPULATION BASED FRAMEWORK WE HAVE DESCRIBED IS INFORMED BY THE MODI lED SCHEME IN 4ABLE WHERE THE ENVIRONMENTAL AND LIFE HISTORY PARAMETERS THAT ARE CASE DEPENDENT ARE NOT THE FOCUS AS IN 2ICHARDSON ET AL ;A= BUT RATHER THE lLTER REGULATING THE CHANGING STATUS OF POPULATIONS OF AN INTRODUCED SPECIES 7E ACKNOWLEDGE IT IS DIFlCULT TO BUILD OPERATIONAL DElNITIONS FOR REGIONAL LISTS OF ALIEN mORA WITH THE LIMITED LIFE HISTORY DATA ON RECORD AND SUGGEST THAT IT IS TIME FOR RESEARCH IN INVASIONS ECOLOGY TO MOVE BEYOND COMPARATIVE ANALYSES OF REGIONAL
)NVASIVENESS IN EXOTIC PLANTS
!PPENDIX 3PECIES INCLUDED IN THE DATASET WITH THEIR ASSOCIATED "IOLOGY OF #ANADIAN 7EEDS "#7 SERIES NUMBER AND REFERENCE "#7 &AMILY 3PECIES 2EFERENCE SERIES !MARANTHACEAE !MARANTHUS POWELLII -ULLIGAN !MARANTHACEAE !MARANTHUS RETROmEXUS -ULLIGAN !PIACEAE !NTHRISCUS SYLVESTRIS $ARBYSHIRE ET AL !PIACEAE $AUCUS CAROTA -ULLIGAN !STERACEAE !CHILLEA MILLEFOLIUM -ULLIGAN SSP MILLEFOLIUM !STERACEAE !CROPTILON REPENS -ULLIGAN !STERACEAE !RCTIUM LAPPA -ULLIGAN !STERACEAE !RCTIUM MINUS -ULLIGAN !STERACEAE !RTEMISIA ABSINTHIUM #AVERS !STERACEAE !RTEMISIA VULGARIS "ARNEY AND $I4OMMASO !STERACEAE #ARDUUS ACANTHOIDES #AVERS !STERACEAE #ARDUUS NUTANS #AVERS !STERACEAE #ENTAUREA DIFFUSA -ULLIGAN !STERACEAE #ENTAUREA MACULOSA -ULLIGAN !STERACEAE #IRSIUM ARVENSE -ULLIGAN !STERACEAE #REPIS TECTORUM -ULLIGAN !STERACEAE 'ALINSOGA PARVImORA -ULLIGAN !STERACEAE 'ALINSOGA QUADRIRADIATA -ULLIGAN !STERACEAE (ELIANTHUS TUBEROSUS #AVERS !STERACEAE (YPOCHAERIS RADICATA -ULLIGAN !STERACEAE ,ACTUCA SERRIOLA 7EAVER AND $OWNS !STERACEAE -ATRICARIA PERFORATA #AVERS !STERACEAE 3ENECIO JACOBAEA #AVERS !STERACEAE 3ENECIO VULGARIS 2OBINSON ET AL !STERACEAE 3ONCHUS ARVENSIS #AVERS !STERACEAE 3ONCHUS ASPER #AVERS !STERACEAE 3ONCHUS OLERACEUS #AVERS !STERACEAE 4ARAXACUM OFlCINALE 3TEWART 7ADE ET AL !STERACEAE 4RAGOPOGON DUBIUS #LEMENTS ET AL !STERACEAE 4RAGOPOGON PORRIFOLIUS #LEMENTS ET AL !STERACEAE 4RAGOPOGON PRATENSIS #LEMENTS ET AL "ORAGINACEAE #YNOGLOSSUM OFlCINALE #AVERS "ORAGINACEAE %CHIUM VULGARE +LEMOW ET AL "RASSICACEAE !LLIARIA PETIOLATA -ULLIGAN "RASSICACEAE "ARBAREA VULGARIS #AVERS "RASSICACEAE #ARDARIA DRABA -ULLIGAN
!PPENDIX #ONTINUED "#7 &AMILY SERIES "RASSICACEAE "RASSICACEAE "RASSICACEAE "RASSICACEAE "RASSICACEAE #ANNABACEAE #ARYOPHYLLACEAE #ARYOPHYLLACEAE #ARYOPHYLLACEAE #ARYOPHYLLACEAE #HENOPODIACEAE #LUSIACEAE #ONVOLVULACEAE $IPSACACEAE %UPHORBIACEAE %UPHORBIACEAE &ABACEAE &ABACEAE &ABACEAE &ABACEAE &ABACEAE &ABACEAE &ABACEAE &ABACEAE &ABACEAE (ALORAGACEAE ,AMIACEAE ,YTHRACEAE -ALVACEAE /XALIDACEAE 0LANTAGINACEAE 0LANTAGINACEAE 0OACEAE 0OACEAE 0OACEAE 0OACEAE
(4 -URPHY ET AL
3PECIES
2EFERENCE
$ESCURAINIA SOPHIA %RUCASTRUM GALLICUM .ESLIA PANICULATA 3INAPIS ARVENSIS 4HLASPI ARVENSE #ANNABIS SATIVA 'YPSOPHILA PANICULATA 3ILENE LATIFOLIA SSP ALBA 3ILENE NOCTImORA 3TELLARIA MEDIA #HENOPODIUM ALBUM (YPERICUM PERFORATUM #ONVOLVULUS ARVENSIS $IPSACUS FULLONUM SSP SYLVESTRIS %UPHORBIA CYPARISSIAS %UPHORBIA ESULA ,OTUS CORNICULATUS -EDICAGO LUPULINA -ELILOTUS ALBA -ELILOTUS OFlCINALIS 4RIFOLIUM REPENS 6ICIA CRACCA 6ICIA SATIVA 6ICIA TETRASPERMA 6ICIA VILLOSA -YRIOPHYLLUM SPICATUM 'ALEOPSIS TETRAHIT ,YTHRUM SALICARIA !BUTILON THEOPHRASTI /XALIS CORNICULATA 0LANTAGO LANCEOLATA 0LANTAGO MAJOR !PERA SPICA VENTI !VENA FATUA "ROMUS TECTORUM %CHINOCHLOA CRUSGALLI
-ULLIGAN 7ARWICK AND 7ALL &RANCIS AND 7ARWICK -ULLIGAN 7ARWICK ET AL -ULLIGAN 7ARWICK ET AL 3MALL AND #AVERS -ULLIGAN -ULLIGAN -ULLIGAN -ULLIGAN -ULLIGAN #AVERS -ULLIGAN -ULLIGAN #AVERS -ULLIGAN -ULLIGAN -ULLIGAN -ULLIGAN -ULLIGAN -ULLIGAN #AVERS #AVERS #AVERS #AVERS -ULLIGAN #AVERS #AVERS #AVERS #AVERS -ULLIGAN -ULLIGAN #AVERS -ULLIGAN #AVERS #AVERS
)NVASIVENESS IN EXOTIC PLANTS
A
0OACEAE 0OACEAE 0OACEAE 0OACEAE 0OACEAE 0OACEAE 0OLYGONACEAE 0OLYGONACEAE 0ORTULACACEAE 0OTAMOGETONACEAE 2ANUNCULACEAE 2OSACEAE 2OSACEAE 2UBIACEAE 2UBIACEAE 3CROPHULARIACEAE 3CROPHULARIACEAE 3CROPHULARIACEAE 3OLANACEAE 3OLANACEAE 3OLANACEAE 3OLANACEAE 6IOLACEAE
(OLCUS LANATUS (ORDEUM JUBATUM 0OA ANNUA 3ETARIA VERTICILLATA 3ETARIA VIRIDIS 3ORGHUM HALEPENSE &AGOPYRUM TATARICUM 0OLYGONUM CONVOLVULUS 0ORTULACA OLERACEA 0OTAMOGETON CRISPUS 2ANUNCULUS REPENS 0OTENTILLA ARGENTEA 0OTENTILLA RECTA 'ALIUM MOLLUGO 'ALIUM SPURIUM ,INARIA DALMATICA ,INARIA VULGARIS 6ERBASCUM THAPSUS $ATURA STRAMONIUM 3OLANUM CAROLINENSE 3OLANUM NIGRUM 3OLANUM ROSTRATUM 6IOLA ARVENSIS
#AVERS -ULLIGAN -ULLIGAN -ULLIGAN #AVERS -ULLIGAN #AVERS -ULLIGAN -ULLIGAN #AVERS #AVERS -ULLIGAN -ULLIGAN -ERSEREAU AND $I4OMMASO #AVERS 6UJNOVIC AND 7EIN 3ANER ET AL -ULLIGAN #AVERS #AVERS #AVERS #AVERS #AVERS
mORA DATASETS IN ORDER TO DEVELOP GENERAL PRINCIPLES THAT WILL ALLOW CARRYING OUT MORE ACCURATE RISK ASSESSMENT OF CASUAL INTRODUCED POPULATIONS OF SPECIES BEFORE THEY NATURALIZE AND SPREAD TO BECOME SERIOUS AND COSTLY INVASIVE POPULATIONS
!#+./7,%$'-%.43 (4- WAS SUPPORTED BY 3(!2#.%4 *6$7 *,$ AND ,,$ ARE SUPPORTED BY .ATURAL 3CIENCES AND %NGINEERING 2ESEARCH #OUNCIL OF #ANADA 7E THANK 2OB #OLAUTTI AN ANONYMOUS REVIEWER AND THE EDITORS FOR COMMENTS THAT GREATLY IMPROVED THE MANUSCRIPT
(4 -URPHY ET AL
2%&%2%.#%3 !K AKAYA ( 2 AND 0 3JÚGREN 'ULVE 0OPULATION VIABILITY ANALYSIS IN CONSERVATION PLANNING !N OVERVIEW %COLOGICAL "ULLETIN !NDERSON 0 + ! ! #UNNINGHAM . ' 0ATEL & * -ORALES 0 2 %PSTEIN AND 0 $ASZAK %MERGING INFECTIOUS DISEASES OF PLANTS PATHOGEN POLLUTION CLIMATE CHANGE AND AGROTECHNOLOGY DRIVERS 4RENDS IN %COLOGY AND %VOLUTION "AKER ( ' #HARACTERISTICS AND MODE OF ORIGIN OF WEEDS PP IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE GENETICS OF COLONIZING SPECIES !CADEMIC 0RESS .EW 9ORK .9 "AKER ( ' 4HE EVOLUTION OF WEEDS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "ARNEY * . AND ! $I4OMMASO 4HE "IOLOGY OF #ANADIAN 7EEDS !RTEMISIA VULGARIS , #ANADIAN *OURNAL OF 0LANT 3CIENCE "LACKBURN 4 - AND 2 0 $UNCAN A $ETERMINANTS OF ESTABLISHMENT SUCCESS IN INTRO DUCED BIRDS .ATURE "LACKBURN 4 - AND 2 0 $UNCAN B %STABLISHMENT PATTERNS OF EXOTIC BIRDS ARE CONSTRAINED BY NON RANDOM PATTERNS IN INTRODUCTION *OURNAL OF "IOGEOGRAPHY "ROOK " 7 * * /'RADY ! 0 #HAPMAN - ! "URGMAN ( 2 !K AKAYA AND 2 &RANKHAM 0REDICTIVE ACCURACY OF POPULATION VIABILITY ANALYSIS IN CONSERVATION BIOLOGY .ATURE "RUNO * & * * 3TACHOWICZ AND - $ "ERTNESS )NCLUSION OF FACILITATION INTO ECOLOGI CAL THEORY 4RENDS IN %COLOGY AND %VOLUTION #ADOTTE - 7 AND * ,OVETT $OUST %COLOGICAL AND TAXONOMIC DIFFERENCES BETWEEN NATIVE AND INTRODUCED PLANTS OF SOUTHWESTERN /NTARIO %COSCIENCE #ADOTTE - 7 " 2 -URRAY AND * ,OVETT $OUST %VOLUTIONARY AND ECOLOGICAL FACTORS INmU ENCING /NTARIO PLANT INVADER SUCCESS %COSCIENCE IN PRESS #ADOTTE - 7 " 2 -URRAY AND * ,OVETT $OUST %COLOGICAL PATTERNS AND BIOLOGICAL INVASIONS 5SING REGIONAL SPECIES INVENTORIES IN MACROECOLOGY "IOLOGICAL )NVASIONS #ALLAWAY 2 - AND % 4 !SCHEHOUG )NVASIVE PLANTS VERSUS THEIR NEW AND OLD NEIGHBORS ! MECHANISM FOR EXOTIC INVASION 3CIENCE #ARR ' 7 %XOTIC mORA OF 6ICTORIA AND ITS IMPACT ON INDIGENOUS BIOTA PP IN $ " &OREMAN AND . ' 7ALSH EDITORS &LORA OF 6ICTORIA )NKATA 0RESS -ELBOURNE !USTRALIA #ASE 4 * )NVASION RESISTANCE ARISES IN STRONGLY INTERACTING SPECIES RICH MODEL COMPETITION COMMUNITIES 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCE #AVERS 0 " EDITOR 4HE "IOLOGY OF #ANADIAN 7EEDS 6OL #ONTRIBUTIONS 4HE !GRICULTURAL )NSTITUTE OF #ANADA /TTAWA /. #AVERS 0 " EDITOR 4HE "IOLOGY OF #ANADIAN 7EEDS 6OL #ONTRIBUTIONS 4HE !GRICULTURAL )NSTITUTE OF #ANADA /TTAWA /.
)NVASIVENESS IN EXOTIC PLANTS
#AVERS " 0 AND 3 7ARWICK 4HE "IOLOGY OF #ANADIAN 7EEDS 2EVISED FORMAT AND INSTRUCTIONS FOR PREPARATION OF UPDATED ACCOUNTS #ANADIAN *OURNAL OF 0LANT 3CIENCE #LEMENTS $ 2 - + 5PADHYAYA AND 3 * "OS 4HE "IOLOGY OF #ANADIAN 7EEDS 4RAGOPOGON DUBIUS 3COP 4RAGOPOGON PRATENSIS , AND 4RAGOPOGON PORRIFOLIUS , #ANADIAN *OURNAL OF 0LANT 3CIENCE #OLAUTTI 2 ) AND ( * -AC)SAAC ! NEUTRAL TERMINOLOGY TO DElNE @INVASIVE SPECIES $IVERSITY AND $ISTRIBUTIONS $AEHLER # # 4HE TAXONOMIC DISTRIBUTION OF INVASIVE ANGIOSPERM PLANTS %COLOGICAL INSIGHTS AND COMPARISON TO AGRICULTURAL WEEDS "IOLOGICAL #ONSERVATION $AEHLER # # A 4WO WAYS TO BE AN INVADER BUT ONE IS MORE SUITABLE FOR ECOLOGY %3! "ULLETIN $AEHLER # # B $ARWINS NATURALIZATION HYPOTHESIS REVISITED !MERICAN .ATURALIST $ARBYSHIRE 3 * 2 (OEG AND * (AVERKORT 4HE "IOLOGY OF #ANADIAN 7EEDS !NTHRISCUS SYLVESTRIS , (OFFM #ANADIAN *OURNAL OF 0LANT 3CIENCE $ARWIN # /N THE ORIGIN OF SPECIES -URRAY ,ONDON $AVIS - ! AND + 4HOMPSON %IGHT WAYS TO BE A COLONIZER TWO WAYS TO BE AN INVAD ER ! PROPOSED NOMENCLATURE SCHEME FOR INVASION ECOLOGY %3! "ULLETIN $AVIS - ! AND + 4HOMPSON )NVASION TERMINOLOGY SHOULD ECOLOGISTS DElNE THEIR TERMS DIFFERENTLY THAN OTHERS .O NOT IF WE WANT TO BE OF ANY HELP %3! "ULLETIN $AVIS - ! AND + 4HOMPSON h.EWCOMERSv INVADE THE lELD OF INVASION ECOLOGY QUESTION THE lELDS FUTURE %3! "ULLETIN %CKERT ' # $ -ANICACCI AND 3 # ( "ARRETT 'ENETIC DRIFT AND FOUNDER EFFECT IN NATIVE VERSUS INTRODUCED POPULATIONS OF AN INVADING PLANT ,YTHRUM SALICARIA ,YTHRACEAE %VOLUTION %LTON # 3 4HE ECOLOGY OF INVASIONS BY ANIMALS AND PLANTS -ETHUEN ,ONDON &ORSYTH $ - AND 2 0 $UNCAN 0ROPAGULE SIZE AND THE RELATIVE SUCCESS OF EXOTIC UNGULATE AND BIRD INTRODUCTIONS TO .EW :EALAND 4HE !MERICAN .ATURALIST &OXCROFT , # - 2OUGET $ - 2ICHARDSON AND 3 -AC &AYDEN 2ECONSTRUCTING YEARS OF /PUNTIA STRICTA INVASION IN THE +RUGER .ATIONAL 0ARK 3OUTH !FRICA ENVI RONMENTAL DETERMINANTS AND PROPAGULE PRESSURE $IVERSITY AND $ISTRIBUTIONS &RANCIS ! AND 3 ) 7ARWICK 4HE "IOLOGY OF #ANADIAN 7EEDS .ESLIA PANICU LATA , $ESV #ANADIAN *OURNAL OF 0LANT 3CIENCE &RECKLETON 2 0 AND 7ATKINSON ! 2 ,ARGE SCALE SPATIAL DYNAMICS OF PLANTS METAPOPULATIONS REGIONAL ENSEMBLES AND PATCHY POPULATIONS *OURNAL OF %COLOGY 'LEASON ( ! 4HE NEW "RITTON AND "ROWN ILLUSTRATED mORA OF THE .ORTHEASTERN 5NITED 3TATES AND ADJACENT #ANADA (AFNER 0RESS .EW 9ORK 'LEASON ( ! AND ! #RONQUIST -ANUAL OF VASCULAR PLANTS OF NORTHEASTERN 5NITED 3TATES AND ADJACENT #ANADA 3ECOND %DITION .EW 9ORK "OTANICAL 'ARDEN .EW 9ORK .9
(4 -URPHY ET AL
'OTELLI . AND # - 4AYLOR A 4ESTING METAPOPULATION MODELS WITH STREAM lSH ASSEMBLAGES %VOLUTIONARY %COLOGY 2ESEARCH 'OTELLI . AND # - 4AYLOR B 4ESTING MACROECOLOGY MODELS WITH STREAM lSH ASSEM BLAGES %VOLUTIONARY %COLOGY 2ESEARCH (ANSKI ) 3INGLE SPECIES METAPOPULATION DYNAMICS CONCEPTS MODELS AND OBSER VATIONS "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY (ANSKI ) ! PRACTICAL MODEL OF METAPOPULATION DYNAMICS *OURNAL OF !NIMAL %COLOGY (ARROD 2 * AND 2 * 4AYLOR 2EPRODUCTION AND POLLINATION BIOLOGY OF #ENTAUREA AND !CROPTILON SPECIES WITH EMPHASIS ON # DIFFUSA .ORTHWEST 3CIENCE (IGGINS 3 ) 2 .ATHAN AND - , #AIN !RE LONG DISTANCE DISPERSAL EVENTS IN PLANTS USUALLY CAUSED BY NONSTANDARD MEANS OF DISPERSAL %COLOGY +AREIVA 0 AND 7ENNERGREN 5 #ONNECTING LANDSCAPE PATTERNS TO ECOSYSTEM AND POPULATION PROCESSES .ATURE +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY AND %VOLUTION +LEMOW + - $ 2 #LEMENTS 0 & 4HREADGILL AND 0 " #AVERS 4HE "IOLOGY OF #ANADIAN 7EEDS %CHIUM VULGARE , #ANADIAN *OURNAL OF 0LANT 3CIENCE +LIRONOMOS * . &EEDBACK WITH SOIL BIOTA CONTRIBUTES TO PLANT RARITY AND INVASIVE NESS IN COMMUNITIES .ATURE +OLAR 3 # AND $ - ,ODGE 0ROGRESS IN INVASION BIOLOGY PREDICTING INVADERS 4RENDS IN %COLOGY AND %VOLUTION +OLBE * * % % 'LOR , 2 3CHETTINO ! # ,ARA ! ,ARSON AND * " ,OSOS 'ENETIC VARIATION INCREASES DURING BIOLOGICAL INVASION BY A #UBAN LIZARD .ATURE +OWARIK ) #LONAL GROWTH IN !ILANTHUS ALTISSIMA ON A NATURAL SITE IN 7EST 6IRGINIA *OURNAL OF 6EGETATION 3CIENCE +REBS # * %COLOGY 4HE EXPERIMENTAL ANALYSIS OF DISTRIBUTION AND ABUNDANCE (ARPER 2OW .EW 9ORK .9 ,EVIN $ ! %COLOGICAL SPECIATION LESSONS FROM INVASIVE SPECIES 3YSTEMATIC "OTANY ,EVINE * - 0 " !DLER AND 3 ' 9ELENIK ! META ANALYSIS OF BIOTIC RESISTANCE TO EXOTIC PLANT INVASIONS %COLOGY ,ETTERS ,EVINS 2 3OME DEMOGRAPHIC AND GENETIC CONSEQUENCES OF ENVIRONMENTAL HETERO GENEITY FOR BIOLOGICAL CONTROL "ULLETIN OF THE %NTOMOLOGICAL 3OCIETY OF !MERICA ,ODGE $ - "IOLOGICAL INVASIONS LESSONS FOR ECOLOGY 4RENDS IN %COLOGY AND %VOLUTION ,ONSDALE - 7 'LOBAL PATTERNS OF PLANT INVASIONS AND THE CONCEPT OF INVASIBILITY %COLOGY -ACK 2 . 0REDICTING THE IDENTITY AND THE FATE OF PLANT INVADERS EMERGENT AND EMERGING APPROACHES "IOLOGICAL #ONSERVATION -ACK 2 . $ 3IMBERLOFF 7 - ,ONSDALE ( %VANS - #LOUT AND & ! "AZZAZ "IOTIC INVASIONS CAUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COLOGICAL !PPLICATIONS
)NVASIVENESS IN EXOTIC PLANTS
-AL 4 + ,OVETT $OUST * , ,OVETT $OUST AND ' ! -ULLIGAN 4HE "IOLOGY OF #ANADIAN 7EEDS ,YTHRUM SALICARIA #ANADIAN *OURNAL OF 0LANT 3CIENCE -ARON * , AND 6ILÉ - 7HEN DO HERBIVORES AFFECT PLANT INVASION %VIDENCE FOR THE NATURAL ENEMIES AND BIOTIC RESISTANCE HYPOTHESES /IKOS -ASTER , , !SSESSING THREATS AND SETTING PRIORITIES FOR CONSERVATION #ONSERVATION "IOLOGY -C.EILL * 4HE "IOLOGY OF #ANADIAN 7EEDS 3ILENE ALBA -ILLER % ( , +RAUSE #ANADIAN *OURNAL OF 0LANT 3CIENCE -ERSEREAU $ AND ! $I4OMMASO 4HE "IOLOGY OF #ANADIAN 7EEDS 'ALIUM MOLLUGO , #ANADIAN *OURNAL OF 0LANT 3CIENCE -ITCHELL # % AND ! ' 0OWER 2ELEASE OF INVASIVE PLANTS FROM FUNGAL AND VIRAL PATHOGENS .ATURE -ORRIS 7 & AND $ & $OAK 1UANTITATIVE CONSERVATION BIOLOGY THEORY AND PRACTICE OF POPULATION VIABILITY ANALYSIS 3INAUER !SSOCIATES 3UNDERLAND -! -OILANEN ! 0ATCH OCCUPANCY MODELS OF METAPOPULATION DYNAMICS %FlCIENT PARAMETER ESTIMATION USING IMPLICIT STATISTICAL INFERENCE %COLOGY -OILANEN ! 4HE EQUILIBRIUM ASSUMPTION IN ESTIMATING THE PARAMETERS OF META POPULATION MODELS *OURNAL OF !NIMAL %COLOGY -OILANEN ! ! 4 3MITH AND ) (ANSKI ,ONG TERM DYNAMICS IN A METAPOPULATION OF THE !MERICAN PIKA !MERICAN .ATURALIST -ORTON * + AND * - 6ENN ! CHECKLIST OF THE mORA OF /NTARIO – 6ASCULAR PLANTS 5NIVERSITY OF 7ATERLOO "IOLOGY 3ERIES .O 7ATERLOO /. -ULLIGAN ' ! EDITOR 4HE "IOLOGY OF #ANADIAN 7EEDS #ONTRIBUTIONS !GRICULTURE #ANADA 0UBL /TTAWA /. -ULLIGAN ' ! EDITOR 4HE "IOLOGY OF #ANADIAN 7EEDS #ONTRIBUTIONS !GRICULTURE #ANADA 0UBL /TTAWA /. -URPHY ( 4 AND * ,OVETT $OUST #ONTEXT AND CONNECTIVITY IN PLANT METAPOPULA TIONS AND LANDSCAPE MOSAICS DOES THE MATRIX MATTER /IKOS .ATURAL (ERITAGE )NFORMATION #ENTRE $ATABASE OF VASCULAR PLANTS HTTPWWW MNR GOV ON CA-.2NHICNHIC CFM .EWMASTER 3 ' ! ,EHELA - * /LDHAM 0 7 # 5HLIG AND 3 -C-URRAY /NTARIO PLANT LIST &OREST 2ESEARCH )NFORMATION 0APER .O /NTARIO &OREST 2ESEARCH )NSTITUTE 3AULT 3TE -ARIE /. .OVAK 3 * AND 2 . -ACK 'ENETIC VARIATION IN "ROMUS TECTORUM 0OACEAE COM PARISON BETWEEN NATIVE AND INTRODUCED POPULATIONS (EREDITY 0YÝEK 0 )S THERE A TAXONOMIC PATTERN TO PLANT INVASIONS /IKOS 0YÝEK 0 $ - 2ICHARDSON - 2EJMÉNEK ' , 7EBSTER - 7ILLIAMSON AND * +IRSCHNER !LIEN PLANTS IN CHECKLISTS AND mORAS TOWARDS BETTER COMMUNICATION BETWEEN TAXONOMISTS AND ECOLOGISTS 4AXON 2ABINOWITZ $ 3EVEN FORMS OF RARITY PP IN ( 3YNGE EDITOR 4HE BIOLOGICAL ASPECTS OF RARE PLANT CONSERVATION 7ILEY .EW 9ORK .9 2EINHART + / ! 0ACKER 7 ( 6AN DER 0UTTEN AND + #LAY 0LANT SOIL BIOTA INTER ACTIONS AND SPATIAL DISTRIBUTION OF BLACK CHERRY IN ITS NATIVE AND INVASIVE RANGES %COLOGY ,ETTERS
(4 -URPHY ET AL
2EJMÉNEK - ! THEORY OF SEED PLANT INVASIVENESS THE lRST SKETCH "IOLOGICAL #ONSERVATION 2EJMÉNEK - AND $ - 2ICHARDSON 7HAT ATTRIBUTES MAKE SOME PLANT SPECIES MORE INVASIVE %COLOGY 2EJMÉNEK - $ - 2ICHARDSON - ' "ARBOUR - * #RAWLEY ' & (RUSA 0 " -OYLE * - 2ANDAL $ 3IMBERLOFF AND - 7ILLIAMSON "IOLOGICAL INVASIONS POLITICS AND THE DISCONTINUITY OF THE ECOLOGICAL TERMINOLOGY %3! "ULLETIN 2ICHARDSON $ - 0 0YÝEK - 2EJMÉNEK - ' "ARBOUR & $ 0ANETTA AND # * 7EST A .ATURALIZATION AND INVASION OF ALIEN PLANTS CONCEPTS AND DElNITIONS $IVERSITY AND $ISTRIBUTIONS 2ICHARDSON $ - . !LLSOPP # - $!NTONIO 3 * -ILTON AND - 2EJMÉNEK B 0LANT INVASIONS THE ROLE OF MUTUALISMS "IOLOGICAL 2EVIEWS 2OBINSON $ % * 4 /$ONOVAN - 0 3HARMA $ * $OOHAN AND 2 &IGUEROA 4HE "IOLOGY OF #ANADIAN 7EEDS 3ENECIO VULGARIS , #ANADIAN *OURNAL OF 0LANT 3CIENCE 2OUGET - AND $ - 2ICHARDSON )NFERRING PROCESS FROM PATTERN IN PLANT INVASIONS A SEMI MECHANISTIC MODEL INCORPORATING PROPAGULE PRESSURE AND ENVIRONMENTAL FACTORS !MERICAN .ATURALIST 3ANER - ! $ 2 #LEMENTS - 2 (ALL $ * $OOHAN AND # 7 #ROMPTON 4HE "IOLOGY OF #ANADIAN 7EEDS ,INARIA VULGARIS -ILL #ANADIAN *OURNAL OF 0LANT 3CIENCE 3AX $ & AND * ( "ROWN 4HE PARADOX OF INVASION 'LOBAL %COLOGY AND "IOGEOGRAPHY 3HAFFER - , -INIMUM POPULATION SIZES FOR SPECIES CONSERVATION "IO3CIENCE 3COGGAN ( * 4HE mORA OF #ANADA .ATIONAL -USEUMS OF #ANADA /TTAWA /. 3IMBERLOFF $ AND " VON (OLLE 0OSITIVE INTERACTIONS OF NON INDIGENOUS SPECIES INVASIONAL MELTDOWN "IOLOGICAL )NVASIONS 3MALL % AND 0 " #AVERS 4HE "IOLOGY OF #ANADIAN 7EEDS #ANNABIS SATIVA , #ANADIAN *OURNAL OF 0LANT 3CIENCE 3TEWART 7ADE 3 - 3 .EUMANN , , #OLLINS AND ' * "OLAND 4HE "IOLOGY OF #ANADIAN 7EEDS 4ARAXACUM OFlCINALE ' ( 7EBER EX 7IGGERS #ANADIAN *OURNAL OF 0LANT 3CIENCE 3TOHLGREN 4 * $ "INKLEY ' 7 #HONG - ! +ALKHAN , $ 3CHELL + ! "ULL 9 /TSUKI ' .EWMAN - "ASHKIN AND 9 3ON %XOTIC PLANT SPECIES INVADE HOT SPOTS OF NATIVE PLANT DIVERSITY %COLOGICAL -ONOGRAPHS 4HOMPSON + * ' (ODGSON AND 4 # ' 2ICH .ATIVE AND ALIEN INVASIVE PLANTS MORE OF THE SAME %COGRAPHY 4ILMAN $ #OMMUNITY INVASIBILITY RECRUITMENT LIMITATION AND GRASSLAND BIODIVER SITY %COLOGY 4UTIN 4 ' 6 ( (EYWOOD . ! "URGESS $ ( 6ALENTINE 3 - 7ALTERS AND $ ! 7EBB &LORA %UROPAEA 6OL ,YCOPODIACEAE TO 0LATANACEAE #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 5+
)NVASIVENESS IN EXOTIC PLANTS
4URKINGTON 2 ! 0 " #AVERS AND % 2EMPEL 4HE "IOLOGY OF #ANADIAN 7EEDS -ELILOTUS ALBA $ESR AND - OFlCINALIS , ,AM #ANADIAN *OURNAL OF 0LANT 3CIENCE 6ANDER 7ALL 3 " AND 7 3 ,ONGLAND $IPLOCHORY ARE TWO SEED DISPERSERS BETTER THAN ONE 4RENDS IN %COLOGY AND %VOLUTION 6ITOUSEK 0 - AND , 2 7ALKER "IOLOGICAL INVASION BY -YRICA FAYA IN (AWAII 0LANT DEMOGRAPHY NITROGEN lXATION ECOSYSTEM EFFECTS %COLOGICAL -ONOGRAPHS 6ON (OLLE " ( 2 $ELCOURT AND $ 3IMBERLOFF 4HE IMPORTANCE OF BIOLOGICAL INERTIA IN PLANT COMMUNITY RESISTANCE TO INVASION *OURNAL OF 6EGETATION 3CIENCE 6UJNOVIC + AND 2 7 7EIN 4HE "IOLOGY OF #ANADIAN 7EEDS ,INARIA DAL MATICA , -ILL #ANADIAN *OURNAL OF 0LANT 3CIENCE 7AHLBERG . ! -OILANEN AND ) (ANSKI 0REDICTING THE OCCURRENCE OF ENDANGERED SPECIES IN FRAGMENTED LANDSCAPES 3CIENCE 7ARWICK 3 ) AND , $ "LACK 4HE "IOLOGY OF #ANADIAN 7EEDS 3ORGHUM HALA PENSE , 0ERS #ANADIAN *OURNAL OF 0LANT 3CIENCE 7ARWICK 3 ) ( * "ECKIE ' ! 4HOMAS AND 4 -C$ONALD 4HE "IOLOGY OF #ANADIAN 7EEDS 3INAPSIS ARVENSIS , UPDATED #ANADIAN *OURNAL OF 0LANT 3CIENCE 7ARWICK 3 ) AND $ ! 7ALL 4HE "IOLOGY OF #ANADIAN 7EEDS %RUCASTRUM GALLICUM 7ILLD / % 3CHULZ #ANADIAN *OURNAL OF 0LANT 3CIENCE 7ARWICK 3 ) ! &RANCIS AND $ * 3USKO 4HE "IOLOGY OF #ANADIAN 7EEDS 4HLASPI ARVENSE , UPDATED #ANADIAN *OURNAL OF 0LANT 3CIENCE 7EAVER 3 % AND - 0 $OWNS 4HE "IOLOGY OF #ANADIAN 7EEDS ,ACTUCA SER RIOLA , #ANADIAN *OURNAL OF 0LANT 3CIENCE 7ILLIAMSON - AND ! &ITTER 4HE VARYING SUCCESS OF INVADERS %COLOGY
#HAPTER FIVE
$ENSITY DEPENDENCE IN INVASIVE PLANTS DEMOGRAPHY HERBIVORY SPREAD AND EVOLUTION 9 - "UCKLEY AND * -ETCALF
).42/$5#4)/. "ECAUSE OF THEIR ENVIRONMENTAL AND ECONOMIC COSTS 0IMENTEL ET AL SOME INVASIVE PLANT SPECIES ARE WELL STUDIED OVER RELATIVELY LONG TIME SCALES "UCKLEY ET AL A AND IN DIFFERENT HABITATS 0AYNTER ET AL 4HESE DATA ARE VALU ABLE FOR THE DEVELOPMENT OR TESTING OF GENERAL THEORETICAL MODELS OF POPULATION DYNAMICS AND SPECIES INTERACTIONS &URTHERMORE KNOWING THE KIND OF DYNAMICS EXHIBITED BY INVASIVES MATTERS IF WE ARE ATTEMPTING TO PREDICT THEIR IMPACT ON AN ECOSYSTEM AND TO ANTICIPATE HOW THEY WILL RESPOND TO NOVEL ENVIRONMENTS OVER ECOLOGICAL AND EVOLUTIONARY TIME SCALES 'ENERAL RECENT REVIEWS OF DENSITY DEPEN DENCE CAN BE FOUND IN 4URCHIN +REBS 3IBLY AND (ONE HERE WE CONCENTRATE ON HOW RECENT ADVANCES IN OUR UNDERSTANDING OF HOW DENSITY DEPENDENT PROCESSES CONTRIBUTE TO OUR UNDERSTANDING OF THE DEMOGRAPHY MANAGEMENT AND EVOLUTION OF INVASIVE PLANT SPECIES $ESPITE CONSIDERABLE CONTROVERSY STRETCHING BACK TO DEBATES BETWEEN .ICHOLSON AND !NDREWARTHA OVER YEARS AGO AND CONTINUING TO SOME EXTENT TODAY -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
9- "UCKLEY AND * -ETCALF
A COMBINATION OF ENDOGENOUS AND EXOGENOUS FORCES IS GENERALLY ACCEPTED TO REGULATE POPULATION SIZE 4URCHIN %NDOGENOUS MECHANISMS ARE USUALLY REFERRED TO AS hDENSITY DEPENDENCEv WHICH IS A SHORTHAND TERM ENCOMPASSING THE RANGE OF MECHANISMS THAT MODIFY VITAL RATES ACCORDING TO THE DENSITY OF CON SPECIlCS 4HESE ARE THEORETICALLY OF GREAT IMPORTANCE AS A NECESSARY CONDITION FOR POPULATION REGULATION BUT ARE OFTEN DIFlCULT TO DETECT CONSISTENTLY UNDER NATURAL CONDITIONS SEE EXAMPLES IN +REBS "Y CONTRAST EXOGENOUS MECHANISMS INCORPORATE EXTERNAL FACTORS SUCH AS RESOURCE AVAILABILITY HERBIVORY OR HARVEST ING %XOGENOUS AND ENDOGENOUS FACTORS ARE INTIMATELY LINKED &OR EXAMPLE THE STRENGTH OF EXOGENOUS FACTORS SUCH AS RESOURCE AVAILABILITY CAN DETERMINE THE EQUILIBRIUM OF A SIMPLE DENSITY DEPENDENT MODEL 4HE WELL KNOWN (ASSELL MODEL (ASSELL RELATES POPULATION SIZE IN YEAR T .T TO POPULATION SIZE IN THE PREVIOUS YEAR .T MODIlED BY A DENSITY DEPENDENT FUNCTION INCORPORATING MAXI MUM FECUNDITY AT LOW DENSITIES h A MEASURE OF HABITAT CARRYING CAPACITY A AND THE STRENGTH AND FORM OF COMPETITION B !LL THREE PARAMETERS ARE POSITIVE h .T .T A.T B 4HE EQUILIBRIUM POPULATION SIZE DEPENDS ON ALL THREE PARAMETERS hB n
. A BUT STABILITY ONLY DEPENDS ON THE VALUES OF h AND B STABILITY ONLY BEING POSSIBLE PROVIDING B n hnB #HANGING THE CARRYING CAPACITY OF THE ENVIRONMENT CHANGING A IN THE (ASSELL MODEL WILL THEREFORE LEAD TO CHANGES IN THE EQUILIBRIUM DENSITY OF THE POPULATION &IG 4HIS IS PARTICULARLY RELEVANT FOR INVASIVE SPECIES TAKEN FROM THEIR NATIVE RANGE TO A NOVEL ENVIRONMENT OFTEN WITHOUT A SUITE OF SPECIALIST HERBIVORES AND PATHOGENS 4HE ENEMY RELEASE HYPOTHESIS %2( OR NATURAL ENEMIES HYPOTHESIS +EANE AND #RAWLEY POSITS THAT INVADERS ARE PARTICULARLY SUCCESSFUL IN THEIR EXOTIC HABITAT BECAUSE THEY ARE RELEASED FROM REGULATION BY SPECIALIST HERBIVORES PATHOGENS OR PARASITES PRESENT IN THEIR NATIVE HABITAT -OST PREDICTIONS STEMMING FROM THE %2( RELATE TO INCREASED VIGOUR BE IT PHENOTYPIC OR GENOTYPIC EXHIBITED BY INDIVIDUALS (OWEVER IF RESOURCES ARE NOT LIMITING IN EITHER EXOTIC OR NATIVE RANGES AND ENEMY RELEASE IS OPERATING WE MIGHT EXPECT POPULATIONS OF INVASIVES IN THE EXOTIC RANGE TO HAVE A HIGHER CARRYING CAPACITY AND EXHIBIT HIGHER EQUI LIBRIUM DENSITIES 4HIS APPEARS TO BE THE CASE FOR SCOTCH BROOM #YTISUS SCOPARIUS
$ENSITY DEPENDENCE IN INVASIVE PLANTS
&IG (ASSELL MODEL AT DIFFERENT CARRYING CAPACITIES EQUILIBRIUM POPULATION DENSITIES ACHIEVED OVER TIME YEARS ON THE X AXIS WITH A SOLID LINE A DASHED LINE AND A DOTTED LINE
WHICH WAS FOUND TO HAVE SIGNIlCANTLY HIGHER DENSITIES IN TWO COUNTRIES IN ITS EXOT IC RANGE !USTRALIA AND .EW :EALAND COMPARED WITH ITS NATIVE RANGE %UROPE 0AYNTER ET AL 4HE ABSENCE OF SPECIALIST HERBIVORES OR PATHOGENS MAY ALSO AFFECT THE COMPETITION PARAMETER B WHICH AT ITS EXTREME VALUES REPRESENTS IDEAL SCRAMBLE AND IDEAL CONTEST COMPETITION #OMPETITION FOR ENEMY FREE SPACE MAY HAVE A DIFFERENT FORM FROM COMPETITION FOR SOIL RESOURCES AND DIFFERENT VALUES OF B IN DIFFERENT ENVIRONMENTS WOULD CHANGE NOT JUST THE EQUILIBRIUM POPULATION DEN SITIES BUT COULD POTENTIALLY LEAD TO POPULATIONS WITH DIFFERENT STABILITY PROPERTIES 4HIS VERY SIMPLE MODEL ILLUSTRATES HOW EXOGENOUS CHANGES TO CONDITIONS CAN LEAD TO DIFFERENT DENSITY DEPENDENT DYNAMICS 4O OUR KNOWLEDGE A DETAILED STUDY OF THE POPULATION DYNAMICS OF AN INVASIVE PLANT IN NATIVE AND EXOTIC HABITATS HAS NOT BEEN CARRIED OUT IN ORDER TO INVESTIGATE HOW DENSITY DEPENDENT CONDITIONS DIFFER BETWEEN HABITATS 7ITH THE USE OF OBSERVATIONS EXPERIMENTS AND MODELLING AN INVASIVE PLANT SYSTEM WOULD BE IDEAL FOR INVESTIGATING THE INmUENCE OF DIFFERENT ENVIRONMENTS ON DENSITY DEPENDENT PROCESSES
9- "UCKLEY AND * -ETCALF
4HE IMPORTANCE OF EXOGENOUS FACTORS FOR DENSITY DEPENDENT POPULATION REGULA TION IS PARTICULARLY WELL ILLUSTRATED BY A RECENT ANALYSIS OF THE DYNAMICS OF RAGWORT 3ENECIO JACOBAEA , AND ITS SPECIALIST HERBIVORE THE CINNABAR MOTH 4YRIA JACOBAEAE , "ONSALL ET AL ,ONG TERM * YEARS TIME SERIES FOR BOTH SPECIES EXIST FOR TWO SITES ONE IN 3ILWOOD 5+ AND THE OTHER IN -EIJENDEL 4HE .ETHERLANDS )N 3ILWOOD RAGWORT POPULATIONS ONLY DIRECT DENSITY DEPENDENCE IE THE INmUENCE OF PLANT DENSITY IN THE PREVIOUS YEAR WAS DETECTED WHEREAS IN -EIJENDEL BOTH DIRECT YEAR PREVIOUS AND DELAYED TWO YEARS PREVIOUS DENSITY DEPENDENCE WAS DETECTED LEADING TO QUALITATIVELY DIFFERENT DYNAMICS AT THE TWO SITES 0OPULATIONS ARE RELATIVELY STABLE IN 3ILWOOD BUT EXHIBIT OSCILLATIONS IN -EIJENDEL 4HE DRIVER FOR THE DIFFERENCES IN DYNAMICS BETWEEN THE SITES MAY BE DIFFERENCES IN RECRUIT MENT 2ECRUITMENT IS MICRO SITE LIMITED AT 3ILWOOD BUT NOT AT -EIJENDEL IMPLYING STRONG DENSITY DEPENDENCE OPERATING AT THE SEEDLING STAGE IN 3ILWOOD POPULATIONS 3ENECIO JACOBAEA IS NATIVE TO %UROPE AND INTRODUCED TO !USTRALASIA THE !MERICAS AND 3OUTH !FRICA (ARPER AND 7OOD 4HIS STUDY IS A LANDMARK FOR ECOLO GISTS WORKING ON INVASIVES AS THE VARIABILITY IN THE QUALITATIVE DYNAMICS OF THIS SPECIES WITHIN ITS NATIVE RANGE ALONE SHOULD LEAD US TO ASK QUESTIONS OF ATTEMPTS TO EXTRAPOLATE MODEL OR EXPERIMENTAL RESULTS FROM NATIVE TO EXOTIC ECOSYSTEMS IN THE ABSENCE OF DATA FROM THE EXOTIC HABITAT )T SHOULD ALSO ENCOURAGE US TO MOVE ON FROM DOCUMENTING TRAIT DIFFERENCES BETWEEN SPECIES IN THEIR NATIVE AND EXOTIC RANGES 3IEMANN AND 2OGERS "UCKLEY ET AL B 3IEMANN AND 2OGERS TO INVESTIGATING THE POPULATION DYNAMIC CONSEQUENCES OF THOSE TRAIT DIFFERENCES AND THEIR INTERACTION WITH HABITAT DIFFERENCES )N ADDITION CONTEXT DEPENDENCY OF THIS SORT MIGHT RESULT IN DENSITY DEPENDENCE BEING OVERLOOKED IF THE SYSTEM STUDIED INCLUDES HABITAT HETEROGENEITY &OR EXAMPLE IN A STUDY OF REEF lSH 3HIMA AND /SENBERG FOUND THAT THE STRENGTH OF DENSITY DEPENDENT MORTALITY DEPENDED ON SITE QUALITY AND A FAILURE TO TAKE HETEROGENEITY IN SITE QUALITY INTO ACCOUNT COULD HAVE LEAD TO THE CONCLUSION THAT DENSITY DEPENDENCE WAS UNIMPORTANT 3HIMA /SENBERG REFER TO THE PATTERNS OBSERVED AS hCRYPTIC DENSITY DEPENDENCEv 7ITHIN A POPULATION DIFFERENCES BETWEEN INDIVIDUALS OR STAGES WILL ALSO AFFECT DENSITY DEPENDENCE AND RESULTING DYNAMICS &OR EXAMPLE POPULATION DENSITY AND ASYMMETRIC COMPETITION CAN INCREASE THE DIFFERENTIAL IN SIZE BETWEEN LEVELS IN HIERARCHIES OF PLANT POPULATIONS 7EINER AND THIS CAN CREATE DIFFER ENCES BETWEEN INDIVIDUAL RESPONSES TO DIFFERENT DENSITIES OF DIFFERENT STAGES 3IMPLE MODELS LIKE THE (ASSELL MODEL SHOWN ABOVE DO NOT ADDRESS THIS (OWEVER WE CAN INCORPORATE SUCH DIFFERENCES BY USING MODELS WITH AGE OR STAGE STRUCTURE "ENTON ET AL AND #AMERON AND "ENTON USE EXPERIMENTALLY MANIPULATED SOIL MITE POPULATIONS AND MODELS TO EXPLORE THE INTERACTION OF DENSITY DEPENDENCE AND ENVIRONMENTAL VARIABILITY ON THE OUTCOME OF HARVESTING DIFFERENT STAGES 4HEY FOUND THAT HARVESTING DIFFERENT STAGES REDUCING SURVIVAL OF EGGS JUVENILES OR ADULTS HAD DIFFERENT IMPACTS ON THE MEAN POPULATION SIZE AND ITS VARIANCE IN EACH STAGE )N A VARIABLE ENVIRONMENT THEY FOUND THAT REMOVAL OF OF EGGS ACTUALLY RESULTED IN AN INCREASE IN MEAN POPULATION SIZE WHEREAS REMOVAL OF
$ENSITY DEPENDENCE IN INVASIVE PLANTS
CORRESPONDING PROPORTIONS OF JUVENILES AND ADULTS LED TO A DECREASE IN MEAN POPULATION SIZE 4HIS WOULD APPEAR TO BE A RESULT OF DENSITY DEPENDENCE ACTING DIFFERENTLY IN DIFFERENT STAGES 4HEY LIKEN REMOVAL OF EGGS TO THINNING SEEDLINGS THIS RELEASES THE SURVIVORS FROM DENSITY DEPENDENT SUPPRESSION AND IF DENSITY DEPENDENCE IS STRONG ENOUGH CAN LEAD TO AN INCREASE IN OVERALL POPULATION SIZE 4HE EFFECTS OF EGG REMOVAL MAY HAVE BEEN MORE PRONOUNCED IN THE VARIABLE ENVIRONMENT BECAUSE OF THE ALTERNATING PERIODS OF STRONG AND WEAK COMPETITION FOR RESOURCES 4HE SAME COUNTER INTUITIVE RESULT HARVESTING LEADING TO INCREASED POPULATION SIZE CAN OCCUR IN A CONSTANT ENVIRONMENT WHERE DENSITY DEPENDENCE IS VERY STRONG OR OVER COMPENSATING EG "UCKLEY ET AL /F RELEVANCE TO THE MANAGEMENT OF INVASIVES IS "ENTON ET ALS CONCLUSION THAT DENSITY INDE PENDENT MODELS FAILED TO PREDICT THE NEGATIVE ELASTICITY OF SURVIVAL AT THE EGG STAGE THEREFORE MANAGEMENT MODELS WHICH DO NOT INCLUDE DENSITY DEPENDENCE WHERE IT IS KNOWN TO BE IMPORTANT RUN THE RISK OF GIVING THE WRONG ANSWER )NCORPORATING THE ADDED STRUCTURE FROM INDIVIDUAL VARIATION TO MODELS IS OFTEN IMPORTANT WITH THIS ADDED COMPLEXITY HOWEVER GREATER CARE SHOULD BE TAKEN TO CHOOSE THE APPROPRIATE MODEL &OX AND +ENDALL ILLUSTRATE THAT FAILURE TO MODEL INDIVIDUAL VARIABILITY CORRECTLY AS SYSTEMATIC VARIATION AMONG INDIVIDUALS RATHER THAN RANDOM VARIATION MAY LEAD TO INACCURATE PREDICTIONS 4HEY CONCLUDE hALMOST ALL POPULATION VIABILITY ANALYSES 06!S OVER ESTIMATE THE IMPORTANCE OF DEMOGRAPHIC STOCHASTICITY AND THEREFORE THE RISK OF EXTINCTIONv -URRELL #HAPTER PRESENTS A MODELLING FRAMEWORK THAT TAKES ACCOUNT OF LOCAL INTERAC TIONS THE hPLANTS EYE VIEWv OF ITS NEIGHBOURHOOD DENSITY WHICH EVEN WITHOUT SPATIAL OR TEMPORAL HETEROGENEITY LEADS TO INVASION DYNAMICS QUITE DIFFERENT FROM THOSE PREDICTED BY MEAN lELD APPROXIMATIONS WHICH TAKE OVERALL DENSITY INTO ACCOUNT .EW TOOLS WHICH ALLOW US TO TAKE ACCOUNT OF VARIATION IN RESOURCES AT DIFFERENT SPATIO TEMPORAL SCALES AND HOW PLANTS RESPOND TO VARIABLE RESOURCES AND CLUSTERING ALLOW BOTH INCREASINGLY ACCURATE PREDICTIONS OF DYNAMICS AND A BETTER UNDERSTANDING OF THE SCALE AND MECHANISMS INVOLVED IN DENSITY DEPEN DENT RESPONSES 3O FAR WE HAVE ONLY ADDRESSED NEGATIVE EFFECTS OF DENSITY DEPENDENCE ON lT NESS OR POPULATION GROWTH HOWEVER DENSITY DEPENDENCE CAN ALSO OPERATE POSI TIVELY 7HERE ANY COMPONENT OF lTNESS INCREASES AS DENSITY OR NUMBERS INCREASE THIS IS KNOWN AS AN !LLEE EFFECT THIS MAY TRANSLATE INTO DEMOGRAPHIC !LLEE EFFECTS WHERE POPULATION GROWTH RATE DECLINES WITH DECREASING DENSITY DEPENDING ON THE STRENGTH OF NEGATIVE DENSITY DEPENDENCE IN THE COMPONENT OF lTNESS IN QUES TION 3TEPHENS ET AL !N EXAMPLE OF A COMPONENT !LLEE EFFECT IS THAT THERE MIGHT BE A GREATER PROBABILITY OF lNDING A MATE IN A LARGER POPULATION &OR INSECT POLLINATED PLANTS SEED SET MAY DEPEND ON THERE BEING NEARBY CON SPECIlCS 0ARKER AND 0ARKER AND (AUBENSAK GIVE EXAMPLES OF POLLINA TOR LIMITATION IN THE INVASIVE 3COTCH BROOM #YTISUS SCOPARIUS !N IMPORTANT CONSEQUENCE OF THE !LLEE EFFECT FOR INVASIONS IS THAT ISOLATED PLANTS OR ISOLATED POPULATIONS CAN EXPERIENCE A SLOWER POPULATION GROWTH RATE RELATIVE TO LARGER POPULATIONS 4HIS MAY BE PARTICULARLY IMPORTANT DURING THE ESTABLISHMENT PHASE
9- "UCKLEY AND * -ETCALF
OF INVASIVE SPECIES OR DETERMINE WHAT LEVEL OF CONTROL WILL LEAD TO ERADICATION OR SLOWER POPULATION GROWTH -ANY INVASIVE SPECIES EXPERIENCE A hLAG TIMEv BETWEEN INITIAL COLONIZATION AND RAPID POPULATION GROWTH 4HIS MIGHT SIMPLY BE DUE TO THE LAG PHASE IN AN EXPONENTIAL GROWTH CURVE BUT IT COULD ALSO INDICATE THE ACTION OF STRONG OR WEAK !LLEE EFFECTS 4HE DISTINCTION BETWEEN STRONG AND WEAK !LLEE EFFECTS IS AN IMPORTANT ONE AND IS OUTLINED IN 7ANG AND +OT $EMOGRAPHIC !LLEE EFFECTS OCCUR WHEN THE POPULATION GROWTH RATE AT SOME SET OF LOW DENSITIES IS SLOWER THAN POPULATION GROWTH RATE AT HIGHER DENSITIES 3TRONG DEMOGRAPHIC !LLEE EFFECTS OCCUR WHEN POPULATION GROWTH RATE AT LOW DENSITY IS NEGATIVE )F STRONG !LLEE EFFECTS WERE OPERATING DURING THE ESTABLISHMENT PHASE OF AN INVA SIVE SPECIES THE POPULATION WOULD NEED TO REACH A THRESHOLD SIZE BEFORE BEING ABLE TO SPREAD RAPIDLY 4HIS COULD BE ACHIEVED THROUGH ONE LARGE INITIAL RELEASE OR THROUGH REPEATED INVASIONS EQUIVALENT TO A RESCUE EFFECT IN META POPULATION MODELS !MARASEKARE %QUALLY THAT POPULATION COULD BE DRIVEN TO EXTINC TION BY REDUCING IT BELOW THE THRESHOLD 7EAK DEMOGRAPHIC !LLEE EFFECTS RESULT IN A POPULATION THAT GROWS MORE SLOWLY AT LOW DENSITIES THAN IT DOES AT HIGH DENSITIES BUT THAT GROWTH IS ALWAYS POSITIVE SO A THRESHOLD DOES NOT EXIST ! CONSEQUENCE OF THE OPERATION OF WEAK !LLEE EFFECTS WOULD BE THAT THE LAG PHASE OF AN INVASION WOULD BE LONGER THAN PREDICTED BY AN EXPONENTIAL GROWTH CURVE !LLEE EFFECTS CAN BE IMPORTANT DURING INVASIVE SPECIES EXPANSION $AVIS ET AL DEMONSTRATE THIS FOR 3PARTINA ALTERNImORA WHICH hSETS VERY LITTLE VIABLE SEED AT THE LEADING EDGES OF AN INVASION IN 7ILLAPA "AY 7ASHINGTON 53! WHERE IT WAS INTRODUCED C YEARS AGOv 3PARTINA ALTERNImORA HAS TWO DISPERSAL MECHA NISMS SHORT DISTANCE SPREAD FROM RHIZOMATOUS GROWTH IN EXISTING PLANTS AND LONG DISTANCE SPREAD VIA SEEDS ,ONG DISTANCE SPREAD FROM THE LEADING EDGE OF THE POPULATION IS LIMITED HOWEVER BY A LACK OF VIABLE SEED UNTIL THE POPULATION HAS lLLED IN THROUGH RHIZOMATOUS GROWTH OR GERMINATION OF OTHER SEEDS DISPERSED FROM EXISTING DENSE POPULATIONS 7EAK !LLEE EFFECTS SUCH THOSE FOUND IN THE INVASIVE 3 ALTERNImORA NOT ONLY AFFECT POPULATION GROWTH RATES AT LOW DENSITY EQUILIBRIUM DENSITIES AND STABILITY &OWLER AND 2UXTON BUT THEIR INCLUSION IN MODELS OF SPREAD CAN ALTER SPREAD VELOCITIES 4HE IMPACT OF WEAK !LLEE EFFECTS ON EQUILIBRIA STABILITY AND SPREAD VELOCITIES HAS ONLY BEEN ADDRESSED RELATIVELY RECENTLY PREVI OUSLY ONLY STRONG !LLEE EFFECTS HAD BEEN CONSIDERED IN ANY DETAIL &OR INTEGRO DIFFERENCE EQUATION )$% MODELS OF SPREAD +OT ET AL SHOWED THAT STRONG !LLEE EFFECTS CAN TURN ACCELERATING INVASIONS INTO CONSTANT SPEED INVASIONS AND 7ANG ET AL SUGGEST USING NUMERICAL SOLUTIONS THAT INCLUDING WEAK !LLEE EFFECTS CAN ALSO SLOW DOWN INVASIONS FROM ACCELERATING TO CONSTANT SPEEDS 7ANG ET AL ALSO SHOW THAT !LLEE EFFECTS DETERMINE THE DIRECTION OF A TRAVELLING WAVE SOLUTION OF )$% MODELS WHERE THE DIRECTION OF THE TRAVELLING WAVE SOLUTION DETERMINES WHETHER AN INVASION WILL SUCCEED OR NOT 4RADITIONAL REACTION DIFFUSION MODELS OF SPREAD HAVE ALSO BEEN INVESTIGATED WITH REGARD TO THE INCLUSION OF !LLEE EFFECTS AGAIN SHOWING THAT !LLEE EFFECTS SLOW DOWN SPREAD #RUICKSHANK ET AL AND EVEN THAT AN INVASION CAN ONLY SUCCEED ONCE A CER TAIN CRITICAL AREA IS OCCUPIED ,EWIS AND +AREIVA
$ENSITY DEPENDENCE IN INVASIVE PLANTS
7HETHER DENSITY DEPENDENCE ACTS NEGATIVELY OR THROUGH !LLEE EFFECTS IT WILL HAVE IMPLICATIONS FOR POPULATION STABILITY 4HIS IS TRUE EVEN IN THE SIMPLEST MOD ELS SEE THE (ASSELL MODEL ABOVE FOR NEGATIVE DENSITY DEPENDENCE AND 3CHEURING WHO SHOWS THAT !LLEE EFFECTS PROMOTE STABILITY IN SIMPLE MODELS )NTEREST IN DENSITY DEPENDENCE OFTEN STEMS FROM THE SEARCH FOR MECHANISMS EITHER PRO MOTING STABILITY IN PLANT POPULATIONS OR DESTABILISING POPULATIONS -OST PLANT POPULATIONS ARE BELIEVED TO EXHIBIT STABLE DYNAMICS DUE TO STABILIZING FEATURES OF THEIR LIFE HISTORIES SUCH AS SOIL SEED BANKS 7ATKINSON 0ACALA AND 3ILANDER *ARRY ET AL PHENOTYPIC PLASTICITY AND ASYMMETRIC COMPETITION 0ALMBLAD 7EINER 0ACALA AND 7EINER 3ILVERTOWN SMALL SIZE THRESHOLDS FOR REPRODUCTION 2EES AND #RAWLEY AND SELF THINNING 7ATKINSON 7ATKINSON AND $AVY $ESTABILIZING PROCESSES INCLUDE OVER COMPENSATING DENSITY DEPENDENT FECUNDITY 4HRALL ET AL TIME LAGS CAUSED BY MATERNAL EFFECTS #RONE LARGE SIZE THRESHOLDS FOR REPRODUCTION 4HRALL ET AL AND DELAYED mOWERING AT HIGH DENSITY "UCKLEY ET AL #YCLIC OR CHAOTIC DYNAMICS CAN RESULT FROM AN OVER COMPENSATING DENSITY DEPEN DENT RESPONSE COMBINED WITH A HIGH lNITE RATE OF POPULATION GROWTH FROM LOW DENSITIES /VER COMPENSATING DENSITY DEPENDENCE OCCURS vWHEN THE PROPORTIONAL DECLINE IN PARAMETER VALUE WITH INCREASING DENSITY EXCEEDS THE CHANGE IN DENSITYv &RECKLETON AND 7ATKINSON -ECHANISMS GIVING RISE TO OVER COMPENSATING DENSITY DEPENDENCE ARE RARE IN PLANT SYSTEMS AND THEREFORE UNSTABLE DYNAMICS SUCH AS CYCLES OR CHAOS ARE EQUALLY RARE #HAOTIC DYNAMICS IN ANNUAL PLANT SYS TEMS ARE REVIEWED BY &RECKLETON 7ATKINSON AND THERE IS LITTLE EVIDENCE FOR CHAOTIC DYNAMICS IN OTHER PLANT LIFE HISTORIES 2EES AND #RAWLEY (OWEVER 2EES ET AL HAVE SHOWN THAT mOWERING DYNAMICS CLOSE TO CHAOTIC OCCUR IN A MAST SEEDING TUSSOCK GRASS #HIONOCHLOA PALLENS POSSIBLY AS AN EVOLU TIONARY RESPONSE TO ATTACK BY SEED AND mOWER FEEDERS 3TABILITY IS AN IMPORTANT ISSUE FOR POPULATIONS OF INVASIVES FOR A NUMBER OF REASONS KNOWING WHETHER A POPULATION IS LIKELY TO BE STABLE OR EXHIBIT CYCLES MAY ALLOW PREDICTION OF LEVELS OF IMPACT LIKELY TO OCCUR STABILITY MAY ALSO AFFECT THE SUCCESS OF BIOCONTROL PROGRAMS &OR PLANT SPECIES WITH LONG LIVED SEED BANKS IT IS IMPORTANT TO MAINTAIN POPULATIONS OF A BIOCONTROL AGENT IN THE SYSTEM IN ORDER TO CONTROL POPULATIONS ARISING FROM THE SEED BANK AT A LATER DATE OR CONTINUOUS RE INTRODUCTION OF THE BIOCONTROL AGENT IS NECESSARY 7HEN CHOOSING A BIOCONTROL AGENT THEREFORE IT MAY BE BETTER TO CHOOSE AN AGENT WHICH MAINTAINS THE PLANT POPULATION AT A LOW STABLE LEVEL RATHER THAN ONE WHICH DRIVES THE ABOVE GROUND POPULATION TO EXTINCTION CAUSING ITS OWN EXTINCTION AND THE SUBSEQUENT RESUR GENCE OF THE INVASIVE PLANT %VEN IF THE HERBIVORE DOES NOT CAUSE PLANT EXTINCTION DIRECTLY UNSTABLE CYCLES CAN RESULT IN A HIGHER PROBABILITY OF STOCHASTIC EXTINCTION OF THE PLANT POPULATION "UCKLEY ET AL USE AN EXPERIMENTALLY PARAMETER ISED PLANT HERBIVORE MODEL TO SHOW THAT DENSITY DEPENDENCE IN BOTH PLANT AND HERBIVORE POPULATIONS CONTRIBUTE TO STABILITY IN THE SYSTEM BUT THAT THE FORM OF DENSITY DEPENDENCE IN THE HERBIVORE IN COMBINATION WITH HIGH ATTACK RATES CAN DESTABILISE THE DYNAMICS 3TUDYING THE FORM OF DENSITY DEPENDENCE EG SCRAMBLE
9- "UCKLEY AND * -ETCALF
OR CONTEST IN POTENTIAL AGENTS MAY THEREFORE GIVE US SOME IDEA OF WHICH AGENTS WOULD BE MOST APPROPRIATE TO INTRODUCE IN SYSTEMS LIKE THIS A BIOCONTROL AGENT COM BINING STRONG SCRAMBLE COMPETITION WITH A HIGH ATTACK RATE MAY NOT BE A GOOD CHOICE 4HE EXACT WAY IN WHICH DENSITY DEPENDENT PROCESSES AFFECT STABILITY CAN BE SUBTLE $ENSITY DEPENDENCE MAY OCCUR AT SEVERAL LIFE HISTORY STAGES WITHIN A SPECIES AND WHICH STAGE IT ACTS ON CAN BE OF CRITICAL IMPORTANCE TO ITS EFFECT FOR POPULATION STABILITY &OR EXAMPLE "UCKLEY AND COLLEAGUES FOUND EVIDENCE FOR DENSITY DEPENDENT SURVIVAL mOWERING AND FECUNDITY IN THE INVASIVE ANNUAL 4RIPLEUROSPERMUM PERFORATUM 4HESE DIFFERENT OCCURRENCES HAD DIFFERENT IMPLICA TIONS FOR POPULATION STABILITY $ENSITY DEPENDENCE IN SURVIVAL AND FECUNDITY WAS STABILISING WHEREAS DENSITY DEPENDENCE IN mOWERING LED TO INSTABILITY IN FACULTA TIVE BIENNIAL SYSTEMS SEE &IG FOR DENSITY DEPENDENT mOWERING PROBABILITY AND &IG FOR MODEL STABILITY (OWEVER DENSITY DEPENDENT mOWERING ALSO MEANS THAT IN THIS FACULTATIVE BIENNIAL DELAYED mOWERING IS FAVOURED AT HIGH DENSITIES 4HIS LEADS TO ASYMMETRIC COMPETITION BETWEEN LARGER OVER WINTERED ROSETTES AND NEW SEEDLINGS IN THE FOLLOWING YEAR WHICH IS GENERALLY A STABILISING FORCE AS THE LARGER ROSETTES ARE MORE COMPETITIVE WITH SEEDLINGS 3O DENSITY DEPENDENCE NOT ONLY AFFECTS THE DYNAMICS IN THIS PREDOMINANTLY ANNUAL SYSTEM BUT ALSO PLAYS A PART IN DETERMINING THE LIFE HISTORY STRATEGY ADOPTED BY THE PLANT AND THE TIMING OF DENSITY DEPENDENCE IS IMPORTANT FOR BOTH OF THESE OUTCOMES 4HIS EXAMPLE ALSO ILLUSTRATES HOW THE TIMING OF DENSITY DEPENDENCE CAN BE CRITICAL FOR DECISIONS RELATING TO MANAGEMENT OF INVASIVE SPECIES -ANAGEMENT STRATEGIES GENERALLY RESULT IN EXOGENOUS MORTALITY THROUGH MOWING FOR EXAMPLE $UE TO OVER COMPENSATING DENSITY DEPENDENCE IN 4 PERFORATUM THE TIMING OF EXOGENOUS MORTALITY AFFECTS THE EQUILIBRIUM SEED DENSITY DRAMATICALLY )F EXOG ENOUS MORTALITY OCCURS EARLY IN THE LIFE CYCLE FREEING THE FEW SURVIVING PLANTS FROM DENSITY DEPENDENT DEPRESSION OF SEED PRODUCTION SEED OUTPUT CAN ACTUALLY INCREASE EXACERBATING THE WEED PROBLEM IN THE LONG TERM "UCKLEY ET AL 'ENERALLY IF DENSITY DEPENDENCE IS IMPORTANT FOR POPULATION REGULATION THE REMOVAL OF SEEDS SEEDLINGS OR PLANTS BEFORE DENSITY DEPENDENCE OCCURS IS UNLIKELY TO LEAD TO SUCCESSFUL CONTROL 4HIS IS OFTEN RELEVANT WHEN CONSIDERING BIOCONTROL AGENTS !S POINTED OUT BY !LEXANDER AND 3CHRAG SEED PREDATORS OR SEEDLING PATHOGENS CAN HAVE A STRONG EFFECT ON SEEDLING NUMBERS %DWARDS AND #RAWLEY !LEXANDER AND -IHAIL #UMMINGS AND !LEXANDER BUT NOT NECESSARILY IMPACT ON lNAL REPRODUCTIVE OUTPUT OF A PATCH DUE TO SUBSEQUENT DENSITY DEPENDENT PROCESSES 7HERE SEED INPUT IS REDUCED LOW DENSITY SEEDLING POPULATIONS ARE PRODUCED WHICH MAY HAVE LOWER RATES OF INTRASPECIlC COMPETI TION AND THUS HIGHER PER CAPITA SEED PRODUCTION COMPENSATING FULLY OR TO SOME EXTENT FOR THE INITIAL SEED OR SEEDLING LOSS 4HE CASE OF !CACIA NILOTICA ILLUSTRATES THIS POINT !CACIA NILOTICA AN INVASIVE SHRUB OR SMALL TREE IS DISPERSED BY CATTLE WHICH EAT SEEDS AND DEPOSIT THEM IN COW PATS 4HE SEEDLINGS ARE THEREFORE AGGREGATED IN SMALL PATCHES AND SELF THINNING ENSURES THAT NO MORE THAN APPROXIMATELY ONE SEEDLING SURVIVES TO ADULTHOOD +RITICOS ET AL AND +RITICOS ET AL ESTIMATE THAT THE INTRODUCTION OF A SEED EATING BIOCONTROL AGENT IS THEREFORE
$ENSITY DEPENDENCE IN INVASIVE PLANTS
&IG $ENSITY DEPENDENT FUNCTION FOR mOWERING PROBABILITY IN 4RIPLEUROSPERMUM PERFORATUM WITH PERMISSION %COLOGY ,ETTERS
&IG ! COMPARISON OF THE DYNAMICS PREDICTED BY THE FULL MODEL INCORPORATING DENSITY DEPENDENT SURVIVAL mOWERING PROBABILITY AND FECUNDITY WITH A MODEL INCORPORATING DENSITY DEPENDENT mOWERING PROBABILITY AND FECUNDITY ONLY ! MODEL USING DENSITY DEPENDENT FECUNDITY ALONE PRODUCES DAMPED OSCILLATIONS AND AN EQUILIBRIUM LEVEL SIMILAR TO THAT OBSERVED IN THE FULL MODEL WITH PERMISSION %COLOGY ,ETTERS
9- "UCKLEY AND * -ETCALF
UNLIKELY TO AFFECT ADULT POPULATION SIZES UNLESS THE NUMBER OF SEEDS PER COW PAT IS REDUCED DRAMATICALLY TO TWO OR LESS 3EVERAL AUTHORS HAVE CALLED FOR A THOROUGH UNDERSTANDING OF THE OCCURRENCE AND EFFECTS OF DENSITY DEPENDENCE AT DIFFERENT STAGES -ORTIMER ET AL 7ATKINSON ET AL 'ILLMAN ET AL !S SHOWN BY THE EXAMPLES GIVEN ABOVE THIS IS ESPECIALLY RELEVANT FOR WEED SPECIES WHERE DENSITY IS MANIPULATED AT ONE OR MORE SPECIlC STAGES FOR CONTROL PURPOSES )N VIEW OF THESE RESULTS IT IS OBVIOUS THAT MODELS SEEKING TO PREDICT THE EFFECTS OF CONTROL STRATEGIES AT DIFFERENT STAGES SHOULD INCORPORATE DENSITY DEPENDENCE )N A SUSTAINABLE HARVESTING STUDY &RECKLETON ET AL POINT OUT THAT THE USE OF DENSITY INDEPENDENT MATRIX MODELS WHERE THE TRANSITION PROBABILITIES ARE CAL CULATED WHEN THE POPULATION IS CLOSE TO EQUILIBRIUM h CLOSE TO COULD GIVE MISLEADING RESULTS WHEN USED TO PREDICT POPULATION INCREASE FROM LOW DENSITY 4HEY CALL FOR EXPLICIT INCORPORATION OF DENSITY DEPENDENCE IN HARVESTING MODELS AND THE SAME CALL SHOULD BE MADE FOR CONTROL MODELS OF INVASIVES WHERE DENSITY DEPENDENCE IS KNOWN OR SUSPECTED TO BE IMPORTANT ! THOROUGH UNDERSTANDING OF THE OCCURRENCE AND EFFECTS OF DENSITY DEPENDENCE WOULD ALSO GREATLY CONTRIBUTE TO INVESTIGATIONS INTO SELECTION PRESSURES AND EVO LUTION )NVASIVE PLANTS CAN BE EXCELLENT MODEL SYSTEMS FOR THE DEVELOPMENT OF MODELS OF LIFE HISTORY EVOLUTION 0LANTS IN THE EXOTIC RANGE MAY BE UNDER DIFFER ENT SELECTION PRESSURES DUE TO ENEMY RELEASE OR COMPETITIVE RELEASE #ONTRASTING MODELS PREDICTING EVOLUTIONARILY STABLE STRATEGIES IN EACH ENVIRONMENT COULD BE DEVELOPED 4HIS APPROACH WOULD COMPLEMENT OBSERVATIONAL AND EXPERIMENTAL STUDIES AIMED AT DETECTING EVOLUTIONARY CHANGE BETWEEN INVASIVES IN THEIR NATIVE AND EXOTIC HABITATS "LOSSEY AND .ÚTZOLD 7ILLIS ET AL 3IEMANN AND 2OGERS (ISTORICALLY WHEN EXPLORING LIFE HISTORY STRATEGIES INVESTIGATORS IGNORED DENSI TY DEPENDENCE AND SIMPLY USED R FROM THE %ULER ,OTKA EQUATION TO DElNE lTNESS 3TEARNS (OWEVER IT BECAME APPARENT THAT DENSITY DEPENDENCE COULD NOT BE IGNORED BECAUSE IN A DENSITY DEPENDENT SITUATION THE lTNESS OF ONE STRATEGY WILL DEPEND ON THE ACTIONS OF OTHER STRATEGIES 'RANT AND "ENTON "ECAUSE OF THIS THE EVOLUTIONARY STABLE STRATEGY %33 IS BEST DETERMINED BY USING THE INVA SION EXPONENT OR THE RATE OF INCREASE OF A RARE MUTANT INTO AN hENVIRONMENTv SET BY A RESIDENT STRATEGY AND CHARACTERISED BY THE RESIDENTS DENSITY )F THEN THE INVADER IS SUCCESSFUL 4HE %33 IS SIMPLY THE STRATEGY THAT CANNOT BE INVADED BY ANY OTHER 5SING THIS FRAMEWORK -YLIUS AND $IEKMANN SHOWED THAT IN A CONSTANT ENVIRONMENT THE %33 MAY SOMETIMES BE THE STRATEGY AT WHICH A RELATIVELY SIMPLE FUNCTION IS MAXIMISED (OWEVER WHICH FUNCTION IS APPROPRIATE IS DETERMINED BY WHEN DENSITY DEPENDENCE ACTS IN THE LIFE CYCLE )F DENSITY DEPEN DENCE ACTS SO THAT ONLY THE EXPECTED LIFETIME OFFSPRING PRODUCTION IS REDUCED THEN AN APPROPRIATE lTNESS MEASURE IS LIFETIME REPRODUCTIVE SUCCESS OR 2 )F DEN SITY DEPENDENCE AFFECTS ONLY THE PROBABILITY PER UNIT TIME OF DYING THEN POPULA TION RATE OF INCREASE h IS APPROPRIATE 4HE TWO MAY PROVIDE DIFFERENT PREDICTIONS SO IT IS IMPORTANT TO USE THE APPROPRIATE MEASURE
$ENSITY DEPENDENCE IN INVASIVE PLANTS
4HIS FRAMEWORK HAS BEEN USED TO PREDICT THE %33 mOWERING STRATEGY IN MONO CARPIC PLANTS 2EES ET AL 2EES AND 2OSE A CATEGORY TO WHICH MANY NUISANCE WEEDS AND INVASIVE SPECIES BELONG $ATA FROM A RANGE OF SPECIES SHOWS THAT NEIGHBOUR DENSITY OR SIZE HAS NO EFFECT ON GROWTH SURVIVAL OR REPRODUC TION IN MONOCARPIC PLANTS -ETCALF ET AL (OWEVER RECRUITMENT IS GENER ALLY UNCORRELATED WITH SEED PRODUCTION SUGGESTING THAT SEED ESTABLISHMENT IS LIMITED BY SUITABLE MICROSITE AVAILABILITY 4OGETHER THESE OBSERVATIONS IMPLY THE OPERATION OF DENSITY DEPENDENT PROCESSES AT THE SEEDLING ESTABLISHMENT LEVEL ONLY 7E CAN DEDUCE THAT THE %33 STRATEGY CORRESPONDS TO MAXIMISING 2 ASSUM ING THE ENVIRONMENT IS CONSTANT ! MATRIX MODEL OR ITS CONTINUOUS ANALOGUE THE )NTEGRAL 0ROJECTION -ODEL %ASTERLING ET AL CAN BE USED TO DESCRIBE THE POPULATION AND CALCULATE 2 FOR A RANGE OF mOWERING STRATEGIES 4HIS APPROACH HAS BEEN USED TO PREDICT %33 mOWERING STRATEGY VALUES THAT ARE VERY CLOSE TO THE OBSERVED 2EES AND 2OSE AND CONTRIBUTE TO OUR UNDERSTANDING OF SELECTION PRESSURES ON MONCARPIC PLANTS
#/.#,53)/.3 $ENSITY DEPENDENT PROCESSES CAN DETERMINE EQUILIBRIUM DENSITIES ACHIEVABLE BY AN INVASIVE POPULATION STABILITY OF THAT POPULATION POPULATION GROWTH RATES AT THE FRONT OF AN INVASION POPULATION RECOVERY AFTER CONTROL MEASURES HAVE BEEN IMPLEMENTED AND THE EVOLUTIONARILY STABLE STRATEGIES ACQUIRED BY POPULATIONS IN DIFFERENT ENVIRONMENTS )N THIS CHAPTER WE HAVE OUTLINED HOW THEORETICAL ECOLOGY HAS CONTRIBUTED BOTH TO OUR UNDERSTANDING OF HOW INVASIVE POPULATIONS ARE REGU LATED BY DENSITY DEPENDENCE AND HOW WORK ON INVASIVES HAS STIMULATED THEORETI CAL WORK ON IMPORTANT ECOLOGICAL PROBLEMS LIKE !LLEE EFFECTS AND SPATIAL SPREAD OF POPULATIONS !S WE DEVELOP MODELS FOR AN INCREASING NUMBER OF THE COMPLEX PROCESSES THAT GOVERN POPULATION DYNAMICS WE CAN START TO COMBINE MODELS AND INVESTIGATE THE INTERACTION OF PROCESSES LIKE !LLEE EFFECTS AND THE SHAPE OF DISPERSAL KERNELS 7ANG ET AL ON SPREAD RATES OR DENSITY DEPENDENCE AT DIFFERENT STAGES IN THE LIFE CYCLE "UCKLEY ET AL 5LTIMATELY THESE MODELS WILL ENABLE US TO APPLY TARGETED AND EFFECTIVE MANAGEMENT STRATEGIES TO INVASIVE PLANT POPULA TIONS IN ORDER TO REDUCE THEIR IMPACT ON BIODIVERSITY LOSS AND ECOSYSTEM FUNCTION
!#+./7,%$'%-%.43 7E THANK $ARREN +RITICOS +AREN 2OSE #AZ 4AYLOR $AVE -URRELL AND AN ANONY MOUS REVIEWER FOR HELPFUL ADDITIONS *#- WAS SUPPORTED BY A .%2# STUDENTSHIP
9- "UCKLEY AND * -ETCALF
2%&%2%.#%3 !LEXANDER ( - AND * $ -IHAIL 3EEDLING DISEASE IN AN ANNUAL LEGUME CONSE QUENCES FOR SEEDLING MORTALITY PLANT SIZE AND POPULATION SEED PRODUCTION /ECOLOGIA !LEXANDER ( - AND ! - 3CHRAG 2OLE OF SOIL SEED BANKS AND NEWLY DISPERSED SEEDS IN POPULATION DYNAMICS OF THE ANNUAL SUNmOWER (ELIANTHUS ANNUUS *OURNAL OF %COLOGY !MARASEKARE 0 )NTERACTIONS BETWEEN LOCAL DYNAMICS AND DISPERSAL )NSIGHTS FROM SINGLE SPECIES MODELS 4HEORETICAL 0OPULATION "IOLOGY "ENTON 4 ' 4 # #AMERON AND ! 'RANT 0OPULATION RESPONSES TO PERTURBATIONS PREDICTIONS AND RESPONSES FROM LABORATORY MITE POPULATIONS *OURNAL OF !NIMAL %COLOGY "LOSSEY " AND 2 .ÚTZOLD %VOLUTION OF INCREASED COMPETITIVE ABILITY IN INVASIVE NONINDIGENOUS PLANTS A HYPOTHESIS *OURNAL OF %COLOGY "ONSALL - " % VAN DER -EIJDEN AND - * #RAWLEY #ONTRASTING DYNAMICS IN THE SAME PLANT HERBIVORE INTERACTION 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES "UCKLEY 9 - $ 4 "RIESE AND - 2EES A $EMOGRAPHY AND MANAGEMENT OF THE INVASIVE PLANT SPECIES (YPERICUM PERFORATUM ) 5SING MULTI LEVEL MIXED EFFECTS MODELS FOR CHARACTERIZING GROWTH SURVIVAL AND FECUNDITY IN A LONG TERM DATA SET *OURNAL OF !PPLIED %COLOGY "UCKLEY 9 - 0 $OWNEY 3 6 &OWLER 2 , (ILL * -EMMOTT ( .ORAMBUENA - 0ITCAIRN 2 ' 3HAW ! 7 3HEPPARD # 7INKS 2 7ITTENBERG AND - 2EES B !RE INVASIVES BIGGER ! GLOBAL STUDY OF SEED SIZE VARIATION IN TWO INVASIVE SHRUBS %COLOGY "UCKLEY 9 - ( , (INZ $ -ATTHIES AND - 2EES )NTERACTIONS BETWEEN DENSITY DEPENDENT PROCESSES POPULATION DYNAMICS AND CONTROL OF AN INVASIVE PLANT SPECIES 4RIPLEUROSPERMUM PERFORATUM SCENTLESS CHAMOMILE %COLOGY ,ETTERS "UCKLEY 9 - - 2EES ! 7 3HEPPARD AND - * 3MYTH 3TABLE COEXISTENCE OF AN INVASIVE PLANT AND BIOCONTROL AGENT A PARAMETERISED COUPLED PLANT HERBIVORE MODEL *OURNAL OF !PPLIED %COLOGY #AMERON 4 # AND 4 ' "ENTON 3TAGE STRUCTURED HARVESTING AND ITS EFFECTS AN EMPIRICAL INVESTIGATION USING SOIL MITES *OURNAL OF !NIMAL %COLOGY #ASWELL ( -ATRIX POPULATION MODELS CONSTRUCTION ANALYSIS AND INTERPRETATION ND EDITION 3INAUER !SSOCIATES )NC 3UNDERLAND -ASSACHUSETTS #RONE % % 0ARENTAL ENVIRONMENTAL EFFECTS AND CYCLICAL DYNAMICS IN PLANT POPULA TIONS 4HE !MERICAN .ATURALIST #RUICKSHANK ) 7 3 # 'URNEY AND ! 2 6EITCH 4HE CHARACTERISTICS OF EPIDEMICS AND INVASIONS WITH THRESHOLDS 4HEORETICAL 0OPULATION "IOLOGY #UMMINGS # , AND ( - !LEXANDER 0OPULATION ECOLOGY OF WILD SUNmOWERS EFFECTS OF SEED DENSITY AND POST DISPERSAL VERTEBRATE SEED PREDATION /ECOLOGIA $AVIS ( ' # - 4AYLOR * # #IVILLE AND $ 2 3TRONG !N !LLEE EFFECT AT THE FRONT OF A PLANT INVASION 3PARTINA IN A 0ACIlC ESTUARY *OURNAL OF %COLOGY
$ENSITY DEPENDENCE IN INVASIVE PLANTS
%ASTERLING - 2 3 0 %LLNER AND 0 - $IXON 3IZE SPECIlC SENSITIVITY !PPLYING A NEW STRUCTURED POPULATION MODEL %COLOGY %DWARDS ' 2 AND - * #RAWLEY 2ODENT SEED PREDATION AND SEEDLING RECRUITMENT IN MESIC GRASSLAND /ECOLOGIA &OWLER 3 6 AND ' $ 2UXTON 0OPULATION DYNAMIC CONSEQUENCES OF !LLEE EFFECTS *OURNAL OF 4HEORETICAL "IOLOGY &OX ' ! AND " % +ENDALL $EMOGRAPHIC STOCHASTICITY AND THE VARIANCE REDUCTION EFFECT %COLOGY &RECKLETON 2 0 $ - 3ILVA -ATOS - , ! "OVI AND ! 2 7ATKINSON 0REDICTING THE IMPACTS OF HARVESTING USING STRUCTURED POPULATION MODELS THE IMPORTANCE OF DENSITY DEPENDENCE AND TIMING OF HARVEST FOR A TROPICAL PALM TREE *OURNAL OF !PPLIED %COLOGY &RECKLETON 2 0 AND ! 2 7ATKINSON !RE WEED POPULATION DYNAMICS CHAOTIC *OURNAL OF !PPLIED %COLOGY 'ILLMAN - * - "ULLOCK * 3ILVERTOWN AND " #LEAR (ILL ! DENSITY DEPENDENT MODEL OF #IRSIUM VULGARE POPULATION DYNAMICS USING lELD ESTIMATED PARAMETER VALUES /ECOLOGIA 'RANT ! AND 4 ' "ENTON %LASTICITY ANALYSIS FOR DENSITY DEPENDENT POPULATIONS IN STOCHASTIC ENVIRONMENTS %COLOGY (ARPER * , AND 7 ! 7OOD "IOLOGICAL &LORA OF THE "RITISH )SLES 3ENECIO JACOBAEA , *OURNAL OF %COLOGY (ASSELL - 0 $ENSITY DEPENDENCE IN SINGLE SPECIES POPULATIONS *OURNAL OF !NIMAL %COLOGY *ARRY - - +HALADI - (OSSAERT -C+EY AND $ -C+EY -ODELING THE POPULA TION DYNAMICS OF ANNUAL PLANTS WITH SEED BANK AND DENSITY DEPENDENT EFFECTS !CTA "IOTHEORETICA +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY %VOLUTION +OT - - ! ,EWIS AND 0 VAN DEN $RIESSCHE $ISPERSAL DATA AND THE SPREAD OF INVADING ORGANISMS %COLOGY +REBS # * 4WO COMPLEMENTARY PARADIGMS FOR ANALYSING POPULATION DYNAMICS 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES +RITICOS $ * "ROWN ) 2ADFORD AND - .ICHOLAS 0LANT POPULATION ECOLOGY AND BIOLOGICAL CONTROL !CACIA NILOTICA AS A CASE STUDY "IOLOGICAL #ONTROL +RITICOS $ * * 2 "ROWN ' & -AYWALD ) $ 2ADFORD $ - .ICHOLAS 2 7 3UTHERST AND 3 7 !DKINS 30!N$8 A PROCESS BASED POPULATION DYNAMICS MODEL TO EXPLORE MANAGEMENT AND CLIMATE CHANGE IMPACTS ON AN INVASIVE ALIEN PLANT !CACIA NILOTICA %COLOGICAL MODELLING ,EWIS - ! AND 0 +AREIVA !LLEE DYNAMICS AND THE SPREAD OF INVADING ORGANISMS 4HEORETICAL 0OPULATION "IOLOGY -ETCALF * # + % 2OSE AND - 2EES %VOLUTIONARY DEMOGRAPHY OF MONOCARPIC PERENNIALS 4RENDS IN %COLOGY %VOLUTION
9- "UCKLEY AND * -ETCALF
-ORTIMER ! - * * 3UTTON AND 0 'OULD /N ROBUST WEED POPULATION MODELS 7EED 2ESEARCH -YLIUS 3 $ AND / $IEKMANN /N EVOLUTIONARILY STABLE LIFE HISTORIES AND THE NEED TO BE SPECIlC ABOUT DENSITY DEPENDENCE /IKOS 0ACALA 3 7 AND * ! 3ILANDER &IELD TESTS OF NEIGHBORHOOD POPULATION DYNAMIC MODELS OF TWO ANNUAL WEED SPECIES %COLOGICAL -ONOGRAPHS 0ACALA 3 7 AND * 7EINER %FFECTS OF COMPETITIVE ASYMMETRY ON A LOCAL DENSITY MODEL OF PLANT INTERFERENCE *OURNAL OF 4HEORETICAL "IOLOGY 0ALMBLAD ) ' #OMPETITION IN EXPERIMENTAL STUDIES ON POPULATIONS OF WEEDS WITH PARTICULAR EMPHASIS ON THE REGULATION OF POPULATION SIZE %COLOGY 0ARKER ) - 0OLLINATOR LIMITATION OF #YTISUS SCOPARIUS 3COTCH BROOM AN INVASIVE EXOTIC SHRUB %COLOGY 0ARKER ) - AND + ! (AUBENSAK #OMPARATIVE POLLINATOR LIMITATION OF TWO NON NATIVE SHRUBS DO MUTUALISMS INmUENCE INVASIONS /ECOLOGIA 0AYNTER 1 0 / $OWNEY AND ! 7 3HEPPARD !GE STRUCTURE AND GROWTH OF THE WOODY LEGUME WEED #YTISUS SCOPARIUS IN NATIVE AND EXOTIC HABITATS IMPLICATIONS FOR CONTROL *OURNAL OF !PPLIED %COLOGY 0IMENTEL $ , ,ACH 2 :UNIGA AND $ -ORRISON %NVIRONMENTAL AND ECONOMIC COSTS OF NONINDIGENOUS SPECIES IN THE 5NITED 3TATES "IOSCIENCE 2EES - AND - * #RAWLEY 'ROWTH REPRODUCTION AND POPULATION DYNAMICS &UNCTIONAL %COLOGY 2EES - AND - * #RAWLEY $O PLANT POPULATIONS CYCLE &UNCTIONAL %COLOGY 2EES - $ +ELLY AND / . "JORNSTAD 3NOW TUSSOCKS CHAOS AND THE EVOLUTION OF MAST SEEDING 4HE !MERICAN .ATURALIST 2EES - AND + % 2OSE %VOLUTION OF mOWERING STRATEGIES IN /ENOTHERA GLAZIOVIANA AN INTEGRAL PROJECTION MODEL APPROACH 0ROCEEDINGS OF THE 2OYAL 3OCIETY ,ONDON 3ERIES " 3CHEURING ) !LLEE EFFECT INCREASES THE DYNAMICAL STABILITY OF POPULATIONS *OURNAL OF 4HEORETICAL "IOLOGY 3HIMA * 3 AND # 7 /SENBERG #RYPTIC DENSITY DEPENDENCE EFFECTS OF COVARIATION BETWEEN DENSITY AND SITE QUALITY IN REEF lSH %COLOGY 3IBLY 2 - AND * (ONE 0OPULATION GROWTH RATE AND ITS DETERMINANTS AN OVERVIEW 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES 3IEMANN % AND 7 % 2OGERS 'ENETIC DIFFERENCES IN GROWTH OF AN INVASIVE TREE SPE CIES %COLOGY ,ETTERS 3IEMANN % AND 7 % 2OGERS 2EDUCED RESISTANCE OF INVASIVE VARIETIES OF THE ALIEN TREE 3APIUM SEBIFERUM TO A GENERALIST HERBIVORE /ECOLOGIA 3ILVERTOWN * -ODULARITY REPRODUCTIVE THRESHOLDS AND PLANT POPULATION DYNAMICS &UNCTIONAL %COLOGY 3TEARNS 3 # 4HE EVOLUTION OF LIFE HISTORIES /XFORD 5NIVERSITY 0RESS /XFORD 3TEPHENS 0 ! 7 * 3UTHERLAND AND 2 &RECKLETON 7HAT IS THE !LLEE EFFECT /IKOS
$ENSITY DEPENDENCE IN INVASIVE PLANTS
4HRALL 0 ( 3 7 0ACALA AND * ! 3ILANDER /SCILLATORY DYNAMICS IN POPULATIONS OF AN ANNUAL WEED SPECIES !BUTILON THEOPHRASTI *OURNAL OF %COLOGY 4URCHIN 0 0OPULATION REGULATION A SYNTHETIC VIEW /IKOS 7ANG - ( - +OT AND - ' .EUBERT )NTEGRODIFFERENCE EQUATIONS !LLEE EFFECTS AND INVASIONS *OURNAL OF -ATHEMATICAL "IOLOGY 7ATKINSON ! 2 $ENSITY DEPENDENCE IN SINGLE SPECIES POPULATIONS OF PLANTS *OURNAL OF 4HEORETICAL "IOLOGY 7ATKINSON ! 2 AND ! * $AVY 0OPULATION BIOLOGY OF SALT MARSH AND SAND DUNE ANNUALS 6EGETATIO 7ATKINSON ! 2 7 - ,ONSDALE AND - ( !NDREW -ODELLING THE POPULATION DYNAMICS OF AN ANNUAL PLANT 3ORGHUM INTRANS IN THE WET DRY TROPICS *OURNAL OF %COLOGY 7EINER * 3IZE HIERARCHIES IN EXPERIMENTAL POPULATIONS OF ANNUAL PLANTS %COLOGY 7ILLIS ! * * -EMMOTT AND 2 ) &ORRESTER )S THERE EVIDENCE FOR THE POST INVASION EVOLUTION OF VIGOUR AMONG INVASIVE PLANT SPECIES %COLOGY ,ETTERS 7ILLIS ! * - " 4HOMAS AND * ( ,AWTON )S THE INCREASED VIGOUR OF INVASIVE WEEDS EXPLAINED BY A TRADE OFF BETWEEN GROWTH AND HERBIVORE RESISTANCE /ECOLOGIA
#HAPTER SIX
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS 2 0 &RECKLETON 0 - $OWLING AND . + $ULVY
).42/$5#4)/. #OMPARED WITH OTHER SCIENCES ECOLOGY HAS FEW GENERAL THEORIES THAT CAN BE APPLIED TO PREDICT THE DYNAMICS OF ITS SYSTEMS FROM lRST PRINCIPLES 4HIS IS PERHAPS NOT SURPRISING GIVEN THE HUGE VARIABILITY OF ECOLOGICAL SYSTEMS ! NUMBER OF BROAD INSIGHTS HAVE EMERGED HOWEVER AND ONE OF THE MOST IMPORTANT OF THESE IS THAT PREDICTING THE DYNAMICS OF ECOLOGICAL SYSTEMS REQUIRES THAT WE UNDERSTAND THE INTERPLAY OF TWO KINDS OF PROCESSES STOCHASTIC AND DETERMINISTIC ,EWONTIN AND #OHEN -AY ,ANDE ET AL 4HIS CONCLUSION IS ESSENTIALLY A CONSENSUS RESULTING FROM A GREAT DEAL OF DEBATE IN THE ECOLOGICAL LITERATURE DATING BACK TO THE S EG !NDREWARTHA AND "IRCH .ICHOLSON (ASSELL 7HITE 0REDICTING BIOLOGICAL INVASIONS IS AN EXTREMELY IMPORTANT APPLIED ECOLOGI CAL PROBLEM BECAUSE INVASIVE SPECIES ARE ECONOMICALLY ENORMOUSLY SIGNIlCANT IN AGRICULTURAL AND CONSERVATION TERMS AND METHODS FOR PREDICTING THE EFFECTS OF CONTROL MEASURES ARE URGENTLY REQUIRED "YERS ET AL /NE OF THE MOST IMPORTANT APPROACHES TO STUDYING BIOLOGICAL INVASIONS IS THROUGH POPULATION MODELLING 0OPULATION MODELS MAY TAKE A RANGE OF FORMS INCLUDING SIMPLE -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
20 &RECKLETON 0- $OWLING AND .+ $ULVY
MATHEMATICAL MODELS (ASSELL -AY -AY ET AL -AYNARD 3MITH 7ATKINSON STATISTICAL MODELS "UCKLEY ET AL A B AND COMPLEX SIMULATIONS 0ACALA ET AL 4HESE MODELS CAN BE USED IN A RANGE OF WAYS FROM MAKING HIGHLY SPECIlC PREDICTIONS ABOUT THE DYNAMICS OF SPECIES IN GIVEN AREAS THROUGH TO GENERAL ANALYSES AIMED AT DEVELOPING A GENERAL UNDERSTANDING OF THE PROCESSES DETERMINING INVASION SUCCESS 5NFORTUNATELY POPULATION MODELS ARE FREQUENTLY EQUATED WITH AN EQUILIBRIUM OR DETERMINISTIC OUTLOOK ON POPULATION DYNAMICS WHICH IS FREQUENTLY CRITICISED (OWEVER EVEN SIMPLE MODELS MAY FREQUENTLY YIELD RATHER COMPLEX OUTCOMES -AY AND /STER &OR INSTANCE A SIMPLE LOGISTIC MODEL OF POPULATION GROWTH MIGHT BE EXPECTED TO YIELD A STRAIGHTFORWARD OUTCOME NAMELY THE SMOOTH GROWTH OF A POPULATION TO ITS CARRYING CAPACITY 7HEN IMPLEMENTED AS A DISCRETE TIME MODEL HOWEVER THE OUTCOME MAY BE FAR MORE COMPLEX AND CHAOTIC DYNAMICS MAY BE POSSIBLE &ROM THE POINT OF VIEW OF PREDICTING POPULATION DYNAMICS THIS RAISED THE POSSIBILITY THAT COMPLETELY DETERMINISTIC SYSTEMS MAY YIELD UNPREDICT ABLE CHANGES IN POPULATION NUMBERS 4HE EARLY S ALSO SAW AN INCREASING REC OGNITION THAT VARIOUS FORMS OF INTERACTIONS AND INTERVENTION COULD YIELD UNSTABLE POPULATION DYNAMICS -AY &OR EXAMPLE HUNTING HARVESTING OR PREDATION COULD POTENTIALLY DESTABILISE POPULATION DYNAMICS TO THE EXTENT THAT OTHERWISE STABLE POPULATIONS MIGHT BECOME EXTINCT GIVEN A PERTURBATION TO THE SYSTEM ! lNAL ELEMENT THAT IS IMPORTANT IN PREDICTING POPULATION CHANGE IS THE STO CHASTIC COMPONENT OF POPULATION CHANGE 3TOCHASTICITY RESULTS FROM RANDOM VARIATIONS IN THE ENVIRONMENT OR FROM RANDOM VARIATION BETWEEN INDIVIDUALS 4HE THEORY FOR STOCHASTIC POPULATION DYNAMICS HAS A LONG HISTORY #OHEN ,EWONTIN AND #OHEN 4ULJAPURKAR AND THERE HAVE BEEN NUMEROUS RECENT DEVELOPMENTS OF THIS ,ANDE ET AL 4HE MAJOR CONCLUSION FROM THIS WORK HAS BEEN THAT THE EFFECTS OF STOCHASTICITY ON POPULATION DYNAMICS MAY BE COMPLEX 0REDICTING THE IMPACTS OF STOCHASTICITY IS NOT A STRAIGHTFORWARD AS MAK ING SOME PARAMETERS OF MODELS RANDOM VARIABLES OR OF CALCULATING AN AVERAGE OF SOME FORM 2ATHER STOCHASTICITY MAY IMPACT IN A PROFOUND AND A QUALITATIVE MANNER ON POPULATION DYNAMICS 4HE PROBLEM OF PREDICTING AND MANAGING POPULATIONS OF INVASIVE SPECIES REQUIRES THAT WE ARE ABLE TO UNDERSTAND THE IMPACTS OF THE FACTORS DETAILED ABOVE ON SEVERAL PHASES OF THE INVASION PROCESS 4HE ELEMENTS OF POPULATION DYNAMICS OF INVASION CAN BE CONCEPTUALLY VIEWED AS CONSISTING OF THREE PHASES ARRIVAL ESTABLISHMENT AND SPREAD $OBSON AND -AY 7ILLIAMSON 4HE PROCESSES DESCRIBED ABOVE MIGHT BE EXPECTED TO PLAY DIFFERENT ROLES DEPEND ING ON WHICH OF THIS PHASES THE INVADING POPULATION IS IN )N THE ARRIVAL AND ESTABLISHMENT PHASES POPULATIONS ARE GROWING FROM LOW DENSITIES AND EXPANDING INTO NEW HABITAT )N THIS PHASE STOCHASTIC FACTORS MAY ARGUABLY BE IMPORTANT AND LIMITING FACTORS LESS SO )N CONTRAST FOLLOWING SUCCESSFUL ESTABLISHMENT AND DURING THE SPREAD PHASE POPULATIONS MAY BE AT MUCH HIGHER DENSITIES AND FACTORS SUCH AS DENSITY DEPENDENCE MAY DOMINATE POPULATION CHANGES #ORRESPONDINGLY THESE DIFFERENCES IN DYNAMICS MAY INmUENCE CONTROL STRATEGIES 4AYLOR AND (ASTINGS
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
-OREOVER WHEN FACTORS SUCH AS !LLEE EFFECTS OPERATE THE DETERMINISTIC COMPONENT OF DYNAMICS MAY BE SIGNIlCANT AT LOW DENSITIES AND INmUENCE POPULA TION PERSISTENCE 4HE KEY TASK FOR POPULATION MODELLING IS TO WORK OUT HOW THESE VARIOUS FACTORS INTERACT WITH EACH OTHER 4HIS CHAPTER IS ORGANISED INTO THREE SECTIONS )N THE lRST SECTION WE REVIEW THE PRINCIPLES OF SIMPLE STOCHASTIC MODELS AND HOW THEY MAY BE APPLIED TO INVASIONS 7E THEN EXAMINE THE DETERMINISTIC COUNTERPARTS OF THESE MODELS AND THE PROB LEMS THESE PRESENT &INALLY WE BRIEmY REVIEW TWO STUDIES THAT EXHIBIT UNSTABLE DYNAMICS AND SPECULATE ON THE GENERALITY OF THESE 34/#(!34)# 0/05,!4)/. $9.!-)#3 !.$ 4(% 34!"),)49 /& 0/05,!4)/.3 )T IS USEFUL TO RECOGNISE TWO SOURCES OF STOCHASTICITY IN POPULATION DYNAMICS %NGEN ET AL SINCE THE SOURCE OF STOCHASTICITY IS IMPORTANT IN UNDERSTAND ING ITS EFFECTS ON POPULATION DYNAMICS %NVIRONMENTAL STOCHASTICITY RESULTS FROM RANDOM VARIATIONS IN DEMOGRAPHIC RATES AS A CONSEQUENCE OF VARIATION IN ENVI RONMENTAL CONDITIONS FOR EXAMPLE RESULTING FROM THE EFFECTS OF WEATHER ! SECOND SOURCE OF STOCHASTICITY IS DEMOGRAPHIC STOCHASTICITY 5NDER DEMOGRAPHIC STOCHAS TICITY THE EXPECTED CONTRIBUTION OF EACH INDIVIDUAL TO THE NEXT GENERATION IS ALSO INDEPENDENT OF THE STATE OF THE POPULATION IN THE PREVIOUS GENERATION HOWEVER THE VARIANCE ABOUT THIS EXPECTATION DOES DEPEND ON THE STATE OF THE POPULATION AS DISTINCT FROM AN !LLEE EFFECT IN WHICH THE EXPECTATION DEPENDS ON DENSITY 3TEPHENS ET AL 3IMPLE STOCHASTIC POPULATION GROWTH
4HE SIMPLEST MODEL FOR POPULATION DYNAMICS IS ONE IN WHICH THE EXPECTED RATES OF DEATH AND FECUNDITY ARE ASSUMED TO BE CONSTANT AND VARY RANDOMLY ABOUT THESE MEANS )F THE NET RATE OF POPULATION CHANGE IN YEAR T IS h T AND .T AND .T ARE POPULATION SIZES IN SUCCESSIVE YEARS THEN THE DYNAMICS OF SUCH A POPULATION CAN BE MODELLED AS .T hT .T
&OR A SPECIES TO BE CAPABLE OF INVASION THE EXPECTED VALUE OF .T 4 .T MUST BE GREATER THAN ONE AS 4 BECOMES LARGE )N A CONSTANT ENVIRONMENT THIS REQUIRES THAT THE VALUE OF h MUST BE GREATER THAN UNITY )N AN ENVIRONMENT IN WHICH THERE IS STOCHASTICITY THE CONDITION ON h IS NOT AS STRAIGHTFORWARD BUT DEPENDS ON THE DISTRIBUTION OF h ABOUT ITS MEAN !CCORDING TO EQUATION POPULATION SIZE AT TIME T 4 IS A NON LINEAR FUNCTION OF hT hT xhT 4 4HIS MEANS THAT THE DISTRI BUTION OF h HAS TO BE UNDERSTOOD IN ORDER TO PREDICT LONG TERM DYNAMICS -ORE COMPLEX EFFECTS SUCH AS THE AUTOCORRELATIONS BETWEEN POPULATION GROWTH RATES IN SUCCESSIVE YEARS MAY ALSO COME INTO PLAY AND FURTHER COMPLICATE PREDICTIONS OF
20 &RECKLETON 0- $OWLING AND .+ $ULVY
POPULATION PERSISTENCE (EINO ET AL !LTHOUGH THE POSSIBILITIES ARE COMPLEX TWO SIMPLE EXAMPLES ILLUSTRATE SOME OF THE MAIN FEATURES OF STOCHASTIC MODELS 4HE MAIN CONCLUSION AT THE END OF THIS SECTION IS THAT THE OUTCOME OF STOCHASTIC MODELS CAN BE MORE COMPLEX THAN ONE MIGHT lRST IMAGINE %NVIRONMENTAL STOCHASTICITY
&IRSTLY ASSUME THAT h IS LOG NORMALLY DISTRIBUTED AS MAY BE THE CASE IN POPULA TIONS SUBJECT TO ENVIRONMENTAL STOCHASTICITY )N THAT CASE EQUATION MAY BE WRITTEN AS WHERE N >LOG . NT NT LOG ;hT =
4HIS IS LINEAR IN N WITH THE CONSEQUENCE THAT THE ARITHMETIC MEAN OF LOG h PREDICTS THE LONG TERM POPULATION TRAJECTORY )T IS EASY TO SHOW THAT THE EXPECTED VALUE OF NT 4 IS NORMALLY DISTRIBUTED WITH MEAN N 4 LOGh AND VARIANCE 4 VAR ;LOGh = IF THE LAMBDAS ARE INDEPENDENT AND NORMALLY DISTRIBUTED &IG A SHOWS EXAMPLES OF A SERIES OF POPULATIONS GROWING IN THIS WAY AND &IG C SHOWS THE DISTRIBUTION OF POPULATION SIZES AFTER A PERIOD OF POPULATION GROWTH !S NOTED ABOVE PREDICTING THE OUTCOME OF STOCHASTICITY REQUIRES THAT THE EFFECTS OF STOCHASTICITY ON POPULATION GROWTH ARE UNDERSTOOD IN DETAIL &OR INSTANCE IF THE DISTRIBUTION OF POPULATION GROWTH RATES IS NOT LOG NORMAL OR IF SUCCESSIVE POPULATION GROWTH RATES ARE NOT INDEPENDENT THEN THE RESULTS IN THE PREVIOUS PARAGRAPH DO NOT HOLD EXACTLY )N SUCH CASES STOCHASTIC CALCULUS HAS TO BE USED IN ORDER TO DETERMINE THE APPROPRIATE METHOD OF TRANSFORMING POPULATION DENSITIES IN ORDER TO PREDICT PERSISTENCE EG ,ANDE $EMOGRAPHIC STOCHASTICITY
4HE SECOND EXAMPLE IS A POPULATION SUBJECT TO DEMOGRAPHIC STOCHASTICITY -AY ,ANDE ,ANDE ET AL $EMOGRAPHIC STOCHASTICITY RESULTS IN VARIABILITY IN WHICH THE VARIANCE DECLINES WITH THE NUMBER OF INDIVIDUALS IN THE POPULATION m $ VAR h . OR AS A HYPERBOLIC FUNCTION OF DENSITY IF . IS THE AVERAGE NUMBER OF INDIVIDUALS PER UNIT AREA AND INDIVIDUALS ARE ASSUMED TO BE RANDOMLY DISTRIBUTED &RECKLETON UNPUB m $ VAR h D. 7HEN COMBINED WITH ENVIRONMENTAL VARIABILITY WHICH HAS VARIANCE m% THE VARIANCE IN POPULATION GROWTH RATE IN THIS MODEL IS
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
m $ VAR h m % .
%XAMPLES OF POPULATIONS GROWING ACCORDING TO THIS MODEL ARE SHOWN IN &IG B 4HE MOST IMPORTANT FEATURE OF THIS MODEL IS THAT IF DENSITY FALLS BELOW A CRITICAL THRESHOLD £ ¥ . m$ ³h n n m% ³ ¤ ¦ THEN EXTINCTION IS HIGHLY LIKELY ,ANDE ET AL 4HE RESULT OF THIS IS A BIMODAL DISTRIBUTION OF POPULATION SIZES AS SHOWN IN &IG D COMPARED WITH THE NORMAL DISTRIBUTION IN &IG C
&IG 3OURCES OF STOCHASTICITY AND EFFECTS ON POPULATION GROWTH A C AND POPULATION SIZE B D 0OPULATION GROWTH WAS DENSITY INDEPENDENT WITH STOCHASTICITY EITHER ENVIRONMENTAL A C OR ENVIRONMENTAL AND DEMOGRAPHIC B D
)N THE MODEL WITH ENVIRONMENTAL STOCHASTICITY ONLY POPULATIONS ARE ABLE TO INVADE IF THE POPULATION GROWTH RATE E XCEEDS A CRITICAL VALUE 4HE GREATER THE
20 &RECKLETON 0- $OWLING AND .+ $ULVY
DIF FERENCE BETWEEN THE LONG TERM AVERAGE AND THIS CRITICAL VALUE THE MORE LIKELY A SPECIES IS TO INVADE /N THE OTHER HAND IF A POPULATION IS SUBJECT TO DEMOGRAPHIC STOCHASTICITY POPULATIONS MUST EXCEED A CRITICAL DENSITY BEFORE INVASION CAN OCCUR 4HEREFORE THE TWO FORMS OF STOCHASTICITY HAVE RATHER DIFFERENT IMPLICA TIONS FOR POPULATION DYNAMICS AND PREDICTING INVASION REQUIRES THAT BOTH OF THESE SOURCES OF STOCHASTICITY ARE UNDERSTOOD IN DETAIL )N NON INVASIVE SPECIES ESTIMATES OF DEMOGRAPHIC AND ENVIRONMENTAL STOCHASTICITY FROM BIRD POPULATIONS SUGGEST THAT BOTH SOURCES MAY BE EXTREMELY SIGNIlCANT AND HENCE THAT THE TWO FORMS NEED TO BE MEASURED SEPARATELY 3AETHER ET AL )MPLICATIONS OF STOCHASTIC MODELS FOR MODELLING INVASIONS
4HE MAIN CONCLUSION FROM THE EXAMPLE MODELS OUTLINED ABOVE IS THAT IN A STO CHASTIC ENVIRONMENT THE LONG TERM POPULATION GROWTH IS NOT A LINEAR FUNCTION OF THE AVERAGE POPULATION GROWTH RATES #OHEN ,EWONTIN AND #OHEN 4ULJAPURKAR .OT ONLY IS IT IMPORTANT TO ESTIMATE THE AMOUNT OF VARI ABILITY IN POPULATION GROWTH RATES &RECKLETON AND 7ATKINSON BUT ALSO TO DISENTANGLE THE RELATIVE ROLES OF DEMOGRAPHIC AND ENVIRONMENTAL VARIATION 4HIS REQUIRES THAT TEMPORALLY REPLICATED MEASURES OF POPULATION GROWTH OR THE COMPONENTS OF POPULATION GROWTH ARE AVAILABLE 7ITHOUT SUCH INFORMATION IT IS NOT POSSIBLE TO PREDICT WHICH SPECIES ARE CAPABLE OF INVADING AND WHICH ARE NOT OR CONDITIONS UNDER WHICH A GIVEN SPECIES WILL BECOME INVASIVE OR NOT OR TO DERIVE REALISTIC MODELS 5NFORTUNATELY SUCH INFORMATION IS RARELY AVAILABLE FOR MANY INVASIVE SPECIES OFTEN BECAUSE INVASIVE SPECIES HAVE RECENTLY BEEN INTRODUCED TO NOVEL ENVIRON MENTS #ONSEQUENTLY LONG TERM DATASETS TEND TO BE RARE 5NDER SUCH CIRCUM STANCES THERE ARE TWO CHOICES FOR THE MODELLER EITHER TO GIVE UP OR TO TRY TO MAKE DO WITH WHATEVER INFORMATION IS AVAILABLE !S AN EXAMPLE OF THE LATTER 2EES AND 0AYNTER DEVELOPED A MODEL FOR THE DYNAMICS AND CONTROL OF INVASIVE POPULATIONS OF 3COTCH "ROOM 4HIS MODEL WAS PARAMETERISED USING A SEVERAL DATA SOURCES FROM BOTH THE NATIVE AND EXOTIC RANGE OF THE SPECIES AS WELL AS AN UNDER STANDING OF ITS BASIC AUTECOLOGY )T SEEMS LIKELY HOWEVER THAT MANY EXISTING MODELS ARE COMPROMISED TO SOME EXTENT IN THEIR PREDICTIVE ABILITY THROUGH A LACK OF DATA ON STOCHASTIC VARIATION IN KEY PARAMETERS 2ECENT WORK HAS SUGGESTED THAT THE DEMOGRAPHIC AND ENVIRONMENTAL COMPO NENTS OF POPULATION GROWTH MAY BE RELATED TO LIFE HISTORY TRAITS IN BIRDS 3AETHER ET AL &OR EXAMPLE DEMOGRAPHIC STOCHASTICITY TENDS TO BE LARGER IN SPECIES WITH GREATER ADULT SURVIVAL AGE AT MATURITY AND GENERATION TIMES 3AETHER ET AL 3IMILARLY THE EXPECTED TIME TO EXTINCTION OF POPULATIONS INCREASED WITH DECREASING CLUTCH SIZE 4HESE RESULTS ARE IMPORTANT BECAUSE THEY SHOW THAT IT IS POSSIBLE TO GENERALIZE ABOUT HOW SENSITIVE POPULATIONS ARE TO DIFFERENT FORMS OF VARIABILITY BASED ON LIFE HISTORY TRAITS 4O DATE THERE HAVE BEEN NO COMPARABLE ANALYSES OF THE DEMOGRAPHICS OF POPULATION DURING THE INITIAL STAGES OF INVASION HOWEVER SUCH ANALYSIS COULD BE ENORMOUSLY REVEALING
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
$%4%2-).)34)# 0/05,!4)/. $9.!-)#3 )F LEFT UNCHECKED THE SYSTEM DElNED BY EQUATION WILL ULTIMATELY BECOME EXTINCT ,EWONTIN #OHEN )F THE VALUE OF h IS GREATER THAN ONE THE EXPECTED MEAN POPULATION SIZE AS 4 BECOMES LARGE IS INlNITE ALTHOUGH COUNTERINTUITIVELY THE PROBABILITY OF EXTINCTION REMAINS EQUAL TO ONE ALBEIT WITH A VERY LONG EXPECTED TIME TO EXTINCTION 4HIS BEHAVIOUR DOES NOT SIT WELL WITH ECOLOGICAL INTUITION #OMMON OBSERVATION APPEARS TO INDICATE THAT THE DYNAMICS OF MANY SPECIES ARE RELATIVELY INVARIANT 3OME INVASIVE SPECIES DO EXHIBIT INTRINSICALLY COMPLEX POPULATION DYNAMIC BEHAVIOUR PARTICULARLY THE VIRUSES THAT CAUSE DISEASES SUCH AS MEASLES AND mU %ARN ET AL #YCLIC DYNAMICS ARE REASONABLY COMMON IN A RANGE OF TAXA +ENDALL ET AL 'INZBURG #OLYVAN HOWEVER THESE TEND TO BE EXTRINSICALLY DRIVEN OR THE CONSEQUENCE OF SPECIES INTERACTIONS SUCH AS PREDATOR PREY DYNAMICS RATHER THAN INTRINSIC PROPERTIES OF POPULATIONS ! GREAT DEAL OF EFFORT HAS BEEN EXPENDED ON UNDERSTANDING lRSTLY WHY POPU LATIONS DO NOT SIMPLY BOOM OR BUST IN ACCORD WITH THE MOST SIMPLE DENSITY INDEPENDENT MODELS AND SECONDLY WHY DIFFERENT SYSTEMS EXHIBIT ALTERNATIVE KINDS OF POPULATION DYNAMICS $ENSITY DEPENDENCE
$ENSITY DEPENDENCE OCCURS WHEN ANY VITAL RATE CHANGES SYSTEMATICALLY WITH DEN SITY 3TRICTLY SPEAKING THIS COULD INCLUDE A RANGE OF POPULATION LEVEL PHENOMENA 2OYAMA BUT TYPICALLY THIS DElNITION IS TAKEN TO IMPLY THAT SOME PER CAPITA RATE SUCH AS MORTALITY OR FECUNDITY VARIES SYSTEMATICALLY WITH DENSITY $ENSITY DEPENDENCE OF THIS SORT MAY RESULT FROM A RANGE OF ECOLOGICAL PROCESSES 4HE MOST COMMONLY RECOGNISED FORM IS NEGATIVE DENSITY DEPENDENCE WHICH RESULTS FROM DIRECT COMPETITION FOR RESOURCES .ICHOLSON SUCH AS FOOD SHELTER OR MATES -ORE INDIRECTLY DENSITY DEPENDENCE MAY ARISE FROM THE IMPACT OF OTHER SPECIES FOR INSTANCE PREDATORS OR PARASITES WHICH MAY INCREASE MORTALITY RATES AT HIGH PREY OR HOST DENSITIES RESPECTIVELY !S NOTED ABOVE DENSITY INDEPENDENT MODELS SUGGEST THAT DENSITY DEPENDENCE SHOULD BE HIGHLY PREVALENT BECAUSE IN THE ABSENCE OF DENSITY DEPENDENCE POPULATIONS ARE LIKELY TO EITHER EXPAND WITHOUT LIMIT OR BECOME EXTINCT $ESPITE THIS MANY MODELS FOR POPULATION DYNAMICS IGNORE DENSITY DEPENDENCE AND THIS CAN SEVERELY COMPROMISE MODEL PREDICTIONS EG SEE &RECKLETON ET AL 4HIS PROBLEM MAY BE ESPECIALLY ACUTE FOR INVASIVE SPECIES WHICH MIGHT BE EXPECT ED TO HAVE A HIGH AVERAGE VALUE OF h AND HENCE BE CAPABLE OF RAPIDLY GROWING TO HIGH DENSITIES )N THE INITIAL STAGES OF AN INVASION THE STOCHASTIC FACTORS THAT DETER MINE h SEEM LIKELY TO PLAY A KEY ROLE IN DETERMINING INVASION SUCCESS (OWEVER AS SHOWN BELOW FOLLOWING SUCCESSFUL INVASION THE ULTIMATE SIZE REACHED BY THE INVADER POPULATION WILL BE IN LARGE PART DETERMINED BY THE FORM NATURE AND STRENGTH OF DENSITY DEPENDENCE
20 &RECKLETON 0- $OWLING AND .+ $ULVY
-ODELS FOR DENSITY DEPENDENT POPULATION GROWTH
! SUITE OF MODELS HAVE BEEN EMPLOYED TO MODEL THE DYNAMICS OF SPECIES GROWING IN A DENSITY DEPENDENT FASHION 4HE BEST KNOWN OF THESE IS THE LOGISTIC MODEL HERE THE DISCRETE TIME VERSION . T .T R.T n .+
)N THIS FORM THE LOGISTIC MODEL IS A POOR MODEL FOR DESCRIBING ECOLOGICAL DYNAM ICS 4HERE ARE A NUMBER OF PROBLEMS WITH THIS MODEL INCLUDING THE EQUILIBRIUM IS INDEPENDENT OF THE lNITE RATE OF INCREASE DENSITY DEPENDENCE IS LINEAR AND STABIL ITY BEHAVIOUR IS DETERMINED SOLELY BY THE MAXIMUM RATE OF INCREASE R SEE BELOW $ESPITE THIS THE LOGISTIC MODEL IS WIDELY EMPLOYED IN THEORETICAL MODELLING PROB ABLY BECAUSE IT IS ANALYTICALLY VERY CONVENIENT TO WORK WITH -ORE REALISTIC MODELS HAVE BEEN SUGGESTED INCLUDING MODIlCATIONS TO THE LOGIS TIC IN ORDER TO MAKE IT MORE REALISTIC EG THE THETA LOGISTIC OF ,ANDE ET AL /NE PARTICULARLY USEFUL MODEL IS THAT OF (ASSELL . T h.T ; A.T = nB
4HIS MODEL HAS TWO PARAMETERS THAT MODEL DIFFERENT ASPECTS OF THE DENSITY DEPENDENT RESPONSE A DETERMINES THE DENSITY AT WHICH THE PER CAPITA EFFECTS OF DENSITY DEPENDENCE BECOME SIGNIlCANT WHILST B VARIES THE RATE OF CHANGE IN POPU LATION GROWTH RATE AS DENSITY BECOMES HIGH AND MAY BE RELATED TO THE NATURE OF COMPETITION CONTEST VERSUS SCRAMBLE (ASSELL OR THE EFlCIENCY WITH WHICH RESOURCES ARE CONVERTED INTO POPULATION GROWTH &IRBANK AND 7ATKINSON &RECKLETON AND 7ATKINSON 4HE EQUILIBRIUM OF THIS MODEL IS GIVEN BY .È hB n A
4HE IMPORTANT ADVANCE OVER THE LOGISTIC MODEL IS THAT THE EQUILIBRIUM IS A COMPOUND OF THREE MODEL PARAMETERS )NCREASING THE lNITE RATE OF INCREASE OR DECREASING A LEADS TO INCREASES IN POPULATION DENSITY 4HESE EFFECTS ARE THEN MODULATED BY B WHICH ALSO DETERMINES THE STABILITY PROPERTIES OF THE MODEL )T SEEMS LIKELY THAT THE THREE PARAMETERS MAY BE RELATED TO EACH OTHER AT A NUMBER OF SCALES 7ITHIN POPULATIONS TEMPORAL VARIABILITY IN THE ENVIRONMENT MAY LEAD TO VARIATION IN ANY OF THE PARAMETERS !S POINTED OUT BY #HESSON AND (UNTLEY UNDERSTANDING HOW THE EFFECTS OF STOCHASTICITY INTERACT WITH THE STRENGTH OF COMPETITION IS THE KEY TO PREDICTING THE OUTCOME OF COMPETI TION IN STOCHASTIC ENVIRONMENTS )N THE MODEL ABOVE THE PROBLEM IS TO UNDERSTAND HOW THE PARAMETERS A AND h COVARY WITH EACH OTHER )F h AND A ARE INDEPENDENT THEN POPULATION GROWTH RATES ARE TERMED ADDITIVE &IG A WITH THE CONSE QUENCE THAT STOCHASTIC ENVIRONMENTAL EFFECTS IMPACT DIRECTLY ON POPULATION SIZES &IG C )N CONTRAST SUB ADDITIVE POPULATION GROWTH RATES OCCUR WHEN h AND
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
&IG )NTERACTIONS BETWEEN DENSITY DEPENDENCE AND STOCHASTICITY ,INES REPRESENT POPULATION GROWTH UNDER DIFFERENT ENVIRONMENTAL CONDITIONS A !DDITIVE POPULATION GROWTH RATES B SUB ADDITIVE POPULATION GROWTH RATES C A POPULATION SUBJECT TO STO CHASTICITY AND ADDITIVE POPULATION GROWTH D A POPULATION SUBJECT TO STOCHASTICITY AND SUB ADDITIVE POPULATION GROWTH
A ARE CORRELATED WITH EACH OTHER &IG A )N SUCH POPULATIONS THE STRENGTH OF COMPETITION CHANGES SO AS TO BUFFER POPULATION GROWTH FROM STOCHASTIC ENVIRON MENTAL CHANGES 4HE CONSEQUENCE IS THAT POPULATIONS SUBJECT TO SUB ADDITIVE POPULATION GROWTH ARE BUFFERED AGAINST ENVIRONMENTAL CHANGE &IG D SHOWS A POPULATION SUBJECT TO PERTURBATIONS IDENTICAL TO THOSE IN &IG C HOWEVER THE SUB ADDITIVE POPULATION GROWTH RATES CLEARLY HAVE AN IMPORTANT BUFFERING EFFECT &ROM THE POINT OF VIEW OF PREDICTING THE DYNAMICS OF INVASIVE SPECIES THE PAT TERNS SHOWN IN &IGS A AND B HAVE TWO IMPORTANT CONSEQUENCES &IRST THE FORM OF DENSITY DEPENDENCE AND ADDITIVITY INmUENCES THE EFFECTS OF STOCHASTICITY 3ECOND THE FORM OF ADDITIVITY CAN INmUENCE THE EFFECTS OF CHANGES TO MANAGEMENT &OR INSTANCE IF POPULATION GROWTH RATES ARE SUB ADDITIVE THEN REDUCTIONS IN h
20 &RECKLETON 0- $OWLING AND .+ $ULVY
RESULTING FROM ATTEMPTS AT CONTROL OR ERADICATION WILL BE COMPENSATED FOR BY REDUCTION IN THE STRENGTH OF DENSITY DEPENDENCE YIELDING NO NET EFFECT ON POPULA TION NUMBERS 4HUS IT IS NOT SUFlCIENT SIMPLY TO DOCUMENT THE EFFECTS OF STOCHAS TICITY OR DENSITY DEPENDENCE IN ISOLATION BUT THE INTERACTION BETWEEN THESE ALSO NEEDS TO BE UNDERSTOOD )N PRACTICE THIS IS VERY DIFlCULT AS THIS REQUIRES THAT THE FORM OF DENSITY DEPENDENCE IS MEASURED UNDER A RANGE OF ENVIRONMENTAL CONDI TIONS WHICH IS HIGHLY DATA INTENSIVE .ON LINEAR DYNAMICS AND STABILITY
!S NOTED ABOVE IN THE MID S IT WAS FOUND THAT SIMPLE ECOLOGICAL MODELS COULD YIELD UNEXPECTEDLY COMPLICATED PATTERNS OF POPULATION DYNAMICS -AY -AY AND /STER &IG A B )N SHORT IN MODELS FOR DENSITY DEPENDENT POPULATION GROWTH FOR ORGANISMS WITH DISCRETE GENERATIONS DENSITY DEPENDENCE AT HIGH DENSITY MAY OVERCOMPENSATE FOR CHANGES IN DENSITY WITH THE RESULT THAT INCREASES IN POPULATION SIZE ABOVE THE DETERMINISTIC EQUILIBRIUM TEND TO BE FOL LOWED BY DISPROPORTIONATELY LARGE DECREASES 4HE CONSEQUENCE OF THIS IS CYCLIC DYNAMICS OR MORE COMPLEX BEHAVIOUR SUCH AS LIMIT CYCLES AND CHAOS 5NDER SUCH CIRCUMSTANCES POPULATIONS EXHIBIT SUSTAINED mUCTUATIONS IN POPULATION SIZE THAT ARE APPARENTLY RANDOM AND SUPERlCIALLY SIMILAR TO THE mUCTUATIONS IN POPULATION SIZES THAT ARE SEEN IN REAL POPULATIONS %XTENSIVE ATTEMPTS HAVE BEEN MADE TO lND EXAMPLES OF POPULATION EXHIBITING CHAOTIC DYNAMICS (OWEVER FEW EXAMPLES EXIST )N FACT IN SOME CASES THERE ARE GOOD REASONS TO EXPECT THAT CHAOTIC DYNAMICS ARE RATHER UNLIKELY )N PLANTS FOR EXAMPLE THE ABSENCE OF REPRODUCTIVE THRESHOLDS THE PRESENCE OF A SEEDBANK AND ASYMMETRIC COMPETITION LEADING TO COMPENSATING DENSITY RESPONSES ALL LEAD TO GENERALLY STABLE POPULATION DYNAMICS 2EES AND #RAWLEY &RECKLETON AND 7ATKINSON )MPORTANTLY THIS MULTIPLICITY OF STABILITY GENERATING MECHANISMS MEANS THAT EVEN WHEN ONE CONDITION FOR INSTABILITY HOLDS OTHERS TEND TO CANCEL THIS OUT EG "UCKLEY ET AL -OREOVER GENERAL REVIEWS OF THE STABILITY PROPERTIES OF NATURAL POPULATIONS APPEAR TO SHOW THAT MOST SINGLE SPECIES POPULATIONS SHOW STABLE DYNAMICS (ASSELL ET AL ,ONSDALE &RECKLETON AND 7ATKINSON !S NOTED ABOVE IN THE MAJORITY OF DOCUMENTED CASES CYCLIC DYNAMICS TEND TO BE DRIVEN BY EXOGENOUS FACTORS OR INTERACTIONS WITH OTHER SPECIES EG SEE +ENDALL ET AL 0OSITIVE DENSITY DEPENDENCE AND INSTABILITY
4HE MODELS DESCRIBED ABOVE EMPHASISE THE NEGATIVE EFFECTS OF DENSITY DEPENDENCE ON POPULATION GROWTH RATES (OWEVER RECENT REVIEWS HAVE POINTED OUT THAT NOT ALL DENSITY DEPENDENT EFFECTS ON POPULATION GROWTH ARE OF THIS FORM 3TEPHENS AND 3UTHERLAND 3TEPHENS ET AL 0OSITIVE DENSITY DEPENDENCE RATHER CONFUSINGLY TERMED hINVERSEv DENSITY DEPENDENCE BY SOME AUTHORS IS MOST WELL KNOWN THROUGH !LLEE EFFECTS !LLEE EFFECTS ARISE MOST COMMONLY IN SOCIAL SPECIES
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
&IG 3TABLE AND UNSTABLE EQUILIBRIA RESULTING FROM !LLEE EFFECTS 4HE RELATIONSHIP BETWEEN POPULATION GROWTH RATE AND DENSITY IS HUMPED 7HERE THE CURVE CUTS THE LINE OF ZERO POPULATION GROWTH RATE THERE IS AN EQUILIBRIUM !S INDICATED BY THE ARROWS THE UPPER EQUILIBRIUM IS STABLE WHEREAS THE LOWER ONE IS UNSTABLE
WHERE COOPERATION BETWEEN INDIVIDUALS BREAKS DOWN AT LOW DENSITIES LEADING TO A DECLINE IN SOME ASPECTS OF lTNESS WITH DECREASING DENSITIES )N THE EXTREME SUCH COMPONENT !LLEE EFFECTS WHICH AFFECT ONE COMPONENT OF lTNESS MAY BE MANIFEST AT THE LEVEL OF POPULATION GROWTH LEADING TO DEMOGRAPHIC !LLEE EFFECTS IE ARE SO IMPORTANT THAT THEY IMPINGE ON RATES OF POPULATION CHANGE 3TEPHENS AND 3UTHERLAND 4HE IMPORTANCE OF !LLEE EFFECTS IN POPULATION GROWTH IS THAT THESE CAN LEAD TO A THRESHOLD DENSITY BELOW WHICH POPULATIONS CANNOT PERSIST SEE &IG 4HIS IS OF COURSE HIGHLY SIGNIlCANT FOR THE DYNAMICS OF INVASIVE SPECIES SINCE INVASIONS REQUIRE THAT SPECIES ARE CAPABLE OF ARRIVING IN NEW ENVIRONMENTS AT LOW DENSITIES AND THEN SUBSEQUENTLY INCREASING 4HIS CAN HAVE IMPORTANT IMPLI CATIONS FOR RATES OF SPATIAL SPREAD ,EWIS AND +AREIVA AS WELL AS RESPONSES OF POPULATIONS TO STOCHASTIC VARIABILITY ,IEBHOLD AND "ASCOMPTE EXPLORED THE CONSEQUENCES OF !LLEE EFFECTS AND STOCHASTICITY FOR THE CONTROL OF INVASIVE SPECIES 4HE MOST IMPORTANT OUTCOME OF !LLEE EFFECTS IN THEIR MODELS WAS THAT !LLEE EFFECTS CAN INmUENCE THE OUTCOMES OF ERADICATION PROGRAMMES &REQUENTLY IT IS FOUND THAT CLOSE TO ERADICATION IS REQUIRED FOR CONTROL PROGRAMMES TO BE EFFECTIVE "ECAUSE SUCH HIGH LEVELS OF CONTROL ARE GENERALLY DIFlCULT TO ACHIEVE THIS MAY PROHIBIT ATTEMPTS AT CONTROL (OWEVER !LLEE EFFECTS MAY LEAD TO EXTINCTION THRESHOLDS AT LOW DENSITIES WITH
20 &RECKLETON 0- $OWLING AND .+ $ULVY
THE RESULT THAT LOWER RATES OF CONTROL MAY YIELD ERADICATION ,IEBHOLD AND "ASCOMPTE STUDIED POPULATIONS OF THE 'YPSY -OTH ,YMANTIA DISPER IN WHICH THEY FOUND THAT ERADICATION COULD BE ACHIEVED WITH C MORTALITY IN A MODEL FOR THE POPULATION WHICH INCLUDED AN !LLEE EFFECT WHEREAS IN THE ABSENCE OF THE !LLEE EFFECT CLOSE TO MORTALITY WOULD BE REQUIRED )N THE CASE STUDY BELOW WE DESCRIBE IN MORE DETAIL A SYSTEM IN WHICH !LLEE EFFECTS ARE EXTREMELY IMPORTANT IN EXPLAINING INVASIONS -ULTISPECIES INTERACTIONS
4HE MAIN FOCUS ON THIS REVIEW SO FAR HAS BEEN ON SINGLE SPECIES DYNAMICS (OWEVER INTERACTIONS BETWEEN SPECIES CAN AFFECT THE STABILITY OF POPULATION DYNAMICS )NDEED MOST SPECIES DO NOT LIVE IN ISOLATION SO THIS POSSIBILITY MAY BE QUITE COMMON AND WE REVIEW TWO EXAMPLES BELOW )N AN INmUENTIAL PAPER -AY SUGGESTED THAT INSTABILITY MAY BE A COM MON PROPERTY OF MANY FORMS OF ECOLOGICAL SYSTEMS (E SHOWED THAT THE SAME MODELLING FRAMEWORK COULD BE APPLIED TO PREDATOR PREY HARVESTED AND OR INDEED ANY CONSUMER RESOURCE SYSTEM 4HIS EFFECT ARISES AS A CONSEQUENCE OF THE FUNC TION RESPONSE OF THE CONSUMER 7HEN CONSUMERS ARE AT LOW DENSITIES THE RATE OF CONSUMPTION OF RESOURCES INCREASES WITH INCREASING RESOURCE DENSITY WITH THE CONSEQUENCE THAT THE RATE OF RESOURCE LOSS IS POSITIVELY RELATED TO RESOURCE DEN SITY !T LOW DENSITIES CONSUMERS CAN POTENTIALLY ERADICATE THEIR RESOURCES AT LOW DENSITIES "Y CONTRAST AT HIGH RESOURCE DENSITIES RESOURCES BECOME SATURAT ING AND EFFECTIVELY THE RATE OF RESOURCE LOSS TO CONSUMERS IS NEGATIVELY RELATED TO RESOURCE DENSITY AT HIGH DENSITIES OF RESOURCES 4HIS DUAL BEHAVIOUR LEADS TO THE POTENTIAL FOR TWO EQUILIBRIA ONE AT LOW RESOURCE DENSITIES THE OTHER AT HIGH RESOURCE DENSITIES )F IT EXISTS THE EQUILIBRIUM AT LOW DENSITIES IS TYPICALLY UNSTABLE 2ECENTLY 'ASCOIGNE AND ,IPCIUS HAVE EXTENDED THIS FRAMEWORK TO CONSIDER THE AGGREGATIVE RESPONSES OF RESOURCES AND HAVE EMPHASISED THAT SUCH BEHAVIOUR HAS BEEN LARGELY IGNORED IN THE APPLIED AND CONSERVATION LITERATURE AND SHOW THAT THERE ARE A GROWING NUMBER OF SYSTEMS THAT IMPLICATE SUCH A MECHANISM #OMPETITIVE INTERACTIONS MAY ALSO YIELD INSTABILITIES IN TWO SOMEWHAT DIFFERENT WAYS &IRST SIMPLE MODELS FOR THE DYNAMICS OF TWO COMPETING SPECIES SHOW THAT THREE DISTINCT OUTCOMES MAY OCCUR I ONE SPECIES OR ANOTHER EXCLUDES THE OTHER II THE COMPETING SPECIES SETTLE AT A STABLE JOINT EQUILIBRIUM III THERE IS A JOINT EQUILIBRIUM BUT WHICH IS UNSTABLE SO THAT PERTURBATIONS FROM THE JOINT EQUILIB RIUM LEAD TO THE SYSTEM BECOMING DOMINATED BY ONE SPECIES OR ANOTHER 4HIS LATTER UNSTABLE CONDITION MAY ARISE IF THE PER CAPITA EFFECTS OF INTER SPECIlC COMPETITION ARE GREATER THAN THE PER CAPITA EFFECTS OF INTRA SPECIlC COMPETITION )N THE CASE STUDIES BELOW WE DETAIL SUCH AN EXAMPLE 3ECOND COMPETITIVE INTERACTIONS MAY YIELD UNSTABLE DYNAMICS WHEN MULTI SPECIES SYSTEMS IN INTERACTIONS ARE STRONG ARE SUBJECTED TO PERTURBATIONS 4ILMAN ET AL 4HE REASON FOR THIS IS THAT IN SUCH A MIXTURE THE DYNAMICS OF ANY SIN GLE SPECIES ARE A COMPLEX FUNCTION OF THE DENSITIES OF ALL THE SPECIES #ONSEQUENTLY
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
THE RESPONSE OF THE SYSTEM TO PERTURBATION MAY BE COMPLEX AND PERTURBATION MAY LEAD TO COMPLEX INTERMEDIATE OR TRANSIENT DYNAMICS 4HE SIGNIlCANCE OF THIS IS THAT FOLLOWING A CHANGE SUCH AS THE INVASION OF A NEW SPECIES THE ENTIRE SYSTEM MAY TAKE MANY GENERATIONS TO RETURN TO EQUILIBRIUM
#!3% 345$)%3 4HE PREVIOUS SECTIONS HAVE EMPHASISED THAT PREDICTING THE DYNAMICS OF INVASIVE SPECIES MAY REQUIRE THAT A SUITE OF PROCESSES ARE DIS ENTANGLED 4HESE INCLUDE THE EFFECTS OF STOCHASTICITY AS WELL AS THE STRENGTHS OF INTRA AND INTER SPECIlC INTERAC TIONS IN THE WIDEST SENSE &OR INVASIVE SPECIES THE KEY QUESTIONS ARE HOW THESE PROCESSES AFFECT THE INVASION OF POPULATIONS INTO NEW ENVIRONMENTS AS WELL AS HOW THEY DETERMINE POPULATION SIZE AND THE OUTCOME OF CONTROL STRATEGIES )N THIS SECTION WE REVIEW IN DETAIL TWO CASE STUDIES OF INVASIVE SPECIES WHICH HAVE BEEN STUDIES USING SIMPLE MODELLING APPROACHES .ECESSARILY IT IS IMPOSSIBLE TO CONSIDER ALL OF THE PROCESSES DESCRIBED ABOVE 4HE lRST EXAMPLE ILLUSTRATES THE KEY ROLE THAT EXTREME STOCHASTICITY MAY PLAY IN DETERMINING INVASION SUCCESS AND HOW THIS MAY BE MODULATED BY THE EFFECTS OF COMPETITION 4HE SECOND EXAMPLE SHOWS THE EFFECT OF PERTURBATION ON A PREDATOR PREY SYSTEM WITH AN INSTABILITY 6ULPIA BROMOIDES IN !USTRALIAN PASTURES THE INTERPLAY OF STOCHASTICITY AND INSTABILITY
4HIS EXAMPLE SHOWS HOW INSTABILITY AND STOCHASTICTY SIMULTANEOUSLY PLAY ROLES IN DETERMINING WHETHER A SPECIES INVADES A SYSTEM 6 BROMOIDES IS A WINTER ANNUAL WHICH ORIGINATES FROM THE -EDITERRANEAN AND HAS BECOME A PROBLEM IN ANNUAL PASTURE SYSTEMS IN !USTRALIA )N CONTRAST IN 3PAIN AND 0ORTUGAL WHERE IT OCCURS NATURALLY IN PASTURES 6 BROMOIDES IS NOT REGARDED AS A PROBLEM SPECIES 6 BROMOIDES WAS PROBABLY INTRODUCED TO !USTRALIA AS A CONTAMINANT OF SEED OR FORAGE 3EVERAL SPECIES OF THE GENUS 6ULPIA WERE INTRODUCED TO !USTRALIA 7E STUDIED THE INVASION DYNAMICS OF ANNUAL PASTURES IN .37 IN WHICH 6BROMOIDES IS THE COMMONEST OF THE SPECIES AND OCCURS IN C OF THE PASTURES WHERE THE GENUS IS PRESENT $OWLING 'IVEN THAT THE 6ULPIA GENUS IS WELL ESTABLISHED IN !USTRALIA THE CURRENT PROBLEM IS TO DETERMINE WHAT FACTORS ENABLE THE PERSIS TENCE AND SPREAD OF THE SPECIES 6 BROMOIDES IS A PROBLEM BECAUSE ALTHOUGH IN THE EARLY STAGES OF THE GROWING SEASON IT MAY PROVIDE SOME USEFUL FORAGE FOR LIVE STOCK THE FORAGE PRODUCED LATE IN THE SEASON IS OF VERY LOW NUTRITIONAL VALUE AND BECAUSE THE SEEDS PRODUCED BY THE WEED BECOME TANGLED IN THE WOOL OF SHEEP AND MAY EVEN CAUSE PHYSICAL INJURIES TO LIVE STOCK ,ONG TERM MANAGEMENT OF 6ULPIA IS DIFlCULT IN PASTURES THAT ARE DOMINATED BY ANNUALS IE IN WHICH THE PERENNIAL COMPONENT IS LOW 4HE PROBLEM OF CONTROLLING 6ULPIA IS COMPOUNDED BY THE HIGH SEED PRODUCTION OF THE SPECIES WHICH ALLOWS FAST POPULATION RECOVERY IN THE YEARS FOLLOWING HERBICIDE
20 &RECKLETON 0- $OWLING AND .+ $ULVY
APPLICATION AS WELL AS HIGH RATES OF COMPENSATORY GROWTH OF SURVIVORS FOLLOWING HERBICIDAL CONTROL $OWLING ET AL 4HE MAIN QUESTIONS THAT ARE IMPORTANT IN UNDERSTANDING THE DYNAMICS OF 6 BROMOIDES AS WELL AS IN PREDICTING THE EFFECTS OF MANAGEMENT ARE I HOW DO INTERACTIONS WITHIN AND BETWEEN SPECIES AFFECT LONG TERM DYNAMICS II (OW ARE POPULATION DYNAMICS AND LONG TERM PERSISTENCE AFFECTED BY STOCHASTICITY &RECKLETON ET AL DEVELOPED A MODEL TO PREDICT THE DYNAMICS OF THIS SPECIES IN A MULTI SPECIES PASTURE MIXTURE IN ORDER TO ADDRESS THESE QUESTIONS 4HE POPULATION DYNAMICS OF 6 BROMOIDES WERE STUDIED IN A YEAR lELD EXPERI MENT CONDUCTED BETWEEN AND !RTIlCIAL PASTURES WERE ESTABLISHED COMPRISING THREE SPECIES 6 BROMOIDES TOGETHER WITH TWO @DESIRABLE SPECIES 4RIFOLIUM SUBTERRANEUM A LEGUME AND ,OLIUM RIGIDUM ANOTHER GRASS 0ASTURES WERE SET UP ORIGINALLY WITH LOW MEDIUM AND HIGH DENSITIES OF 4RIFOLIUM LOW OR ZERO DENSITIES OF ,OLIUM AND LOW OR HIGH DENSITIES OF 6ULPIA 4HESE ARTIlCIAL PAS TURES WERE ALLOWED TO GROW UNTIL SPRING WHEN HALF OF THE PLOTS WERE SPRAYED WITH HERBICIDE IN ORDER TO CREATE A FURTHER DENSITY DIFFERENTIAL OF 6ULPIA 4HE YEAR WAS A DROUGHT YEAR AND WE ESTIMATED THAT DROUGHTS OF THIS SEVERITY OCCUR EVERY YEARS OR SO &RECKLETON ET AL 7E USED THE DATA FROM THIS EXPERIMENT TO PARAMETERISE A MODEL PREDICTING THE NUMBERS NUMBERS OF MATURE PLANTS . AND SEEDS IN THE SEEDBANK 3 OF EACH OF THE THREE SPECIES IE n .I x T hI .I T ³ -_IJ .JT ³ iI 3I T J
n 3I x T hI .I T ³ -_IJ .JT ³ iI 3I T J h AND h MEASURE THE PER CAPITA RATE OF CHANGE IN NUMBERS OF MATURE PLANTS AND SEEDS RESPECTIVELY OWING TO SEED PRODUCTION AT THE VEGETATIVE STAGE p AND p RESPECTIVELY MEASURE THE RECRUITMENT OF PLANTS FROM AND PERSISTENCE OF SEEDS WITHIN THE SEED BANK COMPETITION BETWEEN ANY PAIR OF SPECIES I AND J IS MEASURED BY A PARAMETER _IJ WHICH IS THE PER CAPITA REDUCTION IN POPULATION GROWTH .OTE THAT WHEN I AND J ARE DIFFERENT _IJ REFERS TO INTER SPECIlC COMPETITION IE COM PETITION BETWEEN SPECIES BUT WHEN I J _ MEASURES INTRA SPECIlC COMPETITION IE COMPETITION WITHIN THE SPECIES &OR THE THREE SPECIES MIXTURE THEREFORE THERE ARE NINE IE × COMPETITION COEFlCIENTS !NALYSIS OF THE lTTED MODEL INDICATED A CLEAR DIVISION WITHIN THIS SIMPLE COM MUNITY &IRST COMPETITION BETWEEN 4RIFOLIUM AND THE TWO GRASSES WAS VERY WEAK INDEED AND THERE WAS VERY LITTLE INmUENCE OF THE 4RIFOLIUM ON THE DYNAMICS OF EITHER OF THE GRASSES OR OF THE GRASSES ON THE 4RIFOLIUM 4HIS IS PERHAPS UNSUR
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
PRISING AS LEGUMES AND GRASSES REPRESENT RATHER DIFFERENT FUNCTIONAL GROUPS /N THE OTHER HAND COMPETITION BETWEEN THE TWO GRASSES WAS VERY STRONG AND THEY INmUENCED EACH OTHERS DYNAMICS PROFOUNDLY 3INCE NEITHER OF THE GRASSES POSSESS VERY PERSISTENT SEEDBANKS IN CONTRAST TO THE 4RIFOLIUM THE DYNAMICS OF THESE TWO SPECIES CAN BE MORE SIMPLY MODELLED BY A SIMPLE SPECIES MODEL ., T h, ., T _,, .,T _,6 .6 T n .6 T h6 .6 T _66 .6T _6, ., T n
4HE DYNAMICS OF THIS SYSTEM MAY BE ANALYSED USING A SIMPLE PHASE PLANE ANALYSIS &IG 4HE lTTED COMPETITION COEFlCIENTS FOR EQUATIONS HAD THE PROPERTY THAT IN BOTH MODELS THE INTER SPECIlC COEFlCIENTS WERE LARGER THAN THE INTRA SPECIlC COEFlCIENTS !S A CONSEQUENCE THE EQUILIBRIUM FOR THE TWO SPECIES IS PREDICTED TO BE UNSTABLE &IG A 4HE UNSTABLE EQUILIBRIUM HAS AN IMPORTANT CONSEQUENCE FOR THE INVASION OF 6ULPIA 6ULPIA IS ONLY ABLE TO INVADE COMMUNITIES WHEN THE DENSITY OF ,OLIUM IS LOW %XAMPLES OF THE PREDICTED DYNAMICS ARE SHOWN IN &IG B AND C 6ULPIA IS UNABLE TO INVADE A HIGH DENSITY OF ,OLIUM &IG B IT IS ABLE TO INVADE A LOW DENSITY &IG C !T lRST SIGHT IT APPEARS THAT THE INVASION OF 6ULPIA INTO PASTURES MAY BE DIFlCULT BECAUSE IT NEEDS TO EXCEED A CRITICAL DENSITY IN ORDER TO INVADE )F THE ENVIRONMENT WERE CONSTANT THEN THIS WOULD BE THE CASE )N REALITY HOWEVER THE ENVIRONMENT IS NOT CONSTANT !S NOTED ABOVE PERIODICALLY SEVERE DROUGHTS OCCUR 4HESE GREATLY FACILITATE THE INVASION OF 6ULPIA BECAUSE THESE DROUGHTS REDUCE THE DENSITIES OF ALL SPECIES TO LOW LEVELS &OLLOWING DROUGHT THE lNITE RATE OF INCREASE OF 6ULPIA IS MUCH GREATER THAN THAT OF ,OLIUM h6 WHILST h, #ONSEQUENTLY 6ULPIA POPULATIONS RESPOND MUCH FASTER FOLLOWING DROUGHTS THAN DO ,OLIUM POPULATIONS AND HENCE THE INVASION OF 6ULPIA IS FACILITATED 7E ESTIMATED THAT SEVERE DROUGHTS OCCURRING WITH A FREQUENCY OF EVERY IN TO IN YEARS WOULD GREATLY FACILI TATE THE INVASION OF 6ULPIA 3UGGESTIVELY ANECDOTAL EVIDENCE SUGGESTS THAT 6ULPIA BECAME NOTICED AS A PROBLEM FOLLOWING SEVERE DROUGHTS IN THE EARLY S ALTHOUGH WE HAVE NO QUANTITATIVE DATA WITH WHICH TO SUPPORT THIS CONTENTION )N SUMMARY UNDERSTANDING THE INVASION OF 6ULPIA INTO PASTURES AND ITS PER SISTENCE REQUIRES THAT WE NOT ONLY UNDERSTAND THE DETAILS OF COMPETITION WITH OTHER SPECIES BUT ALSO THE EFFECTS OF LONG TERM STOCHASTICITY 3TOCHASTICITY PLAYS A KEY ROLE BECAUSE THE UNSTABLE EQUILIBRIUM WOULD MAKE INVASION OF 6ULPIA UNLIKELY FROM LOW DENSITIES INTO ESTABLISHED PASTURES (OWEVER THE EFFECTS OF COMPETITION BECOME MODULATED BY PERIODIC DROUGHTS MAKING INVASION FAR MORE LIKELY )NSTABILITY AND OUTBREAKS THE CROWN OF THORNS STARFISH
4HE SECOND EXAMPLE ILLUSTRATES HOW !LLEE EFFECTS RESULTING FROM PREDATOR PREY INTERACTIONS CAN LEAD TO UNSTABLE POPULATION DYNAMICS AND CONSEQUENTLY DETER MINE WHETHER INVASIONS ARE POSSIBLE OR NOT 4HERE HAS BEEN A GREAT DEAL OF RECENT
20 &RECKLETON 0- $OWLING AND .+ $ULVY
&IG A 0HASE PLANE DIAGRAM SHOWING UNSTABLE INTERACTIONS IN MIXTURES OF ,OLIUM AND 6ULPIA B C &REQUENCY DEPENDENT INVASIONS OF COMMUNITIES BY EITHER ,OLIUM lLLED CIRCLES OR 6ULPIA OPEN CIRCLES THE INVADER DEPENDS ON THE RELATIVE INITIAL DENSITIES OF THE TWO SPECIES 4HE DYNAMICS OF THE THIRD SPECIES 4RIFOLIUM SQUARES ARE ESSENTIALLY NEUTRAL WITH RESPECT TO THE OTHER TWO SPECIES
INTEREST IN SUCH SYSTEMS REVIEWED BY 'ASCOIGNE AND ,IPCIUS INSPIRED MAINLY BY THE RESULTS OF SIMPLE MODELS )N BRIEF PREDATORS CAN GENERATE !LLEE EFFECTS IN THE POPULATION DYNAMICS OF THEIR PREY AS A CONSEQUENCE OF THEIR FUNC TIONAL AND NUMERICAL RESPONSES 4HIS HAPPENS IN SYSTEMS WHERE THE DYNAMICS OF THE PREY POPULATION ARE DRIVEN MAINLY BY PREDATION AND WHEN PREY HAVE NO REFUGES SPATIAL OR TEMPORAL FROM THE EFFECTS OF PREDATION !LLEE EFFECTS ARISE IN SUCH SYSTEMS WHEN PREDATORS HONE IN ON PREY AT LOW DENSITIES SO THAT LOW DENSITY POPULATIONS OF PREY TEND TO HAVE NEGATIVE POPULATION GROWTH RATES 3UCH PREDATOR INDUCED !LLEE EFFECTS ARE SIGNIlCANT FOR INVASIVE SPECIES BECAUSE THE POTENTIAL EXISTS FOR PREDATORS TO ERADICATE UNWANTED INVASIVE PREY BY REDUCING
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
THEM TO LOW DENSITIES !LTERNATIVELY IF PREY POPULATIONS CAN BE REDUCED BY CONTROL MEASURES THE POTENTIAL EXITS FOR PREDATORS TO LEAD TO THE ULTIMATE EXTINCTION OF THE PREY #ONVERSELY HOWEVER THE POSSIBILITY EXISTS THAT PREY POPULATIONS MAY BE HELD IN CHECK BY PREDATORS WHICH MAINTAIN NEGATIVE PREY POPULATION GROWTH RATES FROM LOW DENSITIES BUT THAT PERTURBATION TO EITHER POPULATION MAY LEAD TO THE PREY POPULATION ESCAPING PREDATOR CONTROL 4HE SYSTEM WE WORKED WITH CONSISTS OF A LEVEL FOOD WEB INVOLVING PREDATORY lSHES THE INVASIVE CORAL EATING CROWN OF THORNS STARlSH !CANTHASTER PLANCI AND REEF BUILDING CORALS $ULVY ET AL 4HE CROWN OF THORNS STARlSH FEEDS UPON LIVE CORALS CAUSING THE LARGEST KNOWN PEST RELATED DISTURBANCES ON )NDO 0ACIlC CORAL REEFS AND IT IS REGARDED AS A MAJOR MANAGEMENT PROBLEM 3EVERAL MECHA NISMS INCLUDING HYDROGRAPHY HURRICANE DISTURBANCE NUTRIENT INPUTS AND PREDA TOR REMOVAL HAVE BEEN SUGGESTED AS POTENTIAL CAUSES OF STARlSH INVASIONS 7E STUDIED A SERIES OF OCEANIC ISLANDS VARYING IN SIZE AND HUMAN POPULA TION &OR EACH ISLAND AN INDEX OF HUMAN lSHING INTENSITY WAS ESTIMATED !T EACH OF THE SITES DENSITIES OF PREDATORY lSHES STARlSH AND BARRIER REEF COMMUNITIES WERE SURVEYED BY DIVERS 3URVEYING WAS CONDUCTED IN SUCCESSIVE YEARS 7E WISHED TO TEST THE HYPOTHESIS THAT STARlSH POPULATIONS OUTBREAK AND INVADE REEFS WHEN PERTURBATIONS TO THEIR PREDATORS REMOVE THE PREDATOR CONTROL AND MOREOVER THAT PREDATORS ARE RESPONSIBLE FOR GENERATING AN !LLEE EFFECT IN STARlSH POPULATIONS 7E DID NOT HAVE SUFlCIENTLY DETAILED DATA TO BE ABLE TO PARAMETERISE A FULL POPU LATION MODEL (OWEVER WE WERE STILL ABLE TO USE A MODELING FRAMEWORK TO ANALYSE THE DYNAMICS OF THIS SYSTEM &OR THE STARlSH WE CALCULATED PER CAPITA RATES OF POPULATION CHANGE .T n . T n .T FOR EACH ISLAND 4O TEST THE HYPOTHESIS THAT PREDATORS WERE RESPONSIBLE FOR GENERATING !LLEE EFFECTS IN STARlSH POPULA TIONS WE PLOTTED THE PER CAPITA RATE OF POPULATION CHANGE AGAINST STARlSH DENSITY AND PREDATOR DENSITY AS WELL AS TO LOOK AT HOW PREDATOR DENSITIES ARE AFFECTED BY HUMAN lSHING PRESSURE &IRST WE FOUND THAT PREDATORY lSHES WERE LESS ABUNDANT AT THE MOST INTEN SIVELY lSHED SITES AS THE LEAST lSHED SITES 4HIS INDICATES THAT THERE IS AN ENORMOUS RANGE OF VARIATION IN THE PREDATORY lSHING PRESSURE IN THIS SYSTEM 'IVEN THIS THE DATA ON RATES OF POPULATION GROWTH OF THE STARlSH &IG SUGGEST THAT PREDATOR REMOVAL BY SUBSISTENCE EXPLOITATION MAY BE SUFlCIENT TO ALLOW OUTBREAKS OF THE CROWN OF THORNS !S SHOWN IN &IG A THE RELATIONSHIP BETWEEN PER CAPITA RATE OF POPULATION CHANGE AND STARlSH DENSITY IS HUMPED AS WOULD BE EXPECTED IF POPULA TIONS WERE SUBJECT TO AN !LLEE EFFECT 4HE DATA APPEAR TO INDICATE THAT THERE ARE TWO EQUILIBRIA ONE AT LOW DENSITIES THE OTHER AT HIGH DENSITIES 4HE LOWER EQUILIBRIUM WILL BE UNSTABLE )N A VARIABLE ENVIRONMENT LOW DENSITY POPULATIONS WILL EITHER OUTBREAK OR WILL BECOME EXTINCT 4HAT THE !LLEE EFFECT SHOWN IN &IG A ACTUALLY RESULTS FROM THE EFFECTS OF PREDA TORS IS CONlRMED IN &IG B !S SHOWN THERE IS A NEGATIVE RELATIONSHIP BETWEEN THE RATE OF CHANGE IN STARlSH DENSITY AND PREDATOR DENSITY CONlRMING THAT STAR lSH POPULATION DYNAMICS ARE DRIVEN BY PREDATION THUS FULlLLING THE CONDITIONS REQUIRED FOR PREDATOR INDUCED INSTABILITY
20 &RECKLETON 0- $OWLING AND .+ $ULVY
&IG 4HE RELATIONSHIP BETWEEN AVERAGE STARlSH DENSITY AND PER CAPITA POPULATION GROWTH OF STARlSH AND A AVERAGE STARlSH DENSITY B AVERAGE DENSITY OF PREDATORY lSHES $ATA ARE TAKEN FROM ISLANDS PRESENTED IN $ULVY ET AL
)N SUMMARY THIS SYSTEM SUGGESTS THAT INVASION OF THE CROWN OF THORNS STARlSH MAY BE GOVERNED BY UNDERLYING UNSTABLE DYNAMICS AND HOW THIS INTERACTS WITH VARIATIONS IN THE DENSITIES OF PREDATORS )N THIS CASE STUDY VARIATION IN PREDA TOR DENSITY WAS SPATIAL AND THE CONSEQUENCE OF DIFFERENCES IN lSHING INTENSITY AMONG ISLANDS )N OTHER SYSTEMS VARIATION COULD BE THE RESULT OF OTHER FACTORS SUCH AS HABITAT LOSS OR CLIMATIC EFFECTS 7HAT THIS EXAMPLE ILLUSTRATES HOWEVER
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
IS THAT PREDICTING SUCH EFFECTS WILL REQUIRE A DETAILED UNDERSTANDING OF THE NATURE OF POPULATION STABILITY
#/.#,5$).' 2%-!2+3 %XCEPT IN THE UNLIKELY EVENT THAT POPULATION DYNAMICS ARE COMPLETELY DENSITY INDEPENDENT THE LONG TERM DYNAMICS OF POPULATIONS WILL BE DETERMINED BY THE EFFECTS OF VARIOUS FORMS OF INTRA AND INTER SPECIlC INTERACTIONS )N ADDITION TO THIS THE EFFECTS OF DENSITY INDEPENDENT STOCHASTICITY MAY BE COMPLEX PARTICU LARLY WHEN POPULATIONS ARE FORCED TO LOW DENSITIES 4HIS MEANS THAT FORECASTING THE OUTCOME OF INVASION MAY BE COMPLEX AND REQUIRES A DETAILED UNDERSTAND ING OF THE STRUCTURE OF THE SYSTEM IN QUESTION 3IMPLE POPULATION MODELS CAN BE AN EXTREMELY VALUABLE GUIDE IN ANALYSING SUCH PROBLEMS BOTH IN THEORY AND IN PRACTICE
2%&%2%.#%3 !NDREWARTHA ( ' AND "IRCH , # 4HE DISTRIBUTION AND ABUNDANCE OF ANIMALS 5NIVERSITY OF #HICAGO 0RESS #HICAGO "UCKLEY 9 - "RIESE $ 4 AND 2EES - A $EMOGRAPHY AND MANAGEMENT OF THE INVASIVE PLANT SPECIES (YPERICUM PERFORATUM ) 5SING MULTI LEVEL MIXED EFFECTS MODELS FOR CHARACTERIZING GROWTH SURVIVAL AND FECUNDITY IN A LONG TERM DATA SET *OURNAL OF !PPLIED %COLOGY "UCKLEY 9 - "RIESE $ 4 AND 2EES - B $EMOGRAPHY AND MANAGEMENT OF THE INVASIVE PLANT SPECIES (YPERICUM PERFORATUM )) #ONSTRUCTION AND USE OF AN INDI VIDUAL BASED MODEL TO PREDICT POPULATION DYNAMICS AND THE EFFECTS OF MANAGEMENT STRATEGIES *OURNAL OF !PPLIED %COLOGY "YERS * % 2EICHARD 3 2ANDALL * - 0ARKER ) - 3MITH # 3 ,ONSDALE 7 - !TKINSON ) ! % 3EASTEDT 4 2 7ILLIAMSON - #HORNESKY % AND (AYES $ $IRECTING RESEARCH TO REDUCE THE IMPACT OF NON INDIGENOUS SPECIES #ONSERVATION "IOLOGY #HESSON 0 , AND (UNTLY . #OMMUNITY CONSEQUENCES OF LIFE HISTORY TRAITS IN A VARIABLE ENVIRONMENT !NN :OOL &ENNICI #HESSON 0 , AND (UNTLY . 3HORT TERM INSTABILITIES AND LONG TERM COMMUNITY DYNAMICS 4RENDS IN %COLOGY AND %VOLUTION #OHEN $ /PTIMIZING REPRODUCTION IN RANDOMLY VARYING ENVIRONMENTS *OURNAL OF 4HEORETICAL "IOLOGY $OBSON ! 0 AND 2 - -AY 0ATTERNS OF )NVASIONS BY 0ATHOGENS AND 0ARASITES 4HE %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK $OWLING 0 - 4HE ECOLOGY OF 6ULPIA 0LANT 0ROTECTION 1UARTELY 3UPPLEMENT
20 &RECKLETON 0- $OWLING AND .+ $ULVY
$OWLING 0 - 6ERBEEK " ,EMERLE $ AND ,EYS ! 2 2APID REGENERATION OF 6ULPIA 6ULPIA BROMOIDES IN PASTURES )N 0ROCEEDINGS TH !SIAN 0ACIlC 7EED 3OCIETY #ONFERENCE PP 4OSUKUBA *APAN $UFFY * % "IODIVERSITY LOSS TROPHIC SKEW AND ECOSYSTEM FUNCTIONING %COLOGY ,ETTERS $ULVY . + &RECKLETON 2 0 AND 0OLUNIN . 6 # #ORAL REEF CASCADES AND THE INDIRECT EFFECTS OF PREDATOR REMOVAL BY EXPLOITATION %COLOGY ,ETTERS %ARN $ * $ 2OHANI 0 AND 'RENFELL " 4 0ERSISTENCE CHAOS AND SYNCHRONY IN ECOLOGY AND EPIDEMIOLOGY 0ROCEEDINGS OF THE 2OYAL 3OCIETY 3ERIES " %NGEN 3 "AKKE AND ! )SLAM $EMOGRAPHIC AND ENVIRONMENTAL STOCHASTIC ITYnCONCEPTS AND DElNITIONS "IOMETRICS n &IRBANK , ' AND 7ATKINSON ! 2 ! MODEL OF INTERFERENCE WITHIN PLANT POPULA TIONS *OURNAL OF 4HEORETICAL "IOLOGY &RECKLETON 2 0 AND 7ATKINSON ! 2 (OW DOES TEMPORAL VARIABILITY AFFECT PREDIC TIONS OF WEED POPULATION NUMBERS *OURNAL OF !PPLIED %COLOGY &RECKLETON 2 0 AND 7ATKINSON ! 2 !SYMMETRIC COMPETITION BETWEEN PLANT SPECIES &UNCIONAL %COLOGY &RECKLETON 2 0 AND 7ATKINSON ! 2 !RE WEED POPULATIONS CHAOTIC *OURNAL OF !PPLIED %COLOGY &RECKLETON 2 0 7ATKINSON ! 2 $OWLING 0 - AND ,EYS ! 2 $ETERMINANTS OF THE ABUNDANCE OF INVASIVE ANNUAL WEEDS COMMUNITY STRUCTURE AND NON EQUILIBRIUM DYNAMICS 0ROCEEDINGS OF THE 2OYAL 3OCIETY 3ERIES " &RECKLETON 2 0 3ILVA -ATOS $ - "OVI - , ! AND 7ATKINSON ! 2 0ROBLEMS WITH PREDICTING THE IMPACTS OF HARVESTING USING STRUCTURED POPULATION MODELS AN EXAMPLE BASED ON TROPICAL TREES *OURNAL OF !PPLIED %COLOGY 'ASCOIGNE * # AND ,IPCIUS 2 . !LLEE EFFECTS DRIVEN BY PREDATION *OURNAL OF !PPLIED %COLOGY 'INZBURG , 2 AND #OLYVAN - %COLOGICAL ORBITS HOW PLANETS MOVE AND POPULA TIONS GROW /XFORD 5NIVERSITY 0RESS /XFORD (ASSELL - 0 $ENSITY DEPENDENCE IN SINGLE SPECIES POPULATIONS *OURNAL OF !NIMAL %COLOGY (ASSELL - 0 $ETECTING DENSITY DEPENDENCE 4RENDS IN %COLOGY AND %VOLUTION (ASSELL - 0 ,AWTON * ( AND -AY 2 - 0ATTERNS OF DYNAMICAL BEHAVIOUR IN SINGLE SPECIES POPULATIONS *OURNAL OF !NIMAL %COLOGY (EINO - 2IPA * AND +AITALA 6 %XTINCTION RISK UNDER COLOURED ENVIRONMENTAL NOISE %COGRAPHY +ENDALL " % ET AL 7HY DO POPULATIONS CYCLE ! SYNTHESIS OF STATISTICAL AND MECHANISTIC MODELLING APPROCHES %COLOGY ,ANDE 2 $EMOGRAPHIC STOCHASTICITY AND !LLEE EFFECT ON A SCALE WITH ISOTROPIC NOISE /IKOS ,ANDE 2 %NGEN 3 AND 3AETHER " % 3TOCHASTIC POPULATION DYNAMICS IN ECOLOGY AND CONSERVATION /XFORD 5NIVSERSITY 0RESS /XFORD
3TOCHASTICITY NONLINEARITY AND INSTABILITY IN BIOLOGICAL INVASIONS
,EWIS - ! AND +AREIVA 0 !LLEE DYNAMICS AND THE SPREAD OF INVADING ORGANISMS 4HEORETICAL 0OPULATION "IOLOGY ,EWONTIN 2 # AND #OHEN $ /N POPULATION GROWTH IN A RANDOMLY VARYING ENVI RONMENT 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! ,IEBHOLD ! AND "ASCOMPTE * 4HE !LLEE EFFECT STOCHASTIC DYNAMICS AND THE ERADI CATION OF INVASIVE SPECIES %COLOGY ,ETTERS ,ONSDALE 7 - 4HE BALANCE OF WEED POPULATIONS )N &RONTIERS OF 0OPULATION %COLOGY EDS 2 " &LOYD AND ! 7 3HEPPARD #3)2/ 0UBLISHING -ELBOURNE -AY 2 - 3TABILITY AND COMPLEXITY IN MODEL ECOSYSTEMS 0RINCETON 5NIVERSITY 0RESS 0RINCETON .EW *ERSEY -AY 2 - 4HRESHOLDS AND BREAKPOINTS IN ECOSYSTEMS WITH A MULTIPLICITY OF STABLE STATES .ATURE -AY 2 - -ODELS FOR TWO INTERACTING POPULATIONS )N 4HEORETICAL %COLOGY ED 2 - -AY PP "LACKWELL 3CIENTIlC 0UBLICATIONS /XFORD -AY 2 - #ONWAY ' 2 (ASSELL - 0 AND 3OUTHWOOD 4 2 % 4IME DELAYS DENSITY DEPENDENCE AND SINGLE SPECIES OSCILLATIONS *OURNAL OF !NIMAL %COLOGY -AY 2 - AND /STER ' & "IFURCATIONS AND DYNAMIC COMLEXITY IN SIMPLE ECOLOGICAL MODELS !MERICAN .ATURALIST -AYNARD 3MITH * -ODELS IN ECOLOGY #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE .ICHOLSON ! * !N OUTLINE OF THE DYNAMICS OF ANIMAL POPULATIONS !USTRALIAN *OURNAL OF :OOLOGY 0ACALA 3 7 #ANHAM # $ 3APONARA * 3ILANDER * ! +OBE 2 + AND 2IBBENS % &OREST MODELS DElNED BY lELD MEASUREMENTS ESTIMATION ERROR ANALYSIS AND DYNAMICS %COLOGICAL -ONOGRAPHS 2EES - AND #RAWLEY - * 'ROWTH REPRODUCTION AND POPULATION DYNAMICS &UNCTIONAL %COLOGY 2EES - AND #RAWLEY - * $O PLANT POPULATIONS CYCLE &UNCTIONAL %COLOGY 2EES - AND 0AYNTER 1 "IOLOGICAL #ONTROL OF 3COTCH "ROOM MODELLING THE DETER MINANTS OF ABUNDANCE AND THE POTENTIAL IMPACT OF INTRODUCED INSECT HERBIVORES *OURNAL OF !PPLIED %COLOGY 2OYAMA 4 !NALYTICAL 0OPULATION $YNAMICS #HAPMAN (ALL ,ONDON 3CHEFFER - AND #ARPENTER 3 #ATASTROPHIC REGIME SHIFTS IN ECOSYSTEMS LINKING THEORY TO OBSERVATION 4RENDS IN %COLOGY AND %VOLUTION 3AETHER " % ET AL ,IFE HISTORY VARIATION PREDICTS THE EFFECTS OF DEMOGRAPHIC STOHCAS TICITY ON AVIAN POPULATION DYNAMICS !MERICAN .ATURALIST 3AETHER " % ET AL 4IME TO EXTINCTION OF BIRD POPULATIONS %COLOGY IN PRESS 3TEPHENS 0 ! AND 3UTHERLAND 7 * #ONSEQUENCES OF THE !LLEE EFFECT FOR BEHAV IOUR ECOLOGY AND CONSERVATION 4RENDS IN %COLOGY AND %VOLUTION 3TEPHENS 0 ! 3UTHERLAND 7 * AND &RECKLETON 2 0 7HAT IS THE !LLEE EFFECT /IKOS 4AYLOR # - AND (ASTINGS ! &INDING OPTIMAL CONTROL STRATEGIES FOR INVASIVE SPE CIES A DENSITY STRUCTURED MODEL FOR 3PARTINA ALTERNImORA *OURNAL OF !PPLIED %COLOGY
20 &RECKLETON 0- $OWLING AND .+ $ULVY
4ILMAN $ -AY 2 - ,EHMAN # , AND .OWAK - ! (ABITAT DESTRUCTION AND THE EXTINCTION DEBT .ATURE 4ULJAPURKAR 3 0OPULATION DYNAMICS IN VARIABLE ENVIRONMENTS 3PRINGER .EW 9ORK 7ATKINSON ! 2 $ENSITY DEPENDENCE IN SINGLE SPECIES POPULATIONS OF PLANTS *OURNAL OF 4HEORETICAL "IOLOGY 7HITE 4 # 2 /PPOSING PARADIGMS REGULATION OR LIMITATION OF POPULATIONS /IKOS 7ILLIAMSON - "IOLOGICAL )NVASIONS #HAPMAN (ALL ,ONDON 5+
#HAPTER SEVEN
,OCAL INTERACTIONS AND INVASION DYNAMICS POPULATION GROWTH IN SPACE AND TIME $ * -URRELL
).42/$5#4)/. 4HE STUDY OF BIOLOGICAL INVASIONS IS ESSENTIALLY THE STUDY OF POPULATION GROWTH IN BOTH SPACE AND TIME .OT ONLY ARE WE INTERESTED IN THE POPULATION SIZE OF AN INVADER BUT ALSO ITS RATE OF SPREAD ACROSS A LANDSCAPE OR REGION (ENCE THEORETI CAL MODELS OF INVASIONS VERY OFTEN INCORPORATE SOME FORM OF SPATIAL HETEROGENEITY 3KELLAM "OERLIJST AND (OGEWEG (ASSELL ET AL +OT ET AL +EELING ET AL ,EWIS ,EWIS AND 0ACALA 2IETKERK ET AL "ROADLY SPEAKING THERE ARE TWO CLASSES OF SPATIAL HETEROGENEITY THE SO CALLED ENDOGENOUS OR SELF INDUCED SPATIAL HETEROGENEITY TYPE I AND EXOGENOUS HETERO GENEITY TYPE II 4YPE I HETEROGENEITY IS CAUSED BY INTERACTIONS BETWEEN INDIVID UALS OR POPULATIONS AND LEADS TO WHAT IS SOMETIMES CALLED SELF ORGANISED SPATIAL PATTERNS "OERLIJST AND (OGEWEG (ASSELL ET AL +EELING ET AL 2IETKERK ET AL &OR EXAMPLE IN MONOCULTURES OF PINES INTENSE COMPETITION BETWEEN CLOSE NEIGHBOURS LEADS TO AN EVEN SPACING OF ADULT TREES +ENKEL -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
$* -URRELL
4YPE II HETEROGENEITY IS CAUSED BY PROCESSES BEYOND INDIVIDUAL INTERACTIONS SUCH AS SOIL DEPTH TEMPERATURE GRADIENTS ETC 4HIS LEADS TO THE AGGREGATION OF INDIVIDU ALS CAUSED BY SPECIES BEING ASSOCIATED WITH CERTAIN HABITAT TYPES MORE THAN OTHERS &OR EXAMPLE SOME TROPICAL RAINFOREST TREES HAVE BEEN FOUND TO BE ASSOCIATED WITH CERTAIN SOIL TYPES AND IT HAS BEEN ARGUED THAT THIS IS AN IMPORTANT FACTOR IN DETER MINING THEIR AGGREGATED SPATIAL STRUCTURE 0ALMIOTTO ET AL 5NDOUBTEDLY BOTH CLASSES OF HETEROGENEITY ARE IMPORTANT DURING INVASIONS INTERACTIONS WITH OTHER ORGANISMS MAY DETERMINE WHETHER AN INVASION SUCCEEDS &AGAN AND "ISHOP /WEN AND ,EWIS AS WELL AS THE AVAILABILITY AND SPATIAL PATTERNING OF SUITABLE HABITAT 2ICHARDSON ET AL (ILL ET AL (OLWAY ET AL 7ITH (OWEVER THIS CHAPTER WILL FOCUS ON ONLY ENDOGENOUS SPATIAL HETEROGENEITY IN AN ATTEMPT TO SHOW HOW IMPORTANT LOCAL SPATIAL STRUCTURE CAN BE IN DETERMIN ING THE RATE OF SPREAD OF A POPULATION STARTING FROM A LOW DENSITY SEE "OLKER FOR RESULTS FOR A SIMILAR MODEL IN HETEROGENEOUS SPACE %COLOGICAL INTERACTIONS FOR MOST ORGANISMS TEND TO OCCUR BETWEEN INDIVIDUALS THAT ARE NEARBY IN SPACE #OUPLED TO THIS MOST ORGANISMS LARGER THAN MM ARE ARGUED TO BE IN SOME WAY DISPERSAL LIMITED &INLAY AND #LARKE &INLAY ET AL &INLAY -ANY MICROBIAL ORGANISMS ARE SO SMALL THAT THEY CAN BE CARRIED LARGE DISTANCES BY WIND AND TOGETHER WITH LONG LIVED RESTING STAGES THIS MEANS THAT MANY MICROBIAL SPECIES MAY ENJOY A NEAR GLOBAL DISTRIBUTION %ARLY IN ITS HISTORY ECOLOGICAL THEORY NEGLECTED BOTH THESE ASPECTS AND IT WAS ASSUMED THAT INDIVIDUALS RANDOMLY BUMP INTO ONE ANOTHER THE SO CALLED MEAN lELD ASSUMPTION -ORE RECENTLY NON UNIFORM DISPERSAL HAS BEEN INCORPORATED AND HAS BEEN USED WITH MUCH SUCCESS IN DESCRIBING THE RATES OF SPREAD INVASION OF NUMEROUS SPECIES +OT ET AL 6EIT AND ,EWIS (OWEVER MOST OF THESE MODELS HAVE NOT INCLUDED THE DISCRETE NATURE OF INDIVIDUALS AND WITHOUT IT THE TIGHT SMALL SCALE CLUSTERING THAT IS OFTEN EVIDENT IN NATURAL POPULATIONS CANNOT BE INCLUDED !S HAS BEEN OFTEN OBSERVED THERE IS A CRUCIAL FEEDBACK BETWEEN THE SPATIAL PATTERN OF INDIVIDUALS ACROSS THE LANDSCAPE AND THE DYNAMICS OF THE POPULATION "OLKER AND 0ACALA $URRETT AND ,EVIN ,OCAL DISPERSAL EVEN WITHOUT ANY DENSITY DEPENDENT EFFECTS ON DEATH RATES OR FECUNDITY RESULTS IN A CLUSTERED OR PATCHY DISTRIBUTION OF INDIVIDUALS ACROSS THE LANDSCAPE 9OUNG ET AL )N SUCH A SCENARIO THE SPATIAL PATTERN IS NOT IMPORTANT FOR THE POPULATION DYNAM ICS OTHER THAN IN DETERMINING THE RATE OF SPREAD OF AN INVADER ACROSS A LAND SCAPE (OWEVER AS SHALL BE EXPANDED UPON BELOW ONCE LOCAL DENSITY DEPENDENT PROCESSES ARE INCORPORATED THE SPATIAL PATTERN OF INDIVIDUALS MAY BECOME VERY IMPORTANT TO MANY FEATURES OF THE INVASION DYNAMICS AND MAY ULTIMATELY DETER MINE WHETHER AN EXOTIC CAN INVADE OR NOT 7ITH LOCAL SPATIAL STRUCTURE WHAT AN INDIVIDUAL EXPERIENCES IN ITS LOCAL NEIGHBOURHOOD MAY BE VERY DIFFERENT TO THE OVERALL DENSITY OF INDIVIDUALS ACROSS THE LANDSCAPE 4HIS LOCAL SPATIAL STRUCTURE THEN HELPS TO DETERMINE THE LEVELS OF COMPETITION THAT AN INDIVIDUAL EXPERIENCES AND HENCE INDIRECTLY DETERMINES THE LEVEL OF COMPETITION AND LOCAL SPATIAL STRUC TURE IN THE NEXT TIME INTERVAL
0OPULATION GROWTH IN SPACE AND TIME
4HE REST OF THIS CHAPTER WILL FOCUS ON A GENERAL MODEL FOR THE SPATIO TEMPORAL POPULATION DYNAMICS OF AN INVADING SPECIES 7E WILL CONSIDER INDIVIDUALS SIMILAR TO PERENNIAL PLANTS THAT REPRODUCE DISPERSING THEIR OFFSPRING LOCALLY AND DIE AT RATES THAT ARE DEPENDENT ON THEIR LOCAL NEIGHBOURHOOD DENSITY 4WO MODELS WILL BE PRESENTED ONE INDIVIDUAL BASED MODEL AND ITS DETERMINISTIC APPROXIMA TION 4HE LINK BETWEEN THESE MODELS AND THE CLASSICAL NON SPATIAL LOGISTIC MODEL FOR POPULATION GROWTH IS MADE EXPLICIT AND WILL ACT AS A REFERENCE POINT FOR THE RESULTS THAT ARE OBTAINED WHEN INTERACTIONS AND DISPERSAL ARE LOCALISED IN SPACE "OTH SPATIAL MODELS WILL BE USED TO INVESTIGATE THE SCALES OF DISPERSAL AND NEIGH BOURHOOD INTERACTIONS ON THE TRANSIENT DYNAMICS SUCCESS AND SPEED OF INVASION AND ASYMPTOTIC STATE OF THE POPULATION THE lNAL POPULATION DENSITY )T IS ALSO OBSERVED THAT THE EXPECTED REPRODUCTIVE OUTPUT OF AN INDIVIDUAL IN THE ABSENCE OF COMPETITION IS ALSO IMPORTANT IN DETERMINING THE SUCCESS AND SPEED OF AN INVASION AS WELL AS THE lNAL POPULATION SIZE
! 34/#(!34)# ).$)6)$5!, "!3%$ -/$%, )"- )NVASIONS ARE INHERENTLY STOCHASTIC THEY VERY OFTEN START WITH JUST A FEW INDIVIDU ALS AND THE SUCCESS OF AN INVASION OWES A GREAT DEAL TO CHANCE THEREFORE IT MAKES SENSE TO START FROM A STOCHASTIC MODEL THAT FOCUSES ON THE INDIVIDUAL LEVEL MICRO SCOPIC PROCESSES OF BIRTHS AND DEATHS 7E WILL CONCENTRATE ON A SPATIAL EXTENSION TO THE FAMILIAR LOGISTIC MODEL FOR POPULATION GROWTH 0EARL AND 2EAD ONE WHERE BOTH INTERACTIONS AND DISPERSAL ARE LOCALISED IN SPACE #ONSIDER A POPULATION OF ORGANISMS OF A SINGLE SPECIES INVADING A TWO DIMEN SIONAL LANDSCAPE SUCH AS A lELD )N THE )"- SPACE IS CONTINUOUS AS OPPOSED TO A LATTICE OR SITE BASED MODEL AND LARGE ENOUGH FOR EDGE EFFECTS TO BE NEGLIGIBLE 4O REDUCE THE EDGE EFFECTS THE LANDSCAPE IS IN THE SHAPE OF A TORUS FORMERLY SPEAKING THE BOUNDARIES ARE PERIODIC !N INDIVIDUAL I LOCATED AT COORDINATES XI [X X] IS DENOTED BY A $IRAC DELTA FUNCTION bXI X 4HE $IRAC DELTA FUNCTION SERVES TO PICK OUT INDIVIDUALS IT IS A PEAK OF INlNITE HEIGHT AND INlNITELY SMALL WIDTH CENTRED ON THE LOCATION OF EACH INDIVIDUAL GIVING AN AREA UNDERNEATH IT THAT SUMS TO ONE 4HE STATE OF THE POPULATION AT TIME T IS GIVEN BY THE FUNCTION PX T WHICH IS THE SUM OF ALL THE DELTA FUNCTIONS AND THEREFORE DESCRIBES THE NUMBER AND LOCATIONS OF ALL INDIVIDUALS IN THE POPULATION 4HERE ARE THREE DIFFERENT TYPES OF EVENT THAT MAY OCCUR IN THE )"- BIRTH DEATH AND MOVEMENT 4O KEEP IN CLOSE ASSOCIATION WITH THE CLASSICAL LOGISTIC MODEL ONLY DEATHS ARE DENSITY DEPENDENT ALTHOUGH THE MODEL IS mEXIBLE SO THAT BIRTHS AND MOVEMENTS MAY ALSO BE DEPENDENT UPON LOCAL DENSITIES "OLKER AND 0ACALA 4HE PROBABILITY PER UNIT TIME $X X P THAT AN INDIVIDUAL AT LOCATION X DIES IS GIVEN BY $X X P D D q 0WX n X q ;PX n bXX = DX
$* -URRELL
4HE DEATH TERM CONSISTS OF TWO PARTS 4HE lRST IS AN INTRINSIC PER CAPITA DEATH RATE D AND THE SECOND PART MODIlES THE DEATH RATE ACCORDING TO THE PRESENCE OF NEARBY NEIGHBOURS .EIGHBOURS HAVE A PER CAPITA EFFECT D ON THE DEATH RATE OF THE FOCAL INDIVIDUAL (OWEVER IT IS ASSUMED THAT COMPETITIVE EFFECT OF NEIGHBOURS IS DEPENDENT UPON THE DISTANCE BETWEEN THEM 4HE TERM WX n X OTHERWISE CALLED THE COMPETITION KERNEL DESCRIBES THE WEIGHTING THAT NEIGHBOURS AT LOCATION X HAVE ON THE DEATH RATE AT LOCATION X AND IS A FUNCTION OF THE DISTANCE X n X THAT SEPARATES THE PAIR 4HIS WEIGHTING IS MULTIPLIED BY THE DENSITY PX OF INDIVIDUALS AT LOCATION X AND THE INTEGRAL TAKES INTO ACCOUNT THE CONTRIBUTIONS TO THE DEATH RATE AT X OF ALL LOCATIONS X IN THE NEIGHBOURHOOD OF X 4HE LAST TERM bXX IS ONLY SWITCHED ON WHEN X X THEREBY REMOVING THE SPURIOUS EFFECT THAT AN INDIVIDUAL WOULD OTHERWISE HAVE ON ITS OWN DEATH RATE 4HE PROBABILITY PER UNIT TIME "X X P THAT AN INDIVIDUAL LOCATED AT X PRO DUCES AN OFFSPRING AT X IS GIVEN BY "X X P B q MX n X
WHERE B IS THE INTRINSIC PER CAPITA BIRTH RATE AND MX n X IS THE DISPERSAL KERNEL WHICH DESCRIBES THE PROBABILITY THAT THE NEWBORN INDIVIDUAL COMES TO REST AT A DISPLACEMENT X X FROM ITS PARENT 4HE DISPERSAL AND COMPETITION KERNELS ARE VERY mEXIBLE AND CAN TAKE ON PRACTI CALLY ANY SHAPE SEE FOR VARIATIONS SEE "OLKER AND 0ACALA )T SEEMS SENSIBLE TO ENSURE THAT THEY ARE BOTH MONOTONICALLY DECREASING FUNCTIONS AND WE CHOOSE TO USE BIVARIATE 'AUSSIAN DISTRIBUTIONS ¨ \X n X\ ¬ MX n X EXP " n " - ª SM ®
A
¨ \X n X\ ¬ WX n X EXP " n " 7 ª SW ®
B
EACH HAVING ONE PARAMETER SM SW THAT MEASURES THE WIDTH OF THE KERNEL ! SMALL VALUE FOR SM MEANS THAT OFFSPRING FALL VERY CLOSE TO THEIR PARENT SHORT SCALE DIS PERSAL ! SMALL VALUE FOR SW MEANS THAT COMPETITION IS VERY INTENSE BETWEEN CLOSE NEIGHBOURS BUT THAT IT SOON DIMINISHES WITH DISTANCE SHORT SCALE INTERACTIONS /N THE OTHER HAND LARGE VALUES FOR SM SW REDUCES THE IMPORTANCE OF SPACE &OR PRACTICAL PURPOSES WE TRUNCATE THE KERNELS AT A DISTANCE OF TIMES THE PARAMETER VALUE THE EFFECT THIS HAS ON THE DYNAMICS IS NEGLIGIBLE 4HE KERNELS ARE NORMALISED SO THAT THAT THEIR INTEGRALS OVER X n X ARE UNITY - AND 7 BEING THE NORMALISATION CONSTANTS
0OPULATION GROWTH IN SPACE AND TIME
30!4)!, 34!4)34)#3 )N THE )"- EACH INDIVIDUAL AND EACH EVENT NEEDS TO BE CONSTANTLY TRACKED )N ORDER TO INVESTIGATE THE IMPLICATIONS OF INCORPORATING LOCAL INTERACTIONS AND LOCAL DISPER SAL INTO THE LOGISTIC MODEL FOR POPULATION GROWTH IT HELPS TO HAVE SOME SUMMARY STATISTICS THAT CAN BE OUTPUT FROM THE )"- 4HESE WILL LATER BECOME STATE VARIABLES IN THE DETERMINISTIC APPROXIMATION SO IT IS IMPORTANT THAT THEY ARE DElNED 4HE lRST SPATIAL MOMENT IS THE FAMILIAR AVERAGE DENSITY .P T q 0 PX T DX !
4HIS SIMPLY SUMS OVER ALL INDIVIDUALS IN THE POPULATION AT TIME T AND DIVIDES BY THE AREA ! IN WHICH THE POPULATION LIVES 4HE lRST SPATIAL MOMENT DOES NOT GIVE ANY INFORMATION ON HOW INDIVIDUALS ARE SPREAD ACROSS THE LANDSCAPE IN ORDER TO GET A FEEL FOR THE SPATIAL PATTERN HIGHER ORDER SPATIAL MOMENTS ARE REQUIRED 4HERE ARE A NUMBER OF HIGHER ORDER SPATIAL MOMENTS THAT COULD BE USED $IGGLE #RESSIE BUT THE ONE USED HERE IS #j P T q 0 PX T q ;PX j T n bXX j = DX !
4HE SECOND SPATIAL MOMENT IS THE AVERAGE DENSITY OF PAIRS SEPARATED BY A DISTANCE j )T CAN BE THOUGHT OF AS THE INDIVIDUALS EYE VIEW SINCE IT DESCRIBES THE EXPECTED NEIGHBOUR DENSITY AT DIFFERENT DISTANCES AND HENCE DESCRIBES THE VARIATION IN THE DENSITY OF INDIVIDUALS ACROSS THE LANDSCAPE /NCE AGAIN THE DELTA TERM REMOVES THE SELF PAIR TERM THAT ARISES WHEN X jX 4HIS FORM OF SECOND MOMENT HAS THE BENElT OF BEING MATHEMATICALLY SIMPLE A FEATURE THAT IS USEFUL FOR THE DETERMINISTIC APPROXIMATION THAT FOLLOWS )N THE RESULTS GIVEN BELOW THE SECOND MOMENTS ARE NORMALISED BY DIVIDING BY .P T 4HIS MEANS THAT WHEN #j P T THIS INDICATES A MORE CROWDED NEIGHBOURHOOD THAN WOULD BE EXPECTED IF THE SPATIAL PATTERN OF INDIVIDUALS WERE RANDOM AGGREGATION WHEN #j P T THIS INDICATES A RELATIVELY COMPETITOR FREE NEIGHBOURHOOD COMPARED TO A RANDOM PATTERN SPATIAL SEGREGATION AND WHEN #j P T THIS INDICATES A RANDOM SPATIAL ASSOCIATION OF INDIVIDUALS
! $%4%2-).)34)# !002/8)-!4)/. 4HERE IS MUCH THAT CAN BE GAINED FROM THE )"- BUT KEEPING TRACK OF ALL INDIVIDU ALS AND THEIR DYNAMICS IS COMPUTATIONALLY VERY INTENSIVE 4HE )"- DElNED ABOVE
$* -URRELL
IS STOCHASTIC ANY INDEPENDENT REALISATIONS ARE EXPECTED TO HAVE SLIGHTLY DIFFER ENT PATTERNS AND -ARKOVIAN THE RATE OF CHANGE OF THE SYSTEM DEPENDS ONLY ON THE CURRENT STATE 4HESE MAKE IT HARD TO DISCERN THE ECOLOGICAL SIGNAL FROM THE BACKGROUND NOISE MANY REALISATIONS ARE REQUIRED TO GET A BETTER PICTURE OF PROP ERTIES OF THE MODEL ,AW ET AL AND HENCE FULL ANALYSIS OF THE )"- IS VERY DIFlCULT &OR EXAMPLE KNOWING WHEN THE POPULATION HAS REACHED ITS END STATE CAN BE VERY DIFlCULT TO DETERMINE #OMPLEMENTING THE )"- WITH AN APPROACH THAT DEALS WITH THE MACROSCOPIC PROPERTIES SUCH AS POPULATION DENSITIES IS THEREFORE DESIRABLE 3CALING UP FROM SMALL SCALE PROCESSES TO LARGE SCALE PROPERTIES IS NOT A TRIVIAL TASK ,EVIN BUT RECENT ADVANCES IN MATHEMATICAL TECHNIQUES HAVE EXPANDED THE RANGE OF CASES FOR WHICH THIS IS POSSIBLE IN SPATIAL MODELS "OLKER AND 0ACALA "OLKER "OLKER AND 0ACALA $IECKMANN AND ,AW ,AW AND $IECKMANN -URRELL AND ,AW "OLKER "OLKER ET AL ,AW ET AL -URRELL AND ,AW -URRELL ET AL &ROM THE DESCRIPTION OF THE )"- ABOVE IT IS POSSIBLE TO DERIVE A DETERMINIS TIC APPROXIMATION THAT DESCRIBES THE EXPECTED RATE OF CHANGE OF THE POPULATION $IECKMANN AND ,AW 4HE EXPECTED RATE OF CHANGE IN POPULATION DENSITY IS GIVEN BY .T B.T n D.T n D q 0 Wj #j D j 4HE lRST AND SECOND TERMS DEAL WITH THE CONTRIBUTIONS TO POPULATION DENSITY OF THE INTRINSIC RATES OF BIRTH AND DEATH 4HESE ARE MADE EXPLICIT IN THE SPATIAL MODEL RATHER THAN SUBSTITUTING R B n D BECAUSE AS WILL BE SHOWN BELOW BIRTHS AND DEATHS HAVE VERY DIFFERENT EFFECTS ON THE SPATIAL STRUCTURE 4HE THIRD TERM IS WHERE THE SPATIAL STRUCTURE lRST ENTERS THE DYNAMICAL SYSTEM #OMPETITION IS NOW DEPEN DENT ON THE EXPECTED DENSITY OF NEIGHBOURS AROUND AN INDIVIDUAL #j T AND IS SCALED BY BOTH THE INTERACTION KERNEL Wj WHICH TAKES INTO ACCOUNT THE DISTANCE BETWEEN PAIRS AND BY THE PER CAPITA COMPETITIVE EFFECT D 4HE SPATIAL STRUCTURE SUMMARISED BY #j T HAS DYNAMICS OF ITS OWN THAT ALSO NEED TO BE MADE EXPLICIT 4HE EXPECTED RATE OF CHANGE OF PAIR DENSITIES ARE DESCRIBED BY #j T
n n n
B 0 Mj # j j T D j B Mj . T D # j T D 0 Wj 4 j j T D j D Wj # j T
A
B C D E
%ACH TERM DESCRIBES EVENTS THAT LEAD TO THE CREATION AND DELETION OF PAIRS OR MORE FORMERLY PAIR DENSITIES 4HE lRST TERM A DESCRIBES HOW PAIRS ARE FORMED WHEN A NEWBORN DISPERSES A DISTANCE j FROM ITS PARENT 4HE SECOND TERM B TAKES INTO ACCOUNT PAIRS FORMED WHEN ONE OF THE MEMBERS OF THE PAIR IS THE PARENT
0OPULATION GROWTH IN SPACE AND TIME
4HE OTHER THREE TERMS DEAL WITH LOSS OF PAIRS THROUGH DEATHS 4ERM C DESCRIBES HOW PAIRS ARE LOST THROUGH DENSITY INDEPENDENT DEATHS 4ERM D MODIlES THIS RATE DUE TO NEIGHBOURS AT A DISTANCE j WITH THE INTERACTION KERNEL Wj WEIGHTING THE EFFECT OF THE NEIGHBOURS ACCORDING TO DISTANCE BETWEEN LOCATIONS 3INCE THE PAIR IS AFFECTED BY A THIRD INDIVIDUAL INFORMATION ON THE EXPECTED DENSITY OF TRIP LETS IS REQUIRED AND THIS IS DENOTED BY 4 THE THIRD SPATIAL MOMENT 4HIS REPRESENTS A NON TRIVIAL TECHNICAL PROBLEM THAT IS EXPANDED UPON IN THE !PPENDIX &INALLY E ACCOUNTS FOR DENSITY DEPENDENT DEATHS CAUSED BY COMPETITIVE INTERACTIONS WITHIN THE PAIR .OTE THAT EACH TERM IS DOUBLED BECAUSE BIRTHS OR DEATHS CAN OCCUR AT EITHER LOCATION IN THE PAIR (AVING DElNED BOTH THE STOCHASTIC AND THE DETERMINISTIC MODELS WE CAN NOW TURN TO INVESTIGATE THE EFFECT OF INCORPORATING LOCAL SPATIAL STRUCTURE ON THE SUC CESS AND SPEED OF INVASION AND ALSO ON THE lNAL POPULATION DENSITY !S A REFER ENCE POINT THE RESULTS ARE COMPARED TO THE CONCLUSIONS THAT ARE REACHED FROM THE CLASSICAL LOGISTIC MODEL FOR POPULATION GROWTH 2ECALL THAT IN THE CLASSICAL LOGISTIC MODEL POPULATION GROWTH IS REACHED AT EXACTLY HALF THE lNAL POPULATION SIZE THE GROWTH TRAJECTORY SHOWS AN 3 SHAPED CURVE AND THAT FROM LOW INITIAL DENSI TIES POPULATIONS THAT HAVE LOWER lNAL DENSITIES REACH THEIR EQUILIBRIUM THE FASTEST 4HE READER SHOULD NOTE THAT THE CLASSICAL LOGISTIC MODEL IS A SPECIAL CASE OF BOTH MODELS DElNED HERE AND CAN BE RECOVERED WHENEVER INTERACTIONS OCCUR OVER VERY LARGE SPATIAL SCALES 4HIS IS TRUE EVEN WHEN DISPERSAL IS SHORT RANGE BECAUSE WHEN INTERACTIONS OCCUR OVER SUFlCIENTLY LARGE SPATIAL SCALES ANY SPATIAL PATTERN THAT IS EVIDENT IS IRRELEVANT TO THE DYNAMICS THE POSITIONS OF INDIVIDUALS IN SPACE BECOMES UNIMPORTANT
2%35,43 $ISPERSAL DISTANCE
4HE IMPORTANCE OF DISPERSAL DISTANCE FOR THE INVASION DYNAMICS IS SHOWN IN &IG 3HOWN ARE POPULATIONS ONE WITH RELATIVELY POOR DISPERSAL ONE WITH RELATIVELY GOOD DISPERSAL ABILITIES THE INVADERS ARE OTHERWISE IDENTICAL 3NAPSHOTS OF THE )"- SHOW THAT THE POORER DISPERSER SOON DEVELOPS A CLUMPED DISTRIBUTION AND THIS INHIBITS POPULATION GROWTH BECAUSE INDIVIDUALS EXPERIENCE CROWDED NEIGHBOUR HOODS /N THE OTHER HAND THE BETTER DISPERSER SEEMS TO HAVE FASTER POPULATION DYNAMICS AND REACHES A HIGHER POPULATION DENSITY 4HIS IS BECAUSE MORE OFFSPRING CAN ESCAPE INTENSE COMPETITION WITH THEIR PARENTS AND HENCE THEIR NEIGHBOURHOOD IS RELATIVELY COMPETITOR FREE )NSPECTION OF THE SPATIAL STATISTICS DURING THE INVASION CONlRMS THIS THE BETTER DISPERSER HAS FASTER POPULATION DYNAMICS EXPERIENCES A LESS CROWDED NEIGHBOURHOOD AND REACHES A HIGHER lNAL DENSITY &IG .OTE HOWEVER THAT UNTIL ABOUT TIME UNITS HAVE PASSED EVEN THE BETTER DISPERSER SHOWS SOME DEGREE OF AGGREGATION &IG BUT THIS THEN DISAPPEARS AS POPULATION GROWS AND SPREADS AND EVENTUALLY THE INDIVIDUALS ARE SPATIALLY SEGREGATED
$* -URRELL
&IG 3NAPSHOTS FROM THE )"- SHOWING THE INVASION OF TWO DIFFERENT POPULATIONS )N A THE INDIVIDUALS HAVE SHORT RANGE DISPERSAL SM WHEREAS IN B INDIVIDUALS HAVE LONGER RANGE DISPERSAL SM )N BOTH CASES THE STARTING POPULATION HAS INDIVIDUALS SCATTERED RANDOMLY ACROSS THE LANDSCAPE WHICH IS OF UNIT AREA /THER PARAMETERS HELD CONSTANT ARE B D D SW
0OPULATION GROWTH IN SPACE AND TIME
&IG 4EMPORAL DYNAMICS FOR A THE MEAN DENSITY lRST SPATIAL MOMENTS AND B SECOND SPATIAL MOMENTS AT SHORT DISTANCES FOR THE INVASIONS OF THE SHORT RANGE DISPERSER SOLID LINE AND CIRCLES AND THE LONG RANGE DISPERSER BROKEN LINE AND CROSSES SHOWN IN &IG )N B VALUES GREATER THAN ABOVE THE SOLID LINE INDICATE AGGREGATION OF INDIVIDUALS WHEREAS VALUES LESS THAN BELOW THE SOLID LINE INDICATE SPATIAL SEGREGATION 0ARAMETERS AND STARTING CONDITIONS ARE AS DESCRIBED IN &IG
$* -URRELL
7E NOW TURN TO SEE HOW LOCAL INTERACTIONS AND LOCAL DISPERSAL AFFECT THE INVA SION SUCCESS 0S OF A POPULATION &OR A RANGE OF SCALES OF DISPERSAL POPULATIONS OF INDIVIDUALS ARE INITIALISED IN THE )"- TO INVESTIGATE HOW B THE CRITICAL BIRTH RATE REQUIRED FOR INVASION CHANGES WITH THE DISPERSAL OF THE INVADER &OR EACH INVADING POPULATION THE MODEL IS RUN FOR TIME UNITS AND AN INVASION IS DEEMED A SUCCESS IF IT HAS EXPANDED AFTER THIS TIME IE IF .T .T 4HE PROB ABILITY OF INVASION SUCCESS 0S IS THEN CALCULATED FROM THE PROPORTION OF THE POPULATIONS THAT SHOW THIS INCREASE IN POPULATION DENSITY 7HEN THE INVADER IS RESTRICTED TO ONLY SHORT RANGE DISPERSAL IT TAKES A RELATIVELY LARGE B FOR THE POPU LATION TO BE ABLE TO INVADE WITH ANY DEGREE OF CERTAINTY &IG &OR EXAMPLE FOR SM INVASION SUCCESS DOES NOT EXCEED UNTIL B )N FACT FOR MANY VALUES FOR INTRINSIC BIRTH RATES B THAT WOULD RESULT IN ALMOST GUARANTEED INVA SION SUCCESS IN THE STOCHASTIC VERSION OF THE NON SPATIAL LOGISTIC MODEL NONE OF THE INITIAL POPULATIONS ARE ABLE TO INVADE
&IG 4HE EFFECT OF INTRINSIC BIRTH RATE B AND DISPERSAL DISTANCE EXPRESSED BY THE PARAMETER SM THAT DETERMINES THE WIDTH OF THE DISPERSAL KERNEL ON THE INVASION SUCCESS 0S OF A SINGLE SPECIES 4HE LANDSCAPE OF UNIT AREA IS SEEDED WITH RANDOMLY LOCATED INDIVIDUALS AND EACH SQUARE REPRESENTS THE PROPORTION OF REALISATIONS THAT SHOW POPULATION GROWTH AFTER TIME UNITS HAVE ELAPSED /THER PARAMETERS HELD CONSTANT THROUGHOUT ARE D D SW
0OPULATION GROWTH IN SPACE AND TIME
4HERE ARE NUMEROUS EXAMPLES SHOWING HOW THE INVASION RATE IS AFFECTED BY THE DISPERSAL KERNEL &OR EXAMPLE #ASWELL ET AL SHOWED THAT THE 0IED &LYCATCHER &ICEDULA HYPOLEUCA IN %UROPE IS A SLOWER INVADER THAN THE 3TARLING 3TURNUS VULGARIS IN .ORTH !MERICA AND THAT OF THE DIFFERENCE BETWEEN INVA SION RATES COULD BE EXPLAINED BY THE DIFFERENCES IN DISPERSAL ABILITIES WITH THE REST BEING EXPLAINED BY THE DIFFERENCES IN DEMOGRAPHY /VER LONGER PERIODS OF TIME THE DISPERSAL ABILITIES OF AN INVADER MIGHT BE EXPECTED TO BE UNDER SOME STRONG SELECTIVE PRESSURE 5SING A SIMULATION MODEL 4RAVIS AND $YTHAM WERE ABLE TO SHOW THAT EARLY ON DURING AN INVASION ON AN ISLAND LONG DISTANCE INVASION IS SELECTED FOR BUT THAT SHORTER DISTANCE SUBSEQUENTLY EVOLVES %VIDENCE FOR SUCH PATTERNS CAN BE SEEN IN THE DIFFERENCE BETWEEN WIND DISPERSED PLANTS IN MAINLAND AND SMALL ISLAND SUBPOPULATIONS #ODY AND /VERTON )N NEW ISLAND POPU LATIONS THE DISPERSAL ABILITY OF THE PLANTS TENDS TO BE GREATER THAN THE MAINLAND POPULATIONS /VER TIME SELECTION IS FOR A REDUCTION IN DISPERSAL ABILITY ON THE ISLANDS SO THAT OLD ISLAND PLANT POPULATIONS HAVE A LOWER DISPERSAL ABILITY THAN THE MAINLAND POPULATIONS SEE ALSO $ARLINGTON "ROWN AND ,OMOLINO 7HITTAKER &ILIN AND :IV 2EPRODUCTIVE NUMBER
!S "OLKER AND 0ACALA AND "OLKER POINT OUT THE POPULATION DYNAMICS OF AN INVADING SPECIES IS GREATLY AFFECTED BY THE REPRODUCTIVE NUMBER 2 WHERE 2 BD WHICH IS A MEASURE OF HOW SENSITIVE INDIVIDUALS ARE TO COMPETI TION 2 CAN BE THOUGHT OF AS BEING THE EXPECTED LIFETIME REPRODUCTIVE OUTPUT IN THE ABSENCE OF COMPETITION AND IN THE SPATIAL MODELS 2 BECOMES IMPORTANT IN DETERMINING HOW GOOD A COLONISER A SPECIES IS 7EEDY SPECIES AND HENCE INVAD ERS ARE EXPECTED TO HAVE A LARGE VALUE FOR 2 LESS WEEDY SPECIES WILL HAVE A LOW 2 NUMBER .OTE THAT VARYING 2 IN THE NON SPATIAL LOGISTIC MODEL HAS NO OUTCOME ON POPULATION DYNAMICS 2 IS IMPORTANT ONLY FOR THE SPATIAL DYNAMICS 7HEN 2 IS SMALL THE SPECIES IS A POOR COLONISER AND THE POPULATION GROWTH RATE IS SLOW OR IF 2 IS SMALL ENOUGH THE INVASION MAY FAIL ALTOGETHER &IG -OREOVER NOTE THAT LOW VALUES FOR 2 ARE ASSOCIATED WITH LONG PERIODS OF NEAR LINEAR POPULA TION GROWTH THE CLASSICAL SIGMOIDAL GROWTH CURVE CHARACTERISTIC OF THE NON SPATIAL LOGISTIC MODEL ONLY OCCURS WHEN 2 IS HIGH ANDOR WHEN DISPERSAL IS LONG RANGE SEE ALSO ,AW ET AL !NOTHER FEATURE IS THAT 2 GREATLY AFFECTS THE lNAL POPU LATION SIZE WITH LARGE VALUES FOR 2 LEADING TO HIGHER POPULATION DENSITIES &IG #OUPLED TO THIS IS THE INTERESTING OBSERVATION THAT THE LARGER POPULATIONS TAKE THE SHORTEST AMOUNT OF TIME TO REACH THEIR EQUILIBRIUM THIS IS IN STARK CONTRAST TO THE NON SPATIAL LOGISTIC MODEL WHERE THE SMALLEST POPULATION REACH THEIR lNAL SIZE BEFORE THOSE WITH LARGER POPULATION DENSITIES .OTE ALSO THAT THE AGREEMENT BETWEEN THE )"- AND THE DETERMINISTIC APPROXIMATION MOMENT DYNAMICS IS VERY GOOD &IG /THER RESULTS CONlRM THESE lNDINGS -URRELL AND ,AW ,AW ET AL -URRELL AND ,AW AND THE REST OF THE CHAPTER SHALL CONCENTRATE ON THE DETERMINISTIC APPROXIMATION
$* -URRELL
&IG 4HE EFFECT OF THE REPRODUCTIVE NUMBER 2 ON POPULATION GROWTH 3HOWN IN A ARE MEAN TRAJECTORIES FOR REALISATIONS OF THE )"- AND IN B THE DETERMINISTIC APPROXIMATION USING THE DYNAMICAL SYSTEM AND FOR DIFFERENT VALUES FOR 2 )N ALL CASES THE INTRINSIC GROWTH RATE R IS HELD CONSTANT R )N I B D II B D III B D IV B D V B D /THER PARAMETERS HELD CONSTANT THROUGHOUT ARE D SW SM
0OPULATION GROWTH IN SPACE AND TIME
!NOTHER EXAMPLE SHOWS HOW IMPORTANT 2 CAN BE TO THE INVASION DYNAMICS AND HOW IT CAN REVERSE SOME OF THE CONCLUSIONS OF THE NON SPATIAL LOGISTIC MODEL &IG #ONSIDER IMAGINARY SPECIES LABELLED AND RESPECTIVELY IF R R IE SPECIES HAS A HIGHER INTRINSIC RATE OF GROWTH THAN SPECIES BUT 2 2 AND IF INTERACTIONS AND DISPERSAL ARE LOCALISED IN SPACE THEN IT IS POSSIBLE FOR SPECIES TO BE THE BETTER INVADER BOTH IN TERMS OF SPEED OF INVASION AND EQUILIBRIUM DENSITY 3IMILAR RESULTS COULD EASILY BE PRODUCED FOR SPECIES WITH DIFFERENT SCALES OF DISPERSAL AND THIS SENDS THE MESSAGE THAT KNOWING R MAY NOT BE SUFl CIENT IN DETERMINING WHETHER A SPECIES CAN INVADE OR NOT 4HESE RESULTS ALL POINT TO THE FACT THAT A HIGH REPRODUCTIVE NUMBER 2 IS ADVANTAGEOUS FOR AN INVADER IN HOMOGENEOUS SPACE BUT OTHER RESULTS "OLKER SHOW THAT LOW VALUES FOR 2 CAN BE BENElCIAL IF THERE IS SPATIAL VARIATION IN THE EXTERNAL ENVIRONMENT TYPE II SPATIAL HETEROGENEITY
&IG !N EXAMPLE SHOWING HOW 2 MAY REVERSE A MAIN CONCLUSION OF THE NON SPATIAL LOGISTIC MODEL 3PECIES BROKEN LINES HAS A HIGH VALUE FOR R BUT A LOW 2 NUMBER 3PECIES SOLID LINES HAS A LOWER VALUE FOR R BUT A HIGHER 2 NUMBER )N THE NON SPATIAL MODEL THICK LINES SPECIES IS THE BETTER INVADER AND HAS A HIGHER DENSITY AT EQUILIBRIUM 7HEN INTERACTIONS AND DISPERSAL ARE LOCALISED IN SPACE THIN LINES THIS RESULT IS REVERSED NOW THE SPECIES HAS THE FASTER INVASION RATE AND HIGHER DENSITY AT EQUILIBRIUM &OR SPECIES B D GIVING R 2 AND FOR SPECIES B D GIVING R 2 /THER PARAMETERS ARE IDENTICAL FOR BOTH SPECIES AND ARE D SW SM
$* -URRELL
&INAL POPULATION SIZE
3O FAR WE HAVE CONCENTRATED ON THE TRANSIENT DYNAMICS BUT NEIGHBOURHOOD INTERACTIONS AND LOCAL DISPERSAL CAN ALSO GREATLY AFFECT THE lNAL POPULATION SIZE ,AW ET AL %THERIDGE )F NEIGHBOURHOOD INTERACTIONS ARE SUFlCIENTLY LARGE SCALE THEN THE POSITION OF INDIVIDUALS ACROSS THE LANDSCAPE IS OF LITTLE IMPOR TANCE IN DETERMINING THE COMPETITIVE INTERACTIONS )N SUCH CASES THE RESULTS OF THE MEAN lELD MODEL ARE ASYMPTOTICALLY APPROACHED &IG 4HIS IS IN CONTRAST TO THE CASE WHERE DISPERSAL IS LARGE SCALE )F INTERACTIONS ARE LOCALISED IN SPACE SMALL VALUE FOR SW THEN MANY OFFSPRING CAN ESCAPE FROM COMPETING WITH THEIR PARENT 4HIS LEADS TO A SPATIALLY SEGREGATED POPULATION WHERE MOST INDIVIDUALS EXPERIENCE A RELATIVELY COMPETITOR FREE NEIGHBOURHOOD AND HENCE THE lNAL POPULATION SIZE IS MUCH LARGER THAN THAT UNDER MEAN lELD CONDITIONS /N THE OTHER HAND IF BOTH DISPERSAL AND INTERACTIONS ARE SHORT RANGE SMALL VALUES FOR SM AND SW THEN THE COMPETITIVE NEIGHBOURHOOD IS PERCEIVED AS BEING CROWDED WITH THE RESULT THAT THE lNAL DENSITY IS MUCH LOWER THAN THE MEAN lELD EXPECTATION )N EXTREME CASES WHERE BOTH INTERACTIONS AND DISPERSAL OCCUR OVER SHORT SPATIAL SCALES THEN SELF DRIVEN EXTINCTION OCCURS &IG &IGS AND ,AW ET AL 3ELF DRIVEN EXTINCTION MIGHT AT lRST THOUGHT SEEM ONLY AN INTERESTING MATH EMATICAL ARTEFACT AND OF NO CONCERN TO INVASION ECOLOGY AFTER ALL IF AN ORGANISMS DISPERSAL IS SO SHORT RANGE HOW COULD IT PERSIST AT ANOTHER LOCATION AND SEND OUT EMMIGRANTS (OWEVER IT IS ENTIRELY POSSIBLE FOR A SPECIES DISPERSAL KERNEL TO DIFFER BETWEEN ITS NATURAL AND EXOTIC HABITATS -ANY PLANTS RELY ON SECONDARY DISPER SAL OF SEEDS BY ANIMALS !NDRESEN "OHNING 'AESE ET AL (OSHIZAKI ET AL -ILTON AND $EAN 'ORDON AND VAN DER 6ALK 'UITIAN ET AL AND IF IN A NEW ENVIRONMENT THE SECONDARY DISPERSERS ARE NOT PRESENT THE DISPERSAL KERNEL IS LIKELY TO BE MUCH SHORTER AND HENCE SELF DRIVEN EXTINC TION IS MUCH MORE LIKELY !NOTHER FEATURE OF THE PRESENCE OF SPATIAL AGGREGATION OF CONSPECIlCS IS THAT WHEN LOOKING AT THE INVASION DYNAMICS OF A SPECIES INTO A COMMUNITY IT IS NO LONGER POSSIBLE TO IGNORE THE EFFECT OF INTRASPECIlC COMPETITION AS HAS TRADITIONALLY BEEN THE CASE -ORTON ET AL -ORTON AND ,AW
→ &IG %QUILIBRIUM VALUES FOR A . AND B # AS A FUNCTION OF THE SPATIAL SCALE OF THE INTERACTION KERNEL AND DISPERSAL KERNEL 4HE RESULTS ARE OBTAINED BY NUMERICALLY INTEGRATING THE DETERMINISTIC APPROXIMATION AND UNTIL THE CHANGE IN . OVER AN INTEGRATION STEP FALLS BELOW /THER PARAMETERS ARE HELD CONSTANT ARE B D D &OR COMPARISON THIS SET OF PARAMETERS NON SPATIAL LOGISTIC MODEL GIVES AN EQUILIBRIUM DENSITY OF
0OPULATION GROWTH IN SPACE AND TIME
$* -URRELL
4HIS IS BECAUSE EVEN THOUGH GLOBALLY THE INVADING SPECIES IS AT A LOW DENSITY LOCALLY THE INVADER STILL @SEES A HIGH DENSITY OF CONSPECIlCS THANKS TO THE LOCAL NATURE OF DISPERSAL AND COMPETITION "OLKER AND 0ACALA -URRELL ET AL -URRELL AND ,AW 4HESE RESULTS ALL POINT TO THE IMPORTANCE OF THE RELATIVE SCALES OF DISPERSAL AND NEIGHBOURHOOD INTERACTIONS TO BOTH THE TRANSIENT DYNAMICS AND lNAL POPULATION DENSITY "OLKER AND 0ACALA %LLNER ,AW ET AL &OR MANY ANIMAL SPECIES THE INTERACTION KERNEL IS LIKELY TO BE OVER A MUCH SHORTER DISTANCE THAN THE DISPERSAL KERNEL (OWEVER FOR PLANTS AND OTHER SEDENTARY ORGANISMS THIS MAY NOT BE THE CASE AND IT IS ENTIRELY POSSIBLE THAT THE EFFECTS OF DENSITY MAY BE FELT OVER RELATIVELY LARGE SPATIAL SCALES 0ETERS %COLOGISTS HAVE PUT MUCH EFFORT INTO MEASURING DISPERSAL RATES AND DISTANCES #LOBERT ET AL "ULLOCK ET AL ,EVINE AND -URRELL BUT RATHER LESS IS KNOWN ABOUT THE SHAPES AND SIZES OF INTERACTION KERNELS 0URVES AND ,AW #LEARLY MODELS OF THIS TYPE SHOW THAT THE INTERACTION KERNELS ARE POTENTIALLY VERY IMPORTANT IN DETERMINING INVA SION DYNAMICS
,).+3 4/ /4(%2 -/$%,3 !S HAS BEEN SUGGESTED AT VARIOUS POINTS IN THIS CHAPTER THE MODELS DESCRIBED AND ANALYSED HERE ARE CLOSELY RELATED TO A NUMBER OF OTHER SPATIAL MODELS 9OUNG ET AL SHOWED THAT A POPULATION OF DISCRETE INDIVIDUALS INHABITING A LAND SCAPE AND WITH LOCAL DISPERSAL AND POST BIRTH MOVEMENT WILL QUICKLY AGGREGATE EVEN WITHOUT ANY DENSITY DEPENDENT PROCESSES 4HE MODELS ABOVE HAVE SHOWN THAT INCORPORATING LOCAL DENSITY DEPENDENT PROCESSES CAN LEAD TO ANY OF THE MAIN CLASSES OF SPATIAL STRUCTURE AGGREGATION SEGREGATION OR RANDOM PATTERNING &URTHER THE DYNAMICAL SYSTEM AND COLLAPSES TO THE MODEL OF 9OUNG ET AL WHEN D AND THE SPATIAL PATTERN IS NOW DESCRIBED BY ONLY THREE PAIRS OF TERMS A C TWO OF WHICH ARE CONCERNED WITH BIRTHS AND ONLY ONE OF WHICH IS CONCERNED WITH THE LOSS OF PAIRS )T CAN BE EASILY SEEN THAT IN THE lRST INSTANCE THE BIRTH TERMS WILL OUTWEIGH THE DEATH TERM AND SO AGGREGATIONS OF INDIVIDUALS WILL DEVELOP (OWEVER IT IS NOT CLEAR THAT THE AGGREGATIONS WILL EVER STOP ALTHOUGH THE RATE OF CHANGE WILL SLOW OVER TIME 4HE THETA LOGISTIC MODEL 'ILPIN AND !YAYLA HAS BEEN USED WITH SOME SUCCESS TO MODEL THE POPULATION DYNAMICS OF A NUMBER OF SPECIES 3AETHER AND %NGEN 3AETHER ET AL A 3AETHER ET AL B 4HE MAIN BASIS FOR THE THETA LOGISTIC MODEL IS THAT THE MAXIMUM RATE OF POPULATION GROWTH MAY BE ACHIEVED AT DENSITIES OTHER THAN HALF THE CARRYING CAPACITY 4URCHIN 4HE SPATIAL VERSION OF THE LOGISTIC MODEL ALSO SHOWS THIS FEATURE ,AW ET AL AND MAY THEREFORE ACT AS A MECHANISTIC FOUNDATION FOR THE THETA LOGISTIC MODELS 7HEN INTERACTIONS ARE LOCALISED IN SPACE HOW CROWDED THE NEIGHBOURHOOD IS DETERMINES WHEN THE MAXIMUM GROWTH RATE IS ACHIEVED 7HEN BOTH DISPERSAL AND INTERACTIONS OCCUR OVER SHORT SCALES THE NEIGHBOURHOOD QUICKLY BECOMES
0OPULATION GROWTH IN SPACE AND TIME
CROWDED EVEN IF THE OVERALL DENSITY IS LOW AND THIS LEADS TO THE MAXIMUM GROWTH RATE OCCURRING AT LESS THAN HALF THE lNAL DENSITY /N THE OTHER HAND IF DISPERSAL IS LONG RANGE BUT INTERACTIONS ARE SHORT SCALE THE INDIVIDUALS TEND NOT TO EXPERI ENCE MANY NEIGHBOURS UNTIL THE OVERALL DENSITY IS MUCH HIGHER SO THE MAXIMUM POPULATION GROWTH RATE TENDS TO OCCUR AT DENSITIES THAT ARE HIGHER THAN THE HALF THE lNAL POPULATION DENSITY ,AW ET AL 4HIS CHAPTER HAS FOCUSED ON A MODEL FOR COMPETITION INVESTIGATING THE INVASION DYNAMICS OF A SINGLE SPECIES -ANY ECONOMICALLY IMPORTANT INVASIONS ARE BY PARA SITESPATHOGENS AND THEORETICAL MODELS HAVE BEEN USED TO INVESTIGATE THE EFFECTS OF LOCAL SPATIAL STRUCTURE ON INVASION DYNAMICS OF THE PESTPATHOGEN "OLKER +EELING )N A SUSCEPTIBLE INFECTED RECOVERED 3)2 HOST PATHOGEN MODEL WITH LOCAL DISPERSAL OF THE PATHOGEN +EELING SHOWS HOW THE REPRODUC TIVE RATIO REQUIRED FOR INVASION IN A NETWORK WITH LOCAL AND lNITE CONNECTIONS IS ALWAYS LARGER THAN THE MEAN lELD CASE 'ENERALLY SPEAKING THE AGGREGATION OF HOSTS IS GOOD AT SLOWING THE RATE OF SPREAD OF A PESTPATHOGEN IF ITS DISPERSAL IS FAIRLY SHORT RANGE AND THIS HAS IMPORTANT IMPLICATIONS FOR EVOLUTION OF VIRULENCE "OOTS AND 3ASAKI "OOTS ET AL
#/.#,53)/.3 )NVASIONS ARE ESSENTIALLY THE STUDY OF POPULATION GROWTH IN SPACE AND TIME "OTH DISPERSAL AND COMPETITIVE INTERACTIONS TEND TO BE LOCALISED IN SPACE AND ACTING TOGETHER THEY MAY PRODUCE STRONG SPATIAL STRUCTURES THAT FEED BACK ONTO POPU LATION DYNAMICS AND SO GREATLY AFFECT THE INVASION DYNAMICS 4HIS CHAPTER HAS INVESTIGATED THE EFFECTS OF LOCAL INTERACTIONS AND LOCAL DISPERSAL ON POPULATION GROWTH USING SPATIAL EXTENSIONS OF THE CLASSICAL LOGISTIC EQUATION &ROM A STOCHAS TIC INDIVIDUAL BASED MODEL A DETERMINISTIC APPROXIMATION HAS BEEN DERIVED WHICH GREATLY AIDS THE ANALYSIS OF THE MODEL ! NUMBER OF QUALITATIVE AND QUANTITATIVE PATTERNS EMERGE POPULATION GROWTH MAY BE EITHER FASTER OR SLOWER THAN THE CLASSICAL MODEL THE RATIO OF DENSITY INDEPENDENT BIRTHS TO DENSITY INDEPENDENT DEATHS 2 CAN GREATLY AFFECT THE PROBABILITY AND SPEED OF INVASION AS WELL AS THE lNAL POPULATION SIZE POPULATION GROWTH MAY BE LINEAR RATHER THAN THE FAMIL IAR SIGMOID SHAPE DETERMINISTIC EXTINCTION MAY OCCUR PURELY DUE TO PARENT OFFSPRING COMPETITION MEANING THAT INTRASPECIlC COMPETITION CANNOT BE IGNORED IN THE ANALYSIS OF INVASIONS AND THAT COUNTER INTUITIVELY POPULATIONS WITH THE LOWEST EQUILIBRIUM DENSITY MAY TAKE THE LONGEST TO REACH THIS STATE !LL OF THESE PROPERTIES ARE DEPENDENT NOT ONLY ON THE ABSOLUTE SPATIAL SCALES OF NEIGHBOURHOOD INTERACTIONS AND LOCAL DISPERSAL BUT ALSO THEIR RELATIVE SCALES )T HAS LONG BEEN KNOWN THAT DISPERSAL IS IMPORTANT FOR THE INVASIVE ABILITY OF A SPECIES BUT THESE RESULTS ALSO SHOW THAT 2 MAY BE JUST AS IMPORTANT AS THE INTRINSIC GROWTH RATE R IN DETERMINING POPULATION GROWTH
$* -URRELL
!#+./7,%$'%-%.43 4HE WORK PRESENTED HERE OWES A GREAT DEAL TO 2ICHARD ,AW AND 5LF $IECKMANN WHO SOLVED MANY OF THE DIFlCULT INITIAL PROBLEMS TO DO WITH DERIVING THE DETER MINISTIC APPROXIMATION AND WHO HELPED AND ENCOURAGED ME TO THINK LONG AND HARD ABOUT THE PROBLEM OF MOMENT CLOSURES ) WOULD ALSO LIKE TO THANK "EN "OLKER #ALVIN $YTHAM $ANIEL ,LAMBI AND $REW 0URVES FOR VARIOUS HELPFUL AND INFORMA TIVE DISCUSSIONS ALONG THE WAY AND TO -ARC #ADOTTE 2ENE 3ALINAS *ESSICA -ETCALF AND 9VONNE "UCKLEY FOR COMMENTS ON EARLIER DRAFTS OF THIS CHAPTER 4HIS WORK WAS PARTLY SUPPORTED BY THE .ATURAL %NVIRONMENT 2ESEARCH #OUNCIL AND ALSO THE #ENTRAL 3CIENCE ,ABORATORY $%&2! )MPERIAL #OLLEGE 0ARALLEL #OMPUTING #ENTRE )#0# KINDLY DONATED COMPUTER PROCESSOR TIME THAT HELPED TO GENERATE SOME OF THE RESULTS REPORTED IN THE lGURES
!00%.$)8 4HE PRESENCE OF THE THIRD MOMENT IN THE DYNAMICS FOR THE SECOND MOMENTS MEANS THAT THE DYNAMICAL SYSTEM IS NOT YET CLOSED )N PRINCIPLE IT IS POSSIBLE TO DERIVE THE DYNAMICS OF THE THIRD MOMENTS BUT APART FROM CAUSING A HEADACHE DUE TO THE NUMBER OF TERMS INVOLVED THEY WOULD THEMSELVES BE FUNCTIONS OF FOURTH MOMENTS QUAD DENSITIES (OW TO DEAL WITH THIS MOMENT HIERARCHY IS THE CENTRAL PROBLEM TO THIS TECHNIQUE #LASSICAL THEORY EFFECTIVELY TRUNCATES AT THE lRST MOMENT BY ASSUMING THAT THERE IS NO SPATIAL STRUCTURE BUT THIS ONLY DEALS WITH A LIMITING CASE OF THE )"- SEE BELOW ! BETTER SOLUTION IS TO CLOSE THE HIERARCHY AT THE SECOND MOMENTS BY REPLACING THE THIRD MOMENTS BY A TERM THAT IS A FUNCTION OF THE lRST AND SECOND MOMENTS 2ECENT WORK HAS SUGGESTED A FORM OF SECOND ORDER MOMENT CLOSURE THAT GIVES GOOD APPROXIMATIONS TO THE )"- FOR A WIDE RANGE OF SPATIAL STRUCTURES ,AW ET AL -URRELL AND ,AW -URRELL ET AL AND IT IS USED HERE # j # j # j # j n j # j # j n j n . 4 j j . . .
!
4HIS CLOSURE DOES HOWEVER MEAN THAT ANALYTICAL SOLUTIONS TO THE DYNAMICAL SYSTEM ARE VERY HARD TO ACHIEVE AND SO THE ANALYSIS OF THE DYNAMICAL SYSTEM PRO CEEDS BY NUMERICAL METHODS
2%&%2%.#%3 !NDRESEN % 3EED DISPERSAL BY MONKEYS AND THE FATE OF DISPERSED SEEDS IN A 0ERUVIAN RAIN FOREST "IOTROPICA "OERLIJST - # AND 0 (OGEWEG 3PIRAL 7AVE 3TRUCTURE IN 0RE "IOTIC %VOLUTION n (YPERCYCLES 3TABLE AGAINST 0ARASITES 0HYSICA $
0OPULATION GROWTH IN SPACE AND TIME
"OHNING 'AESE + " ( 'AESE AND 3 " 2ABEMANANTSOA )MPORTANCE OF PRIMARY AND SECONDARY SEED DISPERSAL IN THE -ALAGASY TREE #OMMIPHORA GUILLAUMINI %COLOGY "OLKER " AND 3 7 0ACALA 5SING MOMENT EQUATIONS TO UNDERSTAND STOCHASTICALLY DRIVEN SPATIAL PATTERN FORMATION IN ECOLOGICAL SYSTEMS 4HEORETICAL 0OPULATION "IOLOGY "OLKER " - !NALYTIC MODELS FOR THE PATCHY SPREAD OF PLANT DISEASE "ULLETIN OF -ATHEMATICAL "IOLOGY "OLKER " - #OMBINING ENDOGENOUS AND EXOGENOUS SPATIAL VARIABILITY IN ANALYTICAL POPULATION MODELS 4HEORETICAL 0OPULATION "IOLOGY "OLKER " - AND 3 7 0ACALA 3PATIAL MOMENT EQUATIONS FOR PLANT COMPETITION 5NDERSTANDING SPATIAL STRATEGIES AND THE ADVANTAGES OF SHORT DISPERSAL !MERICAN .ATURALIST "OLKER " - 3 7 0ACALA AND # .EUHAUSER 3PATIAL DYNAMICS IN MODEL PLANT COM MUNITIES 7HAT DO WE REALLY KNOW !MERICAN .ATURALIST "OOTS - 0 * (UDSON AND ! 3ASAKI ,ARGE SHIFTS IN PATHOGEN VIRULENCE RELATE TO HOST POPULATION STRUCTURE 3CIENCE "OOTS - AND ! 3ASAKI @3MALL WORLDS AND THE EVOLUTION OF VIRULENCE INFECTION OCCURS LOCALLY AND AT A DISTANCE 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES "ROWN * ( AND ,OMOLINO - 6 "IOGEOGRAPHY 3INAUER !SSOCIATES 3UNDERLAND -! "ULLOCK * - 2 % +ENWARD AND 2 3 (AILS EDITORS $ISPERSAL ECOLOGY "LACKWELL /XFORD #ASWELL ( 2 ,ENSINK AND - ' .EUBERT $EMOGRAPHY AND DISPERSAL ,IFE TABLE RESPONSE EXPERIMENTS FOR INVASION SPEED %COLOGY #LOBERT * % $ANCHIN ! ! $HONDT AND * $ .ICHOLS EDITORS $ISPERSAL /XFORD 5NIVERSITY 0RESS /XFORD #ODY - , AND * - /VERTON 3HORT TERM EVOLUTION OF REDUCED DISPERSAL IN ISLAND PLANT POPULATIONS *OURNAL OF %COLOGY #RESSIE . ! # 3TATISTICS FOR SPATIAL DATA 7ILEY .EW 9ORK $ARLINGTON 0 * *R #ARABIDAE OF MOUNTAINS AND ISLANDS DATA ON THE EVOLUTION OF ISOLATED FAUNAS AND ON ATROPHY OF WINGS %COLOGICAL -ONOGRAPHS $IECKMANN 5 AND 2 ,AW 2ELAXATION PROJECTIONS AND THE METHOD OF MOMENTS 0AGES IN 5 $IECKMANN 2 ,AW AND * ! * -ETZ EDITORS 4HE 'EOMETRY OF ECOLOGICAL INTERACTIONS SIMPLIFYING SPATIAL COMPLEXITY #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE $IGGLE 0 * 3TATISTICAL ANALYSIS OF SPATIAL POINT PATTERNS !CADEMIC 0RESS ,ONDON %LLNER 3 0 0AIR APPROXIMATION FOR LATTICE MODELS WITH MULTIPLE INTERACTION SCALES *OURNAL OF 4HEORETICAL "IOLOGY %THERIDGE ! - 3URVIVAL AND EXTINCTION IN A LOCALLY REGULATED POPULATION !NNALS OF !PPLIED 0ROBABILITY
$* -URRELL
&AGAN 7 & AND * ' "ISHOP 4ROPHIC INTERACTIONS DURING PRIMARY SUCCESSION (ERBIVORES SLOW A PLANT REINVASION AT -OUNT 3T (ELENS !MERICAN .ATURALIST &INLAY " * 'LOBAL DISPERSAL OF FREE LIVING MICROBIAL EUKARYOTE SPECIES 3CIENCE &INLAY " * AND + * #LARKE 5BIQUITOUS DISPERSAL OF MICROBIAL SPECIES .ATURE &INLAY " * ' & %STEBAN * , /LMO AND 0 ! 4YLER 'LOBAL DISTRIBUTION OF FREE LIVING MICROBIAL SPECIES %COGRAPHY &ILIN ) AND :IV 9 .EW THEORY OF INSULAR EVOLUTION UNIFYING THE LOSS OF DISERSABILITY AND BODY MASS CHANGE %VOLUTIONARY %COLOGY 2ESEARCH 'ILPIN - % AND & * !YAYLA 'LOBAL MODELS OF GROWTH AND COMPETITION 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES OF THE 5NITED 3TATES OF !MERICA 'ORDON % AND ! ' VAN DER 6ALK 3ECONDARY SEED DISPERSAL IN -ONTRICHARDIA ARBO RESCENS , SCHOTT DOMINATED WETLANDS IN LAGUNA GRANDE 6ENEZUELA 0LANT %COLOGY 'UITIAN 0 - -EDRANO AND * 'UITIAN 3EED DISPERSAL IN %RYTHRONIUM DENS CANIS , ,ILIACEAE VARIATION AMONG HABITATS IN A MYRMECOCHOROUS PLANT 0LANT %COLOGY (ASSELL - 0 ( . #OMINS AND 2 - -AY 3PECIES #OEXISTENCE AND 3ELF /RGANIZING 3PATIAL $YNAMICS .ATURE (ILL * + 9 # #OLLINGHAM # $ 4HOMAS $ 3 "LAKELEY 2 &OX $ -OSS AND " (UNTLEY )MPACTS OF LANDSCAPE STRUCTURE ON BUTTERmY RANGE EXPANSION %COLOGY ,ETTERS (OLWAY $ ! ! 6 3UAREZ AND 4 * #ASE 2OLE OF ABIOTIC FACTORS IN GOVERNING SUS CEPTIBILITY TO INVASION ! TEST WITH ARGENTINE ANTS %COLOGY (OSHIZAKI + 7 3UZUKI AND 4 .AKASHIZUKA %VALUATION OF SECONDARY DISPERSAL IN A LARGE SEEDED TREE !ESCULUS TURBINATA A TEST OF DIRECTED DISPERSAL 0LANT %COLOGY +EELING - * 4HE EFFECTS OF LOCAL SPATIAL STRUCTURE ON EPIDEMIOLOGICAL INVASIONS 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES +EELING - * $ ! 2AND AND ! * -ORRIS #ORRELATION MODELS FOR CHILDHOOD EPIDEMICS 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES +ENKEL . # 0ATTERN OF SELF THINNING IN JACK PINE TESTING THE RANDOM MORTALITY HYPOTHESIS %COLOGY +OT - - ! ,EWIS AND 0 VANDEN$RIESSCHE $ISPERSAL DATA AND THE SPREAD OF INVAD ING ORGANISMS %COLOGY ,AW 2 AND 5 $IECKMANN ! DYNAMICAL SYSTEM FOR NEIGHBORHOODS IN PLANT COM MUNITIES %COLOGY ,AW 2 $ * -URRELL AND 5 $IECKMANN 0OPULATION GROWTH IN SPACE AND TIME 3PATIAL LOGISTIC EQUATIONS %COLOGY ,EVIN 3 ! 4HE 0ROBLEM OF 0ATTERN AND 3CALE IN %COLOGY %COLOGY ,EVINE * - AND $ * -URRELL #OMMUNITY LEVEL CONSEQUENCES OF SEED DISPERSAL PATTERNS !NNUAL 2EVIEW OF %COLOGY %VOLUTION AND 3YSTEMATICS
0OPULATION GROWTH IN SPACE AND TIME
,EWIS - ! 3PREAD RATE FOR A NONLINEAR STOCHASTIC INVASION *OURNAL OF -ATHEMATICAL "IOLOGY ,EWIS - ! AND 3 0ACALA -ODELING AND ANALYSIS OF STOCHASTIC INVASION PROCESSES *OURNAL OF -ATHEMATICAL "IOLOGY -ILTON 3 * AND 7 2 * $EAN 3EEDS DISPERSED IN DUNG OF INSECTIVORES AND HERBI VORES IN SEMI ARID SOUTHERN !FRICA *OURNAL OF !RID %NVIRONMENTS -ORTON 2 $ AND 2 ,AW 2EGIONAL SPECIES POOLS AND THE ASSEMBLY OF LOCAL ECOLOGI CAL COMMUNITIES *OURNAL OF 4HEORETICAL "IOLOGY -ORTON 2 $ 2 ,AW 3 , 0IMM AND * ! $RAKE /N MODELS FOR ASSEMBLING ECOLO GICAL COMMUNITIES /IKOS -URRELL $ 5 $IECKMANN AND 2 ,AW /N MOMENT CLOSURES FOR POPULATION DYNAM ICS IN CONTINUOUS SPACE *OURNAL OF 4HEORETICAL "IOLOGY -URRELL $ * AND 2 ,AW "EETLES IN FRAGMENTED WOODLANDS A FORMAL FRAMEWORK FOR DYNAMICS OF MOVEMENT IN ECOLOGICAL LANDSCAPES *OURNAL OF !NIMAL %COLOGY -URRELL $ * AND 2 ,AW (ETEROMYOPIA AND THE SPATIAL COEXISTENCE OF SIMILAR COM PETITORS %COLOGY ,ETTERS -URRELL $ * $ 7 0URVES AND 2 ,AW 5NITING PATTERN AND PROCESS IN PLANT ECOL OGY 4RENDS IN %COLOGY %VOLUTION /WEN - 2 AND - ! ,EWIS (OW PREDATION CAN SLOW STOP OR REVERSE A PREY INVA SION "ULLETIN OF -ATHEMATICAL "IOLOGY 0ALMIOTTO 0 ! $AVIES 3 * 6OGT + ! !SHTON - 3 6OGT $ * AND !SHTON 0 3 3OIL RELATED HABITAT SPECIALIZATION IN DIPTEROCARP RAN FOREST TREE SPECIES IN "ORNEO *OURNAL OF %COLOGY 0EARL 2 AND , * 2EAD /N THE RATE OF GROWTH OF THE POPULATION OF THE 5NITED 3TATES SINCE AND ITS MATHEMATICAL REPRESENTATION 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES OF THE 5NITED 3TATES OF !MERICA 0ETERS ( ! .EIGHBOUR REGULATED MORTALITY THE INmUENCE OF POSITIVE AND NEGATIVE DENSITY DEPENDENCE ON TREE POPULATIONS IN SPECIES RICH TROPICAL FORESTS %COLOGY ,ETTERS 0URVES $ 7 AND 2 ,AW %XPERIMENTAL DERIVATION OF FUNCTIONS RELATING GROWTH OF !RABIDOPSIS THALIANA TO NEIGHBOUR SIZE AND DISTANCE *OURNAL OF %COLOGY 2ICHARDSON $ - . !LLSOPP # - $!NTONIO 3 * -ILTON AND - 2EJMANEK 0LANT INVASIONS n THE ROLE OF MUTUALISMS "IOLOGICAL 2EVIEWS 2IETKERK - - # "OERLIJST & VAN ,ANGEVELDE 2 (ILLE2IS,AMBERS * VAN DE +OPPEL , +UMAR ( ( 4 0RINS AND ! - DE 2OOS 3ELF ORGANIZATION OF VEGETATION IN ARID ECOSYSTEMS !MERICAN .ATURALIST 3AETHER " % AND 3 %NGEN 0ATTERN OF VARIATION IN AVIAN POPULATION GROWTH RATES 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES 3AETHER " % 3 %NGEN & &ILLI 2 !ANES 7 3CHRODER AND 2 !NDERSEN A 3TOCHASTIC POPULATION DYNAMICS OF AN INTRODUCED 3WISS POPULATION OF THE IBEX %COLOGY
$* -URRELL
3AETHER " % 3 %NGEN 2 ,ANDE # "OTH AND - % 6ISSER B $ENSITY DEPENDENCE AND STOCHASTIC VARIATION IN A NEWLY ESTABLISHED POPULATION OF A SMALL SONGBIRD /IKOS 3KELLAM * ' 2ANDOM DISPERSAL IN THEORETICAL POPULATIONS "IOMETRIKA 4RAVIS * - * AND # $YTHAM $ISPERSAL EVOLUTION DURING INVASIONS %VOLUTIONARY %COLOGY 2ESEARCH 4URCHIN 0 #OMPLEX POPULATION DYNAMICS 0RINCETON 5NIVERSITY 0RESS 0RINCETON 6EIT 2 2 AND - ! ,EWIS $ISPERSAL POPULATION GROWTH AND THE !LLEE EFFECT $YNAMICS OF THE HOUSE lNCH INVASION OF EASTERN .ORTH !MERICA !MERICAN .ATURALIST 7ITH + ! 4HE LANDSCAPE ECOLOGY OF INVASIVE SPREAD #ONSERVATION "IOLOGY 7HITTAKER 2 * )SLAND "IOGEOGRAPHY %COLOGY %VOLUTION AND #ONSERVATION /XFORD 5NIVERSITY 0RESS /XFORD 9OUNG 7 2 ! * 2OBERTS AND ' 3TUHNE 2EPRODUCTIVE PAIR CORRELATIONS AND THE CLUSTERING OF ORGANISMS .ATURE
#HAPTER EIGHT
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA - ! ,EWIS - ' .EUBERT ( #ASWELL * 3 #LARK AND + 3HEA
).42/$5#4)/. /NE MEASURE OF BIOLOGICAL INVASIVENESS IS THE RATE AT WHICH AN ESTABLISHED INVADER WILL SPREAD SPATIALLY IN ITS NEW ENVIRONMENT 3LOW SPREAD SIGNIlES SLOW INCREASE IN ECOLOGICAL IMPACT WHEREAS FAST SPREAD SIGNIlES THE CONVERSE )F ONE CAN PREDICT SPREAD RATES FROM LIFE HISTORY ATTRIBUTES SUCH AS GROWTH RATES AND DISPERSAL DIS TANCES THEN POTENTIAL INVASIVENESS CAN BE ASSESSED BEFORE THE INVASION OCCURS
4HIS WORK WAS CONDUCTED AS PART OF THE $EMOGRAPHY AND $ISPERSAL 7ORKING 'ROUP SUP PORTED BY THE .ATIONAL #ENTER FOR %COLOGICAL !NALYSIS AND 3YNTHESIS A #ENTER FUNDED BY .3& $%" THE 5NIVERSITY OF #ALIFORNIA AND THE 3ANTA "ARBARA CAMPUS 4HIS RESEARCH WAS ALSO SUPPORTED IN PART BY A #ANADA 2ESEARCH #HAIR THE .ATURAL 3CIENCES AND %NGINEERING 2ESEARCH #OUNCIL OF #ANADA AND THE .ATIONAL 3CIENCE &OUNDATION $%" $%" $%" $-3 $-3 $%" 4HANKS TO THE $EMOGRAPHY AND $ISPERSAL 7ORKING 'ROUP MEMBERS FOR THEIR HELP AND SUPPORT WITH THE RESEARCH
-7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
-! ,EWIS E T AL
! PREDICTION OF THIS SORT REQUIRES MODELS FOR POPULATION SPREAD !S OUTLINED BELOW SUCH MODELS HAVE A LONG AND DISTINGUISHED HISTORY IN QUANTITATIVE ECOLOGY 7HEREAS EARLY MATHEMATICAL MODELS FOR POPULATION SPREAD WERE PRIMAR ILY CONCEPTUAL AND QUALITATIVE IN NATURE A NEW GENERATION OF REALISTIC MODELS IS EMERGING 4HESE NEW MODELS ARE TIED DIRECTLY TO THE DEMOGRAPHY AND DISPERSAL OF INDIVIDUALS (OWEVER THERE ARE NEW CHALLENGES IN THE LINKING OF THESE MODELS TO THE BIOLOGICAL PROCESSES !S WE WILL ILLUSTRATE IN THIS CHAPTER SPREAD RATE PREDICTIONS ARE VERY SENSITIVE TO ASSUMPTIONS ABOUT LONG DISTANCE DISPERSAL !RE THERE ROBUST METHODS FOR ESTIMAT ING SPREAD RATES 4HIS IS ONE QUESTION WE WILL ADDRESS &URTHERMORE ALMOST ALL MATHEMATICAL MODELS ASSUME THAT THE SPREAD OCCURS IN ONE SPATIAL DIMENSION ALONG A LINE 4HIS IS NOT BECAUSE MATHEMATICIANS HAVE NOT NOTICED THAT MOST POPULATION SPREAD TAKES PLACE IN TWO DIMENSIONS EXCEPT CASES LIKE DISPERSAL ALONG A COASTLINE OR RIVER 2ATHER IT IS BECAUSE THE MAIN QUALITA TIVE FEATURES OF INVASIONS ARE APPARENT IN ONE DIMENSIONAL MODELS ALTHOUGH AS WE WILL SHOW THE QUANTITATIVE RESULTS IN SPECIlC CASES CAN DEPEND VERY MUCH ON THE THE DIMENSIONALITY OF THE DISPERSAL DATA AND OF THE MODEL USED FOR ANALYSIS )N PARTICULAR WE WILL SHOW THAT THE NAIVE APPLICATION OF ONE DIMENSIONAL MODELS TO TWO DIMENSIONAL DISPERSAL DATA WILL PRODUCE A SYSTEMATIC BIAS SOMETIMES POSI TIVE SOMETIMES NEGATIVE IN SPREAD RATE ESTIMATES )N THIS CHAPTER WE WILL OUTLINE NEW lTTING METHODS FOR AVOIDING THESE BIASES
-/$%,).' "!#+'2/5.$ 4HE ISSUE OF SPREAD RATE FOR BIOLOGICAL INVADERS WAS CONSIDERED IN DETAIL BY 3KELLAM WHERE &ISHERS PARTIAL DIFFERENTIAL EQUATION MODEL WAS USED TO DESCRIBE THE RATE OF CHANGE OF LOCAL POPULATION DENSITY WITH TIME ,N £ N ¥ , N lN ² n ´ $ ,T ¤ g ¦ ,X
(ERE NX T IS THE LOCAL POPULATION DENSITY l IS THE INTRINSIC GROWTH RATE g IS THE CARRYING CAPACITY $ IS THE DISCUSION COElCIENT X IS THE ONE DIMENSIONAL SPACE COORDINATE AND T IS TIME 4HE RATE OF SPREAD OF A POPULATION OBEYING THIS EQUATION ASYMPTOTICALLY APPROACHES C 3l$ FOR LARGE TIMES +OLMOGOROV ET AL !RONSON AND 7EINBERGER &IG 7HEREAS THE SPREAD RATE PREDICTIONS ARE ON A LANDSCAPE SCALE THE PARAMETERS R AND $ CAN BE MEASURED ON THE INDIVIDUAL LEVEL USING LIFE TABLE ANALYSIS AND MARK RECAPTURE &URTHERMORE COMPARISONS OF HISTORICALLY OBSERVED INVASIVE SPREAD RATES WITH THE ASYMPTOTIC SPREAD RATE FOR MULA HAVE HELD UP FOR A WIDE VARIETY OF SPECIES !NDOW ET AL MAKING THE INTERPLAY BETWEEN INVASION THEORY AND SPREAD DATA A MODERN DAY SUCCESS STORY IN QUANTITATIVE ECOLOGY 3HIGESADA AND +AWASAKI
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
&IG 0OPULATION SPREAD FOR &ISHERS EQUATION ! TYPICAL SOLUTION OF &ISHERS EQUATION ILLUSTRATES GROWTH AND SPREAD IN ONE DIMENSIONAL LINEAR SPACE !T LEFT THE SOLUTION IS PLOTTED FOR EQUALLY SPACED TIME INTERVALS !T RIGHT THE GRAY AREA DENOTES THE REGION IN SPACE WHERE THE POPULATION IS LARGER THAN A THRESHOLD LEVEL N 4HE BOUNDARIES OF THIS AREA HAVE SLOPES EQUAL TO THE ASYMPTOTIC SPREAD RATE C 3l$ &OR THIS lGURE l g $ AND NX COS/X FOR \X\ ) "ASED ON .EUBERT AND 0ARKER
! MAJOR PROBLEM WITH &ISHERS MODEL IS THAT IT IMPOSES ONE PARTICULAR FORM OF DISPERSAL 4HE ASSUMPTION OF DIFFUSION IN EQUATION WHICH IMPLIES NORMALLY DISTRIBUTED DISPERSAL PROPAGULES IS OFTEN VIOLATED WHEN DISPERSAL IS MEASURED FOR BIOLOGICAL POPULATIONS ,EWIS 7HILE THERE IS TREMENDOUS VARIABILITY IN SUCH DISPERSAL DATA THERE IS A STRONG TENDENCY FOR THE DISTRIBUTION OF DISPERSAL DISTANCES TO BE LEPTOKURTIC WITH A LARGER NUMBER OF DISTANCES NEAR THE CENTER AND IN THE TAILS THAN IN A NORMAL DISTRIBUTION WITH COMPARABLE VARIANCE 4HE EFFECT OF THE LONG DISTANCE DISPERSERS AS DESCRIBED BY THE TAILS OF THE DISTRIBU TION OF DISTANCES IS DRAMATIC #ASWELL ET AL 0REDICTIONS FOR INVASION RATES CAN SPEED UP BY AN ORDER OF MAGNITUDE OR MORE WHEN THE LONG DISTANCE DISPERSERS ARE INCLUDED +OT ,EWIS AND VAN DEN $RIESSCHE 7HEN THE DISPERSAL DISTRIBUTION IS FAR FROM NORMAL THE PARTIAL DIFFERENTIAL EQUA TION MODEL NO LONGER SUCCES )T IS THEN NECESSARY TO DElNE A DISPERSAL KERNEL KX Y IN ONE SPATIAL DIMENSION WHICH DESCRIBES THE PROBABILITY THAT A PROPAGULE THAT STARTS AT Y MOVES TO THE INTERVAL X X DX BY KX Y DX 4HE UNITS FOR THE DISPERSAL KERNEL K ARE PER UNIT LENGTH 4HE SPATIAL REGION OF INTEREST IS THE INTERVAL 1 nú ú 7HEN MODELLING INVASIONS WE TYPICALLY ASSUME ú IS ARBITRARILY LARGE )N THE ABSENCE OF IMMIGRATION FROM OUTSIDE 1 EVERY DISPERSER MUST ORIGINATE AT SOME OTHER POINT IN SO THAT Gú KX Y DY Hnú
-! ,EWIS E T AL
)N A HOMOGENEOUS HABITAT DISPERSAL BETWEEN TWO LOCATIONS WILL ONLY DEPEND UPON UPON THE RELATIVE LOCATIONS OF THE START AND lNISH POINTS )N THIS CASE TO WHICH WE WILL RESTRICT OUR ATTENTION FOR THE REMAINDER OF THE CHAPTER WE WRITE KX Y KX n Y 3HIGESADA +AWASAKI AND 4ERAMOTO EXAMINE INVASIONS IN HETEROGENEOUS ENVIRONMENTS 4O INCLUDE POPULATION DYNAMICS POPULATION GROWTH FROM ONE GENERATION TO THE NEXT CAN BE DESCRIBED WITH A NON LINEAR FUNCTION NT dNT NTGNT
WHERE G DElNES THE PER CAPITA GROWTH RATE AS A FUNCTION OF LOCAL POPULATION DENSITY NT .ON OVERLAPPING GENERATIONS ARE ASSUMED BUT HERE AND IN THE SUBSEQUENT ANALYSIS THE ASSUMPTION CAN BE RELAXED TO INCLUDE MODELS WITH STAGE STRUCTURE SEE .EUBERT AND #ASWELL FOR DETAILS 4HE NONSPATIAL POPULATION MODEL IS THEN MODIlED TO ALLOW FOR DISPER SAL BETWEEN REPRODUCTION EVENTS )F WE DESIGNATE THE POPULATION DENSITY AT LOCATION X AND TIME T BY NTX THESE MODELS TAKE THE FORM OF A SCALAR INTEGRODIFFER ENCE EQUATION Gú NTX dNTY KX n Y DY Hnú
%ARLY ANALYSES OF POPULATION SPREAD USING INTEGRODIFFERENCE EQUATIONS APPEARED IN THE MATHEMATICAL LITERATURE PRIMARILY IN THE CONTEXT OF GENETICS 7EINBERGER ,UI A B 7EINBERGER ,UI A B (OWEVER INTEGRODIFFERENCE EQUATIONS AND GENERALIZATIONS OF THEM ARE NOW BEING USED BY A GROWING LIST OF ECOLOGISTS TO INVESTIGATE THE SPREAD RATE OF ECOLOGICAL POPULATIONS +OT !LLEN ET AL !LLEN ET AL +OT ET AL 6EIT AND ,EWIS ,EWIS (ART AND 'ARDNER #LARK ET AL #LARK (IGGINS AND 2ICHARDSON .EUBERT AND #ASWELL .EUBERT ET AL 4AKASU ET AL 7OOLCOCK AND #OUSENS 7ITH 3CHOlELD #ASWELL ET AL #LARK ET AL -ARCHANT .EUBERT AND 0ARKER 0OWELL AND :IMMERMANN !MONG THE RESULTS OF THESE INVESTIGATIONS ARE TWO KEY lNDINGS &IRST INTEGRODIFFERENCE MODELS PRODUCE A RICHER SET OF INVASION DYNAMICS THAN CAN BE GENERATED BY THE REACTION DIFFUSION EQUATION INCLUDING FOR EXAMPLE THE POSSIBILITY OF ACCELERATING SPREAD +OT ET AL 3ECOND THE SHAPE OF THE DISPERSAL KERNEL ESPECIALLY THE SHAPE OF THE TAILS WHICH DETERMINE THE PROBABILITY OF LONG DISTANCE DISPERSAL PLAYS A CRUCIAL ROLE IN DETERMINING THE RATE OF SPREAD 4HE EFFECT OF LONG DISTANCE DISPERSAL ON SPREAD RATES WAS HIGHLIGHTED BY +OT ET AL WHO lT DISPERSAL KERNELS TO A DATA SET DESCRIBING THE DISPLACEMENT OF OF GENETICALLY MARKED $ROSOPHILA $OBZHANSKY AND 7RIGHT AND PREDIC TIONS FOR THE CORRESPONDING ASYMPTOTIC SPREAD RATE WERE LINKED TO THE SHAPES OF
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
THE KERNELS 4HESE PREDICTED SPREAD RATES VARIED OVER AN ORDER OF MAGNITUDE DEPENDING UPON THE FATNESS OF THE TAILS OF THE RELATED DISPERSAL KERNELS SEE &IG
&IG &ITTED FUNCTIONS TO $ PSEUDOOBSCURA DISPERSAL DATA PROVIDE INGREDIENTS FOR AN INTEGRODIFFERENCE MODEL FOR INSECT SPREAD 4HE LEFT PANELS SHOW AVERAGE NUMBER OF INSECTS CAUGHT PER TRAP PER DAY IN $OBZHANSKY AND 7RIGHTS EXPERIMENTS )T WAS ASSUMED THAT DISPERSAL WAS EQUALLY LIKELY IN BOTH DIRECTIONS SO THE DISPERSAL KERNELS WERE KX GX GnX WHERE G IS THE lTTED FUNCTION 4HE RIGHT PANEL SHOWS SIMULATIONS OF THE INTEGRODIFFERENCE EQUATIONS 3IMULATIONS ASSUME "EVERTON (OLT POPULATION DYNAMICS FOR FN WITH A GEOMETRIC GROWTH RATE OF h 4HE CARRYING CAPACITY WAS SCALED TO EQUAL ONE %ACH INTEGRODIFFERENCE WAS ITERATED FOR GENERATIONS "ASED ON +OT ET AL (ERE IS IS ASSUMED THAT ALL REPRODUCTION AND DISPERSAL OCCURS ALONG A ONE DIMENSIONAL STRIP OF SUITABLE HABITAT 4HE SPREAD RATE CAN BE CALCULATED BY DIVIDING THE TOTAL DISTANCE MOVED BY THE POPULATION FRONT BY THE GENERATIONS TAKEN TO MOVE THE DISTANCE
-! ,EWIS E T AL
4HE ISSUE OF LONG DISTANCE DISPERSAL HOWEVER GOES BEYOND THE CHOICE OF A PARAMETRIC DISPERSAL DISTRIBUTION TO DESCRIBE A SET OF DATA )T CAN ALSO REmECT REAL BIOLOGICAL PROCESSES &OR EXAMPLE .EUBERT AND #ASWELL COMPUTED THE SPREAD RATE FOR THE HERBACEOUS PLANT $IPSACUS SYLVESTRIS BASED ON DATA FROM A SEED TRAP EXPERIMENT 7ERNER 4EASEL SEEDS ARE KNOWN TO mOAT BUT DISPERSAL BY STREAMS OR RIVERS WAS OBVIOUSLY NOT MEASURED BY THE SEED TRAP EXPERIMENT .EUBERT AND #ASWELL CALCULATED THE ASYMPTOTIC SPREAD RATE RESULTING FROM HYPO THETICAL MIXTURES OF THE SEED TRAP DATA AND DISPERSAL BY WATER WITH A LONGER MEAN DISTANCE 4HEY FOUND THAT LONG DISTANCE DISPERSAL OF EVEN ONE SEED IN A MILLION WAS ENOUGH TO MAKE THE SPREAD RATE DEPENDENT ON THE WATER DISPERSAL ALONE 3IMILARLY THE SEEDS OF THE TROPICAL PLANT #ALATHEA OVANDENSIS ARE DISPERSED BY AT LEAST FOUR SPECIES OF ANT EACH WITH ITS OWN TYPICAL DISPERSAL DISTANCE (ORVITZ AND 3CHEMSKE .EUBERT AND #ASWELL FOUND THAT OVER OF THE ASYMPTOTIC SPREAD RATE WAS ACCOUNTED FOR BY THE ANT SPECIES WITH THE LONGEST DISPERSAL DISTANCE EVEN THOUGH IT DISPERSED ONLY OF THE SEEDS #LASSICAL MODELS FOR POPULATION SPREAD LIKE AND CONSIDER THE CASE WHERE THE SPATIAL DOMAIN IS ONE DIMENSIONAL AND LINEAR AND A SMALL BEACHHEAD OF INDIVIDUALS IS INTRODUCED LOCALLY 4HIS IS ONLY DIRECTLY APPLICABLE TO CASES SUCH AS POPULATION SPREAD ALONG A ROADSIDE COASTLINE ,UBINA AND ,EVIN OR A RIVER 3PEIRS AND 'URNEY 0ACHEPSKY ET AL ,ATER WE WILL INTRODUCE MODELS THAT DESCRIBE DISPERSAL IN TWO SPATIAL DIMEN SIONS 4HESE MODELS PRODUCE ASYMPTOTIC SPREAD RATE PREDICTIONS THAT CAN DIFFER IN DIFFERENT DIRECTIONS IF THE DISPERSAL KERNEL IS NOT RADIALLY SYMMETRIC )N BOTH ONE AND TWO DIMENSIONS THE DISPERSAL KERNEL PLAYS A CRUCIAL ROLE IN DETERMINING THE ASYMPTOTIC RATE OF SPREAD 4HERE ARE MANY METHODS FOR ESTIMATING DISPERSAL KERNELS AND FOR ESTIMATING THE PROPERTIES OF THOSE KERNELS THAT ENTER INTO THE FOR MULAE FOR SPREAD RATE FROM DATA SEE FOR EXAMPLE 3ILVERMAN 7E WILL DISCUSS SOME OF THESE METHODS LATER IN THE CHAPTER &IRST WE DISCUSS SOME OF THE KINDS OF DISPERSAL DATA THAT ARE TYPICALLY COLLECTED ANDOR PUBLISHED
$)30%23!, +%2.%,3 ). /.% !.$ 47/ $)-%.3)/.3 7E lRST CONSIDER FORMS IN WHICH DATA ARE COLLECTED 4HESE FALL LOOSELY INTO TWO KINDS DISPERSAL DATA AND DENSITY DATA $ISPERSAL DATA DESCRIBE THE LOCATION OF DISPERSERS RELATIVE TO THE PARENTS 4HESE DATA COME FROM FOLLOWING INDIVIDUAL DISPERSERS EG BANDING AND RECAPTURE OF BIRDS MARK AND RECAPTURE OF SEEDS USING COLORING ANDOR RADIO TAGGING AND IS RECORDED AS EITHER DISPLACEMENTS OR DISPLACEMENT DISTANCES )N CONTRAST DENSITY DATA DESCRIBE THE DENSITY OF DISPERS ERS NUMBER PER UNIT AREA OBSERVED AT A GIVEN POINT TYPICALLY AS A FUNCTION OF DISTANCE FROM A NATAL SITE OR SOURCE OF DISPERSERS 4HESE DATA COME FROM SEED TRAPS PHEREMONE TRAPS FOR INSECTS AND SO FORTH )F WE ASSUME THAT THE POPULATION LIVES ALONG A ONE DIMENSIONAL STRIP OF SUITABLE HABITAT ALONG WHICH ALL DISPERSAL AND REPRODUCTION OCCURS THE ONE DIMENSIONAL
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
DISPERSAL KERNEL NUMBER OF DISPERSERS PER UNIT LENGTH IS NEEDED IN EQUATION 4HIS KERNEL CAN BE lTTED EITHER DIRECTLY FROM THE ONE DIMENSIONAL DISPERSAL DATA OR FROM THE DENSITY DATA NUMBER OF DISPERSERS PER UNIT AREA MULTIPLIED BY THE WIDTH OF THE STRIP 4HE CONSTRAINT THAT THE KERNEL MUST BE SCALED TO INTEGRATE TO EQUA TION MEANS THAT THE KERNEL K WILL ACTUALLY BE INDEPENDENT OF THE WIDTH OF THE STRIP MULTIPLICATION IS ONLY DONE FORMALLY TO ENSURE THE CORRECT UNITS FOR K )F WE ASSUME THAT THE POPULATION LIVES IN A TWO DIMENSIONAL HABITAT IT IS lRST NECESSARY TO EXTEND THE DElNITION OF DISPERSAL TO TWO SPATIAL DIMENSIONS (ERE DISPERSAL IS BETWEEN POINTS X ;X X=4 AND Y ;Y Y=4 IN TWO DIMENSIONAL SPACE 4HE THE TWO DIMENSIONAL DISPERSAL KERNEL +X Y DESCRIBES THE PROBABIL ITY OF A PROPAGULE WHICH STARTS AT Y MOVING TO THE RECTANGLE WITH CORNERS X AND X DX BY +X Y DX DX 4HE SPATIAL REGION OF INTEREST IS GIVEN BY 1 )N THE CASE OF INVASIONS THIS IS TYPICALLY ASSUMED TO BE ARBITRARILY LARGE )N THE ABSENCE OF IMMIGRATION FROM OUTSIDE 1 EVERY DISPERSER MUST ORIGINATE AT SOME OTHER POINT IN 1 SO THAT G +X Y DY H1 )F THE KERNEL +X Y DEPENDS ONLY UPON THE RELATIVE LOCATIONS OF THE START AND lNISH POINTS WE WRITE +X Y +X n Y 4O UNDERSTAND THE DIFFERENCE BETWEEN ONE AND TWO DIMENSIONAL DISPERSAL KERNELS WE CONSIDER THE CASE WHERE THE DISPERSAL IS ISOTROPIC IDENTICAL IN ALL DIRECTIONS )N THIS CASE THE TWO DIMENSIONAL DISPERSAL KERNEL + CAN BE WRITTEN AS A FUNCTION OF THE DISPERSAL RADIUS R \X n Y\ )N A LINEAR ONE DIMENSIONAL ENVIRON MENT THE SCALED DISTRIBUTION OF DENSITIES DISPERSERS PER UNIT LENGTH AND A DISTRI BUTION OF DISTANCES THAT THE DISPERSERS TRAVEL FROM THE PARENT ARE THE SAME AND ARE GIVEN BY THE KERNEL K )N A TWO DIMENSIONAL ENVIRONMENT THE SCALED DISTRIBU TION OF DENSITIES DISPERSERS PER UNIT AREA GIVEN BY +R AND THE DISTRIBUTION OF DISTANCES THAT DISPERSERS TRAVEL FROM FROM THE PARENT DISPERSERS PER UNIT LENGTH GIVEN BY +É /R+R ARE NOT THE SAME BECAUSE THERE IS MORE AREA AVAILABLE AT DISTANCES FURTHER FROM THE PARENT
0/05,!4)/. 302%!$ ). ! /.% $)-%.3)/.!, ,).%!2 %.6)2/.-%.4 4HE $OBZHANSKY AND 7RIGHT INSECT DATA WERE COLLECTED FROM TRAPS PLACED ALONG LINEAR TRANSECTS RADIATING FROM A POINT SOURCE 4HUS THE TRAPS GIVE A RELATIVE MEA SURE OF THE DENSITY OF DISPERSERS NUMBER PER UNIT AREA AS A FUNCTION OF DISTANCE
4HROUGHOUT THIS CHAPTER WE WILL USE BOLDFACE 2OMAN CHARACTERS SUCH AS U AND V TO REPRE SENT VECTORS (ERE \U\ 3U U DENOTES THE LENGTH OF THE VECTOR U AND U q V UV UV \U\ \V\ COS e DENOTES THE @DOT PRODUCT OR PROJECTION OF ONE VECTOR ONTO THE OTHER WHERE e IS THE ANGLE BETWEEN U AND V
+! 3CHIERENBECK AND -, !ÕNOUCHE
FROM THE RELEASE SITE 4HE MOST REASONABLE ASSUMPTION IS THAT THE TRANSECT DATA DESCRIBE THE RADIAL DROP OFF IN SETTLED INSECT DENSITY IN A TWO DIMENSIONAL HABITAT NEXT SECTION (OWEVER FOR THE SAKE OF ILLUSTRATION IN THIS PAPER WE lRST CON SIDER THE ASSUMPTION THAT THE INSECTS AND TRANSECTS ARE FOUND ALONG A ONE DIMEN SIONAL STRIP OF SUITABLE HABITAT ALONG WHICH ALL DISPERSAL AND REPRODUCTION OCCURS NEXT SECTION 4HIS IS A STANDARD ASSUMPTION IN POPULATION SPREAD MODELS AND IS THE ASSUMPTION MADE IN THE ORIGINAL ANALYSIS OF THE INSECT SPREAD RATES IN +OT ET AL !S WE WILL SHOW THE DIFFERENT ASSUMPTIONS ABOUT THE HABITAT AND DISPERSAL GIVE RISE TO QUITE DIFFERENT SPREAD RATE ESTIMATES 4HEORY
!S THE INTRODUCED BEACHHEAD OF INDIVIDUALS GROWS AND DISPERSES WE EXPECT GROWTH OF THE RANGE BOUNDARY WITH TIME &IGURE SHOWS A TYPICAL PROGRESSION ! PLOT OF RANGE BOUNDARY VERSUS TIME GIVES LINES WHOSE SLOPE EVENTUALLY BECOME CONSTANT 4HE EVENTUAL SLOPE OF THESE LINES THE ASYMPTOTIC RATE OF SPREAD OF THE INVASION HENCEFORTH REFERRED TO SIMPLY AS SPREAD RATE CAN BE PREDICTED USING MATH EMATICAL THEORY WHICH RELATES THE SLOPE TO MODEL PARAMETERS )N THIS SECTION WE OUTLINE THE THEORY )T IS lRST NECESSARY TO MAKE SOME ASSUMPTIONS ABOUT THE GROWTH DYNAMICS 4HE SIMPLEST POPULATION DYNAMICS EXHIBIT NO OVERCOMPENSATION OR !LLEE EFFECT 4HIS ASSUMPTION TRANSLATES INTO A GROWTH FUNCTION d IN THAT IS MONOTONICALLY INCREASING WITH MAXIMUM PER CAPITA GROWTH RATES AT LOWEST POPULATION LEVELS 4HE ASSUMPTION THAT THE MAXIMUM PER CAPITA GROWTH RATE h OCCURS AT THE LOWEST POSSIBLE DENSITY MEANS h G * GN FOR N ! GROWING POPULATION REQUIRES h !S DESCRIBED ABOVE LOCAL INTRODUCTION OF INDIVIDUALS COUPLED WITH A GROWTH RATE h AND A DISPERSAL KERNEL KZ Z X n Y IN MEANS THE POPULA TION SPREADS AS IT GROWS AND DISPERSES &IG 7EINBERGER SHOWED THAT UNDER THE ABOVE ASSUMPTIONS ON GROWTH DYNAMICS THE POPULATION SPREADS TO THE RIGHT AT A RATE WHICH APPROACHES SPEED C AS THE TIME SINCE INTRODUCTION INCREASES WHERE C MIN LN ;h -S = S S AND -S IS THE MOMENT GENERATING FUNCTION FOR THE DISPERSAL KERNEL KZ G' -S KZ EXPSZ DZ Hn'
4HE PARAMETER S CAN BE UNDERSTOOD AS A MEASURE OF THE STEEPNESS OF THE WAVE N | EXPnSZ AT THE LEADING EDGE OF THE RIGHTWARD SPREADING POPULATION 4O lND THE SPEED OF THE LEFTWARD SPREADING FRONT ONE SHOULD USE THE MOMENT GENERATING FUNCTION FOR KnZ IN EQUATION
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
4HUS THE POPULATION SPREAD RATE DEPENDS ONLY UPON TWO FEATURES THE GEOMETRIC GROWTH RATE OF THE POPULATION h AND THE SHAPE OF THE DISPERSAL KERNEL K 4HE SPEED FOR &ISHERS EQUATION C 3l$ CAN BE REGAINED FROM EQUATIONS BY THE CHOICE OF K . $ AND l LOGh $ETAILS ARE GIVEN IN +OT ET AL )N PRACTICE CALCULATION OF THE SPREAD RATE MUST BE DONE NUMERICALLY EITHER BY USING A STANDARD MINIMIZATION ROUTINE OR BY SOLVING THE DOUBLE ROOT CONDITION EQUATIONS EXPSC h-S AND C EXPSC h-S FOR THE WAVE SPEED C AND WAVE STEEPNESS S &OR A SIMPLE EXAMPLE WRITTEN IN -APLE CODE SEE THE !PPENDIX (ERE IT IS ASSUMED THAT THE KERNEL K IS EXPONENTIALLY BOUNDED SO THAT THE MOMENT GENERATING FUNCTION CAN BE CALCULATED 7HEN THE KERNEL K HAS TAILS THAT ARE FATTER THAN EXPONENTIAL THERE IS NO ASYMPTOTIC RATE OF SPREAD THE SPREAD RATE CONTINUES TO INCREASE WITH INCREASING TIME +OT ET AL &IG THIRD PANEL FROM THE TOP )N THIS SITUATION AN ALTERNATIVE DElNITION OF SPREAD RATE BASED ON THE CHANGE IN LOCATION OF THE FURTHEST FORWARD INDIVIDUAL IN THE POPU LATION FROM GENERATION TO GENERATION FURTHEST FORWARD VELOCITY IS APPROPRIATE #LARK ,EWIS AND (ORVATH SEE $ISCUSSION 7HEN THE GROWTH RATE h IS KNOWN BUT THE DISPERSAL KERNEL IS UNKNOWN ESTI MATES FOR POPULATION SPREAD RATES USING EQUATION CAN VARY WIDELY DEPENDING UPON THE PARAMETRIC FORM OF THE KERNEL CHOSEN AS WITH THE SIMULATIONS SHOWN IN &IG 7HEN APPROPRIATE DATA ARE AVAILABLE THIS PROBLEM CAN BE ADDRESSED BY MEANS OF A NONPARAMETRIC ESTIMATOR FOR THE MOMENT GENERATING FUNCTION WHICH MAKES NO ASSUMPTION ABOUT THE FORM OF THE UNDERLYING KERNEL )N THIS CASE THE MOMENT GENERATING FUNCTION IS ESTIMATED FROM RAW ONE DIMENSIONAL LINEAR DIS PERSAL DISPLACEMENT DATA ZxZ. . -%S - EXP SZI . I
4HE SUPERSCRIPT IS USED TO INDICATE AN EMPIRICAL ESTIMATE OF THE MOMENT GENERAT ING FUNCTION #LARK (ORVATH AND ,EWIS (ERE THE DISPERSAL MEASUREMENTS ARISE FROM TRACKING A SERIES OF INDIVIDUALS !S A DISPLACEMENT XI GIVES THE DISTANCE AND DIRECTION THAT THE I TH INDIVIDUAL MOVES "Y CONVENTION LEFTWARD MOVEMENTS ARE ASSIGNED NEGATIVE VALUES )T IS ASSUMED THAT THE TRACKING EFFORT AND TRACKING EFlCIENCY REMAIN CONSTANT OVER THE ENTIRE LINEAR ONE DIMENSIONAL DISPERSAL REGION &UJIWARA ET AL CONSIDER THE EFFECTS OF CHANGES IN SAMPLING EFFORT OR DETEC TION PROBABILITY )N THE CASE WHERE ZxZ. ARE NONNEGATIVE DISTANCES RATHER THAN DISPLACEMENTS THE ASSUMPTION OF A SYMMETRIC DISPERSAL KERNEL WHEREBY INDIVIDU ALS ARE AS LIKELY TO MOVE TO THE LEFT AS TO THE RIGHT LEADS TO . -%S - COSH SZI . I
+! 3CHIERENBECK AND -, !ÕNOUCHE
3UBSTITUTION OF -%S INSTEAD OF -S IN LEADS TO AN EMPIRICALLY ESTIMATED WAVE SPEED C% 4HIS EMPIRICALLY ESTIMATED WAVE SPEED HAS MANY NICE PROPERTIES #LARK ET AL &OR EXAMPLE IT IS UNBIASED C% CONVERGES TO TO THE TRUE POPU LATION SPREAD RATE C AS . A ' 4HIS IS NOT GENERALLY THE CASE WHEN PARAMETRIC KERNELS ARE lTTED TO THE DISPERSAL DATA )N THAT CASE THE TRUE POPULATION DISPERSAL KERNEL IS NOT KNOWN AND DIFFERENT lTTED KERNELS CAN GIVE VERY DIFFERENT WAVE SPEED PREDICTIONS 7HEN THE NUMBER OF DATA POINTS . IS lNITE EACH EMPIRICALLY ESTIMATED WAVE SPEED WILL BE DIFFERENT AS IT WILL DEPEND ON THE PRECISE DATA SET USED (OWEVER THE DISTRIBUTION OF THE EMPIRICAL WAVE SPEED C% ABOUT THE TRUE WAVE SPEED C IS APPROXIMATELY 'AUSSIAN AND THE VARIANCE OF THE 'AUSSIAN APPROACHES ZERO AS . APPROACHES INlNITY #LARK ET AL !LTHOUGH THERE IS NO CLOSED FORM EXPRESSION FOR THE VARIANCE IT CAN BE ESTIMATED USING BOOTSTRAPPING METHODS #LARK ET AL 7HEN THE DATA COLLECTION OR RECORDING METHODS DO NOT PROVIDE DISPERSAL DATA BUT HISTOGRAM DENSITY DATA ARE AVAILABLE IT MAY BE NECESSARY TO USE SUCH A HISTOGRAM AS AN ESTIMATOR FOR THE KERNEL ¨ 4 K( Z © I ª
IF OTHERWISE
j ) Z jI I n
WHERE 4I IS THE BIN HEIGHT FOR THE HISTOGRAM ) I ) , AND ,
- jI n jI n 4I
I
4HIS YIELDS , -(S - 4I EXPSjI n EXPSjI n S I
AND SUBSTITUTION OF -(S INSTEAD OF -S IN LEADS TO A @HISTOGRAM ESTIMATOR FOR THE WAVE SPEED C( $UE TO THE ARBITRARY NATURE OF LOCATION OF THE HISTOGRAM BINS IT CAN BE SHOWN THAT THE HISTOGRAM ESTIMATOR DOES NOT PROVIDE AN UNBIASED ESTIMATOR FOR THE TRUE SPEED C (OWEVER IN THE ABSENCE OF OTHER DATA THIS HISTO GRAM ESTIMATOR IS A USEFUL ALTERNATIVE TO THE EMPIRICAL ESTIMATOR GIVEN ABOVE AND IN PRACTICE GIVES VERY SIMILAR RESULTS !S THE SIZES OF THE BINS jI n jI n APPROACHES ZERO THE TWO ESTIMATORS ARE IDENTICAL )N THE CASE WHERE THE HISTOGRAM DATA IS FOR DISTANCES AS OPPOSED TO DISPLACEMENTS THE ASSUMPTION OF A SYMMETRIC REDISTRIBU TION KERNEL CAUSES TO BE MODIlED TO , -(S - 4I SINHSjI n SINHSjI n S I
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
7E NOW APPLY THE HISTOGRAM SPREAD RATE ESTIMATE AND TO THE $OBZHANSKY AND 7RIGHT DATA UNDER THE ASSUMPTION THAT THE INSECTS AND TRANSECTS ARE FOUND ALONG A ONE DIMENSIONAL STRIP OF SUITABLE HABITAT ALONG WHICH ALL DISPERSAL AND REPRODUCTION OCCURS SEE DISCUSSION IN -ODELING "ACKGROUND 4HIS ESTIMATE WHICH USES THE DATA SHOWN IN &IG GIVES A SPREAD RATE OF KM PER YEAR 4HIS IS HIGHER THAN THE SPREAD RATE PREDICTION MADE BY USING THE EXPONENTIAL AND 'AUSSIAN KERNELS IN &IG BUT IS SUBSTANTIALLY LOWER THAN THE PREDICTION MADE BY THE FAT TAILED KERNEL !S WITH THE EMPIRICAL ESTIMATOR BOOT STRAPPING GIVES THE DISTRIBUTION OF WAVE SPEEDS FROM WHICH CONlDENCE INTERVALS CAN BE CALCULATED &IG
&IG "OOTSTRAPPING GIVES A RANGE OF POSSIBLE VALUES FOR THE HISTOGRAM WAVE SPEED 4HE HISTOGRAM WAVE SPEED ESTIMATOR EQUATIONS AND IS APPLIED TO A HISTOGRAM BASED ON THE TOTAL NUMBER OF INSECTS CAUGHT PER TRAP STARTING AT DISTANCE ZERO lNISHING AT DISTANCE KM WITH INTER TRAP SPACING OF KM WERE AND "OOTSTRAPPING WAS DONE BY RE SAMPLING FROM THE DISPERSAL DISTANCES WITH REPLACEMENT TO PRODUCE NEW DATA SETS 4HE WAVE SPEED WAS CALCULATED FOR EACH OF THESE NEW DATA SETS AND THE DISTRIBUTION OF SPEEDS IS SHOWN HERE .INETY PER CENT OF THE SPEEDS FELL IN THE RANGE KMYEAR KMYEAR #OMPARE THE ESTIMATE HERE WITH THE SPREAD RATES SIMULATED IN &IG
+! 3CHIERENBECK AND -, !ÕNOUCHE
0/05,!4)/. 302%!$ ). 47/ $)-%.3)/.3 )NVASION IN TWO SPATIAL DIMENSIONS INVOLVES LOCAL INTRODUCTION AT A BEACHHEAD FOLLOWED BY GROWTH AND SPREAD IN SPACE (ERE THE PROCESS CAN BE DIVIDED INTO THREE STAGES THE INITIAL ESTABLISHMENT THE EARLY RADIAL EXPANSION UNTIL WELL ESTABLISHED IN SPACE AND THE LATER SPREAD OF THE ESTABLISHED POPULATION &IG !LTHOUGH EACH OF THESE THREE STAGES IS OF INTEREST BIOLOGICALLY THE FOCUS OF THIS CHAPTER IS ON ANA LYZING THE LATER SPREAD OF AN ESTABLISHED POPULATION !T THIS STAGE WE CAN APPROXI MATE THE INVADING FRONT BY A PLANAR FRONT MOVING WITH A WELL DElNED SPEED 4HE CALCULATION OF SPREAD IN TWO DIMENSIONS REQUIRES A UNIT VECTOR U ;U U=4 DESCRIBING THE DIRECTION PERPENDICULAR TO THE WAVE FRONT IN WHICH THE SPREAD IS BEING CONSIDERED &IG 4HE ASYMPTOTIC SPREAD RATE IN THE DIRECTION U IS GIVEN BY CU MIN LN ;h -US = S S
&IG ! SKETCH OF THE THREE STAGES OF POPULATION SPREAD IN A HOMOGENEOUS ENVIRONMENT 3HADED AREAS INDICATE INVADED HABITAT !S TIME PROGRESSES THE INITIAL hBEACHHEADv GROWS AND BECOMES MORE ELLIPTICALLY SHAPED &OR LONG TIMES THE INVASION FRONT IS APPROXIMATELY PLANAR IN ALL DIRECTIONS 4HE SPEED IN THE DIRECTION U PERPENDICULAR TO THE FRONT IS FOUND USING THE MARGINAL DISPERSAL KERNEL IN THAT DIRECTION KUU CF EQUATION 4HE MARGINAL KERNEL IN TURN IS FOUND BY INTEGRATING THE ORIGINAL DIMENSIONAL DISTRIBUTION OVER THE DIRECTION V
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
WHERE -US IS THE @DIRECTIONAL MOMENT GENERATING FUNCTION THE MOMENT GENER ATING FUNCTION OF + EVALUATED IN THE DIRECTION OF U !PPENDIX 4WO APPROACHES FOR CALCULATION OF THE DIRECTIONAL MOMENT GENERATING FUNCTION ARE GIVEN IN THE THE !PPENDIX )N GENERAL THE PLANAR SPREAD RATE CU WILL DEPEND ON THE DIRECTION U (OWEVER WHEN THE DISPERSAL KERNEL IS DIRECTIONALLY ISOTROPIC IS IDENTICAL IN ALL DIRECTIONS THE PLANAR SPREAD RATE WILL ALSO BE ISOTROPIC 7E NOW CONSIDER THE CASE WITH DIRECTIONAL ISOTROPY SO THAT +Z Z X n Y CAN BE REWRITTEN AS +R R 3Z Z .OTE THAT +R IS A TWO DIMENSIONAL DENSITY FUNCTION WHICH DENOTES THE RELATIVE NUMBER OF SEEDS PER UNIT AREA FALLING AT DISTANCE R FROM THE SOURCE 4HE AREA UNDER +R IS EQUAL TO ONE G/ G' +R R DRDe Hn' Hn' ! RELATED KERNEL DENOTES THE NUMBER OF SEEDS PER UNIT LENGTH FALLING A DISTANCE R FROM THE SOURCE 4HIS RELATED KERNEL IS FOUND BY MULTIPLYING +R BY THE PERIMETER OF A CIRCLE OF RADIUS R TO ACCOUNT FOR THE FACT THAT AT LARGER RADII THERE IS MORE AVAILABLE AREA FOR SEEDS TO FALL +ÉR /R+R )F THE DATA HAVE BEEN COLLECTED IN THIS FORM A SIMPLE RESCALING BY /R WILL TRANSFORM +É TO + 7E NOW CONSIDER HOW TO CALCULATE THE PLANAR SPREAD RATE SEE EQUATION WHEN THE KERNEL IS RADIALLY SYMMETRIC 7E ILLUSTRATE THE TWO OPTIONS THAT ARE GIVEN IN THE !PPENDIX FOR CALCULATING THE DIRECTIONAL MOMENT GENERATING FUNC TION FOR THIS CASE (ERE WE CONSIDER A WAVE SPREADING IN THE X DIRECTION SO THAT U ; =4 %VALUATE THE MARGINAL DISTRIBUTION OF + BY INTEGRATING OVER THE Z DIRECTION TO YIELD A ONE DIMENSIONAL DISPERSAL KERNEL THAT DESCRIBES DISPERSAL IN THE Z DIRECTION G' +UZ +3Z Z DZ Hn'
AND THEN CALCULATE THE DIRECTIONAL MOMENT GENERATING FUNCTION -U OF THE KER NEL KUZ AND THUS THE SPEED CU SEE EQUATIONS AND FOR DETAILS 4HIS METHOD EFFECTIVELY REDUCES THE TWO DIMENSIONAL SPREAD PROBLEM TO ONE SPATIAL DIMENSION BY lRST TAKING THE MARGINAL DISTRIBUTION OF THE DISPERSAL KERNEL AND THEN PROCEEDING AS WITH THE ONE DIMENSIONAL CASE 4HIS APPROACH IS CONCEPTUALLY STRAIGHTFORWARD BUT MANY MARGINAL DISTRIBUTIONS CANNOT BE CALCULATED ANALYTICALLY EVEN FOR SIMPLE KERNELS %VALUATE THE MOMENT GENERATING FUNCTION IN THE Z DIRECTION SEE EQUATION DIRECTLY AS G' G' -U S +R EXPSZ DZDZ Hn'Hn'
+! 3CHIERENBECK AND -, !ÕNOUCHE
G/ G' +R EXPSR COSe R DRDe H H
/
G' +R R )SR DR H
G' +R )SR DR H
É
AND THEN USE THIS TO CALCULATE OF THE SPEED CU (ERE ) IS THE MODIlED "ESSEL FUNCTION OF THE lRST KIND AND ZEROTH ORDER !BRAMOWIZ AND 3TEGUN 7HEN THERE ARE RAW ONE DIMENSIONAL RADIAL DISPERSAL DISTANCE DATA RxR. THEN THE EMPIRICAL MOMENT GENERATING FOR THE PLANAR WAVE SPEED CALCULATION BECOMES . -U%S - ) SRI . I AND SUBSTITUTION INTO GIVES THE EMPIRICAL ESTIMATOR FOR THE PLANAR WAVE SPEED (ERE THE RI MEASUREMENTS ARISE FROM TRACKING A SERIES OF INDIVIDUALS AS THEY DIS PERSE )T IS ASSUMED THAT THE TRACKING EFFORT PER UNIT AREA AND TRACKING EFlCIENCY PER UNIT AREA REMAINS CONSTANT OVER THE ENTIRE DISPERSAL AREA 'IVEN A HISTOGRAM OF RADIAL DENSITY DATA ¨ 4 IF l ) R lI +( R © I I n OTHERWISE ª WHERE ) I ) , THE CONSTRAINT THAT THE AREA UNDER THE HISTOGRAM INTEGRATES TO ONE MEANS
,
/ -lI n lI n 4I
I
)F THE HISTOGRAM IS MEASURED IN TERMS OF THE RELATIVE NUMBER OF DISPERSERS THAT MOVE A DISTANCE R RATHER THAN THE RELATIVE DENSITY IT IS NECESSARY TO RESCALE THE KERNEL BY /R n AS ABOVE 4HE DIRECTIONAL MOMENT GENERATING FUNCTION FOR THE HISTOGRAM COMES FROM SUBSTITUTING INTO TO OBTAIN / , -U(S - 4I lI ) SlI n lI n ) SlI n S I
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
COMPARE WITH AND SUBSTITUTION INTO GIVES THE PLANAR WAVE SPEED (ERE ) IS THE MODIlED "ESSEL FUNCTION OF THE lRST KIND AND lRST ORDER !BRAMOWIZ AND 3TEGUN &OR THE SAKE OF ILLUSTRATION WE EARLIER CONSIDERED THE CASE WHERE THE $OBZHANSKY AND 7RIGHT DATA DESCRIBED INSECT MOVEMENT ALONG LINEAR TRANSECTS OF AVAILABLE HABITAT !CCORDINGLY THE HISTOGRAM ESTIMATOR FOR THE SPREAD RATE FOR THE SITUA TION SHOWN IN &IG WAS CALCULATED USING EQUATIONS AND AS KM PER YEAR 4O COMPARE THE DIFFERENCE BETWEEN THE RESULTS OF THIS SECTION AND OUR EARLIER RESULTS WE REVISIT THE $OBZHANSKY AND 7RIGHT DATA UNDER THE MORE REASONABLE ASSUMPTION THAT THE TRANSECT DATA DESCRIBE THE RADIAL DROP OFF IN SETTLED INSECT DENSITY IN A TWO DIMENSIONAL HABITAT )N THIS CASE THE HISTOGRAM ESTIMATOR FOR THE PLANAR SPREAD RATE IS CALCULATED FROM EQUATIONS AND AS KM PER YEAR HIGHER THAN THE PREVIOUS ESTIMATE 2EPEATING THE COMPARISON OF SPREAD RATES FOR DIFFERENT hS SHOWS THAT THE SPREAD RATE ASSUMING RADIAL DISPERSAL AND GROWTH IN THE TWO DIMENSIONAL HABITAT IS SIGNIlCANTLY HIGHER THAN THE SPREAD RATE ASSUMING GROWTH AND DISPERSAL IN A LINEAR ONE DIMENSIONAL HABITAT SEE 4ABLE 4HIS DIFFERENCE IS MOST PRONOUNCED FOR A LOW GROWTH RATES h 4HIS ORDERING OF SPREAD RATES $ SPEED LARGER THAN $ SPEED 4ABLE APPEARS ONLY FOR DENSITY DATA NOT DISPERSAL DATA )N FACT IF THE ORIGINAL DATA DESCRIBE DISPERSAL THEN IT CAN BE SHOWN THAT THE ORDERING WILL BE REVERSED WITH THE $ SPEED BASED ON GROWTH AND DISPERSAL IN A LINEAR ONE DIMEN SIONAL HABITAT EG EQUATION AND LARGER THAN $ SPEED BASED ON RADIAL DISPER SAL AN GROWTH IN A TWO DIMENSIONAL HABITAT EG EQUATION AND
4ABLE 3PREAD RATES FOR VARYING GROWTH RATES h $ISPERSAL DATA ARE AS GIVEN BY THE LEFT PANELS IN &IG )N COLUMN LABELED $ IT IS ASSUMED THAT THE GROWTH AND DISPERSAL OCCUR IN A $ LINEAR HABITAT 3PREAD RATES ARE CALCULATED USING EQUATIONS AND )N COLUMN LABELED $ IT IS ASSUMED THAT THE DISPERSAL IS RADIAL AND THAT GROWTH AND DISPERSAL OCCUR IN A $ HABITAT (ERE THE PLANAR SPREAD RATE IS CALCULATED FROM EQUATIONS AND 4HE LAST COLUMN SHOWS THE RATIO OF THE SECOND TO THE lRST COLUMNS ENTRIES 4HE DIFFERENCE BETWEEN THE SPREAD RATES IS MOST PRONOUNCED FOR LOW GROWTH RATES h
$ SPEED KMYEAR
$ SPEED KMYEAR
RATIO OF SPEEDS
+! 3CHIERENBECK AND -, !ÕNOUCHE
-/.4% #!2,/ -%4(/$3 4HE SIMPLEST ESTIMATOR OF THE MOMENT GENERATING FUNCTION IS THE EMPIRICAL ESTIMATOR CALCULATED FROM ONE DIMENSIONAL DISPLACEMENT DATA EQUATION )T IS NOT ONLY SIMPLE TO IMPLEMENT NUMERICALLY BUT IN MANY CASES IS APPEALINGLY NONPARAMETRIC )T IS SOMETIMES USEFUL TO GENERATE APPROPRIATE $ DISPLACEMENT DATA FROM SOME OTHER FORM USING -ONTE #ARLO METHODS 4HE RESULTING DIS PLACEMENTS CAN THEN BE USED AS INPUT TO THE EMPIRICAL ESTIMATOR &OR EXAMPLE #ASWELL ET AL ANALYZED THE INVASION RATES OF SEVERAL SPECIES OF %UROPEAN BIRDS USING DISPERSAL DATA COMPILED BY VAN DEN "OSCH ET AL 4HE DISPER SAL DATA WERE OBTAINED IN THE FORM OF HISTOGRAMS OF DISPLACEMENT DISTANCES NOT DENSITIES 4HUS THEY WERE INTERPRETED AS GIVING A SET OF DISTANCES IN TWO DIMENSIONAL SPACE MOVED BY A SET OF MARKED INDIVIDUALS /BTAINING THE APPROPRIATE ONE DIMENSIONAL DISPERSAL KERNEL REQUIRES THE MARGINAL DISTRIBUTION OF THE TWO DIMENSIONAL DISTRIBUTION OF DISPLACEMENTS 4HIS WAS OBTAINED BY GENERATING A LARGE NUMBER OF RANDOM DISPLACEMENT DISTANCES FROM THE HISTOGRAM ASSUMING A UNIFORM DISTRIBUTION OF DISPLACEMENT DISTANCE WITHIN EACH HISTOGRAM BIN !SSUMING TWO DIMENSIONAL ISOTROPY EACH OF THESE DISTANCES WAS ASSIGNED A DIRECTION UNIFORMLY DISTRIBUTED BETWEEN AND / 4HIS PRODUCED A SET OF ARTIlCIAL DIMENSIONAL DISPLACEMENT DATA THE DISTANCE COMPONENT OF WHICH MATCHES THE REPORTED HISTOGRAM 4HE MARGINALIZED DISTRIBUTION WAS EASILY GENERATED BY TAKING THE Z COMPONENT OF EACH OF THE POINTS 4HE RESULTING SET OF DISTANCES WAS THEN INPUT TO THE EMPIRICAL MOMENT GENERATING FUNCTION TO PRODUCE AN ESTIMATE OF WAVE SPEED 4HIS -ONTE #ARLO METHOD IS APPROPRIATE BECAUSE WE KNOW MATHEMATICALLY THAT PROVIDING THE DISPERSAL KERNEL IS EXPONENTIALLY BOUNDED THE EMPIRICAL ESTIMATOR FOR THE WAVE SPEED IS UNBIASED IE APPROACHES THE TRUE WAVE SPEED AS . A' $ETAILS ON CONVERGENCE CAN BE FOUND IN #LARK ET AL
$)3#533)/. 4HE FOCUS OF THIS PAPER IS METHODS TO RELIABLY CONNECT POPULATION SPREAD RATE THEORY TO BIOLOGICAL DATA 4HERE ARE TWO FEATURES THAT WE FOCUS ON I SENSITIVITY OF SPREAD RATE ESTIMATES TO MODEL ASSUMPTIONS ABOUT LONG DISTANCE DISPERSAL AND II MODEL lTTING ISSUES THAT ARISE FROM lTTING TWO DIMENSIONAL DISPERSAL DATA TO ONE DIMENSIONAL MODELS 4HE EMPIRICAL AND HISTOGRAM ESTIMATORS PROVIDE A METHOD TO BYPASS ASSUMPTIONS ABOUT LONG DISTANCE DISPERSAL 4HESE ARE REALLY @WHAT YOU SEE IS WHAT YOU GET ESTIMATORS )NDEED FORMALLY SUBSTITUTING THE OBSERVED SUM OF POINT DISPERSAL JUMPS KZ - .I bZ n ZI INTO EQUATION LEADS TO THE EMPIRI CAL MOMENT GENERATING FUNCTION 7HEREAS THE ABOVE SUM OF DELTA FUNCTIONS PROVIDES A POOR ESTIMATOR FOR THE KERNEL THE PROCESS LEADS TO THE EMPIRICAL MOMENT GENERATING FUNCTION AND A GOOD ESTIMATE FOR THE SPREAD RATE WHICH IS THE QUANTITY OF INTEREST 4HE HISTOGRAM ESTIMATOR BEHAVES IN A MANNER WHICH IS SIMILAR TO THE
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
EMPIRICAL ESTIMATOR ALTHOUGH THE LOCATION OF BINS CAN PRODUCE SMALL BIASES IN THE SPREAD RATE ESTIMATE 7E RECOMMEND THAT THE EMPIRICAL AND HISTOGRAM SPREAD RATE ESTIMATORS SHOULD BE A BASIC TOOL FOR ANY MODELING EXERCISE WHICH INVOLVES SPREAD RATES WHERE LONG DISTANCE DISPERSAL PLAYS A ROLE &ITTED PARAMETRIC DISPERSAL KERNELS MAY BE PREFER ABLE WHEN THERE IS REASON TO BELIEVE THAT EXTRAPOLATION OF THE DISPERSAL FUNCTION BEYOND THE FURTHEST OBSERVED DISPERSAL DISTANCE CAN BE JUSTIlED (OWEVER EVEN IN THIS CASE IT IS USEFUL TO COMPARE SPREAD RATE RESULTS FROM THE PARAMETRIC lTTED KERNEL WITH THE EMPIRICAL OR HISTOGRAM SPREAD RATES 4HE DIFFERENCE BETWEEN THE SPREAD RATES WILL HIGHLIGHT THE IMPLICATIONS OF ASSUMPTIONS ABOUT LONG DISTANCE DISPERSAL DISTANCES THAT GO INTO THE PARAMETRIC KERNEL 4HE NEW MODEL lTTING ISSUE WE FOCUS ON IS THE CORRECT METHOD TO CALCULATE PLA NAR POPULATION SPREAD FROM RADIALLY SYMMETRIC DISPERSAL DATA .AIVELY lTTING THE LINEAR ONE DIMENSIONAL DISPERSAL KERNEL TO THE RADIALLY SYMMETRIC DISPERSAL DATA WILL GIVE THE WRONG SPREAD RATE WHEN THE ONE DIMENSIONAL SPREAD MODEL IS USED BIASED DOWNWARD FOR DENSITY DATA AND UPWARD FOR DISPERSAL DATA )N A LINEAR ONE DIMENSIONAL ENVIRONMENT THE SCALED DISTRIBUTION OF DENSITIES DISPERSERS PER UNIT LENGTH AND A DISTRIBUTION OF DISTANCES THAT THE DISPERSERS TRAVEL FROM THE PARENT ARE THE SAME AND ARE GIVEN BY THE KERNEL K )N A TWO DIMEN SIONAL ENVIRONMENT THE SCALED DISTRIBUTION OF DENSITIES DISPERSERS PER UNIT AREA GIVEN BY + AND THE DISTRIBUTION OF DISTANCES THAT DISPERSERS TRAVEL FROM FROM THE PARENT GIVEN BY +É /R+R ARE NOT THE SAME BECAUSE THERE IS MORE AREA AVAILABLE AT DISTANCES FURTHER FROM THE PARENT 4HE CORRECT METHOD FOR CALCULATING THE SPREAD IN THE TWO DIMENSIONAL ENVIRONMENT INVOLVES A DIRECTIONAL MOMENT GENERATING FUNCTION OF THE TWO DIMENSIONAL DISPERSAL KERNEL 4HIS IS FOUND EITHER BY EVALUATING THE MOMENT GENERATING FUNCTION OF THE MARGINAL DISTRIBUTION OF THE DISPERSAL KERNEL +R OR BY USING +É R IN A MODIlED MOMENT GENERATING FUNC TION CALCULATION 4O SEE THE DIFFERENCE BETWEEN THE LINEAR ONE DIMENSIONAL HISTOGRAM DENSITY KERNEL AND THE MARGINAL DISTRIBUTION OF ITS RADIALLY SYMMETRIC ANALOG WE CAN COMPUTE THE MARGINAL DISTRIBUTION OF THE RADIALLY SYMMETRIC HISTOGRAM DENSITY KERNEL DIRECTLY ¨ , K( U Z ©-I dI n dI 3l I n Z ª
IF lI n ) \Z\ lI
OTHERWISE
4HE TWO KERNELS K(Z AND K(U Z ARE SHOWN IN &IG !S CAN BE SEEN FROM THE RESULTS IN 4ABLE THE INCREASE IN NUMBER OF LONG DISTANCE DISPERSERS IN THE MARGINAL DISTRIBUTION SPEEDS UP THE SPREAD RATE SIGNIlCANTLY 4HE CORRECT FORMULAE FOR CALCULATING SPREAD RATES ARE GIVEN IN 4ABLES AND 4O THE BEST OF OUR KNOWLEDGE THESE FORMULAE HAVE NOT BEEN WIDELY DEVELOPED OR DISCUSSED ELSEWHERE IN THE LITERATURE )T IS OUR HOPE THAT THESE TABLES ALONG WITH THE DISCUSSION IN THE CHAPTER WILL FORM A USERS GUIDE TO CALCULATING SPREAD RATES
+! 3CHIERENBECK AND -, !ÕNOUCHE
&IG (ISTOGRAM DISPERSAL KERNEL EQUATION FOR$OBZHANSKY AND 7RIGHTS $ROSOPHILA DISPERSAL DATA UNDER THE ASSUMPTION THAT DISPERSAL OCCURS IN A LINEAR ONE DIMENSIONAL HABITAT GREY -ARGINAL DISTRIBUTION EQUATION OF HISTOGRAM DISPERSAL KERNEL EQUATION UNDER THE ASSUMPTION THAT DISPERSAL OCCURS IN A TWO DIMENSIONAL HABITAT AND IS RADIALLY SYMMETRIC
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
FOR DISCRETE TIME MODELS AND IN TURN WILL LEAD TO A CLOSER CONNECTION BETWEEN ECOLOGICAL THEORY AND DATA 7HEN THE DISPERSAL DATA COME FROM A @FAT TAILED KERNEL KERNEL WITH NO MOMENT GENERATING FUNCTION THEORY PREDICTS A CONSTANTLY ACCELERATING WAVE WITH AN ASYMPTOTICALLY INlNITE SPEED (OWEVER THE SPREAD RATES BASED ON THE EMPIRICAL MOMENT GENERATING FUNCTION EG EQUATION OR THE HISTOGRAM MOMENT GEN ERATING FUNCTION EG EQUATION ARE lNITE 4HIS IS BECAUSE THE THESE SPREAD RATES ARE CALCULATED FROM A lNITE NUMBER OF DISPERSAL OBSERVATIONS OR ON DENSI TIES MEASURED OVER A lNITE REGION (ERE ADDITIONAL SAMPLING EFFORT MAY lND RARE LONG DISTANCE DISPERSERS OR MAY MEASURE NONZERO DENSITIES OF DISPERSERS FAR FROM THEIR NATAL SOURCE AND THUS THE SPREAD RATE ESTIMATE CAN INCREASE WITH SAMPLING EFFORT 7HEN THERE IS GOOD REASON TO BELIEVE THAT THE DISPERSAL KERNEL IS FAT TAILED OR NEARLY FAT TAILED A MORE APPROPRIATE MEASURE OF SPREAD RATE IS THE @FURTHEST FORWARD VELOCITY #LARK ,EWIS AND (ORVATH WHICH REMAINS BOUNDED ! MORE GENERAL DISCUSSION OF UNCERTAINTY IN SPREAD RATES ASSOCIATED WITH LONG DISTANCE DISPERSAL IS GIVEN IN #LARK ET AL
4ABLE -ETHODS TO CALCULATE THE MOMENT GENERATING FUNCTION NEEDED FOR THE SPREAD RATE CALCULATION EQUATION WHEN THE POPULATION LIVES IN A ONE DIMENSIONAL LINEAR HABITAT $ATA
-'& ;-S =
%QUATION
PARAMETRIC KERNEL
G' KZ EXPSZ DZ Hn'
DISPERSAL DISPLACEMENT DATA
. - I EXP SZI .
DISPLACEMENT DISTANCE DATA
. - I COSH SZI .
DISPLACEMENT HISTOGRAM
, - I 4I EXPSjI n EXPSjI n S
DISTANCE HISTOGRAM
, - I 4I SINHSjI n SINHSjI n j S
+! 3CHIERENBECK AND -, !ÕNOUCHE
4ABLE -ETHODS TO CALCULATE THE DIRECTIONAL MOMENT GENERATING FUNCTION NEEDED FOR THE PLANAR SPREAD RATE CALCULATION EQUATION WHEN THE POPULATION LIVES IN A TWO DIMENSIONAL HABITAT $ATA
-'& ;-XS = G' G' +Z EXPSZ DZDZ Hn' Hn'
PARAMETRIC $ KERNEL
%QUATION
PARAMETRIC RADIAL KERNEL
G' / +R R )SR DR H
RADIAL DISPLACEMENT DATA
. - I ) RIS .
RADIAL HISTOGRAM DATA
, / - I 4I lI ) SlI n lI n ) SlI n S
) AND ) ARE MODIFED "ESSEL FUNCTIONS OF ZEROTH AND FIRST ORDER CF !BRAMOWIZ AND 3TEGUN
!00%.$)8 #ALCULATING THE SPREAD RATE WITH MAPLE
4HE FOLLOWING IS -APLE CODE THAT CAN BE USED TO CALCULATE THE SPREAD RATE FOR A POPULATION WITH GEOMETRIC GROWTH RATE h AND THE COMPOSITE ,APLACE DISPERSAL KERNEL KZ P_ EXPn_\Z\ n P _ EXPn_\Z\ 'LJLWV :RUNRXWVSHHG JDPIRUWKHIROORZLQJ SDUDPHWHUYDOXHV ODPEGD DOSKDB DOSKDB
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
S GHÀQHWKHPRPHQWJHQHUDWLQJIXQFWLRQDQGH[SRQHQWLDO YB DOSKDBA DOSKDBAVA YB DOSKDBA DOSKDBAVA IQ H[S V JDP IQ ODPEGD S YB S YB )LQGWKHGRXEOHURRW HT IQ IQ HT GLII IQV GLII IQV IVROYH ^HTHT`^VJDP`V DOSKDB
4HE DIRECTIONAL MOMENT GENERATING FUNCTION
4HE DIRECTIONAL MOMENT GENERATING FUNCTION IS G' G' -US +Z EXPSZ DZDZ Hn' Hn'
2ECALL THAT THE DISPERSAL KERNEL +Z NOW DESCRIBES THE PROBABILITY DENSITY FOR JUMPS WHOSE DIRECTIONS AND MAGNITUDE ARE DESCRIBED BY THE VECTOR ;Z Z=4 4HE TERM U q Z UZ UZ IN EQUATION IS THE COMPONENT OF THE DISPERSAL JUMP Z THAT LIES IN THE U DIRECTION )F THE KERNEL HAS NO DIRECTIONAL BIAS IS ISO TROPIC DEPENDING ONLY UPON DISTANCE AND HENCE +Z +3Z Z THEN THE MOMENT GENERATING FUNCTION -US AND HENCE THE SPEED CU IS INDEPEN DENT OF THE DIRECTION VECTOR U 7E CONSIDER THIS CASE IN THE SECTION 0OPULATION 3PREAD IN 4WO $IMENSIONS 4HE @DIRECTIONAL MOMENT GENERATING FUNCTION -U CAN BE INTERPRETED AS THE MOMENT GENERATING FUNCTION OF THE KERNEL +Z MARGINALIZED IN THE DIRECTION OF THE UNIT VECTOR V WHICH IS PERPENDICULAR TO U G' -US KUU EXPSU DU Hn' WHERE G' KUU +Z DV Hn' AND U U q Z V V q Z
+! 3CHIERENBECK AND -, !ÕNOUCHE
2%&%2%.#%3 !BRAMOWIZ - AND ) 3TEGUN (ANDBOOK OF -ATHEMATICAL &UNCTIONS $OVER 0UBLICATIONS )NC !LLEN % * , * 3 !LLEN AND 8 'ILLIAM $ISPERSAL AND COMPETITION MODELS FOR PLANTS *OURNAL OF -ATHEMATICAL "IOLOGY !LLEN , * 3 % * !LLEN AND 3 0ONWEERA ! MATHEMATICAL MODEL FOR WEED DISPER SAL AND CONTROL "ULLETIN OF -ATHEMATICAL OF "IOLOGY !NDOW $ ! 0 - +AREIVA 3 ! ,EVIN AND ! /KUBO 3PREAD OF INVADING ORGAN ISMS ,ANDSCAPE %COLOGY !RONSON $ ' AND ( & 7EINBERGER .ONLINEAR DI L USION IN POPULATION GENETICS COMBUSTION AND NERVE PULSE PROPAGATION )N * ! 'OLDSTEIN %D ,ECTURE .OTES IN -ATHEMATICS 6OLUME PP "ERLIN 3PRINGER 6ERLAG #ASWELL ( 2 ,ENSINK AND - ' .EUBERT $EMOGRAPHY AND DISPERSAL #OMPARING INVASION SPEEDS USING LIFE TABLE RESPONSE EXPERIMENTS %COLOGY #LARK * 3 7HY TREES MIGRATE SO FAST #ONFRONTING THEORY WITH DISPERSAL BIOLOGY AND THE PALEORECORD 4HE !MERICAN .ATURALIST #LARK * 3 # &ASTIE ' (URTT 3 4 *ACKSON # *OHNSON ' ! +ING - ,EWIS * ,YNCH 3 0ACALA # 0RENTICE % 7 3CHUPP 4 7 ))) AND 0 7YCOFF 2EIDS PARADOX OF RAPID PLANT MIGRATION "IO3CIENCE #LARK * 3 , (ORVATH AND - ! ,EWIS /N THE ESTIMATION OF SPREAD RATE FOR A BIO LOGICAL POPULATION 3TATISTICS AND 0ROBABILITY ,ETTERS #LARK * 3 - ! ,EWIS AND , (ORVATH )NVASION BY EXTREMES 0OPULATION SPREAD WITH VARIATION IN DISPERSAL AND REPRODUCTION !MERICAN .ATURALIST #LARK * 3 - ! ,EWIS * 3 -C,ACHLAN AND * ( 2IS,AMBERS %STIMATING POPULA TION SPREAD 7HAT CAN WE FORECAST AND HOW WELL %COLOGY $OBZHANSKY 4 AND 3 7RIGHT 'ENETICS OF NATURAL POPULATIONS X $ISPERSION RATES IN DROSOPHILA PSEUDOOBSCURA 'ENETICS &ISHER 2 ! 4HE WAVE OF ADVANCE OF ADVANTAGEOUS GENES !NN %UGEN ,ONDON &UJIWARA - + !NDERSON ( #ASWELL AND - ' .EUBERT /N THE ESTIMATION OF DISPERSAL KERNELS FROM INDIVIDUAL CAPTURE RECAPTURE DATA %NVIRONMENTAL AND %COLOGICAL 3TATISTICS )N PRESS (ART $ 2 AND 2 ( 'ARDNER ! SPATIAL MODEL FOR THE SPREAD OF INVADING ORGANISMS SUBJECT TO COMPETITION * -ATH "IOL (IGGINS 3 ) AND $ - 2ICHARDSON 0REDICTING PLANT MIGRATION RATES IN A CHANGING WORLD THE ROLE OF LONG DISTANCE DISPERSAL !M .AT (ORVITZ # # AND $ 7 3CHEMSKE 3EED DISPERSAL OF A NEOTROPICAL MYRMECOCHORE VARIATION IN REMOVAL RATES AND DISPERSAL DISTANCE "IOTROPICA +OLMOGOROV ! 0ETROVSKY AND . ) 0ISCOUNOV ³TUDE DE LÏQUATION DE LA DIFFUSION AVEC CROISSANCE DE LA QUANTITÏ DE MATIÒRE ET SON APPLICATION A UN PROBLÒME BIOLOGIQUE "ULL -OSCOW 5NIV -ATH -ECH +OT - $ISCRETE TIME TRAVELLING WAVES %COLOGICAL EXAMPLES * -ATH "IOL
! GUIDE TO CALCULATING DISCRETE TIME INVASION RATES FROM DATA
+OT - - ! ,EWIS AND 0 VAN DEN $RIESSCHE $ISPERSAL DATA AND THE SPREAD OF INVADING ORGANISMS %COLOGY ,EWIS - ! 6ARIABILITY 0ATCHINESS AND *UMP $ISPERSAL IN THE 3PREAD OF AN )NVADING 0OPULATION #HAPTER PP 0RINCETON .EW *ERSEY 0RINCETIN 5NIVESITY 0RESS ,UBINA * ! AND 3 ! ,EVIN 4HE SPREAD OF A REINVADING SPECIES RANGE EXPANSION IN THE #ALIFORNIA 3EA /TTER !MERICAN .ATURALIST ,UI 2 A ! NONLINEAR INTEGRAL OPERATOR ARISING FROM A MODEL IN POPULATION GENETICS ) MONOTONE INITIAL DATA 3)!- * -ATH !NAL ,UI 2 B ! NONLINEAR INTEGRAL OPERATOR ARISING FROM A MODEL IN POPULATION GENETICS )) )NITIAL DATA WITH COMPACT SUPPORT 3)!- * -ATH !NAL ,UI 2 ! NONLINEAR INTEGRAL OPERATOR ARISING FROM A MODEL IN POPULATION GENETICS ))) )NITIAL DATA WITH COMPACT SUPPORT 3)!- * -ATH !NAL ,UI 2 ! NONLINEAR INTEGRAL OPERATOR ARISING FROM A MODEL IN POPULATION GENETICS )6 #LINES 3)!- * -ATH !NAL ,UI 2 A "IOLOGICAL GROWTH AND SPREAD MODELED BY SYSTEMS OF RECURSIONS ) -ATHEMATICAL THEORY -ATHEMATICAL "IOSCIENCES ,UI 2 B "IOLOGICAL GROWTH AND SPREAD MODELED BY SYSTEMS OF RECURSIONS )) "IOLOGICAL THEORY -ATHEMATICAL "IOSCIENCES -ARCHANT 3 !NALYSIS OF AN INTEGRODIFFERENCE MODEL FOR BIOLOGICAL INVASIONS WITH A QUASI LOCAL INTERACTION -ASTERS THESIS 5NIVERSITY OF "RITISH #OLUMBIA .EUBERT - ' AND ( #ASWELL $EMOGRAPHY AND DISPERSAL #ALCULATION AND SENSITIVITY ANALYSIS OF INVASION SPEED FOR STAGE STRUCTURED POPULATIONS %COLOGY .EUBERT - ' - +OT AND - ! ,EWIS )NVASION SPEED IN mUCTUATING ENVIRON MENTS 0ROC 2OY 3OC ,OND " .EUBERT - ' AND ) 0ARKER 5SING INTEGRODIFFERENCE EQUATIONS TO PROJECT RATES OF SPREAD FOR INVASIVE SPECIES 2ISK !NALYSIS IN PRESS 0ACHEPSKY % & ,UTSCHER AND - ! ,EWIS 0ERSISTENCE SPREAD AND THE DRIFT PARA DOX 4HEORETICAL 0OPULATION "IOLOGY IN PRESS 0OWELL * AND . % :IMMERMANN !NALYSIS OF ACTIVE SEED DISPERSAL CONTRIBUTES TO RESOLVING 2EIDS PARADOX %COLOGY 3CHOlELD 0 3PATIALLY EXPLICIT MODELS OF 4URELLI (OFFMANN WOLBACHIA INVASIVE WAVE FRONTS *OURNAL OF 4HEORETICAL "IOLOGY 3HIGESADA . AND + +AWASAKI "IOLOGICAL )NVASIONS 4HEORY AND 0RACTICE /XFORD /XFORD 5NIVERSITY 0RESS 3HIGESADA . + +AWASAKI AND % 4ERAMOTO 4RAVELING PERIODIC WAVES IN HETEROGENEOUS ENVIRONMENTS 4HEOR 0OP "IOL 3ILVERMAN " 7 $ENSITY %STIMATION FOR 3TATISTICS AND $ATA !NALYSIS #HAPMAN AND (ALL 3KELLAM * ' 2ANDOM DISPERSAL IN THEORETICAL POPULATIONS "IOMETRIKA 3PEIRS $ # AND 7 3 # 'URNEY 0OPULATION PERSISTENCE IN RIVERS AND ESTUARIES %COLOGY
+! 3CHIERENBECK AND -, !ÕNOUCHE
4AKASU & . 9AMAMOTO + +AWASAKI + 4OGASHI AND . 3HIGESADA -ODELING THE RANGE EXPANSION OF AN INTRODUCED TREE DISEASE "IOLOGICAL )NVASIONS VAN DEN "OSCH & 2 (ENGEVELD AND * ! * -ETZ !NALYSING THE VELOCITY OF ANIMAL RANGE EXPANSION *OURNAL OF "IOGEOGRAPHY 6EIT 2 2 AND - ! ,EWIS $ISPERAL POPULATION GROWTH AND THE ALLEE EFFECT $YNAMICS OF THE HOUSE lNCH INVASION OF EASTERN NORTH !MERICA 4HE !MERICAN .ATURALIST 7EINBERGER ( & ,ONG TIME BEHAVIOR OF A CLASS OF BIOLOGICAL MODELS 3)!- JOURNAL ON MATHEMATICAL ANALYSIS 7EINBERGER ( & ,ONG TIME BEHAVIOUR OF A CLASS OF BIOLOGICAL MODELS )N 7 % & ))) %D )N 2ESEARCH .OTES IN -ATHEMATICS .O PP -ARSHlELD -! 0ITMAN 0UBLISHING ,TD 7ERNER 0 ! ! SEED TRAP FOR DETERMINING PATTERNS OF SEED DEPOSITION IN TERRESTRIAL PLANTS #ANADIAN *OURNAL OF "OTANY 7ITH + ! 4HE LANDSCAPE ECOLOGY OF INVASIVE SPREAD #ONSERVATION "IOLOGY 7OOLCOCK * , AND 2 #OUSENS ! MATHEMATICAL ANALYSIS OF FACTORS AFFECTING THE RATE OF SPREAD OF ANNUAL WEEDS IN AN ARABLE lELD 7EED 3CIENCE
#HAPTER NINE
4HE ROLE OF EVOLUTIONARY GENETICS IN STUDIES OF PLANT INVASIONS + ! 3CHIERENBECK AND - , !ÕNOUCHE
).42/$5#4)/. )NVASIVE SPECIES HAVE LONG RAISED THE INTEREST OF EVOLUTIONISTS AS THEY PROVIDE IDEAL SYSTEMS TO UNDERSTAND THE EVOLUTIONARY PROCESSES THAT DETERMINE AND ACCOMPANY THE EXPANSION OF A SPECIES "AKER AND 3TEBBINS 0RAGMATICALLY INVASIONS OF NON NATIVE SPECIES OR GENOTYPES POSE A MAJOR BIOLOGICAL THREAT TO NATIVE BIO DIVERSITY AND ECOSYSTEM FUNCTIONING 7HILE THE ECOLOGY OF THESE INVASIONS HAS RECEIVED CONSIDERABLE INTERNATIONAL ATTENTION UNDERSTANDING THE EVOLUTIONARY DIMENSIONS OF THIS PROBLEM REMAINS RUDIMENTARY 4HE OBSERVATION CAN BE MADE HOWEVER THAT INVASIONS HAVE TWO MAIN EVOLUTIONARY CONSEQUENCES lRST THEY CAN RESULT IN THE RAPID EVOLUTION OF INTRODUCED POPULATIONS IN NEW ENVIRONMENTS AND SECONDLY THEY CAN PROMOTE RETICULATE GENE mOW WITH RELATED TAXA AT THE POPULATION ECOTYPE OR SPECIES LEVEL -OONEY AND #LELAND "OTH PROCESSES WILL RESULT IN NEW GENOTYPE BY ENVIRONMENT INTERACTIONS AND SUBSEQUENT GENETIC DIVERSIlCATION $ESPITE MUCH CONJECTURE ABOUT THE GENETIC CHARACTERISTICS OF INVASIVE SPECIES DATA COLLECTION HAS RESULTED IN AMBIGUOUS CONCLUSIONS !LLOZYME DATA INDICATE "ROMUS TECTORUM CHEATGRASS MAY HAVE A hGENERAL PURPOSE GENOTYPEv .OVAK -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
+! 3CHIERENBECK AND -, !ÕNOUCHE
AND -ACK QUANTITATIVE GENETIC DATA INDICATE 3APIUM SEBIFERUM #HINESE TALLOW MAY UNDERGO POST INTRODUCTORY ADAPTATIONS 3IEMANN AND 2OGERS AND OTHER SPECIES MAY REQUIRE A NOVEL COMBINATION OF INTRA OR INTERSPECIlC GENET IC VARIATION FROM THE HOME RANGE TO PRODUCE A SUCCESSFUL INVADER e.g., 4AMARIX SPECIES 'ASKIN AND 3CHAAL )T IS BECOMING CLEAR THAT INVASIONS CAN RESULT IN RAPID EVOLUTIONARY EVENTS VIA A NUMBER OF GENETIC MECHANISMS %LLSTRAND AND 3CHIERENBECK ,EE 4HE RECENT DEVELOPMENT OF GENETIC AND GENOMIC APPROACHES HAS ALLOWED THE INVES TIGATION OF MODEL OR CULTIVATED SYSTEMS AT THE SEQUENCE LEVEL $ATA HAVE ACCUMU LATED RAPIDLY IN THE PAST FEW YEARS TO ELUCIDATE MOLECULAR LEVEL MECHANISMS THAT PROMOTE SPECIES FORMATION AND EXPANSION 2IESEBERG AND 7ENDEL !MONG THE QUESTIONS THAT CAN NOW BE ADDRESSED ARE THE GEOGRAPHIC AND EVOLUTIONARY ORIGIN OF INVASIVE SPECIES THE IDENTIlCATION OF THE PARENTAL GENOTYPES THAT ARE INVOLVED IN THE FORMATION OF NEW RECENT INVASIVE SPECIES THE POSSIBLE GENETIC EXCHANGES BETWEEN INVASIVE AND NATIVE SPECIES GENOME EVOLUTION OF INVASIVE SPECIES COMPARED TO RELATED NON INVASIVE SPECIES THE MOLECULAR BASIS OF ADAP TIVE TRAITS THAT MAY PROMOTE INVASIVENESS IMPORTANCE OF NEUTRAL VERSUS ADAPTIVE PROCESSES THAT HAVE ACCOMPANIED GENOME EVOLUTION OF INVASIVE SPECIES !LLENDORF AND ,UNDQUIST AND ,EE ARE AMONG THOSE THAT EMPHA SIZE THAT GENETIC CONSIDERATIONS SHOULD PLAY A LARGER ROLE IN THE DEVELOPMENT OF INVASIVE SPECIES MANAGEMENT AND CONTROL 3ADLY ADEQUATE GENETIC DATA RARELY EXIST TO SET POLICY AT A REGIONAL OR GLOBAL LEVEL 7E HOPE TO COMPEL THE READER OF THIS CHAPTER THAT THE GENETICS OF INVASIVE SPECIES ARE INTERESTING AND IMPORTANT FROM A THEORETICAL EVOLUTIONARY PERSPECTIVE AND MERIT FUNDAMENTAL CONSIDERATION AT THE MANAGEMENT LEVEL 2ESEARCHERS JUST ENTERING THE STUDY OF EVOLUTIONARY GENETICS CAN BE ASSURED OF MANY DECADES OF WORK WITH INVASIVE SPECIES AT THE MOLECULAR POPULATION OR SPECIES LEVEL (OWEVER UNFORTUNATE THE CIRCUMSTANCE SPECIES INVA SIONS ARE IDEAL FOR THE PROVISION OF SYNTHESES BETWEEN ECOLOGY AND GENETICS
2/,% /& -/,%#5,!2 %6/,54)/. ). ).6!3)6% !"),)49 0OSSIBLE HERITABLE FACTORS THAT CONTRIBUTE TO INVASIVE ABILITY HAVE BEEN CONJECTURED SINCE $ARWIN !LTHOUGH SOPHISTICATED TECHNIQUES TO EXPLORE THE GENETICS OF INVASIVE ABILITY ARE NOW AVAILABLE THE lELD STILL HAS FAR TO GO TO lND PRACTICAL METHODOLOGIES TO ELUCIDATE THE COMPLEX GENETIC AND ECOLOGICAL INTERACTIONS OF INVASIVE SPECIES 7HETHER INVASIVE PLANT SPECIES ARE hBORN OR MADEv %LLSTRAND AND 3CHIERENBECK IF A PARTICULAR GENETIC CHARACTERISTIC IS IDENTIlED WE CAN NOW DETERMINE WHETHER ALLELIC VARIABILITY FOR A TRAIT EXISTS AND ASSESS ITS EVOLUTION ARY IMPORTANCE IN SYNTHESIS PATHWAYS OR GENE EXPRESSION !S AGRICULTURAL WEED SCIENTISTS REALIZED OVER YEARS AGO WEED CONTROL GENET ICS AND MOLECULAR BIOLOGY ARE BASICALLY AND INTIMATELY RELATED VIA STUDIES ON CHEMICAL DISRUPTION OF COMPLEX METABOLIC PATHWAYS 'RESSEL !S A RESULT OF ENZYMES THAT ARE BLOCKED BY HERBICIDES THE PATHWAYS IN WHICH THEY OCCUR
%VOLUTION AND PLANT INVASIONS
BECOME ELUCIDATED AND MAY SUBSEQUENTLY BECOME IMPORTANT IN TRANSGENIC EXPERI MENTATION 'RESSEL /F PARTICULAR NOTE AGRICULTURAL SCIENTISTS USE BASIC EVOLUTIONARY PRINCIPLES WHEN FACED WITH THE OFTEN INEVITABLE RESISTANCE PROBLEMS THAT RESULT FROM HERBICIDE USE &OR EXAMPLE THE HERBICIDE PARAQUAT HAS BEEN SUC CESSFUL IN A hPRETESTv FOR A GENETIC PREDISPOSITION FOR TRANSIENT DROUGHT TOLERANCE BECAUSE BOTH DROUGHT AND HERBICIDE RESISTANCE CAUSE OXIDATIVE STRESS 'RESSEL 4ESTS FOR SCREENING FAVORABLE GENOTYPES IN CROP SITUATIONS MAY BE USEFUL IN SCREENING UNWANTED NON NATIVE HORTICULTURAL GENOTYPES THAT MAY CONTAIN TRAITS SUCH AS RESISTANCE TO DROUGHT STRESS THAT ARE KNOWN TO CONTRIBUTE TO INVASIVENESS "AZZAZ !N IMPORTANT STEP IN THE DEVELOPMENT OF A MANAGEMENT POLICY OF INVASIVES IS THE INTEGRATION OF TECHNIQUES THAT ARE mEXIBLE ENOUGH TO RESPOND TO GENETIC TRAITS THAT MAY CHANGE AS A RESULT OF ADAPTATION AND CONTROL 4HE ROLE OF THE ECOLOGIST AND LAND MANAGER SHOULD NOT BE UNDERESTIMATED IN THE DETERMINA TION OF THE ECOLOGICAL IMPORTANCE OF THE GENETIC TRAITS OF INVADERS 7E CONSIDERED lVE MAJOR ASPECTS OF THE ROLE OF MOLECULAR EVOLUTION TO INVASIVE ABILITY &IRST THE GENETIC VARIABILITY NECESSARY TO RESPOND TO NEW ENVIRONMENTAL PRESSURES EXISTS WITHIN SOME TAXA IE EITHER hUNTAPPEDv GENETIC VARIATION OR A hGENERAL PURPOSE GENOTYPEv "AKER 3ECONDLY MORE RAPID EVOLUTION CAN RESULT FROM ADAPTIVE RADIATION INTO UNINHABITED NICHES SIMILAR TO THAT FOUND WITH ADAPTIVE RADIATION IN ISLAND ECOSYSTEMS $EPENDING ON AGE AND DISTURBANCE HIS TORY SOME OF THESE NICHES MAY BE MORE AVAILABLE THAN OTHERS AND THUS BECOME RECEPTACLES FOR RAPID EVOLUTIONARY CHANGE /UR THIRD TOPIC CONSIDERS AN IDEA HYPOTHESIZED UPON FOR MANY YEARS 3TEBBINS MAINLY THAT POLYPLOIDY MAY CREATE AN ADVANTAGE IN INVASIONS DUE TO MOLECULAR EVOLUTION OF GENE DUPLICA TIONS AND INCREASED GENETIC VARIATION &OURTH THE CREATION OF NEW VARIATION CAN RESULT FROM HYBRIDIZATION AT EITHER THE INTER OR INTRASPECIlC LEVEL AND THIS GENETIC VARIATION CAN ORIGINATE FROM REPEATED INTRODUCTIONS AND SEED BANKS ,ASTLY NOT ALL ASPECTS OF THE EVOLUTION OF INVASIVE SPECIES RESULT FROM GENETIC VARIATION INSIGHTS HAVE RECENTLY ACCUMULATED THAT STRESS THE IMPORTANCE OF EPIGENETIC MECHANISMS AND THE ROLE OF EXPRESSION PLASTICITY IN SHAPING PHENOTYPES %XISTING GENETIC VARIATION -OLECULAR 'ENETICS
1UESTIONS REGARDING THE IMPORTANCE OF MOLECULAR MARKERS TO MEASURE RESPONSE TO SELECTION ARE PART OF THE LARGER DEBATE OVER hNEARLY NEUTRALv VERSUS SELECTION IST THEORY /HTA AND 'ILLESPIE )F THE QUESTION IS @IS THE HETEROZYGOSITY OF MOLECULAR MARKERS NECESSARY FOR A RESPONSE TO SELECTION THE ANSWER IS A QUALI lED hNOv 2EED AND &RANKHAM HAVE GONE AS FAR AS TO SUGGEST THAT GENETIC DIVERSITY DATA HAVE LITTLE PLACE IN THE CONTEXT OF THE INVASIVE SPECIES QUESTION $ESPITE THIS VIEW A NUMBER OF EXAMPLES DEMONSTRATE THAT VARIABLE MOLECULAR MARKERS CAN BE USEFUL IN UNDERSTANDING PLANT INVASIONS 'ENOTYPES THAT ARE CLEAR LY MORE INVASIVE THAN OTHERS HAVE BEEN IDENTIlED IN 4AMARIX SALT CEDAR SPECIES
+! 3CHIERENBECK AND -, !ÕNOUCHE
'ASKIN AND 3CHAAL AND 0HRAGMITES AUSTRALIS COMMON REED 3ALTONSTALL )N ADDITION WE ARE NOW ABLE TO IDENTIFY VARIATION IN CHROMOSOMAL REGIONS IF NOT FOR PARTICULAR GENES THAT CONFER A lTNESS ADVANTAGE IN INVASIONS #LAUSS AND -ITCHELL /LDS HAVE DEMONSTRATED A DIRECT RELATIONSHIP BETWEEN TRYPSIN INHIBITOR LOCI IMPORTANT IN PLANT DEFENSE IN !RABIDOPSIS MOUSE EAR CRESS AND THE EVOLUTION OF LIFE HISTORY TRAITS ! QUANTITATIVE TRAIT LOCUS IN (ELIANTHUS PARADOXUS PECOS SUNmOWER SUGGESTS #A DEPENDENT SALT TOLERANCE AND HIGHER lTNESS IN A RANGE OF ENVIRONMENTS IN THE HYBRID SPECIES ,EXER ET AL !LTHOUGH ADMIT TEDLY THERE IS MUCH TO LEARN ABOUT THE RELATIONSHIP BETWEEN THE MOLECULAR GENETIC VARIATION OF POPULATIONS AND SELECTION IT REMAINS A FRUITFUL AND SEMINAL AREA OF INQUIRY PARTICULARLY WITH PLANT INVASIONS 'ENETIC MARKERS ARE OFTEN USED IN SELECTION AND OTHER GENETIC MANIPULATIONS OF AGRICULTURAL CROPS $EKKER "ASIC POPULATION GENETICS HAVE BEEN USEFUL IN THE SEPARATION OF TWO HYBRIDIZING !MARANTHUS PIGWEED SPECIES TO PREVENT THE INTROGRESSION OF TRANSGENICS 7ETZEL ET AL -OLECULAR MARKERS HAVE BEEN USEFUL IN /RYZA RICE SPECIES IN THE IDENTIlCATION OF VARIETIES THAT MAY OR MAY NOT BE ABLE TO HYBRIDIZE AND SUBSEQUENTLY WHETHER THESE VARIETIES ARE APPROPRIATE FOR A PARTICULAR GROWING REGION #OHEN ET AL 4HE SIMILAR APPLICATION OF SUCH MARKERS TO INVASIVE SPECIES WILL LEAD TO REMOVAL PRIORITIZATION OF PROBLEMATIC GENOTYPES IN PARTICULAR GEOGRAPHIC REGIONS ASSUMING THEY CAN BE VISUALLY DIF FERENTIATED IN THE lELD /NE OF THE PROBLEMS WITH USING EXISTING GENETIC VARIATION AS AN EXPLANATION FOR INVASIVE ABILITY IS THAT IT OFTEN REQUIRES WIDESPREAD AND INTENSIVE SAMPLING FROM BOTH THE NATIVE AND INTRODUCED RANGES 4HE MOST DElNITIVE WORK IN THE COM PARISON OF NATIVE AND INTRODUCED GENOTYPES IS WITH "ROMUS TECTORUM .OVAK AND -ACK .OVAK ET AL "ARTLETT ET AL "ROMUS TECTORUM IS A CLEIS TOGAMOUS PLANT WITH VARIOUS HOMOZYGOUS MULTILOCUS GENOTYPES REPEATED INTRO DUCTIONS OF DIFFERENT /LD 7ORLD GENOTYPES THAT HAVE INVADED .ORTH !MERICA HAVE RESULTED IN THE REDISTRIBUTION OF THE GENETIC DIVERSITY AVAILABLE IN THE NATIVE AREA OF THE SPECIES !LTHOUGH THE " TECTORUM WORK IS VERY THOROUGH FURTHER DATA COLLECTION IS NEEDED TO DETERMINE WHETHER PREDICTIONS CAN BE MADE ABOUT INVASIVE " TECTORUM GENOTYPES "ROAD TOLERANCES NEEDED FOR PHENOLOGY SEED SET DROUGHT AND FREEZING ARE FOUND IN " TECTORUM AND OBVIOUSLY THESE TRAITS HAVE SOME GENETIC BASIS &OR SPECIES LIKE " TECTORUM THAT HAVE REDUCED GENETIC VARIATION THE IDEAL MATCH BETWEEN INVADER CHARACTERISTICS AND NEW RANGE ENVIRONMENT MAY BE SIMPLY IDIOSYNCRATIC IE A GENOTYPE IS hPRE ADAPTEDv FOR THE NEW RANGE /N THE OTHER HAND MILLENIA OF SELECTIVE PROCESSES AND INBREEDING IN " TECTORUM MAY HAVE WORKED TOGETHER TO RESULT IN THE hIDEAL INVADERv 4HESE ARE THE hGENERAL PURPOSE GENOTYPESv OF "AKER GENOTYPES THAT CAN GROW IN A VARIETY OF DIFFERENT ENVIRON MENTS WITH NO NEED TO UNDERGO FURTHER SELECTION 7ILLIAMS 4HERE REMAINS A LACK OF CONSENSUS REGARDING THE RELATIONSHIP OF GENETIC VARI ABILITY TO THE INVASIVE ABILITY OF PLANTS IE SOME INVASIVE SPECIES MAINTAIN LOW LEVELS OF GENETIC VARIATION "AUMEL ET AL 9E ET AL WHEREAS OTHERS ARE HIGHLY VARIABLE "ARRETT AND 2ICHARDSON $ESPITE CONJECTURE ON THIS
%VOLUTION AND PLANT INVASIONS
MATTER SINCE "AKER AND 3TEBBINS EXPERIMENTAL EVIDENCE IN THIS AREA HAS BEEN SLOW TO ACCUMULATE ! NUMBER OF AUTHORS HAVE FOUND THAT INVASIVE SPECIES WITH LOW LEVELS OF GENETIC DIVERSITY OFTEN SHARE TRAITS SUCH AS INBREEDING OR AN ANNUAL LIFE HABIT WITH A SELF BREEDING SYSTEM "ROWN AND -ARSHALL 7ARWICK .OVAK AND -ACK 7ANG ET AL 3QUIRRELL ET AL "ARTLETT ET AL 4HESE CONCLUSIONS AS WITH MANY OTHER CONCLUSIONS ABOUT INVASIVE SPECIES HAVE EXCEPTIONS FOR EXAMPLE 6IOLA RIVINIANA COMMON DOG VIO LET IS A PRIMARILY CLONAL CLEISTOGAMOUS SPECIES WITH HIGH LEVELS OF GENETIC VARIA TION !UGE ET AL 'ROUPING SPECIES BY LIFE HISTORY TRAITS AND GEOGRAPHICAL RANGE HAS BEEN SUCCESS FUL IN DETECTING ASSOCIATION BETWEEN GENETIC DIVERSITY AND LIFE HISTORY CHARACTERIS TICS FOR PLANT SPECIES IN GENERAL (AMRICK ET AL ,OVELESS AND (AMRICK (AMRICK ET AL 4HUS IT MAYBE USEFUL TO lRST CATEGORIZE INVASIVE SPECIES BY LIFE HISTORY TRAITS AND THEN LOOK FOR PATTERNS IN GENETIC DIVERSITY 3CHIERENBECK ET AL (AMRICK ET AL FOUND THAT WEEDY AND EARLY SUCCESSIONAL SPECIES ARE LESS VARIABLE THAN SPECIES OF MID AND LATE SUCCESSIONAL STAGES ! RECENT STUDY WITH THE HERBACEOUS PERENNIAL !LTERNANTHERA PHILOXERIODES ALLIGATOR WEED A NATIVE OF 3OUTH !MERICA SUPPORTS THIS PATTERN #ONSIDERED ONE OF THE WORLDS WORST WEEDS ! PHILOXERIODES IS A PARTIALLY SUBMERGED AQUATIC WITH WIDESPREAD CLONAL PROPAGA TION AND VERY LOW GENETIC DIVERSITY THROUGHOUT SOUTHERN #HINA (4 8U ET AL !MONG LONG LIVED WOODY SPECIES FOR WHICH GENETIC VARIATION HAS BEEN MEA SURED CORRELATIONS BETWEEN LIFE HISTORY TRAITS AND GENETIC VARIATION ARE LESS CLEAR AND FOR MOST STUDIES ON INVASIVE WOODY ANGIOSPERMS GENETIC VARIATION IS REPORTED FOR THE HOME RANGE ONLY &OR EXAMPLE THERE ARE HOME RANGE STUDIES FOR 2OBINIA PSEUDOACACIA BLACK LOCUST 3URLES ET AL 0ROSOPIS GLANDULOSA HONEY MESQUITE 0ANEIDA AND #ARSTAIRS #ASUARINA CUNNINGHAMIANA RIVER SHE OAK -OORE AND -ORAN !CACIA MELANOXYLON BLACKWOOD WATTLE -ORAN ET AL !CACIA DECURRENS GREEN WATTLE -ORAN ET AL AND %UCALYPTUS OBLIQUA MESSMATE "ROWN ET AL AND ALL SHOW HIGHER LEVELS OF VARIATION THAN EXPECTED FOR SPECIES WITH SIMILAR LIFE HISTORY TRAITS 3CHIERENBECK ET AL !LL BUT ONE OF THESE SPECIES %UCALYPTUS OBLIQUA ARE NITROGEN lXERS AND IT SHOULD BE NOTED THAT THE TRAIT FOR NITROGEN lXATION IS WELL ASSOCIATED WITH ABIL ITY TO INVADE NEW RANGES RAPIDLY 6ITOUSEK ,ONICERA JAPONICA *APANESE HONEYSUCKLE AN INVASIVE WOODY VINE NATIVE TO !SIA AND INVASIVE THROUGHOUT WARM TEMPERATE AND TROPICAL CLIMATES WORLDWIDE HAS LEVELS OF VARIATION WITHIN THE RANGE EXPECTED FOR SPECIES WITH SIMILAR LIFE HISTORY TRAITS 3CHIERENBECK ET AL !N INVASIVE CLONAL VINE OF THE SOUTHEASTERN 53 0UERARIA LOBATA KUDZU HAS A HIGH LEVEL OF GENETIC VARIATION IN ITS INTRODUCED RANGE THAT IS SUGGESTIVE OF MULTIPLE INTRODUCTIONS %XCESS HETEROZYGOSITY IN INTRODUCED POPULATIONS OF 0 LOBATA ALSO SUGGESTS THAT SELECTION MAY BE ACT IN FAVOR OF HETEROZYGOUS INDI VIDUALS 0APPERT ET AL 2UBUS ALCEIFOLIUS GIANT BRAMBLE A SHRUB NATIVE TO SOUTHEAST !SIA HAS GREATER GENETIC VARIATION IN ITS HOME RANGE REDUCED VARIATION IN ITS NEW RANGE OF -ADAGASCAR AND A SINGLE INVASIVE GENOTYPE AS MEASURED BY
+! 3CHIERENBECK AND -, !ÕNOUCHE
!&,0S IN ITS NEW RANGE IN THE )NDIAN /CEAN !MSELLEM ET AL )N A MORE RECENT EXAMPLE $E7ALT FOUND #LIDEMIA HIRTA SOAPBUSH A SHRUB NATIVE TO #ENTRAL AND 3OUTH !MERICA AND INVASIVE IN (AWAII HAD LOW LEVELS OF GENETIC VARIATION IN BOTH THE INTRODUCED AND HOME RANGE 3URPRISINGLY TO OUR KNOWLEDGE THERE ARE NO MORE RECENT REVIEWS THAT EXAMINE THE RELATIONSHIP BETWEEN GENETIC VARIABILITY INVASIVENESS AND LIFE HISTORY TRAITS 2EGARDLESS OF THE EXPECTATIONS OF GENETIC VARIABILITY IN NATIVE OR INTRODUCED POPULATIONS EFFECTIVE STUDIES OF INTRASPECIlC GENETIC VARIATION REQUIRE THE USE OF A NUMBER OF GENES #OALESCENCE ANALYSES OF GENE GENEALOGIES ALLOW A DETERMINA TION OF THE GEOGRAPHIC ORIGINS OF INVASIVE GENOTYPES 'ASKIN AND 3CHAAL 3CHAAL ET AL AND THE EXPANSION OF GENOTYPES DURING INVASION CAN BE RETRACED THROUGH STAR LIKE PHYLOGENETIC PATTERNS THAT INDICATE RECENT AND RAPID POPULATION GROWTH 3LATKIN AND (UDSON !LTHOUGH HAPLOTYPE PHYLOG ENIES ARE USEFUL IN THE RECONSTRUCTION OF HISTORICAL AND RECENT GENE mOW PATTERNS THE ANALYTICAL TECHNIQUES FOR THE DETERMINATION OF HISTORICAL GENE mOW PATTERNS HAVE ONLY RECENTLY BECOME AVAILABLE 4EMPLETON #OMPLICATIONS CAN ARISE HOWEVER IN HYBRID LINEAGES THAT FORM NEW RECOMBINING COASLESCENT COMPLEXES 1UANTITATIVE 'ENETICS
4HE LONG TERM CONJECTURE THAT CERTAIN TRAITS ARE ASSOCIATED WITH INVASIVENESS "AKER "AZZAZ IS NOW SUPPORTED BY EXPERIMENTAL EVIDENCE FOR THE GENETIC BASIS OF PHENOLOGY IN #APSELLA BURSA PASTORIS SHEPARDS PURSE .EUFFER AND (URKA 3OLIDAGO ALTISSIMA TALL GOLDENROD 3 GIGANTEA LATE GOLDENROD 7EBER AND 3CHMID HIGH RELATIVE GROWTH RATES AND EARLY REPRODUCTION FOR 0INUS PINE SPP 2EJMANEK AND 2ICHARDSON 'ROTKOPP ET AL AND TRADE OFFS BETWEEN HERBIVORE DEFENSE AND lTNESS 3TRAUSS ET AL 0ARKER ET AL CONCLUDED BASED ON MEASURED GROWTH RATES FREEZING TOLERANCE AND GROWTH HABITS THAT THE INVASIVENESS OF 6ERBASCUM THAPSUS MULLEIN IS MORE LIKELY DUE TO A GENERAL PURPOSE GENOTYPE THAT IS INmUENCED MORE BY ENVIRONMENTAL CONDITIONS THAN BY HERITABLE FACTORS ! SMALL NUMBER OF QUANTITATIVE GENETIC STUDIES OF NATIVE AND INTRODUCED GENOTYPES HAVE FOUND POST COLONIZATION EVOLUTION OF GENETIC TRAITS &OR EXAMPLE IN 3APIUM SEBIFERUM INTRODUCED POPULATIONS HAD A GREATER SEED SET THAN NATIVE POPULATIONS BUT LESS PROTECTION FROM HERBIVORY 3IEMANN AND 2OGERS ,EGER AND 2ICE FOUND SELECTION WITHIN YEARS FOR GENETICALLY BASED GROWTH AND REPRODUCTIVE TRAITS IN GENOTYPES OF THE #ALIFORNIA NATIVE %SCHSCHOLZIA CALIFOR NICA #ALIFORNIA POPPY INVASIVE IN #HILE ,EE SUGGESTS INVASIVE ABILITY MAY BE MORE OF REmECTION OF ABILITY TO RESPOND TO SELECTION THAN TO PHENOTYPIC PLASTICITY BUT THIS LEADS US BACK TO THE QUESTION OF WHETHER INVASIVE SPECIES ARE BORN OR MADE AND DElNITIVE DATA WITH WHICH TO ANSWER THIS QUESTION SIMPLY DO NOT EXIST
%VOLUTION AND PLANT INVASIONS
2APID EVOLUTION RESULTING FROM ADAPTIVE RADIATION
!DAPTIVE RADIATION IN THE CLASSICAL SENSE IS THE COLONIZATION AND SUBSEQUENT DIVERSIlCATION OF SPECIES FROM A COMMON ANCESTOR INTO NEW HABITATS 4HE PROCESS OF ADAPTIVE RADIATION IN PART INSPIRED $ARWINS THEORY OF NATURAL SELECTION AND HAS BEEN SUPPORTED EMPIRICALLY FOR AT LEAST FOUR DECADES AT MANY SPATIAL AND TEM PORAL SCALES 4HE RECENT SPREAD RADIATION AND EVOLUTION OF INVASIVE SPECIES LIKELY FOLLOWS SIMILAR PROCESSES OF ADAPTIVE RADIATION 1UESTIONS REMAIN HOWEVER ABOUT THE RAPIDITY AND SPATIAL SCALE WITH WHICH THIS PROCESS CAN OCCUR #AN FRAGMENTED DISTURBED LANDSCAPES DEVOID OR PARTIALLY DEVOID OF NATIVE BIOTA BE CONSIDERED ISLAND SITUATIONS AND RECEPTACLES FOR ADAPTIVE RADIATION 7E KNOW VIRTUALLY NOTHING ABOUT WHAT EVOLUTIONARY PROCESSES WILL OCCUR IN SITUATIONS IN WHICH SPECIES FROM REMOTE AREAS OF THE GLOBE ARE BROUGHT TOGETHER INTO A NEW HABITAT 4HE HUMAN MEDIATED MIGRATION OF PROPAGULES IS NOT UNLIKE NON HUMAN MEDIATED DISPERSAL ALTHOUGH ON A DIFFERENT TEMPORAL SCALE 2EZNICK AND 'HALAMBOR REVIEWED STUDIES TO CONCLUDE THAT THE RAPID EVOLUTION FOLLOWING COLONIZATION OF NEW HABITATS IS PROMOTED BY NEW ECOLOGICAL CONDITIONS .OVEL ECOLOGICAL CONDITIONS IN THEIR STUDY INCLUDED NEW FOOD RESOURCES BIOTIC OR ABIOTIC INTERACTIONS PREDATORS AND COMPETITORS 3PECIES POOR COMMUNITIES THAT SUBSEQUENTLY BECAME VESSELS FOR RAPID EVOLUTIONARY CHANGE OFTEN WERE A RESULT OF ANTHROPOGENIC DISTURBANCE 2EZNICK AND 'HALAMBOR 7E KNOW OF NO WORK WHICH HAS EXAMINED THE RAPID EVOLUTIONARY CONSEQUENCES OF DISPERSAL OF A SINGLE PLANT SPECIES INTO A RANGE OF NEW AND DIFFERENT HABITATS ALTHOUGH THERE ARE SOME ANIMAL EXAMPLES (UEY ET AL ,OSOS ET AL 7E PRIMARILY CAN DRAW FROM EXAMPLES WHICH ILLUS TRATE THE RAPIDITY WITH WHICH EVOLUTION CAN OCCUR FOLLOWING ADAPTIVE RADIATION #LASSIC EXAMPLES OF ADAPTIVE RADIATION IN ISLAND HABITATS ARE NOT ONLY EXAMPLES OF RAPID EVOLUTIONARY CHANGE BUT PROVIDE IDEAL OPPORTUNITIES TO STUDY THE GENET ICS AND ECOLOGY OF INVASIONS !N EXAMPLE OF VERY EFFECTIVE COLONIZATION INTO NEW UNOCCUPIED HABITATS HAS BEEN WELL SUPPORTED IN THE MAGNIlCENT DIVERSIlCATION OF THE (AWAIIAN SILVERSWORD ALLIANCE OVER THE LAST MILLION YEARS "ARRIER ET AL "ARRIER ET AL #OMPARISIONS OF MUTATION RATES BETWEEN GENES IMPORTANT IN THE REGULATION OF mORAL AND INmORESCENCE DEVELOPMENT AND NON REGULATORY GENES IN THE (AWAIIAN SILVERSWORD ALLIANCE PROVIDE EVIDENCE THAT ADAPTIVE RADIATION MAY BE MORE CORRELATED WITH VARIATION IN REGULATORY LOCI "ARRIER ET AL 2ETICULATE GENE mOW CAN FACILITATE ADAPTIVE RADIATION VIA NEW GENE COMBINA TIONS 3EEHAUSEN )F RETICULATE GENE mOW IS IMPORTANT IN THE SPREAD OF COLONIZING SPECIES ANY GENE mOW NEEDS TO OCCUR PRIOR TO THE SPREAD BUT THERE COULD BE REPEATED OPPORTUNITIES FOR THIS TO HAPPEN THROUGH REPEATED INTRODUC TIONS 3UPPORT OF HYPOTHESES FOR RAPID ADAPTIVE RADIATION REQUIRES VARIATION AT FUNCTION LOCI AND MULTIPLE hOPPORTUNITIESv FOR ADAPTIVE DIVERGENCE WITH REPEATED INTRODUCTIONS 3EEHAUSEN 4HUS A COMBINATION OF REPEATED INTRODUCTIONS NEW GENE COMBINATIONS AND UNOCCUPIED OR PARTIALLY lLLED NICHES RESULT CREATE A VULNERABILITY TO INVASION FROM PREVIOUSLY UNSEEN GENOTYPES 4HE HUMAN MEDIATED ADAPTIVE RADIATION OF PLANT SPECIES INTO NEW HABITATS PROVIDES AN IDEAL
+! 3CHIERENBECK AND -, !ÕNOUCHE
SITUATION FOR THE EXPERIMENTAL STUDY OF HUMAN INDUCED EVOLUTIONARY CHANGE (OWEVER HIGH RATES OF HUMAN FACILITATED PLANT DISPERSAL MAY ALSO PREVENT OR SLOW RADIATION BY PROMOTING GENE mOW AND PANMIXIS (YBRIDIZATION
4HE PREVALENCE OF RETICULATE EVOLUTION THAT IS THE MERGING OF DIVERGENT GENOMES THROUGH INTERSPECIlC GENE mOW IS KNOWN AS AN IMPORTANT EVOLUTIONARY FORCE IN PLANTS !NDERSON AND 3TEBBINS 4HE USE OF MOLECULAR MARKERS HAS GREATLY HELPED TO DOCUMENT ORIGINS AND OCCURRENCE OF HYBRID LINEAGES AND THE GENETIC CONSEQUENCES OF INTROGRESSIVE HYBRIDIZATION 2IESEBERG !RNOLD -OLECULAR PHYLOGENETIC APPROACHES THAT COMBINE MULTIPLE SEQUENCE DATA SETS HAVE ALLOWED THE DETECTION OF ANCIENT INTROGRESSION EVENTS AND REVEAL THAT RETICULATION IS EVEN MORE FREQUENT THAN PREVIOUSLY THOUGHT EG $OYLE ET AL #RONN AND 7ENDEL 3MALL ET AL (YBRIDIZATION IS RELATED TO INVASION IN TWO WAYS &IRST INTRODUCED INVASIVE PLANTS MAY HYBRIDIZE WITH NATIVE SPECIES AND GIVE RISE TO NEW SUCCESSFUL AND RAPIDLY EXPANDING TAXA !BBOTT !BBOTT ET AL 3ECOND HYBRIDIZATION BETWEEN NON INVASIVE SPECIES CAN RESULT IN NEW AGGRESSIVE HYBRIDS THAT COMPETE WITH THE PARENTS AND INVADE NEW HABITATS 2IESEBERG AND 7ENDEL 'ENETIC INTROGRESSION BETWEEN INVASIVE SPECIES AND CLOSELY RELATED NATIVES MAY HAVE CRITI CAL AND RAPID EVOLUTIONARY CONSEQUENCES (UXEL 4HE SALTMARSH SPECIES 3PARTINA ALTERNImORA WAS DELIBERATELY INTRODUCED FROM THE !TLANTIC !MERICAN COAST TO #ALIFORNIA WHERE IT HYBRIDIZED WITH THE NATIVE 3 FOLIOSA $AEHLER AND 3TRONG (YBRIDIZATION WAS SHOWN TO OCCUR IN BOTH DIRECTIONS ALTHOUGH THE INTRO DUCED SPECIES HAS HIGHER MALE lTNESS !NTILLA ET AL 2ATHER THAN SUFFERING FROM COMPETITION WITH 3 ALTERNImORA 3 FOLIOSA IS NOW THREATENED BY INTROGRESSANT HYBRIDS THAT RESULT FROM RECURRENT BACKROSSES AND THAT THREATEN THE GENETIC INTEG RITY OF THE NATIVE SPECIES !YRES ET AL 0OLLEN SWAMPING IS ALSO THOUGHT TO HAVE REPRESENTED AN IMPORTANT MECHANISM ALLOWING HYBRIDIZATION AND INVASION IN OAKS 0ETIT ET AL (UMAN ACTIVITIES HAVE INCREASED ECOLOGICALLY DISTURBED AREAS BRINGING TOGETH ER PREVIOUSLY ISOLATED TAXA AND GENERATING OPEN ARRAYS OF NICHES THAT ARE BET TER SUITED TO HYBRIDS THAN TO THEIR PARENTS %LLSTRAND AND 3CHIERENBECK (YBRIDS DO WELL IN DISTURBED HABITAT !NDERSON AND INVASIVE SPECIES ARE EMPIRICALLY ASSOCIATED WITH DISTURBED ECOSYSTEMS 6ITOUSEK 4HIS IS PAR TICULARLY WELL ILLUSTRATED IN THE TWO CLASSICAL EXAMPLES OF INTROGRESSIVE HYBRIDIZA TION AND HYBRID SPECIATION IN THE ,OUISIANA IRISES !NDERSON !RNOLD AND IN (ELIANTHUS SPECIES SUNmOWERS 2IESEBERG ET AL (YBRIDIZATION AND INTROGRESSION BETWEEN )RIS HEXAGONA AND )RIS FULVA OCCUR PRIMARILY IN DISTURBED AREAS THAT ALLOW SYMPATRY BETWEEN THE PARENTAL SPECIES (YBRID GENOTYPES DIS PLAY VARIOUS COMBINATIONS OF PARENTAL ECOLOGICAL TRAITS SUCH AS SHADE TOLERANCE THAT CONFER DIFFERENT lTNESSES ACROSS DIFFERENT ENVIRONMENTS !RNOLD AND REFERENCES THEREIN 3TUDIES ON THE )RIS FULVA X ) BREVICAULIS COMPLEX HAVE ALSO
%VOLUTION AND PLANT INVASIONS
DEMONSTRATED THE IMPORTANCE OF CONSIDERING ALL LIFE STAGES IN EXPERIMENTATION TO UNDERSTAND HYBRID EVOLUTION *OHNSTON ET AL (ELIANTHUS IS A GENUS PARTICULARLY AFFECTED BY RETICULATE EVOLUTION INVOLVING INTROGRESSIVE HYBRIDIZA TION AND HOMOPLOID HYBRID SPECIATION AS ILLUSTRATED BY ( ANNUUS AND ( DEBILIS +IM AND 2IESEBERG !DDITIONALLY HYBRIDIZATION BETWEEN ( ANNUUS AND ( PETIOLARIS GAVE RISE TO THREE HOMOPLOID HYBRID SPECIES ( ANOMALUS ( DESERTI COLA ( PARADOXUS THESE STABLE NEW LINEAGES DIPLAY NOVEL ECOLOGICAL ADAPTATIONS 4RANSGRESSIVE SEGREGATION HAS RESULTED IN EXTREME PHENOTYPES IN THESE (ELIANTHUS SPECIES AND IS THOUGHT TO BE THE KEY FOR THEIR ABILITY TO INVADE NOVEL HABITATS 2IESEBERG ET AL e.g., AS DEMONSTRATED WITH SALT ADAPTATION IN THE HYBRID SPECIES ( PARADOXUS ,EXER ET AL 4HERE ARE NOW MANY EXAMPLES IN WHICH HYBRID GENOTYPES ARE MORE lT THAN ONE OR BOTH OF THE PARENTAL GENOTYPES "URKE AND !RNOLD %LLSTRAND AND 3CHIERENBECK FOUND EXAMPLES IN WHICH THE OCCURRENCE OF NEW INVASIVE TAXA NESS WAS PRECEDED BY HYBRIDIZATION AND FOR WHICH THERE WAS STRONG MOLECU LAR EVIDENCE 'ASKIN AND 3CHAAL PROVIDE BOTH NUCLEAR AND CP$.! EVI DENCE THAT THE MOST COMMON INVASIVE HAPLOTYPES OF THE VORACIOUS 4AMARIX IN THE 53 ARE POST INTRODUCTION HYBRID COMBINATIONS BETWEEN PRIMARILY 4 RAMOSISSIMA AND 4 CHINENSIS WITH SOME ADDITIONAL GENE mOW FROM 4 PARVImORA AND 4 GALLICA "IRCHLER ET AL SUGGEST THAT REGULATORY GENE ALLELIC INTERACTION IN HYBRID GENOTYPES MIGHT ACCOUNT FOR THE WELL KNOWN HETEROSIS EFFECT IE HYBRID HETEROZY GOSITY RESULTS IN GREATER VIGOR BIOMASS SPEED OF DEVELOPMENT AND FERTILITY THAN IN THE PARENTAL GENOTYPES &OR INSTANCE UPREGULATION OF HOUSEKEEPING GENES MAY CAUSE GENE EXPRESSION THAT IS DIFFERENT IN HYBRIDS THAN THE MIDPARENT PREDICTIONS &UTURE STUDIES LINKING PHENOTYPIC CHANGES AND INVESTIGATIONS AT THE GENOME LEVEL SHOULD PROVIDE NEW INSIGHTS INTO MOLECULAR MECHANISMS THAT ARE INVOLVED IN THE ADAPTIVE SUCCESS OF HYBRID LINEAGES 4HERE IS NOW LITTLE DOUBT THAT HYBRIDIZATION IS AN IMPORTANT EVOLUTIONARY MECHANISM IN PLANTS AND THE CONCERN WITH HYBRIDIZATION IN INVASIVE SPECIES IS NOT WHETHER IT CAN HAPPEN BUT THE SPEED WITH WHICH HUMANS ACCELERATE THIS EVOLUTIONARY PROCESS (OMOGENIZATION IS A PROCESS THAT IS OCCURRING NOT ONLY AT THE COMMUNITY LEVEL BUT ALSO AT THE GENETIC LEVEL WITHIN TAXA /LDEN ET AL ,OCALLY ADAPTED GENOTYPES ARE BECOMING LOST THROUGH HOMOGENIZATION AND INVA SION OF DOMINANTS 0OLYPLOIDY
0OLYPLOIDY RESULTING FROM WHOLE GENOME DUPLICATION IS A WIDESPREAD EVOLUTION ARY PHENOMENON AND A COMMON SPECIATION MECHANISM IN PLANTS 3TEBBINS ,EWIS 'RANT /NE OF THE MOST CONSPICUOUS CONTRIBUTIONS THAT HAS RESULTED FROM THE DEVELOPMENT OF RECENT GENOMIC APPROACHES IS THE AWARENESS OF THE PREVALENCE OF POLYPLOIDY IN MOST EUKARYOTIC LINEAGES EG 7OLFE "LANC ET AL 4HIS HAS CONTRIBUTED TO A RENEWED INTEREST IN THE EVOLUTIONARY SUCCESS AND POTENTIAL SELECTIVE ADVANTAGE OF GENOME DUPLICATION /TTO AND 7HITTON
+! 3CHIERENBECK AND -, !ÕNOUCHE
-ANY POLYPLOID SPECIES ARE WELL ADAPTED SUCCESSFUL WEEDY SPECIES WHICH REIN FORCES THE IDEA THAT POLYPLOIDY MAY HAVE PREDISPOSED SPECIES TO BECOME INVADERS "ROWN AND -ARSHALL "ARRETT AND 2ICHARDSON )NTERESTINGLY NEWLY FORMED POLYPLOIDS ARE FREQUENTLY INVASIVE SPECIES WHICH SUGGESTS THAT POLYPLOIDY CONFERS AN IMMEDIATE ECOLOGICAL APTITUDE TO INVADE NEW HABITATS )NVASIVE SPECIES OF RECENT ORIGIN ARE EXCELLENT MODEL SYSTEMS TO INVESTIGATE THE EARLY EVOLUTIONARY MECHANISMS ASSOCIATED WITH INVASIVENESS AND PROVIDE THE UNIQUE OPPORTUNITY TO COMPARE THE NEW LINEAGE TO ITS PARENTS THAT ARE GENERALLY IDENTIlED AND STILL EXTANT 4HE ALLOPOLYPLOIDS 3PARTINA ANGLICA CORDGRASS !ÕNOUCHE ET AL A 4RAGOPOGON MIRUS AND 4 MISCELLUS GOATSBEARD 3OLTIS ET AL 3ENECIO CAMB RENSIS 7ELSH RAGWORT AND 3 EBORACENCIS !BBOTT AND ,OWE AND #ARDAMINE SCHULZII BITTERCRESS 5RBANSKA ET AL FORMED DURING THE LAST YEARS HAVE WELL DOCUMENTED ORIGINS HAVE SPREAD RAPIDLY AND DISPLAY A LARGER ECOLOGI CAL AMPLITUDE THAN THEIR PROGENITORS 4HESE SPECIES ARE EITHER PERENNIALS OR ANNU ALS BIENNIALS AND DISPLAY VARIOUS BREEDING OR POLLINATION SYSTEMS 'ENOME DUPLICATION MAY HAVE DIFFERENT IMPACTS ON FERTILITY AND MODES OF INHER ITANCE THAT IS DEPENDENT ON CHROMOSOME BEHAVIOR AND GENETIC SEGREGATION )T IS GENERALLY PREDICTED THAT DUPLICATION OF THE SAME GENOME WITHIN SPECIES IE STRICT AUTOPOLYPLOIDY WILL RESULT IN RANDOM PAIRING POLYSOMIC INHERITANCE AT DUPLI CATED LOCI IRREGULAR MEIOSIS AND THUS LIMITED FERTILITY WHEREAS THE DUPLICATION OF MORE DIFFERENTIATED HOMOEOLOGOUS GENOMES IE ALLOPOLYPLOIDY WILL RESULT IN PREFERENTIAL CHROMOSOME PAIRING BIVALENTS REGULAR MEIOSIS HIGH FERTILITY AND DISOMIC INHERITANCE $A 3ILVA AND 3OBRAL )N FACT AUTOPOLYPLOIDS AND ALLO POLYPLOIDS OCCUR ON A CONTINUUM IN NATURE AS THE ONGOING EVOLUTIONARY PROCESS RESULTS IN MORE OR LESS DIVERGENT PARENTAL POPULATIONS OF THE POLYPLOID 3TEBBINS 7ENDEL AND $OYLE -OREOVER CHROMOSOME PAIRING MAY BE AFFECTED BY VARIOUS GENETIC AND GENOMIC FACTORS AND VARY WITH THE AGE OF THE POLYPLOID IT IS THEN RECOMMENDED TO DISTINGUISH BETWEEN THE MODE OF FORMATION OF A POLYPLOID SPECIES AND ITS MODE OF CHROMOSOMAL SEGREGATION /TTO AND 7HITTON 2ECENT RESEARCH HAS RESULTED IN A PARTICULARLY DYNAMIC VISION OF POLYPLOID GENOMES OVER BOTH A SHORT AND LONG TERM EVOLUTIONARY TIME SCALE 7ENDEL 3OLTIS AND 3OLTIS 4HE DEVELOPMENT OF MOLECULAR MARKERS AND PARTICULARLY THE COMBINED USE OF MATERNALLY INHERITED CYTOPLASMIC MARKERS WITH BIPARENTALLY INHERITED NUCLEAR MARKERS HAS ALLOWED THE DETECTION OF MULTIPLE AND RECURRENT ORIGINS OF POLYPLOID SPECIES 3OLTIS AND 3OLTIS !S MULTIPLE SEQUENCE DATAS ETS ARE NOW AVAILABLE FOR PHYLOGENETIC ANALYSES IT IS POSSIBLE TO DETECT RECURRENT AND BI DIRECTIONAL RETICULATE EVOLUTION EVEN IN OLD POLYPLOID LINEAGES EG 'LYCINE $OYLE ET AL WHERE THEY OTHERWISE WOULD HAVE BEEN UNDETECTED 4HE PROCESS OF RECURRENT POLYPLOID FORMATION WITH RETICULATE GENE mOW MAY IN VOLVE VARIOUS PARENTAL GENOTYPES AND INCREASES THE LEVEL OF GENETIC DIVERSITY AVAILABLE TO NEWLY FORMED SPECIES 3CHIERENBECK ET AL &OR INSTANCE AT LEAST LINEAGES OF SEPARATE ORIGINS FOR THE ALLOTETRAPLOID 4RAGOPOGON MISCELLUS AND FOR 4 MIRUS HAVE BEEN DOCUMENTED IN THE 0ALOUSE ACCORDING TO VARIOUS MORPHOLOGICAL AND MOLECULAR ALLOZYMES CHLOROPLAST AND NUCLEAR $.! LINES OF
%VOLUTION AND PLANT INVASIONS
EVIDENCE REVIEWED IN 3OLTIS ET AL THESE RECURRENT ORIGINS INVOLVE EITHER ONLY ONE DIPLOID SPECIES AS THE MATERNAL PARENT EG 4 PORRIFOLIUS FOR THE ALLO TETRAPLOID 4 MIRUS OR ALTERNATIVELY BOTH THE PARENTAL SPECIES 4 PORRIFOLIUS AND 4 DUBIUS IN RECIPROCAL CROSSES E.g. FOR THE ALLOTETRAPLOID 4 MISCELLUS 4HIS HAS RESULTED IN VARIOUS GENOTYPES AND DRAMATIC mORAL DIFFERENCES IN THE ALLOPOLYPLOID POPULATIONS THAT ARE PROGRESSIVELY REPLACING DIPLOIDS AS PREVALENT WEEDS 3OLTIS ET AL 3IMILARLY TWO SEPARATE ORIGINS HAVE BEEN DOCUMENTED IN .ORTH 7ALES AND 3COTLAND FOR THE RUDERAL ALLOHEXAPLOID 3ENECIO CAMBRENSIS THAT ORIGINATED IN "RITAIN DURING THE PAST YEARS REVIEWED IN !BBOTT AND ,OWE /NE OF THE MOST COMPLEX EXAMPLES OF MULTIPLE ALLOPOLYPLOID ORIGINS IS REPRESENTED BY THE POLYPLOID AGAMIC COMPLEX !NTENNARIA ROSEA PUSSYTOES THAT HAS FORMED FROM MULTIPLE CROSSES INVOLVING VARIOUS DIPLOID TAXA OCCURRING IN SPECIlC HABITATS OF THE 2OCKY -OUNTAINS "AYER 4HE POLYPLOID LINEAGES OF THIS hCOMPILOSPECIESv ARE GAMETOPHYTIC APOMICTS THAT DISPLAY LARGER ECOLOGICAL AMPLITUDE THAN THEIR DIPLOID PROGENITORS .OT ALL SUCCESSFUL ALLOPOLYPLOIDS HAVE MULTIPLE ORIGINS )N CONTRAST TO 4RAGOPOGON SPP 3ENCECIO CAMBRENSIS AND !NTENNARIA ROSEA THE INVASIVE SALTMARSH SPECIES 3PARTINA ANGLICA HAS UNDERGONE A SEVERE GENETIC BOTTLENECK AT THE TIME OF ITS FORMATION IN THE "AY OF 3OUTHAMPTON 5+ 4HIS DODECAPLOID SPECIES FORMED AFTER CHROMOSOME DOUBLING OF THE lRST GENERATION HYBRID 3PARTINA X TOWNSENDII THAT HAS RESULTED FROM HYBRIDIZATION BETWEEN THE INTRODUCED %AST !MERICAN HEXA PLOID 3PARTINA ALTERNImORA AND THE NATIVE HEXAPLOID 3PARTINA MARITIMA 2AYBOULD ET AL "OTH PARENTAL SPECIES LACK GENETIC DIVERSITY IN THE HYBRIDIZATION SITE A LIMITED NUMBER OF 3 ALTERNImORA GENOTYPES HAVE BEEN INTRODUCED IN 7ESTERN %UROPE "AUMEL ET AL WHEREAS A STRIKING LACK OF MOLECULAR VARIATION IS ENCOUNTERED IN POPULATIONS OF THE NATIVE 3 MARITIMA 9ANNIC ET AL %UROPEAN POPULATIONS OF 3 ANGLICA ARE MOSTLY COMPOSED OF ONE MAJOR MULTILO CUS GENOTYPE THAT HAS FORMED IN 3OUTHAMPTON AND THAT IS IDENTICAL TO THE lRST GENERATION HYBRID 3 X TOWNSENDII "AUMEL ET AL A #HLOROPLAST $.! ANALYSIS HAS REVEALED ALL POPULATIONS OF 3 ANGLICA IN WESTERN %UROPE DISPLAY IDEN TICAL PLASTOME TO 3 ALTERNImORA WHICH IS THEN CONSIDERED AS THE MATERNAL GENOME DONOR &ERRIS ET AL "AUMEL ET AL 3PARTINA ANGLICA HAS RAPIDLY INVADED THE "RITISH SALTMARSHES SINCE ITS FORMATION 4HOMPSON AND IT HAS BEEN NATURALLY OR DELIBERATELY INTRODUCED IN VARIOUS CONTINENTS SUCH AS #HINA OR !USTRALIA WHERE IT IS NOW CONSIDERED AS A SERIOUS THREAT TO NATIVE mORA AND FAUNA !ÕNOUCHE ET AL A AND REFERENCES THEREIN !LTHOUGH IT HAS LIMITED INTER INDI VIDUAL GENETIC DIVERSITY 3 ANGLICA CONTAINS TWO WELL DIFFERENTIATED HOMOELOGOUS GENOMES INHERITED FROM ITS HEXAPLOID PARENTS WHICH PROVIDES lXED HETEROZYGOS ITY AT HOMOEOLOGOUS LOCI "AUMEL ET AL B !ÕNOUCHE ET AL B 3PARTINA IS AN IDEAL SYSTEM IN WHICH TO EXPLORE THE GENETIC AND GENOMIC CONSEQUENCES OF HYBRIDIZATION AND GENE DUPLICATION IN SUCCESSFUL INVASIVE SPECIES ALTHOUGH PREVIOUS ATTEMPTS OF RE SYNTHESIZING EXPERIMENTALLY THE ALLOPOLYPLOID HAVE FAILED TIME SINCE SPECIES FORMATION AND THE PARENTAL SPECIES ARE KNOWN IT IS POS SIBLE TO DIFFERENTIATE BETWEEN THE EFFECTS OF HYBRIDIZATION IN 3 X TOWNSENDII AND
+! 3CHIERENBECK AND -, !ÕNOUCHE
GENOME DUPLICATION IN 3 ANGLICA POPULATIONS MOREOVER TWO NATURAL REPLICATES OF HYBRIDIZATION EVENTS BETWEEN 3 MARTIMA AND 3 ALTERNImORA ARE AVAILABLE IN 3 X TOWSENDII AND 3 X NEYRAUTII ANOTHER HYBRID THAT HAS FORMED AT THE SAME PERIOD IN SOUTHEWEST &RANCE WITH NO GENOME DOUBLING "AUMEL ET AL 4HE IMMEDIATE CONSEQUENCE OF POLYPLOIDY IS A GREATER INTRA INDIVIDUAL GENETIC DIVERSITY AND HETEROZYGOSITY AT DUPLICATED LOCI THAN IN DIPLOIDS THAT RESULTS IN INCREASED BIOCHEMICAL DIVERSITY 2OOSE AND 'OTTLIEB AND CONFERS A GREATER TOLERANCE TO ENVIRONMENT VARIATION AND MAY PROMOTE SUCCESSFUL COLONIZATION "ROWN AND -ARSHALL 'ENE DUPLICATIONS RESULTING FROM POLYPLOIDY ARE ALSO BELIEVED TO HAVE A BUFFERING EFFECT AGAINST DELETERIOUS MUTATIONS /HNO ,YNCH AND #ONERY ,AWTON 2AUH !DDITIONALLY POLYPLOIDS OF HYBRID ORIGIN ALLOPOLYPLOIDS MAY BENElT FROM HIGHER lTNESS DUE TO HETEROSIS 3IMILARLY TRAITS WHICH RESULT IN THE hGIGASv EFFECT OR A GENERAL INCREASE IN MORPHOLOGICAL CHARACTERISTICS DE 6RIES ARE ASSOCIATED WITH BOTH POLYPLOIDY AND INVA SIVE PLANT SPECIES "AKER 2IESEBERG ET AL (YPERICUM PERFORATUM 3T *OHNS WORT A TETRAPLOID THOUGHT TO BE OF ALLOPOLYPLOID ORIGIN HAS HIGH REPRO DUCTIVE PLASTICITY -ATZKE ET AL BUT REPRODUCES MOST COMMONLY VIA FACULTA TIVE APOMIXIS &IELD COLLECTIONS OF ( PERFORATUM IN !USTRALIA FOUND A LACK OF WITHIN POPULATION VARIATION -AYO AND ,ANGRIDGE BUT HIGH INTERPOPULATIONAL GENETIC DIVERSITY (YPERICUM PERFORATUM HAS HIGH LEVELS OF HYPERICIN A CHEMICAL THAT CAUSES PHOTOSENSITIZATION AND REDUCED HERBIVORY THAT ARE HYPOTHESIZED TO BE A DIRECT RESULT OF ALLOPOLYPLOIDIZATION -AYO AND ,ANGRIDGE )NTRODUCED INTO .ORTH !MERICAN IN THE S THE ALLOPOLYPLOID AND NEARLY MONOMORPHIC 3ETARIA FABERI GIANT FOXTAIL IS NOW PRESENT THROUGHOUT THE DISTURBED AREAS ON THE CONTINENT 0OHL (AmIGER AND 3CHOLZ $EKKER NAMED THE ALLOPOLYPLOIZATION OF 3 FABERI THE hWEED SPECIATION EVENTv AS THE POLYPLOID HAS HIGHER lTNESS IN AGRICULTURAL SYSTEMS THAN ITS DIPLOID ANCESTORS /NE OF THE WORLDS WORST WEEDS IS THE POLYPLOID 3ORGHUM HALEPENSE *OHNSON GRASS A PRODUCT OF HYBRIDIZATION BETWEEN THE CULTIVAR 3 BICOLOR AND THE WILD 3 PROPIN QUUM AND WHICH RESPONDS WELL TO CULTIVATION AND IS EXTREMELY PERNICIOUS TO DUE THE RHIZOMATOUS GROWTH HABIT 0ATERSON ! GROWING BODY OF EVIDENCE CONTINUES TO ACCUMULATE IN REGARD TO THE DYNAMIC AND PLASTIC NATURE OF POLYPLOID GENOMES THAT WOULD EXPLAIN THEIR EVOLUTIONARY SUCCESS !LLOPOLYPLOID GENOMES ARE PARTICULARLY DYNAMIC AT BOTH THE STRUCTURAL AND EXPRESSION LEVELS OVER THE LONG AND ALSO SHORT TERM EVOLUTIONARY TIME SCALE REVIEWED IN 7ENDEL ,IU AND 7ENDEL /SBORN ET AL 3IGNIlCANT ADVANCES IN REVEALING THE OCCURRENCE AND NATURE OF THE EARLY EVOLUTIONARY CHANGES IN POLYPLOID GENOMES ARE POSSIBLE DUE TO EXPERIMENTALLY RESYNTHESIZED ALLOPOLYPLOIDS INVOLVING WELL KNOWN MODEL SYSTEMS SUCH AS "RASSICA OILSEED RAPE !RABIDOPSIS 'OSSYPIUM COTTON OR 4RITICUM !EGILOPS WHEAT 4HESE MODEL SYSTEMS ALLOW THE EXPLORATION OF ALLOPOLYPLOID MATERIAL OF KNOWN ORIGIN WITH THE COMPARISON OF THEIR ACTUAL PARENTAL GENOTYPES A CONDITION RARELY MET FOR MOST NAT URAL ALLOPOLYPLOIDS 2APID AND BIASED STRUCTURAL CHANGES HAVE BEEN ENCOUNTERED IN THE lRST GENERATIONS FOLLOWING POLYPLOIDIZATION IN "RASSICA 3ONG ET AL
%VOLUTION AND PLANT INVASIONS
AND WHEAT &ELDMAN ET AL ,IU ET AL A B /ZKAN ET AL (OWEVER ,IU ET AL DID NOT lND CONSISTENT STRUCTURAL CHANGES IN NEWLY SYNTHESIZED ALLOPOLYPLOID 'OSSYPIUM 6ARIOUS EVOLUTIONARY MECHANISMS APPEAR TO AFFECT ALLOPOLYPLOID GENOMES OVER A LONGER TERM AND INCLUDE THE INDEPENDENT EVOLUTION OF DUPLICATED GENES IN ALLOTETRAPLOID COTTON THAT FORMED ONE TO TWO MILLION YEARS AGO #RONN ET AL 3ENCHINA ET AL INTERACTION BETWEEN THE HOMOELOGOUS SUBGENOMES FOR REPETITIVE SEQUENCES VIA CONCERTED EVOLUTION e.g., 'OSSYPIUM 7ENDEL ET AL .ICOTIANA TOBACCO 6OLKOV OR SPREAD OF TRANSPOSABLE ELEMENTS :HAO ET AL 4HE FATE OF DUPLICATED HOMOEOLOGOUS GENES HAS BEEN PARTICULARLY WELL INVESTIGATED IN THE 'OSSYPIUM SYSTEM BY *ONATHAN 7ENDEL AND HIS COLLEAGUES EG !$( GENES 3MALL AND 7ENDEL -9" GENES #EDRONI ET AL AND REVEALS VARIOUS EVOLUTIONARY PATTERNS INCLUDING COPY NUMBER LABILITY PSEUDOGENIZATION GENE ELIMINATION OR ACCELERAT ED RATE OF NUCLEOTIDE SUBSTITUTION EG FOR !$( # GENES (OWEVER A RECENT ANALY SIS OF NUCLEAR GENES 3ENCHINA ET AL INDICATED THAT POLYPLOIDY LED TO AN OVERALL MODEST ENHANCEMENT IN RATES OF NUCLEOTIDE SUBSTITUTION IN 'OSSYPIUM 7HEN COMPARED TO RESYNTHESIZED ALLOPOLYPLOIDS NATURALLY NASCENT ALLOPOLY PLOIDS DISPLAY DIFFERENT PATTERNS OF GENOME EVOLUTION VARIOUS LEVELS OF CONCERTED EVOLUTION SEEM TO HAVE AFFECTED R$.! SEQUENCES OF THE YOUNG ALLOPOLYPLOID POPULATIONS IN 4RAGOPOGON 3OLTIS ET AL WHEREAS NO HOMOGENIZATION OF THE PARENTAL SEQUENCES IS OBSERVED IN 3PARTINA ANGLICA !ÕNOUCHE ET AL A )N THE LATTER SYSTEM NO MAJOR CHANGE OF THE PARENTAL GENOMES ARE OBSERVED FOR VARIOUS MULTILOCUS MARKERS )332S 2!0$S !&,0S ALTHOUGH SOME PREFERENTIAL LOSS OF MATERNAL FROM 3 ALTERNImORA !&,0 FRAGMENTS ARE OBSERVED IN 3 x TOWNSEN DII AND 3 ANGLICA !ÕNOUCHE ET AL B 3ALMON ! ET AL UNPUBLISHED ! TRANS POSON DISPLAY ANALYSIS INDICATES NO BURST OF RETRO ELEMENT ACTIVATION IN 3 ANGLICA "AUMEL ET AL A AND SUGGESTS THAT DIFFERENT BIOLOGICAL SYSTEMS RESPOND VARI OUSLY TO POLYPLOIDY ,IU ET AL )N SPITE OF THE STRUCTURAL GENOMIC STASIS ENCOUNTERED FOR MOST OF THE MARKERS INVESTIGATED TO DATE 3PARTINA ANGLICA POPULA TIONS EXHIBIT CONSISTENT MORPHOLOGICAL PLASTICITY 4HOMPSON AND SUGGEST A PROBABLE FUNCTIONAL PLASTICITY IN THE EXPRESSION OF THE DUPLICATED LOCI !ÕNOUCHE ET AL A 2ECENT STUDIES HAVE POINTED OUT THAT THERE IS MODULATED EXPRESSION OF DUPLI CATED LOCI IN POLYPLOIDS #OMAI 3HAKED ET AL +ASHKUSH ET AL +ASHKUSH ET AL (E ET AL !DAMS ET AL 4HESE EXPRESSION CHANG ES MAY INVOLVE VARIOUS MECHANISMS INCLUDING INCREASED VARIATION IN DOSAGE REGULATED GENE EXPRESSION ALTERED REGULATORY NETWORKS AND GENETIC OR EPIGENETIC CHANGES 2IDDLE AND "IRCHLER /SBORN ET AL )N WHEAT POLYPLOIDY WAS ACCOMPANIED BY TRANSCRIPTIONAL ACTIVATION OF RETROELEMENTS THAT LED TO NOVEL EXPRESSION PATTERNS +ASHKUSH ET AL ,EVY AND &ELDMAN %XPRESSION CHANGES MAY HAVE PROFOUND IMPACT ON lTNESS WHEN THEY RESULT IN VARIABLE PHENOTYPES 'ENE SILENCING RESULTED IN PHENOTYPIC VARIATION AND INSTABILITY IN EXPERIMENTALLY RESYNTHESIZED !RABIDOPSIS ALLOTETRAPLOIDS THAT DISPLAYED CONSIDER ABLE VARIATION IN MORPHOLOGY mOWERING TIME AND FERTILITY #OMAI ET AL
+! 3CHIERENBECK AND -, !ÕNOUCHE
.OVEL mOWERING TIME VARIATION WAS ALSO OBSERVED IN RESYNTHESIZED ALLOPOLYPLOID "RASSICA NAPUS 3CHRANZ AND /SBORN %XPRESSION OF HOMOEOLOGOUS GENE PAIRS WAS ANALYSED BY !DAMS ET AL IN NATURAL TO MYR OLD AND SYN THETIC ALLOTETRAPLOID 'OSSYPIUM 4HE DUPLICATED GENES SHOWED UNEQUAL LEVELS OF EXPRESSION AND ORGAN SPECIlC RECIPROCAL SILENCING SUGGESTING A PARTITIONING OF THE ANCESTRAL FUNCTIONS AS BOTH IMMEDIATE IN SYNTHETIC POLYPLOIDS AND LONG TERM IN NATURAL POLYPLOIDS RESPONSES TO POLYPLOIDIZATION )N RECENTLY FORMED NATURAL ALLOPOLYPLOIDS SUCH EXPRESSION CHANGES APPEAR TO TAKE PLACE ALSO AS REVEALED BY C$.! !&,0 INVESTIGATIONS IN 4RAGOPOGON WHERE ABOUT OF THE GENES EXAMINED IN THE ALLOPOLYPLOIDS HAVE BEEN SILENCED AND AN ADDITIONAL EXHIBIT NOVEL GENE EXPRESSION RELATIVE TO THEIR DIPLOID PARENTS 3OLTIS ET AL %PIGENETIC CHANGES ASSOCIATED WITH INVASIVE ABILITY
%PIGENETICS REFERS TO HERITABLE CHANGES IN PHENOTYPE THAT DO NOT RESULT FROM CHANGES IN GENE SEQUENCE BUT RATHER FROM REGULATORY MECHANISMS OF GENE EXPRES SION 7OLFFE AND -ATZKE 4HESE MECHANISMS ARE KNOWN TO BE INVOLVED IN GROWTH AND DEVELOPMENT &INNEGAN ET AL AND CAN RESULT IN VARIOUS MORPHOLOGICAL CHANGES INCLUDING mOWER STRUCTURE EG #UBAS ET AL #OMAI ET AL 3UCH MECHANISMS HAVE IMPORTANT EVOLUTIONARY CONSEQUENCES BECAUSE THEY INCREASE PHENOTYPIC PLASTICITY WHICH IN TURN BUFFERS ENVIRONMEN TAL PRESSURES ON GENOTYPES 4HIS MAY BE ASTONISHING TO OUR NAÕVE PERSPECTIVE OF GENOMIC INTERACTIONS BUT EPIGENETIC PROCESSES ARE PROVING TO BE PREDICTABLY ASSOCIATED WITH THE STRUCTURAL LIMITATIONS OF GENOMES %PIGENETICS IS CONSEQUENTLY BECOMING A VERY ACTIVE lELD OF RESEARCH IN EVOLUTIONARY GENOMICS REVIEWED IN &INNEGEAN ET AL #OMAI ,IU AND 7ENDEL -ECHANISTICALLY EPIGENETIC CHANGES RESULT FROM VARIOUS INTERACTING PROCESSES WHICH INCLUDE CYTOSINE METHYLATION OF $.! -ARTIENSSEN AND #OLOT HIS TONE DEACETYLATION 4IAN AND #HEN AND SHORT 2.!S -ETTE ET AL THAT MODULATE GENE SILENCING %PIGENETIC ALTERATIONS ARE KNOWN TO BE TRIGGERED BY ENVIRONMENTAL STRESS &INNEGAN AND IN SOME CASES ARE VIEWED AS GENOME DEFENSE MECHANISMS 9ODER ET AL -ATZKE ET AL )N INTROGRESSED HYBRID RICE PLANTS ,IU AND 7ENDEL OBSERVED RETROTRANSPOSON ACTIVATION THAT WAS RAPIDLY REPRESSED BY CYTOSINE METHYLATION 4HE REUNION OF TWO DIVERGENT GENOMES IN THE SAME NUCLEUS IN HYBRID AND ALLO POLYPLOID SPECIES MAY BE CONSIDERED AS A GENOMIC STRESS THAT GENERATES EPIGENETIC CHANGES ALTERING GENE EXPRESSION AND PHENOTYPES #OMAI ET AL )N SYN THETIC !RABIDOPSIS ALLOTRETRAPLOIDS #OMAI ET AL OBSERVED THAT ABOUT OF THE GENES WERE SILENCED COMPARED TO THEIR PARENTS 4HE SILENCED GENES WERE BOTH NORMAL GENES OR GENES RELATED TO TRANSPOSONS 4HESE CHANGES WERE FURTHER FOUND TO BE RELATED TO METHYLATION MODIlCATIONS THAT WERE ASSOCIATED TO PHENOTYPIC INSTABILITY -ADLUNG ET AL 3IMILAR LEVELS OF SILENCING RELATED TO CYTOSINE METHYLATION WERE ALSO ENCOUNTERED IN THE CORRESPONDING NATURAL ALLOTETRAPLOID !RABIDOPSIS SUECICA ,EE AND #HEN )N EXPERIMENTALLY RE SYNTHESIZED ALLO
%VOLUTION AND PLANT INVASIONS
POLYPLOID WHEAT OF THE LOCI INVESTIGATED USING -ETHYLATION 3ENTITIVE !&,0 -3!0 WERE FOUND METHYLATED 3HAKED ET AL AND TRANSCRIPTIONAL ACTI VATION OF RETROTRANSPOSONS WAS SHOWN TO ALTER THE EXPRESSION OF ADJACENT GENES +ASHKUSH ET AL ,EVY AND &ELDMAN !LTHOUGH NO CHANGES IN METH YLATION PATTERNS WERE OBSERVED IN NEWLY SYNTHESIZED 'OSSYPIUM ALLOPOLYPLOIDS ,IU ET AL THE ORGAN SPECIlC AND RECIPROCAL GENE SILENCING FOUND BY !DAMS ET AL IS INTERPRETED AS RESULTING FROM EPIGENETIC REGULATION THROUGH MECHA NISMS THAT HAVE YET TO BE ELUCIDATED !DAMS AND 7ENDEL 3PARTINA ANGLICA IS TO OUR KNOWLEDGE THE lRST INVASIVE SPECIES THAT HAS BEEN INVESTIGATED IN THE CONTEXT OF EPIGENETIC GENE EXPRESSION !ÕNOUCHE ET AL B 3ALMON ET AL HAVE ATTEMPTED TO DIFFERENTIATE BETWEEN THE GENOMIC CON SEQUENCES THAT RESULT FROM HYBRIDIZATION AND THOSE THAT RESULT FROM GENOME DUPLICATION 4HIS WAS MADE POSSIBLE BY THE COMPARISON OF THE ALLOPOLYPLOID TO THE NATURAL & HYBRID SPECIES 3 X TOWNSENDII THE PROGENITOR OF 3 ANGLICA AND 3 X NEYRAUTII THE OTHER HYBRID THAT HAS FORMED INDEPENDENTLY IN SOUTHWEST &RANCE "AUMEL ET AL -3!0 DATA ANALYSIS REVEALED CONSISTENT METHYLA TION CHANGES THAT CONTRAST WITH THE STRUCTURAL ADDITIVITY OF THE PARENTAL GENOMES MENTIONED ABOVE -OST METHYLATION CHANGES WERE FOUND IN BOTH 3 X TOWNSENDII AND 3 X NEYRAUTII WHICH INDICATES THE REPRODUCIBILITY OF THE CHANGES IN THE TWO DIFFERENT HYBRIDISATION EVENTS 4HE METHYLATION ALTERATIONS FOUND IN 3 ANGLICA WERE ALREADY PRESENT OR INITIATED IN 3 X TOWNENDII SUGGESTING THAT EPIGENETIC CHANGES WERE TRIGGERED BY HYBRIDIZATION RATHER THAN BY GENOME DUPLICATION 4HE EXTENT OF SUCH CHANGES AND THEIR VARIABILITY WHEN PLANTS ARE FACING DIFFERENT ENVIRONMENTAL CONDITIONS NEED TO BE EXPLORED AT THE POPULATION LEVEL AND THE SEQUENCES THAT ARE EPIGENETICALLY AFFECTED HAVE TO BE IDENTIlED )N THE CONTEXT OF RAPID EXPANSION OF INVASIVE SPECIES THAT EXPLORE NEW HABI TATS EPIGENETIC PROCESSES ARE OF MAJOR INTEREST AS THEY DElNITELY INmUENCE lTNESS "ECAUSE EPIGENETIC CASES OF GENE SILENCING WILL NOT BE REmECTED IN SEQUENCE DATA THE ASSESSMENT OF GENE EXPRESSION IS KEY TO THE UNDERSTANDING OF GENE FUNCTION AND ITS IMPORTANCE IN SPECIES ADAPTATION AND INVASIVENESS -OLECULAR EVOLUTION ISTS ARE BECOMING MORE AWARE OF THE NECESSITY TO APPROACH ADAPTIVE PROCESSES AT BOTH GENE AND GENOME LEVELS
3%,%#4)/. $%6%,/0-%.4!, 2%30/.3% !.$ ).6!3)/.3 'ENETIC CHANGE AND SUBSEQUENT ALTERATIONS IN DEVELOPMENTAL RESPONSE HAVE BEEN MINIMALLY ADDRESSED IN INVASIVE PLANT SPECIES 3IMILARLY ALTHOUGH THE EVALUA TION OF DEVELOPMENTAL QUANTITATIVE TRAITS HAS BEEN CONSIDERED THEORETICALLY THERE IS LITTLE EMPIRICAL EVIDENCE FOR OR AGAINST THEIR IMPORTANCE IN PLANT INVASIONS 4HE GENETIC AND ECOLOGICAL INTERACTIONS THAT RESULT FROM CHANGES IN DEVELOPMENTAL GENES OR FROM GENES OF MAJOR EFFECT COULD HAVE PROFOUNDLY COMPLEX REPERCUS SIONS &OR EXAMPLE THE RELEASE FROM ENEMIES MAY ALLOW FOR DECREASED ALLOCATION TO PROTECTIVE MECHANISMS AND A CONCOMITANT INCREASE IN lTNESS THAT RESULTS FROM
+! 3CHIERENBECK AND -, !ÕNOUCHE
DEVELOPMENTAL RESPONSES 7E KNOW LITTLE ABOUT THE ECOLOGICAL IMPACTS OF DEVELOP MENTAL CHANGES AND INTERACTIONS IN PREDATOR PREY RELATIONSHIPS .IJHOUT !CTION FROM JUST A FEW PARTICULARLY IMPORTANT GENES SUCH AS THESE MAY BE KEY TO THE ABILITY TO INVADE 0ATERSON ET AL !LL ADAPTATIONS IMPORTANT TO INVASIVENESS e.g., HIGH SEED PRODUCTION BREED ING SYSTEM CHANGES AND VEGETATIVE PROPAGATION ARE AMENABLE FOR STUDY IN A DEVELOPMENTAL GENETIC AND ECOLOGICAL CONTEXT 0URAGGANAN 'ILBERT AND "OLKER 'ENES SUCH AS TEOSINTE BRANCHED IN MAIZE ILLUSTRATE THE IMPORTANCE OF DEVELOPMENTAL GENES IN PLANT ESTABLISHMENT AND SPREAD 1 #RONK PERS COMM $OEBLEY ET AL 4EOSINTE BRANCHED WHICH CONTROLS TILLERING IN MAIZE IS RESPONSIBLE FOR THE DIFFERENCE BETWEEN TEOSINTE THAT IS PERSISTENT IN THE ENVIRON MENT AND VARIETIES THAT ARE NOT ECOLOGICALLY COMPETITIVE $OEBLEY ET AL 6ARIATION IN REGULATORY GENES MAY BE KEY TO THE PROVISION OF THE GENETIC VARIATION NECESSARY TO ALTER PHENOLOGICAL DEVELOPMENTAL PATHWAYS mORAL VARIATION SECOND ARY PLANT COMPOUND PRODUCTION AND CLONAL GROWTH ,IFE HISTORY STRATEGIES OFTEN EMPHASIZED AS KEY TO UNDERSTANDING INVASIVE ABILITY HAVE BEEN ILLUSTRATED AS PHENOTYPICALLY ENVIRONMENTALLY DEPENDENT 0IGLIUCCI 4HE DEVELOPMENTAL RESPONSE OF REACTION NORMS IS BASED ON MEAN PHENOTYPIC TRAIT VALUES THUS THE VARIATION MUST BE EXPLAINED BY ADDITIVE GENETIC VARIANCE OR GENES FOR hADAPTIVE PLASTICITYv 3ULTAN ! COMPARISON BETWEEN 0OLYGONUM SPECIES WITH BROAD ECOLOGICAL TOLERANCE TO THOSE LIMITED BY ENVIRON MENTAL FACTORS DEMONSTRATE THAT DEVELOPMENTAL TIMING OF PLASTIC RESPONSES IS IMPORTANT TO ENVIRONMENTAL BREADTH 3ULTAN 'ENE EXPRESSION IS ALTERED BY BOTH INTERNAL AND MORE IMPORTANTLY WITHIN THE INVASIVE SPECIES CONTEXT EXTER NAL CUES 3CHLICHTING /F PARTICULAR IMPORTANCE TO INVASIVE ABILITY MAY BE THE DEVELOPMENTAL PLASTICITY OF GENDER AND BREEDING SYSTEM mEXIBILITY WHICH WILL IMPACT SEX RATIOS IN PROPAGULES RESPONDING TO NEW RANGE ENVIRONMENTAL FACTORS $ELPH !S 3CHAAL ET AL SUGGEST GENE GENEALOGIES WILL BE IMPOR TANT TO TEST HYPOTHESES FOR ADAPTATION AND WE FURTHER SUGGEST THAT THIS SHOULD INCLUDE DEVELOPMENTAL TRAITS THAT MAY BE CLOSELY RELATED TO SELECTION AND ADAPTIVE DIVERGENCE /UR EXPECTATION IS THAT THE PHENOMENON OF RAPID DIVERGENCE OF DEVEL OPMENTAL TRAITS WILL BE FOUND IN OTHER EXAMPLES OF ISLAND RADIATION OR IN REGIONS SIMILARLY SUSCEPTIBLE TO INVASION )N CASES OF GENE DUPLICATION AND POLYPLOIDY THE RATE OF THIS PROCESS MAY BE INCREASED BECAUSE OF THE hBACKUPvGENETIC EXPRES SION AND COPIES WITH WHICH SELECTIVE PROCESSES CAN hTINKERv
2%3%!2#( .%%$3 ). 4(% !2%! /& 4(% '%.%4)#3 !.$ %6/,54)/. /& ).6!3)6% 30%#)%3 4HE DISTRIBUTION OF GENETIC VARIATION IN POPULATIONS OF INVASIVE SPECIES AND THE RELATIVE INVASIVENESS OF DIFFERENT GENOTYPES REMAINS ELLUSIVE WITH FEW DElNITIVE STUDIES OUTSIDE OF AGRICULTURAL BUT SEE 'ASKIN AND 3CHAAL AND 3ALTONSTALL /F PARTICULAR NEED IN UNDERSTANDING THE DYNAMICS OF ADAPTATION AND
%VOLUTION AND PLANT INVASIONS
SPREAD IS AN ASSESSMENT OF THE MOLECULAR POPULATION GENETICS OF REGULATORY LOCI 0URAGGANAN 3OIL SEEDBANK ANALYSIS AS A SOURCE OF NEW GENETIC VARIATION HAS NOT BEEN ADEQUATELY ADDRESSED IN PLANT INVASIONS 3EED DORMANCY IS AN ADAPTIVE TRAIT AND ALTHOUGH DORMANCY PERIODS ARE WELL DESCRIBED FOR MANY AGRICULTURAL WEEDS "ASKIN AND "ASKIN $EKKER VIRUTALLY NOTHING IS KNOWN ABOUT THE IMPORTANCE OF THIS TRAIT FOR THE MAINTAINANCE OF GENETIC DIVERSITY IN INVASIVE PLANT SPECIES 3EED VIABILITY FOR #YTISUS SCOPARIUS CAN BE AS LONG AS YEARS AND A TWO OR THREE YEAR OLD PLANT CAN PRODUCE UP TO SEEDSYEAR 0ARKER ET AL 4HUS GENE mOW FROM SEED BANKS MAY BE CONSIDERABLE #HROMOLAENA ODORATA TRIFlD WEED A SHRUB NATIVE TO THE NEOTROPICS AND INVASIVE THROUGHOUT THE 0ACIlC )SLANDS IS QUITE AGGRESSIVE AND EVEN THE OCCURRENCE OF AN OCCASSIONAL SEEDLING SIX YEARS PAST AN IRRADICATION EFFORT MAY BE A POTENTIALLY IMPORTANT SOURCE OF GENETIC VARIATION 7ATERHOUSE AND :EIMER 1UANTITATIVE TRAIT LOCI ANALYSES HAVE PROVEN TO BE VERY USEFUL IN AGRICUL TURAL GENETICS AND THERE ARE NUMEROUS EXAMPLES 0ATERSON )N 3ORGHUM HALEPENSE VARIATION IN THE NUMBER OF RHIZOMES HAS BEEN ASSOCIATED WITH THREE 14,S AND THE NUMBER OF VEGETATIVE BUDS WITH AN ADDITIONAL 14, 0ATERSON ET AL 4HE POTENTIAL IMPORTANCE OF THIS TYPE OF WORK CAN NOT BE OVERSTATED IT HAS BEEN WELL ESTABLISHED THAT CLONAL GROWTH AND THE ABILITY TO FORM MORE VEGETATIVE BUDS CAN BE IMPORTANT TO INVASIVE ABILITY 0ATERSON #ONTINUED WORK WITH AGRICULTURE SPECIES WILL AID THE STUDY OF THOSE GENES THAT MAY BE IMPORTANT IN WEEDINESS SUCH AS mORAL OR FRUIT REGULATION AND VEGETATIVE GROWTH &OR EXAMPLE THE VEGETATIVE GROWTH TRAITS FOUND IN 3 HALEPENSE CORRESPOND WITH THE SAME 14,S IN RICE WHEAT CORN AND LIKELY OTHER BUT INVASIVE GRASSES !S SO ASTUTELY NOTED BY 0ATERSON ET AL 14, ANALYSIS CAN LEAD TO THE CLONING OF CANDIDATE GENES IMPORTANT IN VEGETATIVE GROWTH /NCE THESE GENES ARE IDENTIlED IT MAY HELP IN THE SPECIlC ERADICATION OF SOME INVADERS THAT HAVE LARGE AMOUNTS OF VEGETATIVE PROPAGATION THROUGH GENETIC OR CHEMICAL METHODS )MPORTANT CONTRIBUTIONS OF THE QUANTITATIVE GENETICS IN UNDERSTANDING INVASIVE SPECIES EVOLUTION WILL RESULT FROM STUDIES WHICH CONSIDER THE ADAPTIVE RESPONSE OR ADDITIVE GENETIC VARIANCE OF A PARTICULAR TRAIT ,YNCH AND 7ALSH -àLLER 3CHËRER AND 3TEINGER 3UCH STUDIES WILL BE FURTHER STRENGTHENED BY THE IDENTIlCATION OF 14,S ASSOCIATED WITH THESE TRAITS AND THEIR EVENTUAL MOLECU LAR CHARACTERIZATION 4HE INTEGRATION OF QUANTITATIVE GENETICS AND THE MOLECULAR BASIS OF THESE TRAITS WILL EVENTUALLY ALLOW AN ASSESSMENT OF THE LARGE SCALE ECOLOGI CAL EFFECTS OF GENETIC TRAITS !S PREVIOUSLY DISCUSSED HOMEOLOGOUS GENES OR THOSE GENES DUPLICATED BY POLYPLOID EVENTS MAY UNDERGO VARIOUS EVOLUTIONARY PROCESSES /F PARTICULAR INTEREST ARE THOSE GENES THAT HAVE ADAPTIVE SIGNIlCANCE 3PECIlC QUESTIONS THAT CAN BE ADDRESSED TO ASSESS THE DYNAMICS OF THE GENES IN POLYPLOID SYSTEMS INCLUDE CHARACTERIZATION IN SEQUENCE AND FUNCTION BETWEEN THE DIFFERENT COPIES OF THE GENES AND IN BOTH THE PARENTAL SPECIES AND POLYPLOID OFFSPRING CHARACTER IZATION OF DIVERGENCE TIMES AMONG THE PARENTAL SPECIES AND POLYPLOID OFFSPRING
+! 3CHIERENBECK AND -, !ÕNOUCHE
-OST IMPORTANTLY THE DETERMINATION OF THE EFFECTS OF POLYPLOIDY ON DUPLICATE GENE EXPRESSION AND ADAPTIVE FUNCTION IS NOW POSSIBLE -UCH REMAINS TO BE LEARNED ABOUT THE DYNAMICS AND SUBSEQUENT GENOTYPIC AND PHENOTYPIC CHANGES DUE TO THE HYBRIDIZATION BETWEEN HISTORICALLY ALLOPATRIC TAXA HOMEOLOGOUS GENES AND ALLOPOLYPLOIDIZATION !LTHOUGH CURRENTLY LIMITED IN THEIR APPLICATION TO MODEL SYSTEMS OR CLOSELY RELATED TAXA THE EXPLORATION OF THE USE OF NEW GENOMIC TOOLS e.g., MICROARRAYS MAY PROVE USEFUL FOR THE INVESTIGATION OF GENOMIC AND ECOLOGICAL INTERACTIONS *ACKSON ET AL
#/.#,53)/.3 !S EVOLUTIONARY BIOLOGISTS MANY OF US HAVE WORKED TOWARD THE DAY IN WHICH WE CAN LINK GENE AND GENOMES TO THE LEVEL OF THE ECOSYSTEM 4HIS DAY HAS ARRIVED AND FOR BETTER OR WORSE A FORUM THAT OFFERS ONE OF THE BEST OPPORTUNITIES FOR THE INTEGRATION OF GENETICS AND ECOLOGY IN AN EVOLUTIONARY CONTEXT IS THE STUDY OF INVASIVE SPECIES !LTHOUGH THE PARTICIPANTS OF THE hGENETICS OF COLONIZING SPECIESv SYMPOSIUM MADE THIS SAME OBSERVATION IN ONLY NOW DO WE HAVE THE TOOLS TO ADDRESS THE MYRIAD OF QUESTIONS ASSOCIATED WITH THE EVOLUTION OF INVASIVE ABIL ITY 7E ARE WELL AWARE THAT IT IS PERHAPS MORE THAN A COINCIDENCE THAT MANY OF THE EXAMPLES OF INVASIVE SPECIES WE HAVE CITED OFTEN SHARE THE PHENOMENA OF RAPID EXPANSION INTO NEW RANGES POLYPLOIDY AND HYBRIDIZATION 4HE INTEGRATION OF MOLECULAR GENETICS ECOLOGY AND LARGE SCALE lELD EXPERI MENTATION IS TOO LARGE FOR ANY SINGLE INVESTIGATOR TO STUDY IN INVASIVE SPECIES OR ANY OTHER CONTEXT )NCREASED KNOWLEDGE IN THE RESPECTIVE lELDS OF GENOMICS PROTEOMICS CELL BIOLOGY POPULATION GENETICS PHYLOGENETICS AND ECOLOGY WILL REQUIRE THE COOPERATION OF LABORATORIES WITH EXPERTISE IN THESE RESPECTIVE AREAS 0ERHAPS INVASIVE SPECIES GENETICS WILL BE THE lELD THAT BRINGS TOGETHER EVOLUTION ISTS FROM VARIOUS DISCIPLINES FOR BOTH A BETTER UNDERSTANDING AND THE MANAGEMENT OF CONTEMPORARY ENVIRONMENTS
!#+./7,%$'%-%.43 7E THANK THE .ATIONAL 3CIENCE &OUNDATION IN THE 53 THE #ENTRE .ATIONAL DE LA 2ECHERCHE 3CIENTIlQUE AND THE #ENTRE !RMORICAIN DE 2ECHERCHES EN %NVIRONNEMENT IN &RANCE FOR THEIR SUPPORT OF COLLABORATIVE RESEARCH ON GENOME EVOLUTION OF INVASIVE PLANTS 7E ALSO ACKNOWLEDGE AND THANK THE CONTRIBUTIONS OF OUR STUDENTS AND MANY COLLABORATORS TO OUR WORK PARTICULARLY .ORMAN %LLSTRAND #URT $AEHLER AND ONE ANONYMOUS REVIEWER ARE THANKED FOR HELPFUL COMMENTS ON THE MANUSCRIPT
%VOLUTION AND PLANT INVASIONS
2%&%2%.#%3 !BBOTT 2 * 0LANT INVASIONS INTERSPECIlC HYBRIDIZATION AND THE EVOLUTION OF NEW PLANT TAXA 4RENDS IN %COLOGY AND %VOLUTION !BBOTT 2 * * + *AMES 2 ) -ILNE AND ! # - 'ILLIES 0LANT INTRODUCTIONS HYBRID IZATION AND GENE mOW 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY OF ,ONDON " !BBOTT 2 7 AND ! * ,OWE /RIGINS ESTABLISHMENT AND EVOLUTION OF NEW POLYPLOID SPECIES 3ENECIO CAMBRENSIS AND 3 EBORANENSIS IN THE "RITISH ISLES "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY )N PRESS !DAMS + , 2 #RONN 2 0ERCIlELD AND * & 7ENDEL 'ENES DUPLICATED BY POLYPLOIDY SHOW UNEQUAL CONTRIBUTIONS TO THE TRANSCRIPTOME AND ORGAN SPECIlC RECIPROCAL SILENC ING 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES !DAMS + , AND * & 7ENDEL %XPLORING THE GENOMIC MYSTERIES OF POLYPLOIDY IN COT TON "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY )N PRESS !ÕNOUCHE - , ! "AUMEL AND ! 3ALMON A 3PARTINA ANGLICA A NATURAL MODEL SYSTEM FOR STUDYING EARLY EVOLUTIONARY CHANGES THAT AFFECT ALLOPOLYPLOID GENOMES "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY In press. !ÕNOUCHE - , ! "AUMEL ! 3ALMON AND ' 9ANNIC B (YBRIDIZATION POLYPLOIDY AND SPECIATION IN 3PARTINA 0OACEAE .EW 0HYTOLOGIST !LLENDORF & 7 AND , , ,UNDQUIST )NTRODUCTION POPULATION BIOLOGY EVOLUTION AND CONTROL OF INVASIVE SPECIES #ONSERVATION "IOLOGY !MSELLEM , * , .OYER 4 ,E "OURGEOIS AND - (OSSAERT -C+EY #OMPARISON OF GENETIC DIVERSITY OF THE INVASIVE WEED 2UBUS ALCEIFOLIUS 0OIR 2OSACEAE IN ITS NATIVE RANGE AND IN AREAS OF INTRODUCTION USING !&,0 MARKERS -OLECULAR %COLOGY !NDERSON % )NTROGRESSIVE HYBRIDIZATION .EW 9ORK 53! *OHN 7ILEY !NDERSON % AND ' , 3TEBBINS (YBRIDIZATION AS AN EVOLUTIONARY STIMULUS %VOLUTION !NTTILA # + 2 ! +ING # &ERRIS $ 2 !YRES AND $ 2 3TRONG 2ECIPROCAL HYBRID FORMATION OF 3PARTINA IN 3AN &RANCISCO "AY -OLECULAR %COLOGY !NTILLA # + # # $AEHLER . % 2ANK AND $ 2 3TRONG 'REATER MALE lTNESS OF A RARE INVADER 3PARTINA ALTERNImORA THREATENS A COMMON NATIVE 3PARTINA FOLIOSA WITH HYBRIDIZATION !MERICAN *OURNAL OF "OTANY !RNOLD - , .ATURAL HYBRIDIZATION AND EVOLUTION /XFORD 5+ /XFORD 5NIVERSITY 0RESS !RNOLD - , 4RANSFER AND ORIGIN OF ADAPTATIONS THROUGH NATURAL HYBRIDIZATION 7ERE !NDERSON AND 3TEBBINS RIGHT 4HE 0LANT #ELL !UGE ( " .EUFFER & %RLINGHAGEN 2 'RUPE AND 2 "RANDL $EMOGRAPHIC AND RANDOM AMPLIlED POLYMORPHIC $.! ANALYSES REVEAL HIGH LEVELS OF GENETIC DIVERSITY IN A CLONAL VIOLET -OLECULAR %COLOGY !YRES $ 2 $ 'ARCIA 2OSSI ( ' $AVIS $ 2 3TRONG %XTENT AND DEGREE OF HYBRID IZATION BETWEEN EXOTIC 3PARTINA ALTERNImORA AND NATIVE 3 FOLIOSA CORDGRASS 0OACEAE IN #ALIFORNIA 53! DETERMINED BY RANDOM AMPLIlED POLYMORPHIC $.! 2!0$S -OLECULAR %COLOGY
+! 3CHIERENBECK AND -, !ÕNOUCHE
"AKER ( ' #HARACTERISTICS AND MODES OF ORIGINS OF WEEDS 0AGES "AKER ( ' AND ' , 3TEBBINS EDITORS 4HE 'ENETICS OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK "AKER ( ' AND ' , 3TEBBINS 4HE 'ENETICS OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK "AKER ( ' 4HE EVOLUTION OF WEEDS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "ARTLETT % 3 * .OVAK AND 2 . -ACK 'ENETIC VARIATION IN "ROMUS TECTORUM 0OACEAE DIFFERENTIATION IN THE EASTERN 5NITED 3TATES !MERICAN *OURNAL OF "OTANY "ARRETT 3 # ( AND " * 2ICHARDSON 'ENETIC ATTRIBUTES OF INVADING SPECIES 0AGES IN 'ROVES 2 ( AND "URDON * * EDITORS %COLOGY OF "IOLOGICAL )NVASIONS #AMBRIDGE 5NIVERSITY 0RESS -ELBOURNE !USTRALIA "ARRIER - " ' "ALDWIN 2 ( 2OBICHAUX AND - $ 0URUGGANAN )NTERSPECIlC HYBRID ANCESTRY OF A PLANT ADAPTIVE RADIATION ALLOPOLYPLOIDY OF THE (AWAIIAN SILVER SWORD ALLIANCE !STERACEAE INFERRED FROM mORAL HOMEOTIC GENE DUPLICATIONS -OLECULAR "IOLOGY AND %VOLUTION "ARRIER - 2 ( 2OBICHAUX AND - $ 0URUGGANAN !CCELERATED REGULATORY GENE EVOLUTION IN AN ADAPTIVE RADIATION 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES "ASKIN # # AND * - "ASKIN 3EEDS %COLOGY "IOGEOGRAPHY AND %VOLUTION OF $ORMANCY AND 'ERMINATION !CADEMIC 0RESS .EW 9ORK "AUMEL ! - , !ÕNOUCHE AND * % ,EVASSEUR -OLECULAR INVESTIGATIONS IN POPULA TIONS OF 3PARTINA ANGLICA # % (UBBARD 0OACEAE INVADING COASTAL "RITTANY &RANCE -OLECULAR %COLOGY "AUMEL ! - , !ÕNOUCHE 2 +ALENDAR ! ( 3CHULMAN A 2ETROTRANSPOSONS AND GENOMIC STABILITY IN POPULATIONS OF THE YOUNG ALLOPOLYPLOID SPECIES 3PARTINA ANGLICA # % (UBBARD 0OACEAE -OLECULAR "IOLOGY AND %VOLUTION "AUMEL ! - , !ÕNOUCHE 2 * "AYER ! + !INOUCHE AND - 4 -ISSET B -OLECULAR PHYLOGENY OF HYBRIDIZING SPECIES FROM THE GENUS 3PARTINA Schreb 0OACEAE -OLECULAR 0HYLOGENETICS AND %VOLUTION "AUMEL ! - , !ÕNOUCHE - 4 -ISSET * 0 'OURRET AND 2 * "AYER 'ENETIC EVIDENCE FOR HYBRIDIZATION BETWEEN THE NATIVE 3PARTINA MARITIMA AND THE INTRODUCED 3PARTINA ALTERNImORA 0OACEAE IN 3OUTH 7EST &RANCE 3PARTINA x NEYRAUTII RE EXAMINED 0LANT 3YSTEMATICS AND %VOLUTION "AYER 2 * !NTENNARIA ROSEA !STERACEAE ! MODEL GROUP FOR THE STUDY OF THE EVOLU TION OF POLYPLOID AGAMIC COMPLEXES /PERA "OTANICA "AZZAZ & ,IFE HISTORY OF COLONIZING PLANTS SOME DEMOGRAPHIC GENETIC AND PHYSIOLOGICAL FEATURES 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF BIOLOGICAL INVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG (EIDELBERG 'ERMANY "IRCHLER * ! $ , !UGER AND . # 2IDDLE )N SEARCH OF A MOLECULAR BASIS OF HETEROSIS 4HE 0LANT #ELL
%VOLUTION AND PLANT INVASIONS
"LANC ' + (OKAMP AND + ( 7OLFE ! RECENT POLYPLOIDY SUPERIMPOSED ON OLDER LARGE SCALE DUPLICATIONS IN THE !RABIDOPSIS GENOME 'ENOME 2ESEARCH "ROWN ! ( $ AND $ 2 -ARSHALL %VOLUTIONARY CHANGES ACCOMPANYING COLONIZA TION IN 0LANTS 0AGES IN ' # % 3CUDDER AND * , 2EVEAL EDITORS #OLONIZATION 3UCCESSION AND 3TABILITY "LACKWELL 3CIENTIlC 0UBLICATIONS /XFORD "URKE * - AND - , !RNOLD 'ENETICS AND THE lTNESS OF HYBRIDS !NNUAL 2EVIEW OF 'ENETICS #EDRONI - % 2 # #RONN + , !DAMS 4 ! 7ILKINS AND * & 7ENDEL %VOLUTION AND EXPRESSION OF -9" GENES IN DIPLOID AND POLYPLOID COTTON 0LANT -OLECULAR "IOLOGY #HEN : * , #OMAI AND # 3 0IKAARD 'ENE DOSAGE AND STOCHASTIC EFFECTS DETER MINE DIRECTION AND SEVERITY OF UNIPARENTAL R2.! GENE SILENCING NUCLEOLAR DOMINANCE IN !RABIDOPSIS ALLOPOLYPLOIDS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES #LAUSS - * AND 4 -ITCHELL /LDS 0OPULATION GENETICS OF TANDEM TRYPSIN INHIBI TOR GENES IN Arabidopsis SPECIES WITH CONTRASTING ECOLOGY AND LIFE HISTORY -OLECULAR %COLOGY #OHEN - " - 4 *ACKSON " 2 ,U 3 2 -ORIN ! - -ORTIMER * , 0HAM AND , * 7ADE 0REDICTING THE ENVIRONMENTAL IMPACT OF TRANSGENIC OUTCROSSING TO WILD AND WEEDY RICES IN !SIA 0AGES IN 3YMPOSIUM 0ROCEEDINGS .O 'ENE &LOW AND !GRICULTURE 2ELEVANCE FOR 4RANSGENIC #ROPS "#0#5NIVERSITY OF +EELE 3TAFFORDSHIRE #OMAI , 'ENETIC AND EPIGENETIC INTERACTIONS IN ALLOPOLYPLOID PLANTS 0LANT -OLECULAR "IOLOGY #OMAI , ! 0 4YAGI + 7INTER 2 (OLMES $AVIS 3 2EYNOLDS 9 3TEVENS AND " "YERS 0HENOTYPIC INSTABILITY AND RAPID GENE SILENCING IN NEWLY FORMED !RABIDOPSIS ALLO TETRAPLOIDS 0LANT #ELL #OMAI , ! -ADLUNG # *OSEFSSON AND ! 0 4YAGI $O THE DIFFERENT PARENTAL @HETEROMES CAUSE GENOMIC SHOCK IN NEWLY FORMED ALLOPOLYPLOIDS 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY OF ,ONDON ,ONDON " #RONN 2 3MALL 2 , AND * & 7ENDEL $UPLICATED GENES EVOLVE INDEPENDENTLY FOLLOWING POLYPLOID FORMATION IN COTTON 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! #RONN 2 # 2 , 3MALL 4 (ASELKORN AND * & 7ENDEL #RYPTIC REPEATED GENOMIC RECOMBINATION DURING SPECIATION IN 'OSSYPIUM GOSSYPIOIDES %VOLUTION #RONN 2 AND * & 7ENDEL #RYPTIC TRYSTS GENOMIC MERGERS AND PLANT SPECIATION .EW 0HYTOLOGIST #UBAS 0 # 6ICENT AND % #OEN !N EPIGENETIC MUTATION RESPONSIBLE FOR NATURAL VARIATION IN mORAL SYMMETRY .ATURE $OEBLEY * ! 3TEC AND # 'USTUS 4EOSINTE BRANCHED AND THE ORIGIN OF MAIZE EVI DENCE FOR EPISTASIS AND THE EVOLUTION OF DOMINANCE 'ENETICS $ARWIN # 4HE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION TH EDN ,ONDON 5+ *OHN -URRAY $AEHLER # # AND $ 2 3TRONG (YBRIDIZATION BETWEEN INTRODUCED SMOOTH CORD GRASS 3PARTINA ALTERNImORA 0OACEAE AND NATIVE #ALIFORNIA CORDGRASS 3 FOLIOSA IN 3AN &RANCISCO "AY #ALIFORNIA 53! !MERICAN *OURNAL OF "OTANY
+! 3CHIERENBECK AND -, !ÕNOUCHE
DA3ILVA * AND " 7 3 3OBRAL 0OLYPLOID GENETICS 0AGES IN 4HE )MPACT OF 0LANT -OLECULAR 'ENETICS " 7 3 3OBRAL EDITOR "IRKHËUSER "OSTON PP $ELPH , & 3EXUAL DIMORPHISM IN GENDER PLASTICITY AND ITS CONSEQUENCES FOR BREEDING SYSTEM EVOLUTION %VOLUTION AND $EVELOPMENT $EKKER * 7EED DIVERSITY AND WEED MANAGEMENT 7EED 3CIENCE $EKKER * 3OIL WEED SEED SEED BANKS AND WEED MANAGEMENT *OURNAL OF #ROP 0RODUCTION $EKKER * 4HE EVOLUTIONARY BIOLOGY OF THE FOXTAIL 3ETARIA SPECIES GROUP 0AGES IN 0RINCIPLES AND 0RACTICES IN 7EED -ANAGEMENT 7EED "IOLOGY AND -ANAGEMENT )NDERJIT EDITOR +LUWER !CADEMIC 0UBLISHERS 4HE .ETHERLANDS DE 6RIES ( 3PECIES AND 6ARIETIES THEIR /RIGIN BY -UTATION /PEN #OURT 0UBLISHING #OMPANY #HICAGO ), $E7ALT 3 4HE INVASIVE TROPICAL SHRUB #LIDEMIA HIRTA -ELASTOMATACEAE IN ITS NATIVE AND INTRODUCED RANGES TESTS OF HYPOTHESES OF INVASION 0H$ $ISSERTATION ,OUISIANA 3TATE 5NIVERSITY $OYLE * * * , $OYLE * 4 2AUSCHER AND ! ( $ "ROWN $IPLOID AND POLYPLOID RETICULATE EVOLUTION THROUGHOUT THE HISTORY OF THE PERENNIAL SOYBEANS 'LYCINE SUBGENUS 'LYCINE .EW 0HYTOLOGIST %LLSTRAND . AND + ! 3CHIERENBECK (YBRIDIZATION AS A STIMULUS FOR THE EVOLUTION OF INVASIVENESS IN PLANTS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! &ELDMAN - " ,IU ' 3EGAL 3 !BBO ! ! ,EVY AND * - 6EGA 2APID %LIMINATION OF LOW COPY $.! SEQUENCES IN POLYPLOID WHEAT A POSSIBLE MECHANISM FOR DIFFERENTIATION OF HOMOEOLOGOUS CHROMOSOMES 'ENETICS &ERRIS # 2 ! +ING AND ! * 'RAY -OLECULAR EVIDENCE FOR THE MATERNAL PARENTAGE IN THE HYBRID ORIGIN OF 3PARTINA ANGLICA # % (UBBARD -OLECULAR %COLOGY &INNEGAN % * %PIALLELES A SOURCE OF RANDOM VARIATION IN TIMES OF STRESS #URRENT /PINION IN 0LANT "IOLOGY &INNEGAN % * 2 + 'ENGER 7 * 0EACOCK AND % 3 $ENNIS $.! METHYLATION IN PLANTS !NNUAL 2EVIEW OF 0LANT 0HYSIOLOGY 0LANT -OLECULAR "IOLOGY &INNEGAN % * 7 * 0EACOCK AND % % $ENNIS $.! METYLATION A KEY REGULATOR OF PLANT DEVELOPMENT AND OTHER PROCESSES #URRENT /PINION IN 'ENETICS AND $EVELOPMENT 'ASKIN * & AND " ! 3CHAAL (YBRID 4AMARIX WIDESPREAD FROM 5 3 INVASION AND UNDECTED IN NATIVE !SIAN RANGE 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! 'ILBERT 3 & AND * ! "OLKER %COLOGICAL DEVELOPMENTAL BIOLOGY PREFACE TO THE SYM POSIUM %VOLUTION AND $EVELOPMENT 'RANT 6 0LANT SPECIATION .EW 9ORK 53! #OLUMBIA 5NIVERSITY 0RESS 'RESSEL * -OLECULAR BIOLOGY OF WEED CONTROL 4RANSGENIC 2ESEARCH 'ROTKOPP % - 2EJMANEK AND 4 , 2OST 4OWARD A CAUSAL EXPLANATION OF PLANT INVA SIVENESS SEEDLING GROWTH AND LIFE HISTORY STRATEGIES OF PINE 0INUS 3PECIES !MERICAN .ATURALIST
%VOLUTION AND PLANT INVASIONS
(AmIGER % AND ( 3CHOLZ 'RASS WEEDS 7EEDS OF THE 3UBFAMILY 0ANICOIDEAE #IBA 'EIGY ,TD "ASEL 3WITZERLAND PP (AMRICK * , - * 7 'ODT AND 3 , 3HERMAN "ROYLES &ACTORS INmUENCING LEVELS OF GENETIC DIVERSITY IN WOODY PLANT SPECIES .EW &ORESTS (AMRICK * , 9 " ,INHART AND * " -ITTON 2ELATIONSHIPS BETWEEN LIFE HISTORY CHARACTERISTICS AND ELECTROPHORETICALLY DETECTABLE GENETIC VARIATION IN PLANTS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS (E 0 " &RIEBE " 3 'ILL " 3 AND * :HOU !LLOPOLYPLOIDY ALTERS GENE EXPRESSION IN THE HIGHLY STABBLE HEXAPLOID WHEAT 0LANT -OLECULAR "IOLOGY (EGDE 3 ' * 6ALKOUN AND * ' 7AINES 'ENETIC DIVERSITY IN WILD AND WEEDY !EGILOPS !MBLYOPYRUM AND 3ECALE SPECIES ! PRELIMINARY SURVEY #ROP 3CIENCE (UEY 2 " ' 7 'ILCHRIST - , #ARLSON $ "ERRIGAN AND , 3ERRA 2APID EVOLUTION OF A GEOGRAPHIC CLINE IN SIZE IN AN INTRODUCED mY 3CIENCE (UXEL ' 2 2APID DISPLACEMENT OF NATIVE SPECIES BY INVASIVE SPECIES EFFECTS OF HYBRIDIZATION "IOLOGICAL CONSERVATION )LTIS (UGO ,IFE OF -ENDEL TRANS %DEN AND #EDAR 0AUL (AFNER 0UBLISHING *ACKSON 2 " # 2 ,INDER - ,YNCH - 0URUGGANAN 3 3OMERVILLE AND 3 3 4HAYER ,INKING MOLECULAR INSIGHT AND ECOLOGICAL RESEARCH 4RENDS IN %COLOGY AND %VOLUTION *OHNSTON * ! - , !RNOLD AND , ! $ONOVAN (IGH HYBRID lTNESS AT SEED AND SEEDLING LIFE HISTORY STAGES IN ,OUISIANA IRISES *OURNAL OF %COLOGY +ASHKUSH + - &ELDMAN AND ! ! ,EVY 'ENE ,OSS 3ILENCING AND !CTIVATION IN A .EWLY 3YNTHESIZED 7HEAT !LLOTETRAPLOID 'ENETICS +ASHKUSH + - &ELDMAN AND ! ! ,EVY 4RANSCRIPTIONAL ACTIVATION OF RETROTRANSPO SONS ALTERS THE EXPRESSION OF ADJACENT GENES IN WHEAT .ATURE 'ENETICS n +IM 3 # AND , ( 2IESEBERG 'ENETIC ARCHITECTURE OF SPECIES DIFFERENCES IN ANNUAL SUNmOWERS IMPLICATIONS FOR ADAPTIVE TRAIT INTROGRESSION 'ENETICS +OLAR # AND $ - ,ODGE 0ROGRESS IN INVASION BIOLOGY PREDICTING INVADERS 4RENDS IN %COLOGY AND %VOLUTION ,AWTON 2AUH ! %VOLUTIONARY DYNAMICS OF DUPLICATED GENES IN PLANTS -OLECULAR 0HYLOGENETICS AND %VOLUTION ,EE # % %VOLUTIONARY GENETICS OF INVASIVE SPECIES 4RENDS IN %COLOGY AND %VOLUTION ,EE ( AND : * #HEN 0ROTEIN CODING GENES ARE EPIGENETICALLY REGULATED IN Arabidopsis POLYPLOIDS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCE 53! ,EGER % ! AND + * 2ICE )NVASIVE #ALIFORNIA POPPIES %SCHSCHOLZIA CALIFORNICA #HAM GROW LARGER THAN NATIVE INDIVIDUALS UNDER REDUCED COMPETITION %COLOGY ,ETTERS ,EVY ! ! AND - &ELDMAN 'ENETIC AND EPIGENETIC REPROGRAMMING OF THE WHEAT GENOME UPON ALLOPOLYPLOIDISATION "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY )N PRESS ,EWIS 7 ( 0OLYPLOIDY BIOLOGICAL RELEVANCE 0LENUM .EW 9ORK .EW 9ORK 53!
+! 3CHIERENBECK AND -, !ÕNOUCHE
,EXER # - % 7ELCH * , $URPHY AND , ( 2IESEBERG .ATURAL SELECTION FOR SALT TOL ERANCE QUANITATIVE TRAIT LOCI 14,S IN WILD SUNmOWER HYBRIDS )MPLICATIONS FOR THE ORIGIN OF Helianthus paradoxus, A DIPLOID HYBRID SPECIES -OLECULAR %COLOGY ,EXER # : ,AI AND , ( 2IESEBERG #ANDIDATE GENE POLYMORPHISMS ASSOCIATED WITH SALT TOLERANCE IN WILD SUNmOWER HYBRIDS IMPLICATIONS FOR THE ORIGIN OF (ELIANTHUS PARA DOXUS A DIPLOID HYBRID SPECIES .EW 0HYTOLOGIST ,OSOS * " + ) 7ARHEIT AND 4 7 3CHOENER !DAPTIVE DIFFERENTIATION FOLLOWING EXPERIMENTAL ISLAND COLONIZATION IN !NOLIS LIZARDS .ATURE ,IU " 6EGA * - 3EGAL ' !BBO 3 2ODOVA - AND - &ELDMAN A 2APID GENOMIC CHANGES IN NEWLY SYNTHETIZED AMPHIPLOIDS OF 4RITICUM AND !EGILOPS ) #HANGES IN LOW COPY NONCODING $.! SEQUENCES 'ENOME ,IU " 6EGA * - 3EGAL ' !BBO 3 2ODOVA - AND - &ELDMAN B 2APID GENOMIC CHANGES IN NEWLY SYNTHETIZED AMPHIPLOIDS OF 4RITICUM AND !EGILOPS )) #HANGES IN LOW COPY CODING $.! SEQUENCES 'ENOME ,IU " AND * & 7ENDEL 2ETROTRANSPOSON ACTIVATION FOLLOWED BY RAPID REPRESSION IN INTROGRESSED RICE PLANTS 'ENOME ,IU " # , "RUBAKER ' -ERGEAI 2 # #RONN * & 7ENDEL 0OLYPLOID FORMATION IN COTTON IS NOT ACCOMPANIED BY RAPID GENOMIC CHANGES 'ENOME ,IU " AND * & 7ENDEL .ON -ENDELIAN PHENOMENA IN ALLOPOLYPLOID GENOME EVOLU TION #URRENT 'ENOMICS n ,IU " AND * & 7ENDEL %PIGENETIC PHENOMENA AND THE EVOLUTION OF PLANT ALLOPOLY PLOIDS -OLECULAR 0HYLOGENETICS AND %VOLUTION ,INDE - 3 $IEL AND " .EUFFER &LOWERING ECOTYPES OF #APSELLA BURSA PASTORIS , Medik "RASSICACEAE ANALYSED BY A COSEGREGATION OF PHENOTYPIC CHARACTERS 14, AND MOLECULAR MARKERS !NNALS OF "OTANY ,OVELESS - AND * , (AMRICK %COLOGICAL DETERMINANTS OF GENETIC STRUCTURE IN PLANT POPULATIONS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS ,YNCH - AND " 7ALSH 'ENETICS AND !NALYSIS OF 1UANTITATIVE 4RAITS 3INAUER !SSOCIATES 3UNDERLAND -ASSACHUSETTS ,YNCH - AND * 3 #ONERY 4HE EVOLUTIONARY FATE AND CONSEQUENCES OF DUPLICATED GENES 3CIENCE -ADLUNG ! -ASUELLI 2 7 7ATSON " 2EYNOLDS 3 ( $AVISON * AND , #OMAI REMODELING OF $.! METHYLATION AND PHENOTYPIC AND TRANSCRIPTIONAL CHANGES IN SYN THETIC Arabidopsis ALLOTETRAPLOIDS 0LANT 0HYSIOLOGY -ARTIENSSEN 2 ! AND 6 #OLOT -ETHYLATION AND EPIGENETIC INHERITANCE IN PLANTS AND lLAMENTOUS FUNGI 3CIENCE -ATZKE - ! -ETTE - & AND ! * - -ATZKE 4RANSGENE SILENCING BY THE HOST GENOME DEFENSE IMPLICATIONS FOR THE EVOLUTION OF EPIGENETIC CONTROL MECHANISMS IN PLANTS AND VERTEBRATES 0LANT -OLECULAR "IOLOGY -ATZKE - ! -ATZKE ! * 0RUSS ' * AND 6 " 6ANCE 2.!BASED SILENCING STRATE GIES IN PLANTS #URRENT /PINIONS IN 'ENETICS AND $EVELOPMENT -AYO ' - AND 0 ,ANGRIDGE -ODES OF REPRODUCTION IN !USTRAILIAN POPULATIONS OF (YPERICUM PERFORATUM , 3T *OHNS WORT REVEALED BY $.! lNGERPRINTING AND CYTOLOGI CAL METHODS 'ENOME
%VOLUTION AND PLANT INVASIONS
-ETTE - & 7 !UFSATZ * VAN DER 7INDEN - ! -ATZKE AND ! * - -ATZKE 4RANSCRIPTIONAL GENE SILENCING AND PROMOTER METHYLATION TRIGGERED BY DOUBLE STRANDED 2.! %-"/ *OURNAL -OORE . * AND ' & -ORAN -ICROGEOGRAPHIC PATTERNS OF ALLOZYME VARIATION IN #ASUARINA CUNNINGHAMIANA WITHIN AND BETWEEN THE -URRUMBIDGE AND COASTAL DRAIN AGE SYSTEMS !USTRALIAN *OURNAL OF "OTANY -OONEY ( ! AND % % #LELAND 4HE EVOLUTIONARY IMPACT OF INVASIVE SPECIES 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! -ORAN ' & / -UONA AND * # "ELL "REEDING SYSTEMS AND GENETIC DIVERSITY IN !CACIA AURICULIFORMIS AND ! CRASSICARPA "IOTROPICA -ORAN ' & * # "ELL AND * 7 4URNBULL ! CLINE IN GENETIC DIVERSITY IN 2IVER SHE OAK #ASUARINA CUNNINGHAMIANA !USTRALIAN *OURNAL OF "OTANY -àLLER 3CHËRER ( AND 4 3TEINGER 0REDICTING EVOLUTIONARY CHANGE IN INVASIVE EXOTIC PLANTS AND ITS CONSEQUENCES FOR PLANT HERBIVORE INTERACTIONS 0AGES IN 'ENETICS %VOLUTION AND "IOLOGICAL #ONTROL , % %HLER 2 3FORZA AND 4 -ATEILLE EDITORS #!" )NTERNATIONAL .EUFFER " AND ( (URKA #OLONIZATION HISTORY AND INTRODUCTION DYNAMICS OF #APSELLA BURSA PASTORIS "RASSICACEAE IN .ORTH !MERICA ISOZYMES AND QUANTITATIVE TRAITS -OLECULAR %COLOGY .IJHOUT ( & $EVELOPMENT AND EVOLUTION OF ADAPTIVE POLYPHENISMS %VOLUTION AND $EVELOPMENT .OVAK 3 * AND 2 . -ACK 'ENETIC VARIATION IN "ROMUS TECTORUM 0OACEAE COMPARISON BETWEEN NATIVE AND INTRODUCED POPULATIONS (EREDITY .OVAK 3 * 2 . -ACK AND 0 3 3OLTIS 'ENETIC VARIATION IN "ROMUS TECTORUM 0OACEAE )NTRODUCTION DYNAMICS IN .ORTH !MERICA #ANADIAN *OURNAL OF "OTANY /HNO 3 %VOLUTION BY GENE DUPLICATION 3PRINGER 6ERLAG .EW 9ORK /HTA 4 AND * ( 'ILLESPIE $EVELOPMENT OF NEUTRAL AND NEARLY NEUTRAL THEORIES 4HEORETICAL 0OPULATION "IOLOGY /LDEN * $ . , 0OFF - 2 $OUGLAS - % $OUGLAS AND + $ &AUSCH %COLOGICAL AND EVOLUTIONARY CONSEQUENCES OF BIOTIC HOMOGENIZATION 4RENDS IN %COLOGY AND %VOLUTION /SBORN 4 # * # 0IRES * ! "IRCHLER $ , !UGER : * #HEN ( 3 ,EE , #OMAI ! -ADLUNG 2 7 $OERGE 6 #OLOT AND 2 ! -ARTIENSSEN 5NDERSTANDING MECH ANISMS OF NOVEL GENE EXPRESSION IN POLYPLOIDS 4RENDS IN 'ENETICS /TTO 3 0 AND * 7HITTON 0OLYPLOID INCIDENCE AND EVOLUTION !NNUAL 2EVIEW OF 'ENETICS /ZKAN ( ! ! ,EVY AND - &ELDMAN !LLOPOLYPLOIDY INDUCED RAPID GENOME EVOLU TION IN THE WHEAT !EGILOPS 4RITICUM GROUP 0LANT #ELL 0ANEIDA & $ AND 3 ! #ARSTAIRS )SOZYMIC DISCRIMINATION OF TROPICAL !USTRALIAN POP ULATIONS OF MESQUITE 0ROSOPIS SPP IMPLICATIONS FOR BIOLOGICAL CONTROL 7EED 2ESEARCH 0APPERT 2 ! * , (AMRICK AND , ! $ONOVAN 'ENETIC VARIATION IN 0UERARIA LOBATA &ABACEAE AN INTRODUCED CLONAL INVASIVE PLANT OF THE SOUTHEASTERN 5NITED 3TATES !MERICAN *OURNAL OF "OTANY
+! 3CHIERENBECK AND -, !ÕNOUCHE
0ARKER " ' -ILLER AND , # "URRILL 3COTCH BROOM Cytisus scoparius , ,INK 0ACIlC .ORTHWEST %XTENSION 0UBLICATION 0ARKER ) - * 2ODRIGUEZ AND - % ,OIK !N EVOLUTIONARY APPROACH TO UNDERSTAND ING THE BIOLOGY OF INVASIONS ,OCAL ADAPTATION AND GENERAL PURPOSE GENOTYPES IN THE WEED Verbascum thapsus. #ONSERVATION "IOLOGY 0ATERSON ! ( + & 3CHERTZ 9 2 ,IN 3 # ,IU AND 9 , #HANG 4HE WEEDINESS OF WILD PLANTS -OLECULAR ANALYSIS OF GENES INmUENCING DISPERSAL AND PERSISTENCE OF JOHN SONGRASS 3ORGHUM HALEPENSE , 0ERS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! 0ATERSON ! ( 7HAT HAS 14, MAPPING TAUGHT US ABOUT PLANT DOMESTICATION .EW 0HYTOLOGIST n 0ETIT 2 * # "ODÏNÒS ! $UCOUSSO ' 2OUSSEL AND ! +REMER (YBRIDIZATION AS A MECHANISM OF INVASION IN OAKS .EW 0HYTOLOGIST 0IGLIUCCI - 0HENOTYPIC 0LASTICITY "EYOND .ATURE AND .URTURE *OHN (OPKINS 5NIVERSITY 0RESS "ALTIMORE 0OHL 2 7 4HE GENUS 3ETARIA IN )OWA )OWA 3TATE *OURNAL OF 3CIENCE 0OHL 2 7 4HE GRASSES OF )OWA )OWA 3TATE *OURNAL OF 3CIENCE 0URUGGANAN - 4HE MOLECULAR POPULATION GENETICS OF REGULATORY GENES -OLECULAR %COLOGY 2AYBOULD ! ! * 'RAY - * ,AWRENCE $ & -ARSHALL 4HE EVOLUTION OF 3PARTINA ANGLICA # % (UBBARD 'RAMINEAE ORIGIN AND GENETIC VARIABILITY "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY 2EED $ ( AND 2 &RANKHAM (OW CLOSELY CORRELATED ARE MOLECULAR AND QUANTITATIVE MEASURES OF GENETIC VARIATION ! META ANALYSIS %VOLUTION 2EJMANEK - AND $ - 2ICHARDSON 7HAT ATTRIBUTES MAKE SOME PLANT SPECIES MORE INVASIVE %COLOGY 2EZNICK $ . AND # + 'HALAMBOR 4HE POPULATION ECOLOGY OF CONTEMPORARY ADAP TATIONS WHAT EMPRICAL STUDIES REVEAL ABOUT THE CONDITIONS THAT PROMOTE ADAPTIVE EVOLU TION 'ENETICA 2IDDLE . # AND * ! "IRCHLER %FFECTS OF REUNITED DIVERGED REGULATORY HIERARCHIES IN ALLOPOLYPLOIDS AND SPECIES HYBRIDS 4RENDS IN 'ENETICS 2IESEBERG , ( (YBRID ORIGINS OF PLANT SPECIES !NNUAL REVIEW IN %COLOGY AND 3YSTEMATICS 2IESEBERG , ( AND * & 7ENDEL )NTROGRESSION AND ITS CONSEQUENCES IN PLANTS )N (ARRISSON 2 ED (YBRID ZONES AND THE EVOLUTIONARY PROCESS .EW 9ORK 53! /XFORD 5NIVERSITY 0RESS 2IESEBERG , ( AND * 7ENDEL 0LANT SPECIATION n RISE OF THE POOR COUSINS .EW 0HYTOLOGIST 2IESEBERG , ( - ! !RCHER AND 2 + 7AYNE 4RANSGRESSIVE SEGREGATION ADAPTA TION AND SPECIATION (EREDITY 2IESEBERG , ( / 2AYMOND $ - 2OSENTHAL : ,AI + ,IVINGSTONE 4 .AKAZATO * , $URFY ! % 3CWARZABACH , ! $ONOVAN AND # ,EXER -AJOR ECOLOGICAL TRANSITIONS IN WILD SUNmOWERS FACILITATED BY HYBRIDIZATION 3CIENCE
%VOLUTION AND PLANT INVASIONS
2OOSE - , AND , $ 'OTTLIEB 'ENETIC AND BIOCHEMICAL CONSEQUENCES OF POLYPLOIDY IN 4RAGOPOGON %VOLUTION 3ALTONSTALL + #RYPTIC INVASION BY A NON NATIVE GENOTYPE OF THE COMMON REED 0HRAGMITES AUSTRALIS INTO .ORTH !MERICA 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! 3CHAAL " ! * & 'ASKIN AND ! , #AICEDO 0HYLOGEOGRAPHY HAPLOTYPE TREES AND INVASIVE PLANT SPECIES *OURNAL OF (EREDITY 3CHIERENBECK + ! ' , 3TEBBINS AND 2 7 0ATTERSON -ORPHOLOGICAL AND CYTOLOGI CAL EVIDENCE FOR POLYPHYLETIC ALLOPOLYPLOIDY IN !RCTOSTAPHVLOS MEWUKKA %RICACEAE 0LANT 3YSTEMATICS AND %VOLUTION 3CHIERENBECK + ! * , (AMRICK 2 . -ACK #OMPARISON OF ALLOZYME VARIABILITY IN A NATIVE AND AN INTRODUCED SPECIES OF Lonicera. (EREDITY 3CHRANZ - % AND /SBORN 4 # .OVEL mOWERING TIME VARIATION IN THE RESYNTHESIZED POLYPLOID Brassica napus. *OURNAL OF (EREDITY 3CHLICHTING # $ /RIGINS OF DIFFERENTIATION VIA PHENOTYPIC PLASTICITY %VOLUTION AND $EVELOPMENT 3CHRANZ - % AND /SBORN 4 # .OVEL mOWERING TIME VARIATION IN RESYNTHESIZED POLYPLOID Brassica napus. *OURNAL OF (EREDITY 3EEHAUSEN / (YBRIDIZATION AND ADAPTIVE RADIATION 4RENDS IN %COLOGY AND %VOLUTION IN PRESS 3HAKED ( + +ASHKUSH ( /ZKAN - &ELDMAN AND ! ! ,EVY 3EQUENCE ELIMINA TION AND CYTOSINE METHYLATION ARE RAPID AND REPRODUCIBLE RESPONSES OF THE GENOME TO WIDE HYBRIDIZATION AND ALLOPOLYPLOIDY IN WHEAT 0LANT #ELL 3IEMANN % AND 7 % 2OGERS 'ENETIC DIFFERENCES IN GROWTH OF AN INVASIVE TREE SPECIES %COLOGY ,ETTERS 3ENCHINA $ 3 ) !LVAREZ 2 # #RONN " ,IU * 2ONG 2 $ .OYES ! ( 0ATERSON 2 ! 7ING 4 ! 7ILKINS AND * & 7ENDEL 2ATE VARIATION AMONG NUCLEAR GENES AND THE AGE OF POLYPLOIDY IN Gossypium. -OLECULAR "IOLOGY AND %VOLUTION 3LATKIN - AND 2 2 (UDSON 0AIRWISE #OMPARISONS OF -ITOCHONDRIAL $.! 3EQUENCES IN 3TABLE AND %XPONENTIALLY 'ROWING 0OPULATIONS 'ENETICS 3MALL 2 , AND * & 7ENDEL 0HYLOGENY DUPLICATION AND INTRASPECIlC VARIATION OF !DH SEQUENCES IN .EW 7ORLD DIPLOID COTTONS 'OSSYPIUM -ALVACEAE -OLECULAR 0HYLOGENETICS AND %VOLUTION 3MALL 2 , AND * & 7ENDEL $IFFERENTIAL EVOLUTIONARY DYNAMICS OF DUPLICATED PARAL OGOUS !DH LOCI IN ALLOTETRAPLOID COTTON 'OSSYPIUM -OLECULAR "IOLOGY AND %VOLUTION 3OLTIS $ % AND 0 3 3OLTIS 0OLYPLOIDY RECURRENT FORMATION AND GENOME EVOLUTION 4RENDS IN %COLOGY AND %VOLUTION 3OLTIS 0 3 AND $ % 3OLTIS 4HE ROLE OF GENETIC AND GENOMIC ATTRIBUTES IN THE SUCCESS OF POLYPLOIDS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! 3OLTIS $ % 0 3 3OLTIS * # 0IRES ! +OVARIK AND * ! 4ATE 2ECENT AND RECURRENT POLYPLOIDY IN 4RAGOPOGON !STERACEAE CYTOGENETIC GENOMIC AND GENETIC COMPARISONS "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY )N PRESS 3ONG + 0 ,U + 4ANG AND 4 # /SBORN 2APID GENOME CHANGE IN SYNTHETIC POLYPLOIDS OF "RASSICA AND ITS IMPLICATIONS FOR POLYPLOID EVOLUTION 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53!
+! 3CHIERENBECK AND -, !ÕNOUCHE
3QUIRRELL * 0 - (OLLINGSWORTH 2 - "ATEMAN * ( $ICKSON - ( 3 ,IGHT - -AC#ONAILL AND - 4EBBITT 0ARTITIONING AND DIVERSITY OF NUCLEAR AND ORGANELLE MARKERS IN NATIVE AND INTRODUCED POPULATIONS OF %PIPACTIS HELLEBORINE /RCHIDACEAE !MERICAN *OURNAL OF "OTANY 3TEBBINS ' , 6ARIATION AND EVOLUTION IN PLANTS .EW 9ORK 53! #OLUMBIA 5NIVERSITY 0RESS 3TEBBINS ' , #OLONIZING SPECIES OF THE NATIVE #ALIFORNIA mORA 0P IN ( ' "AKER AND ' , 3TEBBINS EDITORS 4HE GENETICS OF COLONIZING SPECIES !CADEMIC 0RESS .EW 9ORK PP 3TEBBINS ' , #HROMOSOMAL EVOLUTION IN HIGHER PLANTS !DDISON 7ESLEY 2EADING 3TRAUSS 3 9 * ! 2UDGERS * ! ,AU AND 2 % )RWIN $IRECT AND ECOLOGICAL COSTS OF RESISTANCE TO HERBIVORY 4RENDS IN %COLOGY AND %VOLUTION 3ULTAN 3 0HENOTYPIC PLASTICITY IN PLANTS A CASE STUDY IN ECOLOGICAL DEVELOPMENT %VOLUTION AND $EVELOPMENT 3URLES 3 # * (AMRICK AND " # "ONGARTEN !LLOZYME VARIATION IN BLACK LOCUST 2OBINIA PSEUDOACACIA #ANDIAN *OURNAL OF &OREST 2ESEARCH 4EMPLETON ! 2 3TATISTICAL PHYLOGEOGRAPHY METHODS OF EVALUATING AND MINIMIZING INFERENCE ERRORS -OLECULAR %COLOGY 4HOMPSON * $ -ORPHOLOGICAL VARIATION AMONG NATURAL POPULATIONS OF 3PARTINA ANGLI CA 0AGES IN 3PARTINA ANGLICA A RESEARCH REVIEW ! * 'RAY AND 0 % - "ENHAM EDITORS )NSTITUTE OF 4ERRESTRIAL %COLOGY .ATURAL %NVIRONMENT 2ESEARCH #OUNCIL ,ONDON 4HOMPSON * $ 4HE BIOLOGY OF AN INVASIVE PLANT 7HAT MAKES 3PARTINA ANGLICA SO SUCCESSFUL "IOSCIENCE 4IAN , AND : & #HEN "LOCKING HISTONE DEACETYLATION IN Arabidopsis INDUCES PLEIO TROPIC EFFECTS ON PLANT GENE REGULATION AND DEVELOPMENT 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! 5RBANSKA + - ( (URKA % ,ANDOLT " .EUmER AND + -UMMENHOFF (YBRIDIZATION AND EVOLUTION IN #ARDAMINE "RASSICACEAE AT 5RNERBODEN #ENTRAL 3WTITZERLAND BIOSYS TEMATIC AND MOLECULAR EVIDENCE 0LANT 3YSTEMATICS AND %VOLUTION 6OLKOV 2 ! "ORISJUK . 6 0ANCHUK ) ) 3CHWEIZER $ AND 6 (ELMLEBEN %LIMINATION AND REARRANGEMENT OF PARENTAL R$.! IN THE ALLOTETRAPLOID .ICOTIANA TABA CUM -OLECULAR "IOLOGY AND %VOLUTION 6ITOUSEK 0 "IOLOGICAL INVASIONS AND ECOSYSTEM PROPERTIES CAN SPECIES MAKE A DIFFER ENCE 0AGES IN %COLOGY OF "IOLOGICAL )NVASIONS IN .ORTH !MERICA AND (AWAII ( ! -OONEY AND * ! $RAKE EDITORS 3PRINGER 6ERLAG .EW 9ORK 7ANG 2 , * & 7ENDEL AND * ( $EKKER 7EEDY ADAPTATION IN 3ETARIA SPP ) )SOZYME ANALYSIS OF GENETIC DIVERSITY AND POPULATION GENETIC STRUCTURE IN 3ETARIA VIRIDIS !MERICAN *OURNAL OF "OTANY 7ARWICK 3 ) !LLOZYME AND LIFE HISTORY VARIATION IN lVE NORTHWARDLY COLONIZING .ORTH !MERICAN WEED SPECIES 0LANT 3YSTEMATICS AND %VOLUTION 7ATERHOUSE " - AND / :EIMER @/N THE BRINK THE STATUS OF #HROMOLAENA ODORATA IN .ORTHERN !USTRALIA 0AGES IN 0ROCEEDINGS OF THE lFTH INTERNATION WORKSHOP
%VOLUTION AND PLANT INVASIONS
ON "IOLOGICAL #ONTRAL AND -ANAGEMENT OF #HORMOLAENA ODORATA $URBAN 3OUTH !FRICA :ACHARIADES # 2 -UNIAPPAN AND , 7 3TRATHIE EDITORS 7EBER % AND " 3CHMID ,ATITUDINAL POPULATION DIFFERENTIATION IN TWO SPECIES OF 3OLIDAGO !STERACEAE INTRODUCED INTO %UROPE !MERICAN *OURNAL OF "OTANY 7ENDEL * & ! 3CHNABEL AND 4 3EELANAN "I DIRECTIONAL INTERLOCUS CONCERTED EVOLUTION FOLLOWING ALLOPOLYPLOID SPECIATION IN COTTON 'OSSYPIUM 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES OF THE 53! 7ENDEL * & 'ENOME EVOLUTION IN POLYPLOIDS 0LANT -OLECULAR "IOLOGY 7ENDEL * & AND * * $OYLE 0OLYPLOIDY AND EVOLUTION IN PLANTS )N $IVERSITY AND %VOLUTION IN 0LANTS 2 (ENRY %D #!" 0UBLISHING /XON 5 + 7ETZEL $ + - * (ORAK $ : 3KINNER AND 0 ! +ULAKOW 4RANSFER OF HERBICIDE RESISTANCE TRAITS FROM !MARANTHUS PALMERI TO !MARANTHUS RUDIS 7EED 3CIENCE 7ILLIAMS $ ' 0HYSIOLOGICAL ECOLOGY OF THE INVASIVE GRASS 0ENNISETUM SETACEUM ON (AWAII 0H$ $ISSERTATION 7ASHINGTON 3TATE 5NIVERSITY 7OLFE + ( 9ESTERDAYS POLYPLOIDS AND THE MYSTERY OF DIPLOIDIZATION .ATURE 2EVIEWS 'ENETICS 7OLFFE ! 0 AND - ! -ATZKE %PIGENETICS REGULATION THROUGH EXPRESSION 3CIENCE 8U # 9 7 * :HANG # : &U AND " 2ONG 'ENETIC DIVERSITY OF ALLIGATOR WEED IN #HINA BY 2!0$ ANALYSIS "IODIVERSITY AND #ONSERVATION 9ANNIC ' ! "AUMEL AND - , !ÕNOUCHE 5NIFORMITY OF THE NUCLEAR AND CHLORO PLAST GENOMES OF 3PARTINA MARITIMA 0OACEAE A SALT MARSHES SPECIES IN DECLINE ALONG THE 7ESTERN %UROPEAN #OAST (EREDITY )N PRESS 9E 7 ( * ,I ( , #AO AND 8 * 'E 'ENETIC UNIFORMITY OF !LTERNANTHERA PHILOXEROI DES IN 3OUTH #HINA 7EED 2ESEARCH 9ODER * ! 7ALSH # 0 "ESTOR 4 ( #YTOSINE METHYLATION AND THE ECOLOGY OF INTRAGENOMIC PARASITES 4RENDS IN 'ENETICS :HAO 8 0 3I 9 (ANSON 2 % #RANE # 2 0RICE ( * 3TELLY $ - 7ENDEL * & AND ! ( 0ATERSON $ISPERSED REPETITIVE $.! HAS COLONIZED NEW GENOMES SINCE POLY PLOID FORMATION IN COTTON 'ENOME 2ESEARCH
#HAPTER TEN
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS AND THEIR COMMUNITY CONSEQUENCES A THEORETICAL CONSIDERATION ON THE ROLE OF ADAPTATION IN BIOLOGICAL INVASIONS - +ONDOH
).42/$5#4)/. %COLOGICAL THEORY SUGGESTS THAT INTERSPECIlC INTERACTIONS ARISING BETWEEN AN ALIEN SPECIES AND NATIVE SPECIES HOLD THE KEY TO INVASION SUCCESS BY AN ALIEN SPECIES 4HE WELL KNOWN HYPOTHESIS THAT AN ALIEN SPECIES THAT HAS FEW NATURAL ENEMIES IS MORE LIKELY TO BE A SUCCESSFUL INVADER EG "LOSSEY AND .ÚTZOLD -ITCHELL AND 0OWER IMPLIES THE IMPORTANCE OF A TROPHIC INTERACTION 4HE HYPOTHESIS THAT A COMMUNITY WITH HIGHER SPECIES RICHNESS IS MORE RESISTANT TO A BIOLOGICAL INVASION 3TACHOWICZ ET AL +ENNEDY ET AL IS STRONGLY BASED ON THE COMPETITION THEORY 4ILMAN &URTHER THE WAY THROUGH WHICH A BIOLOGICAL -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY 225n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
- +ONDOH
INVASION AFFECTS THE LOCAL COMMUNITY IS AN ALIEN NATIVE INTERSPECIlC INTERACTION SUCH AS RESOURCE COMPETITION TROPHIC INTERACTION AND ALLELOPATHY 4HE IMPORTANT ROLE OF INTERSPECIlC INTERACTIONS IN A BIOLOGICAL INVASION SUGGESTS THE DETAILED EVALUATION OF THE INTERSPECIlC INTERACTIONS BETWEEN ALIEN AND NATIVE SPECIES AS AN INTERESTING APPROACH TO THE BIOLOGICAL INVASION ISSUES 4HERE ARE TWO DIFFERENT BUT NOT MUTUALLY EXCLUSIVE VIEWS OF WHAT CHARAC TERIZES AN ALIEN NATIVE INTERACTION THE hSPECIES IDENTITYv AND hCONTACT EXPERI ENCEv VIEWS 4HE SPECIES IDENTITY VIEW FOCUSES ON THE IDENTITY OF THE FOCAL SPECIES EG "AKER 2OY +OLAR AND ,ODGE 4HE ALIEN AND NATIVE SPECIES ARE CHARACTERIZED BY lXED SETS OF SPECIES SPECIlC TRAITS SUCH AS COMPETITIVE ABILITY (ERBOLD AND -OYLE 0ETREN AND #ASE (OLWAY "YERS WHICH INmUENCE THEIR INTERACTION AND THUS THE INVASION SUCCESS AND ITS IMPACT ON THE LOCAL COMMUNITY EG 7ILLIAMS )N THIS VIEW AN INTERSPECIlC INTER ACTION THAT ARISES BETWEEN AN ALIEN AND NATIVE SPECIES IS EXPLAINED MAINLY BY THEIR INHERENT SPECIES SPECIlC TRAITS AND SO ARE ITS POPULATION LEVEL CONSEQUENCES -ACK ET AL 4HE CONTACT EXPERIENCE VIEW 3AKAI ET AL FOCUSES ON THE LACK OF hCONTACT EXPERIENCEv BETWEEN ALIEN AND NATIVE SPECIES AS THE MAJOR FACTOR CHARACTERIZING THEIR INTERACTION .ATIVE SPECIES THAT COEXIST IN THE LOCAL HABITAT HAVE THE EXPERI ENCE OF ENCOUNTERS OR INTERACTIONS WITH EACH OTHER OVER VARYING TIMESCALES WHICH PROVIDES THE OPPORTUNITY FOR LOCAL SPECIES TO ADAPT TO EACH OTHER EG ,AWLOR AND -AYNARD 3MITH )N CONTRAST AN ALIEN SPECIES AND A NATIVE SPECIES DUE TO TEMPORAL OR SPATIAL SEPARATION SHARE A RELATIVELY SHORT HISTORY AND ARE LESS LIKELY TO ADAPT TO EACH OTHER 4HE LACK OF ADAPTATION SHOULD HAVE MAJOR IMPACT ON THE ALIEN NATIVE INTERSPECIlC INTERACTION EG 7ARE $ILL -ARURRAN #ROY AND (UGHES (UGHES ET AL -ALONEY AND -CLEAN #ALLAWAY AND !SCHEHOUG 2EHAGE ET AL AND THE RESULTANT COMMUNITY STRUCTURE 'RIFlN ET AL 2ICCIARDI ET AL 2ICCIARDI AND !TKINSON (OWEVER ONLY A FEW STUDIES HAVE COMPREHENSIVELY CONSIDERED THE CONTACT EXPERI ENCE EFFECT IN THE CONTEXT OF BIOLOGICAL INVASION ISSUES BUT SEE 3AKAI ET AL .OW WE NEED A STRONG CONCEPTUAL BASIS FOR THE ISSUE OF HOW CONTACT EXPERIENCE INmUENCES A BIOLOGICAL INVASION FOR GUIDING FURTHER RESEARCH )N THIS CHAPTER ) PRESENT A THEORETICAL FRAMEWORK FOR APPLYING THE CONTACT EXPERIENCE VIEW TO ALIEN NATIVE TROPHIC INTERACTIONS ) CHOSE THIS PARTICULAR INTER ACTION AS IT IS KNOWN TO PLAY THE ESSENTIAL ROLE IN SHAPING COMMUNITY STRUCTURE EG (AIRSTONE ET AL &RETWELL 0OWER )T DRIVES DIVERSE PREY PREDATOR POPULATION DYNAMICS INmUENCES POPULATION DENSITY AND DISTRIBUTION (AIRSTONE ET AL GENERATES TWO MAJOR INTERSPECIlC INDIRECT INTERACTIONS [RESOURCE COMPETITION 4ILMAN AND APPARENT COMPETITION (OLT "ONSALL AND (ASSELL BUT SEE #HANETON AND "ONSALL ] THAT LIMIT THE NUMBER OF COEXISTING SPECIES AND FORMS A MAJOR COMPONENT OF THE NATURAL SELECTION PRESSURE %NDLER &URTHER THE MACROSCOPIC FOOD WEB TOPOLOGY CAN BE AN ESSENTIAL DETERMINANT OF POPULATION STABILITY 0IMM AND ECOSYS TEM FUNCTION 4HÏBAULT AND ,OREAU
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
4HE TWO MAJOR QUESTIONS OF THE PRESENT CHAPTER ARE OF HOW THE LACK OF CON TACT EXPERIENCE INmUENCES A TROPHIC INTERACTION AND WHAT IS THE POPULATION TO COMMUNITY LEVEL CONSEQUENCE OF A CONTACT EXPERIENCE FREE INTERACTION 4O ANSWER THESE QUESTIONS ) lRST EXPLAIN THE BEHAVIORAL BASIS OF A TROPHIC INTERACTION 4HEN ) WILL PROVIDE SEVERAL HYPOTHESES ON HOW ALIEN NATIVE INTERSPECIlC TROPHIC INTERACTIONS DIFFER FROM INTERACTIONS BETWEEN NATIVES AND HOW THIS DIFFERENCE AFFECTS THE POPULATION OR COMMUNITY FOLLOWING A BIOLOGICAL INVASION
4(% #/.4!#4 %80%2)%.#% 6)%7 /& !,)%. .!4)6% 42/0()# ).4%2!#4)/.3 &AILURE OF RECOGNITION
#ONSIDER A DOG AND A PIECE OF MEAT THAT IS RELEASING AN ODOR )F HUNGRY ENOUGH THE DOG WILL FOLLOW THE ODOR AND EAT THE MEAT THERE IS AN INDIVIDUAL LEVEL TROPHIC INTERACTION 4HE DOGS FORAGING BEHAVIOR CONSISTS OF THREE SUB PROCESSES EG 'RIFlN ET AL hINFORMATION RECEPTIONv hINFORMATION PROCESSINGv AND hBEHAVIORAL RESPONSEv 4HE DOG DETECTS THE ODOR USING CHEMICAL RECEPTORS AND THE NERVOUS SYSTEM INFORMATION RECEPTION 4HE ODOR IS ASSOCIATED WITH MEAT BASED ON THE DOGS PREVIOUS EXPERIENCE OR AN INBORN ASSOCIATION INFORMATION PROCESSING 5SING THIS INFORMATION THE DOG MAKES A DECISION TO FOLLOW THE ODOR AND LOCATES AND EATS THE MEAT BEHAVIORAL RESPONSE )NFORMATION PROCESSING IS THE SUB PROCESS BY WHICH A MEANING e.g., hTHERE IS MEATv THAT IS CONVEYED BY THE CUE THE ODOR IS hUNDERSTOODv )N GENERAL CUE ALONE OFTEN HAVE LITTLE TO DO WITH THE INFORMATION THAT IS CONVEYED 4HIS IS ANALOGOUS TO THE FACT THAT HOW A WORD SOUNDS HAS LITTLE TO DO WITH WHAT THE WORD ACTUALLY MEANS 4HUS SUCCESSFUL INFORMATION PROCESSING OR WHETHER THE MEANING OF THE CUE IS CORRECTLY UNDERSTOOD DEPENDS ON THE CAPABILITY OF CUE INFORMATION ASSOCIATION EG 4HORNDIKE 0AVLOV )N THE CASE OF THE DOG AND THE MEAT FOR EXAMPLE THE CHEMICAL COMPOSITION OF THE MEATS ODOR DOES NOT NECESSAR ILY MEAN A BLOCK OF MEAT OR POTENTIAL FOOD WITHOUT THE CORRECT ASSOCIATION 4HE CUE INFORMATION ASSOCIATION THE CORE OF INFORMATION PROCESSING IS SHAPED THROUGH hEXPERIENCEv ON VARIOUS TIME SCALES .ATURAL SELECTION MIGHT CREATE THE CORRECT ASSOCIATION IF THE CAPABILITY OF INFORMATION PROCESSING AFFECTS REPRO DUCTIVE SUCCESS 2OEDER AND 4REAT WHILE AN INDIVIDUAL MIGHT LEARN THE VISUAL CHEMICAL OR PHONIC CUES OF POTENTIAL PREY THROUGH CONTINUOUS ENCOUNTER EXPERIENCES WITH THE PREY ON THE SHORTER TIME SCALE $OMJAN AND "URKHARD &OSTER 4HIS EXPERIENCE DEPENDENCE IMPLIES THAT THE LACK OF CONTACT EXPERIENCE BETWEEN A PREY AND PREDATOR INmUENCES THE BEHAVIORAL RESPONSES OF ONE TO THE OTHER BY ALTERING INFORMATION PROCESSING AND CONSEQUENTLY AFFECTS THEIR TROPHIC INTERACTION )N TROPHIC INTERACTIONS IT IS CONVENIENT TO CONSIDER TWO DIFFERENT LEVELS OF RECOG NITION hTROPHIC ROLE RECOGNITIONv AND hTROPHIC SPECIES RECOGNITIONv 4HE FORMER
- +ONDOH
IS RECOGNITION OF WHETHER THE INDIVIDUAL IS POTENTIAL PREY POTENTIAL PREDATOR OR NEITHER WHILE THE LATTER IS RELATED TO MORE DETAILED RECOGNITION WITHIN A TROPHIC ROLE SUCH AS DISTINCTION BETWEEN SPECIES OR ORGANISM TYPES THAT REQUIRE DIFFERENT STRATEGIES TO COPE WITH )F TROPHIC ROLE RECOGNITION FAILS ALL THE BEHAVIORS WHICH SHOULD FOLLOW A CONTACT WITH POTENTIAL PREYPREDATOR DOES NOT FOLLOW &ORAGING BEHAVIOR WHICH NORMALLY FOLLOWS CONTACT WITH PREY MIGHT NOT OCCUR BETWEEN TWO SPECIES THAT HAVE NO CONTACT EXPERIENCE WITH EACH OTHER EG 7ARE #ROY AND (UGHES "OND AND +AMIL ! PREY MIGHT FAIL TO RECOGNIZE #URIO AND CAN BE MORE VULNERABLE TO A NOVEL PREDATOR EG $ILL -AGURRAN -ALONEY AND -CLEAN )F TROPHIC SPECIES RECOGNITION FAILS AN INCORRECT BEHAVIORAL RESPONSE WHICH SHOULD FOLLOW A CONTACT WITH ANOTHER TROPHIC SPECIES MAY FOLLOW THE ENCOUNTER 0OSSIBLE CONSEQUENCES OF THIS WILL BE DISCUSSED LATER &AILURE OF THE BEHAVIORAL RESPONSE
!NOTHER POSSIBLE MECHANISM THROUGH WHICH THE LACK OF CONTACT EXPERIENCE ALTERS A TROPHIC INTERACTION IS A FAILURE IN THE THIRD SUB PROCESS BEHAVIORAL RESPONSE 4HE STRATEGY REQUIRED TO CONSUME A PREY IS OFTEN PREY SPECIES SPECIlC ! PREDATOR HAS TO CHOOSE THE CORRECT PLACE AND TIME TO lND A PREY OR MIGHT NEED A SPECIlC TECHNIQUE TO CAPTURE OR CONSUME THE PREY )N THIS SITUATION WHETHER A PREDATOR CAN USE A NOVEL PREY DEPENDS ON THE APPLICABILITY OF THE PREDATORS FORAGING STRAT EGY WHICH IS SHAPED THROUGH PREVIOUS INTERACTIONS WITH OTHER PREY SPECIES TO THE NOVEL PREY SPECIES SKILL TRANSFER THEORY %LLIS (AZLETT )F THE NOVEL PREY BEHAVES OR RESPONDS LIKE A PREY FAMILIAR TO THE PREDATOR THE PREDATOR MIGHT BE ABLE TO HANDLE THE NOVEL PREY 2ICCIARDI AND !TKINSON AND A TROPHIC INTERACTION WOULD OCCUR NORMALLY )F PREVIOUS FORAGING BEHAVIOR IS NOT APPLICABLE TO THE NOVEL PREY THE PREDATOR IS UNLIKELY TO CONSUME THE NOVEL PREY SUCCESSFULLY 4HUS THE LACK OF CONTACT EXPERIENCE CAN PREVENT SUCCESSFUL CONSUMPTION BEHAV IOR 7ARE #ROY AND (UGHES (UGHES ET AL 4HE SAME SHOULD BE TRUE FOR THE PREYS ANTI PREDATION BEHAVIOR 3OLUK 3IH ET AL AS A BEHAVIOR REQUIRED TO AVOID A PREDATOR IS PREDATOR SPECIlC )F THE PREY HAS NO CONTACT EXPERIENCE WITH THE FOCAL PREDATOR AND IF THE PREYS ANTI PREDATION STRATEGY IS NOT APPLICABLE TO THE NOVEL PREDATOR THE CORRECT PREDATOR SPECIlC DEFENCE MIGHT NOT FOLLOW THE CONTACT )N AN ALIEN NATIVE INTERACTION THE BEHAVIORAL RESPONSE EITHER PREY CONSUMP TION OR PREDATOR AVOIDANCE MIGHT FAIL EVEN IF THE COUNTERPART SPECIES IS NOT NOVEL TO THE FOCAL SPECIES 4HIS IS BECAUSE A HABITAT SPECIlC HISTORY CAN LEAD TO DIVERGENCE IN THE WAY IN WHICH PREY IS USED OR PREDATORS ARE AVOIDED IN DIFFERENT HABITATS EG "RODIE AND "RODIE 4HOMPSON #ONSIDER TWO SEPA RATE HABITATS ! AND " INHABITED BY THE SAME SET OF PREY AND PREDATOR SPECIES 0REY PREDATOR CO ADAPTATION OCCURS INDEPENDENTLY IN THE TWO HABITATS IMPLY ING THAT THE PREY AND PREDATOR FROM DIFFERENT HABITATS ARE NOT EXPERIENCED WITH EACH OTHER 4HEREFORE THE PREY PREDATOR INTERACTION ARISING FROM THE OPPOSITE
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
COMBINATION PREY FROM ! AND PREDATOR FROM " OR VICE VERSA CAN DIFFER FROM THE ORIGINAL INTERACTION WITHIN (ABITAT ! OR "
#/.3%15%.#%3 /& 4(% #/.4!#4 %80%2)%.#% &2%% 42/0()# ).4%2!#4)/.3 (IGH VARIANCE IN ALIEN NATIVE INTERACTION STRENGTH
!CCORDING TO BIOLOGICAL INVASION THEORY AN ALIEN PREY SPECIES CAN HAVE MORE ADVANTAGES THAN A NATIVE PREY SPECIES IN THE LOCAL HABITAT BECAUSE THE ALIEN SPE CIES IS LESS LIKELY TO HAVE NATURAL ENEMIES IN THE NEW HABITAT EG %LTON "LOSSEY AND .ÚTZOLD -ACK ET AL +EANE AND #RAWLEY -ITCHELL AND 0OWER 4ORCHIN ET AL 4HIS IS KNOWN AS ENEMY RELEASE HYPOTHESIS 4HIS HYPOTHESIS SUGGESTS THAT THE LACK OF A NATIVE CONSUMERS CONTACT EXPERIENCE WITH THE ALIEN PREY SPECIES LOWERS THE STRENGTH OF THE TROPHIC INTERACTION BETWEEN THEM &ROM THE CONTACT EXPERIENCE POINT OF VIEW THERE ARE THREE POTENTIAL REASONS FOR THIS HYPOTHETICAL PATTERN &IRST A NATIVE CONSUMER DOES NOT RECOGNIZE THE ALIEN SPECIES AS POTENTIAL PREY 3ECOND THE NATIVE CONSUMER DOES NOT hKNOWv HOW TO HANDLE THE NOVEL PREY SPECIES 4HIRD EVEN IF THE ALIEN PREY SPECIES IS NOT NOVEL IT MIGHT BEHAVE IN A NOVEL WAY DUE TO A HABITAT SPECIlC EVOLUTIONARY PROCESS (OWEVER ) SUGGEST THAT THE ENEMY RELEASE HYPOTHESIS ONLY CONSIDERS A PART OF THE TOTAL PICTURE OF ALIEN NATIVE TROPHIC INTERACTIONS &IRST THE HYPOTHESIS OVERLOOKS THE PREYS ANTI PREDATORY BEHAVIOR !S THE LACK OF CONTACT EXPERIENCE MAY LOWER THE ALIENS DEFENCE EFlCIENCY AGAINST THE NATIVE PREDATOR 2EHAGE ET AL THEN THEIR INTERACTION STRENGTH CAN BE STRONGER 4AKING THIS EFFECT INTO ACCOUNT THE LACK OF CONTACT EXPERIENCE HAS TWO OPPOSITE CONSEQUENCES LOW PREDATION EFlCIENCY WHICH DECREASES THE INTERACTION STRENGTH AND LOW DEFENCE EFlCIENCY WHICH INCREASES THE STRENGTH 3ECOND THE ENEMY RELEASE HYPOTHESIS OVERLOOKS ALIENS PREY )F THE LACK OF CONTACT EXPERIENCE AFFECTS THE ALIENS VULNERABILITY TO NATIVE NATURAL ENEMIES THIS SHOULD BE ALSO APPLICABLE TO THE INTERACTION OF THE FOCAL ALIEN AS A PREDATOR AND A POTENTIAL PREY IN THE LOCAL HABITAT )N THIS INTERACTION THE BEHAVIORS INmUENCED BY THE CONTACT EXPERIENCE ARE THE ALIENS FORAGING BEHAVIOR AND THE NATIVES DEFENCE BEHAVIOR )N SUMMARY FOUR DIFFERENT BEHAVIORS MUST BE CONSIDERED TO EVALUATE THE EFFECT OF THE LACK OF CONTACT EXPERIENCE ON INTERACTION STRENGTH AND INVASION SUCCESS THE ALIENS FORAGING BEHAVIOR AND ANTI PREDATORY BEHAVIOR AND THE NATIVES FORAG ING BEHAVIOR ON THE ALIEN AND ANTI PREDATORY BEHAVIOR AGAINST THE ALIEN &IG 4HE COMPLEX INTERACTION BETWEEN THE FOUR INTER RELATED BEHAVIORS MAKES CONSIS TENT PREDICTION MORE DIFlCULT THAN PREVIOUSLY THOUGHT !SSUME THAT 3PECIES ! IS INTRODUCED TO A LOCAL HABITAT IN WHICH IT INTERACTS WITH A NATIVE NATURAL ENEMY 3PECIES % AND A NATIVE PREY 3PECIES 2 AND ASSUME THAT THE STRENGTH OF A TROPHIC INTERACTION IS DETERMINED BY THE BALANCE BETWEEN THE PREYS ANTI PREDATORY DEFENCE AND THE PREDATORS FORAGING BEHAVIOR 7HETHER THE LACK OF CONTACT EXPERIENCE
- +ONDOH
&IG &OUR BEHAVIORS AFFECTING THE TROPHIC INTERACTIONS BETWEEN AN ALIEN SPECIES AND A NATIVE SPECIES )F PREDATOR AVOIDANCE IS MORE DEPENDENT ON CONTACT EXPERIENCE THAN IS PREY CONSUMPTION AN ALIEN SPECIES WILL HAVE A STRONGER INTERACTION WITH THE NATIVE SPECIES )F PREY CONSUMPTION IS MORE DEPENDENT ON CONTACT EXPERIENCE THAN IS PREDATOR AVOIDANCE AN ALIEN SPECIES WILL HAVE A WEAKER INTERACTION WITH THE NATIVE SPECIES )F THERE IS NO CONSISTENT TREND THE INTERACTION STRENGTH WILL BE CHARACTERIZED BY A HIGHER VARIANCE
BENElTS THE ALIEN SPECIES DEPENDS ON THE LEVEL OF EACH SPECIES CONTINGENT PRE ADAPTATION !GRAWAL AND +OTANEN 2ICCIARDI AND !TKINSON TO AN INTERACTING SPECIES 4HE ALIEN SPECIES WOULD BE AT AN ADVANTAGE IF ITS PRE ADAPTIVE DEFENCE LEVEL TO 3PECIES % WERE HIGHER THE PRE ADAPTIVE DEFENCE LEVEL OF 3PECIES 2 TO 3PECIES ! WERE LOWER THE PRE ADAPTIVE FORAGING LEVEL OF 3PECIES % TO 3PECIES ! WERE LOWER OR THE PRE ADAPTIVE FORAGING LEVEL OF 3PECIES ! TO 3PECIES 2 WERE HIGHER )F THERE IS A CONSISTENT PATTERN IN WHICH BEHAVIOR FORAGING OR ANTIPRE DATORY DEFENCE OR TROPHIC ROLE IS MORE DEPENDENT ON CONTACT EXPERIENCE THEN IT IS POSSIBLE TO MAKE A CONSISTENT PREDICTION ON HOW THE CONTACT EXPERIENCE AFFECTS THE INTERACTION STRENGTH &OR EXAMPLE IF PREDATOR RELIES MORE ON THE EXPERIENCE THAN PREY DOES A TROPHIC INTERACTION IN THE ABSENCE OF CONTACT EXPERIENCE WILL BE WEAKER THAN AN IN ITS PRESENCE )F THE PREY IS MORE DEPENDENT ON THE EXPERIENCE A TROPHIC INTERACTION BETWEEN NOVEL SPECIES WOULD BE STRONGER THAN THE NORMAL ONE )F THERE IS NO CONSISTENT PATTERN IN WHICH ONE TROPHIC ROLE IS MORE DEPENDENT ON CONTACT EXPERIENCE THE DISRUPTION OF THE PREDATION DEFENCE BALANCE SHOULD LEAD TO MORE VARIABLE TROPHIC INTERACTION STRENGTH 7HICH IS THE REAL PATTERN IN NATURE )T WOULD BE INTERESTING TO EXAMINE HOW THE FREQUENCY DISTRIBUTION OF THE INTERACTION STRENGTH OF ALIEN NATIVE INTERACTIONS DIFFERS FROM THAT OF NATIVE NATIVE INTERACTIONS )T IS WELL RECOGNIZED THAT COMPETITIVE ABILITY IS AFFECTED BY THE INTERACTING EFFECTS OF RESOURCE AVAILABILITY BOTTOM UP EFFECT AND VULNERABILITY TO NATURAL ENEMIES
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
TOP DOWN EFFECT EG 0OWER ,EIBOLD 4HEORY SUGGESTS THAT THE COEXISTENCE OF SPECIES SHARING A SIMILAR RESOURCE AND NATURAL ENEMY REQUIRES A TRADE OFF BETWEEN RESOURCE COMPETITION AND NATURAL ENEMY AVOIDANCE ,UBCHENCO ,EIBOLD )F THE STRENGTH OF AN ALIEN NATIVE TROPHIC INTERACTION IS CHAR ACTERIZED BY A HIGH VARIANCE IT MIGHT LEAD TO THE PREDICTION THAT THE COMPETITIVE SUPERIORITY OF AN ALIEN SPECIES SHOULD BE ABNORMALLY HIGH OR LOW )F THE TROPHIC LINK TO THE CONSUMPTION OF THE ALIEN SPECIES IS WEAK AND THE LINK FROM THE ALIEN SPECIES IS STRONG THE ALIEN WILL HAVE A HIGH POPULATION DENSITY )F THE TROPHIC LINK TO THE CONSUMPTION OF THE ALIEN SPECIES IS STRONG AND THE LINK FROM THE ALIEN SPECIES IS WEAK THE ALIEN WILL HAVE A LOW POPULATION DENSITY 4HIS IMPLIES THAT ALTHOUGH THERE ARE MANY ALIEN SPECIES THAT CANNOT BECOME ESTABLISHED WHEN AN ALIEN SPECIES SUCCEEDS IN BECOMING ESTABLISHED IT TENDS TO BE VERY ABUNDANT !LIEN NATIVE MISMATCHING IN ADAPTIVE SPEED AND hBOOM AND BUSTv PATTERN OF ALIEN POPULATIONS
!LTHOUGH THE LACK OF CONTACT EXPERIENCE MAY AS ) HAVE ARGUED IN THE LAST SECTION LOWER THE FORAGING EFlCIENCY OR DEFENCE EFlCIENCY AT THE INITIAL STAGE OF INVASION THE EFlCIENCY IS LIKELY TO BE GRADUALLY IMPROVED AS AN ALIEN SPECIES AND RESIDENT SPE CIES LEARN OR EVOLVE TO ADAPT EACH OTHER #ARROLL AND $INGLE -ARON AND 6ILA 4HE PREVIOUS STUDIES THAT CONSIDER THE COADAPTIVE PROCESS HAVE STRESSED THE DISADVANTAGE OF AN ALIEN SPECIES BY SUGGESTING THAT AN ALIEN SPECIES IS OFTEN CHARAC TERIZED BY A LOW POPULATION DENSITY AND LOW GENETIC DIVERSITY WHICH LOWERS EVOLU TION SPEED 4SUTSUI ET AL 4HIS IS WHY MULTIPLE INTRODUCTIONS WHICH INCREASE GENETIC DIVERSITY ENHANCE ALIENS INVASION SUCCESS +OLBE ET AL (OWEVER THE DISADVANTAGE OF ALIEN SPECIES CAN BE COMPENSATED !N EXAMPLE IS ALIENS BEHAVIORAL PLASTICITY 'RAY 3OL AND ,EFEBVRE ANALYZED THE RELATIONSHIP BETWEEN BRAIN SIZE IN BIRDS AND INVASION SUCCESS IN .EW :EALAND THEY FOUND THAT SPECIES WITH LARGER BRAINS HAD A HIGHER PROBABILITY OF INTRODUCTION SUCCESS THAN DID SPECIES WITH SMALLER BRAINS 4HIS PATTERN IS EXPLAINED BY THE EFFECT OF BRAIN SIZE ON THE BIRDS INTERACTION WITH RESOURCES A BIRD WITH A LARGER BRAIN IS BETTER AT DISCOVERING NEW FOODS IN THE NEW HABITAT 3OL AND ,EFEBVRE 4HIS VIEW PROVIDES A SPECIES IDENTITY EXPLANATION FOR INVASION SUCCESS IE A SPE CIES WITH HIGH PLASTICITY IS A SUCCESSFUL INVADER (ERE FROM THE VIEWPOINT OF CONTACT EXPERIENCE ) SHOW ANOTHER FACTOR THAT MAY OVERCOME THE ALIENS DISADVANTAGE #ONSIDER THAT A SMALL NUMBER OF 3PECIES ! IS INTRODUCED TO A COMMUNITY WHERE A POTENTIAL PREDATOR 3PECIES % EXISTS &IGS !FTER ITS INTRODUCTION THE ALIEN 3PECIES ! WOULD LEARN OR EVOLVE TO LOWER THE PREDATION PRESSURE BY 3PECIES % WHILE 3PECIES % WOULD ADAPT TO INCREASE THE PREDATION PRESSURE ON 3PECIES ! .OTE THAT IN THIS CO ADAPTATION PROCESS THE ADAPTIVE SPEEDS WOULD DIFFER DUE TO DIFFERENCES IN THE CONTACT OPPORTUNITIES BETWEEN ALIEN AND NATIVE SPECIES 7HEN AN ALIEN SPECIES IS INTRODUCED ITS ABUN DANCE SHOULD BE MUCH LOWER THAT THAT OF NATIVE SPECIES 4HIS IMPLIES THAT THE ALIEN PREY HAS MORE OPPORTUNITY TO GAIN EXPERIENCE IN HANDLING THE NATIVE PREDATOR
- +ONDOH
&IG !LIEN NATIVE MISMATCHING IN EVOLUTIONARY SPEED LEADS TO BOOM AND BUST PATTERN OF ALIEN POPULATIONS %ACH COLUMN IS FOR AN ALIEN PREDATOR AND ITS PREY LEFT COLUMN AND AN ALIEN PREY AND ITS PREDATOR RIGHT COLUMN IN THE PRESENCE OF PREY PREDATOR COEVOLUTION %ACH PANEL SHOWS POPULATION DYNAMICS TOP #. #! 2. 2! ADAPTIVE LEVEL MIDDLE THE FRACTION OF ADAPTED INDIVIDUALS #!#. #! FOR THE PREDATOR AND 2!2. 2! FOR THE PREY AND PER CAPITA PREDATION RATE BOTTOM ANN #. 2. ANA #! 2. AAN #. 2! AAA #! 2! ;#. #! 2. 2! = )N THE TOP AND MIDDLE PANELS THE THICK LINES AND THIN LINES ARE FOR PREDATOR AND PREY RESPECTIVELY #ONSIDER POPULATIONS OF AN ALIEN SPECIES AND NATIVE SPECIES EACH OF WHICH CONSISTS OF MANY NON ADAPTED INDIVIDUALS WITH LOW DEFENCE ABILITY OR LOW FORAGING ABILITY AND A FEW ADAPTED INDIVIDUALS WITH HIGH DEFENCE ABILITY OR HIGH FORAGING ABILITY 4HE POPULATION DYNAMICS IS DESCRIBED BY D #. D T RC +C n #. n #! #. E ANN #. 2. E AAN #. 2! n MC #. D #! D T RC +C n #. n #! #! E AAA #. 2. E AAN #. 2! n MC #! D 2. D T RR +R n 2. n 2! 2. n ANN #. 2. n ANA #! 2. n MR 2. D 2! D T RR +R n 2. n 2! 2! n AAN #. 2! n AAA #! 2! n MR 2! WHERE #. #! 2. AND 2! ARE POPULATION ABUNDANCES OF NON ADAPTED PREDATOR ADAPTED PREDATOR NON ADAPTED PREY AND ADAPTED PREY RESPECTIVELY RI IS THE INTRINSIC GROWTH RATE +I IS CARRYING CAPACITY SUPPORTED BY RESOURCES THAT ARE NOT EXPLICITLY REPRESENTED BY THE EQUATIONS MI IS THE MORTALITY RATE OF THE PREY I R AND PREDATOR C E IS THE ASSIMILATION EFlCIENCY 4HE PER CAPITA PREDATION RATES HOLD THAT ANA ANN AAA AAN IMPLYING THAT THE PREDATION RATE OF THE NON ADAPTED PREDATOR ON THE NON ADAPTED PREY IS SAME WITH THAT OF THE ADAPTED PREDATOR ON THE ADAPTED PREY 0ARAMETERS ANN AND AAA ARE SET TO A VALUE WITH WHICH AN ALIEN SPECIES CANNOT PERSIST 4HIS SETTING CONlRMS THAT A TEMPORAL INCREASE OF AN ALIEN SPECIES IS DUE TO THE ALIEN NATIVE MISMATCH IN EVOLUTIONARY SPEED 4HE INITIAL CONDITION IS THAT #. #! 2. 2! FOR PREDATORS INVASION AND FOR PREYS INVASION 0ARAMETERS THAT ARE USED ARE RC RN +C +N MC MN ANN ANA AAN AAA E FOR PREDATORS INVASION AND FOR PREYS INVASION
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
&IG !LIEN NATIVE MISMATCHING IN SPEED OF ADAPTIVE BEHAVIORAL PLASTICITY LEADS TO BOOM AND BUST PATTERN OF ALIEN POPULATIONS %ACH COLUMN IS FOR AN ALIEN PREDATOR SPECIES AND ITS PREDATOR PREY LEFT COLUMN AND AN ALIEN PREY SPECIES AND ITS PREDATOR RIGHT COLUMN IN THE PRESENCE OF THE LEARNING PROCESS %ACH PANEL SHOWS POPULATION DYNAMICS TOP # 2 ADAPTIVE LEVEL MIDDLE !# FOR THE PREDATOR !2 FOR THE PREY AND INTERACTION STRENGTH BOTTOM !# n A !2 )N THE TOP AND MIDDLE PANELS THE THICK LINES AND THIN LINES ARE FOR PREDATOR AND PREY RESPECTIVELY ! SCALE FOR PREY POPULATION LEVEL IS INDICATED ON THE RIGHT OF EACH PANEL #ONSIDER POPULATIONS OF A PREY SPECIES AND A PREDATOR SPECIES WHOSE POPULATION DYNAMICS IS DESCRIBED BY D # D T RC +C n # # E & # 2 n MC # AND D 2 D T RR +R n 2 2 n & # 2 n MR 2 WHERE # AND 2 ARE POPULATION ABUNDANCES OF THE PREDATOR AND PREY RESPECTIVELY RI IS THE INTRINSIC GROWTH RATE +I IS CARRYING CAPACITY SUPPORTED BY RESOURCES THAT ARE NOT EXPLICITLY REPRESENTED BY THE EQUATIONS MI IS THE MORTALITY RATE OF THE PREY I R AND PREDATOR C E IS THE ASSIMILATION EFlCIENCY 4HE PER CAPITA PREDATION RATE & IS A TEMPORAL VARIABLE AND DETERMINED BY PREDATORS FORAGING RELATED ADAPTIVE LEVELS !# AND PREYS DEFENCE RELATED ADAPTIVE LEVEL !2 THAT IS & B !# n A !2 4HE ADAPTIVE DYNAMICS IS GIVEN BY D !# D T 'C !#MAX n !# 2 AND D !2 D T 'R !2MAX n !2 !# n A !2 # WHERE 'C AND 'R ARE THE LEARNING RATES !#MAX AND !2MAX ARE THE MAXIMUM LIMITS OF ADAPTIVE LEVELS FOR THE PREDATOR AND PREY RESPECTIVELY ) USED THE PARAMETERS 'C 'R !#MAX !2MAX ; n !#=A AND INITIAL CONDITION !# !2 !# 4HIS ASSUMPTION IMPLIES THAT THE PREDATION RATE OF THE NAIVE PREY WHOSE !2 AND NAIVE PREDATOR !# !# IS SAME WITH THAT OF THE MAXIMALLY ADAPTED PREDATOR !# !#MAX ON THE MAXIMALLY ADAPTED PREY !2 ; n !#=A 0ARAMETER !# IS SET TO A VALUE WITH WHICH AN ALIEN SPECIES CANNOT PERSIST TO CONlRM THAT A TEMPORAL INCREASE OF AN ALIEN SPECIES IS DUE TO THE ALIEN NATIVE MISMATCH IN ADAPTIVE SPEED 4HE INITIAL CONDITION IS THAT # 2 !# FOR PREDATORS INVASION AND FOR PREYS INVASION 0ARAMETERS THAT ARE USED ARE RC RN +C +N MC MN A B E FOR PREDATORS INVASION AND FOR PREYS INVASION
- +ONDOH
THAN VICE VERSA 4HEREFORE THE ADAPTATION PROCESS IS ALIEN BIASED AND THE TROPHIC INTERACTION BETWEEN A NATIVE PREDATOR AND AN ALIEN PREY IS LIKELY TO BE KEPT LOW AFTER THE INTRODUCTION &IGS 4HE SAME IS TRUE FOR THE INTERACTION BETWEEN THE ALIEN SPECIES 3PECIES ! AS A PREDATOR AND THE NATIVE PREY 3PECIES 2 &IGS "ECAUSE THE OPPORTUNITY FOR THE ALIEN PREDATOR TO GAIN EXPERIENCE WITH THE NATIVE PREY IS GREATER THAN FOR THE OPPOSITE SITUATION AN IMBALANCE CAN EXIST BETWEEN THE ALIENS PREDATION EFlCIENCY AND THE NATIVES DEFENCE EFlCIENCY 4HEREFORE THE TROPHIC INTERACTION BETWEEN THE ALIEN PREDATOR AND NATIVE PREY WOULD TEND TO BE RELATIVELY HIGH IN THE TRANSIENT DYNAMICS 4HIS ALIEN NATIVE MISMATCH IN ADAPTIVE SPEED SUGGESTS THAT THE ALIEN SPECIES HAS AN ADVANTAGE IN NOT BEING EXPERIENCED BY INTERACTING SPECIES 4HIS MAKES AN ALIEN SPECIES LESS VULNERABLE TO NATURAL ENEMIES AND LOWERS THE PREYS DEFENCE LEVEL AGAINST THE ALIEN SPECIES ALLOWING THE ALIEN SPECIES TO INCREASE ITS POPULATION QUICKLY AFTER INTRODUCTION 4HIS ADVANTAGE WILL LAST UNTIL THE ALIEN SPECIES BECOMES ABUNDANT AT WHICH POINT IT BECOMES EASIER FOR THE NATIVE SPECIES TO HAVE CONTACT EXPERIENCE WITH THE ALIEN SPECIES !FTER THE ALIEN SPECIES BECOMES ABUNDANT THE NATIVE SPECIES WILL CATCH UP WITH THE ALIEN SPECIES DEFENCE AND PREDATION BEHAVIOR AGAINST THE ALIEN SPECIES WILL DEVELOP AND THE ALIEN SPECIES WILL BE CON TROLLED MORE EFlCIENTLY 4HIS SUCCESSFULLY GENERATES THE hBOOM AND BUSTv PATTERN OF ALIEN POPULATIONS THAT IS OFTEN OBSERVED IN NATURE &IGS 7ILLIAMSON AND &ITTER $ISRUPTION OF SWITCHING BEHAVIOR AND COMMUNITY INSTABILITY
!N ORGANISM CAN CHANGE THE SPECIES OR TROPHIC SPECIES TO INTERACT IN RESPONSE TO A CHANGE IN THE RELATIVE ABUNDANCE OF POTENTIAL INTERACTING SPECIES !BRAMS "OLKER ET AL 4HIS IS CALLED hSWITCHING BEHAVIORv -URDOCH 4HERE ARE TWO TROPHIC INTERACTION RELATED SWITCHING BEHAVIORS FORAGING -URDOCH AND DEFENCE &RYXELL AND ,UNDBERG SWITCHES ! FORAGING SWITCH REFERS TO A CHOICE OF DIET WITH HIGHER QUALITY OR QUANTITY FROM A SET OF NUTRITIONALLY SUBSTITUTABLE POTENTIAL DIETS A FORAGING SWITCH OR FORAGING SHIFT 3TEPHENS AND +REBS )T IS A SIMPLE STRATEGY TO MAXIMIZE THE ENERGETIC OR MATERIAL GAIN PER UNIT EFFORT WHEN DIFFERENT STRATEGIES ARE REQUIRED TO lND OR CAPTURE DIFFERENT DIETS THE USE OF A LESS PROlTABLE RESOURCE LOWERS THE GAIN PER UNIT EFFORT 4HERE ARE A NUMBER OF EXAMPLES IN WHICH ORGANISMS SWITCH TO MORE VALUABLE OR ABUNDANT DIETS AS THE RELATIVE ABUNDANCE OR QUALITY OF THE POTENTIAL DIETS CHANGE SEE 3TEPHENS AND +REBS 4HE OTHER SWITCHING BEHAVIOR IS A DEFENCE SWITCH #ONSIDER A PREY SPECIES WITH MULTIPLE PREDATORS AND ASSUME THAT THE AVOIDANCE OF DIFFERENT PREDATORS REQUIRES DIFFERENT STRATEGIES WITH TRADE OFFS BETWEEN THEM 4HIS MIGHT OCCUR WHEN PREDATORS ATTACK IN DIFFERENT MANNERS OR THE TOTAL PREDA TOR AVOIDANCE EFFORT IS LIMITED 3OLUK 3IH ET AL )N SUCH A CASE A PREY MUST ALLOCATE ITS DEFENCE EFFORT AMONG THE POTENTIAL PREDATORS WITH MORE EFFORT BEING ALLOCATED TO THE MORE RISKY PREDATOR ,IMA
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
&IG &ROM THE VIEWPOINT OF CONTACT EXPERIENCE A BIOLOGICAL INVASION IS DIVIDED INTO FOUR PHASES THE ) PRE ADAPTATION )) ADAPTIVE MISMATCHING ))) NATIVE ADAPTATION AND )6 POST ADAPTATION PHASES &IRST JUST AFTER THE INTRODUCTION THE ALIEN AND NATIVE SPECIES ARE NOT EXPERIENCED WITH EACH OTHER AND THEIR TROPHIC INTERACTION WHICH DEPENDS ON THE PRE ADAPTATION LEVEL OF EITHER SPECIES IS UNLIKELY TO HAVE A CONSISTENT PATTERN IE 0HASE ) PRE ADAPTATION PHASE 3ECOND THE ALIEN SPECIES STARTS TO GAIN EXPERIENCE WITH THE NATIVE SPECIES HOWEVER THE NATIVE SPECIES CANNOT GAIN EXPERIENCE WITH THE ALIEN SPECIES BECAUSE THE ABUNDANCE OF THE ALIEN SPECIES IS LOW 4HIS ALIEN BIASED ADAPTIVE PROCESS PROVIDES THE ALIEN SPECIES WITH A MINORITY ADVANTAGE RESULTING IN THE RAPID GROWTH OF THE ALIEN SPECIES IE 0HASE )) ADAPTIVE MISMATCHING PHASE 4HIRD AFTER THE ALIEN SPECIES BECOMES ABUNDANT THE NATIVE SPECIES BEGINS TO GAIN EXPERIENCE WITH THE ALIEN SPECIES IE 0HASE ))) NATIVE ADAPTATION PHASE $URING THIS THIRD PHASE THE LOCAL COMMUNITY CAN EFlCIENTLY SUPPRESS AN ALIEN SPECIES )N THE LAST PHASE THE ALIEN AND NATIVE SPECIES ARE WELL ADAPTED TO EACH OTHER 0HASE 6) POST ADAPTATION PHASE AND THE POPULATION OF THE ALIEN SPECIES WILL BECOME COMPARABLE TO THAT OF THE NATIVE SPECIES 4HE SOLID AND DOTTED LINES REPRESENT THE SUPERIORITY OF AN ALIEN SPECIES TO A NATIVE SPECIES AND THE POPULATION ABUNDANCE OF THE ALIEN SPECIES RESPECTIVELY ;3UPERIORITY= MEANS NO SUPERIORITY ;POPULATION LEVEL= MEANS COMPARABLE ABUNDANCE OF THE ALIEN SPECIES TO THAT OF NATIVE SPECIES
4HEORY SUGGESTS THAT A FORAGING SWITCH ENHANCES SPECIES COEXISTENCE EG 4ANSKY 'LEESON AND 7ILSON #ONSIDER A SIMPLE TROPHIC SYS TEM CONSISTING OF TWO PREY SPECIES AND ONE PREDATOR SPECIES )N THE ABSENCE OF A FORAGING SWITCH THE TWO PREY SPECIES MIGHT NOT COEXIST BECAUSE THE SPECIES WITH LOW VULNERABILITY TO PREDATION TENDS TO OUT COMPETE THE OTHER THROUGH THE NEGATIVE INDIRECT EFFECT MEDIATED BY THE SHARED PREDATOR APPARENT COMPETITION (OLT "Y CONTRAST IN THE PRESENCE OF A FORAGING SWITCH THE TWO PREY SPECIES CAN COEXIST BECAUSE THE SPECIES THAT IS LESS ABUNDANT TENDS TO BE ATTACKED LESS OFTEN BY THE SWITCHING PREDATOR /NE PREY SPECIES CAN PROVIDE ANOTHER PREY SPECIES WITH AN OPPORTUNITY TO AVOID THE PREDATOR 4HE SAME IS TRUE FOR MORE COMPLEX SYSTEMS +ONDOH
- +ONDOH
! DEFENCE SWITCH ALSO ENHANCES SPECIES COEXISTENCE ,IMA -ATSUDA ET AL )N A SIMPLE SYSTEM CONSISTING OF TWO PREDATOR SPECIES AND ONE PREY SPECIES THE TWO PREDATOR SPECIES TEND NOT TO COEXIST BECAUSE RESOURCE COMPETITION LEADS TO THE EXTINCTION OF THE INFERIOR PREDATOR SPECIES 4ILMAN )N THE PRES ENCE OF AN ADAPTIVE DEFENCE SWITCH HOWEVER A COMPLETELY DIFFERENT PICTURE ARISES !N ADAPTIVE PREY IS MORE LIKELY TO BE DEFENSIVE AGAINST THE MORE ABUNDANT PREDA TOR SPECIES CREATING A MECHANISM OF MINORITY ADVANTAGE 4HEREFORE THE SWITCH ING PREY CAN ENHANCE THE PREDATORS COEXISTENCE -ATSUDA ET AL SHOWED THAT AN ADAPTIVE DEFENCE PREVENTS THE EXTINCTION OF THE PREDATOR SPECIES IN A TWO TROPHIC LEVEL SYSTEM WITH HIGHER SPECIES RICHNESS SUGGESTING THAT THE DEFENCE SWITCH CAN ENHANCE SPECIES COEXISTENCE IN A COMPLEX FOOD WEB 4HIS IS ALSO TRUE IN AN EVEN MORE COMPLEX FOOD WEB +ONDOH UNPUBLISHED MANUSCRIPT )N GENERAL ADAPTIVE SWITCHING BEHAVIOR REQUIRES THE ABILITY TO DISCRIMINATE MULTIPLE PREY OR PREDATOR SPECIES AND KNOWLEDGE OF THE RELATIVE QUANTITY OR QUAL ITY OF THE POTENTIALLY INTERACTING SPECIES 3TEPHENS AND +REBS #ONSIDER ONE PREDATOR AND MULTIPLE PREY SPECIES FOR EXAMPLE 4HE FORAGER IS UNLIKELY TO BE ABLE TO CHOOSE THE MORE ABUNDANT OR MORE NUTRITIOUS PREY SPECIES IF THIS PREY SPECIES IS NOT DIFFERENTIATED FROM OTHER PREY SPECIES 3IMILARLY IN THE ABSENCE OF SPE CIES RECOGNITION ABILITY A PREY SPECIES IS UNLIKELY TO MAKE A CORRECT SWITCH IN ITS DEFENCE BEHAVIOR AGAINST PREDATORS 4HE FACT THAT TROPHIC INTERACTION RELATED SWITCHING BEHAVIOR WHICH REQUIRES CORRECT RECOGNITION OF THE INTERACTING SPECIES TENDS TO ENHANCE SPECIES COEX ISTENCE SUGGESTS ANOTHER IMPORTANT ROLE OF CONTACT EXPERIENCE IN MAINTAINING BIODIVERSITY !N ALIEN NATIVE INTERACTION IN WHICH SPECIES RECOGNITION IS LESS LIKELY TO OCCUR MIGHT AFFECT BIODIVERSITY MAINTENANCE IN A COMPLETELY DIFFERENT WAY FROM THAT OF A NATIVE NATIVE INTERACTION -ORE SPECIlCALLY AN ALIEN NATIVE INTERACTION MIGHT BE MORE LIKELY TO LOWER THE PROBABILITY OF SPECIES COEXISTENCE THAN WOULD A NATIVE NATIVE INTERACTION 4HIS INTERPRETATION IS BASED ON A MODEL ANALYSIS BY +ONDOH 5SING A DYNAMIC MATHEMATICAL MODEL OF A FOOD WEB &IG +ONDOH REVEALED AN IMPORTANT ROLE OF THE FORAGING SWITCH IN BIODIVERSITY MAINTENANCE #ONSIDER A FOOD WEB OF . SPECIES EACH OF WHICH IS CONNECTED BY A DIRECTED TROPHIC LINK WITH PROBABILITY # CONNECTANCE )N THIS MODEL # DETERMINES THE NUMBER OF POTENTIAL PREY SPECIES THAT A CONSUMER CAN USE IE ;. =# ON AVERAGE ! CONSUMER SPE CIES IS CAPABLE OF CHOOSING THE MORE ABUNDANT PREY SPECIES FROM THE POTENTIAL DIET WITH PROBABILITY & "Y CONTRAST A FRACTION & OF PREDATORS DOES NOT DISCRIMINATE BETWEEN PREY SPECIES AND USES EVERY POTENTIAL PREY +ONDOH ANALYZED THE INTERACTIVE EFFECT OF THE PREDATORS CAPABILITY OF AN ADAPTIVE FORAGING SWITCH AND THE FOOD WEB COMPLEXITY ON COMMUNITY PERSISTENCE 4HE ANALYSIS SHOWED THAT AN ADAPTIVE FORAGING SWITCH POTENTIALLY INVERTS THE COMPLEXITY STABILITY RELA TIONSHIP OF A FOOD WEB )N THE ABSENCE OF ADAPTIVE SWITCHING BEHAVIOR INCREASING FOOD WEB COMPLEXITY LOWERS COMMUNITY PERSISTENCE WHILE IN THE PRESENCE OF ADAPTIVE SWITCHING A COMMUNITY IS MORE LIKELY TO BE PERSISTENT WHEN THE FOOD WEB STRUCTURE IS MORE COMPLEX +ONDOH &URTHER THE RELATIONSHIP BECOMES
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
&IG 0OPULATION PERSISTENCE CHANGING WITH CHANGING FRACTION OF ADAPTIVE FORAGERS FOR VARYING FOOD WEB COMPLEXITY # n . n #ONSIDER A FOOD WEB WITH . SPECIES AND CONNECTION PROBABILITY # 0OPULATION DYNAMICS OF 3PECIES I IS GIVEN BY Æ 8I "RI n SI 8I -EIK FKI AKI 8K n -FKI AKI 8K " K D SP IS PREY K D SP IS PREDATOR WHERE RI IS THE INTRINSIC GROWTH RATE SI THE SELF REGULATION STRENGTH EIJ THE CONVERSION EFlCIENCY FIJ THE FORAGING EFlCIENCY OF PREDATOR I ON PREY J AIJ THE FORAGING EFFORT OF PREDATOR I ALLOCATED TO PREY J 4HE FORAGING EFFORT OF ADAPTIVE FORAGER CHANGES TO INCREASE THE ENERGY GAIN PER UNIT EFFORT ÆIJ 'AIJ "EIJ FIJ 8J n -EIK FKI AKI 8K " K D SP IS PREY 3EE +ONDOH FOR MORE DETAIL ) USED THE FOLLOWING PARAMETERS TO CREATE THIS lGURE 8I AIJ RI SI EIJ FIJ ' RAN; = THE NUMBER OF POTENTIAL PREY SPECIES RAN; = RAN; = 2ANDOM MODEL IS USED AS A FOOD WEB TOPOLOGY 0OPULATION PERSISTENCE IS DElNED BY LN;THE PROBABILITY THAT NO SPECIES GO EXTINCT=.
- +ONDOH
CLOSER TO NEGATIVE AS THE FRACTION OF ADAPTIVE FORAGERS DECREASES OR THE SPEED OF THE ADAPTIVE SWITCH DECREASES +ONDOH ! POSSIBLE INTERPRETATION OF +ONDOHS RESULT IS THAT A COMMUNITY WITH A GREATER FRACTION OF ALIEN SPECIES IS MORE LIKELY TO LOSE A SPECIES ESPECIALLY IN A MORE COMPLEX FOOD WEB &IG "ECAUSE AN ALIEN SPECIES IS LESS LIKELY TO DISCRIMI NATE BETWEEN NOVEL NATIVE SPECIES IT MIGHT NOT BE ABLE TO SWITCH DIETS CORRECTLY IMPLYING THAT A CORRECT FORAGING SWITCH IS LESS LIKELY TO OCCUR AS THE FRACTION OF ALIEN SPECIES INCREASES IN THE FOCAL FOOD WEB &URTHER IF A NATIVE PREDATOR CONFUSES AN ALIEN SPECIES WITH A NATIVE PREY THE PREDATOR MIGHT FAIL TO EVALUATE THE RELA TIVE ABUNDANCE OR QUALITY OF THE NATIVE SPECIES 4HUS THE INTRODUCTION OF AN ALIEN SPECIES INTERRUPTS SWITCHING BEHAVIOR AND CAN THREATEN LOCAL BIODIVERSITY BY LOW ERING THE POPULATION STABILITY )N THIS SCENARIO THE EFFECT OF AN ALIEN SPECIES IS ANALOGOUS TO THE CONFUSION OF THE BODYS SIGNALING SYSTEM CAUSED BY ENDOCRINE DISRUPTORS #OLBORN ET AL %NDOCRINE DISRUPTORS OCCUPY A HORMONE RECEPTOR AND ARE MISTAKENLY RECOG NIZED AS THE CORRECT HORMONE RESULTING IN A BODY DISORDER #OLBORN ET AL 4HE OCCUPATION INTERFERES WITH THE PROPER HORMONE SIGNAL AND PRODUCES AN EXCESSIVE OR INSUFlCIENT CELLULAR RESPONSE #OLBORN ET AL )F BIODIVERSITY IS MAINTAINED BY ADAPTIVE SWITCHING BEHAVIOR AS +ONDOH SUGGESTS AN ALIEN SPECIES THAT CONFUSES SPECIES RECOGNITION MIGHT BE REGARDED AS AN ENDOCRINE DISRUPTOR AT THE COMMUNITY LEVEL
35--!29 4HIS CHAPTER PRESENTS A HYPOTHESIS OF THE WAY IN WHICH THE LACK OF CONTACT EXPERI ENCE INmUENCES THE TROPHIC INTERACTION BETWEEN ALIEN AND NATIVE SPECIES ! LACK OF CONTACT EXPERIENCE CAN LEAD TO A FAILURE OF TROPHIC ROLE RECOGNITION PREY HANDLING OR PREDATOR AVOIDANCE WHICH CAN RESULT IN A TROPHIC INTERACTION WITH ABNORMALLY HIGH OR LOW STRENGTH AND DESTABILIZED PREY PREDATOR INTERACTIONS ! MISMATCH IN THE ADAPTATION SPEED BETWEEN ALIEN AND NATIVE SPECIES CAN PRODUCE A TEMPORAL EXPLOSION IN THE ALIEN SPECIES ABUNDANCE ! FAILURE OF SPECIES DISCRIMINATION IN AN ALIEN NATIVE INTERACTION CAN DISRUPT THE ADAPTIVE RESPONSE TO QUALITATIVE AND QUANTITATIVE CHANGES IN THE PREY OR PREDATOR AND CAN THEREBY THREATEN BIODI VERSITY 4HESE HYPOTHESES IMPLY THAT AN ALIEN NATIVE INTERACTION IS QUALITATIVELY DIFFERENT FROM A NATIVE NATIVE INTERACTION AND CREATE A GENERAL PATTERN OF ALIEN SPECIES INVASIONS AND THEIR EFFECTS ON LOCAL COMMUNITIES .EVERTHELESS THESE HYPOTHESES STILL RELY ON A NUMBER OF SIMPLIFYING ASSUMP TIONS CONCERNING THE EFFECT OF EXPERIENCE ON A TROPHIC INTERACTION 4HESE ASSUMPTIONS TIONS ARE REQUIRED BECAUSE WE KNOW LITTLE ABOUT HOW CONTACT EXPERIENCE AFFECTS SUCH MACROSCOPIC PROPERTIES AS TROPHIC INTERACTION STRENGTH TROPHIC LINK mEXIBIL ITY AND POPULATION STABILITY 7E NEED TO EXAMINE THE BEHAVIORAL BASIS OF A TROPHIC INTERACTION AND TEST THE POSSIBILITY THAT AN ALIEN NATIVE INTERACTION IS QUALITATIVELY DIFFERENT FROM A NATIVE NATIVE INTERACTION )N SO DOING IT IS IMPORTANT TO ISOLATE
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
THE EFFECT OF THE ABSENCE OF EXPERIENCE FROM THAT OF SPECIES IDENTITY ! SWAPPING EXPERIMENT BETWEEN TWO COMMUNITIES WITH THE SAME SPECIES COMPOSITION AND DIFFERENT HISTORIES MAY PROVIDE AN INTERESTING OPPORTUNITY THIS TEST
!#+./7,%$'-%.4 4HIS STUDY WAS PARTIALLY SUPPORTED BY A *303 2ESEARCH &ELLOWSHIP FOR 9OUNG 3CIENTISTS AND AN -%84 'RANT IN !ID FOR THE ST #ENTURY #/% 0ROGRAM ! TO +YOTO 5NIVERSITY
2%&%2%.#%3 !BRAMS 0 ! &ORAGING TIME OPTIMIZATION AND INTERACTIONS IN FOOD WEBS 4HE !MERICAN .ATURALIST !GRAWAL ! ! AND 0 - +OTANEN (ERBIVORES AND THE SUCCESS OF EXOTIC PLANTS A PHYLOGENETICALLY CONTROLLED EXPERIMENTS %COLOGY ,ETTERS "AKER ( ' 4HE EVOLUTION OF WEEDS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "LOSSEY . AND 2 .ÚTZOLD %VOLUTION OF INCREASED COMPETITIVE ABILITY IN INVASIVE NON INDIGENOUS PLANTS A HYPOTHESIS *OURNAL OF %COLOGY "OLKER " - (OLYOAK 6 +ĥIVAN , 2OWE AND / 3CHMITZ #ONNECTING THEORETICAL AND EMPIRICAL STUDIES OF TRAIT MEDIATED INTERACTIONS %COLOGY "OND ! " AND ! # +AMIL !POSTATIC SELECTION BY BLUE JAYS PRODUCES BALANCED POLYMORPHISM IN VIRTUAL PREY .ATURE "ONSALL - " AND - 0 (ASSELL !PPARENT COMPETITION STRUCTURES ECOLOGICAL ASSEM BLAGES .ATURE "RODIE % $ AND % $ "RODIE %VOLUTIONARY RESPONSE OF PREDATORS TO DANGEROUS PREY REDUCTION OF TOXICITY OF NEWTS AND RESISTANCE OF GARTER SNAKES IN ISLAND POPULATIONS %VOLUTION "YERS * % #OMPETITION BETWEEN TWO ESTUARINE SNAILS IMPLICATIONS FOR INVASIONS OF EXOTIC SPECIES %COLOGY #ALLAWAY 2 - AND % 4 !SCHEHOUG )NVASIVE PLANTS VERSUS THEIR NEW AND OLD NEIGHBORS A MECHANISM FOR EXOTIC INVASION 3CIENCE #ARROLL 3 AND ( $INGLE 4HE BIOLOGY OF POST INVASION EVENTS "IOLOGICAL #ONSERVATION #HANETON % * AND - " "ONSALL %NEMY MEDIATED APPARENT COMPETITION EMPIRICAL PATTERNS AND THE EVIDENCE /IKOS #OLBORN 4 $ $UMANOSKI AND * 0 -YERS /UR 3TOLEN &UTURE 0ENGUIN "OOKS .EW 9ORK .9 #ROY - ) AND 2 . (UGHES 4HE ROLE OF LEARNING AND MEMORY IN THE FEEDING BEHAVIOUR OF THE lFTEEN SPINED STICKLEBACK 3PINACHIA SPINACHIA , !NIMAL "EHAVIOUR
- +ONDOH
#URIO % 0ROXIMATE AND DEVELOPMENTAL ASPECTS OF ANTIPREDATOR BEHAVIOR !DVANCES IN THE 3TUDY OF "EHAVIOR $ILL , - 4HE ESCAPE RESPONSE OF THE ZEBRA DONIO "RACHYDANIO RERIO )) 4HE EFFECT OF EXPERIENCE !NIMAL "EHAVIOUR $OMJAN - AND " "URKHARD 4HE PRINCIPLES OF LEARNING BEHAVIOR ND EDITION "ROOKS #OLE -ONTERY #! %LLIS ( # 4HE TRANSFER OF ,EARNING -ACMILLAN .EW 9ORK .9 %LTON # 3 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS -ETHUEN ,ONDON 5+ %NDLER * ! $EFENCE AGAINST PREDATORS 0AGES IN 0REDATOR 0REY 2ELATIONSHIPS - % &EDER AND ' 6 ,AUDER EDITORS 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), &OSTER 3 ! 4HE GEOGRAPHY OF BEHAVIOR AN EVOLUTIONARY PERSPECTIVES 4RENDS IN %COLOGY AND %VOLUTION &RETWELL 3 $ 4HE REGULATION OF PLANT COMMUNITIES BY FOOD CHAINS EXPLOITING THEM 0ERSPECTIVE IN "IOLOGY AND -EDICINE &RYXELL , - AND 0 ,UNDBERG )NDIVIDUAL "EHAVIOR AND #OMMUNITY $YNAMICS #HAPMAN (ALL .EW 9ORK .9 'LEESON 3 + AND $ 3 7ILSON %QUILIBRIUM DIET OPTIMAL FORAGING AND PREY COEXIS TENCE /IKOS 'RAY ! * $O INVADING SPECIES HAVE DElNABLE GENETIC CHARACTERISTICS 0HILOS 4RANS 2 3OC ,ONDON 3ER " 'RIFlN ! 3 $ 4 "LUMSTEIN AND # 3 %VANS 4RAINING ANIMALS ABOUT PREDATORS A CRITICAL REVIEW AND SYNTHESIS #ONSERV "IOLO (AIRSTONE . ' & % 3MITH AND , " 3LOBODKIN #OMMUNITY STRUCTURE POPULATION CONTROL AND COMPETITION 4HE !MERICAN .ATURALIST (AZLETT " ! "EHAVIOURAL PLASTICITY IN CRUSTACEA WHY NOT MORE *OURNAL OF %XPERIMENTAL -ARINE "IOLOGY AND %COLOGY (ERBOLD " AND 0 -OYLE )NTRODUCED SPECIES AND VACANT NICHES 4HE !MERICAN .ATURALIST (OLT 2 $ 0REDATION APPARENT COMPETITION AND THE STRUCTURE OF PREY COMMUNITIES 4HEORETICAL 0OPULATION "IOLOGY (OLWAY $ ! #OMPETITIVE MECHANISMS UNDERLYING THE DISPLACEMENT OF NATIVE ANTS BY THE INVASIVE ARGENTINE ANTS %COLOGY (UGHES 2 . - * +AISER 0 ! -ACKNEY AND + 7ARBURTON /PTIMIZING FORAGING BEHAVIOUR THROUGH LEARNING *OURNAL OF &ISH "IOLOGY +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY AND %VOLUTION +ENNEDY 4 3 .AEEM + (OWE * - ( +NOPS $ 4ILMAN AND 0 " 2EICH "IODIVERSITY AS A BARRIER TO ECOLOGICAL INVASION .ATURE +OLAR # AND $ - ,ODGE 0ROGRESS IN INVASION BIOLOGY PREDICTING INVADERS 4RENDS IN %COLOGY AND %VOLUTION +OLBE * * 2 % 'LOR , 2ODRIGUEZ 3CHETTINO ! # ,ARA ! ,ARSON ! AND * " ,OSOS 'ENETIC VARIATION INCREASES DURING THE BIOLOGICAL INVASION OF A #UBAN LIZARD .ATURE
#ONTACT EXPERIENCE ALIEN NATIVE INTERACTIONS
+ONDOH - &ORAGING ADAPTATION AND THE RELATIONSHIP BETWEEN FOOD WEB COMPLEXITY AND STABILITY 3CIENCE ,AWLOR , 2 AND * -AYNARD 3MITH 4HE COEVOLUTION AND STABILITY OF COMPETING SPE CIES 4HE !MERICAN .ATURALIST ,EIBOLD - ! ! GRAPHICAL MODEL OF KEYSTONE PREDATORS IN FOOD WEBS TROPHIC REGU LATION OF ABUNDANCE INCIDENCE AND DIVERSITY PATTERNS IN COMMUNITIES 4HE !MERICAN .ATURALIST ,IMA 3 , ,IFE IN A MULTI PREDATOR ENVIRONMENT SOME CONSIDERATIONS FOR ANTIPREDA TORY VIGILANCE !NNALES :OOLOGICI &ENNICI ,UBCHENCO * 0LANT SPECIES DIVERSITY IN A MARINE INTERTIDAL COMMUNITY IMPORTANCE OF HERBIVORE FOOD PREFERENCE AND ALGAL COMPETITIVE ABILITIES 4HE !MERICAN .ATURALIST -ACK 2 . $ 3IMBERLOFF 7 - ,ONSDALE ( %VANS - #LOUT AND & ! "AZZAZ "IOTIC INVASIONS CAUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COLOGICAL !PPLICATIONS -ALONEY 2 & AND ) ' -CLEAN (ISTORICAL AND EXPERIMENTAL LEARNED PREDATOR RECOGNITION IN FREE LIVING .EW :EALAND 2OBINS !NIMAL "EHAVIOUR -ARON * , AND - 6ILA 7HEN DO HERBIVORES AFFECT PLANT INVASION %VIDENCE FOR THE NATURAL ENEMIES AND BIOTIC RESISTANCE HYPOTHESES /IKOS -AGURRAN ! % !CQUIRED RECOGNITION OF PREDATOR ODOUR IN THE %UROPEAN MINNOW 0HOXINUS PHOXINUS %THOLOGY -ATSUDA ( 0 ! !BRAMS AND - (ORI 4HE EFFECT OF ADAPTIVE ANTIPREDATOR BEHAVIOR ON EXPLOITATIVE COMPETITION AND MUTUALISM BETWEEN PREDATORS /IKOS -ATSUDA ( - (ORI AND 0 ! !BRAMS %FFECTS OF PREDATOR SPECIlC DEFENSE ON BIO DIVERSITY AND COMMUNITY COMPLEXITY IN TWO TROPHIC LEVEL COMMUNITIES %VOLUTIONARY %COLOGY -ITCHELL # % AND ! ' 0OWER 2ELEASE OF INVASIVE PLANTS FROM FUNGAL AND VIRAL PATHOGENS .ATURE -URDOCH 7 7 3WITCHING IN GENERAL PREDATORS EXPERIMENTS ON PREDATOR SPECIlCITY AND STABILITY OF PREY POPULATIONS %COLOGICAL -ONOGRAPHS 0AVLOV ) 0 #ONDITIONED RELAXES /XFORD 5NIVERSITY 0RESS .EW 9ORK .9 0ETREN + AND #ASE 4 * !N EXPERIMENTAL DEMONSTRATION OF EXPLOITATIVE COMPETITION IN AN ONGOING INVASION %COLOGY 0IMM 3 , 4HE "ALANCE OF .ATURE 5NIVERSITY OF #HICAGO 0RESS #HICAGO 0OWER - % 4OP DOWN AND BOTTOM UP FORCES IN FOOD WEBS $O PLANTS HAVE PRIMACY %COLOGY 2EHAGE * 3 "ARNETT " + AND 3IH ! "EHAVIORAL RESPONSES TO A NOVEL PREDATOR AND COMPETITOR OF INVASIVE MOSQUITOlSH AND THEIR NON INVASIVE RELATIVES 'AMBUSIA SP "EHAVIOURAL %COLOGY AND 3OCIOBIOLOGY ONLINE $/) S 2ICCIARDI ! 2 * .EVES AND * " 2ASMUSSEN )MPENDING EXTINCTIONS OF .ORTH !MERICAN FRESHWATER MUSSELS 5NIONOIDA FOLLOWING THE ZEBRA MUSSEL $REISSENA POLY MORPHA INVASION *OURNAL OF !NIMAL %COLOGY 2ICCIARDI ! AND 3 + !TKINSON $ISTINCTIVENESS MAGNIlES THE IMPACT OF BIOLOGICAL INVADERS IN AQUATIC ECOSYSTEMS %COLOGY ,ETTERS
- +ONDOH
2OEDER + $ AND ! % 4REAT 4HE DETECTION AND EVASION OF BATS BY MOTHS !MERICAN 3CIENTIST 2OY * )N SEARCH OF THE CHARACTERISTICS OF PLANT INVADERS 0AGES IN & DI #ASTRI ! * (ANSEN AND - $EBUSSCHE EDITORS "IOLOGICAL INVASIONS IN %UROPE AND THE -EDITERRANEAN "ASIN +LUWER $ORDORECHT 4HE .ETHERLANDS 3AKAI ! + & 7 !LLENDORF * 3 (OLT $ - ,ODGE * -OLOFSKY + ! 7ITH 3 "AUGHMAN 2 * #ABIN * % #OHEN . # %LLSTRAND $ % -C#AULEY 0 /.EIL ) - 0ARKER * . 4HOMPSON AND 3 ' 7ELLER 4HE POPULATION BIOLOGY OF INVASIVE SPECIES !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS 3IH ! ' %NGLUND AND $ 7OOSTER %MERGENT IMPACTS OF MULTIPLE PREDATORS ON PREY 4RENDS IN %COLOGY AND %VOLUTION 3OL $ AND , ,EFEBVRE &OREBRAIN SIZE AND FORAGING INNOVATIONS PREDICT INVASION SUCCESS IN BIRDS INTRODUCED TO .EW :EALAND /IKOS 3OLUK $ ! -ULTIPLE PREDATOR EFFECTS PREDICTING COMBINED FUNCTIONAL RESPONSE OF STREAM lSH AND INVERTEBRATE PREDATORS %COLOGY 3TACHOWICZ * * 2 " 7HITLATCH AND 2 7 /SMAN 3PECIES DIVERSITY AND INVASION RESISTANCE IN A MARINE ECOSYSTEM 3CIENCE 3TEPHENS $ 7 AND * 2 +REBS &ORAGING 4HEORY 0RINCETON 5NIVERSITY 0RESS 0RINCETON .* 4ANSKY - 3WITCHING EFFECT IN PREY PREDATOR SYSTEM *OURNAL OF 4HEORETICAL "IOLOGY 4HÏBAULT % AND - ,OREAU &OOD WEB CONSTRAINTS ON BIODIVERSITYnECOSYSTEM FUNC TIONING RELATIONSHIPS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 4HOMPSON * . 4HE COEVOLUTIONARY PROCESS 5NIVERSITY OF #HICAGO 0RESS #HICAGO 4HORNDIKE % , !NIMAL INTELLIGENCE EXPERIMENTAL STUDIES -ACMILLAN .EW 9ORK .9 4ILMAN $ 2ESOURCE #OMPETITION AND #OMMUNITY 3TRUCTURE 0RINCETON 5NIVERSITY 0RESS 0RINCETON .* 4ORCHIN - % + $ ,AFFERTY ! 0 $OBSON 6 * -C+ENZIE AND ! - +URIS )NTRODUCED SPECIES AND THEIR MISSING PARASITES .ATURE 4SUTSUI . $ ! 6 3UAREZ $ ! (OLWAY AND 4 * #ASE 2EDUCED GENETIC VARIATION AND THE SUCCESS OF AN INVASIVE SPECIES 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCE 53! 7ARE $ - 0REDATION BY RAINBOW TROUT THE EFFECT OF EXPERIENCE *OURNAL OF THE &ISHERIES 2ESEARCH "OARD OF #ANADA 7ILLIAMS $ & %XOTIC !NTS "IOLOGY )MPACT AND #ONTROL OF )NTRODUCED 3PECIES 7ESTVIEW 0RESS "OULDER #/ 7ILLIAMSON - ( AND ! &ITTER 4HE CHARACTERS OF SUCCESSFUL INVADERS "IOLOGICAL #ONSERVATION
#HAPTER ELEVEN
5SE OF BIOLOGICAL INVASIONS AND THEIR CONTROL TO STUDY THE DYNAMICS OF INTERACTING POPULATIONS & #OURCHAMP AND 3 #AUT
).42/$5#4)/. /NE OF THE DIFlCULTIES OF CONSERVATION BIOLOGY IS THE GENERAL LACK OF EXPERIMENTAL APPROACHES "ECAUSE IT IS OFTEN UNETHICAL OR SIMPLY BECAUSE THIS NEW DISCIPLINE DEALS WITH SMALL ANDOR FRAGILE POPULATIONS EXPERIMENTS ON THOSE POPULATIONS ARE NOT ALWAYS FEASIBLE !S A RESULT THE KNOWLEDGE ON POPULATION DYNAMICS WHEN NOT DEALING WITH LABORATORY POPULATIONS OF CAGED INVERTEBRATES HAS OFTEN COME FROM THEORETICAL STUDIES WITH NOTABLE EXCEPTIONS SUCH AS THOSE BASED ON OF SOME POPULATIONS ISOLATED ON PARTICULAR ISLANDS EG #LUTTON "ROCK AND #OULSON 'RENFELL ET AL (OWEVER ONE ASPECT THAT IS OFTEN LACKING FROM THEORETICAL STUDIES AS WELL AS FROM NATURAL ISOLATED POPULATIONS IS THE INTERSPECIlC DIMENSION IN THE ABOVE CASES IT IS RATHER EXCEPTIONAL TO TAKE INTO ACCOUNT MORE THAN TWO INTERACTING POPULATIONS 9ET AS WE HOPE TO SHOW IN THIS CHAPTER DIRECT AND INDIRECT hCOMPLEXv INTERSPECIlC RELATIONSHIPS MAY BE THE MAJOR ECOLOGICAL FORCES IN SOME COMMUNITIES 4HEY CAN THUS BE CRUCIAL FOR APPLIED ECOLOGY AS WELL -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
& #OURCHAMP AND 3 #AUT
AS REPRESENT HEURISTIC TOOLS FOR STUDENTS AND INTELLECTUAL CANDIES FOR FUNCTIONAL ECOLOGISTS (OWEVER THERE IS AN ENORMOUS SET OF ECOLOGICAL EVENTS THAT CAN BE VIEWED AS NATURAL LARGE SCALE EXPERIMENTS BIOLOGICAL INVASIONS 3EVERAL ASPECTS MAKE BIO LOGICAL INVASIONS AN INTERESTING TOOL FOR THE STUDY OF INTERSPECIlC INTERACTIONS THEY ARE OF VARIOUS TYPES INVOLVE MANY DIFFERENT ORGANISMS AND HAPPEN IN CONTRASTED ECOSYSTEMS "IOLOGICAL INVASIONS ARE OFTEN A VERY RICH SOURCE OF INFORMATION FOR THE UNDERSTANDING OF ECOSYSTEM FUNCTIONING AS THEY ORIGINATE FROM INTRODUCTIONS THAT ARE GENERALLY RELATIVELY WELL DOCUMENTED )N ADDITION IN MANY CASES THE INVADED ECOSYSTEM IS AN ISLAND WITH ALL THE ADVANTAGES THAT INSULAR ECOSYSTEMS PROVIDE FOR FUNDAMENTAL RESEARCH CLOSED ECOSYSTEMS WITH LIMITED SIZE AND OF RELATIVELY SIMPLE AND NON REDUNDANT TROPHIC WEBS )N THE SAME WAY THAT THE PHYSIOLOGY OF AN INDIVIDUAL MAY BE BETTER UNDERSTOOD DURING ILLNESS THE DISFUNCTIONING OF AN ECOSYSTEM MAY HELP GAIN KNOWLEDGE ABOUT ITS NORMAL FUNCTIONING )N THIS REGARD THE CHANGES GENERATED BY THE SIMPLE MODIlCATIONS THAT ARE SPECIES INTRODUCTIONS AND THEIR CONSECUTIVE SPREAD PROVIDE MANY DIFFERENT TYPES OF INFORMATION 4HUS BIOLOGICAL INTRODUCTIONS REPRESENT SIMPLE EXPERIMENTS OF SPECIES ADDITION INTO A NEW TROPHIC WEB 3UCH EXPERIMENTS CAN BENElT FROM CONTROLS AND REPLICAS IN THE CASE OF ARCHIPELAGOES 3IMILARLY SPECIES DELETIONS CAN BE STUDIED IN LARGE SCALE EXPERIMENTS THAT ARE EVEN MORE ACCESSIBLE TO POPULATION OR COMMUNITY BIOLOGISTS AS THEY CAN BE DESIGNED BY THEM THE CONTROL OR ERADICATION OF THE ALIEN SPECIES 7ITH THIS NEW TOOL OF SPECIES ADDITION AND DELETION FROM THE COMPARATIVELY SIMPLE ISLAND ECOSYS TEMS ONE MAY GAIN MORE KNOWLEDGE OF BASIC PROCESSES SUCH AS COLONIZATION DIS PERSION SPATIAL SPREAD AS WELL AS THE DYNAMICS OF INTERACTING POPULATIONS 7E WILL HERE FOCUS ON THIS LATTER ASPECT RESTRICTING OUR ANALYSIS ON THREE AND FOUR SPECIES INTERACTIONS AND SHAMELESSLY BASING IT ON OUR PREVIOUS STUDIES )N THIS CHAPTER WE WILL PRESENT A NUMBER OF MATHEMATICALLY SIMPLE MODELS THAT DEPICT SOME hCOMPLEXv INTERSPECIlC RELATIONSHIPS WITH THE AIM OF SHOWING HOW THE STUDY OF BIOLOGICAL INVASIONS AND THEIR CONTROL CAN BE USEFUL FOR THE STUDY OF FUNDAMENTAL ECOLOGICAL PROCESSES THAT ARE MORE PROBLEMATICAL TO UNDERSTAND IN OTHER CONTEXTS (ERE COMPLEX RELATIONSHIPS ARE DElNED AS INTERACTIONS WITHIN TROPHIC WEBS THAT ENCOMPASS MORE THAN TWO POPULATIONS WITH POSSIBLE INDIRECT PROCESSES AND THAT MAY NOT BE REALLY COMPLEX IN A BIOLOGICAL SENSE BUT THAT ARE MORE DEMANDING TO STUDY ANALYTICALLY 7E ALSO USE @CONTROL IN A SOMEWHAT LENIENT STYLE 4HIS TERM CAN HAVE TWO MEANINGS IT CAN BE A GENERAL TERM OF ACTION AGAINST AN ALIEN SPECIES RANGING FROM SIMPLE REDUCTION UP TO ERADICATION AND IT CAN MORE SPECIlCALLY MEAN REDUCTION OF THE POPULATION SIZE DOWN TO ACCEPTABLE LEVELS IN ECOLOGICAL OR ECONOMIC TERMS 4HE LATTER IS CALLED @MITIGATION OR @REDUC TION AND IS OPPOSED TO @ERADICATION )N THIS #HAPTER WE WILL USE @MITIGATION FOR PARTIAL POPULATION REMOVAL @ERADICATION WHEN REMOVAL IS TOTAL AND @CON TROL AS A GENERAL TERM 7E WILL ARTICULATE OUR PRESENTATION IN TWO PARTS THE lRST PART DEPICTS SYSTEMS WHERE SPECIES ARE ADDED TO A TROPHIC WEB THE BIOLOGICAL INVASIONS AND THE SECOND PART DEPICTS SYSTEMS WHERE SPECIES ARE REMOVED CON
$YNAMICS OF INTERACTING POPULATIONS
SERVATION PROGRAMS FOCUSING ON THE POSSIBLE ASSOCIATED INDIRECT PROCESSES IN EACH CASE ! SECONDARY OBJECTIVE OF THIS CHAPTER IS TO CONVINCE THE READERS BE THEY STUDENTS IN BIOLOGY OR CONSERVATION MANAGERS THAT MATHEMATICAL MODELING IS A POWERFUL TOOL TO UNDERSTAND AND IN SOME CASE TO PREDICT ECOSYSTEM FUNCTIONING AND REACTIONS 9ET FOR PEDAGOGIC PURPOSES WE WILL PRESENT OUR ANALYSES BASED ON THE DESCRIPTION OF SEVERAL CONCRETE EXAMPLES WITH LITTLE OR NO EMPHASIS ON THE TECHNICAL ASPECTS OF THE MATHEMATICAL MODELS 7E PROVIDE REFERENCES FOR MORE DETAILS ABOUT THE MODELS AND THEIR ANALYSIS !LL THE MODELS PRESENTED HERE ARE DETERMINISTIC COUPLED DIFFERENTIAL EQUATIONS BASED ON CLASSICAL ,OTKA 6OLTERRA PREDATION OR COMPETITION MODELS %ACH POPULA TION IS DESCRIBED BY A SIMPLE LOGISTIC EQUATION MODIlED TO TAKE INTO ACCOUNT ITS RELATIONSHIP WITH THE OTHER POPULATIONS !LTHOUGH BIOLOGICALLY SIMPLE THE MOD ELS PRESENTED HERE CAN SHOW A RELATIVELY HIGH MATHEMATICAL COMPLEXITY WHEN IT COMES TO FOR EXAMPLE DETERMINING EQUILIBRIUM POINTS #ONlDENT THAT THE SIM PLEST MODELS ARE THE MOST USEFUL 'INZBURG AND *ENSEN WE SYSTEMATICALLY REFRAINED FROM UNDULY ADDING COMPLEXITY TO OUR EQUATIONS WHICH RESULTS IN A LACK OF PREDICTIVE POWER 4HESE MODELS ARE THEREFORE NOT AIMED AT PROVIDING PRECISE VALUES OF POPULATION TRENDS OR OF CONTROL MEASURES IN THE lELD NEITHER THE NATURE OF THE MODELS NOR THE STATE OF CURRENT KNOWLEDGE IN THE lELD WOULD ALLOW USEFUL QUANTITATIVE PREDICTIONS 2ATHER THE AIM OF THIS EXERCISE IS TO EMPHASIZE THE LINK BETWEEN SPECIES THE IMPORTANCE OF INDIRECT INTERACTIONS AND THE UNEXPECTED OUT COME OF CONTROL ACTIONS IF THEY ARE NOT THOROUGHLY TAKEN INTO ACCOUNT 7E BELIEVE THAT THE QUALITATIVE INFORMATION PROVIDED BY OUR MECHANISTIC MODELS IS SUITABLE TO OFFER THE INFORMATION WE SEEK IN THIS CONTEXT !LSO WHILE PARAMETERISING MODELS TO REPRODUCE lELD RESULTS IS A VERY USEFUL WAY OF IDENTIFYING PLAUSIBLE MECHANISMS OF TROPHIC INTERACTIONS IT DOES NOT IN ITSELF PROVIDE A DIRECT TEST OF THE IMPORTANCE OF THOSE PLAUSIBLE MECHANISMS 4HE INFORMATION THEY GENERATE SHOULD ALWAYS BE COMPLETED BY INFORMATION COMING FROM EMPIRICAL AND EXPERIMENTAL STUDIES )N THIS #HAPTER WE WILL ONLY DEAL WITH THE MODELING PART )N ORDER TO RENDER THE READING OF THIS CHAPTER LESS TEDIOUS WE WILL DESCRIBE IN DETAIL THE PROCESS LEADING TO THE MODEL FOR THE lRST EXAMPLE ONLY AND WILL ONLY GIVE THE MODEL FOR THE OTHER EXAMPLES !LTHOUGH SOME WILL DIFFER IN DETAILS ALL MODELS ARE BASED ON SIMILAR PRINCIPLES !PART FROM THE MORE COMPLETE DESCRIPTION OF THE lRST CASE ALL EXAMPLES WILL BE PRESENTED IN A SIMILAR WAY TO ALLOW EASY COMPARI SONS BETWEEN CASES
& #OURCHAMP AND 3 #AUT
.!452!, %#/3934%- %80%2)-%.43 !$$)4)/.3 !.$ $%,%4)/.3 /& 30%#)%3 "IOLOGICAL INVASIONS AS A SPECIES ADDITION EXPERIMENT 4HE HYPERPREDATION PROCESS THREE SPECIES INTERACTIONS
A 4HE CASE )NTRODUCED SPECIES ARE NOTORIOUS FOR THEIR DELETERIOUS IMPACT ON INVADED COM MUNITIES AND THEIR DIRECT EFFECTS ON TROPHIC SYSTEMS SUCH AS DECREASE OF PREY OR COMPETITOR POPULATIONS 7HILE THEY REPRESENT CATASTROPHIC EVENTS IN TERMS OF BIODIVERSITY CONSERVATION THOSE EFFECTS ARE NOT OF MAJOR INTEREST TO THEORETICAL ECOLOGY &OR THIS REASON WE WILL FOCUS ON LESS OBVIOUS EFFECTS STARTING WITH AN EXAMPLE CONCERNING THE EXTINCTION OF AN ENDEMIC PARROT CAUSED BY THE INTRODUC TION OF RABBITS TO AN INSULAR SYSTEM 4HE RABBIT IS ONE OF THE MOST DOCUMENTED INTRODUCED MAMMAL SPECIES OFTEN ASSOCIATED WITH A DRAMATIC IMPACT ON ENDEMIC PLANT SPECIES 4O DATE THIS HER BIVORE HAS BEEN INTRODUCED MOST OF THE TIME PURPOSEFULLY TO MORE THAN ISLANDS &LUX AND &ULLAGAR 2ABBITS HAVE A HIGH ECOLOGICAL ADAPTABILITY AND AS SUCH EASILY SUCCEED WHEN INTRODUCED IN TO ECOSYSTEMS WHERE INDIGENOUS GRAZERS ARE LESS NUMEROUS AND COMPETITIVE &LUX 4HE VERY RAPID INCREASE OF THEIR POPULATIONS CAN LEAD TO A DRAMATIC QUANTITATIVE AND QUALITATIVE IMPOVER ISHMENT OF THE VEGETATION #HAPUIS ET AL 3ELKIRK ET AL RESULTING IN DRAMATIC DENUDATION OF THE SOIL 3COTT AND HAVE AN IMPACT ON ANIMAL SPECIES WHICH DEPEND ON THE VEGETATION 'ILLHAM %FFECTS OF RABBITS ON INDIGENOUS VERTEBRATE SPECIES CAN ALSO BE MORE COMPLEX 4HESE MAMMALS ARE PREYED UPON BY OTHER INTRODUCED VERTEBRATES IN PARTICULAR BY FERAL DOMESTIC CATS #ATS FOR EXAMPLE ARE OPPORTUNISTIC PREDATORS WHICH SWITCH PREY ACCORDING TO RELATIVE SPATIAL ANDOR TEMPORAL AVAILABILITY &ITZGERALD 7HEN RABBITS ARE ABUNDANT DOMESTIC CATS ARE KNOWN TO PREY LARGELY UPON THEM (OWEVER RABBITS CAN CONSTITUTE A SMALLER PART OF THE CAT DIET WHEN BIRDS REPTILES OR OTHER MAMMALS ARE RELATIVELY MORE ABUNDANT )N SEVERAL SUB !NTARCTIC ISLANDS RABBITS ARE ONLY A SECONDARY PREY ITEM IN MONTHS WHEN SEABIRDS ARE PRESENT BUT APPEAR TO ENABLE CATS TO SUBSIST OVER WINTER WHEN SEABIRDS ARE ABSENT #HAPUIS A B ! SIMILAR EFFECT IS DOCUMENTED IN THE SPATIAL DIMENSION RABBITS OFTEN ENABLE CATS TO REACH REMOTE COLONIES OR POPULATIONS OF INDIGENOUS PREY IN ISLANDS WITH HETEROGENEOUS INDIGENOUS PREY DISTRIBUTION "ROTHERS AND #OPSON )N THESE CASES THE PRESENCE OF RABBITS HAS AN INDIRECT EFFECT ON OTHER PREY SPECIES USED BY INTRODUCED CATS 0REDATION BY CATS INTRODUCED TO -ACQUARIE )SLAND CAUSED THE DECLINE OF BURROW NESTING PETRELS "ROTHERS AND THE EXTINCTION OF AN ENDEMIC PARAKEET AND A BANDED RAIL 4AYLOR #ATS WERE INTRODUCED TO THE ISLAND YEARS BEFORE THE INTRODUCTION OF RABBITS HOWEVER THE CAT DRIVEN EXTINCTION OF BIRDS DATES BACK
$YNAMICS OF INTERACTING POPULATIONS
TO JUST YEARS FOLLOWING THE INTRODUCTION OF RABBITS 4AYLOR 2ABBITS WERE NOT OBSERVED AS HAVING ANY DIRECT EFFECTS ON THE LAND BIRDS )N FACT IT IS BELIEVED THAT THE RABBIT POPULATION ALLOWED A SIGNIlCANT INCREASE IN THE CAT POPULATION RESULTING IN AN INCREASED PREDATION PRESSURE ON THE LAND BIRD SPECIES 4HIS PRO CESS RELATED TO THE MORE GENERAL hAPPARENT COMPETITIONv EG !BRAMS !BRAMS ET AL (OLT HAS BEEN TERMED HYPERPREDATION #OURCHAMP ET AL 3MITH AND 1UIN )T IS GENERALLY ASSUMED THAT LIFE HISTORY TRAITS AND BEHAVIOR OF THE INTRODUCED PREY MAKE IT RESISTANT TO HIGH LEVELS OF PREDATION PRESSURE ! HIGHER REPRODUCTIVE RATE HIGH DENSITY AND EFlCIENT ANTI PREDATOR RESPONSES WHICH ARE OFTEN LACKING IN THE INDIGENOUS SPECIES EXHIBITED BY THE INTRODUCED PREY COULD ENABLE AN INCREASE IN THE PREDATOR POPULATION WITHOUT A LARGE DECREASE IN THE INTRODUCED PREY POPU LATION &URTHERMORE THE LACK OF SERIOUS COMPETITORS AND THE RELATIVELY FEW PARA SITES TYPICALLY FOUND IN INTRODUCED POPULATIONS CAN ALSO INCREASE THEIR POTENTIAL FOR DRAMATIC POPULATION GROWTH THE ENEMY RELEASE HYPOTHESIS +EANE AND #RAWLEY 4HESE FEATURES IMPLY THE ABILITY TO SUSTAIN HIGH PREDATION PRESSURE AS CATS ARE SUPPOSED TO REMOVE ONLY THE INDIVIDUALS WITH LOW SURVIVAL DISPERSING YOUNG SICK AND DEAD 3MITH AND 1UIN 4HE RESULTING INCREASED POPULATION OF PREDATORS CANNOT BE SUSTAINED BY THE INDIGENOUS PREY SPECIES WHICH COMPARED WITH THE INTRODUCED PREY SPECIES HAS INFERIOR LESS WELL ADAPTED REPRODUCTIVE AND ANTI PREDATOR CHARACTERISTICS 4HE CONJUNCTION OF A LOW ADAPTATION TO PREDATION AND AN ARTIlCIALLY HIGH PREDATION PRESSURE CAN LEAD TO A DRAMATIC DECREASE IN AN INDIGENOUS PREY POPULATION UP TO TOTAL EXTIRPATION B 4HE MODEL 7E WILL THUS PRESENT A SIMPLE MODEL OF HYPERPREDATION TO ILLUSTRATE HOW THE EXTINCTION OF THE BIRD POPULATION ON -ACQUARIE )SLAND CAN BE EXPLAINED BY AN INDIRECT EFFECT OF THE INTRODUCED RABBITS &OR HEURISTIC PURPOSES WE lRST PRESENT A TWO SPECIES MODEL AND THEN MODIFY IT INTO A THREE SPECIES MODEL 7E HOPE THAT THIS WILL HELP THE UNDERSTANDING OF THIS MODEL AND OF THE OTHER SETS OF EQUATIONS IN THIS CHAPTER WHICH ARE ALL BASED ON THE SAME PRINCIPLE 7E USE THE EXAMPLE OF BIRD LOCAL PREY RABBIT INTRODUCED PREY AND CAT INTRODUCED PREDATOR AND WILL REFER TO THESE SPECIES FOR THE SAKE OF SIMPLICITY BUT OTHER SPECIES CAN PRESENT SIMILAR RELATIONSHIPS 4HE BIRD CAT MODEL CAN BE GIVEN THE FOLLOWING FORM ¨ µ µ © µ µ ª
¨ " ¬ D" RB" µ n µ n «B#" D" ª +B ® D# hB «B"# n i# DT
& #OURCHAMP AND 3 #AUT
WHERE THE NUMBER OF INDIVIDUALS AT TIME T IN THE BIRD RABBIT AND CAT POPULA TIONS ARE " 2 AND # RESPECTIVELY 4HE RABBIT CAT MODEL IS THE SAME 4HE INTRINSIC GROWTH RATES OF THE BIRD AND THE RABBIT POPULATIONS ARE RB AND RR RESPECTIVELY 4HE PREDATION RATE IS +B ON THE BIRD POPULATION AND +R ON THE RABBIT POPULATION 4HE CARRYING CAPACITY OF THE ENVIRONMENT FOR THE BIRD POPULATION IS +B AND THE CARRYING CAPACITY OF THE ENVIRONMENT FOR THE RABBIT IS +R 4HE RATE AT WHICH EATEN PREY ARE TURNED INTO NEW PREDATORS IS hB FOR BIRDS AND hR FOR RABBITS AND i IS THE PREDATOR MORTALITY RATE )N A MORE GENERAL MANNER THE SAME PARAMETERS WILL BE USED FOR THE NEXT MODELS WITH INDEXES CORRESPONDING TO THE lRST LETTER OF THE SPECIES CONSIDERED )F TWO PREY SPECIES ARE TO BE CONSIDERED SIMULTANEOUSLY THE FORMULATION OF THE PREDATION RATES AND OF THE GROWTH RATE OF THE PREDATOR MUST BE CHANGED ACCORD INGLY INSTEAD OF +B# AND +R# THE PREDATION RATES ARE GIVEN THE FORM
" +B# " 2
AND
2 + R# " 2
FOR THE BIRD AND THE RABBIT PREDATION RATES RESPECTIVELY SO THAT THE PREDATION RATE IS STILL A FUNCTION OF THE AVAILABILITY OF THE PREY BUT VARIES WITH RELATIVE PREY PROPORTIONS 4HE ADAPTATION OF THE INTRODUCED PREY IN TERMS OF AN ANTI PREDATOR BEHAVIORAL RESPONSE IS GIVEN BY A PREFERENCE OF THE PREDATOR FOR THE INDIGENOUS PREY WHICH IS MORE EASILY DETECTED ANDOR CAUGHT OVER THE INTRODUCED PREY 4HIS PREFERENCE IS A RATIO _ WITH A SIMPLE BIOLOGICAL MEANING GIVEN EQUAL AVAIL ABILITY THE PREDATOR WILL PREY UPON THE INDIGENOUS PREY _ TIMES MORE OFTEN THAN ON THE INTRODUCED PREY 7E ASSUME THAT _ * AND THAT ONE RABBIT AND ONE BIRD PREY ITEMS ARE ENERGETICALLY EQUALLY VALUABLE TO THE CAT 4HE PREDATION TERMS ARE NOW GIVEN BY
_" +B# _" 2
AND
2 + R# _" 2
ON THE INDIGENOUS AND INTRODUCED PREY RESPECTIVELY 4HIS CHANGE IS REmECTED IN A SIMILAR WAY IN THE PREDATOR GROWTH RATE
¨ _" ¬ ¨ 2 ¬ µ « # h 2 µ µ «R# hB" µ B R ª _" 2 ® ª _" 2 ®
IT DEPENDS ON BOTH THE NUMBERS AND THE PROPORTION OF PREY 7E HAVE NOW THE FOL LOWING SYSTEM
$YNAMICS OF INTERACTING POPULATIONS
¨ µ µ µ © µ µ µ ª
D" ¨ " ¬ _" RB" µ n µ n «B#" DT ª +B ® _" 2 ¨ D2 2 ¬ 2 RR2 µ n µn « #2 +R ® _" 2 R DT ª D# hB «B _" hR «R 2 # n i# DT _" 2
.OTE THAT SIMILAR FORMULATIONS OF THE MODEL COULD BE USED AND THAT THE AFORE MENTIONED CHOICES ARE ARBITRARY )N PARTICULAR WE USED A PREDATION TERM PROPOR TIONAL TO THE NUMBER OF PREY 7E DID SO TO KEEP THE FORMULATION OF THE ORIGINAL PAPER #OURCHAMP ET AL BUT ALTERNATIVE MODELS CAN REPRODUCE THE HYPER PREDATION PROCESS !LSO LIKE FOR THE REST OF THE MODELS PRESENTED IN THIS CHAPTER WE DO NOT TAKE INTO ACCOUNT THE FURTHER RISKS ENCOUNTERED BY POPULATIONS WHEN AT SMALL SIZES ENVIRONMENTAL AND DEMOGRAPHIC STOCHASTICITY !LLEE EFFECTS ETC -OST OF THOSE WOULD ANYWAY ONLY STRENGTHEN OUR POINT 4HE CLASSICAL COMPARTMENTAL REPRESENTATION OF THE MODEL IS PRESENTED IN &IG ! THE CORRESPONDING SET OF EQUA TIONS IS SHOWN IN &IG " AND A SELECTED REPRESENTATION OF THE POPULATION TRENDS WITH TIME IS GIVEN IN &IG # 4HE OTHER EXAMPLES WILL BE ILLUSTRATED WITH lGURES FOLLOWING THE SAME FORMAT 4HE STUDY OF THIS SET OF EQUATIONS BOTH ANALYTICALLY AND NUMERICALLY SEE #OURCHAMP ET AL SHOWS THAT THE INDIRECT EFFECT OF THE INTRODUCED PREY MAY BE VERY IMPORTANT )NDEED ACCORDING TO THE VALUES OF THE PARAMETERS THE INCREASE OF THE PREDATOR POPULATION TRIGGERED BY THE PRESENCE OF THE INTRODUCED PREY CAN DRIVE THE INDIGENOUS PREY TO VERY LOW NUMBERS AND POTENTIALLY TO EXTINC TION 4HE EFFECT OF HYPERPREDATION IS THE STRONGEST FOR SPECIES WITH LOW INTRINSIC GROWTH RATE AND LOW ENVIRONMENTAL CARRYING CAPACITY 4HIS MODEL ALSO ILLUSTRATES THAT THE HYPERPREDATION PROCESS MAY BE DUE TO A COMBINATION OF WELL ADAPTED LIFE HISTORY TRAITS AND EFlCIENT BEHAVIORAL RESPONSE OF PREY BUT THAT THE hBETTER ADAPTEDv BEHAVIORAL RESPONSE MAY HAVE MORE IMPORTANCE THAN hBETTER ADAPTEDv LIFE HISTORY TRAITS AT LEAST FOR THE CASES CONSIDERED #OURCHAMP ET AL 4HUS A PREY SPE CIES INTRODUCED INTO AN ENVIRONMENT IN WHICH A PREDATOR HAS ALSO BEEN INTRODUCED IS LIKELY TO ALLOW SO HIGH AN INCREASE OF THIS PREDATOR THAT LOCAL PREY LESS ADAPTED TO HIGH LEVELS OF PREDATION COULD SUFFER A POPULATION DECLINE AND POSSIBLY EVEN EXTINC TION 3UCH A PROCESS HAS CONSEQUENCES WHEN IT COMES TO MANAGEMENT ACTIONS C #ONSERVATION CONSEQUENCES (ISTORICALLY CONSERVATION PROGRAMS FOR MANY ISLANDS HAVE PROCESSED CASE BY CASE 5NTIL RECENTLY INTRODUCED SPECIES WERE ALWAYS CONSIDERED SEPARATELY WITH AT BEST SEPARATE PROGRAMS FOR EACH SPECIES AND TIMINGS DEPENDING MOSTLY ON FUNDING AND LOGISTICS OR MORE FREQUENTLY ONE SINGLE PROGRAM FOR THE VISIBLY MOST
& #OURCHAMP AND 3 #AUT
&IG 2EPRESENTATION OF THE HYPERPREDATION MODEL WITH THE INTRODUCED PREY INDI GENOUS PREY AND INTRODUCED PREDATOR BEING ILLUSTRATED BY RABBITS 2 BIRDS " AND CATS # RESPECTIVELY ! COMPARTMENTAL REPRESENTATION AND ILLUSTRATION OF THE ISLAND FROM WHERE THE EXAMPLE IS TAKEN HERE -ACQUARIE )SLAND OFF .EW :EALAND %ACH BOX REPRESENTS A POPULATION AND THE ARROWS REPRESENT mUXES BETWEEN THEM 4HE LARGE CURVED ARROW REPRESENTS AN INDIRECT EFFECT %ACH SPECIES IS ILLUSTRATED IN A COLOR THAT IS ALSO USED FOR THE SET OF EQUATIONS " AND FOR THE DRAWINGS THAT REPRESENT THE POPULATION DYNAMICS OF THE INTERACTING SPECIES AFTER INTRODUCTION OF A SPECIES # OR CONTROL OF AN INTRODUCED SPECIES $ )N THIS EXAMPLE FOLLOWING THE CAT INTRODUCTION RED ARROW THE INCREASE OF THE CAT POPULATION ALLOWED BY THE LARGE POPULATION OF RABBITS LEADS TO BIRD EXTINCTION # &OLLOWING CONTROL GREEN ARROW IN $ THE BIRD POPULATION ONLY PARTIALLY RECOVERS IF ONLY THE CAT IS CONTROLLED TOP PANEL OF $ (OWEVER THE SAME CAT CONTROL LEVEL LEADS TO CAT ERADICATION AND FULL RECOVERY OF BIRDS IF BOTH THE RABBITS AND THE CAT ARE CONTROLLED BOTTOM PANEL OF $
$YNAMICS OF INTERACTING POPULATIONS
DEVASTATING SPECIES !S A RESULT WHEN A CONSERVATION PROGRAM INVOLVED AN ISLAND SUCH AS THE ONE WE JUST MENTIONED WITH A HYPERPREDATION PROCESS TAKING PLACE THE KEY ROLE OF THE INTRODUCED PREY WAS NOT SYSTEMATICALLY OBVIOUS 0REDATORS ARE OFTEN PERCEIVED AS HAVING THE MOST IMPORTANT DELETERIOUS EFFECTS ON INVADED ECO SYSTEMS AND CONSEQUENTLY CONTROL PROGRAMS WERE MORE OFTEN DIRECTED AT THEM SOMETIMES NEGLECTING THE INTRODUCED PREY 9ET WE HAVE JUST SEEN THAT IN THE PRES ENCE OF INTRODUCED PREDATORS INTRODUCED PREY COULD HAVE AN INDIRECT IMPACT ON INDIGENOUS PREY "ASING OUR EFFORTS ON THE MODEL PRESENTED IN THE PREVIOUS SECTION OF THIS CHAPTER WE STUDIED THE RELATIVE EFlCIENCY OF CONTROL PROGRAMS AIMING EITHER AT THE PREDATOR ONLY OR AT THE INTRODUCED PREY AND PREDATOR SIMULTANEOUSLY 4HE MODEL ON WHICH WE BASED THIS HAS BEEN PUBLISHED IN #OURCHAMP ET AL AND THIS MODEL IS ONLY SLIGHTLY DIFFERENT FROM THE ASSOCIATED MODEL WITHOUT CONTROL #OURCHAMP ET AL 7E WILL NOT REPRODUCE THE MODEL HERE AS THE INTEREST LIES NOT IN THE DETAILS OF THE EQUATIONS 4HE ONLY IMPORTANT POINT IS THE ADDITION OF A CONTROL EFFORT ON EITHER THE ALIEN PREY OR THE ALIEN PREDATOR OR BOTH 4HIS CONTROL IS ADDED TO THE CORRESPONDING EQUATION BY A SIMPLE LINEAR TERM 7E EMPHASIZE THE FACT THAT IN THE MODEL THE INTRODUCED PREY RABBIT STILL HAS NO DIRECT EFFECT ON THE LOCAL PREY BIRD 3OME POSSIBLE POPULATION TRENDS OF THE SYSTEM IN PRESENCE OF CONTROL ARE SHOWN IN &IG $ 4HE STUDY OF THIS MODEL SHOWS THAT CONTROL OF RABBITS CAN FACILITATE THE ERADICATION OF CATS )NDEED WHEN NO CONTROL IS UNDERTAKEN THE CAT POPULA TION STAYS LARGE MAINLY BECAUSE OF THE PRESENCE OF RABBITS AND CAN ELIMINATE THE BIRDS IN THE LONG TERM 7HEN CATS ONLY ARE CONTROLLED THE PRESENCE OF RABBITS CAN PRECLUDE CAT ERADICATION AND THE BIRD POPULATION RECOVERY IS ONLY PARTIAL )N CON TRAST FOR THE SAME CAT CONTROL EFFORT ERADICATION OF RABBITS ALLOWS ERADICATION OF CATS AND TOTAL RECOVERY OF BIRDS !CTUALLY IF THE CONTROL OF INTRODUCED PREY IS NOT SUFlCIENT THE INDIGENOUS PREY WILL BE DESTROYED EVEN IF THE PREDATOR POPULATION IS BEING CONTROLLED /BVIOUSLY WE ARGUE HERE THAT EVEN IN ABSENCE OF VISIBLE DIRECT EFFECT INTRO DUCED PREY SHOULD BE CONTROLLED WHEN A PREDATOR HAS BEEN INTRODUCED IN ORDER TO PREVENT AN ARTIlCIAL PREDATOR POPULATION INCREASE )N ADDITION REMOVING AN INTRODUCED PREDATOR POPULATION WITHOUT CONTROLLING THE INTRODUCED PREY MAY BE DIFlCULT TO ACHIEVE SINCE THEY CONSTITUTE A CONSTANT SOURCE OF FOOD TO THE PREDATOR !LSO IT WOULD NOT BE AN APPROPRIATE SOLUTION BECAUSE REMOVING THE PREDA TION PRESSURE WOULD INCREASE THE DIFlCULTIES OF LATER COPING WITH INTRODUCED PREY WHICH ARE OFTEN CHARACTERIZED BY HIGH REPRODUCTIVE RATES /N THE OTHER HAND CONTROLLING ONLY THE INTRODUCED PREY IS UNSATISFACTORY IN THE LONG TERM BECAUSE PREDATORS COULD REPORT HIGH PREDATION PRESSURE ON THE INDIGENOUS PREY #OMBINED CONTROL OF BOTH SPECIES SEEMS HERE TO BE THE BEST RESTORATION STRATEGY )N ADDITION STARTING BOTH CONTROL PROGRAMS TOGETHER WOULD ALSO RESULT IN ADVANTAGES DUE TO SYNERGETIC EFFECTS COSTS MAY BE REDUCED IF COSTS RELATED TO TRANSPORTATION OR HUNTING AND TRAPPING CAN BE SHARED BY THE TWO PROGRAMS AND EFlCIENCY MIGHT BE INCREASED EG THROUGH THE ADDITIVE EFFECTS OF PRIMARY AND SECONDARY POISONING OF PREDATORS &LUX 2AMMELL ET AL 2OBERTSON ET AL
& #OURCHAMP AND 3 #AUT
4O CONCLUDE IT IS WORTH REITERATING THAT THE HIGHER EFlCIENCY OF DUAL CONTROL IS NOT DUE TO DIRECT EFFECTS OF RABBITS ON BIRDS HABITAT DESTRUCTION AND COMPETITION FOR FOOD AND SHELTER SINCE THEY ARE NOT TAKEN INTO ACCOUNT HERE .OR IS THE PREDICTED SUCCESS OF DUAL CONTROL DUE TO THE PREFERENCE OF THE PREDATOR SINCE THIS PREFER ENCE IS SET IN FAVOR OF THE INDIGENOUS PREY IN THE MODEL 4HIS SUCCESS IS DUE TO THE ADDRESSING OF THE HYPERPREDATION PROCESS 4HE HYPERPREDATION PROCESS FOUR SPECIES INTERACTIONS
A 4HE CASE 4HE CAT IS A WELL KNOWN PREDATOR OF BOTH INSULAR BIRDS AND SMALL INTRODUCED MAM MALS SO THE EXAMPLE ABOVE SHOULD BE RELATIVELY EASY TO SPOT 7HENEVER A LOCAL POPULATION IS THREATENED BY AN INTRODUCED PREDATOR A DIET STUDY OF THE PREDATOR IN QUESTION SHOULD BE CONDUCTED IN ORDER TO ASSESS THE IMPORTANCE OF THE IMPACT ON THE LOCAL POPULATION BUT ALSO POTENTIAL HYPERPREDATION PROCESSES (OWEVER THERE ARE CASES WHERE THIS STRATEGY IS NOT OBVIOUS BECAUSE THE CAUSE OF A PREY POPULA TION DECLINE MAY NOT BE SPOTTED AS EASILY !N INTERESTING ILLUSTRATION OF THIS IS THE SEVERE DECLINE OF THE INSULAR FOX ON THE #HANNEL )SLANDS IN THE S 4HE #HANNEL )SLANDS GROUP IS MADE UP OF EIGHT SMALL ISLANDS OFF THE #ALIFORNIAN COAST 53! 4HE ISLAND GREY FOX 5ROCYON LITTORALIS IS A SMALL CARNIVORE THAT ARRIVED ON THE lRST ISLAND YEARS AGO 4HE FOX NOW INHABITS THE SIX LARGEST ISLANDS AND HAS EVOLVED ON EACH OF THESE IN ISOLATION RESULTING IN SIX POPULATIONS REPRESENTING SIX DIFFERENT SUBSPECIES ALL ENDEMIC TO THESE ISLANDS /N THE THREE NORTHERN ISLANDS THE INSULAR FOXES AND THEIR MAIN COMPETITOR THE ENDEMIC SPOT TED SKUNKS 3PILOGALE GRACILIS AMPHIALA WERE THE TWO TERRESTRIAL TOP PREDATORS OF THE #HANNEL )SLANDS )N THE EARLY S A STUDY CONDUCTED ON THE HOME RANGE OF THE FOXES WITNESSED A CONSIDERABLE DECLINE IN THE THREE NORTHERN ISLAND POPU LATIONS 2OEMER 4HIS SEVERE DECLINE HAD NO OBVIOUS CAUSE AT lRST AND MANY CLASSICAL ECOLOGICAL FORCES WERE INVESTIGATED LACK OF SUFlCIENT RESOURCES COMPETITION WITH THE SPOTTED SKUNK AND DISEASES 0REDATION WAS ALSO INVESTIGATED ALTHOUGH THE INSULAR FOX WAS THE TOP TERRESTRIAL PREDATOR OF THESE ECOSYSTEMS 3USPICION THAT FOXES WERE KILLED BY GOLDEN EAGLES LED TO A NEW EFFORT OF RESEARCH IN THIS DIRECTION 'OLDEN EAGLES HAVE HISTORICALLY BEEN SEEN VISITING THE ISLANDS BUT THEY NEVER STAYED LONG ENOUGH TO CONSTITUTE A THREAT TO THE LOCAL PREY ! STUDY COMBINING METABOLIC AND ENERGETIC APPROACHES WITH POPULATION MODELING DEM ONSTRATED THAT THE LOCAL PREY WERE TOO FEW TO ALLOW A PAIR OF DISPERSING EAGLES TO BREED ON AND COLONIZE THE ISLANDS 9ET IT BECAME OBVIOUS THAT EAGLES WERE KILLING FOXES AS WELL AS SPOTTED SKUNKS /N ONE OF THESE ISLANDS 3ANTA #RUZ lELD WORKERS EVENTUALLY DISCOVERED A GOLDEN EAGLE NEST IN WHICH FOX REMAINS ATTESTED FOR THE SUSPECTED PREDATION ON THIS SPECIES "UT THE PROBLEM REMAINED (OW WOULD THE EAGLE THREATEN FOX SURVIVAL THROUGH PREDATION IF THERE WAS NOT ENOUGH LOCAL PREY ON THE ISLAND TO ALLOW THE CONTINUOUS PRESENCE OF THE EAGLES 4HE DISCOVERY OF THE NEST PROVIDED THE ANSWER REMAINS OF PIGLETS WERE ALSO FOUND IN THE NEST &ERAL
$YNAMICS OF INTERACTING POPULATIONS
PIGS 3US SCROFA WERE INTRODUCED ON TO THE THREE NORTHERN ISLANDS WHERE THE FOXES ARE DECLINING THEY WERE ALSO PRESENT ON TWO OF THE SOUTHERN ISLANDS BUT HAVE ALREADY BEEN OR ARE ALMOST ERADICATED THERE )N ADDITION TO THE DIRECT DAMAGES THAT INTRODUCED PIGS ARE KNOWN TO CAUSE TO THE mORA AND FAUNA THEY INVADE (ONE THIS ALIEN SPECIES ALSO THREATENED SOME LOCAL SPECIES THROUGH AN INDIRECT PROCESS "Y PRODUCING PIGLETS ALL YEAR ROUND THEY PROVIDED VISITING EAGLES WITH ENOUGH RESOURCES FOR THEM TO COLONIZE THE ISLANDS %AGLES ALSO IRREGULARLY DEPRE DATED OTHER LOCAL PREY SUCH AS FOXES OR SKUNKS (OWEVER EVEN THIS LOW PREDATION RATE ON A SPECIES THAT IS ILL ADAPTED TO AVIAN PREDATION BEHAVIORALLY AS WELL AS AT THE POPULATION LEVEL WAS SUFlCIENT TO DRIVE THE FOX POPULATION TOWARDS EXTINC TION 4HE DECLINE WAS ALL THE MORE DRAMATIC THAT THE BREEDING EAGLE POPULATION RAPIDLY GREW IN NUMBERS THEREBY INCREASING THE PRESSURE ON THE FOX POPULATION )N THE MEAN TIME THE NOCTURNAL SKUNKS BENElTED FROM THE ARRIVAL OF THE EAGLE BECAUSE THEY BENElTED FROM THE RELEASE OF COMPETITION PRESSURE FROM THE DECLIN ING FOX POPULATIONS WHILE ALSO BEING KILLED LESS OFTEN THAN THEM 4HE HYPOTHESIS WAS THUS THAT THE ARRIVAL OF PIGS HAD ALLOWED VISITING EAGLES TO STAY AND BREED AND THEREBY THEY ATTRACTED A SHARED PREDATOR TO INSULAR PREY 0IGS ARE WELL ADAPTED TO PREDATION THEY PRODUCE NUMEROUS PIGLETS THAT CAN ESCAPE EAGLE PREDATION ONCE THEY REACH THREE MONTHS OF AGE 4HEREFORE THERE WERE LESS CONSEQUENCES FOR THE PIG POPULATION THAN THE LOCAL PREY DUE TO THE ARRIVAL OF THE EAGLE 2OEMER ET AL B 4HE MODEL 4O TEST THIS HYPOTHESIS A MODEL OF THE POPULATION DYNAMICS OF THE INTERACTING SPECIES WAS CONSTRUCTED AND PARAMETERIZED WITH DATA OBTAINED FROM THE lELD 4HE MODEL WAS BASED ON A SIMPLE COMBINATION OF TWO CLASSICAL ,OTKA 6OLTERRA MOD ELS ONE OF COMPETITION AND ONE OF PREDATION 4HE SKUNK AND THE FOX POPULATION DYNAMICS WERE DESCRIBED BY A COMPETITION MODEL THE PIG AND THE EAGLE POPULA TION DYNAMICS WERE DESCRIBED BY A PREDATION MODEL AND A PREDATION TERM OF THE EAGLE WAS ADDED ON BOTH FOX AND SKUNK POPULATIONS 5SING A CORRECTION TERM FOR PROPORTIONS AND PREFERENCE COEFlCIENTS q AND m RESPECTIVELY AS IN THE PREVIOUS EXAMPLE WE END UP WITH A SYSTEM OF FOUR EQUATIONS ONE PREDATOR AND ITS THREE PREY TWO OF WHICH ARE COMPETITORS 4HE SYSTEM AND ILLUSTRATIONS OF POPULATION TRENDS ARE SHOWN IN &IG -ORE DETAILS CAN BE FOUND IN 2OEMER ET AL 3IMPLE SIMULATIONS SHOW THAT IN ABSENCE OF THE PIGS IF THE SYSTEM IS RUN WITH AN INITIAL NUMBER OF PIGS SET AT ZERO ANY INTRODUCTION OF EAGLES HOWEVER LARGE WILL EVENTUALLY LEAD TO COLONIZATION FAILURE AND FOX POPULATION PERSISTENCE (OWEVER WHEN PIGS ARE PRESENT A SINGLE PAIR OF EAGLES WILL BE ABLE TO COLONIZE THE ISLAND AND BUILD A POPULATION THAT IS SO LARGE THAT FOXES WILL GO EXTINCT WHILE PIGS WILL REMAIN AT MODERATE DENSITIES )T IS ALSO INTERESTING TO NOTE THAT THE DECLINE IN FOX NUMBERS CONSECUTIVE TO THE HYPERPREDATION PROCESS TRIGGERED BY THE INTRODUCTION OF PIGS IS CONCOMITANT WITH AN INCREASE OF THE ENDEMIC SKUNK )N FACT THE ARRIVAL OF EAGLES REVERSED THE
& #OURCHAMP AND 3 #AUT
&IG 2EPRESENTATION OF THE HYPERPREDATION MODEL EXAMPLE WITH FOUR SPECIES FOX & BLUE SKUNK 3 GREEN PIG 0 YELLOW AND EAGLE % RED !S IN &IG ! IS THE COMPARTMENTAL REPRESENTATION " IS THE RESULTING SET OF EQUATIONS # IS THE ILLUSTRATION OF POPULATIONS TRENDS GIVEN BY " FOLLOWING PIG INTRODUCTION AND EAGLE COLONIZATION AND $ IS THE POPULATIONS TRENDS FOLLOWING PIG ANDOR EAGLE CONTROL 4HE PARAMETERS ARE THE SAME THAN PREVIOUSLY WITH q AND m BEING THE PREFERENCE PARAMETERS OF THE EAGLE FOR THE FOX AND THE SKUNK OVER THE PIG RESPECTIVELY SAME AS _ IN &IG 4HE CONTROL STRATEGY $ IS REPRESENTED IN THREE DIMENSIONS 4O HELP VISUALIZE THE $ EFFECT THE COLORS DO NOT REFER TO SPECIES BUT TO DIFFERENT POPULATION SIZES 4HIS GRAPH SHOWS THAT THE POPULATION SIZE OF FOXES IS PROPORTIONAL TO EAGLE CONTROL BUT INVERSELY PROPORTIONAL TO PIG CONTROL !S A RESULT IF EAGLES ARE NOT CONTROLLED SIMULTANEOUSLY FOXES WILL DECLINE FOLLOWING PIG CONTROL ONLY )N ABSENCE OF SIGNIlCANT EAGLE MITIGATION HIGH LEVELS OF PIG MITIGATION CAN RESULT IN FOX EXTINCTION DARK AREA
$YNAMICS OF INTERACTING POPULATIONS
COMPETITIVE OUTCOME BETWEEN THE TWO TOP TERRESTRIAL PREDATORS SHIFTING FORCES FROM DIRECT COMPETITION IN FAVOR OF THE FOX TO APPARENT COMPETITION IN FAVOR OF THE SKUNK 4HIS SECOND APPARENT COMPETITION PROCESS EMBEDDED IN THE lRST ONE RENDERS ANY CONSERVATION STRATEGY AT THE LEAST COMPLICATED AS THE INSULAR SPOTTED SKUNK IS ENDEMIC FROM THE NORTHERN #HANNEL )SLANDS AND IS CURRENTLY BENElTING FROM THE FOX DECLINE C #ONSERVATION CONSEQUENCES &OXES ARE NOW EXTINCT IN THE WILD ON TWO OF THE THREE NORTHERN ISLANDS WITH THE POPULATION ON THE THIRD ISLAND 3ANTA #RUZ ON THE VERGE OF EXTINCTION INDIVIDUALS IN THE WILD AT THE END OF /UR MODELING EXERCISE SUGGESTS THAT THE EXTINCTION OF TWO POPULATIONS OF THE TOP PREDATOR IN TWO INSULAR ECOSYSTEMS IS LIKELY DUE TO AN INDIRECT PROCESS A PROCESS WHERE AN INTRODUCED PREY ATTRACTED A SHARED PREDATOR AND ELIMINATED AN ENDEMIC PREY THROUGH APPARENT COMPETITION ONLY /BVIOUSLY THE SOLUTION TO THIS PROBLEM LIES WITH THE PIGS 4HE MOST EVIDENT PLAN OF ACTION WAS TO REMOVE THE PIGS FROM THE NORTHERN ISLANDS 4HIS WOULD HAVE THE DOUBLE ADVANTAGE OF STOPPING THEIR DIRECT DELETERIOUS EFFECTS ON THE LOCAL mORA AND FAUNA AS WELL AS ELIMINATING THE PREY BASIS FOR THE EAGLES LEADING THEM WITH LITTLE MORE CHOICE THAN STARVATION OR EMIGRATION )N FACT SEVERAL CONSERVATION STRATE GIES WERE IMPLEMENTED SIMULTANEOUSLY !MONG THEM EAGLE LIVE TRAPPING WAS QUITE SUCCESSFUL WITH LESS THAN TEN INDIVIDUALS PROVING IMPOSSIBLE TO TRAP OR THAT KEPT COMING BACK FROM THE TRANSLOCATION AREA (OWEVER IT WAS EASY TO SEE THAT AS LONG AS PIGS REMAINED EAGLES WOULD START BREEDING ON THE ISLAND AGAIN AND THUS START A NEW POPULATION 4HE SOLUTION THEREFORE SEEMED TO BE THE COMPLETE REMOVAL OF PIGS FROM 3ANTA #RUZ )SLAND 9ET THE STUDY OF A MODEL BASED ON THE PREVIOUS ONE SHOWED ONCE MORE THAT INDIRECT INTERACTIONS MAY LEAD TO COUNTER INTUITIVE RESULTS #OURCHAMP ET AL B !S FOR THE PREVIOUS EXAMPLE THE BASIC MODEL SHOWN IN &IG " WAS CHANGED SIMPLY BY ADDING A LINEAR CONTROL TERM TO THE PIG AND TO THE EAGLE EQUATIONS "Y VARYING THE CONTROL RATE OF PIGS AND EAGLES FROM ZERO NO CONTROL TO ONE ERADICATION WE CAN MIMIC DIFFERENT CONTROL STRATEGIES CONTROL OF PIGS ONLY OF EAGLES ONLY OR OF BOTH SPECIES WITH DIFFERENT STRENGTH AND COMPARE THEIR RELATIVE EFlCIENCY WITH NO RISK TO THE LOCAL POPULATIONS $OING SO REVEALED THAT MITIGATION OF PIGS WOULD IN FACT LEAD TO A DECREASE IN THE FOX POPULATION &IG $ %RADICATION OF PIGS THE INTENDED COURSE OF ACTION ON 3ANTA #RUZ WOULD LEAD TO FOX EXTINCTION $UE TO THE LOW FOX POPULATION AND THE LARGE EAGLE POPULATION THE FOXES WOULD BE ENTIRELY DESTROYED BEFORE THE EAGLES DIED OR EMIGRATED )N THEORY THE SOLU TION IS THUS SIMPLE REMOVE BOTH THE EAGLES AND THE PIGS (OWERVER IN PRACTICE THE REMOVAL OF SUCH A LARGE PIG POPULATION IS LOGISTICALLY DIFlCULT )N ADDITION THE REMOVAL OF THE EAGLE WOULD BE IMPOSSIBLE THROUGH LIVE TRAPPING ONLY AND ETHICALLY AND LEGALLY CHALLENGING BECAUSE GOLDEN EAGLES ARE PROTECTED SPECIES IN THE 53! AND THEREFORE CANNOT BE KILLED
& #OURCHAMP AND 3 #AUT
4O CONCLUDE THIS PART IT MAY BE INTERESTING TO NOTE THAT WHEN MORE SPECIES AND MORE INTERACTIONS ARE TAKEN INTO ACCOUNT NEW PROCESSES MAY BE UNVEILED THAT COULD NOT BE PERCEIVED WITH ONLY TWO SPECIES STUDIES 9ET IF BETTER UNDERSTAND ING A SYSTEM IS UNDOUBTEDLY USEFUL FOR CONSERVATION MANAGERS IT IS NOT ALWAYS SUFlCIENT FOR THEM TO BE ABLE TO KNOW HOW TO ACT )N THE PRESENT CASE A STUDY TAKING ALL SPECIES INTO ACCOUNT REVEALED THAT A SEEMINGLY OBVIOUS LINE OF ACTION PIG REMOVAL WOULD INDEED LIKELY ACHIEVE RESULTS OPPOSITE TO THOSE DESIRED AND POSES A DIFlCULT DECISION TO MAKE REMOVE A PROTECTED POPULATION IN ORDER TO SAVE AN ENDANGERED SUBSPECIES )F IT IS OBVIOUSLY NOT TRIVIAL TO MAKE CONSERVATION CHOICES EVEN IN THE SIMPLEST SITUATIONS IT CAN SOMETIMES BECOME A CHALLENG ING DILEMMA THEORETICALLY LOGISTICALLY LEGALLY AND MORALLY )N THE PRESENT CASE THE ONLY REMAINING POPULATIONS OF SEVERAL FOX SUBSPECIES WERE THREATENED WITH IMMINENT EXTINCTION (OWEVER THE PROXIMATE CAUSE OF THIS THREAT IS THE PRESENCE OF A PROTECTED BIRD &URTHERMORE THE DECLINE OF THE FOX BENElTS THE ONLY POPULA TIONS OF AN ENDEMIC SKUNK !S WE HAVE SEEN WHEN A DIFlCULT CHOICE IS MADE THE OPPOSITE OUTCOME MAY WELL ARISE &URTHERMORE ALL THIS IS WITHOUT CONSIDERING SPECIES OUTSIDE THIS SIMPLISTIC SYSTEM /NE COULD ALSO CONSIDER THE QUESTION UNDER A WIDER ANGLE FOR EXAMPLE INCLUDING THE 3AN #LEMENTE LOGGERHEAD SHRIKE ,ANIUS LUDOVICIANUS MEARNSI A CRITICALLY ENDANGERED BIRD TO WHICH THE INSULAR FOX IS THE MAIN PREDATOR /N 3AN #LEMENTE )SLAND THE FOX POPULATION HAS BEEN IRONICALLY ADVERSELY IMPACTED BY A 53 .AVY PROGRAM TO PROTECT THIS BIRD ATTEMPTING TO THWART ANY PREDATION OF SHRIKES FOX WERE INITIALLY TRAPPED AND SHIPPED OFF ISLAND OR EUTHANIZED DURING THE SHRIKE NESTING SEASON FOXES REMOVED IN OF WHICH PERMANENTLY "UT THIS IS ANOTHER STORYx !LONG THE SAME LINE OF THIS CONSERVATION RIDDLE THE NEXT PART OF THIS CHAPTER INVESTIGATES THE IMPORTANCE OF DIRECT INTERACTIONS IN CONTROL PROGRAMS WITH THE AIM OF SHOWING THAT THE REMOVAL OF THE PRIMARY CAUSE OF A ECOSYSTEM DISFUNCTION WILL NOT ALWAYS HELP RESTORE THE INITIAL CONDITIONS )N SOME CASES NOT TAKING INTO ACCOUNT INDIRECT INTERACTION MAY LEAD TO EVEN FURTHER DAMAGE TO THE POINT THAT IT MAY BE WISER TO ADVOCATE NOT TO REMOVE POPULATIONS THAT ARE KNOWN TO CAUSE DIRECT NEGATIVE IMPACTS ON INVADED COMMUNITIES AT LEAST UNTIL ADEQUATE KNOWL EDGE IS GAINED AND RELEVANT CONTROL STRATEGIES ARE INFERRED #ONTROL OF INVADERS AS A SPECIES REMOVAL EXPERIMENT 2ELEASE FROM INTRODUCED HERBIVORES
/NE CONCEPT THAT IS RELATIVELY NEW IN THE STUDY OF INVADING SPECIES AND THAT HAS BEEN THE CORE PRINCIPLE OF OUR OWN STUDIES IS THAT EVEN IF A SPECIES IS PROVEN TO BE INmICTING IMPORTANT DAMAGES TO A COMMUNITY IT INVADES THE MERE REMOVAL OF THAT SPECIES MAY NOT SYSTEMATICALLY BE THE SOLUTION TO RESTORING THE COMMUNITY !S WE HAVE SHOWN WITH THE #ALIFORNIA #HANNEL )SLANDS EXAMPLE UNCONSIDERED CONTROL MAY EVEN LEAD TO THE OPPOSITE OUTCOME THAT IS FURTHER DAMAGE INCLUD ING POSSIBLE EXTINCTION OF THE SPECIES INTENDED TO BE PROTECTED 4HIS FACT HIGHLIGHTS
$YNAMICS OF INTERACTING POPULATIONS
THE NEED TO HAVE A CLEAR AND COMPLETE VIEW OF THE RELATIONSHIPS AMONG SPECIES THAT ARE CONNECTED DIRECTLY OR INDIRECTLY WITH THE INTRODUCED SPECIES THAT IS SUBJECT TO CONTROL )T NOWADAYS SOUNDS TRIVIAL TO STATE THAT ALL THE SPECIES THAT INTERACT WITH A POPULATION FOR WHICH REMOVAL IS PLANNED ARE LIKELY TO BE AFFECTED IN DIVERSE WAYS BY ANY SUCH ACTIONS 4HUS THE SUCCESS OF AN ERADICATION PROGRAM IS MEASURED NOT ONLY BY THE COMPLETE REMOVAL OF THE CONTROLLED SPECIES BUT ALSO BY THE ABSENCE OF FURTHER DYSFUNCTION 9ET SUCH ERRORS STILL OCCUR REGULARLY DURING CONSERVATION PROGRAMS SOMETIMES SIMPLY BECAUSE CONSERVATION PROGRAMS HAVE INSUFlCIENT FUNDS TO ALLOW THOROUGH PRE CONTROL STUDIES OF THE INVADED COMMUNITY AS WELL AS LONG TERM POST CONTROL MONITORING 3OMETIMES SIMPLY BECAUSE CONSERVATION ACTION IS URGENTLY NEEDED AND THERE IS NO TIME FOR SUCH PRE CONTROL STUDY 4HE IMPORTANCE OF KNOWING THE RELATIONSHIPS BETWEEN INVADING SPECIES AND THOSE IN THE INVADED COMMUNITY IS WELL ILLUSTRATED BY THE GOAT AND PIG ERADICATION ON THE 3ARIGAN )SLAND 4HIS ISLAND IS PART OF THE #OMMONWEALTH OF THE .ORTHERN -ARIANA )SLAND IN THE 0ACIlC /CEAN )NTRODUCED PIGS AND GOATS THREATENED THE LOCAL mORA AND FAUNA TRIGGERING A CONSERVATION PROGRAM CONSISTING MAINLY OF GOAT AND PIG ERADICATION +ESSLER !S THE ISLAND IS ISOLATED AND HENCE DIFlCULT TO ACCESS THE PROGRAM DESIGNED INCLUDED ONLY A MINIMAL PRE ERADICA TION STUDY 4HE PROGRAM WAS CONSIDERED A FULL SUCCESS IN TERMS OF REMOVING THE INTRODUCED MAMMALS HOWEVER IT FAILED IN ITS ABILITY TO DETECT THAT THE ISLAND HAD ALSO BEEN COLONIZED BY AN INTRODUCED VINE /PERCULINA VENTRICOSA WHICH APPEARED TO BE A PREFERENTIAL FOOD ITEM FOR THE GOATS )T IS PERHAPS NOT SURPRISING THAT THIS VINE WAS NOT FOUND IN THE PRE CONTROL STUDY AS IT WAS LIKELY TO HAVE BEEN AT A LOW DENSITY DUE TO SELECTIVE GRAZING BY GOATS %VEN A VERY THOROUGH STUDY MIGHT HAVE FAILED TO SEE IT 9ET IT MAY BE VALUABLE TO POINT OUT THAT WHEN POSSIBLE SIMPLE FENCED EXCLOSURE STUDIES PRIOR TO ERADICATIONS CAN OFTEN HELP LAND MANAGERS SEE IF UNWANTED RESULTS WILL ARISE AFTER AN ERADICATION OF HERBIVORES )F SO THEN APPROPRI ATE CONTROL OF NON NATIVE PLANTS CAN BE PLANNED ALONG WITH THE HERBIVORE REMOVAL 5NFORTUNATELY THIS WAS NOT DONE AND THE CONTROL PROGRAM WHICH AIMED AT RELEAS ING PLANT SPECIES FROM GOAT GRAZING HAD A DIFFERENT IMPACT ON THE OVERALL PLANT COMMUNITY THAN THE ONE EXPECTED !S THE PRESSURE OF GRAZING WAS REMOVED FROM ALL GRAZED PLANTS INTRODUCED PLANTS WERE ABLE TO FULLY EXPRESS THEIR COMPETITIVE SUPERIORITY WITH REGARDS TO NATIVE PLANTS RESULTING IN THE RAPID INVASION OF THE COMMUNITY &IG SHOWS HOW WITHIN ONLY TWO YEARS THE REMOVAL OF AN EXOTIC GRAZER LED TO A COMPLETE INVASION OF THE ISLAND COMMUNITY BY AN EXOTIC PLANT THAT APPEARS TO HAVE A COMPETITIVE SUPERIORITY OVER LOCAL PLANTS !S MOST OF THE 3ARIGAN )SLAND ECOSYSTEM IS NOW COVERED BY VINES ONE CAN EASILY IMAGINE HOW THE INDIRECT EFFECT OF HAVING REMOVED GOATS IS NOW DELETERIOUS FOR THE LOCAL PLANTS AS WELL AS ANIMALS THAT DEPEND UPON THEM 4HE MESOPREDATOR RELEASE EFFECT
4HE PROCESS WE HAVE SEEN WITH THE RELEASE OF AN EXOTIC PLANT MAINTAINED AT LOW DENSITY BY A BROWSER CAN BE GENERALIZED TO RELEASES FROM ALMOST ANY OTHER TYPE OF
& #OURCHAMP AND 3 #AUT
&IG %VOLUTION OF THE LANDSCAPE OF 3ARIGAN )SLAND FOLLOWING THE ERADICATION OF GOATS !S THIS INTRODUCED HERBIVORE NO LONGER HELD IN CHECK THE EXPANSION OF THE INTRODUCED VINE A FAVORED FOOD ITEM THE VINE RAPIDLY INCREASED COVERING MOST OF THE INSULAR PLANT COMMUNITIES WITHIN TWO YEARS 4HIS ILLUSTRATES HOW AN EXOTIC GRAZER AFFECTED THE COMPETITION RELATIONSHIPS BETWEEN LOCAL AND INTRODUCED PLANTS AND HOW ITS REMOVAL CAN LEAD TO DRAMATIC AND UNEXPECTED OUTCOME FOR THE COMMUNITIES WHICH PROTECTION WAS AIMED AT
$YNAMICS OF INTERACTING POPULATIONS
NATURAL ENEMY 7E WILL ILLUSTRATE THIS WITH THE NEXT TWO EXAMPLES 4HIS IS HOW EVER NOT TO BE MISTAKEN WITH THE ENEMY RELEASE HYPOTHESIS +EANE AND #RAWLEY WHICH PROPOSES THAT INVADING SPECIES ARE SO SUCCESSFUL PARTLY BECAUSE THEY ARE RELEASED IN THE INVADED HABITAT FROM THE PRESSURE OF THEIR NATURAL ENEMIES RARELY INTRODUCED WITH THEM /N 3TEWART )SLAND .EW :EALAND A POPULATION OF INTRODUCED CATS WAS THREAT ENING ONE OF THE LAST POPULATIONS OF KAKAPO 3TRIGOPS HABROPTILUS AN ENDEMIC mIGHTLESS PARROT ! DIET STUDY REVEALED KAKAPO REMAINS IN OF COLLECTED CAT SCATS +ARL AND "EST 4HIS SEEMINGLY LOW PREDATION PRESSURE CAN HAVE A DRAMATIC EFFECT ON INSULAR POPULATIONS WHICH EVOLVED IN THE ABSENCE OF SUCH PREDATORS AND ARE THEREFORE NOT ADAPTED TO EVEN LOW LEVELS OF PREDATION -OREOVER THE KAKAPO POPULATION WAS ALREADY SMALL AND FRAGILE ADDING TO THE WEIGHT THAT INTRODUCED CATS COULD HAVE ON ITS FATE 4HIS COULD HAVE BEEN SUFlCIENT TO TRIGGER A PROGRAM OF CAT CONTROL ON THE ISLAND (OWEVER RATS KNOWN TO BE IMPORTANT BIRD PREDATORS HAD ALSO BEEN INTRODUCED ON 3TEWART )SLAND )N THE SAME DIET STUDY +ARL AND "EST RAT REMAINS WERE FOUND IN OF THESE CAT FAECES 4HIS SHOWS THE INDIRECT ROLE CATS MIGHT PLAY IN PRESERVING NATIVE FAUNA THROUGH REDUCTION OF RAT PREDATION PRESSURE ON KAKAPO )N FACT IT IS EASY TO SEE THAT IN SOME CASES THE INDIRECT POSITIVE EFFECT OF CAT PREDA TION ON RATS IS MORE BENElCIAL FOR THE LOCAL PREY THAN THE DIRECT NEGATIVE EFFECTS OF CAT PREDATION ON THE PREY THEMSELVES )N SUCH CASES THE ELIMINATION OF THE FERAL CAT POPULATION COULD LEAD TO A MORE SEVERE NEGATIVE IMPACT ON THE LOCAL SPECIES THROUGH AN INCREASE IN THE RODENT POPULATION AS A CONSEQUENCE OF THE REMOVAL OF THEIR PREDATORS 4HE ATTEMPTED REDUCTION OF THE CAT POPULATION ON !MSTERDAM )SLAND HAS BEEN ABANDONED AS IT IS ALLEGED TO HAVE CAUSED A COMPENSATING RISE IN THE NUMBER OF RATS AND MICE (OLDGATE AND 7ACE 4HIS PROCESS TERMED hMESOPREDATOR RELEASEv HAS BEEN DESCRIBED IN FRAGMENTED INSULAR ECOSYSTEMS 3OULÏ ET AL AND APPLIES WELL TO MANY INSULAR FOOD WEBS EG 3CHOENER AND 3PILLER #ONVERSELY THE ERADICATION OF RODENTS lRST WHICH HAS NOW PROVEN FEASIBLE EVEN ON RELATIVELY LARGE ISLANDS MIGHT INDUCE CATS TO SWITCH PREY RESULTING IN A BRUTAL INCREASE IN PREDATION PRESSURE ON THE THREATENED INDIGENOUS SPECIES AS EXPERIENCED FOR STOATS AND RATS IN .EW :EALAND -URPHY AND "RADlELD 4HIS IS A SIMILAR PROCESS TO THE ONE DESCRIBED ABOVE FOR THE PIG CONTROL IN PRESENCE OF EAGLES ON 3ANTA #RUZ )SLAND !S THE OPTIMAL CONTROL STRATEGY IS NEITHER SIMPLE TO lND NOR INTUITIVE IT IS CONVENIENT TO STUDY IT THROUGH THE ANALYSIS OF A MATH EMATICAL MODEL WHICH MIMICS THE DYNAMICS OF THE THREE SPECIES IN THIS SYSTEM 4HE MAIN RESULTS OF SUCH A STUDY #OURCHAMP ET AL A ARE REPRODUCED BELOW TO ILLUSTRATE HOW THE CONTROL OF AN INVADING SPECIES CAN PROVIDE AN IDEAL OPPORTU NITY TO PROGRESS IN THE UNDERSTANDING OF THE NUMEROUS AND OFTEN COMPLEX INTERAC TIONS AMONG POPULATIONS &OR THE SAKE OF CLARITY WE WILL NOT PRESENT THE MODEL EQUATION IN ANY DETAIL 3UFlCE TO SAY THAT THE SYSTEM IS DESCRIBED BY A SET OF THREE COUPLED EQUATIONS ONE PREY PARROT ITS PREDATOR THE RAT IN THIS CASE A MESOPREDATOR AND ONE
& #OURCHAMP AND 3 #AUT
SUPERPREDATOR CAT WHICH EATS BOTH THE PREY AND THE MESOPREDATOR 4HE MODEL AND THE RESULTING POPULATION TRENDS ARE REPRESENTED IN &IG 4HE STUDY OF THE ABOVE SYSTEM LEADS TO THE QUITE OBVIOUS CONCLUSION THAT BOTH PREDATORS SHOULD BE ERADICATED AT THE SAME TIME (OWEVER NOT ONLY IS SUCH A STRATEGY CHALLENGING FROM A LOGISTICAL POINT OF VIEW BUT IN ADDITION IT MAY NOT ALWAYS BE THE BEST SOLUTION ESPECIALLY IF THE SYSTEM INCLUDES MORE INTRODUCED PREDATORS )NDEED THE PREY MESOPREDATOR SUPERPREDATOR SYSTEM THAT WE HAVE JUST DESCRIBED CAN BE FURTHER COMPLICATED 4HERE ARE CASES WHERE THE PRESENCE OF A THIRD PREDATOR CAN RENDER THE ERADICATION OF THE MESOPREDATOR PROBLEMATIC IF IT ALSO ACTS AS A PREDATOR TO THIS THIRD PREDATOR AND THUS AT THE SAME TIME AS A MESOPREDATOR AND A SUPERPREDATOR "EING AWARE OF THE POTENTIAL DANGERS OF REMOVING A SUPERPREDATOR WHEN A MESOPREDATOR IS PRESENT THE MANAGERS OF THE CONSERVATION PROGRAM OF "IRD )SLAND 3EYCHELLES DECIDED RIGHTLY TO SIMULTANE OUSLY REMOVE INTRODUCED CATS AND RATS IN ORDER TO PROTECT THE LOCAL BIRD COLONIES 4HEY HAD HOWEVER OVERLOOKED THE PRESENCE OF THE INTRODUCED CRAZY ANT !NOPLOLEPIS LONGIPES WHICH WERE PRESENT IN VERY LOW NUMBERS ON THE ISLAND &EARE 4HE LARVAE OF THESE ANTS SEEM TO HAVE BEEN AN IMPORTANT PREY ITEM OF THE INTRODUCED RODENTS SUCH THAT THE RAT ERADICATION LED TO A DEMOGRAPHIC EXPLOSION OF THE ANTS 4HIS RESULTED IN THE ANTS COVERING A LARGE PART OF THE ISLAND WITH A HEAVY IMPACT ON LAND CRABS AND BIRD COLONIES )N FACT THIS PROBLEM OF CHAIN REACTION FOLLOWING THE REMOVAL OF AN INTRODUCED SPECIES ALSO CALLED SURPRISE EFFECT OR 3YSIPHUS EFFECT -ACK AND ,ONSDALE CAN BE GENERALIZED TO OTHER NATURAL ENEMIES SUCH AS HERBIVORES OR COMPETITORS 4HE COMPETITOR RELEASE EFFECT
4HE CONTROL OF AN INVADER HAS THE POTENTIAL TO RELEASE ANY SPECIES INTERACTING WITH THE CONTROLLED INVADERS FROM ITS PRESSURE BE IT EXPLOITATION OR INTERFER ENCE 4HEREFORE ONE CAN IMAGINE VERY SIMILAR PROCESSES WITH A BROWSER OR A COMPETITOR ,ET US CONSIDER AS A lNAL EXAMPLE A hCOMPETITOR RELEASE EFFECTv ,ET US SET THE SCENE AN ISLAND INVADED BY SAY A RAT SPECIES 4HE ISLAND IS NORTH OF .EW #ALEDONIA IN THE %NTRECASTEAUX 2EEF ,ET US CALL IT 3URPRISE )SLAND WHICH SUITS VERY WELL A STUDY ON SURPRISE EFFECTS ! THOROUGH STUDY OF THE INVADED ECO SYSTEM COMPLETED TO CHARACTERIZE THE IMPACT OF INTRODUCED RATS ON THAT ISLAND REVEALED THE PRESENCE OF A SMALL ISOLATED POPULATION OF INTRODUCED DOMESTIC MICE 4HE POPULATION SEEMS SMALL AND RESTRICTED SO THAT THEIR IMPACT ON THE ECOSYSTEM IS LIKELY TO BE NEGLIGIBLE )N FACT IN SIMILAR SITUATIONS THEY HAVE BEEN IN THE PAST NEGLECTED PARTLY BECAUSE MOUSE POPULATIONS ARE DIFlCULT TO ERADICATE PARTLY BECAUSE SUCH SMALL POPULATIONS WERE NOT VIEWED AS A THREAT AND PARTLY BECAUSE THE CONSERVATION PROGRAM CONCERNED ANOTHER SPECIES AND FUNDS AND PROTOCOLS WERE NOT AVAILABLE TO DEAL WITH MICE !S AN EXAMPLE THE RAT AND RABBIT CONTROL OF 3AINT 0AUL )SLAND IN THE !NTARCTIC OCEAN HAS BEEN VERY SUCCESSFUL IN ERADICATING THESE TWO INTRODUCED MAMMALS IT WAS EVEN AT THE TIME THE GREATEST AREA EVER CLEANED UP FROM INTRODUCED RABBITS BUT THE PROGRAM DID NOT FOCUS ON THE SMALL
$YNAMICS OF INTERACTING POPULATIONS
&IG 2EPRESENTATION OF THE MESOPREDATOR RELEASE PROCESS WITH THE INTRODUCED SUPERPREDATOR BEING THE CAT # RED THE INTRODUCED MESOPREDATOR BEING THE RAT 2 YELLOW AND THE INDIGENOUS PREY BEING THE BIRD " BLUE !S IN &IG ! IS THE COMPARTMENTAL REPRESENTATION THE EXAMPLE COMING FROM 3TEWART )SLAND OFF THE .EW :EALAND MAINLAND " IS THE RESULTING SET OF EQUATIONS AND THE TWO FOLLOWING PANELS ARE TYPICAL POPULATION TRENDS FOLLOWING INTRODUCTIONS OF THE SUPERPREDATOR # TOP AND OF THE MESOPREDATOR # BOTTOM OR CONTROL OF THE SUPERPREDATOR ONLY $ TOP AND OF BOTH THE SUPERPREDATOR AND THE MESOPREDATOR $ BOTTOM 0ANEL # SHOWS THAT IN SOME CASES A SUPERPREDATOR INTRODUCTION WILL DECREASE THE PREDATION PRESSURE ON LOCAL PREY VIA ITS PREDATION ON THE MESOPREDATOR TOP WHILE A MESOPREDATOR INTRODUCTION WILL ALLOW AN INCREASE OF THE SUPERPREDATOR PROCESS SIMILAR TO THE HYPERPREDATION LEADING TO A FURTHER DECREASE OF THE PREY VIA A COMBINATION OF INCREASED PREDATION OF THE INCREASED SUPERPREDATOR POPULATION AND ADDITIONAL PREDATION FROM THE NEWLY INTRODUCED MESOPREDATOR BOTTOM 0ANEL $ SHOWS THAT CONTROL OF BOTH INTRODUCED PREDATOR NEEDS TO BE DONE TO PROTECT THE PREY BOTTOM AS THE CONTROL OF ONLY THE SUPERPREDATOR CAN TRIGGER A MESOPREDATOR RELEASE WHICH EVENTUALLY LEADS TO THE LOCAL PREY EXTINCTION TOP
& #OURCHAMP AND 3 #AUT
MOUSE POPULATION THAT WAS KNOWN TO OCCUR ON THE ISLAND -ICOL AND *OUVENTIN 4HE STUDY OF THE 3URPRISE ECOSYSTEM SUGGESTS THAT RESOURCES ARE ABUNDANT ENOUGH FOR THE INTRODUCED MICE TO DEVELOP A LARGER POPULATION THAN THEY HAVE DONE 4HIS SUGGESTS THAT THE MOUSE POPULATION IS RESTRICTED BY A NATURAL ENEMY AND IT COMES NATURALLY TO MIND THAT IT IS THE COMPETING RAT THAT RESTRICTED THEM FROM FURTHER EXPANDING THEIR RANGE !LTHOUGH IT IS QUITE DIFlCULT TO UNAMBIGU OUSLY DEMONSTRATE SUCH COMPETITION RELATIONSHIPS lELD SPECIALISTS SEEM UNANI MOUS IN THE VIEW THAT RATS ARE STRONG COMPETITORS OF MICE TO THE POINT OF OFTEN EXCLUDING THEM WHEN COMMON RESOURCES ARE FEW )T SEEMS THEN QUITE PREDICTABLE ESPECIALLY AFTER HAVING READ THE PREVIOUS EXAMPLES OF hSURPRISE EFFECTSv IN THIS CHAPTER THAT THE PLANNED ERADICATION OF THE INTRODUCED RATS ON 3URPRISE )SLAND IS LIKELY TO RELEASE THE MICE FROM RAT COMPETITION AND THUS TO ALLOW THEM TO INCREASE IN NUMBERS 3UCH AN OUTCOME IS NOT ONLY INTUITIVELY LOGICAL IT IS ALSO VERY EASY TO DEMONSTRATE THROUGH THE ANALYSIS OF A BASIC ,OTKA 6OLTERRA COMPETITION MODEL TO WHICH A CONTROL TERM IS ADDED TO ONE OF THE COMPETITORS &OR THE SAKE OF SIMPLIC ITY WE STUDY THIS THREE SPECIES SYSTEM ONE PREY AND TWO COMPETING PREDATORS THROUGH ONLY A TWO COMPETITORS MODEL THE SHARED PREY IS IGNORED HERE WHICH ALSO ALLOWS A GENERALIZATION OF THE SYSTEM TO NON PREDATOR COMPETITORS !NALYSIS OF THIS SYSTEM CLEARLY SHOWS THAT THE MITIGATION OF THE HIGHER COM PETITOR THE RAT WILL LEAD TO AN INCREASE OF THE LOWER COMPETITOR AS PRESSURE FROM COMPETITION IS LIFTED 4HE HIGHER THE MITIGATION THE LARGER THE MOUSE POPULATION ! SUDDEN COMPLETE REMOVAL OF THE RAT POPULATION IS LIKELY TO RESULT IN A DEMO GRAPHIC EXPLOSION OF THE MOUSE POPULATION 4HIS WAS THE CASE ON 3AINT 0AUL )SLAND FOLLOWING THE REMOVAL OF RATS IN -ICOL AND *OUVENTIN RELEASED FROM THEIR COMPETITORS MICE NUMBERS INCREASED DRAMATICALLY TO SUCH A POINT THAT FOR A TIME THEY FAR EXCEEDED THE CARRYING CAPACITY OF THE HABITAT /BVIOUSLY MICE ARE LESS HARMFUL THAN RATS AND THUS IN SOME CASES THE END BENElT OF THE RAT REMOVAL IS POSITIVE EVEN IF THE MOUSE POPULATION INCREASES 9ET MOUSE OUTBREAKS CAN BE VERY PROBLEMATIC AS MICE HAVE BEEN SHOWN TO BE ACTIVE PREDATORS OF INVERTE BRATES REPTILES AND EVEN BIRDS THAT CAN BE TIMES THEIR WEIGHT #AMPOS AND 'RANADEIRO #UTHBERT AND (ILTON &ITZGERALD ET AL ,E 2OUX ET AL .EWMAN 3MITH ET AL "UT THIS COMPETITOR RELEASE EFFECT IS IN FACT NEITHER SURPRISING NOR VERY INTER ESTING FOR THE STUDY OF INTERSPECIlC RELATIONSHIPS 4HE OBVIOUS APPROACH TO SUCH SITUATIONS SEEMS SIMPLY TO APPLY A SIMULTANEOUS CONTROL TO BOTH COMPETITORS !ND IT IS ALL THE BETTER THAT WE ARE DEALING WITH COMPETING RODENTS AS A SIMULTANEOUS CONTROL IS EASILY FEASIBLE WITH A COMMON RODENTICIDE FOR EXAMPLE %ND OF STORY OR SO IT SEEMS )N FACT JUST TO MAKE SURE NO MORE SURPRISES ARE GOING TO EMERGE FROM THE SYSTEM IT IS POSSIBLE TO COMPLETE THE MODEL BY ADDING A SIMULTANEOUS CONTROL TERM TO THE INFERIOR COMPETITOR AS WELL SEE &IGS ! AND " )T SEEMS LOGICAL TO LINK THE TWO CONTROL RATES FOR THEY WILL OFTEN BE AT LEAST IN THE CASE OF RODENTS CON TROLLED IN THE SAME PROGRAM &OR EXAMPLE ONE CAN HAVE tR b tM WITH tM BEING THE CONTROL RATE OF THE MICE THE LOWER COMPETITOR THE MOUSE AND b THE CONTROL
$YNAMICS OF INTERACTING POPULATIONS
SPECIlCITY ! VALUE OF SAY FOR b MEANS THAT SUPERIOR COMPETITORS ARE CONTROLLED TWICE AS MUCH AS INFERIOR COMPETITORS 4HIS IS VERY LIKELY IF FOR EXAMPLE BAITS ARE ACCESSIBLE IN PRIORITY TO HIGHER COMPETITORS OR IF THE TRAPPING DESIGN IS AIMED AT THE HIGHER COMPETITOR BUT THEY ALSO ALLOW TO TRAP THE LOWER COMPETITOR ALTHOUGH WITH A LOWER EFlCIENCY THE PROGRAM AIM IS TO REMOVE THE RATS BUT RAT TRAPS ALSO CAN CATCH MICE 3TUDYING THIS VERY SIMPLE SYSTEM REVEALS IN FACT A SUBTLER AND LESS EXPECTED COMPETITOR RELEASE EFFECT !S SHOWN IN &IG # THE SIMULTANEOUS MITIGA TION OF BOTH COMPETITORS CAN LEAD TO A RELEASE OF THE LOWER COMPETITOR )N SOME CASES THIS RELEASE CAN AMOUNT TO ACTUAL POPULATION EXPLOSIONS )T IS POSSIBLE THAT AIMING AT CONTROLLING SAY AN INTRODUCED RODENT A CONTROL PROGRAM WILL LEAD TO A DRAMATIC INCREASE OF ANOTHER RODENT EVEN IF THAT ONE IS CONTROLLED TOO -OREOVER &IG $ SHOWS THAT THE COMPETITOR RELEASE IS DIRECTLY PROPORTIONAL TO THE CONTROL RATE 4HIS MEANS THAT THE MORE THE TARGETED SPECIES IS CONTROLLED THE MORE IMPORTANT THE COMPETITOR RELEASE EFFECT WILL BE 4HIS IS NOT SO OBVIOUS TO PREDICT AS IT IMPLIES THAT THE INFERIOR COMPETITOR IS CONTROLLED TOO WITH A CONTROL EFFORT THAT INCREASES AT THE SAME RATE AS THAT OF THE SUPERIOR COMPETITOR )N OTHER WORDS THE MORE RODENTS ARE CONTROLLED THE MORE MICE APPEAR %VEN IF MICE ARE ACTUALLY CAUGHT IN TRAPS AND KILLED BY POISON THE MORE WE KILL THEM THE MORE THEIR POPULATION WILL INCREASE 1UITE THE OPPOSITE OF AN EXPECTED OUTCOME !LTHOUGH THIS PROCESS MAY BE LESS INTUITIVE AND THEREFORE LESS OFTEN FORESEEN IT IS A POSTERIORI QUITE EASY TO UNDERSTAND 4HIS IS LIKELY TO OCCUR AS SOON AS THE LOWER COMPETITOR BENElTS FROM THE DIFFERENTIAL EFFECT OF THE SIMULTANEOUS CONTROL OF BOTH COMPETITORS WHEN ITS INDIRECT POSITIVE EFFECT THE REMOVAL OF THEIR COMPETITORS EXCEEDS ITS DIRECT NEGATIVE EFFECT THEIR OWN REMOVAL /BVIOUSLY SUCH A PROCESS CAN BE INTERESTING IF THE LOWER COMPETITOR IS A LOCAL SPECIES WHICH SURVIVAL WAS THREATENED BY THE CONTROLLED POPULATION )N THIS CASE THE DRAMATIC INCREASE OF ITS POPULATION FOLLOWING COMPETITION RELEASE IS NOTH ING LESS THAN THE PROGRAM OBJECTIVES 4HIS CAN BE CONSIDERED IN CASES WHERE AN INTRODUCED SPECIES IS TO BE REMOVED BECAUSE IT THREATENS A LOCAL POPULATION THROUGH COMPETITION BUT WHERE CONTROL PROGRAMS WERE NOT IMPLEMENTED FOR FEAR OF DAMAGE TO NON TARGET SPECIES )N THOSE CASES ANY UNINTENDED NON TARGET DEATH SHOULD BE MORE THAN BALANCED BY THE DEATH OF THE INTRODUCED COMPETITORS 4HERE IS NO HAPPY ENDING HOWEVER IF THE LOWER COMPETITOR APPEARS TO BE ANOTHER INTRODUCED SPECIES WHICH INCREASE CAN INmICT FURTHER DAMAGES TO THE INVADED ECOSYSTEM ESPECIALLY IF THAT INCREASE IS DRAMATIC !GAIN IN MANY CONSERVATION SITUATIONS MANAGERS HAVE TO MAKE TRADE OFF CHOICES AND IT MAY APPEAR THAT A COMPETITOR RELEASE BE EVENTUALLY LESS DETRIMENTAL THAN ALLOWING THE PRESENCE OF THE INTRODUCED PREDATOR 9ET DRAMATIC INCREASES OF ALIEN SPECIES ARE OFTEN VERY HARMFUL TO ECOSYSTEMS AND THIS EVENTUALLY SHOULD ALWAYS BE ASSESSED 4HERE IS MUCH MORE THAT COULD BE SAID ABOUT SUCH A SYSTEM EVEN AS SIMPLE AS IT IS AND ABOUT THE CASE STUDIES IN WHICH THE OVERLOOKING OF AN ENEMY RELEASE LED TO SURPRISE EFFECTS THAT EVENTUALLY CAUSED FURTHER DAMAGES TO INVADED ECOSYS TEMS (OWEVER BEING THAT THE AIM OF THIS CHAPTER IS TO CONVINCE THE READER THAT BIOLOGICAL INVASIONS AND THEIR CONTROL CAN PROVIDE AN EXCELLENT MODEL SYSTEM FOR
& #OURCHAMP AND 3 #AUT
&IG )LLUSTRATION OF THE COMPETITOR RELEASE EFFECT 0ANEL ! SHOWS THE COMPARTMENTAL REPRESENTATION OF THE EXAMPLE TAKEN FROM 3URPRISE )SLAND OFF .EW #ALEDONIA WHERE TWO RODENTS ARE COMPETITORS RATS 2 RED BEING A SUPERIOR COMPETITOR OVER THE MICE - YELLOW 4HE EQUATION SET IN THE PRESENCE OF SIMULTANEOUS CONTROL IS GIVEN IN PANEL " (ERE BOTH # AND $ REPRESENT POPULATION TRENDS FOLLOWING CONTROL 0ANEL # SHOWS THE POPULATION TRENDS OF THE TWO COMPETITORS AS A FUNCTION OF TIME FOR TWO DIFFERENT COMBINATIONS OF CONTROL EFFORT AND CONTROL SPECIlCITY SEE TEXT )N BOTH CASES THE RODENT CONTROL CAN LEAD TO THE DEMOGRAPHIC EXPLOSION OF ONE OF THE RODENT POPULATIONS 0ANEL $ SHOWS THE POPULATION TRENDS OF THE LOWER COMPETITOR AS A FUNCTION OF THE CONTROL EFFORT AND THE CONTROL EFlCIENCY !S IN &IG $ THE COLORS ARE GIVEN HERE TO FACILITATE THE $ EFFECT 4HIS PANEL SHOWS THAT IF THE COMPETITION IS STRONG THE DEMOGRAPHIC EXPLOSION OF THE LOWER COMPETITOR IS PROPORTIONAL TO ITS CONTROL !S THE COMPETITION PRESSURE FROM THE SUPERIOR COMPETITOR IS LIFTED BY THE CONTROL THE RESULTING GAIN IN POPULATION GROWTH IS COMPENSATING THE LOSSES OCCURRED BY THE CONTROL RESULTING IN A LARGER POPULATION THAN IN ABSENCE OF CONTROL
$YNAMICS OF INTERACTING POPULATIONS
THE STUDY OF INTERSPECIlC RELATIONSHIPS WE WILL ONLY CLOSE THIS EXAMPLE BY AN OBVIOUS IF OVERLOOKED STATEMENT )N SOME CASES THE DIRECT NEGATIVE IMPACT OF A SPECIES CAN HIDE AN INDIRECT POSITIVE EFFECT ON THE SAME COMMUNITY SOMETIMES ON THE VERY SAME SPECIES )N A CLASSICAL SYSTEM WHERE SPECIES ADDITION OR REMOVAL IS NOT THE RULE SUCH INTERACTIONS CAN REMAIN HIDDEN )N THE CASE OF INVADED COM MUNITIES AND OF ASSOCIATED CONSERVATION PROGRAMS SPECIES REMOVAL CAN HIGHLIGHT THESE UNDETECTED RELATIONSHIPS 3UCH HIGHLIGHT IS HOWEVER DONE IN THE FORM OF FURTHER DAMAGE IN THE SYSTEM WITH A RISK OF BIODIVERSITY LOSS AND SHOULD THERE FORE BE ANTICIPATED )F INDIRECT POSITIVE EFFECTS ARE GREATER THAN THE DIRECT NEGATIVE EFFECTS ONE MUST BE EXTREMELY CAUTIOUS IN ANY RESTORATION ACTION INTENDED TO PROTECT THE AFFECTED SPECIES
#/.#,53)/. "IOLOGICAL INVASIONS ARE PRIMARILY CONSIDERED FOR THEIR HARMFUL EFFECTS ON BIO DIVERSITY IN INVADED ECOSYSTEMS ESPECIALLY ON ISLANDS 4HIS IS FAR FROM SURPRIS ING AS ISLANDS ARE PLACES OF MAJOR BIOLOGICAL DIVERSITY AND ARE OFTEN INCLUDED IN ECOLOGICAL HOTSPOTS -YERS ET AL 2EID AND OF HIGH PROBABILITY OF EXOTIC SPECIES INTRODUCTION &OR EXAMPLE MAMMAL INTRODUCTIONS HAVE BEEN DOCUMENTED ON ISLANDS %BENHARD WHILE 'ARGOMINY ET AL RECORDED MORE THAN EXOTIC SPECIES OF mOWERING PLANTS IN THE WILD IN .EW #ALEDONIA ALONE 'ARGOMINY ET AL 4HESE lGURES HAVE UNDOUBTEDLY INCREASED NOWADAYS 4HE NUMBER OF SPECIES THAT WENT EXTINCT AS A RESULT OF THESE INVASIONS IS IMPOSING TOO #ONSEQUENTLY THE NUMBER OF CONTROL PROGRAMS HAS BEEN ON THE RISE THIS LAST DECADE AND HERE AGAIN THERE ARE A GREAT NUMBER OF DOCUMENTED EXAMPLES WITH FOR EXAMPLE OVER ERADICATION PROGRAMS JUST FOR EXOTIC MAMMALS IN .EW :EALAND #2 6EITCH PERS COMM 7E HAVE SO FAR INSISTED MUCH ON CAUTION AND PLANNING IN ANY MITIGATIONERADI CATION EFFORT IN MANAGEMENT PROGRAMS 7E FEEL IT IS NEVERTHELESS ESSENTIAL TO START OUR CONCLUSION BY REWORDING THE OBVIOUS THE BEST RESPONSE TO BIOLOGICAL INVASION IS ALMOST ALWAYS MITIGATE AND WHEN POSSIBLE ERADICATE THE ALIEN POPULATION )N MANY CASES A HESITANCY TO PROCEED WITH THIS HAS CAUSED MORE DAMAGE TO BIODI VERSITY THAN HAVE THE UNEXPECTED RESULTS OF POORLY PLANNED OR SIMPLY UNLUCKY ERADICATIONS (OWEVER THE AIM OF THIS CHAPTER WAS TO TAKE A DIFFERENT POINT OF VIEW REGARD ING BIOLOGICAL INVASIONS AND TO SHOW THAT SUCH EVENTS HOWEVER NOT SYSTEMATIC CAN BE VIEWED AS OPPORTUNITIES TO INCREASE FUNDAMENTAL KNOWLEDGE IN ECOLOGY !DDITIONS AND DELETIONS OF SPECIES IN TROPHIC WEBS THAT ARE COMPARATIVELY MUCH SIMPLER THAN USUAL SHOULD GREATLY ENHANCE OUR ABILITY TO DISCERN INTRINSIC DYNAMICAL PROCESSES AS WELL AS DIRECT AND INDIRECT INTERACTIONS BETWEEN SPECIES AND HERE WE VIEW POPULATION DYNAMICS AS GOOD MARKERS OF SUCH MECHANISMS 4HIS APPROACH ALSO HAS THE DUAL ADVANTAGE OF ADDRESSING MECHANISMS ON A REAL SCALE SOMETHING IMPOSSIBLE IN LABORATORY BASED STUDIES AND OF ENCOMPASSING
& #OURCHAMP AND 3 #AUT
ALL THE CHARMING CONSTRAINTS OF BIOLOGICAL REALITY SOMETHING MISSING IN PURELY THEORETICAL ECOLOGY )T IS OF COURSE NOT OUR PURPOSE TO MINIMIZE THE CONTRIBUTION OF THEORY IN THIS REGARD $ESPITE THEIR INDUBITABLE ADVANTAGE IN THIS DOMAIN lELD BASED STUDIES THAT USE INVASIONS AS AN EXPERIMENT HAVE MUCH TO GAIN FROM A SYNERGY WITH CONCOMITANT LABORATORY AND THEORETICAL APPROACHES 7E EVEN URGE CONSERVATION BIOLOGISTS AND BIODIVERSITY MANAGERS TO USE THEORETICAL BASED RESULTS TO FOUND THEIR CONSERVATION PROGRAM DESIGN AND TO LOOK INTO HISTORICAL CASES IN ORDER NOT TO ENDLESSLY REPEAT MISTAKES OF THE PAST !N IDEA ASSOCIATED TO THIS IS THE NEED FOR CONSERVATIONISTS AS WELL AS BIODIVERSITY MANAGERS TO KNOW WHEN TO STOP A PRO GRAM AND RETHINK THE STRATEGY #OURCHAMP ET AL A 4O KNOW WHEN WE ARE STARTING TO PLAY THE WITCHS SORCERER AND WHEN TO STOP IS AN ESSENTIAL YET DIFlCULT FACULTY (ISTORY HAS SHOWN US THAT OFTEN MORE HARM IS GENERATED WHEN TRIAL AND ERROR PROCESSES ARE USED INDISCRIMINATELY /NE GOOD EXAMPLE OF THIS IS GIVEN BY THE ATTEMPTED MITIGATION OF RATS IN SUGARCANE lELDS IN *AMAICA 4HERE CANE GROWERS INTRODUCED ANTS &ORMICA OMNIVORA WHICH DID NOT REDUCE RAT NUMBERS BUT SOON BECAME A PROBLEM THEMSELVES 4O REMOVE RATS AND ANTS TOGETHER IT WAS THEN DECIDED TO INTRODUCE TOADS "UFO MARINUS "UT TOADS STILL DID NOT CONTROL RATS AND BECAME A PEST THEMSELVES &INALLY SMALL )NDIAN MONGOOSES WERE INTRODUCED TO CONTROL RATS AND TOADS -ONGOOSES FAILED TO CONTROL EITHER AND BEGAN PREYING ON NATIVE BIRDS POSING NEW THREATS TO WILDLIFE 3ILVERSTEIN AND 3ILVERSTEIN 7E RECOGNIZE THAT THERE HAS BEEN MUCH TO GAIN FROM THESE KINDS OF HISTORICAL MISTAKES AND THAT THESE HARD WON LESSONS MIGHT EVEN TURN OUT TO BE GLOBALLY BENElCIAL FOR THE BIODIVERSITY IN THE LONG RUN (OWEVER WE BELIEVE THE TRIAL AND ERROR APPROACH TIME HAS NOW PASSED AND BIODIVERSITY MANAGERS SHOULD PERSEVERE IN THE CURRENT TREND OF BASING RESTORATION STRATEGIES ON SOUND SCIEN TIlC GROUNDS 4HIS CAN ONLY BE DONE IN DEVELOPING SPECIlC STUDIES ON POPULATIONS INTERACTING IN INVADED COMMUNITIES AS WELL AS THOSE THAT USE SUCH INVASIONS AS A DIDACTIC TOOL TO UNDERSTAND BASIC PROCESSES IN POPULATION ECOLOGY
!#+./7,%$'-%.43 4HIS WORK WAS FUNDED BY THE )NSTITUT &RAN AIS DE "IODIVERSITÏ 7E THANK ,EIGH "ULL FOR HER HELP WITH THE %NGLISH
2%&%2%.#%3 !BRAMS 0 ! )NDIRECT INTERACTIONS BETWEEN SPECIES THAT SHARE A PREDATOR VARIETIES OF INDIRECT EFFECTS )N 0REDATION $IRECT AND )NDIRECT )MPACTS ON !QUATIC #OMMUNITIES EDS 7 # +ERFOOT ! 3IH PP 5NIVERSITY 0RESS OF .EW %NGLAND (ANOVER !BRAMS 0 ! (OLT 2 $ AND 2OTH * $ !PPARENT COMPETITION OR APPARENT MUTUAL ISM 3HARED PREDATION WHEN POPULATIONS CYCLE %COLOGY
$YNAMICS OF INTERACTING POPULATIONS
"ROTHERS . 0 "REEDING DISTRIBUTION AND STATUS OF BURROW NESTING PETRELS AT -ACQUARIE )SLAND !USTRIALIAN 7ILDLIFE 2ESEARCH "ROTHERS . 0 AND #OPSON ' 2 -ACQUARIE )SLAND mORA AND FAUNA MANAGEMENT INTERPRETING PROGRESS AND PREDICTIONS FOR THE FUTURE 0APERS AND 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF 4ASMANIA #AMPOS ! 2 AND 'RANADEIRO * 0 "REEDING BIOLOGY OF THE 7HITE FACED 3TORM PETREL ON 3ELVAGEM 'RANDE )SLAND .ORTH EAST !TLANTIC 7ATERBIRDS #HAPUIS * , A !LIEN MAMMALS IN THE &RENCH 3UBANTARCTIC )SLANDS )N 0ROGRESS IN CONSERVATION OF THE 3UBANTARCTIC )SLANDS ED 0 2 $INGWALL 6OL PP )5#. 4HE 7ORLD #ONSERVATION 5NION #ONSERVATION OF THE 3OUTHERN 0OLAR 2EGION #HAPUIS * , B 2ESTORATION OF TWO ISLANDS IN THE +ERGUELEN !RCHIPELAGO BY ERADICATION OF THE RABBIT /RYCTOLAGUS CUNICULUS )N 0ROGRESS IN CONSERVATION OF THE 3UBANTARCTIC )SLANDS ED 0 2 $INGWALL 6OL PP )5#. 4HE 7ORLD #ONSERVATION 5NION #ONSERVATION OF THE 3OUTHERN 0OLAR 2EGION #HAPUIS * , "OUSSÒS 0 AND "ARNAUD ' !LIEN MAMMALS IMPACT AND MANAGE MENT IN THE &RENCH SUB ! NTARCTIC ISLANDS "IOLOGICAL #ONSERVATION #LUTTON "ROCK 4 ( AND #OULSON 4 #OMPARATIVE UNGULATE DYNAMICS THE DEVIL IS IN THE DETAIL 0HILOSOPHICAL 4RANSACTIONS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES " "IOLOGICAL 3CIENCES #OURCHAMP & #HAPUIS * , AND 0ASCAL - A -AMMAL INVADERS ON ISLANDS IMPACT CONTROL AND CONTROL IMPACT "IOLOGICAL 2EVIEWS #OURCHAMP & ,ANGLAIS - AND 3UGIHARA ' #ONTROL OF RABBITS TO PROTECT ISLAND BIRDS FROM CAT PREDATION "IOLOGICAL #ONSERVATION #OURCHAMP & ,ANGLAIS - AND 3UGIHARA ' 2ABBITS KILLING BIRDS MODELLING THE HYPERPREDATION PROCESS *OURNAL OF !NIMAL %COLOGY #OURCHAMP & 7OODROFFE 2 AND 2OEMER ' B 2EMOVING PROTECTED POPULATIONS TO SAVE ENDANGERED SPECIES 3CIENCE #UTHBERT 2 AND (ILTON ' )NTRODUCED HOUSE MICE -US MUSCULUS A SIGNIlCANT PREDATOR OF THREATENED AND ENDEMIC BIRDS ON 'OUGH )SLAND 3OUTH !TLANTIC /CEAN "IOLOGICAL #ONSERVATION %BENHARD 4 )NTRODUCED BIRDS AND MAMMALS AND THEIR ECOLOGICAL EFFECTS 3WEDISH 7ILDLIFE 2ESEARCH &EARE # !NTS TAKE OVER FROM RATS ON "IRD )SLAND 3EYCHELLES "IRD #ONSERVATION )NTERNATIONAL &ITZGERALD " - $IET OF DOMESTIC CATS AND THEIR IMPACT ON PREY POPULATIONS )N 4HE DOMESTIC CAT THE BIOLOGY OF ITS BEHAVIOUR EDS $ # 4URNER 0 "ATESON PP #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE &ITZGERALD " - $ANIEL - * &ITZGERALD ! % +ARL " * -EADS - * AND .OTMAN 0 2 &ACTORS EFFECTING THE NUMBERS OF HOUSE MICE -US MUSCULUS IN HARD BEECH .OTHOFAGUS TRUNCATA FOREST *OURNAL OF THE 2OYAL 3OCIETY OF .EW :EALAND &LUX * % # 2ELATIVE EFFECT OF CATS MYXOMATOSIS TRADITIONAL CONTROL OR COMPETITORS IN REMOVING RABBITS FROM ISLANDS .EW :EALAND *OURNAL OF :OOLOGY &LUX * % # AND &ULLAGAR 0 * 7ORLD DISTRIBUTION OF THE RABBIT /RYCTOLAGUS CUNICULUS ON ISLANDS -AMMAL 2EVIEW
& #OURCHAMP AND 3 #AUT
'ARGOMINY / "OUCHET 0 0ASCAL - *AFFRE 4 AND 4OURNEUR * # #ONSEQUENCES FOR BIODIVERSITY OF PLANT AND ANIMAL SPECIES INTRODUCTIONS IN .EW #ALEDONIA 2EVUE $ %COLOGIE ,A 4ERRE %T ,A 6IE 'ILLHAM - % 3OME INTERACTIONS OF PLANTS RABBITS AND SEABIRDS ON 3OUTH !FRICAN ISLANDS *OURNAL OF %COLOGY 'INZBURG , 2 AND *ENSEN # 8 * 2ULES OF THUMB FOR JUDGING ECOLOGICAL THEORIES 4RENDS IN %COLOGY %VOLUTION 'RENFELL " 4 7ILSON + &INKENSTADT " & #OULSON 4 . -URRAY 3 !LBON 3 $ 0EMBERTON * - #LUTTON "ROCK 4 ( AND #RAWLEY - * .OISE AND DETERMINISM IN SYNCHRONIZED SHEEP DYNAMICS .ATURE (OLDGATE - 7 AND 7ACE . - 4HE INmUENCE OF MAN ON THE mORAS AND FAUNAS OF 3OUTHERN )SLANDS 0OLAR 2ECORD (OLT 2 $ 0REDATION APPARENT COMPETITION AND THE STRUCTURE OF PREY COMMUNITIES 4HEORETICAL 0OPULATION "IOLOGY (ONE * 3PATIAL AND 4EMPORAL !SPECTS OF 6ERTEBRATE 0EST $AMAGE WITH %MPHASIS ON &ERAL 0IGS *OURNAL OF !PPLIED %COLOGY +ARL " * AND "EST ( ! &ERAL CATS ON 3TEWART )SLAND THEIR FOODS AND THEIR EFFECTS ON KAKAPO .EW :EALAND *OURNAL OF :OOLOGY +EANE 2 - AND #RAWLEY - * %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY %VOLUTION +ESSLER # # %RADICATION OF FERAL GOATS AND PIGS FROM 3ARIGAN )SLAND #OMMONWEALTH OF THE .ORTHERN -ARIANA )SLANDS METHODS AND RESULTS )N %RADICATION OF ISLANDS )NVASIVES PRACTICAL ACTIONS AND RESULTS ACHIEVED ED - #LOUT PP 5NIVERSITY OF !UCKLAND .EW :EALAND ,E 2OUX 6 #HAPUIS * , &RENOT 9 AND 6ERNON 0 $IET OF THE HOUSE MOUSE -US MUSCULUS ON 'UILLOU )SLAND +ERGUELEN ARCHIPELAGO 3UBANTARCTIC 0OLAR "IOLOGY -ACK 2 . AND ,ONSDALE 7 - %RADICATING INVASIVE PLANTS HARD WON LESSONS FOR ISLANDS )N 4URNING THE 4IDE THE %RADICATION OF )NVASIVE 3PECIES EDS # 2 6EITCH - #LOUT )NVASIVE 3PECIES 3PECIALTY 'ROUP OF THE 7ORLD #ONSERVATION 5NION )5#. !UCKLAND .EW :EALAND -ICOL 4 AND *OUVENTIN 0 %RADICATION OF RATS AND RABBITS FROM 3AINT 0AUL )SLAND &RENCH 3OUTHERN 4ERRITORIES )N 4URNING THE TIDE THE ERADICATION OF INVASIVE SPECIES EDS # 2 6EITCH - . #LOUT PP )5#. 33# )NVASIVE 3PECIES 3PECIALIST 'ROUP )5#. 'LAND 3WITZERLAND AND #AMBRIDGE 5+ -URPHY % AND "RADlELD 0 #HANGE IN DIET OF STOATS FOLLOWING POISONING OF RATS IN A .EW :EALAND FOREST .EW :EALAND *OURNAL OF %COLOGY -YERS . -ITTERMEIER 2 ! -ITTERMEIER # ' DA &ONSECA ' ! " AND +ENT * "IODIVERSITY HOTSPOTS FOR CONSERVATION PRIORITIES .ATURE .EWMAN $ ' %FFECTS OF A -OUSE -US MUSCULUS %RADICATION 0ROGRAM AND (ABITAT #HANGE ON ,IZARD 0OPULATIONS OF -ANA )SLAND .EW :EALAND WITH 3PECIAL 2EFERENCE TO -CGREGOR 3KINK #YCLODINA MACGREGORI .EW :EALAND *OURNAL OF :OOLOGY 2AMMELL # ' (OOGENBOOM * * , #OTTER - 7ILLIAMS * - AND "ELL * "RODIFACOUM RESIDUES IN TARGET AND NON TARGET ANIMALS FOLLOWING RABBIT POISONING TRIALS .EW :EALAND *OURNAL OF %XPERIMENTAL !GRICULTURE
$YNAMICS OF INTERACTING POPULATIONS
2EID 7 6 "IODIVERSITY HOTSPOTS 4RENDS IN %COLOGY %VOLUTION 2OBERTSON ( ! (AY * 2 3AUL % + AND -C#ORMACK ' 6 2ECOVERY OF THE +AKERORI AN %NDANGERED &OREST "IRD OF THE #OOK )SLANDS #ONSERVATION "IOLOGY 2OEMER ' 7 $ONLAN # * AND #OURCHAMP & 'OLDEN EAGLES FERAL PIGS AND INSU LAR CARNIVORES (OW EXOTIC SPECIES TURN NATIVE PREDATORS INTO PREY 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES OF THE 5NITED 3TATES OF !MERICA 3CHOENER 4 7 AND 3PILLER $ ! )NDIRECT EFFECTS IN AN EXPERIMENTALLY STAGED INVASION BY A MAJOR PREDATOR !MERICAN .ATURALIST 3COTT * * 2ABBIT DISTRIBUTION HISTORY AND RELATED LAND DISTURBANCE -ACQUARIE )SLAND !USTRALIA 0APERS AND 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF 4ASMANIA 3ELKIRK 0 - #OSTIN ! " 3EPPELT 2 $ AND 3COTT * * 2ABBITS VEGETATION AND ERO SION ON -ACQUARIE )SLAND 0ROCEEDINGS OF THE ,INNEAN 3OCIETY . 3 7 3ILVERSTEIN ! AND 3ILVERSTEIN 6 !NIMAL INVADERS 4HE STORY OF IMPORTED WILDLIFE !THENUM .EW 9ORK 3MITH ! 0 AND 1UIN $ ' 0ATTERNS AND CAUSES OF EXTINCTION AND DECLINE IN !USTRALIAN CONILURINE RODENTS "IOLOGICAL #ONSERVATION 3MITH 6 2 !VENANT . , AND #HOWN 3 , 4HE DIET AND IMPACT OF HOUSE MICE ON A SUB !NTARCTIC ISLAND 0OLAR "IOLOGY 3OULÏ - % "OLGER $ 4 !LBERTS ! # 7RIGHT * 3ORICE - AND (ILL 3 2ECONSTRUCTED DYNAMICS OF RAPID EXTINCTIONS OF CHAPARRAL REQUIRING BIRDS IN URBAN HABITAT ISLANDS #ONSERVATION "IOLOGY 4AYLOR 2 ( (OW THE -ACQUARIE ISLAND PARAKEET BECAME EXTINCT .EW :EALAND *OURNAL OF %COLOGY
#HAPTER TWELVE
)NVASIBILITY OF SEED PREDATORS ON SYNCHRONIZED AND INTERMITTENT SEED PRODUCTION OF HOST PLANTS ! 3ATAKE / . "JRNSTAD AND 9 )WASA
).42/$5#4)/. 4HE SPATIOTEMPORAL DISTRIBUTION OF RESOURCES THAT INVADERS REQUIRE FOR THEIR GROWTH AND REPRODUCTION IS A KEY FACTOR IN CONTROLLING SUCCESS OF INVASION $AVIS ET AL 4HE ABUNDANCE OF ABIOTIC RESOURCES SUCH AS WATER SUPPLY AND NUTRIENT LEVELS MAY mUCTUATE DUE TO VARIABLE CLIMATIC CONDITION AND DISTURBANCE REGIME EG DROUGHT mOOD OR lRE REGIMES 4HEREFORE THE INTENSITY OF COMPETITION FOR THESE LIMITED RESOURCES VARIES RESULTING IN TEMPORAL mUCTUATION OF A COMMUNITYS SUSCEPTIBILITY TO INVASION $AVIS AND 0ELSOR 7HEN INVADING SPECIES ARE CONSUMERS OF BIOTIC RESOURCES EG HERVIVORES AND SEED PREDATORS SUCCESSFUL INVASION MAY TRIGGER THE EVOLUTION OF TRAITS OF HOST SPECIES THAT ENHANCE RESISTANCE TO INVADERS &OR EXAMPLE MAST SEEDING OR MASTING THE INTERMITTENT AND SYNCHRONIZED REPRODUCTION BY PLANT POPULATIONS +ELLY REPORTED ACROSS A BROAD GROUP OF TREE SPECIES (ERRERA ET AL IS OFTEN EXPLAINED TO HAVE EVOLVED TO REDUCE SEED LOSSES TO AND HENCE TO PREVENT -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
! 3ATAKE /. "JRNSTAD AND 9 )WASA
INVASION OF SEED PREDATORS THE hPREDATOR SATIATION HYPOTHESISv *ANZEN 3ILVERTOWN %SSENTIALLY LARGER SEED CROPS ARE SYNCHRONIZED AMONG INDI VIDUALS AND SATIATE SEED PREDATORS AND THEREFORE EXPERIENCE A LOWER PERCENTAGE OF SEED PREDATION !T THE SAME TIME YEARS WITH LOW SEED PRODUCTION WILL REDUCE THE GROWTH OF THE SEED PREDATOR POPULATIONS -ANY STUDIES CONlRM PREDATOR SATIATION BY SHOWING LOWER PREDATION RATES IN HIGH SEED YEARS 3MITH ET AL 3ORK +ELLY AND 3ULLIVAN 3PERENS 3HIBATA ET AL +ELLY ET AL -C+ONE ET AL 3ATAKE ET AL 4HE PROPERTIES OR ADAPTATIONS OF THE INVADING CONSUMERS ALSO PLAY AN IMPORTANT ROLE PARTICULARLY THE TRAITS ASSOCIATED WITH DISPERSAL %VEN IF FOOD RESOURCES SHOW UNPREDICTABLE mUCTUATION AT A SINGLE PATCH OR PLANT DISPERSAL BETWEEN PATCHES BUFFERS VARIATION IN lTNESS BY SPREADING RISK OVER SPACE (OPPER $ISPERSAL AMONG PATCHES IS ADVANTAGEOUS IF mUCTUATIONS OF LOCAL CONDITIONS ARE INDEPENDENT ACROSS SPACE ,EVIN ET AL BUT IF THERE IS POSITIVE CORRELATION EITHER IN TIME OR ACROSS SPACE DISPERSAL IS LESS FAVORED %LLNER AND 3HMIDA #OHEN AND ,EVIN (OLT AND -C0EEK )N THIS CHAPTER WE DISCUSS A RESOURCE CONSUMER MODEL TO UNDERSTAND THE SPATIOTEMPORAL DYNAMICS OF A SEED PREDATOR ON A MASTING RESOURCE AND EXPLORE THE INVASIBILITY OF THE PREDATORS 3ATAKE AND "JRNSTAD 3PATIOTEMPORAL mUCTUATIONS IN SEEDING ARE REPRESENTED BY THE POLLEN COUPLED TREE MODEL )SAGI 3ATAKE AND )WASA A B IN WHICH REPRODUCTIVE BEHAVIOR OF INDIVIDUAL PLANTS IS CONSTRAINED BY THE LEVEL OF INTERNAL ENERGY RESERVES AND LOCAL POLLEN PRODUCTION 7E CONSIDER SPECIALIZED INSECT SEED PREDATORS 4HE DYNAMICS OF THE PREDATOR AT A SINGLE HOST PLANT IS ASSUMED TO FOLLOW A SPA TIALLY EXTENDED .ICHOLSON "AILEY MODEL (ASSELL ET AL 3ATAKE AND "JRNSTAD AND THE ADULTS HAVING A SEMELPAROUS LIFECYCLE DISPERSE TO NEIGHBORING HOST PLANTS TO SEARCH RANDOMLY FOR SEEDS BERRIES OR mOWERHEADS ON WHICH TO LAY THEIR EGGS AND THE LARVAE SUBSEQUENTLY COMPLETE THE LIFECYCLE THROUGH FEEDING ON THE SEEDS 7E CALCULATE AN APPROXIMATE INVASION CRITERION FOR THE PREDATORS WHICH ILLUSTRATES HOW VARIABLE AND SYNCHRONIZED SEED PRODUCTION OF PLANTS MAY PREVENT INVASION OF SEED PREDATORS POPULATION
2%3/52#% $9.!-)#3 /& 3%%$ 02/$5#4)/. 3PATIOTEMPORAL mUCTUATION OF FOOD RESOURCE FOR SEED PREDATORS IS MODELED AS FOL LOWS 7E CONSIDER A FOREST OF OUT CROSSING PLANTS EACH WITH AN INTERNAL ENERGY RESERVE THAT CHANGES WITH NET ENERGY GAIN THROUGH PHOTOSYNTHESIS AND ENERGY EXPENDITURE THROUGH REPRODUCTION AND MAINTENACEGROWTH %ACH PLANT GAINS NET ENERGY 0S EVERY YEAR FROM PHOTOSYNTHESIS ,ET 3I T BE THE ENERGY RESERVES OF A PLANT LOCATED AT SITE I AT THE BEGINNING OF YEAR T ! PLANT WILL NOT REPRODUCE UNLESS ITS ACCUMULATED ENERGY RESERVES 3I T 0S EXCEEDS A CRITICAL THRESH OLD ,4 /THERWISE THE PLANT PRODUCES mOWERS INVESTING ENERGY hmOWERING COSTv PROPORTIONAL TO THE EXCESS GIVEN BY A3I T 0S n ,4 WHERE A IS CONSTANT
) NVASIBILITY OF SEED PREDATORS
OF PROPORTIONALITY 3ATAKE AND )WASA !LL mOWERS ARE POLLINATED AND THE PLANT THEN INVESTS ADDITIONAL ENERGY DUE TO THE COST OF FRUIT PRODUCTION 2C A3I T 0S n ,4 WHERE 2C IS THE RATIO OF FRUITING COST TO mOWERING COST 4HE ENERGY RESERVE LEVEL THUS FALLS TO 3I T 0S n A2C 3I T 0S n ,4 SO THAT THE OVERALL RESOURCE DYNAMICS ARE IF 3I T 0S ) ,4 ¨ 3I T 0S 3I T © ª 3I T 0S n A2C 3I T 0S n ,4 IF 3I T 0S ,4
#ONSIDERING THE NON DIMENSIONALIZED VARIABLE 9I T 3I T 0S n ,4 0 EQUATION IS REWRITTEN AS ¨ 9I T 9I T © ª n K9I T
IF 9I T ) IF 9I T
IN WHICH K A2C n IS A DEPLETION CONSTANT )F A K IS EQUAL TO THE RATIO OF FRUITING COST TO mOWERING COST 2C %QUATION REPRESENTS A hTENT MAPv THAT PREDICTS STABLE ANNUAL REPRODUCTION FOR K AND CHAOTIC REPRODUCTION FOR K 3ATAKE AND )WASA 3UCH TEMPORAL ENERGY DYNAMICS AT THE LEVEL OF THE INDI VIDUAL PLANT IS EASILY ILLUSTRATED THROUGH BIFURCATION DIAGRAMS &IG 4HE LONG TERM TRAJECTORIES OF ENERGY LEVEL DElNED IN EQ ARE PLOTTED ACROSS A RANGE OF VALUES OF K 7HEN K TRAJECTORIES VISIT A SINGLE POSITIVE VALUE WHICH REPRESENTS ANNUAL AND CONSTANT REPRODUCTION &OR K THE ORBIT EVENTUALLY REPRESENTS CHAOTIC mUCTUATION !S K INCREASES THE INTERVAL BETWEEN NON REPRODUCTIVE YEARS BECOMES LONGER BECAUSE THE PLANT NEEDS MORE YEARS TO REBUILD ENERGY RESERVES TO THE THRESHOLD LEVEL 0OLLEN LIMITATION
)F PLANTS ARE SELF INCOMPATIBLE FRUITING RATES MAY DEPEND ON THE mOWERING ACTIVITY OF OTHER TREES IN A FOREST BECAUSE POLLINATION EFlCIENCY CHANGES WITH THE NUMBER OF mOWERING PLANTS .ILSSON AND 7ËSTLJUNG 3MITH ET AL 4O MODEL THE POLLEN LIMITATION OF PLANT REPRODUCTION THE POLLEN AVAILABILITY 0I T TO INDIVIDUAL I WAS INTRODUCED IN THE NON DIMENSIONALIZED ENERGY DYNAMICS )SAGI ET AL 3ATAKE AND )WASA ¨ 9I T 9I T © ª n K0I T 9I T
IF 9 T ) I IF 9I T
A
WHERE 0I T IS DETERMINED BY THE AVERAGE mOWERING INTENSITY OF THE PLANTS IN THE NEIGHBORHOOD AROUND THE FOCAL PLANT 5I )T IS GIVEN BY
! 3ATAKE /. "JRNSTAD AND 9 )WASA
&IG "IFURCATION DIAGRAM OF AN INDIVIDUAL PLANT (ORIZONTAL AXIS IS DEPLETION COEFlCIENT K AND THE VERTICAL AXIS IS THE NON DIMENSINALIZED ENERGY LEVEL 0ARAMETERS ` W
0I T
£ ¥` ² - 9J T µ ¤W J D5I ¦
B
WHERE 9 9 IF 9 AND ZERO OTHERWISE 4HE PARAMETER W IS THE NUMBER OF PLANTS INCLUDED IN THE NEIGHBORHOOD 5I NOTE THAT THE NEIGHBORHOOD DOES NOT INCLUDE ONESELF AND ` DETERMINES THE DEGREE OF NEIGHBOR DEPENDENCE ON THE POL LEN LIMITATION )F `IS CLOSE TO FRUIT PRODUCTION IS ALMOST INDEPENDENT OF THE mOW ERING INTENSITY OF OTHER PLANTS )N CONTRAST A LARGE ` IMPLIES A STRONG DEPENDENCE OF SEED AND FRUIT PRODUCTION ON THE POLLEN PRODUCTION OF OTHER PLANTS 4HUS WE CALL ` THE POLLEN COUPLING STRENGTH )N THIS CHAPTER WE CONSIDER A SITUATION OF hLOCAL POLLEN COUPLINGv IN WHICH POLLINATION IS LIMITED TO THE EIGHT NEAREST NEIGHBORS AROUND THE FOCAL PLANT W 0/05,!4)/. $9.!-)#3 /& 3%%$ 02%$!4/23 ! SPECIALIZED INSECT SEED PREDATOR WITH A SEMELPAROUS LIFECYCLE IS CONSIDERED IN AN ALL FEMALES MODEL !DULTS DISPERSE TO NEARBY HOST PLANTS TO SEARCH RANDOMLY FOR SEEDS AND BERRIES ON WHICH TO LAY THEIR EGGS 4HE LARVAE HATCH TO COMPLETE THEIR LIFECYCLE FEEDING ON THE SEED LEAVE THE SEEDS TO PUPATE AND EMERGE AS ADULTS AT THE BEGINNING OF NEXT GENERATION 4HESE ASSUMPTION ARE MOTIVATED BY STUDIES OF THE APPLE FRUIT MOTH !RGYRESTHIA CONJUGELLA :ELLER WHICH IS A PRE DISPERSAL SEED PREDA TOR OF ROWAN 3ORBUS AUCUPARIA , 4HE LARVAE OF THE APPLE FRUIT MOTH RELIES HEAVILY
) NVASIBILITY OF SEED PREDATORS
ON ROWAN BERRIES THAT VARIES SUBSTANTIALLY BETWEEN YEARS IN A GEOGRAPHICALLY SYN CHRONIZED FASHION +OBRO ET AL 3ATAKE ET AL 7E ASSUME THAT HOST PLANTS ARE ARRANGED ON LATTICE POINTS OF A TWO DIMENSIONAL SQUARE GRID 4HE NUMBER OF EMERGED ADULTS AT SITE I AT THE BEGINNING OF YEAR T IS DENOTED BY :I T ! FRACTION + OF THE ADULTS LEAVES THE PLANT WHERE THEY WERE BORN AND DISPERSES TO ADJACENT PLANTS 4HE POST DISPERSAL NUMBER OF ADULTS AT SITE I DENOTED AS :I T IS GIVEN BY + :I T n + :I T - :J T W J D2I
4HE PARAMETER 2I IS THE NEIGHBORHOOD OF SITE I AND W IS THE NUMBER OF HOST PLANTS INCLUDED IN 2I &OR SIMPLICITY WE ALSO ASSUME THAT SEED PREDATOR DISPERSES TO THE EIGHT NEAREST NEIGHBORS W 7HEN A SINGLE PLANT AT SITE I PRODUCES A CERTAIN AMOUNT OF SEEDS &I T IN YEAR T THE NUMBER OF PRE DISPERSAL ADULTS IN THE NEXT GENERATION T IS GIVEN BY :I T a&IT n E n_:IT
WHERE a IS THE PER CAPITA EMERGENCE RATE AND _ IS THE PER CAPITA ATTACK RATE THE SEARCHING EFlCIENCY &I T ITSELF IS GOVERNED BY THE POLLEN COUPLED TREE MODEL EQUATIONS n ACCORDING TO ¨ &I T © ª CK0I T 9I T
IF 9 T ) I IF 9I T
WHERE C IS A CONSTANT K IS THE DEPLETION COEFlCIENT AND 0I T IS THE POLLEN AVAIL ABILITY GIVEN BY EQN B
3%%$ 02%$!4)/. /. -!34).' 2%3/52#% 4HE REPRODUCTIVE BEHAVIOR PREDICTED BY THE POLLEN COUPLED TREE MODEL AND SEVERITY OF SEED PREDATION IS ILLUSTRATED IN &IG 7HEN THE DEPLETION COEFlCIENT K IS LESS THAN EACH PLANT PRODUCES SEEDS EVERY YEAR WHICH IS ANNUAL REPRODUCTION &IG ! !NNUAL REPRODUCTION CAN BE FURTHER CLASSIlED INTO hANNUAL AND CONSTANT REPRODUCTIONv SHADED AREA IN &IG ! IN WHICH EACH PLANT PRODUCES SEEDS CON STANTLY AND hANNUAL AND YEAR CYCLIC REPRODUCTIONv CHECKER REGION IN &IG ! IN WHICH PRODUCED SEED CROP SIZE ALTERNATES BETWEEN HIGH AND LOW BUT POSITIVE REPRODUCTIVE LEVELS !NNUAL AND CONSTANT SEED PRODUCTION RESULTS IN SEVERE ATTACKS &IG " WHILE ANNUAL AND YR CYCLIC SEED PRODUCTION CAN CAUSE EXTINCTION OF THE PREDATOR &IG " 4HIS EXTINCTION IS DUE TO THE SATIATION OF NUMERICAL RESPONSE OF
! 3ATAKE /. "JRNSTAD AND 9 )WASA
&IG ! #LASSIlCATION OF REPRODUCTIVE PATTERN OF PLANTS PREDICTED BY THE POLLEN COUPLED TREE MODEL WITH AN ASSUMPTION OF LOCAL POLLEN COUPLING 7E CLASSIlED FOUR TYPES OF REPRODUCTIVE PATTERN AS EXPLAINED IN THE TEXT " 4HE DENSITY PLOT FOR PROPORTION OF SEEDS ATTACKED CALCULATED BY NUMERICAL SIMULATION OF THE MODEL 4HE DARKER AREA REPRESENTS MORE SEVERE SEED PREDATION 0ARAMETERS + _ &ROM ! 3ATAKE AND / . "JRNSTAD 3PATIAL DYNAMICS OF SPECIALIST SEED PREDATORS ON SYNCHRONIZED AND INTERMITTENT SEED PRODUCTION OF HOST PLANTS !MERICAN .ATURALIST 2EPRINTED WITH PERMISSION FROM 4HE 5NIVERSITY OF #HICAGO 0RESS
THE PREDATOR THE NUMBER OF THE PREDATORS IS HEAVILY REDUCED BY A VERY SMALL SEED PRODUCTION IN A LOW REPRODUCTIVE YEAR AND THE PREDATOR POPULATION CANNOT COPE WITH A GREAT INCREASE IN SEED PRODUCTION IN A HIGH REPRODUCTIVE YEAR WHICH DECREASES THE POPULATION SIZE AND lNALLY LEADS THE POPULATION TO EXTINCTION 7HEN INDIVIDUAL PLANTS PRODUCE SEEDS INTERMITTENTLY WITH NUMEROUS YEARS WITH NO SEED SET PARAMETER REGION OF K IN &IG ! hLOCALv EXTINCTION OF SEED PREDA TORS IS INEVITABLE (OWEVER THEY MAY NEVERTHELESS PERSIST GLOBALLY DUE TO DISPERSAL WHEN MAST SYNCHRONY IS WEAK &IG )N &IG SIGNIlCANT SYNCHRONY l * IS DISTINGUISHED FROM WEAK SYNCHRONY l BY CALCULATING THE DEGREE OF SPATIAL SYNCHRONY AMONG PLANTS l )N A FOREST EXHIBITING WEAK SYNCHRONY IN SEEDING THERE IS ALWAYS SOME FRACTION OF PLANTS PRODUCING SEEDS 4HIS ENABLES SEED PREDA TORS TO PERSIST GLOBALLY THROUGH DISPERSAL TO ANY ASYNCHRONOUS NEARBY PLANTS
) NVASIBILITY OF SEED PREDATORS
)N CONTRAST IF PLANTS IN A FOREST PRODUCE SEEDS IN A SIGNIlCANTLY SYNCHRONIZED FASH ION SEED PREDATORS CANNOT lND RESOURCES ELSEWHERE WITHIN THE DISPERSAL RANGE AND THEN GO GLOBALLY EXTINCT &IG &OR MASTING PLANTS K THE PROPORTION OF ATTACKED SEEDS IS INVERSELY RELATED TO THE DEGREE OF SPATIAL SYNCHRONY AMONG PLANTS l &IG MEANING THAT SPATIAL SYNCHRONY IN SEED PRODUCTION EFFECTIVELY REDUCES LOSSES TO SEED PREDATORS
&IG ! $EGREE OF SYNCHRONY IN SEED PRODUCTION l " 0ROPORTION OF SEEDS ATTACKED 4HE HORIZONTAL AXIS IS THE DEPLETION COEFlCIENT K 0ARAMETERS ` « _
).6!3)/. 7E DEVELOPED AN APPROXIMATE INVASION CRITERION 1È THAT APPROXIMATELY DESCRIBES WHEN SEED PREDATORS CAN INVADE A SYSTEM WHERE THE HOST PLANTS PRODUCE SEEDS SYNCHRONOUSLY AND INTERMITTENTLY SEE !PPENDIX IN 3ATAKE AND "JRNSTAD 4HOUGH WE HAVE BEEN UNABLE TO OBTAIN EXACT INVASION CRITERIA DUE TO THE NATURE OF MASTING RESOURCES IE mUCTUATION ACROSS TIME AND SPACE IN A C YCLIC OR CHAOTIC MANNER 3ATAKE AND )WASA A 4HE APPROXIMATE INVASION CRITERION
! 3ATAKE /. "JRNSTAD AND 9 )WASA
APPEARS TO GIVE A GOOD PREDICTION OF THE INVASION AND PROVIDES KEY INSIGHTS INTO HOW PREDATOR INVASION IS INmUENCED BY THE MANNER OF mUCTUATIONS OF THE RESOURCE 4HE APPROXIMATE INVASION CRITERION 1È IS THE AVERAGE GROWTH OR DECLINE IN THE PRED ATOR POPULATION DURING TWO GENERATIONS FOLLOWING INTRODUCTION GIVEN AS FOLLOWS 4 n 1È - 1 T 4 T
A
WHERE _ a ¨ + . 1T © n + - &I T &IT I . ª W
. - I
¬ - &I T &JT B J D2I ®
)N THE ABOVE EQUATION . IS THE NUMBER OF PLANTS IN THE FOREST AND W IS THE NUMBER OF PLANTS INCLUDED IN THE NEIGHBORHOOD 2I &I T IS THE AMOUNT OF SEED PRODUCED BY A PLANT AT SITE I IN YEAR T GIVEN BY EQN /THER PARAMETERS ARE AS DElNED IN EQUATIONS AND 4HE lRST TERM IN THE RIGHT HAND SIDE IN EQN B REPRESENTS THE AVERAGE POPULATION INCREASE OR DECLINE THROUGH TWO GENERATIONS FOR THE SEED PREDATORS THAT DO NOT DISPERSE THEIR NEXT YEAR OFFSPRING ARE LEFT TO CONSUME SEEDS PRODUCED BY THE PLANT WHERE THEIR PARENTS WERE BORN 4HE SECOND TERM REPRESENTS THE CORRESPONDING AVERAGE FOR THE PREDATORS THAT DISPERSED TO LAY EGGS ON NEIGHBORING PLANTS "Y A SIMPLE CALCULATION 3TAKE AND "JORNSTAD 1È IS RELATED TO THE TIME LAG AUTO CORRELATION 2 IN SEED PRODUCTION OF INDIVIDUAL PLANTS AND TIME LAG CROSS CORRELATION # BETWEEN NEIGHBORING PLANTS AS FOLLOWS
1È _ a ! n + 2 m +# m &È #
WHERE m IS THE VARIANCE AND &È IS THE TEMPORAL MEAN SEEDSET OF EACH PLANT %QN SHOWS THAT INVASIBILITY IS PROMPTED IF SEED PRODUCTION IS POSITIVELY CORRELATED IN TIME BOTH FOR A GIVEN PLANT AND FOR PLANTS WITHIN THE DISPERSAL NEIGHBORHOOD OF THE PREDATOR )N THE CASE OF MAST SEEDING NEGATIVE TIME LAG OR AUTOCORRELATIONS IN SEED PRODUCTION ARE OFTEN REALIZED .ORTON AND +ELLY 3ORK ET AL +OENIG ET AL +ELLY AND 3ORK )N ADDITION NEGATIVE CROSS CORRELATION AT TIME LAG OFTEN RESULT BECAUSE OF SPATIALLY SYNCHRONIZED REPRODUCTION 4HUS INVASIBILITY TO THE PREDATORS IS REDUCED ON MASTING RESOURCES )F SEED PRODUCTION WITH INTERMITTENCE IS SYNCHRONIZED AT A hLOCALv SPATIAL SCALE NEARBY PLANTS SHOW A STRONGER NEGATIVE CROSS CORRELATION IN SEED PRODUCTION AT TIME LAG THAN DISTANTLY LOCATED PLANTS )N A FOREST SHOWING REGIONALLY NOT LOCALLY SELF ORGANIZED SEED PRODUCTION CROSS CORRELATIONS CALCULATED AT THE LOCAL SPATIAL SCALE WILL BE SIMILAR TO THE AVERAGE ACROSS THE REGIONAL SPATIAL SCALE )N THIS CASE 1T SIMPLIlES TO
) NVASIBILITY OF SEED PREDATORS
_a ¨ + . . 1T © n + - &I T &IT - I . ª . n I
¬ - &I T &JT J &I ®
(ERE THE SECOND TERM IN THE RIGHT HAND SIDE IN EQN B IS REPLACED BY THE AVERAGE OF THE PRODUCT FOR ALL POSSIBLE PAIRS I J OF PLANTS "Y TAKING THE TEMPORAL AVERAGE OF 1T WE HAVE AN APPROXIMATE INVASION CRITERION IN THE ABSENCE OF LOCAL SPATIAL STRUCTURE 1È 7E EVALUATED 1È AND 1È NUMERICALLY BY GENERATING THE SPATIOTEMPORAL PATTERNS IN SEED PRODUCTION FROM A NUMERICAL SIMULATION OF THE POLLEN COUPLED TREE MODEL WITH A RANGE OF PARAMETERS RESULTING IN VARYING DEGREE OF MASTING 3ATAKE AND "JORNSTAD 7E CONlRM THE ACCURACY OF THE APPROXIMATE INVASION CRITERIA THROUGH NUMERICAL SIMULATION OF THE FULL CONSUMER RESOURCE MODEL )N THEORY THE SEED PREDATORS SHOULD ONLY BE ABLE TO INVADE WHEN 1È 4O INVESTIGATE THIS WE INTRODUCED A MINUTE DENSITY OF THE PREDATOR – ON EACH HOST PLANT IN THE MODEL 7E SUBSEQUENTLY TRACED THEIR POPULATION GROWTH FOR GENERATIONS )F THE PREDATORS POPULATION IS STILL EXTANT AT THE END OF THE SIMULATION THE PLANT REPRODUCTIVE STRATEGY IS CONSIDERED INVASIBLE 4HE RESULTS INCLUDING THE TWO APPROXIMATE INVASION CRITERIA ARE ILLUSTRATED IN &IG "OTH CRITERIA ARE SEEN TO DECREASE WITH INCREASING SYNCHRONY OF SEED SET l MEANING THAT INVASIBILITY IS INHIBITED PARTLY OR ENTIRELY WHEN PLANTS SHOW REPRO DUCTIVE SYNCHRONY )N SIMULATIONS ESTABLISHMENT FAILS WHEN 1È IS BELOW AND
&IG 0LOT OF THE APPROXIMATE INVASION CRITERIA 1È OPEN SQUARES AND 1È SOLID CIRCLES ALONG THE DEGREE OF SYNCHRONY IN SEED PRODUCTION AMONG DIFFERENT PLANTS l 3TARS REPRESENT THE VALUES OF 1È IN WHICH EXTINCTION OF SEED PREDATORS OCCURRED 0ARAMETERS « _ &ROM ! 3ATAKE AND / . "JRNSTAD 3PATIAL DYNAMICS OF SPECIALIST SEED PREDATORS ON SYNCHRONIZED AND INTERMITTENT SEED PRODUCTION OF HOST PLANTS !MERICAN .ATURALIST 2EPRINTED WITH PERMISSION FROM 4HE 5NIVERSITY OF #HICAGO 0RESS
! 3ATAKE /. "JRNSTAD AND 9 )WASA
&IG 3PATIAL PATTERNS IN SEED PRODUCTION UPPER ROW AND AMOUNT OF SEED PREDATORS BOTTOM ROW X AND Y AXES REPRESENT SPATIAL LOCATIONS AND Z AXIS REPRESENTS SEED CROP SIZE UPPER THREE lGURES OR SEED PREDATOR ABUNDANCE BOTTOM THREE lGURES 4IME mOWS LEFT TO RIGHT 0ARAMETERS K ` « _ 4HE TOTAL NUMBER OF HOST PLANT IS )N ORDER TO SHOW CLEAR SPATIAL PATTERNS WE APPLY THE POLLEN DISPERSAL RANGE LARGER THAN NEAREST NEIGHBOR PLANTS LOCATED AT ITH LOCATION XI YI AND JTH LOCATION XJ YJ CAN EXCHANGE POLLEN IF \XI XJ\ \YI YJ\ ) 4HE OVERALL SPATIAL PATTERN IS SIMILAR BUT THE SPATIAL SCALE OF THE PATTERN IS LARGER AND BECOMES COARSE GRAINED AS POLLEN DISPERSAL RANGE INCREASES FOR DETAILS SEE 3ATAKE AND )WASA A &ROM ! 3ATAKE AND / . "JRNSTAD 3PATIAL DYNAMICS OF SPECIALIST SEED PREDATORS ON SYNCHRONIZED AND INTERMITTENT SEED PRODUCTION OF HOST PLANTS !MERICAN .ATURALIST 2EPRINTED WITH PERMISSION FROM 4HE 5NIVERSITY OF #HICAGO 0RESS
SUCCEEDS FOR 1È 4HIS SUGGESTS THAT THE APPROXIMATE INVASION CRITERIA BASED ON THE POPULATION GROWTH DURING TWO GENERATIONS APPEARS TO GIVE AN EXCELLENT PREDIC TION OF THE INVASION IN THE FULL SPATIOTEMPORAL SIMULATIONS 4HIS SUCCESS ORIGINATES IN PART FROM HOW THE ENTIRE FOREST EXHIBITS A YEAR CYCLE IN SEED PRODUCTION WHEN THE PLANTS REPRODUCTION IS HIGHLY SYNCHRONIZED &IG 4HE YEAR CYCLIC SEED PRODUCTION BECOMES UNCLEAR AT THE POPULATION LEVEL AS THE DEGREE OF SYNCHRONY DECREASES 4HUS LONGER INTERVALS BETWEEN MAST YEARS EG OR YEARS SHOULD BE TAKEN INTO ACCOUNT TO CORRECT THE SLIGHT OVERESTIMATION OF THE INVASION CRITERION &IG )NTERESTINGLY 1È IS ALMOST ALWAYS LESS THAN 1È 4HIS DIFFERENCE HIGHLIGHTS
) NVASIBILITY OF SEED PREDATORS
THAT SEED PREDATORS SUFFER LOWER INVASIBILITY WHEN REPRODUCTION AMONG PLANTS IS SYNCHRONIZED AT A LOCAL SPATIAL SCALE 4HE SPATIAL PERSISTENCE OF PREDATORS IN THE PRESENCE OF HIGHLY VARIABLE MAST SEEDING IS VISUALIZED IN &IG 4HE UPPER THREE lGURES REPRESENT THE TEMPORAL CHANGE OF SPATIAL DISTRIBUTIONS FOR SEED CROP SIZE PRODUCED BY INDIVIDUAL PLANTS 4HE lGURE ILLUSTRATES HOW LOCALIZED SPATIAL CLUSTERS CAN RESULT FORM LOCAL POLLEN COUPLING 7ITHIN A GIVEN CLUSTER PLANTS SHOW SYNCHRONIZED REPRODUCTION WITH A YEAR CYCLE VISITING HIGH AND VERY LOW REPRODUCTIVE LEVEL 4HE CORRESPONDING SPATIAL DISTRIBUTIONS OF SEED PREDATORS BOTTOM PANEL IN &IG SHOW HOW THE SEED PREDATORS PERSISTENCE IS FACILITATED AT THE BOUNDARIES OF THE CLUSTERS 3EED PREDA TORS CAN lND RESOURCES TO CONSUME ONLY WHEN HOST PLANTS SHOWING OPPOSITE REPRO DUCTIVE PHASES ARE WITHIN THE DISPERSAL RANGE
#/--5.)49 ,%6%, -!34).' !.$ ).6!3)/. )N THIS SECTION WE INTRODUCE A SIMPLE CASE STUDY OF PLANT CONSUMER SYSTEM AND BRIEmY DISCUSS THAT WHEN SEED PREDATORS ARE GENERALISTS MASTING AT COMMUNITY LEVEL IS NECESSARY TO REDUCE THE IMPACT OF THE PREDATOR 2OWAN 3ORBUS AUCUPARIA , IS A DECIDUOUS TREE WHICH IS COMMON IN MUCH OF %UROPE 4UTIN ET AL 4HE mESHY BERRIES PRODUCED BY ROWAN TREES SUFFER FROM ATTACK BY THE APPLE FRUIT MOTH !RGYRESTHIA CONJUGELLA THAT IS A PRIMARY PRE DISPERSAL SEED PREDATOR WHOSE LARVAE RELY HEAVILY ON ROWAN BERRIES 3PERENS A B +OBRO ET AL 3ATAKE ET AL 4HE SPATIOTEMPORAL DATA OBTAINED FROM A CENSUS IN SOUTHERN .ORWAY SHOW THAT BERRY PRODUCTION IN ROWAN IS VARIABLE ACROSS YEARS MEAN #6 AND IS SPATIALLY SYNCHRONIZED l BOOTSTRAPPED CONlDENCE INTERVAL 4HE DEGREE OF SPATIAL SYNCHRONY IN ROWAN POPULATION IS LOWER THAN THE LEVEL OF SYNCHRONY LEADING TO SEED PREDATOR EXTINCTION IE l &IG AND HENCE THE APPLE FRUIT MOTH SUCCESSFULLY INVADE AND IS PERSISTENT IN THIS SYSTEM (OWEVER RELATIVELY HIGH DEGREE OF SPATIAL SYNCHRONY IN ROWAN MASTING EFl CIENTLY REDUCES SEED LOSSES TO THE APPLE FRUIT MOTH AND SUPPRESSES THE POPULATION GROWTH RATE OF SEED PREDATORS AT A LOW LEVEL AS ILLUSTRATED IN &IG 4HE PROPORTION OF SEEDS PREDATED WAS NEGATIVELY CORRELATED WITH THE TOTAL NUMBER OF SEEDS EVI DENCING A SATIATED FUNCTIONAL RESPONSE OF THE SEED PREDATORS BY MASTING )N ADDI TION A NEGATIVE RELATIONSHIP WAS OBSERVED BETWEEN THE SEED PREDATION AND THE RATIO OF BERRY PRODUCTION IN SUCCESSIVE YEARS 4HIS MEANS THAT SEED CROPS FOLLOW ING POOR SEED CROPS TENDED TO ESCAPE PREDATIONS TESTIFYING TO A SATIATION THROUGH NUMERICAL RESPONSE OF THE PREDATORS 3ATAKE ET AL 4HE PREDATOR SATIATION HYPOTHESIS FURTHER PREDICTS THAT THE MORE VARIABLE POPULATIONS SHOULD ATTAIN HIGHER OVERALL SEED SURVIVAL *ANZEN 7ALLER 3ILVERTOWN 4O ASSESS THIS THE TOTAL PROPORTION OF SEEDS LOST TO PREDATION WAS EXAMINED AS A FUNCTION OF TEMPORAL VARIABILITY IN SEED PRODUCTION MEASURED BY THE #6 4HE RESULTANT LOGISTIC REGRESSION REVEALED A SIGNIlCANTLY NEGATIVE RELATIONSHIP BETWEEN THE PROPORTION OF BERRIES PREDATED AND #6 THE SLOPE n P
! 3ATAKE /. "JRNSTAD AND 9 )WASA
&IG 4IME SERIES DATA OF ! ANNUAL BERRY PRODUCTION OF ROWAN TREES AND " PERCENTAGE OF ATTACKED BERRIES BY THE APPLE FRUIT MOTH %ACH LINE REPRESENTS THE TIME SERIES FROM ONE STUDY SITE &ROM ! 3ATAKE / . "JRNSTAD AND 3 +OBRO -ASTING AND TROPHIC CASCADES INTERPLAY BETWEEN ROWAN TREES APPLE FRUIT MOTH AND THEIR PARASITOID IN SOUTHERN .ORWAY /IKOS 2EPRINTED WITH PERMISSION FROM "LACKWELL 0UBLISHING
INDICATING THAT LARGER INTER ANNUAL VARIATION IN BERRY PRODUCTION RESULTED IN SMALLER LOSSES TO PREDATION 4HESE RESULTS SHOW THAT ROWAN MASTING HAS AN ADAP TIVE FOUNDATION WHICH REDUCE SEED LOSSES TO AND PREVENT A RAPID EXPANSION IN A PLANT POPULATION 4HE PERSISTENCE OF THE MOTH IN THE ROWAN MOTH SYSTEM IS IN PART BECAUSE OF THE FACT THAT THE APPLE FRUIT MOTH IS NOT A STRICT SPECIALIST THE PRIMARY AND PRE FERRED HOST OF THE APPLE FRUIT MOTH IS ROWAN BUT WHEN TOO FEW ROWAN BERRIES ARE AVAILABLE FOR EGG LAYING MANY FEMALE MOTHS SWITCH THE HOST TO APPLE !HLBERG )F THERE ARE GENERALIST SEED PREDATORS IN A PLANT COMMUNITY VARIABLE AND SYNCHRONIZED SEED PRODUCTION ONLY WITHIN A SINGLE SPECIES MAY NOT ENOUGH TO PREVENT INVASION OF THE SEED PREDATOR AND EVEN MASTING SPECIES SHOWING A SIGNIl CANT SYNCHRONY IN SEED PRODUCTION MAY SUFFER HEAVY SEED PREDATION 3ILVERTOWN
) NVASIBILITY OF SEED PREDATORS
&IG 0LOT OF PROPORTION OF SEED PREDATION IN ROWAN AS A FUNCTION OF ! SEED CROP SIZE AND " THE RATIO OF SEED CROP SIZE IN YEAR T AND THAT IN YEAR T n LAG ,OG TRANSFORMED VARIABLES ARE USED FOR CALCULATION ,INES REPRESENTS THE LOGISTIC REGRESSION MODEL WHICH HAVE INTERCEPTS AND SLOPES OF ! 3% P n 3% P AND " n 3% P n 3% P # 2ELATIONSHIP BETWEEN THE COEFlCIENT OF VARIATION #6 OF ANNUAL SEED PRODUCTION AND THE TOTAL PROPORTION OF SEED PREDATION %ACH POINT REPRESENTS THE RESULT CALCULATED AT ONE STUDY SITE ,OGISTIC REGRESSION ANALYSIS GAVE THE REGRESSION LINE AS INTERCEPT OF n 3% P AND SLOPE OF n 3% P
! 3ATAKE /. "JRNSTAD AND 9 )WASA
STATED THAT SYNCHRONOUS SEED PRODUCTION BETWEEN POPULATION OF DIFFERENT SPECIES SHARING THE SAME SEED PREDATORS REDUCES THE GROWTH RATE OF THE PREDATOR POPULATION BY PREDATOR SATIATION 3PATIAL SYNCHRONY IN SEED PRODUCTION AMONG SPECIES HAS BEEN REPORTED IN ANIMAL POLLINATED SPECIES IN A RELATIVELY CLOSED COM MUNITY IN THE RAIN FOREST -OMOSE ET AL )NOUE AND (AMID 3AKAI ET AL AND IN WIND POLLINATED SPECIES IN OPEN HABITATS SUCH AS TEMPERATE FOREST AND SAVANNA +OENIG AND +NOPS 3CHAUBER ET AL 3HIBATA ET AL 3UCH A SYNCHRONIZED AND EPISODIC REPRODUCTION IN A COMMUNITY PROVIDES AN INTERESTING INSIGHT INTO THE EVOLUTIONARY PROCESS HOW PLANT COMMUNITIES ENHANCE RESISTANCE AGAINST GENERALIST SEED PREDATORS
#/.#,53)/. 4HIS CHAPTER FOCUSES ON THE SPATIALLY EXTENDED DYNAMICS OF MASTING PLANTS AND THEIR SEED PREDATORS 0LANTS WITHIN A FOREST MAY PRODUCE SEEDS ANNUALLY OR INTER MITTENTLY IN TIME AND SYNCHRONOUSLY OR ASYNCHRONOUSLY ACROSS SPACE 4HIS RANGE OF DYNAMICAL BEHAVIOR IS CAPTURED BY THE POLLEN COUPLED TREE MODEL EQNS )SAGI 3ATAKE AND )WASA A B 4HE EFFECT OF MAST SEEDING ON DYNAMICS AND INVASIBILITY OF SPECIALIST CONSUMERS WAS EXPLORED BY EXAMINING THE POPULATION DYNAMICS OF SEED PREDATORS IN A BOTTOM UP FASHION EQNS 7HEN PLANTS PRODUCE SEEDS INTERMITTENTLY PERSISTENCE AND INVASION OF THE PREDATOR IS MOST CRITICALLY DEPENDENT ON THE DEGREE OF SYNCHRONY OF SEED SET 4HE PREDATOR POPULATION CAN ONLY PERSIST THROUGH DISPERSAL TO ADJACENT HOST PLANTS IN A FOREST SHOWING WEAK SYNCHRONY BECAUSE THERE IS THEN SOME FRACTION OF ASYN CHRONOUSLY REPRODUCING PLANTS WITHIN THE DISPERSAL RANGE OF THE PREDATORS )N CONTRAST EXTINCTION OF SEED PREDATORS IS LIKELY WHEN INTERMITTENT REPRODUCTION IS HIGHLY SYNCHRONIZED AMONG DIFFERENT PLANTS &IG 3PATIAL SYNCHRONY IN SEED PRODUCTION WITH INTERMITTENCE CREATES NEGATIVE TIME LAG AUTO CORRELATION AND CROSS CORRELATION IN SEEDING WHICH MOST EFFECTIVELY REDUCE INVASIBILITY OF THE SEED PREDATORS EQN 4HIS MEANS THAT hCLASSICv MAST SEEDING EXHIBITING SEED SET THAT IS NEGATIVELY CORRELATED IN TIME BUT POSITIVELY CORRELATED ACROSS SPACE IS A GOOD STRATEGY TO REDUCE SEED LOSS TO SEED PREDATORS )N ADDITION ANALYSIS OF INVASION CRITERION SUGGEST THAT SPATIAL SYNCHRONY AT LOCAL SPATIAL SCALES MAY FURTHER REDUCE LOSSES BY PREVENTING INVASION OF SEED PREDATORS &IG 4HE SPATIAL SCALE AT WHICH SYNCHRONY IN SEED PRODUCTION REDUCES SEED LOSSES TO SEED PREDATORS DEPENDS ON THE MOBILITY OF THE PREDATORS +ELLY AND 3ORK )NSECT PREDATORS CONSIDERED IN THIS CHAPTER MAY DISPERSE OVER RELATIVELY SHORT DISTANCES "IRDS OR MAMMALS IN CONTRAST MAY BE HIGHLY MOBILE #URRAN AND ,EIGHTON )N ORDER TO SATIATE SUCH PREDATORS SO AS TO REDUCE SEED LOSSES LARGER SPATIAL SCALES OF REPRODUCTIVE SYNCHRONY MUST BE MAINTAINED 4HE ANALYSIS OF APPROXIMATE INVASION CRITERIA GIVEN IN EQUATIONS AND APPLIES ALSO TO HIGHLY MOBILE SPECIALIST CONSUMERS BECAUSE THE FORMULATIONS CAN BE WRITTEN FOR ARBITRARY NEIGHBORHOOD SIZES NOT RESTRICTED TO NEAREST NEIGHBOR DISPERSAL
) NVASIBILITY OF SEED PREDATORS
4HE COMMUNITY CONSEQUENCES OF MASTING ARE ONLY KNOWN FOR SELECTED CASE STUDIES -ICE AND SQUIRRELS FOR INSTANCE EXPERIENCE ENHANCED SURVIVAL AND RAPID POPULATION GROWTH IN YEARS OF OAK MAST 3UCH POPULATION MAY CONVERSELY CRASH TO LOW LEVELS IN YEARS OF LITTLE ACORN BECAUSE OF A SHORTAGE OF FOOD RESOURCES 7OLFF -C3HEA -ASTING HAS ALSO BEEN SHOWN TO HAVE CASCADING EFFECTS THROUGH FOOD WEBS AND ECOLOGICAL COMMUNITIES IN SYSTEMS RANGING FROM OUT BREAKS OF GYPSY MOTH IN OAK FORESTS TO HUMAN RISK OF ,YME EXPOSURE /STFELD ET AL /STFELD AND +EESING 3UCH STUDIES ON THE TROPHIC CASCADES FOLLOWING VARIABLE MASTING MAY PROVIDE KEY INSIGHTS INTO INVASION AS A COMMUNITY PROCESS 3HEA AND #HESSON )N THIS CHAPTER WE FOCUS ON THE DYNAMICS OF A SINGLE SEED PREDATOR SPECIES ON A SINGLE MASTING RESOURCE )N THE FUTURE IT WILL BE OF INTEREST TO CONSIDER INVASIBIL ITY TO ADDITIONAL SEED PREDATORS AND POSSIBLY EXOTIC SPECIES 7HEN EXOTIC SEED PREDATORS ARE INTRODUCED INTO A PLANT POPULATION THAT SHOW MASTING A POTENTIAL STRATEGY THE PREDATOR MAY EMPLOY TO COPE WITH VARIABLE RESOURCE AVAILABILITY MAY BE AN EXTENDED DIAPAUSE +ELLY ET AL AND -C+ONE ET AL DEMON STRATED THAT PLANT POPULATIONS SUFFERING SEED PREDATION BY THE PREDATORS WHO HAVE EXTENDED DIAPAUSE MAY NEED TO SHOW EXTREMELY HIGH LEVELS OF MAST SEEDING 4HIS DEMONSTRATION HAS BEEN RECENTLY SUPPORTED BY A THEORETICAL STUDY OF 3ATAKE AND "JRNSTAD 4HEREFORE HOW PRE EXISTING MASTING MIGHT MITIGATE THE IMPACT OF INVADING PREDATORS IS DEPENDENT ON THE LEVEL BOTH OF PRE EXISTING MASTING OF PLANT POPULATION AND THE EXTENDED DIAPAUSE OF INVADER 7HEN THE RESIDENT SEED PREDATOR PERSISTS ON A MASTING RESOURCE THE COMPETITIVE INTENSITY BETWEEN THE RESIDENT AND INVADING SPECIES WILL mUCTUATE DUE TO SPATIOTEMPORAL VARIABILITY IN RESOURCE AVAILABILITY )NVASION SUCCESS OF AN EXOTIC SPECIES MAY BE ENHANCED WHEN THE RESIDENT POPULATION IS SATIATED THROUGH LARGE SEED CROPS BECAUSE UNCON SUMED RESOURCES MAY RESULT IN A COMPETITIVE RELEASE 4HIS INCREASE IN INVASIBILITY MAY OCCUR THROUGH TEMPORAL COMPETITIVE RELEASE OR SPATIALLY THROUGH THE FORMA TION OF COMPETITION FREE SPATIAL CLUSTERS )NVASIBILITY OF EXOTIC SEED PREDATORS IS DETERMINED BY THE INTERWINED INTERACTION BETWEEN TEMPORAL PROCESS AND SPATIAL PATTERN ILLUSTRATING THE COMPLEX COMMUNITY CONSEQUENCES OF MASTING
!#+./7,%$'%-%.4 4HIS WORK WAS SUPPORTED IN PART BY A FELLOWSHIP AND A GRANT IN AID FROM THE *APAN 3OCIETY FOR THE 0ROMOTION OF 3CIENCE !3 AND 53$!.2) GRANT NO /." 4HE AUTHORS THANK THE FOLLOWING PEOPLE 5 $IECKMANN 2 ! )MS $ +ELLY ! ,IEBHOLD * ! * -ETZ AND 2 3 /STFELD FOR THEIR HELPFUL COMMENTS
! 3ATAKE /. "JRNSTAD AND 9 )WASA
2%&%2%.#%3 !HLBERG / 2ÚNNBËRSMALEN !RGYRESTHIA CONJUGELLA :ELL %N REDOGÚRELSE FÚR UNDER SÚKNINGAR ÍREN IN 3WEDISH WITH %NGLISH SUMMARY ,ANTBRUKSENTO MOLOGISKA AVDELNINGEN 3TOCKHOLM #OMINS ( . - 0 (ASSELL AND 2 - -AY 4HE SPATIAL DYNAMICS OF HOST PARASITOID SYSTEMS *OURNAL OF !NIMAL %COLOGY #OHEN $ AND 3 ! ,EVIN $ISPERSAL IN PATCHY ENVIRONMENTS THE EFFECTS OF TEMPORAL AND SPATIAL STRUCTURE 4HEORETICAL 0OPULATION "IOLOGY #URRAN , - AND - ,EIGHTON 6ERTEBRATE RESPONSES TO SPATIOTEMPORAL VARIATION IN SEED PRODUCTION OF MAST FRUITING $IPTEROCARPACEAE %COLOGICAL -ONOGRAPH $AVIS - ! * 0 'RIME AND + 4HOMPSON &LUCTUATING RESOURCES IN PLANT COMMUNI TIES A GENERAL THEORY IN INVASIBILITY *OURNAL OF %COLOGY $AVIS - ! AND - 0ELSOR %XPERIMENTAL SUPPORT FOR A RESOURCE BASED MECHANISTIC MODEL OF INVASIBILITY %COLOGY ,ETTERS %LLNER 3 AND ! 3HMIDA 7HY ARE ADAPTATIONS FOR LONG RANGE SEED DISPERSAL RARE IN DESERT PLANTS /ECOLOGIA (ASSELL - 0 ( . #OMINS AND 2 - -AY 3PATIAL STRUCTURES AND CHAOS IN INSECT POPULATION DYNAMICS .ATURE (ERRERA # - 0 *ORDANO * 'UITIAN AND ! 4RAVESET !NNUAL VARIABILITY IN SEED PRODUCTION BY WOODY PLANTS AND THE MASTING CONCEPT REASSESMENT OF PRINCIPLES AND RELATIONSHIP TO POLLINATION AND SEED DISPERSAL !MERICAN .ATURALIST (OLT 2 $ AND - ! -C0EEK #HAOTIC POPULATION DYNAMICS FAVORS THE EVOLUTION OF DISPER SAL !MERICAN .ATURALIST (OPPER + 2 2ISK SPREADING AND BET HEDGING INSECT POPULATION BIOLOGY !NNUAL 2EVIEW OF %NTOMOLOGY )NOUE 4 AND ! ! (AMID 'ENERAL mOWERING OF TROPICAL RAINFORESTS IN 3ARAWAK #ENTER FOR %COLOGICAL 2ESEARCH +YOTO 5NIVERSITY *APAN +YOTO )SAGI 9 + 3UGIMURA ! 3UMIDA AND ( )TO (OW DOES MASTING HAPPEN AND SYN CHRONIZE *OURNAL OF 4HEORETICAL "IOLOGY *ANZEN $ ( 3EED PREDATION BY ANIMALS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS +ELLY $ 4HE EVOLUTIONARY ECOLOGY OF MAST SEEDING 4RENDS IN %COLOGY %VOLUTION +ELLY $ AND 6 , 3ORK -AST SEEDING IN PERENNIAL PLANTS WHY HOW WHERE !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS +ELLY $ AND * * 3ULLIVAN 1UANTIFYING THE BENElT OF MAST SEEDING ON PREDATOR SATIA TION AND WIND POLLINATION IN #HIONOCHLOA PALLENS 0OACEAE /IKOS +ELLY $ ! , (ARRISON 7 ' ,EE ) * 0AYTON 0 0 7ILSON AND 7 - 3CHAUBER 0REDATOR SATIATION AND EXTREME MAST SEEDING IN SPECIES OF #HIONOCHLOA 0OACEAE /IKOS +OBRO 3 , 3REIDE % $JNNE 4 2AFOSS ' *AASTAD AND 0 7ITZGALL -ASTING OF ROWAN 3ORBUS AUCUPARIA , AND CONSEQUENCES FOR THE APPLE FRUIT MOTH !RGYRESTHIA CON JUGELLA :ELLER 0OPULATION %COLOGY
) NVASIBILITY OF SEED PREDATORS
+OENIG 7 $ AND * - ( +NOPS 3CALE OF MAST SEEDING AND TREE RING GROWTH .ATURE ,EVIN 3 ! $ #OHEN AND ! (ASTINGS $ISPERSAL STRATEGIES IN PATCHY ENVIRONMENTS 4HEORETICAL 0OPULATION "IOLOGY -C+ONE - * $ +ELLY ! , (ARRISON * * 3ULLIVAN AND ! * #ONE "IOLOGY OF INSECTS THAT FEED IN THE INmORESCENCES OF #HINOCHLOA 0OACEAE IN .EW :EALAND AND THEIR REL EVANCE TO MAST SEEDING .EW :EALAND *OURNAL OF :OOLOGY -C3HEA 7 * 4HE INmUENCE OF ACORN CROPS ON ANNUAL VARIATION IN RODENT AND BIRD POPULATIONS WITHIN OAK DOMINATED FORESTS %COLOGY -OMOSE + 4 .AGAMITSU AND 4 )NOUE 4HE REPRODUCTIVE ECOLOGY OF AN EMERGENT DEPTEROCARP IN A LOWLAND RAIN FOREST IN 3ARAWAK 0LANT 3PECIES "IOLOGY .ILSSON 3 ' AND 5 7ËTLJUNG 3EED PREDATION AND CROSS POLLINATION IN MAST SEEDING BEECH &AGUS SYLVATICA PATCHES %COLOGY .ORTON $ ! AND $ +ELLY -AST SEEDING OVER YEARS BY $ACRYDIUM CUPRESSINUM ,AMB RIMU 0ODOCARPACEAE IN .EW :EALAND THE IMPORTANCE OF ECONOMIES OF SCALE &UNCTIONAL %COLOGY /STFELD 2 3 *ONES # ' AND 7OLFF * / /F MICE AND MAST ECOLOGICAL CONNECTIONS IN EASTERN DECIDUOUS FORESTS "IO3CIENCE /STFELD 2 3 AND & +EESING 0ULSED RESOURCES AND COMMUNITY DYNAMICS OF CONSUM ERS IN TERRESTRIAL ECOSYSTEMS 4RENDS IN %COLOGY %VOLUTION 2EES - $ +ELLY AND / . "JRNSTAD 3NOW TUSSOCKS CHAOS AND THE EVOLUTION OF MAST SEEDING !MERICAN .ATURALIST 3AKAI 3 + -OMOSE 4 9UMOTO 4 .AGAMITSU ( .AGAMASU ! ! (AMID 4 .AKASHIZUKA 0LANT REPRODUCTIVE PHENOLOGY OVER FOUR YEARS INCLUDING AN EPISODE OF GEN ERAL mOWERING IN A LOWLAND DIPTEROCARP FOREST 3ARAWAK -ALAYSIA !MERICAN *OURNAL OF "OTANY 3ATAKE ! AND 9 )WASA 0OLLEN COUPLING OF FOREST TREES FORMING SYNCHRONIZED AND PERIODIC REPRODUCTION OUT OF CHAOS *OURNAL OF 4HEORETICAL "IOLOGY 3ATAKE ! AND 9 )WASA A 3PATIALLY LIMITED POLLEN EXCHANGE AND A LONG RANGE SYN CHRONIZATION OF TREES %COLOGY 3ATAKE ! AND 9 )WASA B 4HE SYNCHRONIZED AND INTERMITTENT REPRODUCTION OF FOREST TREES IS MEDIATED BY THE -ORAN EFFECT ONLY IN ASSOCIATION WITH POLLEN COUPLING *OURNAL OF %COLOGY 3ATAKE ! / . "JRNSTAD AND 3 +OBRO -ASTING AND TROPHIC CASCADES INTERPLAY BETWEEN ROWAN TREES APPLE FRUIT MOTH AND THEIR PARASITOID IN SOUTHERN .ORWAY /IKOS 3ATAKE ! AND / . "JRNSTAD 3PATIAL $YNAMICS OF 3PECIALIST 3EED 0REDATORS ON 3YNCHRONIZED AND )NTERMITTENT 3EED 0RODUCTION OF (OST !MERICAN .ATURALIST 3ELÍS 6 / (OGSTAD ' !NDERSSON AND 4 VON 0ROSCHWITZ 0OPULATION CYCLES OF AUTUMNAL MOTH %PIRRITA AUTUMNATA IN RELATION TO BIRCH MAST SEEDING /ECOLOGIA 3CHAUBER % - $ +ELLY 0 4URCHIN # 3IMON 7 ' ,EE 2 " !LLEN ) * 0AYTON 0 2 7ILSON 0 % #OWAN AND 2 % "ROCKIE -ASTING BY EIGHTEEN .EW :EALAND PLANT SPECIES THE ROLE OF TEMPERATURE AS A SYNCHRONIZING CUE %COLOGY
! 3ATAKE /. "JRNSTAD AND 9 )WASA
3HIBATA - ( 4ANAKA AND 4 .AKASHIZUKA 3YNCHRONIZED ANNUAL SEED PRODUCTION BY PRINCIPAL TREE SPECIES IN A TEMPERATE DECIDUOUS FOREST *APAN %COLOGY 3CHNURR * , 2 3 /STFELD AND $ #ANHAM $IRECT AND INDIRECT EFFECT OF MASTING ON RODENT POPULATIONS AND TREE SEED SURVIVAL /IKOS 3HEA + AND 0 #HESSON #OMMUNITY ECOLOGY THEORY AS A FRAMEWORK FOR BIOLOGICAL INVASIONS 4RENDS IN %COLOGY AND %VOLUTION 3HIBATA - ( 4ANAKA AND 4 .AKASHIZUKA #AUSE AND CONSEQUENCES OF MAST SEED PRODUCTION OF FOUR CO OCCURRING #ARPINUS SPECIES IN *APAN %COLOGY 3ILVERTOWN * 7 4HE EVOLUTIONALY ECOLOGY OF MAST SEEDING IN TREES "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY 3MITH # # * , (AMRICK AND # , +RAMER 4HE ADVANTAGE OF MAST YEARS FOR WIND POLLINATION !MERICAN .ATURALIST 3ORK 6 , * "RAMBLE AND / 3EXTON %COLOGY OF MAST FRUITING IN THREE SPECIES OF NORTH !MERICAN DECIDUOUS OAKS %COLOGY 3PERENS 5 A &RUIT PRODUCTION IN 3ORBUS AUCUPARIA , 2OSACEAE AND PRE DISPERSAL SEED PREDATION BY THE APPLE FRUIT MOTH !RGYRESTHIA CONJUGELLA :ELL /ECOLOGIA 3PERENS 5 B ,ONG TERM VARIATION IN AND EFFECTS OF FERTILIZED ON mOWER FRUIT AND SEED PRODUCTION IN THE TREE 3ORBUS AUCUPARIA 2OSACEAE %COGRAPHY 4UTIN 4 ' 6 ( (EYWOOD . ! "URGES $ - -OORE $ ( 6ALENTINE 3 - 7ALTERS AND $ ! 7EBB &LORA EUROPAEA ND EDN #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 7OLFF * / 0OPULATION mUCTUATIONS OF MAST EATING RODENTS ARE CORRELATED WITH PRO DUCTION OF ACORNS *OURNAL OF -AMMALOGY
#HAPTER THIRTEEN
)NVASIONS AND THE REGULATION OF PLANT POPULATIONS BY PATHOGENS ' 3 'ILBERT AND ) - 0ARKER
).42/$5#4)/. 4HE POTENTIAL OF PATHOGENS TO HAVE DRAMATIC IMPACTS ON PLANT POPULATIONS IS MADE CLEAR BY FAMILIAR STORIES OF THE )RISH POTATO FAMINE &RY AND 'OODWIN THE ECOLOGICAL EXTINCTION OF CHESTNUTS CAUSED BY CHESTNUT BLIGHT !NAGNOSTAKIS AND THE TRANSFORMATION OF !USTRALIAN *ARRAH FORESTS TO SCRUBLAND BY 0HYTOPHTHORA CINNAMOMI 7ESTE AND -ARKS 3IMILARLY THE ANNUAL WORLDWIDE EXPENDI TURE OF OVER BILLION IN FUNGICIDE APPLICATION $ONALDSON ET AL REmECTS THE TOLL FUNGAL PATHOGENS ALONE CAN TAKE ON PLANT GROWTH AND FECUNDITY IN AGRICULTURAL SYSTEMS 3OME OF THE MOST NOTABLE EXAMPLES OF THESE IMPACTS ARISE WHEN PATHOGENS ARE INTRODUCED INTO NOVEL BIOLOGICAL ENVIRONMENTS INVASIVE AND EMERGENT PATHOGENS CONTINUE TO FRUSTRATE THE BEST EFFORTS OF RESOURCE MANAGERS CONSERVATION BIOLOGISTS AND PLANT PROTECTION AGENCIES 7ESTE AND -ARKS $AUGHTREY ET AL 'OODELL ET AL 'ORDON ET AL -C$ONALD AND (OFF 7INGlELD ET AL 'ILBERT 2IZZO AND 'ARBELOTTO 0ARKER AND 'ILBERT #ONCURRENT WITH EFFORTS TO REDUCE THE IMPACTS OF UNWANTED DISEAS ES THERE IS BROAD INTEREST AMONG RESEARCHERS AGRICULTURALISTS AND LAND MANAGERS TO HARNESS THE DESTRUCTIVE POTENTIAL OF PLANT PATHOGENS TO CONTROL WEEDY PLANTS (ASAN AND !YRES #HARUDATTAN AND $INOOR -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
'3 'ILBERT AND )- 0ARKER
)N NATURAL ECOSYSTEMS PATHOGENS HAVE GREAT POTENTIAL TO INmUENCE THE DYNAM ICS AND COMPOSITION OF PLANT POPULATIONS AND COMMUNITIES THROUGH DENSITY DEPENDENT AND COEVOLUTIONARY DYNAMICS SEE REVIEWS IN $INOOR AND %SHED "URDON *AROSZ AND $AVELOS !LEXANDER ET AL !LEXANDER AND (OLT 'ILBERT )N MANY PLANT COMMUNITIES PLANT PATHOGENS MAY PREVENT COMPETITIVE EXCLUSION AND THUS HELP MAINTAIN SPECIES DIVERSITY 'ILLETT 0ACKER AND #LAY 'ILBERT 7RIGHT 'ILBERT #OLLECTIVE INSIGHTS FROM RESEARCH ON EPIDEMIC DISEASES BIOLOGICAL CONTROL AND THE EVOLUTIONARY ECOLOGY OF DISEASES IN NATURAL ECOSYSTEMS PROVIDE A ROBUST BASIS FOR IDENTIFYING WHEN PATHOGENS ARE LIKELY TO BE IMPORTANT IN REGULATING PLANT POPULATIONS AND THEIR IMPLICATIONS FOR UNDERSTANDING BIOLOGICAL INVASIONS (ERE WE DRAW BROADLY FROM A DIVERSE LITERATURE TO PLACE THE REGULATION OF PLANT POPULATIONS BY PATHOGENS INTO THE CONTEXT OF TWO KEY COMPLEMENTARY THEORIES ABOUT THE ROLE OF PATHOGENS IN BIOLOGICAL INVASIONS "IOTIC 2ESISTANCE -ARON AND 6ILA AND %SCAPE FROM .ATURAL %NEMIES +EANE AND #RAWLEY 4ABLE 7E THEN CONSIDER THE PRACTICAL IMPLICATIONS FOR USING INTRODUCED PATHOGENS FOR CLASSICAL BIOLOGICAL CONTROL OF INTRODUCED INVASIVE PLANTS 4ABLE ILLUSTRATED WITH A DETAILED CASE STUDY OF THE CONTROL OF #HONDRILLA BY RUST FUNGI
0,!.4 $)3%!3%3 !.$ 0/05,!4)/. 2%'5,!4)/. 0ATHOGENS REDUCE THE lTNESS OF INDIVIDUAL PLANTS BY KILLING THEM REDUCING GROWTH IMPEDING COMPETITIVE ABILITY OR BY ROTTING FRUITS OR SEEDS SEE RECENT REVIEW IN 'ILBERT 4HE GREATER PROBABILITY OF PATHOGEN SPREAD BETWEEN CLOSELY SPACED HOST PLANTS MEANS THAT MOST FUNGAL PLANT DISEASES SHOW DENSITY DEPENDENT DEVEL OPMENT )N ADDITION DENSELY SPACED PLANTS MAY CREATE MICROCLIMATES THAT ENCOUR AGE PATHOGEN GROWTH AND HOSTS STRESSED BY COMPETITION MAY BE MORE SUSCEPTIBLE TO DISEASE "URDON AND #HILVERS 'ILBERT 4HE COMBINATION OF STRONG IMPACTS ON INDIVIDUAL HOST PLANTS AND DENSITY DEPENDENT DISEASE DEVELOPMENT SUGGESTS THAT PATHOGENS SHOULD BE POWERFUL REGULATORS OF PLANT POPULATIONS .EVERTHELESS ASIDE FROM EPIDEMICS CAUSED BY INTRODUCED PATHOGENS THERE ARE REMARKABLY FEW EMPIRICAL STUDIES SHOWING THAT PLANT DISEASES ARE RESPONSIBLE FOR REGULATING PLANT POPULATION DYNAMICS IN NATURAL ECOSYSTEMS 'ILBERT )N LARGE PART THIS ABSENCE REmECTS THE DIFlCULTIES OF ISOLATING DISEASE IMPACTS FROM OTHER FACTORS AND THE STRONG FOCUS ON DISEASES WITH ECONOMIC IMPORTANCE "UT PHYSIOLOGICAL OR EVOLUTIONARY RESPONSES BY THE HOST MAY ALSO COUNTERACT THE REGULATORY ACTIONS OF PATHOGENS IN NATURAL ECOSYSTEMS )N PARTICULAR PLANTS THAT SURVIVE AFTER DISEASE HAS KILLED OR STUNTED COMPETING CONSPECIlC NEIGHBORS MAY SHOW A COMPENSATORY RESPONSE THAT OFFSETS NUMERICAL LOSSES FROM DISEASE AT THE POPULATION LEVEL &RIESS AND -AILLET !LEXANDER AND (OLT !LEXANDER AND -IHAIL )N ADDITION MATERNALLY TRANSMITTED INDUCED RESISTANCE CAN GENERATE CROSS GENERATIONAL EFFECTS THAT AMELIORATE THE NUMERICAL IMPACTS OF DISEASE IN SUCCEEDING GENERATIONS !GRAWAL ET AL &INALLY THE GENETICS
0ATHOGENS MAY ACQUIRE INTRODUCED (OST MAY LOSE DEFENSES TO ORIGINAL (OST MAY DEVELOP RESISTANCE TO HOST THROUGH EVOLUTIONARY HOST PATHOGENS AFTER INTRODUCTION INTRODUCED BIOCONTROL AGENT SHIFT 6IRULENCE MAY INCREASE QUICKLY WHEN HOST BECOMES COMMON
2APID EVOLUTIONARY CHANGES
$ENSITY DEPENDENT DISEASE DEVELOPMENT MAY CHANGE IMPACT ON INVADING HOSTS AS INVASION PROCEEDS
.ATURAL HISTORY LIFE HISTORY OF PATHOGEN
0ATHOGENS WITH RESTING STRUCTURES 0ATHOGENS WITH RESTING STRUCTURES OR ALTERNATE LIFE HISTORY STRATEGIES SHOULD SHOW GREATER SUCCESS MOST LIKELY TO ACCOMPANY INTRODUCED PLANTS SUCH PATHOGENS MAY HAVE GREATER VIRULENCE
'ENERALIST PATHOGENS ARE MORE !SSUMES SPECIALIST PATHOGENS PLAY /NLY SPECIALIST PATHOGENS CAN BE LIKELY TO ACQUIRE NEWLY INTRODUCED A UNIQUE ROLE IN REGULATING PLANT UTILIZED AS CONTROL AGENTS HOST SPECIES POPULATIONS
)NTRODUCED BIOCONTROL PATHOGENS MAY FAIL IF POORLY ADAPTED TO LOCAL ENVIRONMENT
(OST RANGE OF PATHOGEN
0LANTS MAY ESCAPE NATURAL ENEMIES IF INTRODUCED INTO AN ENVIRONMENT NOT CONDUCIVE TO DISEASE DEVELOPMENT
,OCAL PATHOGENS ARE ADAPTED TO LOCAL ENVIRONMENT
)NTERACTIONS WITH ENVIRONMENT DISEASE TRIANGLE
4ABLE )MPLICATIONS OF DIFFERENT FEATURES OF PLANT PATHOGEN INTERACTIONS FOR THREE AREAS OF INVASION BIOLOGY THE TWO THEORIES OF BIOTIC RESISTANCE AND ESCAPE FROM NATURAL ENEMIES AND THE lELD OF CLASSICAL BIOLOGICAL CONTROL &EATURES OF PLANT PATHOGEN "IOTIC RESISTANCE %SCAPE FROM NATURAL ENEMIES "IOLOGICAL CONTROL INTERACTIONS )MPACT OF PATHOGEN ON HOST 0RE ADAPTED PATHOGENS IN NEW 0ATHOGENS IN NATIVE RANGE LIMIT 4O BE EFFECTIVE CONTROL AGENTS RANGE ARE HIGHLY VIRULENT ON HOST DENSITY OR DISTRIBUTION PATHOGENS MUST BE IMPORTANT IN NAÕVE HOSTS )NTRODUCED PLANTS LEAVE POPULATION REGULATION IN NATIVE VIRULENT PATHOGENS BEHIND RANGE
0LANT POPULATIONS BY PATHOGENS
'3 'ILBERT AND )- 0ARKER
OF PLANT PATHOGEN INTERACTIONS CAN BE HIGHLY DYNAMIC WITH LARGE CHANGES IN PATHOGEN VIRULENCE OR HOST RESISTANCE EVOLVING IN A FEW GENERATIONS EG "URDON AND 4HOMPSON "ISHOP ET AL 3UCH RAPID EVOLUTIONARY CHANGES ARE EXPECTED TO STRONGLY INmUENCE THE IMPACT OF PATHOGENS ON HOST NUMERICAL DYNAM ICS !LEXANDER ET AL
")/4)# 2%3)34!.#% !.$ %3#!0% &2/- .!452!, %.%-)%3 &OR DISEASE TO DEVELOP VIRULENT PATHOGENS SUSCEPTIBLE HOST PLANTS AND SUITABLE ENVIRONMENTAL CONDITIONS MUST CONVERGE COMMONLY CALLED THE $ISEASE 4RIANGLE #HANGES IN ANY OF THESE COMPONENTS CAN REDUCE OR INCREASE HOW MUCH DISEASES AFFECT PLANT POPULATION DYNAMICS )F PLANTS ARE INTRODUCED TO AN ENVIRONMENT WHERE VIRULENT PATHOGENS ARE NOT PRESENT OR WHERE ENVIRONMENTAL CONDITIONS DO NOT FAVOR DISEASE DEVELOPMENT THE PLANT POPULATION MAY BE RELEASED FROM PREVIOUS REGULATION BY PATHOGENS 3IMILARLY PLANTS INTRODUCED TO A NEW LOCALE WITH NOVEL VIRULENT PATHOGENS OR WHERE ENVIRONMENTAL CONDITIONS FAVOR DISEASE DEVELOPMENT MAY EXPERIENCE UNPRECEDENTED POPULATION REGULATION BY PATHOGENS 3UCH CHANGES IN THE PREVALENCE AND SEVERITY OF DISEASES UNDER DIFFERENT CONDITIONS HAVE LONG BEEN THOUGHT TO PLAY AN IMPORTANT ROLE IN THE PROCESS OF BIOLOGICAL INVASIONS IN TWO HYPOTHETICAL WAYS )N NATURAL HABITATS NATIVE PATHOGENS COLONIZE AND ARE HIGHLY VIRULENT ON NAÕVE INTRODUCED PLANT SPECIES AND PREVENT POPULATION GROWTH "IOTIC 2ESISTANCE 0ATHOGENS WERE IMPORTANT IN REGULATING THE PLANT POPULATION IN ITS NATIVE RANGE BUT ARE NOT IN THE INTRODUCED RANGE %SCAPE FROM .ATURAL %NEMIES "IOTIC RESISTANCE
4HE GREAT MAJORITY OF PLANT INTRODUCTIONS DO NOT RESULT IN INVASIONS -ACK 7ILLIAMSON 2ATHER MANY INTRODUCED SPECIES EITHER FAIL TO THRIVE ALTOGETH ER OR ARE RESTRICTED TO HUMAN CULTIVATION UNABLE TO BUILD SELF SUSTAINING POPULA TIONS IN WILD PLANT COMMUNITIES OR EVEN IN DISTURBED RANGELAND COMMUNITIES 2ESEARCH ATTEMPTING TO IDENTIFY PLANT TRAITS THAT CONFER INVASIVENESS 2EICHARD AND (AMILTON 2EJMÉNEK AND 2ICHARDSON SHOWS THAT OUR PREDICTIVE ABILITY IS IMPERFECT AND IT SEEMS TO BE MORE DIFlCULT TO PREDICT WHICH INTRODUC TIONS WILL FAIL THAN WHICH WILL SUCCEED 2EICHARD AND (AMILTON "IOTIC RESISTANCE IS ONE POSSIBLE EXPLANATION FOR WHY SOME INTRODUCTIONS FAIL WHEN THEY hSHOULDv SUCCEED NATIVE PESTS AND PATHOGENS COLONIZE EXOTIC PLANTS AND ELIMINATE THEM BEFORE THEY CAN ESTABLISH A VIABLE POPULATION %LTON 3IMBERLOFF -ACK 0ATHOGENS WILL CONTRIBUTE TO BIOTIC RESISTANCE ONLY WHEN THREE CONDITIONS ARE MET &IRST THE PATHOGENS INVOLVED MUST NOT BE NARROW HOST SPECIALISTS )N PLANT COMMUNITIES WITH HIGH HOST DIVERSITY AND CORRESPONDING LOW HOST DENSITY GENERALIST PLANT PATHOGENS SHOULD DOMINATE 'ILBERT ET AL 'ILBERT
0LANT POPULATIONS BY PATHOGENS
WHICH COULD CONTRIBUTE TO THE HIGH INVASION RESISTANCE OF HYPER DIVERSE ECO SYSTEMS LIKE TROPICAL RAIN FORESTS &INE 3ECOND BECAUSE DENSITIES OF THE INTRODUCED HOST WILL USUALLY BE LOW IMMEDIATELY FOLLOWING INTRODUCTION PATHO GENS INVOLVED IN BIOTIC RESISTANCE WOULD NOT BE THOSE FOR WHICH TRANSMISSION OR HOST SWITCHING WAS STRONGLY DENSITY DEPENDENT 4HIRD THE PATHOGEN MUST EXACT A HIGH lTNESS COST ON THE HOST #OMBINATIONS OF GENERALIZATION AND HIGH VIRU LENCE ARE NOT UNUSUAL IN PATHOGENS ESPECIALLY FOR SPECIES THAT HAVE LONG RESTING STAGES OR SAPROPHYTIC ABILITY EG 0HYTOPHTHORA CINNAMOMI 6ERTICILLIUM DAHLIAE &USARIUM OXYSPORUM %VEN PATHOGENS THAT CAN ATTACK MANY HOSTS HAVE DIF FERENTIAL IMPACTS ON DIFFERENT HOST SPECIES )F A PATHOGEN HAS A GREATER NEGATIVE EFFECT ON THE COMPETITIVE ABILITY OF THE NON NATIVE HOSTS THAN ON THE NATIVE HOSTS THEN IT WILL CONTRIBUTE TO THE COMPETITIVE EXCLUSION OF THE NON NATIVE +EANE AND #RAWLEY 3INCE EVEN FAIRLY SPECIALIZED PATHOGENS OFTEN INFECT MANY MEMBERS OF THE SAME GENUS OR FAMILY IT IS LIKELY THAT THE NUMBER OF PATHOGENS COMPETENT TO INFECT A NOVEL HOST DEPENDS ON WHETHER IT IS PHYLOGENETICALLY RELATED TO NATIVE SPECIES ALREADY IN THE COMMUNITY 4HEREFORE BIOTIC RESISTANCE SHOULD FAVOR INVASION BY SPECIES WITH NO CLOSE RELATIVES $ESPITE THIS CLEAR PREDICTION AND THE ACCEPTED PRACTICE OF USING PHYLOGENETIC RELATIONSHIPS IN QUARANTINE AND TRADE POLICY TO TARGET RELATIVES OF WEEDY PLANTS OR IDENTIFY POTENTIAL CARRIER HOSTS SURPRISINGLY FEW STUDIES OF INVASION EVEN MENTION THE PHYLOGENETIC STRUCTURE OF THE INVADED COMMUNITIES )N ONE RARE ATTEMPT -ACK FOUND THAT FOR OUT OF REGIONAL mORAS NATURALIZED SPECIES WERE MORE COMMON IN GENERA WITH NO NATIVE CONGENERS THAN THOSE WITH NATIVE CONGENERS CONSISTENT WITH THE IDEA OF BIOTIC RESISTANCE (OWEVER THIS STUDY WAS NOT ABLE TO CONTROL FOR THE EFFECT OF OPPORTUNITY WHETHER PLANTS WITHOUT NATIVE CONGENERS HAVE A HIGHER PROBABILITY OF SUCCESSFUL INVASION GIVEN THEIR PROBABILITY OF INTRODUCTION 5SING A DIFFERENT APPROACH $UNCAN AND 7ILLIAMS COMPILED A LIST OF ALL PLANT SPECIES THAT HAVE EVER BEEN INTRODUCED FOR CULTIVATION IN .EW :EALAND 4HEY FOUND THAT INTRODUCED SPECIES IN GENERA THAT ALREADY HAD RESIDENT NATIVES WERE MORE LIKELY NOT LESS LIKELY TO SUCCESSFULLY NATURALIZE 4HEY SUGGEST THAT SPECIES WITH NATIVE CONGENERS MAY SHARE CHARAC TERISTICS THAT MAKE THEM MORE lT IN THE INTRODUCED RANGE AND THIS FACTOR OVER WHELMS THE POTENTIAL EFFECT OF LOCAL NATURAL ENEMIES 4HERE IS A STRIKING NEED FOR MORE STUDIES TO DETERMINE WHETHER AND WHEN BIOTIC RESISTANCE BY NATIVE PATHOGENS OCCURS "ECAUSE THERE IS LITTLE INFORMATION ON WHERE AND WHEN UNINTENTIONAL SPECIES INTRODUCTIONS FAIL ASSIGNING MECHA NISMS TO THESE FAILURES HAS BEEN NEARLY IMPOSSIBLE (ORTICULTURE FORESTRY AND AGRICULTURE EACH PROVIDE EXAMPLES OF ENDEMIC PATHOGENS THAT HAVE DECIMATED INTRODUCED PLANT SPECIES SO THAT GROWING THESE SPECIES IS NO LONGER ECONOMICALLY VIABLE -ACK #OUTINHO ET AL 7INGlELD ET AL (OWEVER EXTRA P OLATING FROM AGRICULTURAL OR SILVICULTURAL EXAMPLES T O I NVASIVE INTRODUCED SPECIES REQUIRES CAUTION SINCE THE REGENERATION OF HOSTS IS CONTROLLED PREVENTING THE HOST POPULATION FROM EVOLVING RESISTANCE OR TOLERANCE TO THE PATHOGEN !DDITIONALLY SIMPLIlED SYSTEMS IN AGRICULTURE AND FORESTRY MAY SIMPLY LACK MODERATING EFFECTS
'3 'ILBERT AND )- 0ARKER
OF GREATER BIOTIC COMPLEXITY IN LESS MANAGED SYSTEMS EG HYPERPARASITES OF THE PATHOGENS %SCAPE FROM NATURAL ENEMIES
)NTRODUCED PLANTS THAT BECOME INVASIVE WEEDS ARE AMONG OUR MOST CHALLENGING ENVIRONMENTAL PROBLEMS $!NTONIO AND 6ITOUSEK /FlCE OF 4ECHNOLOGY !SSESSMENT 6ITOUSEK ET AL 0ARKER ET AL -ACK ET AL AND ESCAPE FROM NATURAL ENEMIES PROVIDES A MECHANISM TO EXPLAIN THE INCREASED GROWTH AND DENSITY OF INTRODUCED SPECIES $ARWIN #RAWLEY "LOSSEY AND .ÚTZOLD 4ILMAN -ARON AND 6ILA 3IEMANN AND 2OGERS +EANE AND #RAWLEY 4HE h.ATURAL %NEMIES (YPOTHESISv POSITS THAT INTRODUCED SPECIES LEAVE BEHIND THEIR NATURAL ENEMIES HERBIVORES SEED PREDATORS AND PATHOGENS AND ARE THEREBY RELEASED FROM A KEY REGULATING FACTOR LEADING TO A DRAMATIC INCREASE IN PLANT VIGOR POPULATION GROWTH ANDOR COMPETITIVE ABILITY 4HIS IDEA FORMS THE JUSTIlCATION FOR CLASSICAL BIOLOGICAL CONTROL IN WHICH NATURAL ENEMIES ARE BROUGHT FROM THE NATIVE RANGE TO CONTROL WEEDY INVADERS (UFFAKER AND -ESSENGER $E"ACH AND 2OSEN 9ET DESPITE THE IMPORTANCE OF THE .ATURAL %NEMIES (YPOTHESIS RIGOROUS EMPIRICAL TESTS ARE FEW -ARON AND 6ILA ! NUMBER OF STUDIES HAVE TESTED WHETHER INTRODUCED PLANTS TEND TO GROW FASTER OR LARGER AND WHETHER THERE IS EVIDENCE OF REDUCED ALLOCATION TO HERBIVORE DEFENSES IN THE NEW RANGE #RAWLEY "LOSSEY AND .ÚTZOLD 3IEMANN AND 2OGERS BUT SEE 7ILLIS ET AL 4HEBAUD AND 3IMBERLOFF 6ILA ET AL 7HILE SEVERAL OF THESE STUDIES HAVE SUGGESTED ECOLOGICAL RELEASE AND EVOLUTION AWAY FROM DEFENSE TOWARD COMPETITIVE ABILITY THEY LACK DIRECT EVI DENCE OF INVOLVEMENT BY NATURAL ENEMIES "LOSSEY AND .ÚTZOLD 3IEMANN AND 2OGERS /THER STUDIES HAVE TESTED THE .ATURAL %NEMIES (YPOTHESIS BY COMPARING THE IMPACT OF NATURAL ENEMIES ON EXOTIC AND NATIVE SPECIES WITHIN THE INTRODUCED RANGE )N A REVIEW OF STUDIES +EANE AND #RAWLEY FOUND SOME CASES IN WHICH GENERALIST HERBIVORES SHOWED HIGHER IMPACTS ON NATIVE SPECIES THAN NON NATIVES AND OTHERS CHARACTERIZED BY THE REVERSE PATTERN 4HERE HAVE BEEN SURPRISINGLY FEW STUDIES WITH PATHOGENS IN ONE TEST 'OERGEN AND $AEHLER FOUND THAT SMUT FUNGI CAUSED GREATER REPRODUCTIVE LOSS IN A NATIVE GRASS (ETEROPOGON CONTORTUS THAN AN INTRODUCED GRASS 0ENNISETUM SETACEUM %NEMY REMOVAL EXPERIMENTS ARE AN IMPORTANT BUT UNDERUTILIZED TOOL IN COM PARING THE lTNESS EFFECT OF PATHOGENS OR HERBIVORES ON EXOTIC AND NATIVE SPECIES WITHIN THE INTRODUCED RANGE +EANE AND #RAWLEY "LANEY AND +OTANEN USED A FUNGICIDE EXPERIMENT TO REMOVE THE EFFECTS OF SOILBORNE FUNGI AND OOMYCETES ON THE SURVIVAL OF SEEDS OF NATIVE VS INTRODUCED PLANTS IN TWO HABITATS 4HEY FOUND NO SUPPORT FOR A RELEASE FROM FUNGAL PATHOGENS IN THE SEED BANK OF EXOTIC SPECIES COMPARED WITH NATIVE SPECIES -ORE RECENTLY 0ARKER AND 'ILBERT UNPUBLISHED DATA FOUND NO DIFFERENCE IN FREQUENCY OF INFECTION LEAF DAMAGE lTNESS EFFECTS OF FOLIAR AND DAMPING OFF PATHOGENS OR PATHOGEN DIVERSITY BETWEEN
0LANT POPULATIONS BY PATHOGENS
SYMPATRIC SUITES OF NATIVE AND NON NATIVE CLOVERS !LTHOUGH FUNGAL EXCLUSION EXPERIMENTS IN THIS SYSTEM REVEALED SIGNIlCANT IMPACTS OF PATHOGENS THERE WAS NO DIFFERENCE IN THE RESPONSE OF NATIVE AND NON NATIVE SPECIES &INALLY OTHER STUDIES HAVE TAKEN THE APPROACH OF COMPARING DISEASE ON A SINGLE HOST SPECIES IN ITS NATIVE AND INVADED RANGES 7OLFE SURVEYED FOR THE ANTHER SMUT FUNGUS -ICROBOTRYUM VIOLACEUM IN NATIVE POPULATIONS AND INTRODUCED POPULATIONS OF 3ILENE LATIFOLIUM (E FOUND SIGNIlCANTLY MORE POPU LATIONS INFECTED AND AT MUCH HIGHER INFECTION FREQUENCIES IN THE NATIVE RANGE THAN IN THE INTRODUCED RANGE -ITCHELL AND 0OWER USED PUBLISHED RECORDS OF PATHOGEN ASSOCIATIONS WITH PLANT HOSTS IN THEIR NATIVE AND INTRODUCED RANGES 0LANTS WERE INFECTED BY FEWER PATHOGEN SPECIES IN THEIR NATURALIZED RANGE 4HERE WAS ALSO AN INDICATION THAT SPECIES LEAVING BEHIND PROPORTIONALLY MORE NATURAL ENEMIES WERE MORE LIKELY TO BE CATEGORIZED AS NOXIOUS OR INVASIVE SPECIES BY LAND MANAGERS AND PUBLIC AGENCIES 5SING AN EXPERIMENTAL APPROACH "ECKSTEAD AND 0ARKER DIRECTLY MEASURED THE DEMOGRAPHIC EFFECT OF PATHO GENS ON AN INVADER IN THE CONTEXT OF KNOWN INFORMATION FROM THE SPECIES NATIVE RANGE !MMOPHILA ARENARIA IN ITS NATIVE %UROPE IS LIMITED TO AN EARLY SUCCESSIONAL ROLE IN SHIFTING BEACH SANDS BY SOIL BORNE PATHOGENS 6AN DER 0UTTEN ET AL !S AN INVADER ON THE WEST COAST OF THE 53! !MMOPHILA REMAINS DOMINANT FOR LONG PERIODS OF TIME (OWEVER ESCAPE FROM NATURAL ENEMIES DOES NOT EXPLAIN THIS CONTRAST BETWEEN ITS NATIVE AND INVASIVE ECOLOGICAL ROLES "Y REPLICATING EXPERI MENTS DONE IN THE NATIVE RANGE "ECKSTEAD AND 0ARKER FOUND THE NEGATIVE EFFECT OF SOILBORNE PATHOGENS ON EARLY GROWTH IN THE INVADED RANGE WAS AT LEAST AS LARGE OR LARGER THAN THEIR EFFECT IN THE NATIVE RANGE 4O PREDICT WHETHER AN INTRODUCED PLANT IS LIKELY TO BENElT FROM ESCAPING NATURAL ENEMIES WE NEED TO UNDERSTAND THE RELATIVE IMPORTANCE OF HOST SPECIALIST VS HOST GENERALIST PATHOGENS AND PESTS IN THE INVADED HABITAT -ARON AND 6ILA +EANE AND #RAWLEY )F SPECIALIST PATHOGENS PREDOMINATE AND HOST SHIFTS ARE RARE NATIVE PLANTS MAY BE SUPPRESSED MORE THAN COMPETING INVASIVE SPECIES /N THE OTHER HAND IF GENERALIST PATHOGENS DOMINATE IN A SITE AND DO NOT SHOW A PREFERENCE FOR NATIVE HOST SPECIES ONE WOULD NOT EXPECT AN INTRODUCED PLANT TO EXPERIENCE RELEASE 4HEREFORE THE WIDE RANGE OF RESULTS SEEN IN THE ABOVE EMPIRICAL STUDIES MAY BE IN PART EXPLAINED BY THE RELATIVE IMPORTANCE OF SPECIAL IST AND GENERALIST NATURAL ENEMIES ! GREATER UNDERSTANDING OF THE PHYLOGENETIC STRUCTURE OF PATHOGEN HOST RANGES COUPLED WITH ANALYSIS OF THE PHYLOGENETIC STRUCTURE OF NATURAL PLANT COMMUNITIES 7EBB ET AL MAY HELP PREDICT THE RELATIVE IMPORTANCE OF SPECIALIST VS GENERALIST PATHOGENS IN DIFFERENT KINDS OF PLANT COMMUNITIES &OR INSTANCE IN A HIGH DIVERSITY LOWLAND TROPICAL RAINFOREST TREE SPECIES HOST GENERALISTS DOMINATED THE POLYPORE FUNGAL COMMUNITY ALL OF THE MORE COMMON FUNGAL SPECIES WERE FOUND ON MULTIPLE FAMILIES OF HOST TREES 'ILBERT ET AL &ERRER AND 'ILBERT )N CONTRAST IN A NEARBY LOW DIVERSITY MANGROVE FOREST WITH ONLY THREE TREE SPECIES PRESENT EACH FROM A DIFFER ENT FAMILY OF ALL POLYPORE FUNGAL COLLECTIONS BELONGED TO JUST THREE FUNGAL SPECIES AND EACH SPECIES WAS HIGHLY SPECIALIZED ON JUST ONE MANGROVE SPECIES
'3 'ILBERT AND )- 0ARKER
'ILBERT AND 3OUSA 2ESEARCHERS ARE JUST NOW BEGINNING TO ADDRESS THE RANGE OF HOST SPECIALIZATION IN DIFFERENT PLANT COMMUNITIES AND THE WIDE RANGE OF OUTCOMES SUGGESTS THAT MANY MORE STUDIES WILL BE NEEDED BEFORE WE CAN FORMU LATE PREDICTIVE GENERALIZATIONS
).4%.4)/.!,,9 ).42/$5#%$ 0!4(/'%.3 &/2 ")/,/')#!, #/.42/, ! DIRECT APPLICATION OF THE .ATURAL %NEMIES (YPOTHESIS IS DEPLOYING NATURAL ENEMIES FROM THE NATIVE RANGE OF AN INVASIVE PLANT TO CONTROL THE INVADER POPU LATION 3UCH CLASSICAL BIOLOGICAL CONTROL USES PLANTS AND PATHOGENS WITH SHARED EVOLUTIONARY HISTORIES BUT A NEW ENVIRONMENTAL CONTEXT 4HERE ARE SEVERAL WAYS IN WHICH BIOLOGICAL CONTROL INTERACTIONS MAY BE DIFFERENT FROM NATIVE PATHOGENS ATTACKING INTRODUCED HOSTS &IRST UNLIKE NATIVE PATHOGENS WHICH ARE PRESUMABLY ADAPTED TO THE LOCAL CLIMATE THE INTRODUCED BIOLOGICAL CONTROL AGENT EXPERIENCES A NOVEL ENVIRONMENT WHICH COULD HAVE A LARGE IMPACT ON DISEASE DEVELOPMENT #ASE STUDIES OF FAILED BIOLOGICAL CONTROL EFFORTS PROVIDE US WITH MANY EXAMPLES OF THE IMPORTANCE OF THE DISEASE TRIANGLE -ORIN ET AL 3ECOND BOTH THE HOST AND PATHOGEN ARE LIKELY TO BE GENETICALLY DEPAUPERATE (OWEVER THE PATHOGEN WILL HAVE BEEN CHOSEN SPECIlCALLY TO BE VIRULENT ON THE INVASIVE HOST PLACING THE HOST AT A RELATIVE DISADVANTAGE FOR EVOLUTIONARY RESPONSES 4HIRD ONLY FAIRLY HOST SPECIlC PATHOGENS ARE SELECTED FOR BIOLOGICAL CONTROL RELEASES MEANING THAT PATHOGEN NUMERICAL DYNAMICS SHOULD ALWAYS BE CLOSELY LINKED TO INDIVIDUAL HOST DENSITY )N FACT BIOLOGICAL CONTROL RELEASES ARE AN EXCELLENT OPPORTUNITY TO STUDY FACTORS INmUENCING NUMERICAL DYNAMICS .OT ONLY SHOULD THERE BE A TIGHT CONNEC TION BETWEEN PATHOGEN AND HOST DENSITY BUT INITIAL CONDITIONS OF THE INTERACTION ARE WELL KNOWN 4HAT IS THE HOST POPULATION IS ORIGINALLY FREE OF THAT PATHOGEN AND IS USUALLY AT HIGH DENSITY ! SUCCESSFUL EPIDEMIC PROVIDES AN OPPORTUNITY TO QUANTIFY BOTH FREQUENCY DEPENDENCE OF TRANSMISSION OF THE PATHOGEN AND DENSITY DEPENDENCE AS THE HOST DENSITY DECLINES 0REDICTING THE SHORT TERM AND LONG TERM SUCCESS OF PARTICULAR BIOLOGICAL CON TROL INTRODUCTIONS IS A MATTER OF OBVIOUS PRACTICAL IMPORTANCE 4O MAKE SUCH PREDICTIONS WE NEED TO UNDERSTAND HOW THE NUMERICAL DYNAMICS OF A HOST PLANT FOLLOWING INTRODUCTION OF ITS BIOCONTROL AGENT DEPEND ON HOST DENSITY DISEASE INCIDENCE GENETIC VARIATION AND EVOLUTIONARY CHANGES IN VIRULENCE OR RESISTANCE 3URPRISINGLY WHILE THERE ARE SOME CASES FOR WHICH WE HAVE GOOD INFORMATION ON THE DYNAMICS OF HOST NUMBERS AFTER RELEASE OF A CONTROL AGENT EG (ASAN AND !YRES -ORRIS FOR MANY OTHER RELEASES THE DETAILS OF CHANGES ARE NOT WELL DOCUMENTED )N PARTICULAR WE SHOULD ASK I IS CONTROL MORE SUCCESSFUL IN GENETICALLY DEPAUPERATE WEEDS II $O TRANSMISSION RATE AND DEMOGRAPHIC IMPACT OF THE PATHOGEN ATTENUATE AS THE HOST POPULATION DECLINES III $O PATHOGEN AND HOST REACH A STABLE EQUILIBRIUM OR ARE THEY DEPENDENT ON METAPOPULATION DYNAM ICS TO PERSIST IN THE LANDSCAPE $ETAILED INFORMATION ON NUMERICAL DYNAMICS IN BIOLOGICAL CONTROL SYSTEMS IS SCARCE BUT DATA ARE NEARLY NONEXISTENT FOR LONG TERM
0LANT POPULATIONS BY PATHOGENS
GENETIC CHANGES IN THE HOST OR PATHOGEN 4HERE IS GREAT UNTAPPED POTENTIAL FOR BIOLOGICAL CONTROL INTRODUCTIONS TO BE USED TO UNDERSTAND THE FACTORS THAT DRIVE THE ECOLOGICAL END EVOLUTIONARY DYNAMICS OF THE PLANT PATHOGEN INTERACTIONS )N FACT THE ONLY BIOCONTROL STUDY WE FOUND THAT TRACKED CHANGES IN PATHOGEN VIRULENCE OR HOST RESISTANCE FOR A PLANT PATHOGEN SYSTEM WAS FOR THE RUST 0UCCINIA CHONDRILLINA ON #HONDRILLA JUNCEA SEE CASE STUDY BELOW %VOLUTIONARY ECOLOGY OF BIOCONTROL WITH PATHOGENS
4HE EVOLUTIONARY DYNAMICS OF INTERACTIONS BETWEEN WEEDS AND PATHOGEN BIOCON TROL AGENTS HAVE IMPORTANT IMPLICATIONS FOR THE LONG TERM SUCCESS OF BIOLOGICAL CONTROL PROGRAMS 'ENERALLY WE NEED TO KNOW I HAS VIRULENCE OF THE BIOLOGICAL CONTROL PATHOGEN CHANGED OVER TIME AND HAS THIS INCREASED OR DECREASED THE SUCCESS OF CONTROL II (AS THE HOST DEVELOPED RESISTANCE OVER TIME III (AS HOST SPECIlCITY CHANGED OVER TIME 2ECENT ANALYSIS OF EMERGING DISEASES HAS SUGGESTED THAT ECOLOGICAL HOST SHIFTS IE HAVING A PREADAPTED ABILITY TO USE A NEWLY ENCOUN TERED HOST MAY PREDOMINATE AS CAUSES OF NOVEL EPIDEMICS AND THAT HOST SHIFTS MAY ONLY RARELY BE CAUSED BY MUTATIONS THAT ALLOW COLONIZATION OF A NEW HOST 3CHRAG AND 7IENER (OWEVER THE DIFlCULTY OF OBSERVING SUCH GENETIC EVENTS MAY DISTORT OUR PERSPECTIVE 6AN +LINKEN AND %DWARDS SYNTHESIZED INFORMATION ON HOST RANGE FROM BIOLOGICAL CONTROL PROGRAMS USING HERBIVORES 4HEY FOUND THAT HOST SHIFTS WERE MORE QUANTITATIVE THAN QUALITATIVE THAT IS WHILE PREFERENCE AND EFlCIENCY ON NOVEL HOSTS EVOLVED THERE WAS NO EVIDENCE OF EVOLUTIONARY CHANGES IN FUNDAMENTAL HOST RANGE 3UCH AN ANALYSIS SHOULD BE DONE FOR PATHO GENS USED AS BIOLOGICAL CONTROL AGENTS 7HILE PATHOGENS ARE GENERALLY THOUGHT TO OFFER THE OPPORTUNITY FOR HIGH HOST SPECIlCITY SOME HAVE ARGUED THAT HIGH HOST SPECIlCITY MAY BE CORRELATED WITH EVOLUTIONARY LABILITY "ROOKS AND -C,ENNAN 3ECORD AND +AREIVA "ECAUSE THEY ARE UNABLE TO SIMPLY MOVE FROM AN UNACCEPTABLE HOST TO A MORE SUITABLE ONE AS AN ANIMAL MIGHT SPECIALIST PATHOGENS MAY EXPERIENCE EVEN STRONGER SELECTION FOR HOST SHIFTS THAN HERBIVORES 2OY +NOWING THE FREQUENCY OF EVOLUTIONARY HOST SHIFTS IN PATHOGENS AND UNDERSTANDING THE CONDITIONS UNDER WHICH THEY OCCUR ARE CRITICAL TO THE PROCESS OF RISK ASSESSMENT IN BIOLOGICAL CONTROL 3ECORD AND +AREIVA 'ENERAL THEORY OF HOST PATHOGEN INTERACTIONS HAS PLAYED A LARGE ROLE IN THE CHOICE OF BIOLOGICAL CONTROL AGENTS IN THE PAST -C&ADYEN &OR EXAMPLE IT HAS LONG BEEN THOUGHT THAT SEXUALLY REPRODUCING WEEDS WOULD BE HARDER TO CONTROL BECAUSE THEIR HIGHER LEVELS OF GENETIC VARIATION INTERFERE WITH PATHOGEN POPULATION GROWTH "URDON ET AL HOWEVER A MORE RECENT ANALYSIS HAS DISPUTED THIS ASSERTION #HABOUDEZ AND 3HEPPARD 3IMILARLY THE BELIEF THAT PATHOGEN POPULATIONS ARE LOCALLY ADAPTED TO THEIR HOST GENOTYPES HAS HAD A LARGE INmUENCE ON THE PROCESS OF SELECTION OF CONTROL AGENTS WITH GENETIC ANALYSIS PLAYING AN INCREASING ROLE IN THE CAREFUL MATCHING OF AGENT GENOTYPES WITH THE POPULATIONS OF ORIGIN FOR THE WEED EG (OLDEN AND -AHLBERG (OWEVER THE EVIDENCE FOR CLOSE LOCAL ADAPTATION OF PATHOGENS TO THEIR HOST POPULATIONS IS
'3 'ILBERT AND )- 0ARKER
MIXED AND IN FACT RESISTANCE AND GENE FOR GENE VIRULENCE SHOULD mUCTUATE IN AN ASYNCHRONOUS FREQUENCY DEPENDENT WAY REVIEWED IN 0ARKER AND 'ILBERT "IOLOGICAL CONTROL PRACTITIONERS HAVE CLEARLY BASED THEIR INTRODUCTION STRATEGIES ON THEORETICAL CONSIDERATIONS BUT THE SIMPLER RULES ARE NOW COMING UNDER QUESTION -C&ADYEN 4HERE IS A NEED FOR CLEAR PREDICTIONS AND MODERN EMPIRICAL WORK TESTING THOSE PREDICTIONS TO HELP INFORM THE PRACTICE OF BIOLOGICAL CONTROL FOR THE FUTURE !N EVOLUTIONARY ECOLOGY CASE STUDY #HONDRILLA AND 0UCCINIA ON THREE CONTINENTS
.O SYSTEM OF CLASSICAL BIOLOGICAL CONTROL OF A WEED BY A PATHOGEN DEMONSTRATES THE IMPORTANCE OF INTERACTIONS BETWEEN ENVIRONMENT GENETICS AND NUMERICAL DYNAMICS AS WELL AS THAT OF #HONDRILLA JUNCEA RUSH SKELETONWEED !STERACEAE .ATIVE TO %URASIA THIS SPECIES WAS INTRODUCED TO THE EASTERN 5NITED 3TATES IN THE LATE S TO !USTRALIA IN THE EARLY S AND TO THE WESTERN 5NITED STATES IN THE S -C6EAN 0RYOR 3CHIRMAN AND 2OBOCKER 3UPKOFF ET AL #HONDRILLA IS A SIGNIlCANT ECONOMIC PROBLEM IN WHEAT GROWING REGIONS 0ANETTA AND $ODD AND IS ALSO A WIDESPREAD RANGELAND WEED /F THREE BIOCONTROL AGENTS THAT WERE INTRODUCED 0UCCINIA CHONDRILLINA WAS THE MOST EFFECTIVE AT REDUCING PLANT VIGOR 3UPKOFF ET AL AND WITHIN TWO DECADES OF ITS INTRODUCTION INTO !USTRALIA AND #ALIFORNIA #HONDRILLA DENSITIES WERE REDUCED TO THOSE TYPICAL IN ITS NATIVE RANGE 7APSHERE ET AL #ULLEN ET AL 3UPKOFF ET AL 4HE EXTREME HOST SPECIlCITY FOUND IN THE #HONDRILLA0UCCINIA SYSTEM MAKES THIS EXAMPLE PARTICULARLY INTERESTING (ASAN #HONDRILLA IS A TRIPLOID APOMICT AND THUS REPRODUCTION IS CLONAL )N !USTRALIA THREE CLONAL TYPES ARE PRESENT EACH WITH A DIFFERENT LEAF WIDTH 0 CHONDRILLINA CAUSES DISEASE ONLY ON THE NARROW LEAF TYPE 4HE ORIGINAL INFESTATION OF #HONDRILLA WAS PRIMARILY THIS NARROW LEAF TYPE BUT AFTER THE SUCCESSFUL BIOCONTROL OF THAT CLONE THE INTERMEDIATE LEAVED CLONE HAS SPREAD (ANLEY AND 'ROVES .OW THERE IS CONCERTED EFFORT TO INTRODUCE NEW STRAINS OF 0UCCINIA CHONDRILLINA THAT ARE ABLE TO ATTACK AND CONTROL THE OTHER CLONES OF #HONDRILLA (ANLEY AND 'ROVES )N WESTERN .ORTH !MERICA THREE DIFFERENT #HONDRILLA GENOTYPES WERE FOUND DISTINGUISHABLE BY THEIR MULTI LOCUS ISOZYME PHENOTYPES (ASAN ET AL TWO GENOTYPES ARE THOUGHT TO HAVE ORIGINATED IN 9UGOSLAVIA (ASAN AND $ELFOSSE 4HE WESTERN 53 GENOTYPES WERE LARGELY RESISTANT TO THE RUST STRAIN THAT CONTROLLED THE NARROW LEAF #HONDRILLA IN !USTRALIA SO ADDITIONAL RUST ISOLATES WERE EVALUATED FOR USE IN BIOCONTROL 2USTS COLLECTED FROM 9UGOSLAVIA THE PUTATIVE SITE OF ORIGIN OF THE 53 INVADERS SHOWED HIGH VIRULENCE ON SOME OF THE 53 GENO TYPES BUT OTHER PLANTS WERE LITTLE AFFECTED )N ADDITION RUSTS FROM OTHER REGIONS ALSO SHOWED HIGH VIRULENCE 'ENETIC MATCHING OF HOSTS BETWEEN THE NATIVE AND INTRODUCED RANGE MAY YIELD WELL ADAPTED BIOCONTROL PATHOGENS WHEN THE TARGET WEED IS GENETICALLY UNIFORM BUT THIS APPROACH ASSUMES HIGH LOCAL ADAPTATION OF
0LANT POPULATIONS BY PATHOGENS
THE PATHOGEN TO THE HOST !S MENTIONED ABOVE SUCH LOCAL ADAPTATION MAY NOT BE GENERALLY FOUND IN NATURAL POPULATIONS 3EXUAL REPRODUCTION IN BOTH THE HOST AND PATHOGEN PLAY A ROLE IN THIS STORY 4ELIOSPORES OF 0 CHONDRILLINA ONLY GERMINATE AFTER COLD WINTERS !DAMS AND ,INE SO SEXUAL RECOMBINATION OF THE PATHOGEN OCCURS READILY ONLY IN COLDER REGIONS SUCH AS PARTS OF EASTERN CONTINENTAL %UROPE )N THESE AREAS OF THE NATIVE RANGE #HONDRILLA ALSO SHOWS HIGHER CLONAL DIVERSITY AND POSSIBLY DIPLOID SEXUAL POPULATIONS #HABOUDEZ AND 3HEPPARD )NTERESTINGLY POPULATIONS OF #HONDRILLA WITH HIGH VS LOW CLONAL DIVERSITY IN THE NATIVE RANGE APPEAR TO SUFFER SIMILAR DEGREES OF RUST INFECTION #HABOUDEZ AND 3HEPPARD )N NORTHERN .ORTH !MERICA WHERE COLD WINTERS ALLOW FOR SEXUAL RECOMBINATION OF THE PATHO GEN THE EVOLUTIONARY DYNAMICS OF THE HOST PATHOGEN INTERACTION ARE POTENTIALLY MORE COMPLEX (ASAN ET AL )N !USTRALIA THEY ARE PARTICULARLY CONCERNED ABOUT THE POSSIBILITY OF INTRODUCTION OF NEW SEXUAL TYPES OF #HONDRILLA WHICH COULD RESULT IN A SITUATION WHERE THE HOST REPRODUCES SEXUALLY BUT THE PATHOGEN CAN NOT #HABOUDEZ AND 3HEPPARD 4HIS EXAMPLE SHOWS THE IMPORTANCE OF THE hDISEASE TRIANGLEv INTERACTION BETWEEN HOST PATHOGEN AND ENVIRONMENT IN THE DYNAMICS OF PLANT PATHOGEN INTERACTIONS 4HE CASE OF #HONDRILLA 0UCCINIA CHONDRILLINA IS ONE OF THE FEW FOR WHICH WE HAVE SUCH DETAILED INFORMATION ABOUT THE HOSTS AND THE PATHOGENS GENETIC MAKEUP AND MORE IMPORTANTLY ABOUT HOW THE INTERACTION HAS PLAYED OUT IN A NUMBER OF DIFFERENT REGIONS 0ATHOGEN BIOLOGICAL CONTROL CASES OFFER THE POTENTIAL TO LEARN A GREAT DEAL ABOUT THE ROLES OF GENETICS NUMERICAL DYNAMICS EVOLUTIONARY DYNAMICS AND ENVIRONMENTAL FACTORS IN DETERMINING THE LONG TERM OUTCOMES OF HOST PATHOGEN INTERACTIONS
#/.#,53)/.3 &ROM THE STUDIES DESCRIBED ABOVE IT APPEARS THAT PATHOGENS ARE SOMETIMES IMPOR TANT IN THE REGULATION OF NATURAL PLANT POPULATIONS MAY CONSTRAIN POPULATIONS INTRODUCED TO NEW REGIONS AND MAY BY THEIR ABSENCE RELEASE INTRODUCED PLANTS FROM AN IMPORTANT SOURCE OF REGULATION 7E SUGGEST TWO KEY DIRECTIONS THAT WOULD MOST ADVANCE OUR UNDERSTANDING OF THE IMPORTANCE OF PATHOGENS IN PLANT POPULA TION REGULATION AN INTEGRATION OF NUMERICAL AND EVOLUTIONARY DYNAMICS FOR BOTH THE PATHOGENS AND PLANTS AND A GREATER BREADTH OF STUDIES TO INCLUDE MORE PLANT PATHOGEN SYSTEMS "IOLOGICAL CONTROL OF INVASIVE WEEDS OFFERS EXCITING OPPORTUNITIES TO EVALUATE THE IMPORTANCE OF PATHOGENS IN NUMERICAL REGULATION OF PLANT POPULATIONS AND AT THE SAME TIME TO FOLLOW GENETIC CHANGES IN PLANT AND PATHOGEN POPULATIONS #AREFUL MONITORING FOR CHANGES IN HOST AND PATHOGEN GENOTYPES ALONG WITH NUMERI CAL DYNAMICS SHOULD BE INTEGRAL TO ANY INTRODUCTION OF PATHOGENS FOR BIOLOGICAL CONTROL OF INVASIVE WEEDS %QUALLY IMPORTANT WE MUST MOVE BEYOND SPINNING NARRATIVES AND MAKING GENERAL PREDICTIONS FROM A HANDFUL OF EXAMPLES 7E HAVE
'3 'ILBERT AND )- 0ARKER
A GOOD IDEA OF THE ROLE PATHOGENS SHOULD PLAY IN PLANT POPULATION REGULATION AND BIOLOGICAL INVASIONS 4ABLE WE NOW NEED TO COLLECT DATA FROM A DIVERSITY OF SYS TEMS TO EVALUATE OUR PREDICTIONS (OW OFTEN AND UNDER WHAT CONDITIONS ARE PLANT PATHOGENS SIGNIlCANT FORCES IN REGULATING WILD PLANT POPULATIONS IN THEIR NATIVE RANGES (OW OFTEN DO INTRODUCED PLANTS FAIL TO ESTABLISH BECAUSE THEY ARE ATTACKED BY LOCAL PATHOGENS (OW OFTEN IS ESCAPE FROM PATHOGENS A KEY TO DETERMIN ING WHETHER AN INTRODUCED PLANT INVADES NATURAL HABITATS 4HROUGH PATHOGEN EXCLUSION AND ADDITION EXPERIMENTS COMMON GARDENS PHYLOGENETIC ANALYSIS OF HOST RANGES ANALYSIS OF RAPID EVOLUTIONARY CHANGES IN PLANT PATHOGEN INTERAC TIONS AND CAREFUL CREATIVE NATURAL HISTORY OF PLANT DISEASES WE WILL ILLUMINATE THE ROLE OF PLANT PATHOGENS IN BIOLOGICAL INVASIONS
!#+./7,%$'-%.43 7E THANK " !YALA + $LUGOSCH * (AGEN # (AYS " (ARDCASTLE * (EIN 2 (UFFT 3 ,AMBRECHT 3 ,ANGRIDGE - ,OS (UERTOS $ 0LANTE 7 3ATTERTHWAITE 9 3PRINGER AND TWO ANONYMOUS REVIEWERS FOR HELPFUL DISCUSSIONS AND CRITICAL COMMENTS ON DRAFTS OF THIS MANUSCRIPT 0REPARATION WAS SUPPORTED IN PART BY .3& GRANTS $%" TO )-0 $%" AND $%" TO '3' AND 53$! .2) TO )-0
2%&%2%.#%3 !DAMS % " AND 2 & ,INE "IOLOGY OF 0UCCINIA CHONDRILLINA IN 7ASHINGTON 0HYTOPATHOLOGY !GRAWAL ! # ,AFORSCH AND 2 4OLLRIAN 4RANSGENERATIONAL INDUCTION OF DEFENCES IN ANIMALS AND PLANTS .ATURE !LEXANDER ( - AND 2 $ (OLT 4HE INTERACTION BETWEEN PLANT COMPETITION AND DISEASE 0ERSPECTIVES IN 0LANT %COLOGY %VOLUTION AND 3YSTEMATICS !LEXANDER ( - AND * $ -IHAIL 3EEDLING DISEASE IN AN ANNUAL LEGUME CONSE QUENCES FOR SEEDLING MORTALITY PLANT SIZE AND POPULATION SEED PRODUCTION /ECOLOGIA !LEXANDER ( - 0 ( 4HRALL * !NTONOVICS ! - *AROSZ AND 0 6 /UDEMANS 0OPULATIONS DYNAMICS AND GENETICS OF PLANT DISEASE ! CASE STUDY OF ANTHER SMUT DIS EASE %COLOGY !NAGNOSTAKIS 3 , #HESTNUT BLIGHT THE CLASSICAL PROBLEM OF AN INTRODUCED PATHOGEN -YCOLOGIA "ECKSTEAD * AND ) - 0ARKER )NVASIVENESS OF !MMOPHILA ARENARIA 2ELEASE FROM SOIL BORNE PATHOGENS %COLOGY "ISHOP * ' ! - $EAN AND 4 -ITCHELL /LDS 2APID EVOLUTION IN PLANT CHITINASES MOLECULAR TARGETS OF SELECTION IN PLANT PATHOGEN COEVOLUTION 0ROC .ATL !CAD 3CI 53!
0LANT POPULATIONS BY PATHOGENS
"LANEY # 3 AND 0 - +OTANEN %FFECTS OF FUNGAL PATHOGENS ON SEEDS OF NATIVE AND EXOTIC PLANTS ! TEST USING CONGENERIC PAIRS * !PPL %COL "LOSSEY " AND 2 .ÚTZOLD %VOLUTION OF INCREASED COMPETITION ABILITY IN INVASIVE NONINDIGENOUS PLANTS A HYPOTHESIS *OURNAL OF %COLOGY "ROOKS $ 2 AND $ ! -C,ENNAN 0ARASCRIPT PARASITES AND THE LANGUAGE OF EVOLU TION 3MITHSONIAN )NSTITUTION 0RESS 7ASHINGTON "URDON * * $ISEASES AND 0LANT 0OPULATION "IOLOGY #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE "URDON * * AND ' ! #HILVERS (OST DENSITY AS A FACTOR IN PLANT DISEASE ECOLOGY !NNUAL 2EVIEW OF 0HYTOPATHOLOGY "URDON * * 2 ( 'ROVES AND * - #ULLEN 4HE IMPACT OF BIOLOGICAL CONTROL ON THE DISTRIBUTION AND ABUNDANCE OF #HONDRILLA JUNCEA IN SOUTH EASTERN !USTRALIA *OURNAL OF !PPLIED %COLOGY "URDON * * AND * . 4HOMPSON #HANGED PATTERNS OF RESISTANCE IN A POPULATION OF ,INUM MARGINALE ATTACKED BY THE RUST PATHOGEN -ELAMPSORA LINI *OURNAL OF %COLOGY #HABOUDEZ 0 AND ! 7 3HEPPARD !RE PARTICULAR WEEDS MORE AMENABLE TO BIOLOGI CAL CONTROL A RE ANALYSIS OF MODE OF REPRODUCTION AND LIFE HISTORY 0AGES IN % 3 $ELFOSSE AND 2 2 3COTT EDITORS "IOLOGICAL #ONTROL OF 7EEDS 0ROC 6)))TH )NT 3YMP "IOL #ONTR 7EEDS #3)2/ 0UBLICATIONS -ELBOURNE !USTRALIA #HARUDATTAN 2 AND ! $INOOR "IOLOGICAL CONTROL OF WEEDS USING PLANT PATHOGENS !CCOMPLISHMENTS AND LIMITATIONS #ROP 0ROTECTION #OUTINHO 4 ! - * 7INGlELD ! # !LFENAS AND 0 7 #ROUS %UCALYPTUS RUST A DISEASE WITH THE POTENTIAL FOR SERIOUS INTERNATIONAL IMPLICATIONS 0LANT $ISEASE #RAWLEY - * 7HAT -AKES A #OMMUNITY )NVASIBLE 0AGES IN ! * 'RAY - * #RAWLEY AND 0 * %DWARDS EDITOR "RITISH %COLOGICAL 3OCIETY 3YMPOSIUM 6OL #OLONIZATION 3UCCESSION AND 3TABILITY "LACKWELL 3CIENTIlC 0UBLICATIONS /XFORD %NGLAND #ULLEN * - 2 ( 'ROVES AND * & !LEX 4HE INmUENCE OF !CERIA CHONDRILLAE ON THE GROWTH AND REPRODUCTIVE CAPACITY OF #HONDRILLA JUNCEA *OURNAL OF !PPLIED %COLOGY $!NTONIO # - AND 0 - 6ITOUSEK "IOLOGICAL INVASIONS BY EXOTIC GRASSES THE GRASSlRE CYCLE AND GLOBAL CHANGE !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS $ARWIN # /N THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION OR 4HE PRESERVA TION OF FAVOURED RACES IN THE STRUGGLE FOR LIFE * -URRAY ,ONDON $AUGHTREY - , # 2 (IBBEN + / "RITTON - 4 7INDHAM AND 3 # 2EDLIN $OGWOOD !NTHRACNOSE UNDERSTANDING A DISEASE NEW TO .ORTH !MERICA 0LANT $ISEASE $E"ACH 0 AND $ 2OSEN "IOLOGICAL CONTROL BY NATURAL ENEMIES #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE $INOOR ! AND . %SHED 4HE ROLE AND IMPORTANCE OF PATHOGENS IN NATURAL PLANT COMMUNITIES !NNUAL 2EVIEW OF 0HYTOPATHOLOGY
'3 'ILBERT AND )- 0ARKER
$ONALDSON $ 4 +IELY AND ! 'RUBE 0ESTICIDES )NDUSTRY 3ALES AND 5SAGE AND -ARKET %STIMATES /FlCE OF 0ESTICE 0ROGRAMS 5 3 %NVIRONMENTAL 0ROTECTION !GENCY 7ASHINGTON $ # $UNCAN 2 0 AND 0 ! 7ILLIAMS $ARWINS NATURALIZATION HYPOTHESIS CHALLENGED .ATURE %LTON # 3 4HE %COLOGY OF )NVASIONS BY !NIMALS AND 0LANTS -ETHUEN ,ONDON &ERRER ! AND ' 3 'ILBERT %FFECT OF TREE HOST SPECIES ON FUNGAL COMMUNITY COMPOSI TION IN A TROPICAL RAIN FOREST IN PANAMA $IVERSITY AND $ISTRIBUTIONS &INE 0 6 ! 4HE INVASIBILITY OF TROPICAL FORESTS BY EXOTIC PLANTS *OURNAL OF 4ROPICAL %COLOGY &RIESS . AND * -AILLET )NmUENCE OF CUCUMBER MOSAIC VIRUS INFECTION ON THE INTRA SPECIlC COMPETITIV ABILITY AND lTNESS OF PURSLANE 0ORTULACA OLERACEA .EW 0HYTOLOGIST &RY 7 % AND 3 " 'OODWIN 2ESURGENCE OF THE )RISH POTATO FAMINE FUNGUS AFTER YEARS THE LATE BLIGHT FUNGUS IS AGAIN MENACING FARMERS "IOSCIENCE 'ILBERT ' 3 %VOLUTIONARY ECOLOGY OF PLANT DISEASES IN NATURAL ECOSYSTEMS !NNUAL 2EVIEW OF 0HYTOPATHOLOGY 'ILBERT ' 3 4HE DIMENSIONS OF PLANT DISEASE IN TROPICAL FORESTS 0AGES IN $ 2 & 0 "URSLEM - ! 0IINARD AND 3 (ARTLEY EDITORS "IOTIC )NTERACTIONS IN THE 4ROPICS #AMBRIDGE 5NIV 0RESS #AMBRIDGE 'ILBERT ' 3 ! &ERRER AND * #ARRANZA 0OLYPORE FUNGAL DIVERSITY AND HOST DENSITY IN A MOIST TROPICAL FOREST "IODIVERSITY AND #ONSERVATION 'ILBERT ' 3 AND 7 0 3OUSA (OST SPECIALIZATION AMONG WOOD DECAY POLYPORE FUNGI IN A #ARIBBEAN MANGROVE FOREST "IOTROPICA 'ILLETT * " 0EST PRESSURE AN UNDERESTIMATED FACTOR IN EVOLUTION 3YSTEMATICS !SSOCIATION 0UBLICATION .UMBER 'OERGEN % AND # $AEHLER )NmORESCENCE DAMAGE BY INSECTS AND FUNGI IN NATIVE PILI GRASS (ETEROPOGON CONTORTUS VERSUS ALIEN FOUNTAIN GRASS 0ENNISETUM SETACEUM IN (AWAII 0ACIlC 3CIENCE 'OODELL + ) - 0ARKER AND ' 3 'ILBERT "IOLOGICAL IMPACTS OF SPECIES INVASIONS )MPLICATIONS FOR POLICY MAKERS 0AGES IN * #ASWELL EDITOR )NCORPORATING "IOLOGICAL .ATURAL AND 3OCIAL 3CIENCES IN 3ANITARY AND 0HYTOSANITARY 3TANDARDS IN )NTERNATIONAL 4RADE .ATIONAL !CADEMY 0RESS 7ASHINGTON $ # 'ORDON 4 2 ! * 3TORER AND $ , 7OOD 4HE 0ITCH #ANKER EPIDEMIC IN #ALIFORNIA 0LANT $ISEASE (ANLEY - % AND 2 ( 'ROVES %FFECT OF THE RUST FUNGUS 0UCCINIA CHONDRILLINA 45 ON PLANT SIZE AND PLANT SIZE VARIABILITY IN #HONDRILLA JUNCEA 7EED 2ESEARCH (ASAN 3 3PECIlCITY AND HOST SPECIALIZATION OF 0UCCINIA CHONDRILLINA !NNALS OF !PPLIED "IOLOGY (ASAN 3 AND 0 ' !YRES 4ANSLEY 2EVIEW .O 4HE CONTROL OF WEEDS THROUGH &UNGI 0RINCIPLES AND PROSPECTS .EW 0HYTOLOGIST (ASAN 3 0 #HABOUDEZ AND # %SPIAU )SOZYME PATTERNS AND SUSCEPTIBILITY OF .ORTH !MERICAN FORMS OF #HONDRILLA JUNCEA TO %UROPEAN STRAINS OF THE RUST FUNGUS
0LANT POPULATIONS BY PATHOGENS
0UCCINIA CHONDRILLINA 0AGES IN % 3 $ELFOSSE AND 2 2 3COTT EDITORS "IOLOGICAL CONTROL OF WEEDS #3)2/ 0UBLICATIONS %AST -ELBOURNE 6ICTORIA !USTRALIA (ASAN 3 AND % 3 $ELFOSSE 3USCEPTIBILITY OF THE !USTRALIAN NATIVE (ELIOTROPIUM CRISPATUM TO THE RUST FUNGUS 5ROMYCES HELIOTROPII INTRODUCED TO CONTROL COMMON HELIO TROPE (ELIOTROPIUM EUROPAEUM "IOCONTROL 3CIENCE AND 4ECHNOLOGY (OLDEN ! . ' AND 0 ' -AHLBERG 2USTS FOR THE BIOLOGICAL CONTROL OF LEAFY SPURGE %UPHORBIA ESULA IN .ORTH !MERICA 0AGES IN % 3 $ELFOSSE AND 2 2 3COTT EDITORS "IOLOGICAL CONTROL OF WEEDS #3)2/ 0UBLICATIONS %AST -ELBOURNE 6ICTORIA !USTRALIA (UFFAKER # " AND 0 3 -ESSENGER EDITORS 4HEORY AND PRACTICE OF BIOLOGICAL CON
TROL !CADEMIC 0RESS .EW 9ORK *AROSZ ! - AND ! , $AVELOS %FFECTS OF DISEASE IN WILD PLANT POPULATIONS AND THE EVOLUTION OF PATHOGEN AGGRESSIVENESS .EW 0HYTOLOGIST +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY AND %VOLUTION -ACK 2 . 5NDERSTANDING THE PROCESSES OF WEED INVASIONS THE INmUENCE OF ENVIRONMENTAL STOCHASTICITY IN # ( 3TIRTON EDITOR 7EEDS IN A #HANGING 7ORLD "RITISH #ROP 0ROTECTION #OUNCIL "RIGHTON 5+ -ACK 2 . "IOTIC BARRIERS TO PLANT NATURALIZATION 0AGES IN 6 # -ORAN AND * ( (OFFMANN EDITORS 0ROCEEDINGS OF THE )8 )NTERNATIONAL 3YMPOSIUM ON "IOLOGICAL #ONTROL OF 7EEDS 5NIVERSITY OF #APE 4OWN 3TELLENBOSCH 3OUTH !FRICA -ACK 2 . $ 3IMBERLOFF 7 - ,ONSDALE ( %VANS - #LOUT AND & ! "AZZAZ "IOTIC INVASIONS #AUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COLOGICAL !PPLICATIONS -ARON * , AND - 6ILA 7HEN DO HERBIVORES AFFECT PLANT INVASION %VIDENCE FOR THE NATURAL ENEMIES AND BIOTIC RESISTANCE HYPOTHESES /IKOS -C$ONALD ' ) AND 2 * (OFF "LISTER RUST AN INTRODUCED PLAGUE 0AGES IN $ & 4OMBACK 3 & !RNO AND 2 % +EANE EDITORS 7HITEBARK 0INE #OMMUNITIES %COLOGY AND 2ESTORATION )SLAND 0RESS 7ASHINGTON $# -C&ADYEN 2 % # "IOLOGICAL CONTROL OF WEEDS !NNUAL 2EVIEW OF %NTOMOLOGY -C6EAN $ . %COLOGY OF #HONDRILLA JUNCEA , IN SOUTHEASTERN !USTRALIA *OURNAL OF %COLOGY -ITCHELL # % AND ! ' 0OWER 2ELEASE OF INVASIVE PLANTS FROM FUNGAL AND VIRAL PATHOGENS .ATURE -ORIN , ! "! AND 3 (% 2UST EPIDEMICS CLIMATE AND CONTROL OF 8ANTHIUM OCCIDEN TALE 0AGES IN 6 # -ORAN AND * ( (OFFMANN EDITORS 0ROC TH )NT 3YMP "IOL #ONTROL 7EEDS 5NIV #APE 4OWN 0RESS 3TELLENBOSCH -ORRIS - * )MPACT OF THE GALL FORMING RUST FUNGUS 5ROMYCLADIUM TEPPERIANUM ON THE INVASIVE TREE !CACIA SALIGNA IN 3OUTH !FRICA "IOLOGICAL #ONTROL /FlCE OF 4ECHNOLOGY !SSESSMENT (ARMFUL .ON )NDIGENOUS 3PECIES IN THE 5NITED 3TATES /4! & 5 3 #ONGRESS 0ACKER ! AND + #LAY 3OIL PATHOGENS AND SPATIAL PATTERNS OF SEEDLING MORTALITY IN A TEMPERATE TREE .ATURE
'3 'ILBERT AND )- 0ARKER
0ANETTA & $ AND * $ODD #HONDRILLA JUNCEA 0AGES IN 2 ( 'ROVES 2 # ( 3HEPHERD AND 2 ' 2ICHARDSON EDITORS 4HE "IOLOGY OF !USTRALIAN 7EEDS 6OL 2ICHARDSON -ELBOURNE !USTRALIA 0ARKER ) - AND ' 3 'ILBERT 4HE EVOLUTIONARY ECOLOGY OF NOVEL PLANT PATHOGEN INTERACTIONS !NNUAL 2EVIEW OF %COLOGY %VOLUTION AND 3YSTEMATICS 0ARKER ) - $ 3IMBERLOFF 7 - ,ONSDALE + 'OODELL - 7ONHAM 0 - +AREIVA - ( 7ILLIAMSON " 6ON (OLLE 0 " -OYLE * % "YERS AND , 'OLDWASSER )MPACT 4OWARD A FRAMEWORK FOR UNDERSTANDING THE ECOLOGICAL EFFECTS OF INVADERS "IOLOGICAL )NVASIONS 0RYOR - 2 3KELETONWEED CONTROL 0AGES IN TH !NNUAL #ALIFORNIA 7EED #ONFERENCE #ALIFORNIA 7EED #ONFERENCE 3ACRAMENTO #ALIFORNIA 2EICHARD 3 ( AND + (AMILTON 0REDICTING INVASIONS OF WOODY PLANTS INTRODUCED INTO .ORTH !MERICA #ONSERVATION "IOLOGY 2EJMÉNEK - AND $ - 2ICHARDSON 7HAT ATTRIBUTES MAKE SOME PLANT SPECIES MORE INVASIVE %COLOGY 2IZZO $ - AND - 'ARBELOTTO 3UDDEN OAK DEATH ENDANGERING #ALIFORNIA AND /REGON FOREST ECOSYSTEMS &RONTIERS IN %COLOGY AND THE %NVIRONMENT 2OY " ! 0ATTERNS OF ASSOCIATION BETWEEN CRUCIFERS AND THEIR mOWER MIMIC PATHO GENS (OST JUMPS ARE MORE COMMON THAN COEVOLUTION OR COSPECIATION %VOLUTION 3CHIRMAN 2 AND 7 # 2OBOCKER 2USH SKELETONWEED –THREAT TO DRYLAND AGRICUL TURE 7EEDS 3CHRAG 3 * AND 0 7IENER %MERGING INFECTIOUS DISEASE WHAT ARE THE RELATIVE ROLES OF ECOLOGY AND EVOLUTION 4RENDS IN %COLOGY %VOLUTION 3ECORD $ AND 0 +AREIVA 0ERILS AND PITFALLS IN THE HOST SPECIlCITY PARADIGM "IOSCIENCE 3IEMANN % AND 7 % 2OGERS 'ENETIC DIFFERENCES IN GROWTH OF AN INVASIVE TREE SPECIES %COLOGY ,ETTERS 3IMBERLOFF $ )NTRODUCED INSECTS A BIOGEOGRAPHIC AND SYSTEMATIC PERSPECTIVE 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICAN AND (AWAII 3PRINGER 6ERLAG .EW 9ORK 3UPKOFF $ - $ " *OLEY AND * * -AROIS %FFECT OF INTRODUCED BIOLOGICAL CONTROL ORGANISMS ON THE DENSITY OF #HONDRILLA JUNCEA IN #ALIFORNIA 53! *OURNAL OF !PPLIED %COLOGY 4HEBAUD # AND $ 3IMBERLOFF !RE PLANTS REALLY LARGER IN THEIR INTRODUCED RANGES !MERICAN .ATURALIST 4ILMAN $ 4HE ECOLOGICAL CONSEQUENCES OF CHANGES IN BIODIVERSITY A SEARCH FOR GENERAL PRINCIPLES %COLOGY 6AN DER 0UTTEN 7 ( # 6AN $IJK AND " ! - 0ETERS 0LANT SPECIlC SOIL BORNE DISEASES CONTRIBUTE TO SUCCESSION IN FOREDUNE VEGETATION .ATURE VAN +LINKEN 2 $ AND / 2 %DWARDS )S HOST SPECIlCITY OF WEED BIOLOGICAL CONTROL AGENTS LIKELY TO EVOLVE RAPIDLY FOLLOWING ESTABLISHMENT %COLOGY ,ETTERS 6ILA - ! 'OMEZ AND * , -ARON !RE ALIEN PLANTS MORE COMPETITIVE THAN THEIR NATIVE CONSPECIlCS ! TEST USING (YPERICUM PERFORATUM , /ECOLOGIA
0LANT POPULATIONS BY PATHOGENS
6ITOUSEK 0 - # - $!NTONIO , , ,OOPE AND 2 7ESTBROOKS "IOLOGICAL INVA SIONS AS GLOBAL ENVIRONMENTAL CHANGE !MERICAN 3CIENTIST 7APSHERE ! * 3 (ASAN 7 + 7AHBA AND , #ARESCHE 4HE ECOLOGY OF #HONDRILLA JUNCEA IN THE WESTERN -EDITERRANEAN *OURNAL OF !PPLIED %COLOGY 7EBB # / $ $ !CKERLY - ! -C0EEK AND - * $ONOGHUE 0HYLOGENIES AND COMMUNITY ECOLOGY !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS 7ESTE ' AND ' # -ARKS 4HE BIOLOGY OF 0HYTOPHTHORA CINNAMOMI IN !USTRALASIAN FORESTS !NNUAL 2EVIEW OF 0HYTOPATHOLOGY 7ILLIAMSON - ( "IOLOGICAL )NVASIONS #HAPMAN (ALL .EW 9ORK 7ILLIS ! * * -EMMOTT AND 2 ) &ORRESTER )S THERE EVIDENCE FOR THE POST INVASION EVOLUTION OF INCREASED SIZE AMONG INVASIVE PLANT SPECIES %COLOGY ,ETTERS 7INGlELD - * " 3LIPPERS * 2OUX AND " $ 7INGlELD 7ORLDWIDE MOVEMENT OF EXOTIC FOREST FUNGI ESPECIALLY IN THE TROPICS AND THE SOUTHERN HEMISPHERE "IOSCIENCE 7OLFE , - 7HY ALIEN INVADERS SUCCEED 3UPPORT FOR THE ESCAPE FROM ENEMY HYPOTHESIS !MERICAN .ATURALIST 7RIGHT 3 * 0LANT DIVERSITY IN TROPICAL FORESTS A REVIEW OF MECHANISMS OF SPECIES COEXISTENCE /ECOLOGIA
#HAPTER FOURTEEN
%XPLORING THE RELATIONSHIP BETWEEN NICHE BREADTH AND INVASION SUCCESS $ 0 6ÉZQUEZ
).42/$5#4)/. 4HE ULTIMATE GOAL OF INVASIONS BIOLOGY SHOULD BE TO GENERATE A BODY OF GENERAL PREDICTIVE THEORY )DEALLY SUCH THEORY WOULD HELP DETERMINE WHETHER A SPECIES WITH A PARTICULAR SET OF TRAITS WILL BE ABLE TO INVADE A GIVEN SYSTEM )N ITS ALMOST lFTY YEARS THE DISCIPLINE HAS SEEN MANY ATTEMPTS TO PROVIDE SUCH PREDICTABILITY THROUGH A FOCUS ON THE TRAITS OF THE POTENTIAL INVADERS AND THOSE OF THE INVADED COMMUNITY 2EGRETTABLY MOST ATTEMPTS HAVE BEEN SO FAR UNSUCCESSFUL /NE ATTEMPT AT GENERALIZATION THAT HAS BEEN OFTEN DISCUSSED IN THE LITERATURE IS THE IDEA THAT NICHE BREADTH IS POSITIVELY CORRELATED WITH INVASION SUCCESS SO THAT SPECIES WITH BROAD NICHES hGENERALISTSv ARE MORE LIKELY TO INVADE THAN SPE CIES WITH NARROWER NICHES hSPECIALISTSv BECAUSE THEY ARE MORE LIKELY TO lND THE NECESSARY RESOURCES OR ENVIRONMENTAL CONDITIONS THROUGHOUT THIS PAPER ) WILL REFER TO THIS NOTION AS THE hNICHE BREADTHnINVASION SUCCESS HYPOTHESISv !S WITH MANY OTHER IDEAS IN ECOLOGY IT IS DIFlCULT TO TRACK THE HISTORICAL DEVELOPMENT OF THIS HYPOTHESIS 0ROBABLY ONE OF THE lRST TO INCLUDE SOME MEASURE OF NICHE BREADTH IN THINKING ABOUT INVASION SUCCESS WAS ( ' "AKER "AKER DElNED THE TRAITS OF WHAT HE CALLED THE hIDEAL WEEDv SPECIES PRONE TO BECOME -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
$0 6ÉZQUEZ
WEEDY AND INVADE DISTURBED HABITATS !MONG THESE TRAITS THREE WERE RELATED TO NICHE BREADTH NAMELY I THAT THE SPECIES CAN PRODUCE SEEDS IN A WIDE RANGE OF ENVIRONMENTAL CIRCUMSTANCES AND HAS HIGH TOLERANCE OF AND OFTEN PLASTICITY IN FACE OF CLIMATIC AND ENVIRONMENTAL VARIATION II THAT THE SPECIES HAS NO SPECIAL ENVIRONMENTAL REQUIREMENTS FOR GERMINATION IE WIDE ENVIRONMENTAL NICHE AND III THAT WHEN CROSS POLLINATED POLLINATION CAN BE ACHIEVED BY A NONSPECIAL IZED mOWER VISITOR OR BY WIND IE WIDE POLLINATION NICHE NOTE HOWEVER THAT IT IS ASSUMING WIDE NICHE BREADTH OF POLLINATORS NOT OF THE PLANT WHICH BRINGS UP THE ISSUE OF ASYMMETRIC SPECIALIZATION DISCUSSED BELOW -ORE RECENTLY 2EJMÉNEK PROPOSED IDEAS SIMILAR TO THOSE OF "AKERS IN THE BROADER CONTEXT OF PLANT INVASIONS IN GENERAL (E DESCRIBED WHAT HE THINKS ARE TEN MAJOR PREDICTORS OF PLANT INVASIVENESS THREE OF WHICH ARE RELATED TO NICHE BREADTH I hlTNESS HOMEOSTASIS v THE ABILITY OF AN INDIVIDUAL OR POPULATION TO MAINTAIN RELATIVELY CONSTANT lTNESS OVER A RANGE OF ENVIRONMENTS lTNESS HOMEO STASIS WILL DEPEND ON PHENOTYPIC PLASTICITY HOMEOSTASIS AT THE INDIVIDUAL LEVEL AND POPULATION GENETIC POLYMORPHISM HOMEOSTASIS AT THE POPULATION LEVEL II SIZE OF hPRIMARYv NATIVE GEOGRAPHICAL RANGES SEE ALSO $AEHLER AND 3TRONG WHICH ULTIMATELY DEPENDS ON POPULATION lTNESS HOMEOSTASIS AND III SPECIlCITY OF MUTUALISMS SO THAT SPECIES THAT DEPEND ON NON SPECIlC MUTUALISMS ARE MORE LIKELY TO OVERCOME MANY ABIOTIC AND BIOTIC BARRIERS IN NEW ENVIRONMENTS SEE ALSO 2ICHARDSON ET AL -ANY OTHERS HAVE DISCUSSED THE IDEA THAT BROADER NICHES CONFER HIGHER INVA SION SUCCESS &OR EXAMPLE IN A REVIEW ON BIOTIC HOMOGENIZATION -C+INNEY AND ,OCKWOOD CONCLUDED THAT EXTINCTIONnRESISTANT SPECIES AND SUCCESSFUL INVADERS ARE CHARACTERIZED BY OMNIVORY RAPID GROWTH AND DISPERSAL OR BREEDING IN EPHEMERAL HABITATS WHEREAS EXTINCTION PRONE GROUPS HAVE A PREDOMINANCE OF TRAITS ASSOCIATED WITH SPECIALIZATION SLOW REPRODUCTION AND OTHER TRAITS NOT ASSOCIATED WITH OPPORTUNISM 3IMILARLY 2ICHARDSON ET AL STATED THAT h)T IS LOGICAL TO PREDICT THAT PLANTS WITH SPECIALIZED POLLINATION SYNDROMES ARE LESS LIKELY TO BE POLLINATED IN FOREIGN ENVIRONMENTS THAN PLANTS WITHOUT SPECIALIZED REQUIREMENTSv P ,IKEWISE 2ICCIARDI AND 2ASMUSSEN REGARD BROAD GEOGRAPHIC ENVIRONMENTAL AND DIETARY RANGES AS GENERAL ATTRIBUTES OF INVASIVE AQUATIC SPECIES !LTHOUGH THESE IDEAS ARE INTERESTING AND APPEALING THEIR EVALU ATION IS COMPLICATED BY SEVERAL CONCEPTUAL AND METHODOLOGICAL PROBLEMS ) WILL ARGUE THAT PROGRESS TOWARDS A PREDICTIVE THEORY OF INVASIONS WILL BE DIFlCULT UNLESS THESE ISSUES ARE RESOLVED "ELOW ) PRESENT A REVIEW OF THE LITERATURE SUMMARIZING SEVERAL STUDIES THAT HAVE EVALUATED THE RELATIONSHIP BETWEEN DIFFERENT ASPECTS OF NICHE BREADTH AND INVASION SUCCESS ) THEN PROVIDE A CRITICAL EXAMINATION OF THE MECHANISMS POTEN TIALLY INVOLVED IN GENERATING THESE RESULTS STRESSING SEVERAL CONCEPTUAL ISSUES THAT HAVE BEEN OVERLOOKED IN PREVIOUS DISCUSSIONS -Y REVIEW IS NOT EXHAUS TIVE AND IS TAXONOMICALLY BIASED FOCUSING ON PLANTS BIRDS AND HETEROTROPHIC MUTUALISTS OF PLANTS 4HIS BIAS REmECTS THE FACT THAT MOST STUDIES EVALUATING THIS HYPOTHESIS HAVE DEALT WITH THESE GROUPS )N SUMMARIZING THE AVAILABLE LITERATURE
.ICHE BREADTH AND INVASION SUCCESS
) USE A VOTE COUNTING APPROACH BECAUSE THE NUMBER OF STUDIES AVAILABLE PER TAXON AND MEASURE OF NICHE BREADTH WAS TOO SMALL TO ALLOW THE APPLICATION OF MORE QUANTITATIVE META ANALYTICAL TECHNIQUES SEE !RNQVIST AND 7OOSTER 'UREVITCH ET AL 4HE STUDIES REVIEWED HERE ARE BASED ON THREE DIFFERENT KINDS OF COMPARISONS SOME MEASURE OF NICHE BREADTH IN NATIVE REGION OF SUCCESSFUL VS FAILED INVADERS 3) VS &) NICHE BREADTH OF INVADERS IN THEIR NATIVE VS THEIR INTRODUCED REGIONS .2 VS )2 AND NICHE BREADTH OF NATIVE VS INTRODUCED SPECIES IN THE INTRODUCED REGION .3 VS )3 )T IS IMPORTANT TO NOTE SEVERAL SIMILARITIES AND DIFFERENCES ABOUT THE THREE APPROACHES 4HE lRST COMPARISON 3) VS &) USES A BINARY MEASURE OF INVASION SUCCESS ASKING WHETHER SUCCESS IS EXPLAINED BY THE NICHE BREADTH IN THE NATIVE RANGE )N CONTRAST THE SECOND APPROACH .2 VS )2 USES A QUANTITA TIVE MEASURE OF SUCCESS SUCH AS THE SIZE OF THE INTRODUCED RANGE TO DETERMINE WHETHER INVASION SUCCESS IS EXPLAINED BY NICHE BREADTH IN THE NATIVE RANGE 4HE THIRD APPROACH .3 VS )3 COMPARES NICHE BREADTH OF INTRODUCED SPECIES WITH NATIVE SPECIES IN THE INTRODUCED RANGE IE SPECIES NATIVE TO THE RECIPIENT COMMU NITY HERE THE QUESTION IS WHETHER THE SUCCESS OF INVADERS IE THE FACT THAT THEY ESTABLISHED IN A NEW ENVIRONMENT IS EXPLAINED BY THEIR BROADER NICHE COMPARED TO THAT OF NATIVE SPECIES IN SHARP CONTRAST WITH THE QUESTION ASKED IN THE PREVI OUS TWO APPROACHES 4HUS ALTHOUGH THE THREE TYPES OF COMPARISONS ARE INTENDED TO ADDRESS THE QUESTION OF WHETHER NICHE BREADTH OF POTENTIAL INVADERS IS RELATED TO THEIR INVASION SUCCESS THEY ARE NOT EQUIVALENT AND ARE LIKELY TO PROVIDE DIFFER ENT ANSWERS -Y REVIEW CONSISTS OF THREE MAIN PARTS I THE ROLE OF GEOGRAPHIC HABITAT AND CLIMATIC RANGE ON PLANT AND BIRD INVASIONS II THE ROLE OF MUTUALISMS ON PLANT AND POLLINATOR INVASIONS AND III THE ROLE OF TROPHIC BREADTH ON BIRD INVASIONS ) END WITH A SECTION SUMMARIZING THE RESULTS OF THE REVIEW AND OFFERING CONCLUD ING REMARKS
4(% 2/,% /& '%/'2!0()# #,)-!4)# !.$ (!")4!4 2!.'% 0ATTERNS STUDIES ON PLANTS AND BIRDS
3TUDIES THAT HAVE EVALUATED THE INVASION SUCCESS OF PLANTS AND ITS RELATIONSHIP TO GEOGRAPHIC CLIMATIC OR HABITAT RANGE ARE BASED ON THE THREE TYPES OF COM PARISONS OUTLINED ABOVE 3TUDIES BASED ON THE lRST TWO KINDS OF COMPARISONS 3) VS &) AND .2 VS )2 HAVE FOUND THAT INVASION SUCCESS IS POSITIVELY RELATED TO NATIVE GEOGRAPHIC CLIMATIC OR HABITAT RANGE SO THAT MORE SUCCESSFUL INVAD ERS TEND TO HAVE BROADER NATIVE RANGES THAN LESS SUCCESSFUL INVADERS 4ABLE )N GENERAL THESE RESULTS SUPPORT THE NOTION THAT THE NATIVE RANGE OF PLANT SPECIES IS A PREDICTOR OF THEIR SUCCESS AS INVADERS IN NEW REGIONS WHERE THEY DID NOT OCCUR NATURALLY $AEHLER AND 3TRONG 2EJMÉNEK
#OMPOSITAE 'RAMINEAE
!NGIOSPERMS
!NGIOSPERMS
"ROMUS
.2 VS )2
!USTRALIA
!USTRALIA
.ORTH !MERICA
.EW "RUNSWICK #ANADA
-EDITERRANEAN -EDITERRANEAN REGIONS REGIONS
3OUTH !FRICA
3OUTH !FRICA
%URASIA
%UROPE
.O CLIMATIC ZONES IN NATIVE RANGE
7EED STATUS
7EED STATUS
3IZE OF INTRODUCED RANGE
%STABLISHMENT IN NEW REGION
.O -EDITERRANEAN REGIONS OCCUPIED
.O CLIMATIC ZONES
.O NATIVE HABITAT TYPES
.O NATIVE HABITAT TYPES
3IZE OF NATIVE RANGE
0OSITIVE
0OSITIVE
0OSITIVE
0OSITIVE
0OSITIVE
.3 VS )3 (IGHER PLANTS 7ORLD(AWAII (AWAII .O OF HABITAT .O HABITAT TYPES .EGATIVE TYPES OCCUPIED 2EFERENCES 0RINZING ET AL 2EJMÉNEK 3COTT AND 0ANETTA 'OODWIN ET AL 2OY ET AL +ITAYAMA AND -UELLER $OMBOIS
#OMPARISONS INCLUDED 3) VS &) NATIVE RANGE OF SUCCESSFULLY ESTABLISHED SPECIES VS UNSUCCESSFULLY ESTABLISHED SPECIES .2 VS )2 NATIVE RANGE VS INTRODUCED RANGE OF INTRODUCED SPECIES .3 VS )3 RANGE OF NATIVE VS INTRODUCED SPECIES IN THE INTRODUCED REGION e )NDICATES STATISTICAL SIGNIlCANCE OF TEST AND DIRECTION OF EFFECT 0OSITIVE SIGNIlCANT EFFECT IN THE DIRECTION EXPECTED BY THE SPECIALIZATIONnNICHE BREADTH HYPOTHESIS .EGATIVE SIGNIlCANT EFFECT IN THE DIRECTION OPPOSITE TO THE EXPECTED BY THE SPECIALIZATIONnNICHE BREADTH HYPOTHESIS
!NGIOSPERMS
4ABLE 3TUDIES EVALUATING THE RELATIONSHIP BETWEEN BREADTH OF GEOGRAPHIC CLIMATIC OR HABITAT RANGE OF PLANT SPECIES AND INVASION SUCCESS 4YPE OF -AJOR TAXON .ATIVE REGION )NTRODUCED -EASURE OF SUCCESS -EASURE OF NICHE 2ELAT WITH 2EF COMPARISON REGION BREADTH NICHE BREADTHe 3) VS &) (IGHER PLANTS #ENTRAL -ENDOZA AND %STABLISHMENT IN .O NATIVE HABITAT TYPES 0OSITIVE %UROPE "UENOS !IRES NEW REGION PROVINCES !RGENTINA
$0 6ÉZQUEZ
. I CHE BREADTH AND INVASION SUCCESS
)N CONTRAST THE ONE STUDY COMPARING BREADTH OF HABITAT USE BY NATIVE AND INTRODUCED SPECIES .3 VS )3 4ABLE FOUND A PATTERN OPPOSITE TO THE PREDICTION OF THE NICHE BREADTHnINVASION SUCCESS HYPOTHESIS INTRODUCED SPECIES WERE FOUND IN FEWER HABITAT TYPES THAN NATIVE SPECIES 4HIS RESULT IS DIFlCULT TO INTERPRET HOWEVER MAINLY BECAUSE THE NUMBER OF HABITATS IN WHICH A SPECIES IS FOUND WILL DEPEND ON ITS DISPERSAL ABILITY AND THE TIME ELAPSED AFTER ITS ARRIVAL TO THE ENVIRON MENT WHICH MAY OBVIOUSLY BIAS THE RESULTS TOWARDS NATIVE SPECIES GIVEN THEIR LONGER PRESENCE IN THE STUDY AREA 3TUDIES EVALUATING THE RELATIONSHIP BETWEEN GEOGRAPHIC CLIMATIC OR HABITAT RANGE AND INVASION SUCCESS IN BIRDS 4ABLE ALL USED THE lRST APPROACH OUTLINED ABOVE THAT IS THEY COMPARE THE SIZE OF THE NATIVE RANGE BETWEEN SUCCESSFUL AND UNSUCCESSFUL INVADERS 3) VS &) 4HESE STUDIES HAVE USED EITHER SIZE OF NATIVE GEO GRAPHIC RANGE NUMBER OF NATIVE HABITAT TYPES OR CLIMATIC ZONES OCCUPIED IN THE NATIVE REGION AS MEASURES OF NICHE BREADTH )N AGREEMENT WITH STUDIES ON PLANTS DISCUSSED ABOVE STUDIES OF BIRD INVA SIONS IN (AWAII !USTRALIA AND WORLDWIDE FOUND A POSITIVE RELATIONSHIP BETWEEN INVASION SUCCESS AND SIZE OF NATIVE GEOGRAPHIC RANGE USED IN THE NATIVE RANGE 4ABLE (OWEVER TWO STUDIES ONE IN FOUR OCEANIC ISLANDS AND THE OTHER IN .EW :EALAND FAILED TO lND EVIDENCE FOR SUCH AN EFFECT 4ABLE 4HE TWO STUD IES USING THE NUMBER OF HABITAT TYPES OCCUPIED IN THE NATIVE RANGE FOUND THAT SUCCESSFULLY INVADING SPECIES OR FAMILIES HAD SIGNIlCANTLY GREATER NATIVE HABITAT RANGES THAN SPECIES OR FAMILIES THAT FAILED TO INVADE 4ABLE )N SUMMARY IT APPEARS THAT BREADTH OF NATIVE GEOGRAPHIC CLIMATIC AND HABITAT RANGE IS RELATED TO THE INVASION SUCCESS OF PLANT AND BIRD SPECIES !LTHOUGH THERE ARE EXCEPTIONS TO THESE PATTERNS THEY APPEAR TO HAVE SOME DEGREE OF GENERALITY -ECHANISMS
7HY DOES BREADTH OF NATIVE GEOGRAPHIC HABITAT OR CLIMATE RANGE AFFECT INVASION SUCCESS 3PECIES WITH BROAD RANGES MAY BE MORE SUCCESSFUL INVADERS THAN SPE CIES WITH NARROWER RANGES FOR SEVERAL REASONS !S DISCUSSED IN THE INTRODUCTION SPECIES NICHES MAY DETERMINE THEIR DISTRIBUTION SO THAT SPECIES WITH BROADER NICHES TEND TO HAVE BROADER DISTRIBUTIONS AND ARE SO MORE LIKELY TO INVADE NEW ENVIRONMENTS SEE ALSO "ROWN (OWEVER OTHER FACTORS NOT RELATED TO NICHE BREADTH MAY ALSO AFFECT SPECIES DISTRIBUTIONS 5NDER THESE SCENARIOS WIDESPREAD SPECIES WOULD HAVE HIGHER INVASION SUCCESS REGARDLESS OF THEIR NICHE BREADTH &IRST SPECIES SPECIALIZED ON WIDESPREAD RESOURCES OR SPECIES THAT ARE ABLE TO LIVE UNDER ENVIRONMENTAL CHAR ACTERISTICS THAT SPAN LARGE AREAS MAY HAVE WIDE DISTRIBUTIONS IN SPITE OF HAVING A NARROW TOLERANCE TO ENVIRONMENTAL CONDITIONS OR OF BEING ABLE TO USE A NARROW RANGE OF RESOURCES (ANSKI ET AL 'ASTON ET AL 4HIS MECHANISM IS PARTICULARLY IMPORTANT FOR SPECIES THAT ARE ABLE TO EXPLOIT HUMAN DOMINATED ECOSYSTEMS WHICH ARE THEMSELVES VERY WIDESPREAD 3OL ET AL 3ECOND HIGH DISPERSAL ABILITY CAN ALSO LEAD TO WIDE GEOGRAPHIC RANGES AT LEAST IN SOME GROUPS WHEREAS LIMITED DISPERSAL CAN RESULT IN GEOGRAPHIC RANGES MUCH NARROWER
7ORLD
.INE OCEANIC ISLANDS
.EW :EALAND
7ORLD
7ORLD
&OUR OCEANIC ISLANDS
B
0OSITIVE
C
0OSITIVE
.3
A
0OSITIVE
0OSITIVE
0OSITIVE
0OSITIVE
.3
.3
0OSITIVE
"EHAVIORAL mEXIBILITY 3PECIES 7ORLD 0OSITIVE 2EFERENCES -OULTON AND 0IMM $UNCAN ET AL 6ELTMAN ET AL ,OCKWOOD ET AL "LACKBURN AND $UNCAN #ASSEY "ROOKS -C,AIN ET AL 3OL AND ,EFEBVRE 3OL ET AL -EASURES OF DIET BREADTH USED IN STUDIES A$IET BREADTH MEASURED AS CARNIVORE OR HERBIVORE SPECIALIST AND OMNIVORE GENERALIST B$IET BREADTH MEASURED AS FRUGIVORE OR GRANIVORE SPECIALIST AND OMNIVORE EATING FRUITS AND SEEDS GENERALIST A FOURTH CATEGORY WAS INCLUDED FOR SPECIES THAT FED ON NEITHER FRUITS OR NECTAR C$IET BREADTH MEASURED AS NUMBER OF SEVEN MAJOR FOOD TYPES CONSUMED e )NDICATES STATISTICAL SIGNIlCANCE OF TEST AND DIRECTION OF EFFECT 0OSITIVE SIGNIlCANT EFFECT IN THE DIRECTION EXPECTED BY THE SPECIALIZATIONnNICHE BREADTH HYPOTHESIS .3 STATISTICALLY NONSIGNIlCANT RESULT o #ASSEY ALSO DID ANALYSES AT SPECIES LEVEL (OWEVER HIS SPECIES LEVEL MULTIVARIATE ANALYSES ARE MOSTLY DESCRIPTIVE AND ARE DIFlCULT TO COMPARE WITH OTHER STUDIES LISTED IN THE TABLE AND WERE THEREFORE NOT INCLUDED
&AMILIES
o
3PECIES
$IET BREADTH
7ORLD
.O NATIVE HABITAT TYPES &AMILIES
3PECIES
7ORLD
&AMILIES
o
o
.EW :EALAND
!USTRALIA
4ABLE 3TUDIES EVALUATING THE RELATIONSHIP BETWEEN BREADTH OF GEOGRAPHIC HABITAT RANGE TROPHIC OR BEHAVIORAL BREADTH OF BIRD SPECIES AND INVASION SUCCESS -EASURE OF NICHE BREADTH 4AXONOMIC LEVEL OF ANALYSIS )NTRODUCED REGION 2ELATIONSHIP WITH NICHE BREADTHe 2EF 3IZE OF NATIVE RANGE 3PECIES (AWAII 0OSITIVE
$0 6ÉZQUEZ
. I CHE BREADTH AND INVASION SUCCESS
THAN WOULD BE PREDICTED BASED ON A SPECIES NICHE 'ASTON 4HUS SPECIES WITH HIGH DISPERSAL ABILITIES MAY TEND TO HAVE BOTH WIDE NATIVE RANGES AND HIGH CHANCES OF COLONIZING AND SPREADING IN NEW ENVIRONMENTS 4HIRD SPECIES WITH WIDER NATIVE RANGES MAY BE MORE LIKELY TO BE TRANSPORTED TO NEW AREAS BY HUMANS THROUGH PASSIVE SAMPLING 0RINZING ET AL PARTICULARLY CONSIDERING THAT WIDESPREAD SPECIES ALSO TEND TO BE LOCALLY ABUNDANT 'ASTON ET AL #ASSEY ET AL HAVE RECENTLY SHOWN THAT PROPAGULE PRESSURE OF INTRODUCED BIRDS EXPLAINS INVASION SUCCESS WORLDWIDE THESE AUTHORS ALSO FOUND THAT PROPAGULE PRESSURE IS POSITIVELY RELATED TO GEOGRAPHIC AND TROPHIC BREADTH AND SO THESE MEASURES OF NICHE BREADTH ARE NOT INDEPENDENT OF PROPAGULE PRESSURE AND COULD BE CONFOUNDED WITH IT 5NDERSTANDING THE ROLE OF THE HABITAT AND CLIMATIC COMPO NENTS OF NICHE BREADTH IN DETERMINING INVASION SUCCESS WILL REQUIRE TEASING APART THESE FACTORS
4(% 2/,% /& 30%#)!,):!4)/. ). -545!,)34)# ).4%2!#4)/.3 0ATTERNS
3EVERAL STUDIES HAVE EVALUATED THE RELATIONSHIP BETWEEN SPECIALIZATION IN MUTU ALISTIC INTERACTIONS AND INVASION SUCCESS OF PLANTS ANDOR ANIMAL MUTUALISTS 2ICHARDSON ET AL HAVE REVIEWED THE ROLE OF MUTUALISMS IN FACILITATING PLANT INVASIONS 4HEIR REVIEW SUGGESTS THAT PLANTS WITH EXTREMELY SPECIALIZED MUTUAL ISTIC INTERACTIONS INCLUDING INTERACTIONS WITH POLLINATORS SEED DISPERSERS MYCOR RHIZAL FUNGI AND NITROGEN lXING BACTERIA MAY BE PREVENTED FROM ESTABLISHING AND SPREADING IN A NEW ENVIRONMENT (OWEVER THE RARITY OF EXTREME SPECIALIZATION IN MUTUALISTIC INTERACTIONS MAY GREATLY MINIMIZE THE POTENTIAL ROLE OF MUTUALISMS IN LIMITING PLANT INVASION SUCCESS /NE OF THE EXAMPLES OF HOW EXTREMELY SPECIALIZED MUTUALISTIC INTERACTIONS MAY PREVENT THE ESTABLISHMENT AND SPREAD OF INTRODUCED PLANT POPULATIONS DISCUSSED BY 2ICHARDSON ET AL IS THE INVASION ECOLOGY OF lGS &ICUS -ORACEAE /F THE SIXTY SPECIES OF &ICUS INTRODUCED TO &LORIDA 53! ONLY THREE HAVE BECOME INVASIVE AND THEY HAVE DONE SO ONLY AFTER THE ACCIDENTAL INTRODUCTION OF THEIR SPECIlC WASP SEE 2ICHARDSON ET AL AND REFERENCES THEREIN (OWEVER 2ICHARDSON ET AL ALSO DISCUSS THE CASE OF & LUTEA IN 3OUTH !FRICA WHERE ONE ISO LATED FEMALE INDIVIDUAL OF THIS NONINDIGENOUS SPECIES HAS BEEN POLLINATED BY WASPS THAT WERE NOT ITS NORMAL POLLINATOR !LTHOUGH IN THIS CASE THE ABSENCE OF MALE INDIVIDUALS PREVENTED REPRODUCTION HYBRIDS WITH NATIVE &ICUS DID NOT PRODUCE VIABLE SEEDLINGS SPREAD MIGHT HAVE BEEN POSSIBLE IF MALE INDIVIDUALS OF & LUTEA HAD ALSO BEEN INTRODUCED !S A SIDE NOTE 2ICHARDSON ET AL POINT OUT THAT SEVERAL PINE SPECIES 0INUS SPP NATIVE TO .ORTH !MERICA AND THE -EDITERRANEAN "ASIN THAT ARE WIND DISPERSED IN THEIR NATIVE RANGES ARE DISPERSED BY COCKATOOS IN !USTRALIA !LTHOUGH BIRDS DESTROY MOST OF THE SEEDS SOME SURVIVE TO ESTABLISH ISOLATED FOCI IN HABITATS EUCALYPT FORESTS THAT THEY WOULD OTHERWISE NOT HAVE
$0 6ÉZQUEZ
BEEN ABLE TO INVADE 4HUS EVEN APPARENT EXTREME SPECIALIZATION ON A PARTICULAR POLLEN VECTOR FIG WASP OR SEED DISPERSAL AGENT WIND MAY NOT PRECLUDE SURVIVAL AND SUCCESSFUL REPRODUCTION IN A NEW ENVIRONMENT !LBEIT INTRIGUING THE EXTREME SPECIALIZATION OBSERVED FOR &ICUS IS NOT REPRESEN TATIVE OF THE MAJORITY OF POLLINATION INTERACTIONS 7ASER ET AL AND MOST SPECIES WITHIN A COMMUNITY FALL SOMEWHERE ALONG A GRADIENT THAT SPANS FROM EXTREME SPECIALIZATION TO EXTREME GENERALIZATION "ASCOMPTE ET AL *ORDANO ET AL 6ÉZQUEZ AND !IZEN A ! SIMILAR SITUATION OCCURS IN SEED DISPERSAL MUTUALISMS "ASCOMPTE ET AL 4HE QUESTION IS WHETHER SPECIES LOCATED TOWARDS THE SPECIALIZED EXTREME OF THE CONTINUUM ARE LESS LIKELY TO INVADE SUCCESSFULLY THAN MORE GENERALIZED SPECIES )N A RECENT REVIEW OF INTRODUCED BEES AND THEIR ECOLOGICAL IMPACTS 'OULSON POINTS OUT THAT MOST INTRODUCED BEE SPECIES APPEAR QUITE GENERALIZED 'OULSON ARGUES THAT AMONG BEES WHICH DEPEND ON mORAL FOOD RESOURCES THROUGH OUT THEIR ENTIRE LIFE CYCLES DIETARY GENERALIZATION SEEMS TO BE A PRECONDITION FOR BECOMING SUCCESSFUL INVADERS (OWEVER THIS INTERPRETATION SHOULD BE TAKEN WITH CAUTION !LL SPECIES OF BEES KNOWN TO HAVE BEEN INTRODUCED OUTSIDE THEIR NATIVE RANGES THE HONEY BEE lVE BUMBLEBEES TEN MEGACHILLIDS AND ONE HALICTID HAVE BEEN PURPOSEFULLY INTRODUCED BY HUMANS TO ENHANCE CROP POLLINATION USUALLY OF SEVERAL SPECIES 'IVEN THIS GOAL DIETARY GENERALIZATION OF INTRODUCED BEES IS PROB ABLY A DESIRABLE TRAIT AND IT IS THEREFORE DIFlCULT TO TEASE APART THE EFFECT OF HUMAN SELECTION FROM THE EFFECT OF DIETARY SPECIALIZATION ON INVASION SUCCESS !NOTHER WAY OF EVALUATING THE NICHE BREADTHnINVASION SUCCESS HYPOTHESIS AS IT APPLIES TO MUTUALISTIC INTERACTIONS IS BY COMPARING THE DEGREE OF SPECIALIZATION IN MUTUALISTIC INTERACTIONS BETWEEN NATIVE AND INTRODUCED SPECIES IN A GIVEN AREA 4HE EXPECTATION UNDER THE NICHE BREADTHnINVASION SUCCESS HYPOTHESIS IS THAT INTERACTIONS ARE LESS SPECIlC FOR INTRODUCED THAN FOR NATIVE SPECIES BECAUSE EXOTIC SPECIES WITH MORE SPECIlC INTERACTIONS MAY HAVE BEEN hlLTERED OUTv DURING THE ESTABLISHMENT PROCESS ) HAVE FOUND STUDIES IN FOUR SYSTEMS ATTEMPTING TO ANSWER THIS QUESTION BY COMPARING THE DEGREE OF SPECIALIZATION OF PLANT ANDOR POLLINATORS BETWEEN NATIVE AND INTRODUCED SPECIES IE A .3 VS )3 COMPARISON SEE ABOVE )N ADDITION ) HAVE FOUND COMPARABLE DATA FOR A lFTH SYSTEM FOR WHICH ) CALCULATED DEGREE OF SPECIALIZATION IN A WAY COMPARABLE TO THE OTHER STUDIES 4HESE STUD IES ARE SUMMARIZED IN 4ABLE .ONE OF THE STUDIES SUPPORT THE NICHE BREADTHn INVASION SUCCESS HYPOTHESIS AND IN SOME CASES THE OBSERVED PATTERN WAS CONTRARY TO THE EXPECTATION IE INTRODUCED SPECIES HAD MORE SPECIlC INTERACTIONS 4HUS THE FEW AVAILABLE STUDIES TELL US THAT INTERACTION SPECIlCITY OF INTRODUCED PLANTS AND POLLINATORS DOES NOT INmUENCE THEIR INVASION SUCCESS -ECHANISMS
&ROM THE STUDIES REVIEWED ABOVE EVALUATING THE ROLE OF MUTUALISMS IN INVASIONS IT APPEARS THAT ONLY EXTREMELY SPECIALIZED MUTUALISMS HAVE THE POTENTIAL TO INmU ENCE INVASION SUCCESS AND IN GENERAL SPECIlCITY OF MUTUALISTIC INTERACTIONS DOES
&LORES )SLAND !ZORES !ZORES !NGIOSPERMS (YMENOPTERA RARE SPECIES EXCLUDED (YMENOPTERA !PIDAE ONLY
.AHUEL (UAPI !RGENTINA
.AHUEL (UAPI !RGENTINA
.3
.3
.3
.3
.3
.EGATIVE
)LE AUX !IGRETTES -AURITIUS 0OLLINATORS .3 2EFERENCES -EMMOTT AND 7ASER -ORALES AND !IZEN -C-ULLEN /LESEN ET AL e )NDICATES STATISTICAL SIGNIlCANCE OF TEST AND DIRECTION OF EFFECT .EGATIVE SIGNIlCANT EFFECT IN THE DIRECTION OPPOSITE TO THE EXPECTED BY THE SPECIALIZATIONnNICHE BREADTH HYPOTHESIS .3 STATISTICALLY NONSIGNIlCANT RESULT
&LORES )SLAND !ZORES !ZORES 0OLLINATORS
!NGIOSPERMS
)LE AUX !IGRETTES -AURITIUS
!NGIOSPERMS
'ALÉPAGOS )SLANDS
.3
!NGIOSPERMS
.AHUEL (UAPI !RGENTINA
2EF
4ABLE 3TUDIES THAT HAVE COMPARED DEGREE OF SPECIALIZATION OF PLANTS OR POLLINATORS BETWEEN NATIVE AND INTRODUCED SPECIES -EAN NUMBER OF MUTUALIST SPECIES )NTRODUCED REGION -AJOR TAXON .ATIVE %XOTIC 2ESULT OF STATISTICAL TESTe )LLINOIS 53! !NGIOSPERMS .EGATIVE
. I CHE BREADTH AND INVASION SUCCESS
$0 6ÉZQUEZ
NOT SEEM TO INmUENCE INVASION SUCCESS SIGNIlCANTLY 4HESE RESULTS CONTRAST WITH THOSE OBTAINED IN STUDIES EVALUATING THE RELATIONSHIP BETWEEN GEOGRAPHIC HABITAT OR CLIMATIC RANGE AND INVASION SUCCESS REVIEWED IN THE PREVIOUS SECTION (OW CAN WE EXPLAIN THESE CONTRASTING RESULTS 7HY DOES NARROW CLIMATIC OR GEOGRAPHIC RANGE APPEAR TO TRANSLATE INTO LOW LIKELIHOOD OF INVASION WHEREAS NARROW RANGE OF MUTUALISTIC INTERACTIONS DOES NOT 4HE ANSWER TO THIS QUESTION MAY REQUIRE SOME CONCEPTUAL RElNEMENTS IN OUR THINKING ABOUT THE RELATIONSHIP BETWEEN NICHE BREADTH AND INVASION SUCCESS AS IT APPLIES TO MUTUALISM &IRST WE NEED TO DISTINGUISH BETWEEN THE FUNDAMENTAL AND THE REALIZED NICHE (UTCHINSON )N THE CONTEXT OF SPECIES INTERACTIONS FUNDAMENTAL SPECIAL IZATION REFERS TO THE POTENTIAL INTERACTIONS THAT WOULD LEAD TO POSITIVE lTNESS FOR A GIVEN SPECIES UNDER ANY POSSIBLE ECOLOGICAL CIRCUMSTANCES VAN +LINKEN AND %DWARDS 6ÉZQUEZ AND !IZEN B 6ÉZQUEZ 4HUS FUNDAMENTAL SPECIALIZATION WILL ULTIMATELY DEPEND ON THE GENETIC BACKGROUND OF A SPECIES WHEREAS REALIZED SPECIALIZATION REFERS TO THE ACTUAL SPECIALIZATION ATTAINED UNDER A PARTICULAR ECOLOGICAL CONTEXT &OR EXAMPLE MOST FIG SPECIES ARE FUNDAMENTALLY SPECIALIZED ON ONE OR A FEW SPECIES OF POLLINATING WASPS THEY FAIL TO REPRODUCE IF THEY ARE MOVED TO DIFFERENT ENVIRONMENTS UNLESS THEIR SPECIALIZED POLLINATORS ARE INTRODUCED AS WELL #ONVERSELY MANY OTHER PLANT SPECIES THAT ARE POLLINATED BY A SINGLE POLLINATOR IN A PARTICULAR HABITAT ARE OFTEN POLLINATED BY A DIFFERENT SPECIES IN OTHER HABITATS WHERE THEY ARE INTRODUCED 2ICHARDSON ET AL 2EGRETTABLY THE BEST WE CAN DO IN THE lELD IS TO MEASURE THE REALIZED NICHE BUT IF WE WANT TO PREDICT INVASIONS WHAT WE NEED TO KNOW IS THE FUNDAMENTAL NICHE )N OTHER WORDS KNOWING THE NICHE BREADTH OF A SPECIES IN A PARTICULAR ENVIRONMENT DOES NOT TELL US WHAT THE REALIZED NICHE WILL BE IN ANOTHER ENVIRONMENT !LTHOUGH STUDYING THE CLIMATIC COMPONENT OF THE FUNDAMENTAL NICHE MAY BE POSSIBLE BY FOR EXAMPLE EXPERIMENTALLY GROWING A SPECIES UNDER A WIDE RANGE OF ENVIRONMENTAL CONDI TIONS DOING SO IN THE CONTEXT OF SPECIES INTERACTIONS MAY BE SIMPLY UNFEASIBLE BECAUSE IT WOULD REQUIRE EXPOSING THE SPECIES TO ALL POSSIBLE COMBINATIONS OF INTER ACTION PARTNERS THAT IT COULD ENCOUNTER IN ANY GIVEN ENVIRONMENT %VEN MANY SPECIES SELECTED AS BIOCONTROL AGENTS WHICH ARE USUALLY SELECTED TO BE SPECIALISTS EXHIBIT UNEXPECTED HOST SHIFTS IN THEIR INTRODUCED RANGES 3IMBERLOFF AND 3TILING (ENNEMAN AND -EMMOTT VAN +LINKEN AND %DWARDS 0EARSON AND #ALLAWAY AND THESE SHIFTS ARE USUALLY NOT THE RESULT OF CHANGES IN THE FUNDAMENTAL NICHE THROUGH RAPID EVOLUTION BUT AN EXPRESSION OF A DIFFERENT REAL IZED NICHE UNDER THE NEW ENVIRONMENT VAN +LINKEN AND %DWARDS 3ECOND AS ) POINTED OUT ABOVE SPECIES THAT USE WIDESPREAD RESOURCES LIVE UNDER WIDESPREAD ENVIRONMENTAL CONDITIONS OR USE WIDESPREAD HABITATS ARE LIKELY TO BE WIDESPREAD THEMSELVES 4HIS IDEA CAN BE EASILY EXTENDED TO SPECIES INTERACTIONS TO ARGUE THAT SPECIES THAT SPECIALIZE ON WIDESPREAD MUTUALISTS MAY THEMSELVES BE WIDESPREAD !N EMERGING PATTERN IN PLANT ANIMAL MUTUALISTIC INTERACTIONS IS THE EXISTENCE OF HIGHLY ASYMMETRIC SPECIALIZATION WHEREBY SPECIALISTS TEND TO SPECIAL IZE ON GENERALISTS "ASCOMPTE ET AL 6ÉZQUEZ AND !IZEN A 'IVEN THAT ABUNDANT FREQUENTLY INTERACTING SPECIES TEND TO BE MORE GENERALIZED THAN RARE
. I CHE BREADTH AND INVASION SUCCESS
SPECIES $UPONT ET AL 6ÉZQUEZ AND !IZEN A AND THAT LOCALLY ABUNDANT SPECIES TEND TO BE GEOGRAPHICALLY WIDESPREAD 'ASTON ET AL SPECIES SPECIALIZED ON WIDESPREAD MUTUALISTS WILL HAVE A GREATER CHANCE OF lNDING THEIR MUTUALISTS IN THEIR INTRODUCED REGION 4HESE GENERAL FEATURES OF MUTUALISTIC INTERACTIONS MAY SUBSTANTIALLY INCREASE THE LIKELIHOOD OF SUCCESSFUL INVASION BY SPECIES THAT ARE RELATIVELY SPECIALIZED ON THEIR MUTUALISTS
4(% 2/,% /& 42/0()# "2%!$4( 0ATTERNS
!NOTHER ASPECT OF THE NICHE THAT CAN POTENTIALLY AFFECT INVASION SUCCESS IS DIETARY BREADTH AND IT IS FREQUENTLY LISTED AS ONE POTENTIAL CHARACTERISTIC OF SUCCESS FUL INVADERS %HRLICH 2ICCIARDI AND 2ASMUSSEN -C+INNEY AND ,OCKWOOD ) DISCUSS HERE A FEW STUDIES THAT HAVE ADDRESSED THIS ISSUE IN THE CONTEXT OF BIRD INVASIONS 4O MY KNOWLEDGE THREE STUDIES HAVE EVALUATED THE RELATIONSHIP BETWEEN INVA SION SUCCESS AND DIET BREADTH 4ABLE 4HESE STUDIES COMPARED TROPHIC BREADTH IN THE NATIVE REGION OF SUCCESSFUL VS FAILED INVADERS 3) VS &) -C,AIN ET AL DElNED SPECIALISTS AS SPECIES FEEDING ON EITHER FRUITS OR SEEDS AND GENERALISTS AS SPECIES FEEDING ON BOTH THEY FOUND THAT TROPHIC GENERALISTS WERE MORE LIKELY TO BE SUCCESSFUL INVADERS OF OCEANIC ISLANDS THAN TROPHIC SPECIALISTS 6ELTMAN ET AL DElNED HERBIVOROUS OR CARNIVOROUS SPECIES AS DIETARY SPECIALISTS AND OMNIVORES SPECIES FEEDING ON BOTH PLANT AND ANIMAL MATERIAL AS GENERALISTS THEY FAILED TO lND A STATISTICAL EFFECT OF SIZE OF NATIVE TROPHIC RANGE ON THE SUCCESS OF BIRDS INTRODUCED IN .EW :EALAND &INALLY #ASSEY DElNED DIETARY BREADTH AS THE NUMBER OF FOOD TYPES CONSUMED OUT OF SEVEN POSSIBLE CATEGORIES (E FOUND A WEAK BUT SIGNIlCANT EFFECT OF DIETARY BREADTH EXPLAINING THE INVASION SUCCESS OF BIRD FAMILIES -ECHANISMS
&ROM THIS LIMITED NUMBER STUDIES AND FROM THEIR DISPARATE RESULTS IT IS DIFlCULT TO MAKE GENERALIZATIONS ABOUT THE IMPORTANCE OF TROPHIC BREADTH FOR INVASION SUC CESS &URTHERMORE A MAJOR LIMITATION OF THE STUDIES DISCUSSED ABOVE IS THAT THE MEASURE OF SPECIALIZATION USED IS PROBABLY TOO COARSE AND MAY THEREFORE BE A POOR SURROGATE OF TRUE TROPHIC SPECIALIZATION &OR EXAMPLE IN THE STUDY BY -C,AIN ET AL ONLY FRUITS AND SEEDS ARE CONSIDERED TO CHARACTERIZE DIET BREADTH ALTHOUGH THE AUTHORS STATE THAT hVIRTUALLY ALL INTRODUCED SPECIES ;IN THESE ISLANDS= EAT SOME INSECTS AND OFTEN OTHER INVERTEBRATESv P 4HUS IT IS UNCLEAR WHETHER WHAT THE AUTHORS MEASURED ACTUALLY REPRESENTS DIET BREADTH OR RATHER WHETHER IT REPRE SENTS SOMETHING ELSE RELATED TO EATING FRUITS OR SEEDS )N FACT THE QUANTIlCATION OF DEGREE OF SPECIALIZATION IS PROBABLY O NE OF THE MAIN CONCEPTUAL AND METHODOLOGICAL
$0 6ÉZQUEZ
HURDLES IN THE STUDY OF SPECIES INTERACTIONS -ARTINEZ ET AL .OVOTNâ ET AL 6ÉZQUEZ AND !IZEN B -ANY IDEAS IN ECOLOGY EVOLUTION AND BIOGEOG RAPHY DEPEND ON ASSUMPTIONS ABOUT THE DEGREE OF SPECIALIZATION OF SPECIES INTER ACTIONS &OR EXAMPLE BECAUSE THE BULK OF THE %ARTHS SPECIES ARE BELIEVED TO BE TROPICAL HERBIVOROUS INSECTS ESTIMATES OF THE NUMBER OF SPECIES ON %ARTH DEPEND CRITICALLY ON ASSUMPTIONS ABOUT THEIR DEGREE OF SPECIALIZATION 4HE REALIZATION THAT TROPICAL HERBIVOROUS INSECTS WERE LESS SPECIALIZED THAN PREVIOUSLY THOUGHT LED TO REVISING THE ESTIMATED NUMBER OF GLOBAL SPECIES FROM MILLION %RWIN TO APPROXIMATELY MILLION DEGAARD .OVOTNâ ET AL 4O CIRCUMVENT THE PROBLEM OF THE MEASUREMENT OF TROPHIC SPECIALIZATION IN BIRDS 3OL AND ,EFEBVRE AND 3OL ET AL PROPOSED THE USE OF hBEHAVIOR AL mEXIBILITYv AS A SURROGATE OF TROPHIC BREADTH 4HESE AUTHORS DElNED BEHAVIORAL mEXIBILITY AS hTHE FREQUENCY OF NEW AND UNUSUAL FEEDING BEHAVIORS REPORTED IN THE SHORT NOTE SECTION OF ORNITHOLOGY JOURNALSv 3OL ET AL P 4HEY ARGUE THAT A TAXONOMIC GROUP IN WHICH LARGE NUMBERS OF NEW FEEDING BEHAVIORS ARE OBSERVED IS LIKELY TO CHANGE ITS FORAGING TECHNIQUES OR DIET FREQUENTLY TO EAT A SUR PRISINGLY LARGE RANGE OF FOODS AND TO USE HANDLING BEHAVIORS AND NOVEL SITUATIONS IN A WAY THAT STRIKES ORNITHOLOGISTS BY ITS COMPLEXITY AND mEXIBILITY 4HEY FURTHER FOUND THAT BEHAVIORAL mEXIBILITY OF BIRD SPECIES IN THEIR NATIVE RANGE IS RELATED TO THEIR SUCCESS AS INVADERS WORLDWIDE 4HIS APPROACH IS A PROMISING ALTERNATIVE TO ESTIMATING TROPHIC NICHE BREADTH FROM FEEDING RECORDS 2EGARDLESS OF THE PROBLEMS OF ESTIMATION OF TROPHIC SPECIALIZATION TWO ISSUES DISCUSSED ABOVE IN THE CONTEXT OF GEOGRAPHIC RANGE AND MUTUALISMS ALSO APPLY HERE &IRST SPECIES SPECIALIZING ON WIDESPREAD RESOURCES PARTICULARLY THOSE THAT EXPLOIT HUMAN DOMINATED ECOSYSTEMS MAY BE LIKELY TO INVADE IN SPITE OF BEING SPECIALIZED 3ECOND EVEN IF ACCURATE ESTIMATES USING FEEDING RECORDS PROVIDE A MEASURE OF THE REALIZED NICHE BUT NOT OF THE FUNDAMENTAL NICHE WHICH WOULD BE NECESSARY PREDICT INVASION SUCCESS IN A NEW ENVIRONMENT WITH A DIFFERENT SET OF FOOD RESOURCES
#/.#,5$).' 2%-!2+3 -Y REVIEW OF THE LITERATURE SUGGESTS SEVERAL GENERALIZATIONS ABOUT THE ROLE OF NICHE BREADTH AS A DETERMINANT OF INVASION SUCCESS )N PARTICULAR NATIVE HABITAT GEOGRAPHIC OR CLIMATIC RANGE OF PLANTS AND BIRDS APPEAR TO BE GOOD PREDICTORS INVASION SUCCESS WHEREAS SPECIlCITY OF MUTUALISTIC INTERACTIONS AND TROPHIC BREADTH APPEAR TO HAVE A MUCH WEAKER PREDICTIVE POWER (OWEVER EVEN WHEN RESULTS DO lT THE PREDICTIONS OF THE NICHE BREADTHnINVASION SUCCESS HYPOTHESIS IT IS USUALLY NOT POSSIBLE TO KNOW WHETHER NICHE BREADTH IS INVOLVED IN GENERATING THE OBSERVED PATTERN &UTURE STUDIES AIMING AT PREDICTING THE SUCCESS OF INVAD ERS SHOULD TEASE APART THE RELATIVE CONTRIBUTIONS OF NICHE BREADTH FROM OTHER CONFOUNDING FACTORS -ORE BROADLY ) HOPE MY REVIEW CAN SERVE AS AN EXAMPLE OF HOW CONCEPTUAL ELABORATION MAY BE USEFUL TO IMPROVE OUR UNDERSTANDING IN INVASIONS BIOLOGY
. I CHE BREADTH AND INVASION SUCCESS
!#+./7,%$'-%.43 ) THANK THE EDITORS FOR THE INVITATION TO CONTRIBUTE TO THIS VOLUME 3EAN -C-AHON )NGRID 0ARKER $AVID 2ICHARDSON %RIC 3EABLOOM $ANIEL 3OL AND -ONTSERRAT 6ILÌ MADE USEFUL SUGGESTIONS ON THE MANUSCRIPT ) WAS SUPPORTED BY A 0OSTDOCTORAL &ELLOWSHIP AT THE .ATIONAL #ENTER FOR %COLOGICAL !NALYSIS AND 3YNTHESIS FUNDED BY .3& 'RANT $%" THE 5NIVERSITY OF #ALIFORNIA AND THE 3ANTA "ARBARA CAMPUS
2%&%2%.#%3 !RNQVIST ' AND $ 7OOSTER -ETA ANALYSIS SYNTHESIZING RESEARCH lNDINGS IN ECOL OGY AND EVOLUTION 4RENDS IN %COLOGY AND %VOLUTION "AKER ( ' #HARACTERISTICS AND MODES OF ORIGIN OF WEEDS 0AGES IN ( ' "AKER AND # , 3TEBBINS EDITORS 4HE 'ENETICS OF #OLONIZING 3PECIES !CADEMIC 0RESS .EW 9ORK "AKER ( ' 4HE EVOLUTION OF WEEDS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "ASCOMPTE * 0 *ORDANO # * -ELIÉN AND * - /LESEN 4HE NESTED ASSEMBLY OF PLANT ANIMAL MUTUALISTIC NETWORKS 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! "LACKBURN 4 - AND 2 0 $UNCAN $ETERMINANTS OF ESTABLISHMENT SUCCESS IN INTRO DUCED BIRDS .ATURE "ROOKS 4 - !RE UNSUCCESSFUL AVIAN INVADERS RARER IN THEIR NATIVE RANGE THAN SUCCESSFUL INVADERS 0AGES IN * , ,OCKWOOD AND - - -C+INNEY EDITORS "IOTIC (OMOGENISATION THE LOSS OF DIVERSITY THROUGH INVASION AND EXTINCTION +LUWER !CADEMIC 0RESS $ORDRECHT 4HE .ETHERLANDS "ROWN * ( /N THE RELATIONSHIP BETWEEN ABUNDANCE AND DISTRIBUTION OF SPECIES !MERICAN .ATURALIST #ASSEY 0 ,IFE HISTORY AND ECOLOGY INmUENCES ESTABLISHMENT SUCCESS OF INTRODUCED LAND BIRDS "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY $AEHLER # # AND $ 2 3TRONG 0REDICTION AND BIOLOGICAL INVASIONS 4RENDS IN %COLOGY AND %VOLUTION $UNCAN 2 0 - "OMFORD $ - &ORSYTH AND , #ONIBEAR (IGH PREDICTABILITY IN INTRODUCTION OUTCOMES AND THE GEOGRAPHICAL RANGE SIZE OF INTRODUCED !USTRALIAN BIRDS A ROLE FOR CLIMATE *OURNAL OF !NIMAL %COLOGY $UPONT 9 , $ - (ANSEN AND * - /LESEN 3TRUCTURE OF A PLANT mOWER VISITOR NETWORK IN THE HIGH ALTITUDE SUB ALPINE DESERT OF 4ENERIFE #ANARY )SLANDS %COGRAPHY %HRLICH 0 2 7HICH ANIMAL WILL INVADE 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK
$0 6ÉZQUEZ
%RWIN 4 , 4ROPICAL FORESTS THEIR RICHNESS IN COLEOPTERA AND OTHER ARTHROPOD SPE CIES #OLEOPTERISTS "ULLETIN 'ASTON + * 4HE 3TRUCTURE AND $YNAMICS OF 'EOGRAPHIC 2ANGES /XFORD 5NIVERSITY 0RESS /XFORD AND .EW 9ORK 'ASTON + * 4 - "LACKBURN AND * ( ,AWTON )NTERSPECIlC ABUNDANCEnRANGE SIZE RELATIONSHIPS AN APPRAISAL OF MECHANISMS *OURNAL OF !NIMAL %COLOGY 'OODWIN " * ! * -C!LLISTER AND , &AHRIG 0REDICTING INVASIVENESS OF PLANT SPECIES BASED ON BIOLOGICAL INFORMATION #ONSERVATION "IOLOGY 'OULSON $ %FFECTS OF INTRODUCED BEES ON NATIVE ECOSYSTEMS !NNUAL 2EVIEW OF %COLOGY %VOLUTION AND 3YSTEMATICS 'UREVITCH * 0 3 #URTIS AND - ( *ONES -ETA ANALYSIS IN ECOLOGY !DVANCES IN %COLOGICAL 2ESEARCH (ANSKI ) * +OUKI AND ! (ALKKA 4HREE EXPLANATIONS OF THE POSITIVE RELATIONSHIP BETWEEN DISTRIBUTION AND ABUNDANCE OF SPECIES 0AGES IN 2 % 2ICKLEFS AND $ 3CHLUTER EDITORS 3PECIES DIVERSITY IN ECOLOGICAL COMMUNITIES HISTORICAL AND GEOGRAPHI CAL PERSPECTIVES 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), (ENNEMAN - , AND * -EMMOTT )NlLTRATION OF A (AWAIIAN COMMUNITY BY INTRO DUCED BIOLOGICAL CONTROL AGENTS 3CIENCE (UTCHINSON ' % #ONCLUDING REMARKS #OLD 3PRING (ARBOR 3YMPOSIA ON 1UANTITATIVE "IOLOGY *ORDANO 0 * "ASCOMPTE AND * - /LESEN )NVARIANT PROPERTIES IN COEVOLUTIONARY NETWORKS OF PLANT ANIMAL INTERACTIONS %COLOGY ,ETTERS +ITAYAMA + AND $ -UELLER $OMBOIS "IOLOGICAL INVASION ON AN OCEANIC ISLAND MOUNTAIN $O ALIEN PLANT SPECIES HAVE WIDER ECOLOGICAL RANGES THAN NATIVE SPECIES *OURNAL OF 6EGETATION 3CIENCE ,OCKWOOD * , - 0 -OULTON AND + , "ALENT )NTRODUCED AVIFAUNAS AS NATU RAL EXPERIMENTS IN COMMUNITY ASSEMBLY 0AGES IN % 7EIHER AND 0 +EDDY EDITORS %COLOGICAL !SSEMBLY 2ULES 0ERSPECTIVES !DVANCES 2ETREATS #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE -ARTINEZ . $ " ! (AWKINS ( ! $AWAH AND " 0 &EIFAREK %FFECTS OF SAMPLING EFFORT ON CHARACTERIZATION OF FOOD WEB STRUCTURE %COLOGY -C+INNEY - , AND * , ,OCKWOOD "IOTIC HOMOGENIZATION A FEW WINNERS REPLACING MANY LOSERS IN THE NEXT MASS EXTINCTION 4RENDS IN %COLOGY AND %VOLUTION -C,AIN $ + - 0 -OULTON AND * ' 3ANDERSON 3EXUAL SELECTION AND EXTINCTION 4HE FATE OF PLUMAGE DIMORPHIC AND PLUMAGE MONOMORPHIC BIRDS INTRODUCED ONTO ISLANDS %VOLUTIONARY %COLOGY 2ESEARCH -C-ULLEN # + &LOWER VISITING INSECTS OF THE 'ALÉPAGOS )SLANDS 4HE 0AN 0ACIlC %NTOMOLOGIST -EMMOTT * AND . - 7ASER )NTEGRATION OF ALIEN PLANTS INTO A NATIVE mOWER POLLINATOR VISITATION WEB 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON 3ERIES "
. I CHE BREADTH AND INVASION SUCCESS
-ORALES # , AND - ! !IZEN $OES INVASION OF EXOTIC PLANTS PROMOTE INVASION OF EXOTIC mOWER VISITORS ! CASE STUDY FROM THE TEMPERATE FORESTS OF THE SOUTHERN !NDES "IOLOGICAL )NVASIONS -OULTON - 0 AND 3 , 0IMM 3PECIES INTRODUCTIONS TO (AWAII 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK .OVOTNâ 6 9 "ASSET 3 % -ILLER ' $ 7EIBLEN " "REMER , #IZEK AND 0 $ROZD ,OW HOST SPECIlCITY OF HERBIVOROUS INSECTS IN A TROPICAL FOREST .ATURE DEGAARD & (OW MANY SPECIES OF ARTHROPODS %RWINS ESTIMATE REVISED "IOLOGICAL *OURNAL OF THE ,INNEAN 3OCIETY /LESEN * - , ) %SKILDSEN AND 3 6ENKATASAMY )NVASION OF POLLINATION NETWORKS ON OCEANIC ISLANDS IMPORTANCE OF INVADER COMPLEXES AND ENDEMIC SUPER GENERALISTS $IVERSITY AND $ISTRIBUTIONS 0EARSON $ % AND 2 - #ALLAWAY )NDIRECT EFFECTS OF HOST SPECIlC BIOLOGICAL CONTROL AGENTS 4RENDS IN %COLOGY %VOLUTION 0RINZING ! 7 $URKA 3 +LOTZ AND 2 "RANDL 7HICH SPECIES BECOME ALIENS %VOLUTIONARY %COLOGY 2ESEARCH 2EJMÉNEK - 7HAT MAKES A SPECIES INVASIVE 0AGES IN 0 0YÝEK EDITOR 0LANT INVASIONS GENERAL ASPECTS AND SPECIAL PROBLEMS !CADEMIC 0UBLISHING !MESTERDAM 2EJMÉNEK - )NVASIVE PLANTS APPROACHES AND PREDICTIONS !USTRAL %COLOGY 2ICCIARDI ! AND * " 2ASMUSSEN 0REDICTING THE IDENTITY AND IMPACT OF FUTURE BIOLOGICAL INVADERS A PRIORITY FOR AQUATIC RESOURCE MANAGEMENT #ANADIAN *OURNAL OF &ISHERIES AND !QUATIC 3CIENCES 2ICHARDSON $ - . !LLSOPP # - $!NTONIO 3 * -ILTON AND - 2EJMÉNEK 0LANT INVASIONS THE ROLE OF MUTUALISMS "IOLOGICAL 2EVIEWS 2OY * - , .AVAS AND , 3ONIÏ )NVASION BY ANNUAL GRASSES A CASE STUDY CHALLENGING THE HOMOCLIME APPROACH TO INVASIONS 0AGES IN 2 ( 'ROVES AND & DI #ASTRI EDITORS "IOGEOGRAPHY OF -EDITERRANEAN )NVASIONS #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 3COTT * + AND & $ 0ANETTA 0REDICTING THE !USTRALIAN WEED STATUS OF SOUTHERN !FRICAN PLANTS *OURNAL OF "IOGEOGRAPHY 3IMBERLOFF $ AND 0 $ 3TILING (OW RISKY IN BIOLOGICAL CONTROL %COLOGY 3OL $ AND , ,EFEBVRE "EHAVIOURAL mEXIBILITY PREDICTS INVASION SUCCESS IN BIRDS INTRODUCED TO .EW :EALAND /IKOS 3OL $ 3 4IMMERMANS AND , ,EFEBVRE "EHAVIOURAL mEXIBILITY AND INVASION SUCCESS IN BIRDS !NIMAL "EHAVIOUR VAN +LINKEN 2 $ AND / 2 %DWARDS )S HOST SPECIlCITY OF WEED BIOLOGICAL CONTROL AGENTS LIKELY TO EVOLVE RAPIDLY FOLLOWING ESTABLISHMENT %COLOGY ,ETTERS 6ÉZQUEZ $ 0 AND - ! !IZEN .ULL MODEL ANALYSES OF SPECIALIZATION IN PLANT POLLINATOR INTERACTIONS %COLOGY 6ÉZQUEZ $ 0 AND - ! !IZEN A !SYMMETRIC SPECIALIZATION A PERVASIVE FEATURE OF PLANT POLLINATOR INTERACTIONS %COLOGY
$0 6ÉZQUEZ
6ÉZQUEZ $ 0 AND - ! !IZEN B #OMMUNITY WIDE PATTERNS OF SPECIALIZATION IN PLANT POLLINATOR INTERACTIONS REVEALED BY NULL MODELS 0AGES IN PRESS IN * /LLERTON EDITOR 3PECIALIZATION AND GENERALIZATION IN PLANT POLLINATOR INTERACTIONS 5NIVERSITY OF #HICAGO 0RESS #HICAGO 6ÉZQUEZ $ 0 2EVISITANDO EL NICHO HUTCHINSONIANO %COLOGÓA !USTRAL IN PRESS 6ELTMAN # * 3 .EE AND - * #RAWLEY #ORRELATES OF INTRODUCTION SUCCESS IN EXOTIC .EW :EALAND BIRDS !MERICAN .ATURALIST 7ASER . - , #HITTKA - 6 0RICE . - 7ILLIAMS AND * /LLERTON 'ENERALIZATION IN POLLINATION SYSTEMS AND WHY IT MATTERS %COLOGY
#HAPTER FIFTEEN
)NTERACTIONS BETWEEN INVASIVE PLANTS AND SOIL ECOSYSTEMS POSITIVE FEEDBACKS AND THEIR POTENTIAL TO PERSIST ! 3 4HORPE AND 2 - #ALLAWAY
).42/$5#4)/. 0LANTS INDIRECTLY AFFECT THEIR NEIGHBORS IN MANY WAYS BUT ONE OF THE MOST IMPORTANT IS BY ALTERING THE BIOTIC PHYSICAL AND CHEMICAL CHARACTERISTICS OF SOILS (OBBIE !NGERS AND #ARON "ERENDSE "INKLEY AND 'IARDINA .ORTHRUP ET AL 3CHLESINGER AND 0ILMANIS 6AN "REEMEN 7ARDLE ET AL #HEN AND 3TARK %ATON AND &ARRELL 4HESE GEN ERAL EFFECTS HAVE BEEN UNDERSTOOD FOR DECADES BUT ONLY RECENTLY HAVE EXPERIMENTS DEMONSTRATED THAT COMPLEX INTERACTIONS BETWEEN PLANTS AND SOIL MICROBIAL COM MUNITIES CAN HAVE STRONG EFFECTS ON PLANT POPULATIONS "EVER ET AL #LAY AND 6AN DER 0UTTEN 0ACKER AND #LAY INTERACTIONS AMONG PLANT SPECIES 7EST AND THE ORGANIZATION OF PLANT COMMUNITIES 'RIME ET AL 6AN DER 0UTTEN ET AL "EVER 6AN DER 0UTTEN VAN DER (EIJDEN ET AL (OOPER ET AL +LIRONOMOS 3OIL COMMUNITIES ALTER COMPETITIVE OUTCOMES AMONG PLANTS THROUGH THEIR PATHOGENIC EFFECTS 6AN DER 0UTTEN AND -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
!3 4HORPE AND 2- #ALLAWAY
0ETERS BY FAVORING OBLIGATE MYCORRHIZAL SPECIES OVER NON MYCORRHIZAL OR FACULTATIVE MYCORRHIZAL SPECIES (ETRICK ET AL (ARTNETT ET AL AND BY TRANSFERRING RESOURCES AND lXED CARBON BETWEEN SPECIES #HIARELLO ET AL &RANCIS AND 2EAD 'RIME ET AL -OORA AND :OBEL 7ATKINS ET AL 3IMARD ET AL -ARLER ET AL BUT SEE 2OBINSON AND &ITTER "Y ALTERING THE BIOTIC AND ABIOTIC CHARACTERISTICS OF SOILS PLANTS CAN DRIVE POSITIVE OR NEGATIVE FEEDBACKS "OX AND THESE FEEDBACKS CAN PROFOUNDLY AFFECT PLANT POPULATIONS AND COMMUNITIES
"OX 0OSITIVE FEEDBACKS OCCUR WHEN PLANT SPECIES ACCUMULATE MICROBES THAT HAVE BENElCIAL EFFECTS ON THE PLANTS THAT CULTIVATE THEM SUCH AS MYCOR RHIZAL FUNGI AND NITROGEN lXERS 0OSITIVE FEEDBACKS PROMOTE SPECIES DOMINANCE AND ARE THOUGHT TO LEAD TO A LOSS OF LOCAL COMMUNITY DIVERSITY "EVER ET AL "EVER .EGATIVE FEEDBACKS OCCUR WHEN PLANT SPECIES ACCUMULATE PATHOGENIC MICROBES IN THEIR RHIZOSPHERES AND THESE INTERACTIONS OUTWEIGH THE BENElTS RECEIVED FROM MUTUALISTIC INTERACTIONS .EGATIVE FEEDBACKS CREATE CONDITIONS THAT ARE INCREASINGLY HOSTILE TO THE PLANTS THAT CULTIVATE THE PATHOGENS AND ARE THOUGHT TO PROMOTE COMMU NITY DIVERSITY 6AN DER 0UTTEN ET AL "EVER +LIRONOMOS
*IM "EVER "EVER ET AL PROPOSED THE FEEDBACK MODEL IN WHICH A PLANT OR POPULATION OF PLANTS ALTERS THE COMPOSITION OF THE SOIL COMMUNITY 4HIS CHANGE THEN FEEDS BACK TO AFFECT THE GROWTH AND SURVIVAL OF THE PLANT INDI VIDUAL OR POPULATION 4HIS MODEL DESCRIBES HOW TWO DIFFERENT TYPES OF FEEDBACK COULD BE ESTABLISHED POSITIVE FEEDBACK WHICH SHOULD OCCUR WHEN THE NEGATIVE EFFECTS OF SOIL PATHOGENS ARE OUTWEIGHED BY THE BENElCIAL EFFECTS OF MUTUALISTIC MYCORRHIZAE AND NEGATIVE FEEDBACK WHICH IS EXPECTED TO OCCUR EITHER WHEN THE EFFECTS OF PATHOGENS OUTWEIGH THE EFFECTS OF MYCORRHIZAE OR WHEN THE SOIL COMMU NITY ENHANCES THE GROWTH OF COMPETING PLANTS MORE THAN THAT OF THE ASSOCIATED PLANT "EVER "EVER ET AL "Y FAVORING THE LOCAL REPLACEMENT OF SPE CIES NEGATIVE FEEDBACK IS EXPECTED TO MAINTAIN SPECIES DIVERSITY WHEREAS POSITIVE FEEDBACK IS EXPECTED TO LEAD TO SPECIES DOMINANCE AND A DECREASE IN LOCAL SPECIES DIVERSITY "EVER "EVER ET AL 7ATKINSON ! GROWING BODY OF RESEARCH HAS DEMONSTRATED THAT PLANT SOIL FEEDBACKS CAN HAVE IMPORTANT ECO LOGICAL CONSEQUENCES "EVER ET AL 7ARDLE AND .ICHOLSON 7ESTOVER ET AL +LIRONOMOS &OR EXAMPLE IN A STUDY COMPARING FEEDBACK AND RELATIVE ABUNDANCE OF CO EXISTING OLD lELD SPECIES FROM SOUTHERN /NTARIO #ANADA +LIRONOMOS FOUND A STRONG POSITIVE RELATIONSHIP BETWEEN A PLANTS FEEDBACK WITH THE SOIL COMMUNITY AND ITS RELATIVE ABUNDANCE &IG
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
&IG 4HE RELATIONSHIP BETWEEN RELATIVE PLANT ABUNDANCE IN AN OLD lELD SITE AND SOIL FEEDBACK RESPONSE 3QUARES REPRESENT MEANS Y X X R 0 .UMBERS REPRESENT DIFFERENT PLANT SPECIES #AREX GARBERI #AREX AUREA #AREX GRANULARIS $AUCUS CAROTA !GROSTIS GIGANTEA 3OLIDAGO GRAMINIFOLIA 3OLIDAGO NEMORALIS !STER SIMPLEX !STER VIMINEUS !STER NOVAEANGLIAE #IRCIUM VULGARE #HENOPODIUM AMBROSIOIDES /ENOTHERA BIENNIS #AREX mAVA *UNCUS DUDLEYI 3OLIDAGO CANADENSIS ,INARIA VULGARIS #ICHORIUM INTYBUS #IRCIUM ARVENSE 3OLIDAGO RUGOSA 'EUM ALEPPICUM 3ATUREJA VULGARIS 0OTENTILLA RECTA #ORONILLA VARIA !SCLEPIAS SYRIACA !CHILLEA MILLEFOLIUM !POCYNUM CANNABINUM (YPERICUM PERFORATUM !GROSTIS SCABRA 0HLEUM PRATENSE 0OA COMPRESSA %CHIUM VULGARE #ENTAUREA JACEA 2UDBECKIA SEROTINA 0OA PRATENSIS $ACTYLIS GLOMERATA #ERASTIUM VULGATUM 'ALIUM PALUSTRE /ENOTHERA PERENNIS 0RUNELLA VULGARIS 4RIFOLIUM PRATENSE #ONVOLVULUS ARVENSIS 3ILENE CUCUBALUS %RIGERON STRIGOSUS !SPARAGUS OFlCINALIS (IERACIUM AURANTICUM %RIGERON PHILADELPHICUS 6ERONICA OFlCINALIS 0LANTAGO LANCEOLATA 'ALIUM MOLLUGO (IERACIUM PILOSELLA 6ICIA CRACCA (IERACIUM PRATENSE -EDICAGO LUPULINA 2ANUNCULUS ACRIS 4ARAXACUM OFlCINALE &RAGARIA VIRGINIANA #HRYSANTHEMUM LEUCANTHEMUM 4RAGOPOGON PRATENSIS "ROMUS INERMIS 0ANICUM LANUGINOSUM 2EPRINTED FROM +LIRONOMOS
0LANT SPECIES THAT WERE FOUND IN LOW ABUNDANCE IN THE lELD CONSISTENTLY DISPLAYED NEGATIVE FEEDBACK INTERACTIONS WHEREAS PLANTS WITH HIGH ABUNDANCE EITHER HAD LOW NEGATIVE OR POSITIVE FEEDBACK INTERACTIONS +LIRONOMOS
!3 4HORPE AND 2- #ALLAWAY
0LANT INVASIONS PROVIDE AN EXCEPTIONAL OPPORTUNITY FOR UNDERSTANDING HOW PLANTS AFFECT SOILS AND DRIVE FEEDBACK PROCESSES .UMEROUS STUDIES HAVE DOCU MENTED THE EFFECTS OF INVASIVE SPECIES ON THE COMPOSITION OF SOIL BIOTA "ELNAP AND 0HILLIPS +OURTEV ET AL AND SOIL MICROBIAL FUNCTION +OURTEV ET AL %HRENFELD (OWEVER MUCH LESS IS KNOWN ABOUT THE ROLE OF FEEDBACKS IN THE SUCCESS OF EXOTIC PLANTS &EEDBACKS MAY ALSO AFFECT EVOLUTION POTENTIALLY MOST APPARENT IN THE RAPID EVOLUTIONARY CHANGES THAT CAN ACCOMPANY EXOTIC INVASION 2ICE AND %MORY )F PLANT SOIL FEEDBACKS DRIVE VARIATION IN lTNESS DIFFERENCES AMONG INDIVIDUALS THEN ULTIMATELY FEEDBACK INTERACTIONS MAY BE UNDER SELECTIVE PRESSURE 6AN DER 0UTTEN 6AN "REEMAN AND &INZI "ASED ON THEORY DEVELOPED BY "EVER ET AL AND +LIRONOMOS WE HYPOTHESIZE THAT POSITIVE FEEDBACKS IN GENERAL ARE LIKELY TO LEAD THE PLANT COMMUNITY TO SHIFT TOWARDS A MONOCULTURE OF THE INVASIVE SPECIES (OWEVER WE PROPOSE THAT THE LONGEVITY OF POSITIVE FEEDBACK INTERACTIONS IN EVOLUTIONARY TIME MAY DEPEND ON WHETHER THE INVASIVE PLANT IS HAVING ITS STRONGEST EFFECTS ON THE PATHOGENIC OR THE NUTRIENT CYCLING COMPONENTS OF THE SOIL ECOSYSTEM &IG -ICROBES HAVE A SHORT GENERATION TIME AND THUS CAN RESPOND TO EVOLUTIONARY PRESSURES QUICKLY 4HEREFORE PATHOGENS MAY RESPOND RELATIVELY RAPIDLY TO THE INVASION OF NON NATIVE PLANTS 4HIS MAY ULTIMATELY LEAD TO GREATER COEXISTENCE AMONG SPECIES WHERE ALTHOUGH THE INVASIVE MAY STILL BE PRESENT IT WILL NOT BE THE OVER WHELMING COMMUNITY DOMINANT )N CONTRAST FEEDBACKS BETWEEN INVASIVE PLANTS AND NUTRIENT CYCLES MAY BE MUCH MORE LIKELY TO PERSIST 7HEN THE BIOTIC COMPONENT OF THE SOIL NUTRIENT CYCLES IS INVOLVED IT IS EXPECTED THAT THERE WOULD BE A SHIFT IN THE MICROBIAL COMMUNITY TO POPULA TIONS THAT ARE BETTER ADAPTED TO THE NEW NUTRIENT STATUS OF THE ECOSYSTEM &IG !TLAS AND "ARTHA 3CHIMEL AND "ENNETT )N THE CASE OF ALTERATIONS TO ABIOTIC COMPONENTS OF THE SOIL ECOSYSTEM THERE IS NO DIRECT SELECTIVE PRESSURE TO STIMULATE ADAPTATION &IG (ERE WE DISCUSS INTERACTIONS BETWEEN INVASIVE SPECIES AND THE SOIL ECOSYSTEM PATHOGENIC AND NUTRIENT CYCLING COMPONENTS THE MECHANISMS FOR THESE INTER ACTIONS AND EVIDENCE THAT THESE INTERACTIONS HAVE VERY DIFFERENT EFFECTS ON THE SURVIVAL OF INVASIVE VERSUS NATIVE SPECIES
).6!3)6% 0,!.43 !.$ 3/), 0!4(/'%.3 /NE OF THE LEADING HYPOTHESES FOR THE REMARKABLE SUCCESS OF SOME EXOTIC SPECIES IS THAT THEY HAVE ESCAPED THE SPECIALIST ENEMIES THAT CONTROL THEM IN THEIR NATIVE RANGES +EANE AND #RAWLEY %MBEDDED WITHIN THIS HYPOTHESIS IS THE IDEA THAT IF MICROBIAL PATHOGENS LIMIT THE GROWTH OF INVASIVE PLANTS IN THEIR NATIVE RANGE THERE WILL BE NEGATIVE FEEDBACKS BETWEEN THE SOIL MICROBIAL COMMUNITY AND THE PLANT IN THE NATIVE RANGE DUE TO THE ACCUMULATION OF SPECIES SPECIlC SOIL PATHOGENS +LIRONOMOS -ITCHELL AND 0OWER #ALLAWAY ET AL )N CONTRAST POSITIVE FEEDBACKS MAY OCCUR IN THE INVADED RANGE WHERE EXOTIC
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
&IG
!3 4HORPE AND 2- #ALLAWAY
SPECIES ARE LARGELY FREE FROM SPECIES SPECIlC SOIL PATHOGENS BUT CAN STILL INTERACT WITH LESS HOST SPECIlC MUTUALISTS SUCH AS MYCORRHIZAL FUNGI AND BACTERIA THAT DRIVE NUTRIENT CYCLES )N THIS SECTION lRST WE WILL DESCRIBE THE EVIDENCE THAT INVASIVE SPECIES HAVE ESCAPED PRESSURE FROM SOIL PATHOGENS AND THE POTENTIAL FEEDBACK EFFECTS ON THE lTNESS OF INVASIVE SPECIES 3ECOND WE WILL DISCUSS THE IMPLICATIONS OF THIS TYPE OF FEEDBACK FOR ECOSYSTEM STABILITY $O INVASIVE SPECIES BENEFIT FROM ESCAPING SOIL PATHOGENS
)N A REVIEW OF SPECIES THAT WERE NATURALIZED IN THE 5NITED 3TATES -ITCHELL AND 0OWER FOUND THAT FEWER FUNGI AND FEWER VIRUS SPECIES INFECTED THE PLANT SPECIES IN THEIR INVADED RANGES COMPARED TO THEIR NATIVE RANGES &URTHERMORE THEY REPORTED THAT SPECIES THAT EXPERIENCED GREATER RELEASE FROM MICROBIAL PATHOGENS WERE MORE INVASIVE -ITCHELL AND 0OWER (OWEVER THE RELATIONSHIPS WERE RELATIVELY WEAK PARTICULARLY FOR INVADERS OF NATURAL AREAS SOIL PATHOGENS WERE NOT DISTINGUISHED FROM OTHER PATHOGENS AND THE PRESENCE OR ABUNDANCE OF PATHOGENS DOES NOT NECESSARILY CORRELATE WITH THE STRENGTH OF THEIR EFFECTS -ORE RECENTLY EXPERIMENTS USING SOILS FROM NATIVE AND INVADED RANGES HAVE SUGGESTED THAT SOME INVASIVE SPECIES HAVE ESCAPED FROM SOIL PATHOGENS )F INVASIVE SPECIES SUFFER FROM THE EFFECTS OF SOIL PATHOGENS IN THEIR NATIVE SOILS THEN STERIL IZATION OF NATIVE SOILS SHOULD RESULT IN AN INCREASE IN THE GROWTH OF THE INVASIVE )N CONTRAST IN INVADED SOILS THE INVASIVE SHOULD BE RELATIVELY FREE FROM PATHOGENS BUT MAY BENElT FROM LESS HOST SPECIlC MUTUALISTIC MICROBES )F SO STERILIZATION OF INVADED SOILS SHOULD RESULT IN A NEUTRAL TO NEGATIVE EFFECT ON THE INVASIVE SPE CIES 4HESE INTERACTIONS HAVE BEEN EXPLORED FOR 0RUNUS SEROTINA BLACK CHERRY #ENTAUREA MACULOSA SPOTTED KNAPWEED AND TWO !CER MAPLE SPECIES 2EINHART ET AL COMPARED THE EFFECTS OF SOIL MICROBES ON THE GROWTH OF 0RUNUS SEROTINA IN BOTH ITS NATIVE AND INVADED RANGES )N ITS NATIVE .ORTH !MERICAN RANGE THE SOIL MICROBIAL COMMUNITY OCCURRING NEAR 0 SEROTINA STRONGLY INHIBITED THE ESTABLISHMENT OF NEIGHBORING CONSPECIlCS AND REDUCED SEEDLING PERFORMANCE IN THE GREENHOUSE )N CONTRAST IN ITS NON NATIVE %UROPEAN RANGE 0 SEROTINA READILY ESTABLISHES IN CLOSE PROXIMITY TO CONSPECIlCS AND SOIL MICROBIAL COMMUNITIES ENHANCE THE GROWTH OF SEEDLINGS 0REVIOUS RESEARCH IN THE NATIVE RANGE OF 0 SEROTINA DEMONSTRATED THAT SOIL BORNE 0YTHIUM SPECIES /OMYCOTA INHIBIT THE SURVIVAL GROWTH AND ABUNDANCE OF 0 SEROTINA 0ACKER AND #LAY !LTHOUGH THE GENUS 0YTHIUM IS FOUND AROUND THE WORLD GENOTYPES ARE OFTEN HOST SPECIlC $EACON AND $ONALDSON -ILLS AND "EVER 4HUS IN THE NATIVE RANGE 0 SEROTINA EXPERIENCES NEGATIVE PLANT SOIL FEEDBACK INTERACTIONS LIKELY DUE TO THE NEGATIVE EFFECTS OF 0YTHIUM )N CONTRAST IN THE INVADED REGION 0 SEROTINA EXPERIENCES POSITIVE FEEDBACKS DUE TO ESCAPE FROM ITS MAIN NATURAL ENEMY 2EINHART ET AL
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
#ENTAUREA MACULOSA IS ONE OF WESTERN .ORTH !MERICAS WORST INVASIVE WEEDS )N SEVERAL EXPERIMENTS #ALLAWAY ET AL HAVE COMPARED THE EFFECTS OF SOIL MICROBES FROM THE NATIVE RANGE IN %UROPE TO THE EFFECTS OF SOIL MICROBES COLLECTED FROM INVASIVE POPULATIONS IN THE NORTHWESTERN 5NITED 3TATES %UROPEAN SOIL BIOTA HAD MUCH STRONGER INHIBITORY EFFECTS ON # MACULOSA THAN .ORTH !MERICAN SOIL BIOTA 3TERILIZATION OF %UROPEAN SOILS CAUSED ON AVERAGE A INCREASE IN THE TOTAL BIOMASS OF # MACULOSA SUGGESTING A RELEASE FROM PATHOGENIC MICROBES )N CONTRAST STERILIZING INVADED .ORTH !MERICAN SOILS LED AT MOST TO A SLIGHT INCREASE IN TOTAL BIOMASS OF &OR MOST .ORTH !MERICAN SOILS STERILIZATION LED TO A DECREASE IN GROWTH OF SUGGESTING THAT # MACULOSA HAD BENElTED FROM MUTUALISTIC SOIL MICROBES 4HESE RESULTS SUPPORT -ITCHELL AND 0OWERS CON CLUSION THAT INVASIVE SPECIES SHOULD SUFFER MUCH HIGHER FUNGAL AND VIRAL INFECTION IN THEIR HOME RANGES COMPARED TO INVADED RANGES 4HEY ALSO SUGGEST THAT IN SOME CASES MUTUALISMS MAY BE MORE BENElCIAL IN NON NATIVE RANGES BECAUSE THE NEGA TIVE EFFECT OF NATURAL ENEMIES DO NOT ATTENUATE THE POSITIVE EFFECT OF MUTUALISTS -UTUALISTS HAVE ALSO BEEN FOUND TO PLAY AN IMPORTANT ROLE IN THE PLANT SOIL FEEDBACK INTERACTIONS OF TWO !CER SPECIES 2EINHART AND #ALLAWAY )N THE lELD DISTANCES BETWEEN !CER CONSPECIlCS WERE LESS IN THEIR INVADED RANGES THAN IN THEIR NATIVE RANGES )N A GREENHOUSE EXPERIMENT THE EFFECT OF SOIL MICROBIAL COMMUNITIES ALSO DIFFERED BETWEEN NATIVE AND INVADED RANGES 2ELATIVE TO STERILIZED CONTROLS SOIL ASSOCIATED WITH BOTH CONSPECIlCS AND HET EROSPECIlCS FROM THE NATIVE RANGE DECREASED THE TOTAL BIOMASS OF !CER SEEDLINGS BY SUGGESTING INHIBITION BY PATHOGENIC MICROBES )N THE INVADED RANGE SOIL ASSOCIATED WITH CONSPECIlCS DECREASED THE BIOMASS OF !CER SEEDLINGS BY AN EVEN GREATER MAGNITUDE (OWEVER SOIL ASSOCIATED WITH HETEROSPECIlCS IN THE NON NATIVE RANGES INCREASED BIOMASS OF !CER SEEDLINGS BY 4HUS WHILE !CERS ACCUMULATE PATHOGENS IN THEIR INVADED RANGE THE SURROUNDING SOIL IS RELATIVELY FREE FROM INHIBITORY MICROBES POTENTIALLY ENHANCING INVASION BY THESE TREES 4HUS THERE IS EVIDENCE THAT NOT ONLY DO INVASIVE SPECIES ESCAPE THE NEGA TIVE EFFECTS OF SOIL PATHOGENS IN THEIR INVADED RANGES BUT THAT POTENTIALLY DUE TO THE EFFECTS OF MUTUALISTS FEEDBACK EFFECTS IN INVADED RANGES ARE OFTEN POSITIVE .EXT WE WILL EXPLORE THE POTENTIAL FOR THESE FEEDBACK EFFECTS TO AFFECT COMMUNITY STABILITY 7ILL ESCAPE FROM NEGATIVE FEEDBACKS FROM SOIL PATHOGENS PERSIST
4HE EXPERIMENTS DESCRIBED ABOVE INDICATE THAT INVASIVE SPECIES ARE LIKELY TO EXPE RIENCE POSITIVE FEEDBACK IN THEIR INVADED HABITAT BECAUSE THEY ESCAPE SPECIALIST SOIL PATHOGENS AT HOME BUT CAN UTILIZE GENERALIST MUTUALISTS WHERE THEY INVADE 7HAT REMAINS TO BE DETERMINED IS HOW THIS FEEDBACK AFFECTS COMMUNITY DYNAMICS 0LANTS PARTICIPATING IN STRONG POSITIVE FEEDBACKS WITH SOIL BIOTA ARE MORE LIKELY TO BECOME COMMUNITY DOMINANTS THAN THOSE THAT DO NOT 4HE MOST COMPLETE STUDY OF THESE INTERACTIONS WAS DONE BY +LIRONOMOS WHO EXPLORED FEEDBACK
!3 4HORPE AND 2- #ALLAWAY
INTERACTIONS AMONG PLANT SPECIES AND SOIL MICROBIAL COMMUNITIES IN GRASSLANDS IN EASTERN .ORTH !MERICA )N EXPERIMENTS USING ONLY THE MYCORRHIZAL FRACTION OF THE MICROBIAL COMMUNITY HE FOUND THAT THE ORIGIN OF THE lLTRATE FROM SOILS IN WHICH THE SAME SPECIES OR A DIFFERENT SPECIES HAD PREVIOUSLY BEEN GROWN DID NOT ALTER THE RESPONSE EITHER POSITIVE OR NEUTRAL TO MYCORRHIZAL FUNGI )N CONTRAST IN EXPERIMENTS USING ONLY THE PATHOGENICSAPROBIC FRACTIONS THE RARE NATIVE SPECIES EXPERIENCED NEGATIVE FEEDBACKS WHEN THE FRACTIONS WERE FROM SOILS THAT HAD PREVIOUSLY GROWN THE SAME SPECIES (OWEVER THE ORIGIN OF THE PATHOGENIC SAPROBIC FRACTION HAD NO EFFECT ON THE GROWTH OF INVASIVE SPECIES /VERALL RELA TIVELY RARE NATIVE SPECIES CONSISTENTLY EXHIBITED NEGATIVE FEEDBACK INTERACTIONS WITH THE SOIL MICROBIAL COMMUNITY A RELATIVE DECREASE IN GROWTH ON @HOME SOIL IN WHICH CONSPECIlCS HAD PREVIOUSLY BEEN GROWN WHEREAS INVASIVE SPE CIES CONSISTENTLY EXHIBITED POSITIVE FEEDBACK INTERACTIONS WITH THE SOIL COMMU NITY 3IMILARLY !GRAWAL ET AL FOUND THAT INTRODUCED PLANTS WERE SUBJECT TO HALF THE NEGATIVE SOIL FEEDBACK AS CONGENERIC SPECIES (OW LONG IN TERMS OF EVOLUTIONARY TIME SCALES SUCH POSITIVE INTERACTIONS WILL BE MAINTAINED REMAINS AN UNKNOWN 4HE BASIC NATURE OF MICROBES SUGGESTS THAT THEY WILL BE ABLE TO RESPOND RELA TIVELY QUICKLY TO PRESSURES EXERTED BY INVASION BY EXOTIC PLANTS !S DISCUSSED ABOVE SOIL BORNE PATHOGENS CAN BE RELATIVELY HOST SPECIlC .EERGAARD +IRKPATRICK AND "AZZAZ !GARWAL AND 3INCLAIR -ILLS AND "EVER (OWEVER MANY SOIL BORNE PATHOGENS ARE GENERALISTS $IX AND 7EBSTER &OR EXAMPLE "LANEY AND +OTANEN FOUND THAT SEED GERMINATION OF CONGENERIC PAIRS OF INVASIVE AND NATIVE PLANT SPECIES FROM WESTERN /NTARIO DIS PLAYED A SIMILAR POSITIVE RESPONSE TO THE APPLICATION OF FUNGICIDE SUGGESTING NON SPECIES SPECIlCITY OF FUNGAL SEED PATHOGENS IN THEIR SYSTEM &URTHERMORE MICROBES HAVE A SHORT GENERATION TIME AND THUS CAN RESPOND TO EVOLUTIONARY PRESSURES WITHIN A SHORT TIMEFRAME 4HUS PATHOGENIC MICROBES MAY BE ABLE TO RAPIDLY SWITCH TO A NEW INVASIVE HOST 3CLEROTINIA SCLEROTIORUM A FUNGUS NATIVE TO INTERMOUNTAIN PRAIRIES INVADED BY # MACULOSA HAS BEEN FOUND TO DAMAGE # MACULOSA WHEN APPLIED TO THE RHIZOSPHERES AT HIGH CONCENTRATIONS *ACOBS ET AL 2IDENOUR AND #ALLAWAY !S DESCRIBED ABOVE 2EINHART AND #ALLAWAY FOUND THAT WHILE THE SOIL COMMUNITY ASSOCIATED WITH OTHER TREE SPECIES HAD A POSITIVE EFFECT ON THE GROWTH OF INVASIVE !CERS SOILS ASSOCIATED WITH CONSPECIlCS HAD A NEGATIVE EFFECT 4HIS SUGGESTS THAT THE PATHOGENIC SOIL MICROBIAL COMMUNITY MAY HAVE BEEN ABLE TO ADAPT TO THIS NEW HOST AND ACCUMULATION OF SOIL PATHOGENS EVENTUALLY SUPPRESSES THE OFFSPRING OF !CER RECRUITS )N SUMMARY SOME INVASIVE SPECIES APPEAR TO HAVE ESCAPED PRESSURE FROM SOIL PATHOGENS AND THUS BENElT FROM POSITIVE FEEDBACK INTERACTIONS WITH THE SOIL BIOTA WHERE THEY INVADE !LTHOUGH NOT YET EXPLICITLY ADDRESSED IN THE LITERATURE MICRO BIAL COMMUNITIES MAY CHANGE OVER TIME AND THUS BREAK DOWN POSITIVE PLANT SOIL MICROBIAL FEEDBACKS )F THIS OCCURS THE ABUNDANCE OF THE INVASIVE SPECIES SHOULD DECREASE AND THE COMMUNITY SHOULD MOVE TO A POINT WHERE NEGATIVE FEEDBACK INTERACTIONS RESTRICT THE INVASIVES DOMINANCE 4HIS WAS ORIGINALLY SUGGESTED BY
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
+LIRONOMOS WHO OBSERVED THAT PLANT SPECIlC PATHOGEN LOADS ARE MAXI MIZED UNDER HIGH POPULATION DENSITIES PARTICULARLY MONOCULTURES SUCH AS THOSE CREATED BY SOME INVASIVE SPECIES AND WILL EVENTUALLY RESULT IN NEGATIVE FEEDBACK ON ABUNDANT PLANTS .EXT WE CONSIDER HOW FEEDBACKS DRIVEN BY MICROBES IN NUTRI ENT CYCLES MIGHT RESPOND DIFFERENTLY OVER EVOLUTIONARY TIME THAN FEEDBACKS DRIVEN BY SOIL PATHOGENS
).6!3)6% 0,!.43 !.$ 3/), .542)%.4 #9#,).' )N GENERAL PLANT SOIL FEEDBACKS ARE THOUGHT TO BE DETERMINED BY THE DIRECT EFFECTS OF PATHOGENS AND MUTUALISTS "EVER -ILLS AND "EVER 0ACKER AND #LAY "EVER +LIRONOMOS BUT OTHER COMPONENTS OF THE SOIL ECOSYSTEM MAY PARTICIPATE IN FEEDBACKS )N PARTICULAR INDIVIDUAL PLANT CHARACTERISTICS SUCH AS PHENOLOGY NUTRIENT UPTAKE LITTER FALL TISSUE CHEMICAL COMPOSITION AND ASSOCI ATION WITH SYMBIOTIC MICROBES CAN HAVE SIGNIlCANT EFFECTS ON SOIL NUTRIENT CYCLES (OBBIE !NGERS AND #ARON "ERENDSE "INKLEY AND 'IARDINA .ORTHRUP ET AL 3CHLESINGER AND 0ILMANIS 6AN "REEMEN 7ARDLE ET AL #HEN AND 3TARK %ATON AND &ARRELL WHICH MAY IN TURN ALTER THE GROWTH AND SURVIVAL OF THE SPECIES THAT DRIVE THESE EFFECTS "ECAUSE THEY ARE NOVEL MAY HAVE DIFFERENT BIOCHEMICAL CONSTITUENTS "AIS ET AL 6IVANCO ET AL AND ARE OFTEN DOMINANT COMPONENTS OF PLANT COMMUNITIES INVASIVE PLANTS CAN HAVE UNUSUALLY STRONG EFFECTS ON SOIL NUTRIENT CYCLES 6ITOUSEK 6ITOUSEK ET AL 6ITOUSEK $!NTONIO AND 6ITOUSEK %HRENFELD ET AL %HRENFELD AND 3COTT %HRENFELD )N THE PREVIOUS SECTION WE SHOWED THAT MANY INVASIVE SPECIES EXHIBIT POSITIVE FEEDBACKS AFTER ESCAPING SOIL PATHOGENS AND THEN SPECULATED THAT THESE FEEDBACKS MAY EVENTUALLY BECOME NEUTRAL OR NEGATIVE AS GENERALIST PATHOGENS SWITCH TO THE HOST OR SPECIALISTS ADAPT )N CONTRAST TO THIS SCENARIO IN WHICH INVASIVE DOMINANCE MAY FADE POSITIVE FEEDBACKS BETWEEN INVASIVE PLANTS AND SOIL NUTRIENT CYCLES MAY LEAD TO MUCH LONGER TIME PERIODS OF INVASIVE DOMINANCE .UTRITIONAL CONSTRAINTS MAY LEAD TO SIGNIlCANT SHIFTS IN MICROBIAL COMMUNITIES RESULTING IN LONG TERM CHANGES IN NUTRIENT POOLS AND CYCLING RATES 4HESE CHANGES MAY ALSO OCCUR DUE TO THE INTRODUCTION OF NOVEL PLANT MICROBE INTERACTIONS SUCH AS SYMBIOTIC NITROGEN lXATION 3IMILARLY THE DIRECT EFFECTS OF INVASIVE PLANTS ON SOIL NUTRIENTS MAY BE PARTICULARLY LONG LIVED BECAUSE THERE IS NO MEDIATION BY ANOTHER ORGANISM WITH THE POTENTIAL TO EVOLVE )N THIS SECTION WE BRIEmY REVIEW THE MECHANISMS BY WHICH INVASIVE SPE CIES MAY ALTER SOIL NUTRIENT CYCLES AND ILLUSTRATE THE POTENTIAL FOR LONG LIVED POSITIVE FEEDBACK INTERACTIONS BY DESCRIBING THE INTERACTIONS OF "ROMUS TECTORUM CHEATGRASS DOWNY BROME AND -YRICA FAYA lRE TREE WITH SOIL NUTRIENT CYCLES IN INVADED COMMUNITIES IN THE WESTERN 5NITED 3TATES AND (AWAII
!3 4HORPE AND 2- #ALLAWAY
4HE EFFECTS OF INVASIVE SPECIES ON NUTRIENT CYCLES
4HERE ARE MANY MECHANISMS BY WHICH INVASIVE SPECIES MAY ALTER SOIL NUTRIENT CYCLES SEE REVIEW BY %HRENFELD 4HROUGH CHANGES IN LITTER PRODUCTION AND QUALITY INVASIVE PLANTS MAY INCREASE %HRENFELD ET AL -ACK ET AL OR DECREASE 3AGGAR ET AL %HRENFELD ET AL %VANS ET AL MICROBI ALLY MEDIATED DECOMPOSITION ANDOR MINERALIZATION RATES &OR EXAMPLE LITTER OF -ICROSTEGIUM VIMINEUM AN EXOTIC # GRASS THAT HAS INVADED %ASTERN DECIDUOUS FORESTS HAS A HIGHER #. RATIO DECOMPOSES SLOWER AND IMMOBILIZES MORE . THAN LITTER FROM UNINVADED FORESTS %HRENFELD ET AL )NVASIVE SPECIES MAY ALSO ALTER THE INPUT OF NITROGEN BY NITROGEN lXING BACTERIA .EARLY OF THE INVASIVE SPECIES LISTED BY THE 53 $EPARTMENT OF !GRICULTURE ARE IN THE &ABACEAE FAMILY %HRENFELD AND CHANGES IN ECOSYSTEM NITROGEN AVAILABILITY DUE TO ASSOCIATION OF INVASIVE PLANTS WITH SYMBIOTIC NITROGEN lXING BACTERIA HAVE BEEN DOCUMENTED IN SEVERAL ECOSYSTEMS 6ERSFELD AND VAN 7ILGREN 6ITOUSEK ET AL 3TOCK ET AL 9ELENIK ET AL &URTHERMORE CHANGES IN LITTER QUALITY FROM N ON NITROGEN lXING INVADERS MAY ALTER THE ABUN
DANCE AND ACTIVITY OF NON SYMBIOTIC NITROGEN lXING BACTERIA AS FOUND IN (AWAIIAN FORESTS INVADED BY !FRICAN GRASSES ,EY AND $!NTONIO )NVASIVE SPECIES MAY AFFECT SOIL NUTRIENT CYCLES THROUGH THE PRODUCTION OF SECONDARY CHEMICALS 2OOTS OF #ENTAUREA MACULOSA EXUDE THE POLYPHENOL ¢ CATECHIN #ATECHIN DISPLAYS STRONG ANTIMICROBIAL PROPERTIES FOR AT LEAST SOME GROUPS OF BACTERIA "AIS ET AL AND APPEARS TO AFFECT AT LEAST SOME ASPECTS OF THE SOIL NITROGEN CYCLE ! 4HORPE UNPUBLISHED DATA &URTHERMORE BY CHELATING METAL PHOSPHORUS COMPLEXES CATECHIN MAY INCREASE PHOSPHORUS AVAILABILITY IN PHOSPHORUS LIMITED SOILS 4HORPE ET AL IN PRESS 3TEVENSON AND #OLE !N ALLELOCHEMICAL PRODUCED BY #ENTAUREA DIFFU SA HYDROXYQUINOLINE MAY ALSO ALTER NUTRIENT CYCLING THROUGH ANTIMICRO BIAL 6IVANCO ET AL AND CHELATION 4HE -ERCK )NDEX PROPERTIES 4HE DRY MASS OF LEAVES OF -ELALEUCA SPP PAPERBARK WHICH HAS INVADED LARGE AREAS OF THE COASTAL SOUTHEAST 5NITED 3TATES PARTICULARLY THE %VERGLADES IS UP TO MONOTERPENES "OON AND *OHNSTONE 4HESE COMPOUNDS INHIBIT MICRO BIAL COLONIZATION AND DECOMPOSITION OF LEAF LITTER IN BOTH THE NATIVE AND INVADED RANGES OF -ELALEUCA SPP "OONE AND *OHNSTONE )T HAS ALSO BEEN SUGGESTED THAT ALLELOPATHIC CHEMICALS RELEASED BY SOME INVASIVE SPECIES MAY ALTER NITROGEN lXATION IN NEIGHBORING PLANTS 7ARDLE ET AL -ANY OTHER INVASIVE SPECIES PRODUCE CHEMICALS WITH ANTIMICROBIAL ACTIVITY 2ICE %HRENFELD HOWEVER THE ROLE OF THESE CHEMICALS IN THE PLANTS INVASIVE SUCCESS IS GENERALLY UNKNOWN )N SUM THERE IS GOOD EVIDENCE THAT BY INTRODUCING A NOVEL CHARACTERISTIC EG A HIGHER #. RATIO ASSOCIATION WITH NITROGEN lXING BACTERIA OR EXUDATION OF AN ANTI MICROBIAL CHEMICAL INVASIVE SPECIES CAN ALTER SOIL NUTRIENT CYCLES IN INVADED COMMUNITIES !LTHOUGH EXPLICIT STUDIES OF THE RAMIlCATIONS OF SUCH ALTERATION OF NUTRIENT CYCLES ARE RARE THESE EFFECTS MAY ULTIMATELY FEEDBACK TO
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
THE PLANTS THAT CAUSE THEM AND AFFECT THE ORGANIZATION OF PLANT COMMUNITIES 4WO DIFFERENT SPECIES "ROMUS TECTORUM AND -YRICA FAYA PROVIDE EXCELLENT EXAM PLES OF HOW INVASIVE PLANTS MAY AFFECT THE SOIL AND HOW SOIL CHANGES AFFECT THE SURVIVAL OF INVASIVE AND NATIVE SPECIES 4HESE STUDIES ALSO ILLUSTRATE HOW POSITIVE FEEDBACKS BETWEEN INVASIVE PLANTS AND SOIL NUTRIENT CYCLES MAY PERSIST IN AN ECOSYSTEM 4HE EFFECTS OF "ROMUS TECTORUM ON SOIL NUTRIENT CYCLES
"ROMUS TECTORUM IS AN ANNUAL OCCASIONALLY BIENNIAL %URASIAN GRASS THAT HAS INVADED OVER MILLION HA IN THE )NTERMOUNTAIN 7EST OF .ORTH !MERICA 9PSILANTIS 4HE EFFECTS OF " TECTORUM ON NUTRIENT CYCLES DIFFER IN lRE PRONE AND NON lRE PRONE SYSTEMS "ROMUS TECTORUM TENDS TO GERMINATE AND COMPLETE ITS LIFE CYCLE EARLIER THAN MOST NATIVE SPECIES IN THE SYSTEMS IT INVADES AND ITS DEAD DRY STEMS CREATE AN UNUSU ALLY LARGE FUEL LOAD IN THE SUMMER (ARRIS -ACK 5PADHYAYA ET AL 9PSILANTIS )N lRE PRONE SAGEBRUSH GRASSLAND ECOSYSTEMS lRE RECUR RENCE INTERVALS DECREASE FROM YEARS TO YEARS -ACK 5PADHYAYA ET AL 9PSILANTIS 3INCE " TECTORUM GERMINATES EARLIER AND GROWS FASTER THAN MOST NATIVE SPECIES (ARRIS -ACK 5PADHYAYA ET AL 9PSILANTIS THIS INVADER APPEARS TO TAKE BETTER ADVANTAGE OF THE POST lRE mUSH OF NITROGEN THAN NATIVE SPECIES ,OWE ET AL %ARLY NITROGEN UPTAKE BY " TECTORUM REDUCES TOTAL SOIL NITROGEN AND CREATES HIGHER SOIL CARBON TO NITROGEN RATIOS THAN NATIVE VEGETATION "LANK ET AL (ALVORSON ET AL "ROMUS TECTORUM MAY ALSO LIMIT NITROGEN AVAILABILITY BY SHADING BIOLOGICAL SOIL CRUSTS THAT lX NITROGEN 9PSILANTIS )N ECOSYSTEMS THAT LACK lRE THERE ARE VERY DIFFERENT INTERACTIONS BETWEEN " TECTORUM AND THE SOIL ECOSYSTEM 'RASSLAND COMMUNITIES IN 5TAH INVADED BY " TECTORUM HAVE HIGHER LEVELS OF EXCHANGEABLE POTASSIUM AND RATIOS OF POTAS SIUM OR PHOSPHORUS TO CALCIUM CARBONATE AND MAGNESIUM OR IRON OXIDES THAN UNINVADED SOILS "ELNAP AND 0HILLIPS "ELNAP ET AL )T IS UNKNOWN WHETHER THESE NUTRIENT DIFFERENCES ARE DUE TO " TECTORUM INVASION OR IF " TECTORUM PREFERENTIALLY INVADES SITES WITH THESE CHARACTERISTICS HOWEVER IT IS CLEAR THAT " TECTORUM CAN DRAMATICALLY ALTER PHOSPHORUS CYCLING IN I NVADED SOILS !LTHOUGH THERE IS NO NET CHANGE IN TOTAL SOIL PHOSPHORUS POOLS " TECTORUM APPEARS TO ACCESS FORMS OF 0 THAT ARE RECALCITRANT AND UNAVAILABLE TO NATIVES WHICH INCREASES LEVELS OF LABILE PHOSPHORUS 2, 3ANFORD PERSONAL COMMUNICATION "Y ALTERING THE BIOTIC AND ABIOTIC COMPONENTS OF NUTRIENT CYCLES " TECTORUM ALTERS NUTRIENT AVAILABILITY IN WAYS THAT ULTIMATELY FEEDBACK TO INCREASE ITS OWN SURVIVAL RELATIVE TO NATIVE SPECIES "ELNAP AND 0HILLIPS %VANS ET AL "Y ALTERING FUNDAMENTAL ECOSYSTEM CHARACTERISTICS THESE EFFECTS MAY SIGNIlCANTLY ALTER PLANT COMMUNITY STRUCTURE AND DYNAMICS
!3 4HORPE AND 2- #ALLAWAY
4HE EFFECTS OF -YRICA FAYA ON SOIL NUTRIENT CYCLES
)NVASION OF (AWAIIAN ECOSYSTEMS BY THE NITROGEN lXING TREE -YRICA FAYA 'ERRISH AND -UELLER $OMBOIS 6ITOUSEK 6ITOUSEK AND 7ALKER !PLET (UGHES ET AL PROVIDES AN EXAMPLE OF HOW ECOSYSTEM SCALE CHANGES MAY RESULT IN hINVASIONAL MELTDOWNv "OX 3IMBERLOFF AND VAN (OLLE 4HE VOLCANIC SOILS OF (AWAII ARE USUALLY NITROGEN LIMITED 6ITOUSEK 6ITOUSEK AND 7ALKER 4HERE ARE NO NATIVE NITROGEN lXING PLANTS THAT COLONIZE EARLY SUCCESSIONAL HABITATS IN THESE SYSTEMS 6ITOUSEK 6ITOUSEK AND 7ALKER AND INVASION BY - FAYA INTRODUCES A NOVEL ECOSYSTEM PROCESS THAT RESULTS IN SUBSTANTIAL INCREASES IN SOIL NITROGEN 6ITOUSEK 6ITOUSEK AND 7ALKER -OST SUCCESSFUL INVASIONS IN (AWAII HAVE OCCURRED ON SOILS THAT ARE RELATIVELY FERTILE 'ERRISH AND -UELLER $OMBOIS AND THE NITROGEN FERTILIZATION THAT RESULTS FROM INVASION BY - FAYA MAY FACILITATE INVASION BY OTHER SPECIES WITH HIGHER NITROGEN REQUIREMENTS &OR EXAMPLE ANOTHER INVASIVE TREE 0SIDIUM CATTLEIANUM STRAWBERRY GUAVA GREW MUCH LARGER WHEN GROWN IN SOIL FROM UNDER - FAYA THAN FROM SOIL COLLECTED UNDER THE NATIVE -ETROSIDEROS POLY MORPHA {/HI{A LEHUA (UGHES ET AL -YRICA FAYA ALSO ENHANCES POPULATIONS OF EXOTIC EARTHWORMS WHICH INCREASE NITROGEN BURIAL AND FURTHER ALTER NUTRIENT CYCLING !PLET 4HUS INVASION BY - FAYA RESULTS IN POSITIVE FEEDBACKS THAT NOT ONLY ENHANCE THE INVASION OF THIS SPECIES BUT PROMOTE INVASION BY OTHER INVASIVE SPECIES AND LEAD TO FUNDAMENTAL ECOSYSTEM CHANGES
"OX )N 3IMBERLOFF AND VAN (OLLE INTRODUCED THE CONCEPT OF hINVASIONAL MELTDOWNv $URING THIS PROCESS INVASION BY ONE EXOTIC SPECIES PROMOTES INVASION BY OTHER EXOTIC SPECIES 4HESE SPECIES INTERACT SYNERGISTICALLY CAUSING ECOSYSTEM SCALE CHANGES SUCH AS MORE FREQUENT lRE CYCLES OR MORE RAPID NITROGEN CYCLING THROUGH INCREASED NITROGEN lXATION THAT ULTIMATELY RESULT IN THE COLLAPSE OF NATIVE ECOSYSTEMS
7ILL POSITIVE FEEDBACKS BETWEEN INVASIVE PLANTS AND SOIL NUTRIENT CYCLES PERSIST
!S DESCRIBED ABOVE SINCE INVASIVE PLANTS OFTEN DIFFER FROM NATIVE SPECIES IN CHARACTERISTICS SUCH AS PHENOLOGY NUTRIENT UPTAKE LITTER FALL TISSUE CHEMICAL COMPOSITION AND ASSOCIATION WITH SYMBIOTIC MICROBES THEY CAN HAVE SIGNIlCANT EFFECTS ON SOIL NUTRIENT CYCLES 3IMILAR EFFECTS ARE OFTEN SEEN DURING SUCCESSION "ERENDSE 3CHIMEL AND "ENNETT 7E SPECULATE THAT IN CONTRAST TO OUR PREDICTIONS FOR EVOLUTIONARY CHANGE FOR INTERACTIONS BETWEEN INVASIVE PLANTS
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
AND SOIL PATHOGENS POSITIVE FEEDBACKS BETWEEN INVASIVE PLANTS AND SOIL NUTRIENT CYCLES ARE MORE LIKELY TO RESULT IN LONG TERM SHIFTS IN COMMUNITY COMPOSITION THAT RESEMBLE SUCCESSION 4HESE CHANGES MAY PROVIDE EXAMPLES OF INVASIONAL MELT DOWN 3IMBERLOFF AND 6ON (OLLE 7E KNOW OF NO EXAMPLES WHERE DURING SUCCESSION CHARACTERISTICS OF THE SOIL ECOSYSTEM REVERT BACK TO THOSE RESEMBLING THE INITIAL CHARACTERISTICS AFTER DISTUR BANCE 7HAT LITTLE IS KNOWN ABOUT THE BIOTIC COMPONENTS OF THE SOIL ECOSYSTEM DURING SUCCESSION INDICATES THAT CHANGE IN THE MICROBIAL COMMUNITY IS TOWARDS POPULATIONS THAT ARE BETTER ADAPTED TO THE NEW NUTRIENT CONDITIONS OF THE LATER SUCCESSIONAL STAGES 3CHIMEL ET AL 3CHIMEL AND "ENNETT 4HESE SUC CESSIONAL SHIFTS APPEAR TO BE ECOLOGICAL IN NATURE NOT EVOLUTIONARY AND DRIVEN BY SHIFTS IN THE SPECIES COMPOSITION OF COMMUNITIES OVER TIME )N CONTRAST IN THE CASE OF ALTERATIONS TO ABIOTIC COMPONENTS OF THE SOIL ECOSYSTEM THERE IS NO DIRECT SELECTIVE PRESSURE TO STIMULATE ADAPTATION 5LTIMATELY THESE TYPES OF CHANGES REQUIRE THAT THE SOIL AND PLANT COMMUNITIES MAY HAVE TO RESPOND ADAPTIVELY TO NEW NUTRIENT CONDITIONS 7HEN INVADER SOIL ECOSYSTEM FEEDBACKS OCCUR THROUGH EFFECTS ON NUTRIENT CYCLES WE SUGGEST THAT LONG TERM EFFECTS WILL BE SIMILAR TO THOSE THAT OCCUR DURING SUCCESSION THE DEVELOPMENT OF A NEW COMMUNITY COMPOSED OF SPECIES THAT ARE BETTER ADAPTED TO THE SPECIlC NUTRIENT CONDITIONS OF THE SOIL EG "ERENDSE 4HIS HAS BEEN OBSERVED IN SYSTEMS INVADED BY BOTH NATIVE -ARON AND *EFFERIES AND INVASIVE (UGHES ET AL NITROGEN lXING SPECIES )N #ALIFORNIA -ARON AND #ONNORS FOUND THAT NITROGEN RICH PATCHES THAT WERE LEFT BY DEATH OF ,UPINUS ARBOREOUS BUSH LUPINE WERE INVADED BY EXOTIC ANNUAL GRASSES 3IMILARLY AS DESCRIBED IN THE PRECEDING SECTION SOILS THAT HAVE BEEN ENRICHED BY THE EXOTIC NITROGEN lXER - FAYA ARE MORE PRONE TO INVASION BY OTHER EXOTIC PLANTS INCLUDING 0SIDIUM CATTLEIANUM STRAWBERRY GUAVA (UGHES ET AL )N ADDI TION ALTHOUGH ONLY A FEW NATIVE SPECIES HAVE BEEN FOUND TO hMONOPOLIZEv SITES BY CREATING POSITIVE FEEDBACKS VAN DER 0UTTEN INVASIVE SPECIES MAY BE PARTICULARLY CAPABLE OF THIS ESPECIALLY IF THEY INTRODUCE A NOVEL ECOSYSTEM PROCESS TO WHICH NATIVE SPECIES ARE NOT ADAPTED &OR EXAMPLE ALTHOUGH " TECTORUM lRST BECAME ESTABLISHED IN lRE PRONE COMMUNITIES IN THE 'REAT "ASIN OVER YEARS AGO -ACK NO OTHER SPECIES EITHER NATIVE OR INVASIVE HAVE SINCE BEEN ABLE TO ESTABLISH IN SUBSTANTIAL NUMBERS 4HESE EXAMPLES SHOW HOW ECOSYSTEM CHANG ES INVOLVING EXOTIC SPECIES CAN RESULT IN UNPREDICTABLE SUCCESSIONAL TRAJECTORIES
#/.#,53)/. %XOTIC PLANT INVASIONS CAN OFTEN INVOLVE POSITIVE FEEDBACKS BETWEEN THE INVADER AND THE NATIVE SOIL COMMUNITY 0OSITIVE FEEDBACKS HAVE THE POTENTIAL TO LEAD TO LONG LASTING DOMINANCE IN COMMUNITIES (OWEVER THESE FEEDBACKS CAN BE CAUSED BY A NUMBER OF DIFFERENT REASONS AND DIFFERENT DRIVERS OF POSITIVE FEEDBACKS MAY RESULT IN DIFFERENT PREDICTIONS O F HOW LONG I NVADERS M AY DOMINATE A COMMUNITY
!3 4HORPE AND 2- #ALLAWAY
4YPICALLY POSITIVE FEEDBACKS ARE THOUGHT TO BE CAUSED BY THE ABSENCE OF SOIL PATHOGENS BUT THE PRESENCE OF SOIL MUTUALISTS IN INVADED SOILS 3UCH PATHOGEN DRIVEN POSITIVE FEEDBACKS MAY RESULT IN LONG TERM INVASIVE DOMINANCE BUT EVOLUTIONARY CHANGES IN NATIVE PATHOGENS MIGHT ULTIMATELY LEAD TO SUPPRESSION OF THE INVADER AND A RETURN TO NATIVE COEXISTENCE 0OSITIVE FEEDBACKS CAN ALSO BE CAUSED BY THE EFFECTS OF INVASIVE PLANTS ON THE SOIL BIOTA THAT DRIVE NUTRIENT CYCLES OR ON THE ABIOTIC COMPONENTS OF THE NUTRIENT CYCLES THEMSELVES 7E HYPOTHESIZE THAT POSITIVE FEEDBACKS CAUSED BY THE EFFECTS OF THE INVADER ON THE SOIL BIOTA INVOLVED IN NUTRIENT CYCLES ARE LIKELY TO LEAD TO COMMUNITY SHIFTS RESEMBLING SUCCESSION AND PERHAPS INVASIONAL MELTDOWN $OMINANCE BY INVADERS THAT DRIVE POSITIVE FEEDBACKS THROUGH ABIOTIC COMPONENTS OF NUTRIENT CYCLES MAY PERSIST FOR MUCH LONGER THAN DOMINANCE OCCURRING THROUGH POSITIVE FEEDBACKS INVOLV ING THE MICROBIAL COMMUNITY DUE TO THE LACK OF MEDIATION BY AN ORGANISM WITH THE POTENTIAL TO ADAPT (OWEVER UNDERSTANDING POTENTIAL EVOLUTIONARY CHANGES AMONG INVADERS AND SOIL ECOSYSTEMS WILL HELP US TO ACCURATELY PREDICT THE LONG TERM EFFECTS OF BIOLOGICAL INVASIONS
!#+./7,%$'%-%.43 4HE AUTHORS THANK THE .3& 53$! .2) AND THE $/$ FOR lNANCIAL SUPPORT
2%&%2%.#%3 !PLET ' ( !LTERNATION OF EARTHWORM COMMUNITY BIOMASS BY THE ALIEN -YRICA FAYA IN (AWAII /ECOLOGIA !GARWAL 6 + AND * " 3INCLAIR 0RINCIPLES OF 3EED 0ATHOLOGY 3ECOND EDITION ,EWIS 0UBLISHERS "OCA 2ATON !GRAWAL ! ! 0 - +OTANEN # % -ITCHELL ! ' 0OWER 7 'ODSOE AND * +LIRONOMOS %NEMY 2ELEASE !N EXPERIMENT WITH CONGENERIC PLANT PAIRS AND DIVERSE ABOVE AND BELOW GROUND ENEMIES %COLOGY !NGERS $ ! AND * #ARON 0LANT INDUCED CHANGES IN SOIL STRUCTURE PROCESSES AND FEEDBACKS "IOGEOCHEMISTRY !TLAS 2 - AND 2 "ARTHA -ICROBIAL %COLOGY &UNDAMENTALS AND !PPLICATIONS "ENJAMIN #UMMINGS .EW 9ORK "AIS ( 0 2 6EPACHEDU 3 'ILROY 2 - #ALLAWAY AND * - 6IVANCO !LLELOPATHY AND EXOTIC PLANTS FROM GENES TO INVASION 3CIENCE "AIS ( 0 4 3 7ALKER & 2 3TERMITZ 2 ! (UFBAUER AND * - 6IVANCO %NANTIOMERIC DEPENDENT PHYTOTOXIC AND ANTIMICROBIAL ACTIVITY OF ¢ CATECHIN ! RHI ZOSECRETED RACEMIC MIXTURE FROM SPOTTED KNAPWEED 0LANT 0HYSIOLOGY "ELNAP * AND 3 , 0HILLIPS 3OIL BIOTA IN AN UNGRAZED GRASSLAND RESPONSE TO ANNUAL GRASS "ROMUS TECTORUM INVASION %COLOGICAL !PPLICATIONS
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
"ELNAP * 3 + 3HERROD - % -ILLER %FFECTS OF SOIL AMENDMENTS ON GERMINATION AND EMERGENCE OF DOWNY BROME "ROMUS TECTORUM AND (ILARIA JAMESII 7EED 3CIENCE "ERENDSE & %FFECTS OF DOMINANT PLANT SPECIES ON SOILS DURING SUCCESSION IN NUTRIENT POOR ECOSYSTEMS "IOGEOCHEMISTRY "EVER * $ &EEDBACK BETWEEN PLANTS AND THEIR SOIL COMMUNITIES IN AN OLD lELD COM MUNITY %COLOGY "EVER * $ * " -ORTON * !NTONOVICS AND 0 ! 3CHULTZ (OST DEPENDENT SPORULA TION AND SPECIES DIVERSITY OF ARBUSUCLAR MYORRHIZAL FUNGI IN A MOWN GRASSLAND *OURNAL OF %COLOGY "EVER * $ + - 7ESTOVER AND * !NTONOVICS )NCORPORATING THE SOIL COMMUNITY INTO PLANT POPULATION DYNAMICS THE UTILITY OF THE FEEDBACK APPROACH *OURNAL OF %COLOGY "EVER * $ .EGATIVE FEEDBACK WITHIN A MUTUALISM HOST SPECIlC GROWTH OF MYCOR RHIZAL FUNGI REDUCES PLANT BENElT 0ROCEEDINGS 2OYAL 3OCIETY ,UND " "INKLEY $ AND # 'IARDINA 7HY DO TREE SPECIES AFFECT SOILS 4HE WARP AND WOOF OF TREE SOIL INTERACTIONS "IOGEOCHEMISTRY "LANEY # 3 AND 0 - +OTANEN %FFECTS OF FUNGAL PATHOGENS ON SEEDS OF NATIVE AND EXOTIC PLANTS A TEST USING CONGENERIC PAIRS *OURNAL OF !PPLIED %COLOGY "LANK 2 2 & !LLEN AND * ! 9OUNG %XTRACTABLE ANIONS IN SOILS FOLLOWING WILDlRE IN A SAGEBRUSH GRASS COMMUNITY 3OIL 3CIENCE 3OCIETY OF !MERICA *OURNAL "OON 0 ) AND , *OHNSTONE /RGANIC MATTER DECAY IN COASTAL WETLANDS AN INHIBI TORY ROLE FOR ESSENTIAL OIL FROM -ELALEUCA ALTERNIFOLIA LEAVES !RCHIV FUR HYDROBIOLGIE #ALLAWAY 2 - ' # 4HELEN 3 "ARTH 0 7 2AMSEY AND * % 'ANNON 3OIL FUNGI ALTER INTERACTIONS BETWEEN .ORTH !MERICAN PLANT SPECIES AND THE EXOTIC INVADER #ENTAUREA MACULOSA IN THE lELD %COLOGY #ALLAWAY 2 - ' # 4HELEN ! 2ODRIGUEZ AND 7 % (OLBEN 2ELEASE FROM INHIBI TORY SOIL BIOTA IN %UROPE MAY PROMOTE EXOTIC PLANT INVASION IN .ORTH !MERICA .ATURE #HEN * AND * - 3TARK 0LANT SPECIES EFFECTS AND CARBON AND NITROGEN CYCLING IN A SAGEBRUSH CRESTED WHEATGRASS SOIL 3OIL "IOLOGY AND "IOCHEMISTRY #HIARELLO . * # (ICKMAN AND ( ! -OONEY %NDOMYCORRHIZAL ROLE IN INTERSPECIlC TRANSFER OF PHOSPHORUS IN A COMMUNITY OF ANNUAL PLANTS 3CIENCE #LAY + AND 7 ( 6AN DER 0UTTEN 0ATHOGENS AND PLANT LIFE HISTORIES 0AGES IN 4 / 6UORISALO AND 0 + -UTIKAINEN EDITORS ,IFE (ISTORY IN 0LANTS +LUWER !CADEMIC 0UBLISHERS $ORDRECHT $!NTONIO # - AND 0 - 6ITOUSEK "IOLOGICAL INVASION BY EXOTIC GRASSES THE GRASS lRE CYCLE AND GLOBAL CHANGE !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS $EACON * 7 AND $ONALDSON 3 0 -OLECULAR RECOGNITION IN THE HOMING RESPONSES OF ZOOSPORIC FUNGI WITH SPECIAL REFERENCE TO 0YTHIUM AND 0HYTOPHTHORA -YCOLOGICAL 2ESEARCH $IX . AND * 7EBSTER &UNGAL %COLOGY #HAPMAN AND (ALL ,ONDON 5NITED +INGDOM
!3 4HORPE AND 2- #ALLAWAY
%ATON 7 $ AND 2 % &ARRELL #ATABOLIC AND GENETIC MICROBIAL INDICES AND LEVELS OF NITRATE AMMONIUM AND ORGANIC CARBON IN SOIL FROM THE BLACK LOCUST 2OBINIA PSEUDO ACACIA AND TULIP POPLAR ,IRIODENDRON TULIPIFERA TREES IN A 0ENNSYLVANIA FOREST "IOLOGICAL &ERTILITY OF 3OILS %HRENFELD * ' %FFECTS OF EXOTIC PLANT INVASIONS ON SOIL NUTRIENT CYCLING PROCESSES %COSYSTEMS %HRENFELD * ' 0 +OURTEV AND 7 (UANG #HANGES IN SOIL FUNCTIONS FOLLOWING INVASIONS OF EXOTIC UNDERSTORY PLANTS IN DECIDUOUS FORESTS %COLOGICAL !PPLICATIONS %HRENFELD * ' AND . 3COTT )NVASIVE 3PECIES AND THE 3OIL %FFECTS ON /RGANISMS AND %COSYSTEM 0ROCESSES %COLOGICAL !PPLICATIONS %VANS 2 $ 2 2IMER , 3PERRY AND * "ELNAP %XOTIC PLANT INVASION ALTERS NITOGEN DYNAMICS IN AN ARID GRASSLAND %COLOGICAL !PPLICATIONS &RANCIS 2 AND $ * 2EAD $IRECT TRANSFER OF CARBON BETWEEN PLANTS CONNECTED BY VESICULAR ARBUSCULAR MYCORRHIZAL MYCELIUM .ATURE 'ERRISH ' AND $ -UELLER $OMBIOS "EHAVIOR OF NATIVE AND NON NATIVE PLANTS IN TWO TROPICAL RAINFORESTS ON /AHU (AWAIIAN )SLANDS 0HYTOCOENOLOGIA 'RIME * 0 * - , -ACKEY 3 ( (LLIER AND $ * 2EAD &LORISTIC DIVERSITY IN A MODEL SYSTEM USING EXPERIMENTAL MICROCOSMS .ATURE (ALVORSON * * ( "OLTON AND * , 3MITH 4HE PATTERN OF SOIL VARIABLES RELATED TO !RTEMISIA TRIDENTATA IN A BURNED SHRUB STEPPE SITE 3OIL 3CIENCE 3OCIETY OF !MERICA *OURNAL (ARRIS ' ! 3OME COMPETITIVE RELATIONSHIPS BETWEEN !GROPRYON SPICATUM AND "ROMUS TECTORUM %COLOGICAL -ONOGRAPHS (ARTNETT $ # " ! $ (ETRICK ' 7 4 7ILSON AND $ * 'IBSON -YCORRHIZAL INmUENCE ON INTRA AND INTERSPECIlC NEIGHBOUR INTERACTIONS AMONG CO OCCURRING PRAIRIE GRASSES *OURNAL OF %COLOGY (ETRICK " ! $ ' 7 4 7ILSON AND $ # (ARTNETT 2ELATIONSHIP BETWEEN MYCOR RHIZAL DEPENDENCE AND COMPETITIVE ABILITY OF TWO TALLGRASS PRAIRIE GRASSES #ANADIAN *OURNAL OF "OTANY (OBBIE 3 % %FFECTS OF PLANT SPECIES ON NUTRIENT CYCLING 4RENDS IN %COLOGY AND %VOLUTION (OOPER $ 5 $ % "IGNELL AND 6 + "ROWN )NTERACTIONS BETWEEN ABOVEGROUND AND BELOWGROUND BIODIVERSITY IN TERRESTRIAL ECOSYSTEMS PATTERNS MECHANISMS AND FEEDBACKS "IO3CIENCE (UGHES 2 0 - 6ITOUSEK AND 4 4UNISON !LIEN GRASS INVASION AND lRE IN THE SEA SONAL SUBMONTANE ZONE OF (AWAII %COLOGY *ACOBS * 3 2 , 3HELEY AND " $ -AXWELL %FFECT OF 3CLEROTINA SCLEROTIORUM ON THE INTERFERENCE BETWEEN BLUEBUNCH WHEATGRASS !GROPYRON SPICATUM AND SPOTTED KNAP WEED #ENATUAREA MACULOSA 7EED 4ECHNOLOGY +EANE 2 - AND - * #RAWLEY %XOTIC PLANT INVASIONS AND THE ENEMY RELEASE HYPOTHESIS 4RENDS IN %COLOGY AND %VOLUTION
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
+IRKPATRICK " , AND & ! "AZZAZ )NmUENCE OF CERTAIN FUNGI ON SEED GERMINATION AND SEEDLING SURVIVAL OF FOUR COLONIZING ANNUALS *OURNAL OF !PPLIED %COLOGY +LIRONOMOS * &EEDBACK WITH SOIL BIOTA CONTRIBUTES TO PLANT RARITY AND INVASIVENESS IN COMMUNITIES .ATURE +OURTEV 0 3 * ' %HRENFELD AND 7 (UANG %XOTIC SPECIES ALTER MICROBIAL STRUCTURE AND FUNCTION IN THE SOIL %COLOGY ,EY 2 % AND # - $!NTONIO %XOTIC GRASS INVASION ALTERS POTENTIAL RATES OF . lXA TION IN (AWAIIAN WOODLANDS /ECOLOGIA ,OWE 0 . 7 + ,AUENROTH AND ) # "URKE %FFECTS OF NITROGEN AVAILABILITY ON COM PETITION BETWEEN "ROMUS TECTORUM AND "OUTELOUA GRACILIS 0LANT %COLOGY -ACK 2 . )NVASION OF "ROMUS TECTORUM , INTO WESTERN .ORTH !MERICA AN ECOLOGI CAL CHRONICLE !GRO %COSYSTEMS -ACK - # # - $!NTONIO AND 2 % ,EY !LTERATION OF ECOSYSTEM NITROGEN DYNAMICS BY EXOTIC PLANTS A CASE STUDY OF # GRASSES IN (AWAII %COLOGICAL !PPLICATIONS -ARLER - * # ! :ABINSKI AND 2 - #ALLAWAY -YCORRHIZAE INDIRECTLY ENHANCE COMPETITIVE EFFECTS OF AN INVASIVE FORB ON A NATIVE BUNCHGRASS %COLOGY -ARON * , AND 0 ' #ONNORS ! NATIVE NITROGEN lXING SHRUB FACILITATES WEED INVASION /ECOLOGIA -ARON * , AND 2 , *EFFERIES "USH LUPINE MORTALITY ALTERED RESOURCE AVAILABILITY AND ALTERNATIVE VEGETATION STATES %COLOGY -ERCK )NDEX (YDROXYQUINOLINE -ERCK AND #O )NC 7HITEHOUSE .* 0AGE -ILLS + % AND * $ "EVER -AINTENANCE OF DIVERSITY WITHIN PLANT COMMUNITIES SOIL PATHOGENS AS AGENTS OF NEGATIVE FEEDBACK %COLOGY -ITCHELL # ' AND ! ' 0OWER 2ELEASE OF INVASIVE PLANTS FROM FUNGAL AND VIRAL PATHOGENS .ATURE -OORA - AND - :OBEL %FFECT OF ARBUSCULAR MYCORRHIZA ON INTER AND INTRASPECIlC COMPETITION OF TWO GRASSLAND SPECIES /ECOLOGIA .EERGAARD 0 3EED 0ATHOLOGY *OHN 7ILEY .EW 9ORK .EW 9ORK 53! P .ORTHUP 2 2 2 ! $AHLGREN AND * ' -C#OLL 0OLYPHENOLS AS REGULATORS OF PLANT LITTER SOIL INTERACTIONS IN NORTHERN #ALIFORNIAS PYGMY FOREST ! POSITIVE FEEDBACK "IOGEOCHEMISTRY 0ACKER ! AND + #LAY 3OIL PATHOGENS AND SPATIAL PATTERNS OF SEEDLING MORTALITY IN A TEMPERATE TREE .ATURE 0ACKER ! AND + #LAY 3OIL PATHOGENS AND 0RUNUS SEROTINA SEEDLINGS AND SAPLING GROWTH NEAR CONSPECIlC TREES %COLOGY 2EINHART + / ! 0ACKER 7 ( 6AN DER 0UTTEN AND + #LAY 0LANTnSOIL BIOTA INTERACTIONS AND SPATIAL DISTRIBUTION OF BLACK CHERRY IN ITS NATIVE AND INVASIVE RANGES %COLOGY ,ETTERS 2EINHART + / AND 2 - #ALLAWAY 2EGIONAL EFFECTS OF SOIL BIOTA FACILITATE EXOTIC !CER INVASIONS IN %UROPE AND .ORTH !MERICA %COLOGICAL !PPLICATIONS 2ICE % , )NHIBITION OF NITROGEN lXING AND NITRIFYING BACTERIA BY SEED PLANTS %COLOGY
!3 4HORPE AND 2- #ALLAWAY
2ICE + * AND . # %MORY -ANAGING MICROEVOLUTION RESTORATION IN THE FACE OF GLOBAL CHANGE &RONTIERS IN %COLOGY 2IDENOUR 7 , AND #ALLAWAY 2 - 2OOT HERBIVORES PATHOGENIC FUNGI AND COMPETI TION BETWEEN #ENTAUREA MACULOSA AND &ESTUCA IDAHOENSIS 0LANT AND 3OIL 2OBINSON $ AND ! &ITTER 4HE MAGNITUDE AND CONTROL OF CARBON TRANSFER BETWEEN PLANTS LINKED BY A COMMON MYCORRHIZAL NETWORK *OURNAL OF %XPERIMENTAL "OTANY 3AGGAR 3 0 $ -C)NTOSH # " (EDLEY AND ( +NICKER #HANGES IN SOIL MICROBAL BIOMASS METABOLIC QUOTIENT AND ORGANIC MATTER TURNOVER UNDER (IERACIUM ( PILOSELLA , "IOLOGICAL &ERTILITY OF 3OILS 3CHIMEL * 0 AND * "ENNETT .ITROGEN MINERALIZATION CHALLENGES OF A CHANGING PARADIGM %COLOGY 3CHIMEL * 0 2 ' #ATES AND 2 2UESS 4HE ROLE OF BALSAM POPULAR SECONDARY CHEMI CALS IN CONTROLLING SOIL NUTRIENT DYNAMICS THROUGH SUCCESSION IN THE !LASKAN TAIGA "IOGEOCHEMISTRY 3CHLESINGER 7 ( AND ! - 0ILMANIS 0LANT SOIL INTERACTIONS IN DESERTS "IOGEOCHEMISTRY 3IMARD 3 7 $ ! 0ERRY AND - $ *ONES .ET TRANSFER OF CARBON BETWEEN ECTOMY CORRHIZAL TREE SPECIES IN THE lELD .ATURE 3IMBERLOFF $ AND " 6ON (OLLE 0OSITIVE INTERACTIONS OF NONINDIGENOUS SPECIES INVA SIONAL MELTDOWN "IOLOGICAL INVASIONS 3TEVENSON & * AND - ! #OLE #YCLES OF SOIL CARBON NITROGEN PHOSPHORUS SULFUR MICRONUTRIENTS *OHN 7ILEY AND 3ONS )NC .EW 9ORK .9 3TOCK 7 $ + 4 7IENAND AND ! # "AKER )MPACTS OF INVADING . lXING !CACIA SPECIES ON PATTERNS OF NUTRIENT CYCLING IN TWO #APE ECOSYSTEMS EVIDENCE FROM SOIL INCU BATION STUDIES AND . NATURAL ABUNDANCE VALUES /ECOLOGIA 4HORPE ! 3 6 !RCHER AND 4 ( $ELUCA )N 0RESS 4HE INVASIVE FORB #ENTAUREA MACU LOSA INCREASES PHOSPHORUS AVAILABILITY IN -ONTANA GRASSLANDS *OURNAL OF !PPLIED 3OIL %COLOGY 5PADHYAYA * + 2 4URKINGTON AND $ -C)LURIDE 4HE BIOLOGY OF #ANADIAN WEEDS "ROMUS TECTORUM , #ANADIAN *OURNAL OF 0LANT 3CIENCE 6AN "REEMEN . 3OILS AS BIOTIC CONSTRUCTS FAVOURING NET PRIMARY PRODUCTIVITY 'EODERMA 6AN "REEMEN . AND ! # &INZI 0LANT SOIL INTERACTIONS ECOLOGICAL ASPECTS AND EVOLUTIONARY IMPLICATIONS "IOGEOCHEMISTRY VAN DER (EIJDEN - ' ! * . +LIRONOMOS - 5RSIC 0 -OUTOGLIS 2 3TREITWOLF %NGEL 4 "OLLER ! 7IEMKEN AND ) 2 3ANDERS -YCORRHIZAL FUNGAL DIVERSITY DETERMINES PLANT BIODIVERSITY ECOSYSTEM VARIABILITY AND PRODUCTIVITY .ATURE 6AN DER 0UTTEN 7 ( AND " ! - 0ETERS (OW SOIL BORNE PATHOGENS MAY AFFECT PLANT COMPETITION %COLOGY 6AN DER 0UTTEN 7 ( # 6AN $IJK AND " ! - 0ETERS 0LANT SPECIlC SOIL BORNE DISEASES CONTRIBUTE TO SUCCESSION IN FOREDUNE VEGETATION .ATURE 6AN DER 0UTTEN 7 ( 0LANT SOIL FEEDBACK AS A SELECTIVE FORCE 4RENDS IN %COLOGY AND %VOLUTION
)NVASIVE PLANT SOIL ECOSYSTEM FEEDBACKS
6ERSFELD $ " AND " 3 VAN 7ILGREN )MPACT OF WOODY ALIENS ON ECOSYSTEM PROP ERTIES 0AGES IN ) ! 7 -ACDONALD & * +RUGER AND ! ! &ERRAR EDICTORS 4HE ECOLOGY AND MANAGEMENT OF BIOLOGICAL INVASIONS IN SOUTHERN !FRICA /XFORD 5NIVERSITY 0RESS #APE 4OWN 3OUTH !FRICA 6ITOUSEK 0 - "IOLOGICAL INVASIONS AND ECOSYSTEM PROPERTIES CAN SPECIES MAKE A DIFFERENCE 0AGES IN ' ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF "IOLOGICAL )NVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER 6ERLAG .EW 9ORK .9 6ITOUSEK 0 - "IOLOGICAL INVASIONS AND ECOSYSTEM PROCESSES TOWARDS AN INTEGRA TION OF POPULATION BIOLOGY AND ECOSYSTEM STUDIES /IKOS 6ITOUSEK 0 - AND , 2 7ALKER "IOLOGICAL INVASION BY -YRICA FAYA IN (AWAII PLANT DEMOGRAPHY NITROGEN lXATION ECOSYSTEM EFFECTS %COLOGICAL -ONOGRAPHS 6ITOUSEK 0 - , 2 7ALKER , $ 7HITEAKER $ -UELLER $OMBOIS AND 0 ! -ATSON "IOLOGICAL INVASION BY -YRICA FAYA ALTERS ECOSYSTEM DEVELOPMENT IN (AWAII 3CIENCE 6IVANCO * - ( 0 "AIS & 2 3TERMITZ ' # 4HELEN AND 2 - #ALLAWAY "IOGEOGRAPHICAL VARIATION IN COMMUNITY RESPONSE TO ROOT ALLELECHEMISTRY NOVEL WEAP ONS AND EXOTIC INVASION %COLOGY ,ETTERS 9ELENIK 3 ' 7 $ 3TOCK AND $ - 2ICHARDSON %COSYSTEM LEVEL IMPACTS OF INVASIVE !CACIA SALIGNA IN THE 3OUTH !FRICAN FYNBOS 2ESTORATION %COLOGY 9PSILANTIS 7 2ISK OF CHEATGRASS INVASION AFTER lRE IN SELECTED SAGEBRUSH COMMU NITY TYPES 53 "UREAU OF ,AND -ANAGEMENT 7ARDLE $ ! + 3 .ICHOLSON AND ! 2AHMAN %COLOGICLA EFFECTS OF THE INVASIVE WEED SPECIES 3ENECIO JACOBAEA , RAGWORT IN A .EW :EALAND PASTURE !GRICULTURE %COSYSTEMS AND %NVIRONMENT 7ARDLE $ ! AND + 3 .ICHOLSON 3YNERGISTIC EFFECTS OF GRASSLAND PLANT SPECIES ON SOIL MICROBIAL BIOMASS AND ACTIVITY IMPLICATIONS FOR THE ECOSYSTEM LEVEL EFFECTS OF ENRICHED PLANT DIVERSITY &UNCTIONAL %COLOGY 7ARDLE $ ! + 3 .ICHOLSON - !HMED AND ! 2AHMAN )NTERFERENCE EFFECTS OF THE INVASIVE PLANT #ARDUUS NUTANS , AGAINST THE NITROGEN lXATION ABILITY OF 4RIFOLIUM REPENS, 0LANT AND 3OIL 7ARDLE $ ! - .ILSSON # 'ALLET AND / :ACKISSON !N ECOSYSTEM LEVEL PERSPECTIVE OF ALLELOPATHY "IOLOGICAL 2EVIEW 7ATKINS . + ! ( &ITTER * $ 'RAVES #ARBON TRANSFER BETWEEN # AND # PLANTS LINKED BY A COMMON MYCORRHIZAL NETWORK QUANTIlED USING STABLE CARBON ISOTOPES 3OIL "IOLOGY AND "IOCHEMISTRY 7ATKINSON ! 2 4HE ROLE OF THE SOIL COMMUNITY IN PLANT POPULATION DYNAMICS 4RENDS IN %COLOGY AND %VOLUTION 7EST ( - )NmUENCE OF ARBUSCULAR MYCORRHIZAL INFECTION ON COMPETITION BETWEEN (OLCUS LANATUS AND $ACTYLIS GLOMERATA *OURNAL OF %COLOGY 7ESTOVER + - ! # +ENNEDY AND 3 % +ELLEY 0ATTERNS OF RHIZOSPHERE MICROBIAL COMMUNITY STRUCTURE ASSOCIATED WITH CO OCCURRING PLANT SPECIES *OURNAL OF %COLOGY
#HAPTER SIXTEEN
)NVASION BIOLOGY AS A COMMUNITY PROCESS MESSAGES FROM MICROBIAL MICROCOSMS
0 ( 7ARREN 2 ,AW AND ! * 7EATHERBY
).42/$5#4)/. )NVASIONS ARE WIDELY REGARDED AS A SIGNIlCANT CURRENT PROBLEM IN POPULATION ECOSYSTEM AND HABITAT MANAGEMENT WITH CONSEQUENCES INCLUDING GLOBAL HOMOG ENIZATION OF mORAS AND FAUNAS EXTIRPATION OF NATIVE SPECIES AND INTERFERENCE WITH ECOSYSTEM FUNCTIONING $RAKE ET AL 7ILLIAMSON -ACK ET AL 0IMENTEL ET AL 3AKAI ET AL 3UCH INVASIONS OCCUR AND HAVE EFFECTS AT LARGE SCALES IN REAL ECOSYSTEMS 3O WHY CONSIDER INVESTIGATING SUCH PHENOMENA IN ARTIlCIAL MICROCOSM SYSTEMS IN THE LABORATORY 7E BELIEVE THAT THERE ARE SEV ERAL COMPELLING REASONS WHY LABORATORY MICROCOSM SYSTEMS HAVE A VALUABLE ROLE IN THE STUDY OF BIOLOGICAL INVASIONS THESE CENTRE ON THE ISSUES OF MANIPULATION TIME SCALE AND REPLICATION &IRST APPLIED ECOLOGY SEEKS A PREDICTIVE UNDERSTANDING OF INVASIONS WHAT DETERMINES WHICH SPECIES WILL MAKE SUCCESSFUL INVADERS !RE SOME TYPES OF COM MUNITIES INVASION PRONE (OW WILL AN INVADER IMPACT ON A COMMUNITY 4HERE ARE VARIOUS THEORETICAL EXPECTATIONS BUT TESTING THESE IN THE lELD IS LARGELY DEPENDENT ON EXTRACTING STATISTICAL SIGNALS FROM DOCUMENTATION OF THE @NATURAL EXPERIMENTS THAT REAL INVASIONS PROVIDE /PPORTUNITIES FOR CONTROLLED EXPERIMENTATION ARE -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
0( 7ARREN 2 ,AW AND !* 7EATHERBY
LIMITED AND IT IS NOTORIOUSLY DIFlCULT TO DOCUMENT SYSTEMATICALLY INVASION ATTEMPTS THAT FAIL 3IMBERLOFF THE NECESSARY @CONTROL FOR EVALUATION OF THE DETER MINANTS OF INVASION SUCCESS -ICROCOSMS MESOCOSMS AND RELATED TECHNIQUES SUCH AS ENCLOSURE EXPERIMENTS PROVIDE THE POSSIBILITY OF MANIPULATING POTENTIAL INmUENCES ON INVASION SUCCESS ALBEIT AT THE EXPENSE OF REALISM IN COMPLEXITY AND SCALING 3ECOND INVASIONS TAKE TIME 4HE POPULATION DYNAMICS OF AN INVADING SPECIES ITS GEOGRAPHIC SPREAD AND THE ADJUSTMENT OF THE RECEIVING COMMUNITIES ARE ALL TYPICALLY EXPRESSED OVER TENS TO HUNDREDS OF GENERATIONS USUALLY TAKING MANY YEARS (OWEVER DESIRABLE THE EXPLORATION OF SUCH EFFECTS IN INVASIONS CURRENTLY HAPPENING IN THE lELD MAY BE IMPRACTICAL -ICROCOSM SYSTEMS UTILIZING MICROOR GANISMS ALLOW @LONG TERM EFFECTS AND OUTCOMES IN THE RANGE OF TENS TO HUNDREDS OF GENERATIONS TO BE DOCUMENTED $RAKE ET AL ,AWLER 4HIRD AS THE WEALTH OF CASE STUDIES IN THE INVASIONS LITERATURE TESTIlES INVA SIONS ARE RATHER INDIVIDUALISTIC EVENTS A PARTICULAR INVADER INVADING A PARTICU LAR SYSTEM OR REGION UNDER PARTICULAR CIRCUMSTANCES 4HIS MAKES THE APPRAISAL OF GENERAL PATTERNS AND CAUSES DIFlCULT )N PARTICULAR IF WE ARE INTERESTED IN PREDIC TION OR AT LEAST PREDICTABILITY THEN IT BECOMES IMPORTANT TO KNOW THE PROBABILITY OF A PARTICULAR OUTCOME FOR WHAT IS AFTER ALL A PROCESS LIKELY TO BE STRONGLY INmU ENCED BY STOCHASTIC EVENTS )N EXPERIMENTAL SYSTEMS REPLICATION OF COMMUNITIES AND INVASION EVENTS MAKES IT POSSIBLE TO ASSESS THE VARIATION IN THE OUTCOME OF INVASIONS AND THE SOURCE OF THAT VARIATION ! BEAKER IN THE LABORATORY IS FAR FROM A lELD EXPERIMENT IN A NATURAL ECOSYSTEM 3PATIAL AND TEMPORAL SCALES THE TYPES OF ORGANISMS INVOLVED AND THE SIMPLICITY OF THE COMMUNITIES MEAN THAT MICROCOSMS CANNOT SIMPLY BE TAKEN AS ANALOGUES OF LARGE NATURAL ECOSYSTEMS THE SAME IS TRUE FOR OTHER SORTS OF MICROCOSM AND MESO COSM EXPERIMENTS 0ETERSEN AND (ASTINGS ! MICROBIAL MICROCOSM IS BETTER THOUGHT OF AS A SMALL SYSTEM IN ITS OWN RIGHT AND WITH ITS OWN PECULIARITIES RATHER THAN AS A LARGE SYSTEM WRIT SMALL )N A SENSE DECIDING THE EXTENT TO WHICH RESULTS FROM MICROCOSMS CAN BE APPLIED TO OTHER TYPES OF SYSTEM IS EQUIVALENT TO DECID ING THE EXTENT TO WHICH RESULTS FROM ANY ONE TYPE OF COMMUNITY CAN BE APPLIED TO OTHER DISPARATE SYSTEMS FOR INSTANCE THE EXTENT TO WHICH RESULTS FROM PHYTO PLANKTON COMMUNITIES CAN BE APPLIED TO FORESTS -ICROCOSMS OF PROTISTS CERTAINLY TELL US SOMETHING ABOUT THE BEHAVIOUR OF MICROBIAL COMMUNITIES BUT LEAVE OPEN OPEN THE QUESTION OF WHETHER SUCH BEHAVIOUR GENERALIZES THE LATTER IS ALSO TRUE FOR EXPERIMENTS ON FORESTS AND PHYTOPLANKTON -ICROCOSMS CANNOT OF COURSE REPLACE LARGE SCALE lELD EXPERIMENTS ON SPE CIlC ECOYSTEMS /NLY THROUGH SUCH EXPERIMENTS CAN SOME OF THE COMPLEXITY AND SPECIlC FEATURES OF THE SYSTEM OF INTEREST BE CAPTURED (OWEVER LARGE SCALE lELD EXPERIMENTS ARE OFTEN CONCERNED WITH TESTING GENERAL PRINCIPLES SUCH AS THE ROLES OF SPECIES RICHNESS OR SPECIES TYPE EG 7ARDLE (ECTOR ET AL AND THE EFFECTS OF mUCTUATION OR HETEROGENEITY IN THE ABIOTIC ENVIROMENT EG $AVIS AND 0ELSOR 1UESTIONS ABOUT HOW TO GENERALIZE TO OTHER KINDS OF SYSTEM APPLY AS MUCH IN THESE lELD EXPERIMENTS AS IN MICROCOSMS -ANY IMPORTANT
)NVASIONS IN MICROCOSMS
ECOLOGICAL PRINCIPLES CAN BE TESTED IN MICROCOSMS AS WELL AS IN lELD EXPERIMENTS EG 0ETCHEY ET AL AND WE TAKE THE VIEW THAT MICROSOSM EXPERIMENTS SHOULD COMPLEMENT THESE OTHER APPROACHES RATHER THAN BEING ALTERNATIVES TO THEM !RGUABLY THEREFORE LABORATORY MICROCOSMS HAVE A USEFUL ROLE TO PLAY IN INVESTI GATING ECOLOGICAL PRINCIPLES OF INVASION JUST AS THEY HAVE PROVIDED VALUABLE INVES TIGATIVE TOOLS IN OTHER AREAS OF COMMUNITY ECOLOGY ,AWLER )N FACT MANY OF THE PROCESSES HYPOTHESIZED TO BE DETERMINANTS OF INVASION SUCCESS OR IMPACT ARE JUST THOSE OF @NATURAL COMMUNITY CHANGE AND REGULATION POPULATION GROWTH SPECIES INTERACTIONS DISPERSAL TROPHIC POSITION ASSEMBLY ETC $IAMOND AND #ASE 3HEA AND #HESSON )T IS IN THE STUDY OF THESE GENERAL PROCESSES RATHER THAN IN THE STUDY OF FACTORS MORE SPECIlC TO THE BIOGEOGRAPHY OF INVASION FOR EXAMPLE THE LOSS OF COEVOLVED NATURAL ENEMIES 4ORCHIN ET AL -ITCHELL AND 0OWER THAT LABORATORY MICROCOSMS ARE MOST LIKELY TO GENERATE USEFUL INSIGHTS (ERE WE EXAMINE VARIOUS COMPONENTS OF INVASION BIOLOGY AND SOME OF THE INSIGHTS LABORATORY MICROCOSMS HAVE GIVEN US INTO THESE 7E FOCUS ON MICROCOSMS OF HETEROTROPHIC MICROBES WHICH WE KNOW BEST FROM OUR OWN WORK AND WHICH HAVE A LONG HERITAGE IN DIVERSE AREAS OF COMMUNITY ECOLOGY EG SEE REVIEW IN ,AWLER /UR REASON FOR THIS IS THAT SUCH SYSTEMS EXPLOIT ALL THE ADVANTAGES OF MICROCOSMS LISTED ABOVE BUT IT DOES MEAN THAT WE DO NOT COVER OTHER TYPES OF EXPERIMENTAL INVASIONS SUCH AS THOSE OF PLANTS INTO COMMUNITIES IN POTS OR SIMI LAR EXPERIMENTAL SYSTEMS EG $UKES 3TAMPE AND $AEHLER $ICK ET AL WHICH ARE SOMETIMES TERMED MICROCOSMS VALUABLE THOUGH SUCH EXPERI MENTS ARE FOR INVESTIGATING THE DETAILS AND MECHANISMS OF PARTICULAR INVASIONS
!. ).6!3)/. %80%2)-%.4 )N DEVELOPING THE IDEAS BELOW WE DRAW SUBSTANTIALLY ON INFORMATION FROM MICRO COSM EXPERIMENTS ON INVASIBILITY WHICH WE CONDUCTED AS PART OF A STUDY OF COM MUNITY ASSEMBLY 7EATHERBY ET AL ,AW ET AL 7ARREN ET AL 4HERE ARE A NUMBER OF RESULTS THAT EMERGE FROM THIS WORK WHICH WE FEEL ARE BOTH PERTINENT TO QUESTIONS ABOUT INVASIONS IN GENERAL AND ALSO ILLUSTRATIVE OF SOME OF THE AREAS IN WHICH MICROCOSMS SYSTEMS CAN CONTRIBUTE UNIQUELY TO UNDERSTAND ING INVASION PROCESSES &ULL DETAILS OF THE EXPERIMENTAL METHODS CAN BE FOUND IN THE PAPERS ABOVE BUT A BRIEF OUTLINE OF THE EXPERIMENTS IS GIVEN HERE FOR CONVE NIENCE 7E WORKED WITH A SPECIES POOL OF SIX HETEROTROPHIC PROTISTS BACTERIOVORES 4ETRAHYMENA PYRIFORMIS #OLPIDIUM STRIATUM 0ARAMECIUM CAUDATUM AN OMNIVORE "LEPHARISMA JAPONICUM PREDATORS %UPLOTES PATELLA !MOEBA PROTEUS PLUS A MIXED BACTERIAL ASSEMBLAGE IN MICROCOSMS CONTAINING M, OF LIQUID MEDIUM )N AN INITIAL EXPERIMENT 7EATHERBY ET AL ALL POSSIBLE COMBINATIONS OF THE SPECIES WERE TESTED FOR THEIR ABILITY TO COEXIST OF THE POSSIBLE COMBINATIONS OF SPECIES TEN FORMED PERSISTENT COMMUNITIES ON A TIME SCALE OF TENS TO HUNDREDS OF
0( 7ARREN 2 ,AW AND !* 7EATHERBY
GENERATIONS 7E THEN TOOK EACH OF THESE PERSISTENT COMMUNITIES AND CHALLENGED THEM EXPERIMENTALLY WITH EACH NON RESIDENT SPECIES 3IX REPLICATES OF EACH COMBI NATION OF COMMUNITY AND INTRODUCED SPECIES WERE USED STARTING FROM A PRE ESTABLISHED RESIDENT COMMUNITY SET UP FOR WEEKS AND CHALLENGING IT WITH AN INOCULUM OF THE NEW SPECIES CONSISTING OF THIRTY INDIVIDUALS 4HE INITIAL RATE OF INCREASE OF THE INVADER ITS LONG TERM PERSISTENCE UP T O WEEKS AFTER INVASION AND THE CHANGES IN COMMUNITY COMPOSITION WERE ALL RECORDED
&!#4/23 !&&%#4).' %34!",)3(-%.4 /& ).6!$%23 %STABLISHMENT AS A PROBABILISTIC EVENT
#HANCE PLAYS AN IMPORTANT PART IN WHETHER A NEW SPECIES GETS ESTABLISHED LOCALLY #RAWLEY %VEN IF A NEW SPECIES HAS VITAL RATES THAT ENABLE IT TO INCREASE ON THE AVERAGE RANDOM EVENTS CAN CATCH UP WITH IT BEFORE IT IS ABLE TO GET STARTED 3UCH EVENTS INCLUDE DEMOGRAPHIC STOCHASTICITY ENVIRONMENTAL STOCHASTICITY AND THE EXACT STATE OF THE RESIDENT COMMUNITY AT THE TIME WHEN THE NEW SPECIES IS INTRODUCED )T THEREFORE HELPS TO THINK OF ESTABLISHMENT AS A PROBABILISTIC EVENT 4HEORY FROM STOCHASTIC BIRTH DEATH PROCESSES PROVIDES A QUANTITATIVE FRAMEWORK ON WHICH TO BUILD IDEAS AT LEAST SO FAR AS DEMOGRAPHIC STOCHASTICITY IS CONCERNED "AILEY 'OEL AND 2ICHTER $YN 4HIS THEORY CONSIDERS A POPULATION IN WHICH INDIVIDUALS HAVE A CONSTANT PROBABILITY PER UNIT TIME OF GIVING BIRTH B AND OF DYING D WITH AN ASSUMPTION THAT B D )F THE POPULATION STARTS WITH AN INOCU LUM OF N INDEPENDENT INDIVIDUALS IT HAS A PROBABILITY
n DB N 0N . n DB .
OF REACHING SIZE . N BEFORE IT GOES TO EXTINCTION &OR A SPECIES INTRODUCED INTO A WELL MIXED COMMUNITY CLOSE TO STEADY STATE AND AT AN ABUNDANCE MUCH LOWER THAN THE RESIDENT SPECIES B AND D MAY BE TAKEN AS APPROXIMATELY CONSTANT DURING THE EARLY STAGES OF POPULATION GROWTH BECAUSE MOST INTERACTIONS ARE WITH THE RESIDENT SPECIES . CAN BE SET AT A VALUE ABOVE THE LEVEL AT WHICH DEMOGRAPHIC STOCHASTICITY IS IMPORTANT TO GIVE AN EXPRESSION FOR THE PROBABILITY THAT A NEW SPECIES BECOMES SUCCESSFULLY ESTABLISHED 0N n DB N n n RB N
WHERE R B n D IS THE INITIAL PER CAPITA RATE OF INCREASE OF THE NEW SPECIES AND B D 0N IF B D 0LOTTING THIS FUNCTION SHOWS AS ONE WOULD EXPECT THE SPECIES IS MORE LIKELY TO BECOME ESTABLISHED THE GREATER THE INOCULUM SIZE
)NVASIONS IN MICROCOSMS
N AND THE GREATER THE PER CAPITA RATE OF INCREASE R RELATIVE TO THE BIRTH RATE B OR EQUIVALENTLY THE SMALLER THE DEATH RATE D RELATIVE TO THE BIRTH RATE B &IG SEE #HAPTER BY &RECKLETON ET AL FOR A BROADER DISCUSSION OF THE ROLE OF STOCHASTIC ITY IN INVASIONS
&IG 0ROBABILITY 0N THAT AN INTRODUCED ASEXUAL SPECIES REACHES A SIZE ABOVE A LEVEL AT WHICH DEMOGRAPHIC STOCHASTICITY IS IMPORTANT STARTING WITH N PROPAGULES AND HAVING CONSTANT PER CAPITA BIRTH B AND DEATH D RATES WITH R B n D 4HE SURFACE IS CONSTRUCTED FROM %QUATION
!LTHOUGH THE ROLE THAT CHANCE PLAYS IN ESTABLISHMENT OF NEW SPECIES IS RARELY A SUBJECT OF DIRECT EXPERIMENTATION WE FOUND IT PLAYED AN IMPORTANT PART IN THE REPLICATE INVASION TRIALS WE CARRIED OUT DURING OUR WORK ON COMMUNITY ASSEMBLY OF PROTISTS ,AW ET AL )N THIS WORK WE TOOK A SPECIES TO HAVE BECOME ESTAB LISHED IF IT REACHED A THRESHOLD OF INDIVIDUALS AT SOME STAGE DURING THE COURSE OF THE EXPERIMENT (OWEVER IN ABOUT OF THE RESIDENT INTRODUCTION TREATMENTS THE OUTCOME REMAINED UNCERTAIN IN THE SENSE THAT THE INTRODUCED SPECIES BECAME
0( 7ARREN 2 ,AW AND !* 7EATHERBY
ESTABLISHED IN SOME REPLICATES WHILE DISAPPEARING IN OTHERS &IG $EMOGRAPHIC STOCHASTICITY MOST LIKELY PLAYED A PART IN THIS ALTHOUGH THIS DOES NOT PRECLUDE INVOLVEMENT OF OTHER FACTORS AS WELL &OR INSTANCE SPECIES THAT REMAIN AT LOW POPULATION SIZES FOR LONG PERIODS OF TIME ARE ALSO VULNERABLE TO THE CONTINUING EFFECTS OF ENVIRONMENTAL STOCHASTICITY AS IN TWO OF OUR MICROCOSMS WHERE NEITHER EXTINCTION NOR THE THRESHOLD FOR ESTABLISHMENT HAD BEEN REACHED BY THE TIME THE EXPERIMENT ENDED WEEKS AFTER INOCULATION !LSO THE EXACT ABUNDANCE OF THE RESIDENT SPECIES AT THE TIME OF INTRODUCTION WHICH WE COULD NOT CONTROL FOR IN OUR INVASION TRIALS COULD INmUENCE THE OUTCOME 3UCH EFFECTS OF ABUNDANCE ARE SUGGESTED BY THE FACT THAT THE OUTCOME OF INVASIONS WAS NEVER IN DOUBT IN OUR MICROCOSMS LACKING RESIDENT PROTISTS BUT WAS UNCERTAIN IN ABOUT A THIRD OF THE TREATMENTS CONTAINING RESIDENT PROTISTS $RAKE IN MICROCOSMS OF ALGAE AND GRAZING MICROCRUSTACEA SUGGESTED A POSSIBLY SIMILAR EFFECT WHERE SMALL VARIATIONS IN INITIAL DEMOGRAPHY OF INTRODUCED GRAZERS AMONG REPLICATES CAUSED MARKED VARIATION IN GRAZER POPULATION SUCCESS IN SOME COMMUNITIES BUT NOT IN OTHERS
&IG 5NCERTAINTY IN THE OUTCOME OF RESIDENT INTRODUCTION TREATMENTS IN A PROTIST INVASION EXPERIMENT DESCRIBED IN ,AW ET AL 4REATMENTS ARE SHOWN IN THREE CATEGORIES ACCORDING TO WHETHER THE INTRODUCED SPECIES FAILED TO ESTABLISHPERSIST IN ALL REPLICATES SUCCEEDED IN ESTABLISHINGPERSISTING IN ALL REPLICATES OR SUCCESSFULLY INVADED SOME BUT FAILED IN OTHERS MIXED "ARS SHOW THE NUMBER OF TREATMENTS FALLING INTO EACH CATEGORY 3HADED BARS ESTABLISHMENT REACHING A THRESHOLD OF INDIVIDUALS AT SOME POINT IN THE EXPERIMENT OPEN BARS PERSISTENCE STILL PRESENT IN THE COMMUNITY AFTER WEEKS -OST TREATMENTS HAD REPLICATES THOUGH A FEW ONLY HAD OR
)NVASIONS IN MICROCOSMS
0ROPAGULE PRESSURE AND THE PROBABILITY OF ESTABLISHMENT
4HERE IS A GENERAL UNDERSTANDING THAT ESTABLISHMENT OF A NEW SPECIES IS MORE LIKELY THE MORE INDIVIDUALS INTRODUCED AT A TIME 7ILLIAMSON +OLA AND ,ODGE )T IS INTUITIVE FOR INSTANCE THAT DEMOGRAPHIC STOCHASTICITY SHOULD HAVE ITS GREATEST EFFECT ON ESTABLISHMENT OF A SPECIES WHEN JUST A FEW INDIVIDUALS ARE INTRODUCED BECAUSE A SEQUENCE OF RELATIVELY FEW DEATHS CAN TAKE THE NEW POPU LATION TO EXTINCTION !LTHOUGH RATHER LITTLE IS KNOWN ABOUT PROPAGULE PRESSURE THIS MAY WELL CONTRIBUTE IN IMPORTANT WAYS TO PATTERNS OF INVASIONS OBSERVED IN NATURE 7ILLIAMSON ET SEQ ,ONSDALE !MONG THE MOST SYSTEMATIC INVESTIGATIONS HAVE BEEN THE RELEASE OF BIOLOGICAL CONTROL AGENTS EG (OPPER AND 2OUSH WHERE THERE IS PARTICULAR CONCERN TO ENSURE THE CONTROL AGENTS BECOME SUCCESSFULLY ESTABLISHED 3HEA AND 0OSSINGHAM %QUATION ABOVE PROVIDES A CLEAR QUANTITATIVE PREDICTION ABOUT THE EFFECT OF INOCULUM SIZE N ON THE PROBABILITY OF SUCCESSFUL ESTABLISHMENT 4HE QUANTITATIVE DEPENDENCE OF INVASION SUCCESS ON PROPAGULE PRESSURE HAS RECEIVED LITTLE SYSTEMATIC EXPERIMENTAL INVESTIGATION 7ELL MIXED MICROCOSMS CONTAINING SPECIES WITH SHORT GENERATION TIMES WOULD BE A GOOD POINT AT WHICH TO BEGIN EXAMINING THIS RELATIONSHIP
)NITIAL RATE OF INCREASE AND THE PROBABLITY OF ESTABLISHMENT
/NE WOULD EXPECT THAT THE LARGER THE PER CAPITA RATE OF INCREASE OF A RARE INTRO DUCED SPECIES THE GREATER THE LIKELIHOOD THAT IT BECOMES ESTABLISHED !PART FROM HUMAN PATHOGENS EG !NDERSON AND -AY RATHER LITTLE INFORMA TION IS AVAILABLE ON THIS INITIAL RATE OF INCREASE 9ET IT IS INTUITIVE THAT A HIGH RATE OF INCREASE SHOULD ALLOW EARLY ESCAPE FROM THE REGION IN WHICH DEMOGRAPHIC STOCHASTICITY COULD DRIVE THE INTRODUCED SPECIES TO EXTINCTION %QUATION MAKES THIS INTUITION PRECISE SHOWING THAT WHAT ACTUALLY MATTERS IS THE RATIO OF THE DEATH RATE TO BIRTH RATE THE RATIO LEADING TO A DIMENSIONLESS EXPRESSION INDEPENDENT OF THE TIME SCALE ON WHICH THE DYNAMICS ARE OPERATING -ICROCOSMS BECAUSE OF THEIR POTENTIAL FOR HIGH LEVELS OF REPLICATION PROVIDE SCOPE FOR STUDYING INITIAL RATES OF INCREASE AND THE PROBABILITY OF ESTABLISHMENT /UR STUDIES OF PROTIST MICROCOSMS ,AW ET AL ILLUSTRATE THE POTENTIAL TO ESCAPE FROM STOCHASTIC EXTINCTION THROUGH RAPID POPULATION GROWTH &IG 4HE GRAPHS SHOW THE GROWTH OF "LEPHARISMA POPULATIONS EACH STARTING WITH AN INOCULUM OF INDIVIDUALS INTRODUCED INTO FOUR DIFFERENT TYPES OF MICROCOSM THOSE CONTAINING 0ARAMECIUM #OLPIDIUM OR 4ETRAHYMENA AND THOSE WITH NO OTHER PROTISTS 7HEN FACED WITH 0ARAMECIUM MOST "LEPHARISMA POPULATIONS DECLINED RAPIDLY IN FACT TWO WERE EXTINCT BY DAY SIX 7ITH #OLPIDUM "LEPHARISMA TEETERED ALONG AT SMALL POPULATION SIZES DURING THIS TIME THERE WOULD BE A CONTINUING RISK OF EXTINCTION )N THE PRESENCE OF 4ETRAHYMENA "LEPHARISMA POPULATIONS GREW MUCH FASTER AND SOON GOT BEYOND A SIZE AT WHICH EXTINCTION THROUGH DEMOGRAPHIC
0( 7ARREN 2 ,AW AND !* 7EATHERBY
&IG 4IME SERIES OF THE EARLY GROWTH OF POPULATIONS OF "LEPHARISMA INTRODUCED INTO ESTABLISHED POPULATIONS OF A 0ARAMECIUM B #OLPIDIUM C 4ETRAHYMENA D NO OTHER PROTISTS TAKEN FROM AN EXPERIMENT DESCRIBED IN ,AW ET AL )N EACH CASE SIX INDEPENDENT REPLICATE INTRODUCTIONS OF INDIVIDUALS ARE SHOWN
STOCHASTICITY COULD BE AN ISSUE 4HE BEHAVIOUR OF "LEPHARISMA IN THE ABSENCE OF ANY PROTISTS WAS SIMILAR ALTHOUGH THE GROWTH RATE WAS SOMEWHAT SMALLER )NVASION BIOLOGY WOULD BE RELATIVELY STRAIGHTFORWARD IF ECOLOGISTS COULD POINT TO BIOLOGICAL PROPERTIES OF SPECIES THAT MAKE THEIR INITIAL RATES OF INCREASE EITHER POSI TIVE OR NEGATIVE THOUGH SUCCESS IN DOING THIS HAS GENERALLY BEEN MIXED 7ILLIAMSON
)NVASIONS IN MICROCOSMS
-ACK +OLA AND ,ODGE 4HE RESULTS ON "LEPHARISMA ABOVE ARE ALSO NOT ENCOURAGING IN THIS REGARD BECAUSE SUCCESS WAS CLEARLY CONTINGENT ON PROPERTIES OF THE RESIDENT COMMUNITY .ONETHELESS OUR STUDIES DID SHOW SOME LARGE D IFFERENCES AMONG INTRODUCED SPECIES IN THE INITIAL RATES OF INCREASE ,AW )T WAS STRIKING THAT THE BACTERIOVORE 0ARAMECIUM WAS CONSTITUTIVELY A ET AL STRONG INVADER WHATEVER RESIDENT COMMUNITY IT ENCOUNTERED 4HERE ARE EVIDENTLY FEATURES OF 0ARAMECIUM THAT PREDISPOSE IT TO GROW ESPECIALLY WELL IN MICROCOSMS EVEN WHEN IT SEEMS LIKELY TO BE IN COMPETITION FOR RESOURCES WITH OTHER SPECIES 2ESIDENT COMMUNITY AND THE PROBABILITY OF ESTABLISHMENT
!LTHOUGH CERTAIN SPECIES MIGHT BE CONSTITUTIVELY GOOD OR BAD INVADERS IN GENERAL IT IS MORE REALISTIC TO ENVISAGE INVASION AS A JOINT PROPERTY OF AN INTRODUCED SPECIES AND THE SPECIES ALREADY RESIDENT IN THE COMMUNITY CONTINGENT ON THE INTERACTIONS BETWEEN THE NEW SPECIES AND THE RESIDENTS 4HE PER CAPITA BIRTH AND DEATH RATES IN %QUATION NEED TO BE THOUGHT OF AS BEING DETERMINED AS MUCH BY THE RESIDENT COMMUNITY AT THE TIME OF INTRODUCTION AS BY PROPERTIES OF THE INTRODUCED SPECIES 4HE IMPORTANCE OF RESIDENT AND INTRODUCED SPECIES AS CO DETERMINANTS OF INVA SIONS WAS CLEAR IN OUR EXPERIMENTAL INTRODUCTIONS OF PROTISTS INTO DIFFERENT COM MUNITIES ,AW ET AL 7E USED ANALYSIS OF VARIANCE TO PARTITION VARIATION IN INITIAL RATE OF INCREASE BETWEEN INTRODUCED SPECIES RESIDENT COMMUNITY AND INTRODUCTION = COMMUNITY INTERACTION !S ONE MIGHT EXPECT THE ANALYSIS SHOWED A STRONG INTRODUCTION = COMMUNITY INTERACTION 4HE VARIATION IN INITIAL GROWTH RATES OF "LEPHARISMA &IG AND SEE DISCUSSION ABOVE ILLUSTRATES THE EFFECT OF DIFFERENCES IN RESIDENT SPECIES "LEPHARISMA AS AN OMNIVORE IS ABLE TO EAT SMALL PROTISTS AND BACTERIA )N A COMMUNITY WITH 0ARAMECIUM ANOTHER LARGE PROTIST WITH WHICH IT CAN ONLY COMPETE FOR BACTERIA "LEPHARISMA USUALLY DECLINED RAPIDLY &IG A 7HEN WITH #OLPIDIUM WHICH IS SOMEWHAT SMALLER AND ALSO FEEDS ON BAC TERIA "LEPHARISMA WAS JUST ABOUT ABLE TO HOLD ITS OWN &IG B )N THE PRESENCE OF 4ETRAHYMENA A SMALL BACTERIOVORE WHICH "LEPHARISMA CAN EAT AS WELL AS BACTERIA "LEPHARISMA POPULATIONS GREW RAPIDLY &IG C FASTER IN FACT THAN WHEN ALL COM PETITION FOR BACTERIA WAS REMOVED &IG D !LTHOUGH INVASION MAY DEPEND ON INTERACTIONS AMONG SPECIES COULD COMMU NITIES HAVE GENERAL PROPERTIES THAT RENDER THEM MORE OR LESS LIABLE TO INVASION /NE LONG STANDING PREDICTION IS THAT COMMUNITIES WITH A LARGE NUMBER OF SPE CIES SHOULD BE LESS READILY INVADED THAN THOSE WITH FEW SPECIES %LTON ,EVINE AND $!NTONIO THIS IS ON THE GROUNDS THAT THE AVAILABLE NICHE SPACE IS MORE FULLY OCCUPIED !MONG THE FEW MICROCOSM EXPERIMENTS THAT HAVE INVES TIGATED THE RELATIONSHIP BETWEEN SPECIES RICHNESS AND INVASIBILITY ARE THE STUDIES BY -C'RADY 3TEED ET AL AND 2OBINSON AND $ICKERSON 4HE FORMER STUDY FOUND THAT THE PROTIST %UPLOTES WAS ABLE TO INVADE SOME NOT ALL MICROCOSMS OF LOW SPECIES RICHNESS AND ABLE TO INVADE NO COMMUNITIES OF HIGH RICHNESS 4HE LATTER USING THREE DIFFERENT SPECIES OF PROTISTS AS INVADERS APPEARED TO SUG GEST THAT INVASION SUCCESS MEASURED AS PRESENCE OF THE INVADER AFTER THREE WEEKS
0( 7ARREN 2 ,AW AND !* 7EATHERBY
WAS NOT STRONGLY INmUENCED BY COMMUNITY DIVERSITY THOUGH A LATER REANALYSIS ,EVINE AND $!NTONIO FOUND EVIDENCE FOR A NEGATIVE EFFECT OF DIVERSITY ON SUCCESS (OWEVER EXPERIMENTS OF THIS KIND HAVE THE PROPERTY THAT RICHER COMMU NITIES CONTAIN MORE DIFFERENT SPECIES (USTON AND ARE THEREFORE MORE LIKELY TO CONTAIN PARTICULAR SPECIES THAT DISCOURAGE OR POTENTIALLY PROMOTE INVASION BY PARTICULAR NEW SPECIES MAKING IT DIFlCULT TO ATTRIBUTE INVASION OUTCOMES TO EFFECTS OF DIVERSITY PER SE 7ARDLE (ODGSON ET AL LOOKING AT THE ABILITY OF PARTICULAR STRAINS OF THE BACTERIUM 0SEUDOMONAS mUORESCENS TO INCREASE WHEN RARE IN THE PRESENCE OF OTHER STRAINS FOUND AN EFFECT OF DIVERSITY ON THIS MEASURE OF INVASIBILITY BUT THAT IT WAS MUCH WEAKENED BY STATISTICAL REMOVAL OF THIS SAMPLING EFFECT .UMERICAL STUDIES OF COMMUNITY MODELS SUGGEST THAT COMMUNITIES BECOME INCREASINGLY RESISTANT TO INVASION AS TIME GOES ON AS A RESULT OF THE TURNOVER OF SPECIES 0OST AND 0IMM $RAKE B ,AW AND -ORTON )NCREASING INVASION RESISTANCE CAN APPLY EVEN IF THE RESIDENT COMMUNITY IS NOT ACCUMULAT ING SPECIES AND SUGGESTS THAT IT SHOULD BE RELATIVELY HARD FOR NEW SPECIES TO INVADE COMMUNITIES WITH LONG HISTORIES OF ASSEMBLY !LSO ONE MIGHT EXPECT COMMUNITIES CONSTRUCTED FROM LARGE SPECIES POOLS TO BE LESS READILY INVADED BECAUSE WITH MORE COMBINATIONS OF SPECIES TESTED DURING ASSEMBLY A lNER DEGREE OF TUNING TO INVASION RESISTANT STATES BECOMES POSSIBLE 4O DATE WE KNOW OF ONLY ONE MICROCOSM STUDY OF THE EFFECT OF COMMUNITY AGE ON INVASIBILITY ,ONG ET AL UNPUBLISHED MS IN THIS CASE OLDER COMMUNITIES WERE MORE RESISTANT TO TWO OUT OF THREE SPECIES INTRODUCED THAN THE YOUNGER COMMUNITIES (OWEVER THE OLDER COMMUNITIES WERE CREATED BY ALLOWING A LONGER PERIOD OF TIME TO ELAPSE FROM A lXED INITIAL SET OF SPECIES SO INVASION RESISTANCE HERE MAY BE BETTER INTERPRETED AS A CONSEQUENCE OF BEING FURTHER ALONG A TRANSIENT OF COMMUNITY DYNAMICS RATHER THAN AS A CON SEQUENCE OF TURNOVER OF SPECIES %NVIRONMENTAL FACTORS AND THE PROBABILITY OF ESTABLISHMENT
4HE EXTERNAL ENVIRONMENT OF THE COMMUNITY IS A FURTHER IMPORTANT DETERMINANT OF WHETHER A NEW SPECIES BECOMES ESTABLISHED )F RESISTANCE TO INVASION IS A CON SEQUENCE OF INTENSE INTERACTIONS BETWEEN NEW SPECIES AND RESIDENTS THEN FACTORS THAT DISRUPT THOSE INTERACTIONS MIGHT BE EXPECTED TO PROMOTE INVASION )N A RELATED VEIN IF THERE ARE ENVIRONMENTAL CONDITIONS THAT ENHANCE GROWTH OR PERSISTENCE OF SPECIES IN A COMMUNITY GENERALLY AND HENCE DIVERSITY THEN SUCH CONDITIONS MAY ALSO INCREASE THE LIKELIHOOD OF SUCCESS OF AN INTRODUCED SPECIES WHEN THE SUN SHINES IT SHINES ON THE JUST AND THE UNJUST ALIKE ,EVINE 3HEA AND #HESSON "YERS AND .OONBURG "OTH THESE POSSIBILITIES ARGUE FOR A SIGNIlCANT ROLE OF ENVIRONMENTAL VARIATION EITHER OVER TIME OR BETWEEN COMMUNITIES IN DETERMINING THE PROBABILITY OF ESTABLISHMENT OF A NEW SPECIES 4HE ENVIRONMENTAL FACTOR THAT HAS RECEIVED MOST ATTENTION IN THIS RESPECT IS DISTURBANCE THE ESSENTIAL CONCLUSION BEING THAT AT LEAST ON SOME TIMESCALES DISTURBANCE ENHANCES INVASION PRESUMABLY BY REDUCING THE INTENSITY OF BIOTIC
)NVASIONS IN MICROCOSMS
INTERACTIONS #RAWLEY 2EJMANEK (OBBS 4HOMPSON ET AL 3HER AND (YATT $AVIS ET AL 3HEA AND #HESSON !LTHOUGH MICROCOSMS WOULD SEEM AN OBVIOUS SYSTEM IN WHICH TO EXAMINE THIS EFFECT SYS TEMATICALLY WE KNOW OF ONLY ONE SUCH EXPERIMENT ,ONG ET AL UNPUBLISHED MS A STUDY USING HETEROTROPHIC PROTISTS WITH DISTURBANCE GENERATED BY DENSITY INDE PENDENT MORTALITY OF ALL RESIDENT SPECIES )N THIS CASE DISTURBANCE AFFECTED THE INTRODUCED SPECIES "LEPHARISMA 0ARAMECIUM AND #OLPIDIUM IN QUITE DIFFERENT WAYS THE MAIN EFFECTS OF DISTURBANCE WERE TO ENHANCE THE ABUNDANCE OF "LEPHARISMA TO LEAVE 0ARAMECIUM UNCHANGED AND TO REDUCE THE ABUNDANCE OF #OLPIDIUM ! SECOND MICROCOSM STUDY *IANG AND -ORIN WITH PROTISTS AND ROTIFERS PROVIDES ONE OF THE lRST EXPERIMENTAL TESTS OF THE EFFECT OF ANOTHER ENVIRONMENTAL FACTOR ENERGY AVAILABILITY ON INVASION )N THIS CASE INCREASED ENERGY AVAILABILITY PROMOTED INITIAL POPULATION GROWTH OF TWO DIFFERENT INTRODUCED SPECIES SUPPORT ING THE POSSIBILITY PREVIOUSLY SPECULATED ABOUT THEORETICALLY 3HEA AND #HESSON "YERS AND .OONBURG THAT SUCCESSFUL ESTABLISHMENT AND RESIDENT DIVERSITY MIGHT BE POSITIVELY CORRELATED THROUGH THE ACTION OF A COMMON FAC TOR (OWEVER &UKAMI AND -ORIN ALSO SHOW USING MICROCOSM SYSTEMS THAT THE ENERGY DIVERSITY RELATIONSHIPS IN COMMUNITIES ASSEMBLED BY SEQUENTIAL INVASIONS ARE AFFECTED BY THE ORDER IN WHICH INVASIONS OCCUR SUGGESTING THAT THE RELATIONSHIP BETWEEN ENERGY AND INVASION SUCCESS MAY NOT ALWAYS BE A SIMPLE ONE
#(!.'%3 4/ #/--5.)4)%3 &/,,/7).' %34!",)3(-%.4 /& ).6!$%23 &OLLOWING SUCCESSFUL ESTABLISHMENT AN INVADING SPECIES TYPICALLY BUILDS UP TO A SUBSTANTIAL POPULATION SIZE TAKING THE COMMUNITY BEYOND THE POINT AT WHICH %QUATION CAN POSSIBLY BE A GOOD APPROXIMATION )N EFFECT THE INVADING SPECIES BECOMES ABUNDANT ENOUGH TO CHANGE THE BIRTH AND DEATH RATES OF OTHER SPECIES IN THE COMMUNITY POTENTIALLY CAUSING CHANGE IN THEIR DENSITIES 4HE CHANGING DENSITY OF OTHER SPECIES FEEDS BACK TO THE INVADER POTENTIALLY CAUSING CHANGES IN ITS OWN BIRTH AND DEATH RATES !T THIS STAGE THERE IS NO ALTERNATIVE TO DEALING WITH THE FULL DYNAMICS OF THE COMMUNITY AUGMENTED BY THE INVADER AND ALL THE COMPLEXITIES THAT FOLLOW FROM THIS $ESPITE THE GREAT COMPLEXITIES OF COMMUNITY DYNAMICS THERE ARE SOME QUALITA TIVE QUESTIONS ABOUT THE INVADER AND THE COMMUNITY IT ENTERS THAT CAN BE ADDRESSED AND AGAIN WE DRAW ON EXAMPLES FROM OUR EXPERIMENTS WITH PROTISTS TO DO THIS $O INVADERS PERSIST IN THE LONG TERM
! PRIORI THERE IS NO REASON TO EXPECT SPECIES THAT BECOME ESTABLISHED IN THE SHORT TERM TO PERSIST IN THE LONG TERM )T IS QUITE POSSIBLE FOR AN INVADER TO CHANGE THE COMMUNITY IN SOME WAY WHICH IS DELETERIOUS TO ITSELF FOR INSTANCE BY DRIVING ITS PREY TO EXTINCTION (OWEVER IN ANALYSES OF COMMUNITIES WITH ,OTKA 6OLTERRA DYNAMICS SPECIES ABLE TO INCREASE FROM INITIAL LOW NUMBERS WERE ALSO PRESENT IN
0( 7ARREN 2 ,AW AND !* 7EATHERBY
&IG %XAMPLES OF INITIAL GROWTH OF INTRODUCED PROTISTS AND THE COMMUNITIES THAT PERSISTED IN THE LONG TERM WEEKS FROM EXPERIMENTS DESCRIBED IN ,AW ET AL AND 7ARREN ET AL ,INES SHOW THE ABUNDANCES OF THE INTRODUCED SPECIES FOR A PERIOD DETERMINED BY THE POPULATION EITHER SHOWING CONSISTENT POSITIVE GROWTH AND ACHIEVING NUMBERS GREATER THAN THE INITIAL INOCULUM GOING EXTINCT OR IF NEITHER CONDITION WAS SATISlED TO AN ARBITRARY END POINT DAYS 4HE LETTER CODES USED REPRESENT THE SPECIES
→
)NVASIONS IN MICROCOSMS
THE LONG TERM ,AW AND -ORTON 4HESE STUDIES USED AN ASYMPTOTIC CRITE RION CALLED PERMANENCE TO WORK OUT THE SPECIES COMPOSITION OF NEW COMMUNITIES THEREBY JUMPING OVER ANY EFFECTS THAT TRANSIENT DYNAMICS MIGHT HAVE ON PERSIS TENCE OF SPECIES 2EAL COMMUNITIES HAVE TO PASS ALONG THE TRANSIENTS AND IT IS OF COURSE POSSIBLE FOR THESE TRANSIENTS TO BRING THE INVADER TO A POPULATION SIZE LOW ENOUGH FOR EXTINCTION BY DEMOGRAPHIC STOCHASTICITY TO BECOME AN ISSUE AGAIN 1UESTIONS OF LONG TERM PERSISTENCE OF INVADERS CAN BE READILY ADDRESSED IN MICROCOSMS WHERE THE COMPONENT ORGANISMS HAVE SHORT GENERATION TIMES (ERE WE LOOK AT TWO ASPECTS OF THIS lRST THE VARIATION IN LONG TERM PERSISTENCE AMONG REPLICATE INTRODUCTIONS AND SECOND THE CORRESPONDENCE BETWEEN INITIAL ESTAB LISHMENT AND LONG TERM PERSISTENCE OF DIFFERENT COMBINATIONS OF RESIDENTS AND INTRODUCED SPECIES )N OUR EXPERIMENTS THE LONG TERM FATE OF SPECIES INTRODUCED TO COMMUNITIES WAS FAR FROM UNIFORM ACROSS THE REPLICATES WITHIN RESIDENT INTRODUCTION TREAT MENTS )N ABOUT TWO THIRDS OF THE FORTY NINE RESIDENT INTRODUCTION TREATMENTS ALL INVASIONS EITHER FAILED OR SUCCEEDED IN THE REMAINDER THE RESULTS WERE MIXED &IG )N OTHER WORDS ALTHOUGH THE COMMUNITIES CONTAINED THE SAME SPECIES WERE RUN UNDER THE SAME CONDITIONS AND WERE INOCULATED AT THE SAME TIME WITH THE SAME NUMBER OF INDIVIDUALS THERE WAS STILL A SUBSTANTIAL ELEMENT OF INDE TERMINACY ABOUT THE EVENTUAL FATE OF THE INTRODUCED SPECIES !S ALREADY NOTED 3ECTION ONE EXPLANATION IS THE SUCCESS OR FAILURE OF INITIAL ESTABLISHMENT AS ILLUSTRATED BY THE INVASION OF "LEPHARISMA INTO SYSTEMS CONTAINING 0ARAMECIUM EG &IG A &IG A AN INTERESTING CASE IN WHICH THE INVADER ESTABLISHED IN JUST ONE REPLICATE BUT IN THAT SYSTEM THEN PERSISTED IN THE LONG TERM (OWEVER IT IS NOTABLE THAT INITIAL ESTABLISHMENT AND LONG TERM PERSISTENCE WERE BY NO MEANS EQUIVALENT &IG 4HIS IS ILLUSTRATED BY !MOEBA INTRODUCED INTO A COMMUNITY OF 0ARAMECIUM #OLPIDIUM AND 4ETRAHYMENA &IG B IT ALWAYS ESTABLISHED ITSELF AT THE START BUT DID NOT PERSIST IN ALL REPLICATES IN THE LONG RUN )N PASSING IT IS ALSO INTERESTING TO NOTE THAT EVEN WHERE LONG TERM PERSISTENCE OF THE INVADER OCCURS IN ALL REPLICATES THERE COULD BE CONSIDERABLE VARIATION IN THE TIMING AND PATTERN OF ESTABLISHMENT &IG C AGAIN MAKING PREDICTION FROM INITIAL ESTABLISHMENT TO lNAL OUTCOME A DIFlCULT TASK )N OUR EXPERIMENTAL INVASIONS THE MISMATCH BETWEEN THE CONSISTENCY OF ESTAB LISHMENT AND PERSISTENCE IN INDIVIDUAL REPLICATE INTRODUCTIONS &IG WAS LARGELY
! !MOEBA " "LEPHARISMA # #OLPIDIUM % %UPLOTES 0 0ARAMECIUM 4 4ETRAHYMENA 4HE LETTERS IN THE TOP LEFT HAND CORNER OF THE GRAPH INDICATE THE RESIDENT COMMUNITY BEFORE INTRODUCTION THE VERTICAL DASHED LINE SHOWS THE POINT AT WHICH INTRODUCTIONS TOOK PLACE AND THE LETTER AT THE START OF THE TRAJECTORIES INDICATES THE IDENTITY OF THE INTRODUCED SPECIES 4HE LETTER OR COMBINATION OF LETTERS ASSOCIATED WITH EACH LINE SHOW THE COMMUNITY COMPOSITION OF THAT MICROCOSM AT THE END OF THE EXPERIMENT WEEKS AFTER INTRODUCTION ." POPULATION TRAJECTORY LINES ARE ONLY DRAWN TO THE POINT AT WHICH ONE OF THE ABOVE CRITERIA WAS MET WHILE THE lNAL SPECIES COMPOSITION SHOWN WAS THAT RECORDED AFTER WEEKS
0( 7ARREN 2 ,AW AND !* 7EATHERBY
DRIVEN BY PARTICULAR SPECIES &IG )N MOST INVASIONS SPECIES THAT SHOWED CLEAR INITIAL SUCCESS WERE ALSO PRESENT IN THE lNAL COMMUNITY BUT %UPLOTES DESPITE BEING A SUCCESSFUL INVADER IN SOME INSTANCES NEVER PERSISTED IN THE LONG TERM AND !MOEBA THOUGH MORE PERSISTENT OFTEN SHOWED THE SAME PATTERN &IG 3UCH SPECIES PROVIDE A COUNTER EXAMPLE TO THE THEORETICAL PREDICTIONS OUTLINED ABOVE ,AW AND -ORTON WHICH SUGGEST THAT SUCCESSFUL INVADERS SHOULD BECOME PERSISTENT MEMBERS OF THE INVADED SYSTEM EVEN IF THEY CAUSE OTHER CHANGES )NTERESTINGLY THESE SPECIES WERE THE TWO OBLIGATE PREDATORS IN OUR SPECIES POOL AND IT MAY BE THAT THE DISCREPANCY WAS RELATED TO TROPHIC POSITION $EMOGRAPHIC STO CHASTICITY IS A POSSIBLE CAUSE OF THE VULNERABILITY OF INTRODUCED PREDATORS BECAUSE FOR REASONS OF EITHER ENERGY AVAILABILITY OR OSCILLATORY POPULATION DYNAMICS THEIR POPULATION SIZES COULD HAVE BEEN SMALL FROM TIME TO TIME 4HERE IS CLEARLY VARIATION IN THE RELATIONSHIP BETWEEN INITIAL ESTABLISHMENT AND LONG TERM PERSISTENCE AT THE LEVEL OF INDIVIDUAL REPLICATES WHICH HAS OBVIOUS IMPLICATIONS FOR PREDICTING THE OUTCOME OF PARTICULAR INSTANCES OF AN INTRODUCTION
&IG -ISMATCH IN ESTABLISHMENT AND LONG TERM PERSISTENCE OF PROTISTS INTRODUCED INTO MICROCOSMS FROM 7EATHERBY "ARS SHOW THE PERCENTAGE OF MICROCOSMS IN WHICH THE INTRODUCED SPECIES BECAME ESTABLISHED OPEN BARS AND PERSISTED IN THE LONG TERM WEEKS SHADED BARS $ATA ARE GIVEN FOR ALL INDIVIDUAL MICROCOSMS ACROSS ALL RESIDENT COMMUNITIES INTO WHICH THE SPECIES WAS INTRODUCED SO VALUES TAKE INTO ACCOUNT THE MIXED OUTCOMES SHOWN IN &IG N IS THE NUMBER OF MICROCOSMS INTO WHICH EACH SPECIES WAS INTRODUCED USUALLY REPLICATES OF EACH RESIDENT COMMUNITY BUT IN SOME CASES ONLY OR
)NVASIONS IN MICROCOSMS
(OWEVER WE CAN ALSO LOOK AT THE BROADER PICTURE AND FOCUS ON THE RESIDENT INTRO DUCTION COMBINATIONS IN WHICH THE MAJORITY OF REPLICATES HAD THE SAME OUT COME BOTH IN TERMS OF ESTABLISHMENT AND COMPOSITION OF THE lNAL COMMUNITY 4AKING JUST THESE MORE CONSISTENT OUTCOMES A TOTAL OF THIRTY lVE RESIDENT INTRO DUCTION COMBINATIONS IN THE MAJORITY OF CASES THE INTRODUCED SPECIES EITHER ESTABLISHED AND PERSISTED OR FAILED BOTH TO ESTABLISH AND TO PERSIST 4HERE WERE RELATIVELY FEW CASES IN WHICH SPECIES ESTABLISHED AND THEN FAILED TO PERSIST AND NONE IN WHICH SPECIES FAILED TO ESTABLISH BUT YET PERSISTED 4HIS LAST CATEGORY MAY SEEM A TRUISM BUT IT IS NOT SO BECAUSE IT WOULD BE POSSIBLE FOR AN INVADER TO PERSIST WITHOUT SHOWING NET POPULATION GROWTH THEREFORE FAILING TO MEET THE CRITERION FOR ESTABLISHMENT 4HUS THE MESSAGE FROM THESE MICROCOSM STUDIES IS THAT INITIAL ESTABLISHMENT OF AN INTRODUCED SPECIES WITHIN A COMMUNITY WHICH COULD FEASIBLY BE MEASURED EVEN IN THE lELD IS A FAIR BUT NOT PERFECT PREDICTOR OF ITS FATE IN THE LONG TERM $O THE INVADERS HAVE AN IMPACT ON THE RESIDENTS
7E HAVE SO FAR FOCUSED ON THE FATE OF THE INVADER BUT IT IS OFTEN NOT THE INVADER AS SUCH WHICH IS OF PRIMARY CONCERN BUT RATHER THE IMPACT OF THE INVADER ON THE COMMUNITIES IT INVADES 0ARKER ET AL 'ENERALIZATIONS ABOUT THESE IMPACTS ARE BOUND TO BE HARD TO MAKE BECAUSE OF THE COMPLEX NONLINEAR COUPLINGS THAT CHARACTERIZE COMMUNITY DYNAMICS )T IS ENTIRELY POSSIBLE FOR THE IMPACT TO BE NEGLI GIBLE OR FOR OTHER SPECIES TO BE DRIVEN TO EXTINCTION !N INVADER MAY TARGET PARTIC ULAR SPECIES EG $UTCH %LM DISEASE IN THE 5+ 7ILLIAMSON OR HAVE EFFECTS THAT RAMIFY WIDELY THROUGH THE COMMUNITY EG WHOLE ECOSYSTEM EFFECTS OF -YRICA FAYA ON VOLCANIC SITES IN (AWAII 6ITOUSEK AND 7ALKER THE DEMISE OF KELP BEDS FOLLOWING KILLER WHALE ARRIVAL ON THE 0ACIFIC COAST OF . !MERICA %STES ET AL -ICROCOSM COMMUNITIES ARE ESPECIALLY AMENABLE TO SYSTEM ATIC INVESTIGATION OF IMPACTS OF INVADERS BECAUSE WE CAN TAKE THEM APART IN AN ORDERLY REPLICATED WAY TO SEE WHAT EFFECT EACH INVADING SPECIES EVENTUALLY HAS ON THE SPECIES COMPOSITION OF EACH COMMUNITY AND HOW THIS RELATES TO THE INVADERS OWN ABILITY TO PERSIST 6ARIOUS SCENARIOS ARE POSSIBLE THE INVADER PERSISTS AND THE RESIDENT COMMUNITY IS CHANGED THE INVADER PERSISTS AND THE RESIDENT COMMUNITY IS UNCHANGED THE INVADER FAILS TO PERSIST BUT THE RESIDENT COMMU NITY IS CHANGED THE INVADER FAILS AND THE RESIDENT COMMUNITY IS UNCHANGED 3ITUATION IS THE CLASSIC @PROBLEM INVASION AN INVADER THAT BECOMES A PART OF THE COMMUNITY AND CHANGES IT USUALLY BY GENERATING ONE OR MORE EXTINCTIONS IN THE RESIDENTS THE INVASION OF THE COMMUNITY COMPRISING "LEPHARISMA AND #OLPIDIUM BY 0ARAMECIUM &IG A PROVIDES AN EXAMPLE OF THIS FROM OUR MICRO COSM EXPERIMENTS 4HESE ARE ALSO THE BEST DOCUMENTED INVASION CASE STUDIES IN NATURAL SYSTEMS EG %LTON $RAKE ET AL BECAUSE INVADERS THAT PERSIST ARE MOST READILY DOCUMENTED AND STUDIED AND THEIR IMPACTS ARE OF CONCERN )N WE HAVE SIMPLE AUGMENTATION OF THE COMMUNITY BY AN INVADER /F COURSE THE COLONIZING SPECIES MAY ALTER DENSITIES OF OTHER SPECIES BUT NOT TO A SUFlCIENT
0( 7ARREN 2 ,AW AND !* 7EATHERBY
EXTENT TO CAUSE SPECIES LOSSES )NVASION OF "LEPHARISMA SYSTEMS BY 0ARAMECIUM PRO VIDES AN EXAMPLE ALTHOUGH THE RESIDENT PERSISTED &IG B IT WAS ABOUT ONE lFTH AS ABUNDANT IN THE INVADED SYSTEMS AS IN THE UNINVADED CONTROLS AT THE END OF THE EXPERIMENT 4HERE ARE EXAMPLES FROM NATURAL SYSTEMS OF INVADERS WHICH APPEAR TO ADD THEMSELVES TO SYSTEMS BUT CAUSE LITTLE IMPACT EG THE FULMAR &ULMARIS GLACIA LIS AN ARCTIC SEABIRD 7ILLIAMSON ET SEQ 4HE FREQUENCY OF NON IMPACTIVE INVASIONS HOWEVER REMAINS A CONTROVERSIAL ISSUE 0ARKER ET AL FOR EXAMPLE SEE 3IMBERLOFF (ERBOLD AND -OYLE 0IMM BECAUSE IT CAN BE DIF lCULT TO ESTABLISH IMPACTS AND TEST FOR CAUSALITY IF THERE ARE NO SUITABLE UNINVADED SYSTEMS FOR COMPARISON 3CENARIO REQUIRES THAT A SPECIES FAILS TO PERSIST BUT HAS SUFlCIENTLY STRONG EFFECTS ON THE RESIDENT COMMUNITY WHILE IT IS PRESENT TO CAUSE CHANGES IN SPE CIES COMPOSITION 3UCH SPECIES CAN BE TERMED @CATALYSTS )N OUR EXPERIMENTS CATALYSTS WERE NOT COMMON BUT TWO SPECIES DID PLAY THIS ROLE IN SOME SITUA TIONS PRINCIPALLY %UPLOTES AND ALSO !MOEBA IN OCCASIONAL REPLICATES &OR EXAMPLE %UPLOTES ESTABLISHED ITSELF IN A COMMUNITY COMPRISING 0ARAMECIUM #OLPIDIUM AND 4ETRAHYMENA CAUSED THE LATTER TWO SPECIES TO GO EXTINCT IN MOST SYSTEMS AND THEN WENT TO EXTINCTION ITSELF &IG C )N THIS EXAMPLE %UPLOTES DID ESTABLISH INCREASE IN POPULATION SIZE AFTER INTRODUCTION BUT THERE WERE ALSO CASES EG %UPLOTES INVADING THE COMMUNITY OF 0ARAMECIUM AND 4ETRAHYMENA IN WHICH THE INVADER DID NOT CONSISTENTLY INCREASE ABOVE ITS INITIAL NUMBERS BUT NONETHELESS CAUSED AN EXTINCTION OF ONE OF THE RESIDENTS 4ETRAHYMENA BEFORE ITSELF GOING EXTINCT 4HERE IS SOME THEORETICAL EVIDENCE OF SUCH EFFECTS IN MODELS OF INVASIONS INTO COMPETI TIVE SYSTEMS #ASE 3OME EXAMPLES OF SITUATIONS IN NATURAL SYSTEMS SEEM TO SHOW THIS BEHAVIOUR EG &LUX BUT THE APPARENT RARITY OF SUCH OBSERVA TIONS 7ILLIAMSON IS CONSISTENT WITH THE RELATIVE RARITY OF THESE EFFECTS IN OUR EXPERIMENTAL SYSTEMS &INALLY WE HAVE SCENARIO )N THIS CASE THE FAILURE OF THE INTRODUCED SPECIES TO PERSIST COUPLED WITH THE LACK OF CHANGE IN THE RESIDENT COMMUNITY EG &IG D SUGGESTS THAT EFFECTIVELY THERE IS NOTHING WE WOULD RECOGNIZE AS AN INVASION AT ALL )N THE MAJORITY OF INTRODUCTIONS WITH THIS OUTCOME THIS WAS VERY MUCH THE CASE WITH THE INTRODUCED SPECIES SIMPLY DECLINING TO EXTINCTION AFTER INTRODUCTION (OWEVER THERE WERE ALSO A FEW CASES IN WHICH INTRODUCED SPECIES SHOWED SUCCESS FUL INITIAL ESTABLISHMENT WHILE NONETHELESS EVENTUALLY GOING EXTINCT AND LEAVING THE RESIDENT SET UNCHANGED FOR EXAMPLE IN MOST INTRODUCTIONS OF %UPLOTES INTO POPULATIONS OF 4ETRAHYMENA %UPLOTES ACHIEVED POPULATIONS OF SEVERAL THOUSANDS OF INDIVIDUALS BEFORE DISAPPEARING %VIDENTLY AN INTRODUCED SPECIES CAN ACHIEVE A SIGNIlCANT PRESENCE DURING SOME PART OF AN ULTIMATELY UNSUCCESSFUL INVASION "ECAUSE OUR MICROCOSM EXPERIMENTS CONTAINED ALL POSSIBLE PERMUTATIONS OF RESIDENT COMMUNITY AND INTRODUCED SPECIES WE CAN USE THESE RESULTS TO LOOK AT THE FREQUENCIES OF THESE VARIOUS OUTCOMES AND THE CIRCUMSTANCES UNDER WHICH THEY OCCUR 4AKING JUST THE THIRTY SIX RESIDENT INTRODUCTION TREATMENTS IN WHICH THE MAJORITY OF REPLICATES ENDED UP WITH THE SAME SPECIES COMPOSITION IN THE LONG TERM THE RESIDENT COMMUNITY WAS ALTERED IN JUST NINE OF THESE 7ARREN ET AL
)NVASIONS IN MICROCOSMS
&IG %XAMPLES OF INITIAL GROWTH OF INTRODUCED PROTISTS AND THE COMMUNITIES THAT PERSISTED IN THE LONG TERM FOR COMBINATIONS OF PERSISTENCE AND NON PERSISTENCE OF THE INVADER AND IMPACT OR LACK OF IMPACT ON THE RESIDENTS 3TRUCTURE AND NOTATION AS FOR &IG
!S ONE MIGHT EXPECT EG #ASE CHANGES TO THE RESIDENT C OMMUNITY BECAME MORE LIKELY AS THE NUMBER OF RESIDENT SPECIES INCREASED RISING FROM ABOUT IN ONE SPECIES COMMUNITIES TO IN TWO SPECIES COMMUNITIES TO IN THREE SPECIES COMMUNITIES THOUGH THERE ARE ONLY TWO THREE SPECIES COMBINATIONS 4HE EFFECT OF THE INTRODUCED SPECIES WAS MOST OFTEN NEGATIVE CAUSING EXTINCTION OF RESIDENT SPECIES SIX CASES ALTHOUGH THERE WERE THREE INSTANCES OF THE REVERSE EFFECT IE A RESIDENT SPECIES #OLPIDUM IN TWO SYSTEMS AND 0ARAMECIUM IN ONE FOR WHICH PERSISTENCE SEEMED TO BE ENHANCED BY THE PRESENCE OF THE INVADERS !MOEBA 0ARAMECIUM AND %UPLOTES 0UTTING THESE RESULTS TOGETHER WE CAN BREAK DOWN THE THIRTY SIX RESIDENT INTRODUCTION TREATMENTS INTO THOSE IN WHICH THE INTRODUCED SPECIES PERSISTED AND THE RESIDENT COMMUNITY WAS CHANGED THE INTRODUCED SPECIES PERSISTED BUT THE RESIDENT COMMUNITY WAS NOT CHANGED THE INTRODUCED SPECIES DID NOT PER SIST BUT THE RESIDENT COMMUNITY WAS CHANGED AND THE INTRODUCED SPECIES DID NOT PERSIST AND THE RESIDENTS WERE UNCHANGED #LEARLY THERE IS NO SIGNIlCANT ASSOCIATION BETWEEN THE LIKELIHOOD OF ESTABLISHMENT OF INTRODUCED SPECIES AND
0( 7ARREN 2 ,AW AND !* 7EATHERBY
THE LIKELIHOOD OF THE RESIDENT COMMUNITY BEING ALTERED &ISHERS %XACT 4EST P )F THIS SORT OF PATTERN TURNS OUT TO HAVE ANY SORT OF GENERALITY IT LENDS WEIGHT TO THE VIEW THAT KNOWING A SPECIES IS LIKELY TO BECOME ESTABLISHED AND PERSIST IN A SYSTEM MAY PROVIDE NO USEFUL GUIDE TO WHETHER IT IS GOING TO CHANGE THE EXISTING COMMUNITY IN OTHER WAYS
).6!3)/.3 !.$ #/--5.)49 !33%-",9 !LTHOUGH OUR MAIN FOCUS HERE HAS BEEN ON THE COMPONENTS OF INDIVIDUAL INVA SIONS THE ARRIVAL OF A NEW SPECIES AND ANY CHANGES IN COMMUNITY COMPOSITION THAT ACCOMPANY THIS ARE JUST A SINGLE STEP IN A LONGER TERM PROCESS OF COMMUNITY DEVELOPMENT THROUGH THE GRADUAL TURNOVER OF SPECIES 3UCH TURNOVER GENERALLY TERMED @COMMUNITY ASSEMBLY IS DETERMINED BY FACTORS ACTING AT VERY DIFFERENT SCALES FROM BIOGEOGRAPHIC CONSTRAINTS ON THE SPECIES POOL THROUGH TO PATTERNS OF NICHE DIFFERENTIATION AMONG COMPETITORS IN A COMMUNITY $IAMOND AND #ASE $RAKE A 'RAY ET AL 7EIHER AND +EDDY BUT HAS THE SAME UNDERLYING DRIVER THE ARRIVAL ESTABLISHMENT AND SOMETIMES PERSISTENCE OF SPECIES FROM OUTSIDE THE SYSTEM IE INVASION (ERE CERTAINLY THE LINKS BETWEEN COMMUNITY ECOLOGY AND INVASION BIOLOGY ARE EXPLICIT INVASIONS DRIVE COMMUNITY CHANGE /F COURSE IN MOST OF THE @INVASIONS EFFECTING SUCH CHANGES THE INVADER IS NOT FROM A NEW REGION DISSOCIATED FROM THE SPECIES IN THE RESIDENT COMMUNITY BUT NONETHELESS THE COMPONENTS OF THE INVASION PROCESS WE HAVE DISCUSSED ABOVE APPLY EQUALLY TO WHAT MIGHT BE TERMED @LOCAL INVASIONS AND THEREFORE TO COM MUNITY CHANGE IN GENERAL -ICROCOSM SYSTEMS FOR THE SAME REASONS THAT MAKE THEM USEFUL FOR STUDY ING INVASIONS HAVE PLAYED A SIGNIlCANT ROLE IN EXPLORING COMMUNITY ASSEMBLY )N PARTICULAR MICROCOSMS OF ALGAE PROTISTS AND SMALL METAZOANS HAVE BEEN USED TO EXAMINE THE EFFECTS OF NON SIMULTANEOUS INVASION INVASION ORDER AND INVASION RATE ON THE DEVELOPMENT OF COMMUNITY STRUCTURE $ICKERSON AND 2OBINSON 2OBINSON AND $ICKERSON 2OBINSON AND %DGEMON $RAKE &UKAMI AND -ORIN 4HE GENERAL CONCLUSION FROM THESE STUDIES IS THAT CONTINGENCIES IN THE INVASION PROCESS CAN RESULT IN SUBSTANTIAL DIFFERENCES IN THE STRUCTURE OF THE lNAL COMMUNITIES THAT ARE FORMED 3UCH STUDIES ARE GENERALLY PRESENTED IN THE CONTEXT OF COMMUNITY ASSEMBLY AND DOCUMENT THE OUTCOMES OF DIFFERENT SEQUENCES OR RATES OF SPECIES ARRIVAL RATHER THAN THE DETAILS OF INDIVIDUAL INVASIONS WHICH HAVE BEEN OUR FOCUS HERE BUT IT IS CLEAR THAT THE SORTS OF EFFECTS WE SEE IN INDIVIDUAL INVASIONS IN PARTICULAR STOCHASTIC EFFECTS IN LOW POPULATIONS AND THE INTERDEPENDENCE OF SUCCESS ON INVADER AND RESIDENT COMMUNITY IDENTITIES COULD BE THE DRIVERS OF SUCH ASSEMBLY SEQUENCE EFFECTS EG $RAKE $RAKES STUDY EVEN FOUND EVIDENCE TO SUGGEST THAT INVASIBILITY OF SYSTEMS WITH IDENTICAL SPECIES COMPOSITIONS MAY TO BE AFFECTED BY DIFFERENCES IN THEIR ASSEMBLY HISTORY -ICROCOSMS ARE ALSO BEING USED TO EXAMINE THE EFFECTS OF THE CONTINUOUS ASSEMBLY AND DISASSEMBLY OF COMMUNITIES IN MULTIPLE HABITAT PATCHES WHERE INVASIONS ARE
)NVASIONS IN MICROCOSMS
A NECESSARY AND NATURAL PART OF THE MAINTENANCE OF POPULATIONS AND COMMUNITIES WITHIN A @LANDSCAPE $RAKE ET AL (OLYOAK AND ,AWLER A B 7ARREN "URKEY (OLT ET AL AND WITH THE POSSIBLE THOUGH LARGELY UNEXPLORED OPPORTUNITY SUCH WORK PROVIDES FOR EXAMINING THE SPREAD OF INVADERS THROUGH A COMMUNITY LANDSCAPE 0UTTING THESE COMPONENTS TOGETHER ALLOWS US TO CONSTRUCT A DESCRIPTION OF THE COMMUNITY SPACE PERSISTENT COMMUNITIES AND THE ROUTES THAT COMMUNITY ASSEMBLY CAN TAKE THROUGH THAT SPACE AS A RESULT OF INVASIONS INTO EACH COMMUNI TY :IMMERMAN ET AL 7ARREN ET AL WHICH WE CAN TERM AN ASSEMBLY GRAPH EG &IG !SSEMBLY GRAPHS CAN CLARIFY FEATURES OF COMMUNITY ASSEMBLY THAT WOULD OTHERWISE REMAIN OBSCURE &OR EXAMPLE THE GRAPH SHOWN IN &IG HAS A CYCLIC END STATE DRIVEN BY THE PARTICULAR CHARACTERISTICS OF %UPLOTES %UPLOTES INVADES THE COMMUNITY COMPOSED OF 0ARAMECIUM AND 4ETRAHYMENA ELIMINATES THE 4ETRAHYMENA AND THEN ITSELF GOES TO EXTINCTION LEAVING A COMMUNITY OF JUST 0ARAMECIUM WHICH CAN THEN BE REINVADED BY 4ETRAHYMENA TO RETURN TO THE ORIGINAL COMMUNITY !NOTHER FEATURE OF THE GRAPH IS THE EXISTENCE OF COMMUNITIES SUCH AS THAT COMPRISING #OLPIDIUM AND 4ETRAHYMENA WHICH PERSIST IF ALL SPECIES ARE INTRODUCED TOGETHER BUT WHICH CANNOT READILY BE CREATED BY SEQUENTIAL INVASION FROM ANY OTHER PERSISTENT COMMUNITY 4HE GENERALITY OF SUCH FEATURES REMAINS TO BE ESTABLISHED BUT WHAT IS CLEAR IS THAT UNDERSTANDING THE INVASION PROCESS LIES AT THE HEART OF UNDERSTANDING THIS FUNDAMENTAL ASPECT OF COMMUNITY ECOLOGY
-)#2/#/3-3 !3 3934%-3 &/2 345$9).' ).6!3)/. ")/,/'9 2EMARKABLY LITTLE WORK ON BIOLOGICAL INVASIONS HAS BEEN DONE IN MICROCOSM SYS TEMS YET EVEN FROM THE FEW STUDIES THERE ARE A NUMBER OF MESSAGES EMERGE 7ORK IN MICROCOSMS HIGHLIGHTS THE PROBABILISTIC NATURE OF THE INVASION PROCESS THE JOINT DEPENDENCE OF INVASION SUCCESS ON BOTH INVADER IDENTITY AND RESIDENT COMMUNITY COMPOSITION THE RELATIONSHIPS BETWEEN DIFFERENT PHASES OF THE INVASION PROCESS ESTABLISHMENT PERSISTENCE IMPACT AND THE IMPORTANCE OF DISTURBANCE ENERGY AND SPECIES NUMBER 4HIS SEEMS A RESPECTABLE YIELD OF INFORMATION FROM A MODEST AMOUNT OF EXPERIMENTAL WORK 4HESE RESULTS WERE MADE POSSIBLE BY THE HAVING THE FACILITY TO MANIPULATE RESIDENT AND INTRODUCED SPECIES BY FOLLOWING THE OUTCOMES OVER TENS TO HUNDREDS OF GENERATIONS AND BY PUTTING IN PLACE ENOUGH REPLICATION TO PARTITION VARIATION WITHIN AND BETWEEN TREATMENTS 4HERE IS LITTLE LIKELIHOOD OF BEING ABLE TO CARRY OUT EXPERIMENTS AT EQUIVALENT TEMPORAL AND SPATIAL SCALES IN THE lELD &IELD STUDIES HAVE PROVIDED IMPORTANT INSIGHTS INTO ALL THESE ELEMENTS OF INVASIONS BUT MICROCOSMS BRING THE FACILITY TO RELATE THE LONG AND SHORT TERM OUTCOMES OF THE INVASION PROCESS AND QUANTIFY THE STOCHASTICITIES INVOLVED /F COURSE THE SCARCITY OF SUCH STUDIES IN MICROCOSMS PRECLUDES MUCH ASSESSMENT OF THE GENERALITY OF THESE RESULTS AS IT WOULD IN ANY SYSTEM 4HE DIFFERENCE IS THAT IN MICROCOSMS TESTING THIS GENERALITY IS AN ENTIRELY FEASIBLE PROSPECT
0( 7ARREN 2 ,AW AND !* 7EATHERBY
&IG 4HE ASSEMBLY GRAPH FOR THE SIX SPECIES PROTIST SYSTEM DESCRIBED IN 7ARREN ET AL 4HE LETTER CODES AS FOR &IG IN BRACKETS REPRESENT THE PERSISTENT COMMUNITIES AND THE ARROWS REPRESENT TRANSITIONS BETWEEN THOSE COMMUNITIES PRODUCED BY INTRODUCTIONS OF THE SPECIES REPRESENTED BY THE LETTER CODE ON THE ARROW !RROWS ARE BASED ON THE MAJORITY TRANSITIONS OBSERVED IN THE EXPERIMENTS IN EACH CASE SO THAT ONLY A SINGLE OUTCOME FROM ANY PARTICULAR INVASION IS DEPICTED SEE 7ARREN ET AL FOR AN ALTERNATIVE PRESENTATION THAT INCLUDES THE VARIATION IN OUTCOMES $OTTED ARROWS SHOW WHERE CERTAIN RESIDENT COMMUNITIES HAD A TENDENCY TO COLLAPSE EVENTUALLY EVEN IN THE ABSENCE OF INVASIONS AND THE DASHED ARROWS ARE TRANSITIONS THAT ARE BASED ON INFORMATION FROM ONLY TWO REPLICATES 4HE COMMUNITIES DEPICTED IN GREY ARE THOSE FORMED AS A RESULT OF INVASIONS BUT NOT FOUND IN INITIAL EXPERIMENTS TO ESTABLISH WHICH SETS OF SPECIES COULD COEXIST AND HENCE FOR WHICH NO INVASION TRIALS WERE CARRIED OUT AND SO WE HAVE NO INFORMATION ON THEIR INVASIBILITY &IGURE REPRODUCED BY PERMISSION OF THE %COLOGICAL 3OCIETY OF !MERICA
)NVASIONS IN MICROCOSMS
4HAT SUCH QUESTIONS COULD BE ADDRESSED IS THOUGH PERHAPS NOT THE ISSUE 4HOSE SCEPTICAL OF THE MICROCOSM APPROACH WOULD QUESTION WHETHER EVEN IF WE HAD SUCH STUDIES WE WOULD BE ANY THE WISER ABOUT INVASIONS IN THE lELD 4HE ARGUMENTS ABOUT USING MICROCOSMS IN ECOLOGY ARE WELL REHEARSED EG $RAKE ET AL #ARPENTER $RENNER AND -AZUMDER ,AWLER *ESSUP ET AL BUT AGAINST THE LIMITATIONS WE HAVE TO SET THE ADVANTAGES OUTLINED ABOVE -ICROCOSMS DO NOT ALLOW US TO MAKE PRACTICAL MANAGEMENT DECISIONS ABOUT SPECIlC INVASIONS BUT THEY DO ALLOW US TO TEST OUR INTUITION REASONING AND THEORY AS TO THE BASIC ECOLOGICAL PRINCIPLES THAT UNDERPIN THEM $RAKE ET AL ,AWLER 7E TAKE THE VIEW THAT MICROCOSMS CAN AND SHOULD PLAY A SIGNIlCANT ROLE IN DEVELOPING OUR UNDERSTANDING OF INVASION PROCESSES 7E WILL UNDERSTAND INVA SIONS BETTER ARMED WITH GOOD EXPERIMENTAL DATA FROM MICROCOSMS IN COMBINATION WITH THEORY lELD EXPERIMENTS AND OBSERVATIONAL DATA THAN FROM ANY OF THESE SOURCES ALONE AND WE WILL ALSO END UP KNOWING A GREAT DEAL MORE ABOUT HOW COMMUNITIES WORK AS A CONSEQUENCE
!#+./7,%$'%-%.43 7E ARE GRATEFUL TO THE EDITORS FOR THE INVITATION TO CONTRIBUTE TO THIS VOLUME /UR THANKS GO TO 0ETER -ORIN ,IN *IANG AND :AC ,ONG FOR KINDLY SENDING US MANU SCRIPTS PRIOR TO PUBLICATION TO -ARK 7ILLIAMSON AND +EN 4HOMPSON FOR HELPFUL DISCUSSIONS ABOUT INVASIONS AND TO *EREMY &OX 4AD &UKAMI /WEN 0ETCHEY $AVID 7ARDLE AND -ARK 7ILLIAMSON FOR THOUGHTFUL COMMENTS ON THE MANUSCRIPT 4HE EXPERIMENTAL WORK DISCUSSED IN THIS CHAPTER WAS FUNDED BY A GRANT FROM THE 5+ .ATURAL %NVIRONMENT 2ESEARCH #OUNCIL
2%&%2%.#%3 !NDERSON 2 - AND -AY 2 - )NFECTIOUS DISEASES OF HUMANS /XFORD 5NIVERSITY 0RESS /XFORD 5 + "AILEY . 4 * %LEMENTS OF STOCHASTIC PROCESSES 7ILEY .EW 9ORK 5 3 ! "URKEY 4 6 -ETAPOPULATION EXTINCTION IN FRAGMENTED LANDSCAPES USING BACTERIA AND PROTOZOA COMMUNITIES AS MODEL ECOSYSTEMS !M .AT "YERS * % AND .OONBURG % ' 3CALE DEPENDENT EFFECTS OF BIOTIC RESISTANCE TO BIO LOGICAL INVASION %COLOGY #ARPENTER 3 2 -ICROCOSM EXPERIMENTS HAVE LIMITED RELEVANCE FOR COMMUNITY AND ECOSYSTEM ECOLOGY %COLOGY #ARPENTER 3 2 -ICROCOSM EXPERIMENTS HAVE LIMITED RELEVANCE FOR COMMUNITY AND ECOSYSTEM ECOLOGY REPLY %COLOGY #ASE 4 * )NVASION RESISTENCE ARISES IN STRONGLY INTERACTING SPECIES RICH MODELS OF COMPETITION COMMUNITIES 0ROC .ATN !CAD 3CI 5 3 !
0( 7ARREN 2 ,AW AND !* 7EATHERBY
#ASE 4 * 3URPRISING BEHAVIOR FROM A FAMILIAR MODEL AND IMPLICATIONS FOR COMPETI TION THEORY !M .AT #RAWLEY - * 4HE POPULATION BIOLOGY OF INVADERS 0HIL 4RANS 2OY 3OC ,OND " #RAWLEY - * #HANCE AND TIMING IN BIOLOGICAL INVASIONS PP )N $RAKE * ! -OONEY ( ! DI #ASTRI & 'ROVES 2 ( +RUGER & * 2EJMANEK - AND 7ILLIAMSON - EDS "IOLOGICAL INVASIONS A GLOBAL PERSPECTIVE 3#/0% *OHN 7ILEY AND 3ONS #HICHESTER 5+ $AVIS - ! 'RIME * 0 AND 4HOMPSON + &LUCTUATING RESOURCES IN PLANT COMMU NITIES A GENERAL THEORY OF INVASIBILITY * %COL $AVIS - ! AND 0ELSOR - %XPERIMENTAL SUPPORT FOR A RESOURCE BASED MECHANISTIC MODEL OF INVASIBILITY %COL ,ETT $IAMOND * AND #ASE 4 * /VERVIEW INTRODUCTIONS EXTINCTIONS EXTERMINATIONS AND INVASIONS PP )N $IAMOND * AND #ASE 4 * EDS #OMMUNITY %COLOGY (ARPER AND 2OW .EW 9ORK 5 3 ! $ICK * 4 ! 0LATVOET $ AND +ELLY $ 7 0REDATORY IMPACT OF THE FRESHWATER INVADER $IKEROGAMMARUS VILLOSUS #RUSTACEA !MPHIPODA #AN * &ISH !QUAT 3CI $ICKERSON * % AND 2OBINSON * $ 4HE ASSEMBLY OF MICROSCOPIC COMMUNITIES PAT TERNS OF SPECIES IMPORTANCE 4RANS !M -ICROSC 3OC $ICKERSON * % AND 2OBINSON * 6 -ICROCOSMS AS ISLANDS A TEST OF THE -AC!RTHUR 7ILSON EQUILIBRIUM THEORY %COLOGY $ICKERSON * % AND 2OBINSON * 6 4HE CONTROLLED ASSEMBLY OF MICROCOSMIC COM MUNITIES THE SELECTIVE EXTINCTION HYPOTHESIS /ECOLOGIA $RAKE * ! A #OMMUNITIES AS ASSEMBLED STRUCTURES DO RULES GOVERN PATTERN 4RENDS %COL %VOL $RAKE * ! B 4HE MECHANICS OF COMMUNITY ASSEMBLY AND SUCCESSION * 4HEOR "IOL $RAKE * ! #OMMUNITY ASSEMBLY MECHANICS AND THE STRUCTURE OF AN EXPERIMENTAL SPECIES ENSEMBLE !M .AT $RAKE * ! &LUM 4 % 7ITTEMAN ' * 6OSKUIL 4 (OLYMAN ! - #RESON # +ENNY $ ! (UXEL ' 2 ,ARUE # 3 AND $UNCAN * 2 4HE CONSTRUCTION AND ASSEMBLY OF AN ECOLOGICAL LANDSCAPE * !NIM %COL $RAKE * ! (UXEL ' 2 AND (EWITT # , -ICROCOSMS AS MODELS FOR GENERATING AND TESTING COMMUNITY THEORY %COLOGY $RAKE * ! -OONEY ( ! DI #ASTI & 'ROVES 2 ( +RUGER & * 2EJMÉNEK - AND 7ILLIAMSON - ED "IOLOGICAL INVASIONS A GLOBAL PERSPECTIVE 3#/0% *OHN 7ILEY AND 3ONS #HICHESTER 5+ $RENNER 2 7 AND -AZUMDER ! -ICROCOSM EXPERIMENTS HAVE LIMITED RELEVANCE FOR COMMUNITY AND ECOSYSTEM ECOLOGY %COLOGY $UKES * 3 "IODIVERSITY AND INVASIBILITY IN GRASSLAND MICROCOSMS /ECOLOGIA %LTON # 3 4HE ECOLOGY OF INVASIONS BY ANIMALS AND PLANTS -ENTHUEN ,ONDON 5+
)NVASIONS IN MICROCOSMS
%STES * ! 7ILLIAMS - 4 AND $OAK $ & +ILLES WHALE PREDATION ON SEA OTTERS LINKING OCEANIC AND NEARSHORE ECOSYSTEMS 3CIENCE &LUX * % 7ORLD DISTRIBUTION PP )N 4HOMPSON ( 6 AND +ING # - EDS 4HE %UROPEAN RABBIT THE HISTORY AND BIOLOGY OF A SUCCESSFUL INVADER /XFORD 5NIVERSITY 0RESS /XFORD &UKAMI 4 AND -ORIN 0 * 0RODUCTIVITY BIODIVERSITY RELATIONSHIPS DEPEND ON THE HISTORY OF COMMUNITY ASSEMBLY .ATURE 'OEL . 3 AND 2ICHTER $YN . 3TOCHASTIC MODELS IN BIOLOGY !CADEMIC 0RESS .EW 9ORK 5 3 ! 'RAY ! * AND #RAWLEY - * AND %DWARDS 0 * ED #OLONIZATION SUCCESSION AND STABILITY "LACKWELL 3CIENCE /XFORD 5+ (ECTOR ! $OBSON + -INNS ! "AZELEY 7HITE % AND ,AWTON * ( #OMMUNITY DIVERSITY AND INVASION RESISTANCE AN EXPERIMENTAL TEST IN A GRASSLAND ECOSYSTEM AND A REVIEW OF COMPARABLE STUDIES %COL 2ES (ERBOLD " AND -OYLE 0 " )NTRODUCED SPECIES AND VACANT NICHES !M .AT (OBBS 2 * 4HE NATURE AND EFFECTS OF DISTURBANCE RELATIVE TO INVASIONS #H PP )N $RAKE * ! -OONEY ( ! DI #ASTRI & 'ROVES 2 ( +RUGER & * 2EJMÉNEK - AND 7ILLIAMSON - ED "IOLOGICAL INVASIONS A GLOBAL PERSPECTIVE 3#/0% *OHN 7ILEY AND 3ONS #HICHESTER 5+ (ODGSON $ * 2AINEY 0 " AND "UCKLING ! -ECHANISMS LINKING DIVERSITY PRO DUCTIVITY AND INVASIBILITY IN EXPERIMENTAL BACTERIAL COMMUNITIES 0ROC 2OY 3OC ,OND " (OLT ! 2 7ARREN 0 ( AND 'ASTON + * 4HE IMPORTANCE OF BIOTIC INTERACTIONS IN ABUNDANCE OCCUPANCY RELATIONSHIPS * !NIM %COL (OLYOAK - AND ,AWLER 3 0 0ERSISTENCE OF AN EXTINCTION PRONE PREDATOR PREY INTERACTION THROUGH METAPOPULATION DYNAMICS %COLOGY (OLYOAK - AND ,AWLER 3 0 4HE ROLE OF DISPERSAL IN PREDATOR PREY METAPOPULATION DYNAMICS * !NIM %COL (OPPER + 2 AND 2OUSH 2 4 -ATE lNDING DISPERSAL NUMBER RELEASED AND THE SUCCESS OF BIOLOGICAL CONTROL INTRODUCTIONS %COL %NTOMOL (USTON - ! (IDDEN TREATMENTS IN ECOLOGICAL EXPERIMENTS RE EVALUATING THE ECO SYSTEM FUNCTION OF BIODIVERSITY /ECOLOGIA *IANG , AND -ORIN 0 * 0RODUCTIVITY GRADIENTS CAUSE POSITIVE DIVERSITY INVASIBILITY RELATIONSHIPS IN MICROBIAL COMMUNITIES %COL ,ETT *ESSUP # - +ASSEN 2 &ORDE 3 % +ERR " "UCKLING ! 2AINEY 0 " AND "OHANNAN " * - "IG QUESTIONS SMALL WORLDS MICROBIAL MODEL SYSTEMS IN ECOLOGY 4RENDS %COL %VOL +OLA # 3 AND ,ODGE $ - 0ROGRESS IN INVASION BIOLOGY PREDICTING INVADERS 4RENDS %COL %VOL ,AW 2 AND -ORTON 2 $ 0ERMANENCE AND THE ASSEMBLY OF ECOLOGICAL COMMUNI TIES %COLOGY ,AW 2 7EATHERBY ! * AND 7ARREN 0 ( /N THE INVASIBILITY OF PERSISTENT PROTIST COMMUNITIES /IKOS
0( 7ARREN 2 ,AW AND !* 7EATHERBY
,AWLER 3 0 %COLOGY IN A BOTTLE USING MICROCOSMS TO TEST THEORY PP )N 2ESETARITS 7 * AND "ERNADO * EDS %XPERIMENTAL ECOLOGY ISSUES AND PERSPECTIVES /XFORD 5NIVERSITY 0RESS .EW 9ORK ,EVINE * - 3PECIES DIVERSITY AND BIOLOGICAL INVASIONS RELATING LOCAL PROCESSES TO COMMUNITY PATTERNS 3CIENCE ,EVINE * - AND $!NTONIO # - %LTON REVISITED A REVIEW OF EVIDENCE LINKING DIVERSITY AND INVASIBILITY /IKOS ,ONSDALE 7 - 'LOBAL PATTERNS OF PLANT INVASIONS AND THE CONCEPT OF INVASIBILITY %COLOGY -ACK 2 . 0REDICTING THE IDENTITY AND FATE OF PLANT INVADERS EMERGENT AND EMERG ING APPROACHES "IOL #ONSERV -ACK 2 . 3IMBERLOFF $ ,ONSDALE - 7 %VANS ( #LOUT - AND "AZAZZ & ! "IOTIC INVASIONS CAUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COL !PPLIC -C'RADY 3TEED * (ARRIS 0 - AND -ORIN 0 * "IODIVERSITY REGULATES ECOSYSTEM PREDICTABILITY .ATURE -ITCHELL # % AND 0OWER ! ' 2ELEASE OF INVASIVE PLANTS FROM FUNGAL AND VIRAL PATHOGENS .ATURE 0ARKER ) $ 3IMBERLOFF $ ,ONSDALE 7 - 'OODELL + 7ONHAM - +AREIVA 0 - 7ILLIAMSON - ( 6ON (OLLE " -OYLE 0 " "YERS * % AND 'OLDWASSER , )MPACT TOWARD A FRAMEWORK FOR UNDERSTANDING THE ECOLOGICAL EFFECTS OF INVADERS "IOL )NVASIONS 0ETCHEY / , -C0HEARSON 0 4 #ASEY 4 - AND -ORIN 0 * %NVIRONMENTAL WARMING ALTERS FOOD WEB STRUCTURE AND ECOSYSTEM FUNCTION .ATURE 0ETERSEN * % AND (ASTINGS ! $IMENSIONAL APPROACHES TO SCALING EXPERIMENTAL ECOSYSTEMS $ESIGNING MOUSETRAPS TO CATCH ELEPHANTS !M .AT 0IMENTEL $ ,ACH , :UNIGA 2 AND -ORRISON $ %NVIRONMENTAL AND ECONOMIC COSTS OF NONINDIGENOUS SPECIES IN THE 5NITED 3TATES "IOSCIENCE 0IMM 3 , 4HEORIES OF PREDICTING SUCCESS AND IMPACT OF INTRODUCED SPECIES PP )N $RAKE * ! -OONEY ( ! DI #ASTI & 'ROVES 2 ( +RUGER & * 2EJMÉNEK - AND 7ILLIAMSON - ED "IOLOGICAL INVASIONS A GLOBAL PERSPECTIVE 3#/0% *OHN 7ILEY AND 3ONS #HICHESTER 5+ 0OST 7 - AND 0IMM 3 , #OMMUNITY ASSEMBLY AND FOOD WEB STABILITY -ATH "IOSCI 2EJMÉNEK - )NVASIBILITY OF PLANT COMMUNITIES #H PP )N $RAKE * ! -OONEY ( ! DI #ASTI & 'ROVES 2 ( +RUGER & * 2EJMÉNEK - AND 7ILLIAMSON 7ILEY AND 3ONS - ED "IOLOGICAL INVASIONS A GLOBAL PERSPECTIVE 3#/0% *OHN #HICHESTER 5+ 2OBINSON * 6 AND $ICKERSON * % 4ESTING THE INVULNERABILITY OF LABORATORY ISLAND COMMUNITIES TO INVASION /ECOLOGIA 2OBINSON * 6 AND $ICKERSON * % $OES INVASION SEQUENCE AFFECT COMMUNITY STRUC TURE %COLOGY 2OBINSON * 6 AND %DGEMON - ! !N EXPERIMENTAL EVALUATION OF THE EFFECT OF INVASION HISTORY ON COMMUNITY STRUCTURE %COLOGY
)NVASIONS IN MICROCOSMS
3AKAI ! + !LLENDORF & 7 (OLT * 3 ,ODGE $ - -OLOFSKY * 7ITH + ! "AUGHMAN 3 #ABIN 2 * #OHEN * % %LLSTRAND . # -C#AULEY $ % /.EIL 0 0ARKER ) - 4HOMPSON * . AND 7ELLER 3 ' 4HE POPULATION BIOLOGY OF INVASIVE SPECIES !NN 2EV %COL 3YST 3HEA + AND #HESSON 0 #OMMUNITY ECOLOGY THEORY AS A FRAMEWORK FOR BIOLOGICAL INVASIONS 4RENDS %COL %VOL 3HEA + AND 0OSSINGHAM ( 0 /PTIMAL RELEASE STRATEGIES FOR BIOLOGICAL CONTROL AGENTS AN APPLICATION OF STOCHASTIC DYNAMIC PROGRAMMING TO POPULATION MANAGEMENT * !PPL %COL 3HER ! ! AND (YATT , ! 4HE DISTURBED RESOURCE mUX INVASION MATRIX A NEW FRAMEWORK FOR PATTERNS OF PLANT INVASION "IOL )NVASIONS 3IMBERLOFF $ #OMMUNITY EFFECTS OF INTRODUCED SPECIES PP )N .ITECKI - ( ED "IOTIC CRISES IN ECOLOGICAL AND EVOLUTIONARY TIME !CADEMIC 0RESS .EW 9ORK 53! 3IMBERLOFF $ 7HICH INSECT INTRODUCTIONS SUCCEED AND WHICH FAIL #H PP )N $RAKE * ! -OONEY ( ! DI #ASTI & 'ROVES 2 ( +RUGER & * 2EJMÉNEK - AND 7ILLIAMSON - ED "IOLOGICAL INVASIONS A GLOBAL PERSPECTIVE 3#/0% *OHN 7ILEY AND 3ONS #HICHESTER 3TAMPE % AND $AEHLER # # -YCORRHIZAL SPECIES IDENTITY AFFECTS PLANT COMMUNITY STRUCTURE AND INVASION A MICROCOSM STUDY /IKOS 4HOMPSON + (ODGSON * ' AND 'RIME * 0 AND "URKE - * 7 0LANT TRAITS AND TEMPORAL SCALE EVIDENCE FROM A YEAR INVASION EXPERIMENT USING NATIVE SPECIES * %COL 4ORCHIN - % ,AFFERTY + $ $OBSON ! 0 -C+ENZIE 6 * AND +URIS ! - )NTRODUCED SPECIES AND THEIR MISSING PARASITES .ATURE 6ITOUSEK 0 - AND 7ALKER , 2 "IOLOGICAL INVASION BY -YRICA FAYA IN (AWAII PLANT DEMOGRAPHY NITROGEN lXATION ECOSYSTEM EFFECTS %COL -ONOGR 7ARDLE $ ! %XPERIMENTAL DEMONSTRATION THAT PLANT DIVERSITY REDUCES INVASIBIL ITY %VIDENCE OF A BIOLOGICAL MECHANISM OR A CONSEQUENCE OF SAMPLING EFFECT /IKOS 7ARREN 0 ( $ISPERSAL AND DESTRUCTION IN A MULTIPLE HABITAT SYSTEM AND EXPERI MENTAL APPROACH USING PROTIST COMMUNITIES /IKOS 7ARREN 0 ( ,AW 2 AND 7EATHERBY ! * -APPING THE ASSEMBLY OF PROTIST COM MUNITIES IN MICROCOSMS %COLOGY 7EATHERBY ! * 3PECIES COEXISTENCE AND COMMUNITY ASSEMBLY IN PROTIST MICRO COSMS UNPUBLISHED 0,$ THESIS 5NIVERSITY OF 3HEFlELD 5+ 7EATHERBY ! * 7ARREN 0 ( AND ,AW 2 #OEXISTENCE AND COLLAPSE AN EXPERI MENTAL INVESTIGATION OF THE PERSISTENT COMMUNITIES OF A PROTIST SPECIES POOL * !NIM %COL 7EIHER % AND +EDDY 0 EDS %COLOGICAL ASSEMBLY RULES PERSPECTIVES ADVANCES RETREATS #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 5+ 7ILLIAMSON - "IOLOGICAL INVASIONS #HAPMAN AND (ALL ,ONDON %NGLAND :IMMERMANN # 2 &UKAMI 4 AND $RAKE * ! !N EXPERIMENTALLY DERIVED MAP OF COMMUNITY ASSEMBLY SPACE )N -INAI ! AND "AR 9AM 9 EDS 5NIFYING THEMES IN COMPLEX SYSTEMS )) 0ROCEEDINGS OF THE SECOND INTERNATIONAL CONFERENCE ON COMPLEX SYSTEMS .EW %NGLAND #OMPLEX 3YSTEMS )NSTITUTE 0ERSEUS 0RESS
#HAPTER SEVENTEEN
5NDERSTANDING INVASIONS IN PATCHY HABITATS THROUGH METAPOPULATION THEORY + # (ARDING * - -C.AMARA AND 2 $ (OLT
).42/$5#4)/. -ANY INVASIVE SPECIES EXPERIENCE A WORLD THAT IS HETEROGENEOUS AND PATCHY AND EXPERIENCE IT AT MULTIPLE SCALES )N THIS CHAPTER WE WILL SHOW HOW METAPOPULATION THEORY CAN BE USED TO EXPLORE GENERAL MECHANISMS WHICH DETERMINE THE INITIAL SPREAD AND LONG TERM ESTABLISHMENT OF INVASIVE SPECIES IN NOVEL ENVIRONMENTS -ETAPOPULATION ECOLOGY IS A BRANCH OF ECOLOGY THAT IS FOCUSED ON HOW SPECIES PERSIST IN FRAGMENTED OR @SUBDIVIDED HABITATS (ANSKI (ANSKI AND 'AGGIOTTI !LTHOUGH REAL LANDSCAPES ARE OFTEN HIGHLY COMPLEX WITH ADMIXTURES OF SMOOTH GRADIENTS FRACTAL EDGES AND JUXTAPOSED HABITATS VARYING IN QUALITY FOR MANY SPECIES IT IS NATURAL TO CONSTRUE THEIR WORLD AS CONSISTING OF SETS OF SUITABLE HABITAT PATCHES ARRAYED WITHIN A LARGELY INHOSPITABLE MATRIX SEPARATING THOSE PATCHES 3OME SUCH SPECIES INHABIT NATURALLY PATCHY HABITATS SUCH AS ISLANDS OR PONDS &IG 3OME METAPOPULATIONS APPEAR IN ARTIlCIALLY CONSTRUCTED HABITAT NETWORKS SUCH AS THE REMAINING FRAGMENTS OF A RAIN FOREST SURROUNDED BY CATTLE PASTURES OR CONCRETE REEFS IN MARINE SYSTEMS 0ATCH NETWORKS CAN ALSO BE FORMED IN MORE SUBTLE WAYS BUT STILL MAKE FUNCTIONAL METAPOPULATIONS 4HE PATCHY DISTRIBUTION OF A HOST SPECIES FOR A SPECIALIST HERBIVORE PARASITE PARASITOID OR -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
+# (ARDING *- -C.AMARA AND 2$ (OLT
&IG 0ATCHY WORLD PONDS IN THE .ORTHERN 0RAIRIE FARMLAND 0HOTO 3TEWART 2% ET AL &ROM .ORTHERN 0RAIRIE 7ILDLIFE 2ESEARCH #ENTER
COMMENSAL OR INDEED ANY VITAL AND SPATIALLY DELIMITED RESOURCE CAN LEAD TO METAPOPULATION DYNAMICS FOR THE SPECIALIST "IOLOGICAL NONLINEARITIES CAN TRANS FORM SMOOTH ENVIRONMENTAL GRADIENTS INTO PATCHY DISTRIBUTIONS &OR INSTANCE STRONG !LLEE EFFECTS POSITIVE DENSITY DEPENDENCE AT LOW NUMBERS CAN AMPLIFY PATCHINESS IN THE ENVIRONMENT 7HEN DISPERSAL IS LIMITED PERMANENT RANGE LIMITS CAN ARISE IN PATCHY ENVIRONMENTS EVEN WITHOUT OVERALL ENVIRONMENTAL GRADIENTS IN THE LANDSCAPE +EITT ET AL %VEN WITHOUT !LLEE EFFECTS IF THE DENSITY OF SUITABLE PATCHES DECLINES ALONG AN ENVIRONMENTAL GRADIENT A SPECIES RANGE LIMIT MAY EMERGE WHEN THERE IS NO DECLINE IN THE QUALITY OF SUITABLE HABITAT PATCHES (OLT AND +EITT ! METAPOPULATION IS DElNED AS A SET OF POPULATIONS CONNECTED BY DISPERSAL $ISPERSAL BECOMES PARTICULARLY VITAL TO UNDERSTANDING REGIONAL POPULATION PER SISTENCE WHEN LOCAL POPULATIONS CAN BECOME EXTINCT AND MUST BE RE ESTABLISHED VIA COLONIZATION #LASSICAL METAPOPULATION THEORY THUS FOCUSES ON SYSTEMS WHERE THERE IS A POTENTIAL FOR RECURRENT EXTINCTION )N ALL METAPOPULATIONS LONG TERM SPECIES PERSISTENCE RELIES ON THE BALANCE BETWEEN THE RATE OF EXTINCTION OF LOCAL POPULATIONS AND THE RATE OF NEW COLONIZATIONS OF EMPTY HABITAT PATCHES &IG -ETAPOPULATION THEORY IS WELL SUITED FOR DESCRIBING INVASIONS AND THE ESTAB LISHMENT OF NEW SPECIES INTO PATCHY HABITATS 4HERE ARE THREE BASIC QUESTIONS
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
&IG "LUE SQUARES INDICATE PONDS OCCUPIED BY 0ISIDIUM NITIDUM IN THE YEAR OF SAMPLING 7HITE SQUARE ARE PONDS WHERE 0 NITIDUM HAS GONE EXTINCT 3TEWART AND +ANTRUD &ROM .ORTHERN 0RAIRIE 7ILDLIFE 2ESEARCH #ENTER
ONE CAN ASK ABOUT AN INVASION &IRST CAN AN INVASION OCCUR AT ALL 3ECOND GIVEN THAT AN INVASION OCCURS HOW RAPIDLY DOES IT OCCUR &INALLY FOLLOWING INVA SION WHAT IMPACTS DOES THE INVADER HAVE UPON THE PRIOR RESIDENT COMMUNITY -ETAPOPULATION THEORY CAN BE USED TO ADDRESS EACH OF THESE BASIC ISSUES 7E INTRODUCE A SIMPLE MODEL STRUCTURE THAT CAN BE USED TO SUMMARISE AND CLAS SIFY SOME DIFFERENT TYPES OF METAPOPULATION INVASION SCENARIOS 7E EXAMINE SOME SPECIAL CASES STARTING WITH A CASE IN WHICH THE INVASIVE SPECIES DOES NOT COMPETE WITH ANY OTHER ECOLOGICALLY SIMILAR SPECIES 4HE DYNAMICS OF THE INVASION IN THIS CASE IS THEN GOVERNED BY THE BIOLOGY OF THE INVADER ONLY AND CLASSIC SINGLE SPECIES METAPOPULATION THEORY APPLIES 7E THEN CONSIDER A GENERAL METAPOPULATION MODEL IN WHICH THE INVADING SPECIES INTERACTS WITH A NATIVE SPECIES 7E DElNE CRITERIA FOR WHEN INITIAL INVASION OCCURS AND FOR WHEN LONG TERM COEXISTENCE IS POSSIBLE 7E ALSO LOOK AT SOME INTERACTIONS THAT ARE SPECIlC CASES OF THIS GENERAL MODEL A THE INVADER COMPLETELY EXCLUDES THE NATIVE SPECIES B THE INVADER IS DEPENDENT ON THE PRESENCE OF A NATIVE SPECIES AND C THERE IS AN INTERMEDIATE LEVEL OF COMPETITION 7E ALSO TOUCH ON HOW SPATIAL HETEROGENEITY CAN INmUENCE INVASION /UR OVERVIEW HIGHLIGHTS SOME GENERAL INSIGHTS ABOUT THE POPULATION BIOLOGY OF INVASION WHICH EMERGE FROM METAPOPULATION THEORY
+# (ARDING *- -C.AMARA AND 2$ (OLT
./ #/-0%4)4)/. 7)4( .!4)6% 30%#)%3 #,!33)# -%4!0/05,!4)/. ")/,/'9 !00,)%3 ,EVINS METAPOPULATION
3OME INVASIONS OCCUR WITHOUT ANY OBVIOUS COMPETITION FROM NATIVE SPECIES &OR INSTANCE WHEN THE MARSH LOVING MUSKRAT WAS INTRODUCED INTO CENTRAL %UROPE ITS NUMBERS GREW EXPONENTIALLY 3KELLAM )N THAT ENVIRONMENT THERE WERE NO OTHER OBVIOUS AQUATIC MAMMALS WHICH COULD INTERFERE WITH THE INITIAL ESTABLISHMENT AND SUBSEQUENT GROWTH OF THIS SPECIES )N THESE CASES SINGLE SPECIES METAPOPULATION THEORY CAN BE APPLIED TO INVESTIGATE BASIC PROPERTIES OF THE INVA SION EG FOR THE MUSKRAT ITS REQUIRED HABITAT TYPICALLY OCCURS IN DISCRETE PATCHES MARSHES SEPARATED BY A RELATIVELY HOSTILE MATRIX OF TERRESTRIAL HABITATS -OREOVER IF RESIDENT SPECIES ARE RELATIVELY lXED IN ABUNDANCE EG THE INVADER INITIALLY HAS LITTLE IMPACT THEN THE RESIDENTS CAN BE VIEWED AS lXED HABITAT FAC TORS EITHER HAMPERING OR ASSISTING INVASION BY THE FOCAL SPECIES 7E SHALL DISTIN GUISH BETWEEN TWO IMPORTANT STAGES IN THE INVASION PROCESS A THE INITIAL PHASE OF POTENTIAL SUCCESSFUL INVASION OR FAILURE WHEN THE INVADER OCCURS IN RELATIVELY FEW PATCHES AND B THE LONG TERM ESTABLISHMENT OF AN INVASIVE SPECIES &IRST LET US DElNE THE MODEL FRAMEWORK ! SIMPLE MODEL THAT CAPTURES MUCH OF THE SPECIAL METAPOPULATION LEVEL EFFECTS CAN BE BUILT ON THE FOUNDATION OF 2ICHARD ,EVINS SEMINAL PAPER ON METAPOPULATION THEORY (E REGARDED THE ENVI RONMENT AS COMPOSED OF 4 PATCHES OF EQUAL QUALITY WHERE 4 IS LARGE (E MODELLED THE DYNAMICS OF A PARTICULAR SPECIES WITHIN THIS LANDSCAPE ASSUMING THAT EACH PATCH IS EITHER OCCUPIED BY MEMBERS OF THE SPECIES OR EMPTY /CCUPIED PATCHES SEND OUT MIGRANTS THAT SETTLE ON PATCHES AT RANDOM %ACH OCCUPIED PATCH SENDS OUT MIGRANTS THAT ARE SUCCESSFUL IN lNDING ANOTHER PATCH AT RATE M 7E ASSUME FOR THE MOMENT THAT WE CAN IGNORE THE SPATIAL ARRANGEMENT OF PATCHES AND THAT THE DISPERSERS FROM ALL OCCUPIED PATCHES MERGE INTO A REGIONAL MIGRANT POOL &ROM THIS POOL THEY SETTLE UNIFORMLY ACROSS ALL PATCHES BOTH OCCUPIED AND EMPTY )F THERE ARE . OCCUPIED PATCHES THE TOTAL POOL SIZE IS M. AND SO THE RATE OF ARRIVAL OF IMMI GRANTS ON EACH EMPTY OR OCCUPIED PATCH IS SIMPLY _ M.4 3INCE THERE ARE 4 n . EMPTY PATCHES THE RATE OF COLONIZATION OF NEW PATCHES IS +_ 4 n . WHERE + IS THE PROBABILITY THAT A SINGLE EMPTY PATCH IS COLONIZED IE CONVERTED FROM EMPTY TO OCCUPIED BY A RESIDENT POPULATION OF THE SPECIES BY AN IMMIGRANT .OTE THAT IF + THIS MEANS THAT SOME COLONIZATIONS FAIL ,EVINS ALSO ASSUMED THAT EACH OCCUPIED PATCH BECOMES EXTINCT THAT IS CHANGES FROM OCCUPIED TO EMPTY AT CON STANT RATE E 4HESE SIMPLE ASSUMPTIONS CAN LATER BE GENERALIZED BUT ARE VERY USEFUL AS A lRST STEP FOR D EVELOPING AN INTUITIVE FEELING FOR METAPOPULATION DYNAMICS &IG 7ITH THESE ASSUMPTIONS THE RATE OF CHANGE IN THE NUMBER OF OCCUPIED PATCHES IS D. +_ 4 n . n E. DT
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
&IG 4HE CLASSIC ,EVINS METAPOPULATION MODEL FOR A SINGLE SPECIES ! GIVEN PATCH CAN BE IN ONE OF TWO STATES EMPTY OR OCCUPIED BY SPECIES 4HE RATE OF CHANGE IS GIVEN BY THE COLONIZATION AND EXTINCTION RATES AND THE PROPORTION X OF OCCUPIED PATCHES C CORRESPONDS TO +_ IN EQNS AND
,ET X .4 BE THE PROPORTION OF PATCHES THAT ARE OCCUPIED 4HEN THE ABOVE EQUATION CAN BE REWRITTEN IN TERMS OF X AS
DX +_ n X n EX DT
WHERE _ MX
)T CAN BE SEEN FROM THESE EQUATIONS THAT THERE IS AN EQUILIBRIUM WHERE THE RATES OF EXTINCTION AND COLONIZATION ARE EQUAL AT WHICH A CERTAIN PROPORTION X n E+M OF PATCHES ARE OCCUPIED ,EVINS 4HE EQUILIBRIUM IS STABLE SINCE THE FRACTION OF OCCUPIED PATCHES WILL ALWAYS TEND TOWARDS THIS EQUILIB RIUM 4O SEE THAT THE EQUILIBRIUM IS STABLE NOTE THAT IF WE WRITE EQUATION AS DXDT FX THEN F vX %VEN THIS VERY SIMPLE MODEL CAN BE USED TO ILLUMINATE THE CONDITIONS CAUSING SUCCESSFUL VERSUS FAILED INVASIONS 4O SEE HOW AN INVADER WILL DO WHEN IT IS INTRO DUCED TO AN EMPTY PATCH NETWORK WE FOCUS ON VERY LOW X VALUES THIS IS USUALLY A REASONABLE ASSUMPTION REGARDING THE INITIAL CONDITIONS OF NATURAL OR INADVERTENT INVASIONS BUT IT MAY NOT ALWAYS BE APPROPRIATE FOR DELIBERATE LARGE SCALE INTRO DUCTIONS &ROM EQUATIONS AND DX +M n E FOR SMALL X X DT
4HUS THE SPECIES CAN INVADE IF +M E )F INVASION IS POSSIBLE THE INVADING SPE CIES WILL INCREASE ITS PRESENCE UNTIL THE EQUILIBRIUM SIZE X IS REACHED SEE "OX FOR A LIST OF MODEL PARAMETERS
+# (ARDING *- -C.AMARA AND 2$ (OLT
"OX ,EVINS MODEL DEFENITIONS
4 THE NUMBER OF HABITAT PATCHES AVAILABLE . THE NUMBER OF HABITAT PATCHES OCCUPIED BY THE STUDY SPECIES M RATE OF MIGRATION FROM AN OCCUPIED PATCH _ THE RATE OF ARRIVAL OF IMMIGRANTS TO EACH OF THE 4 PATCHES + THE PROBABILITY THAT A SINGLE EMPTY PATCH IS COLONIZED IE CONVERTED FROM EMPTY TO OCCUPIED BY A RESIDENT POPULATION BY A SINGLE IMMIGRANT E RATE AT WHICH AN OCCUPIED PATCH GOES EXTINCT /VERALL RATE OF COLONIZATION +_4 n . /VERALL RATE OF EXTINCTION E. X EQUILIBRIUM PATCH OCCUPANCY WHERE RATE OF COLONIZATION AND RATE OF EXTINCTION ARE EQUAL (ABITAT LOSS MODEL
5 THE NUMBER OF UNSUITABLE PATCHES H FRACTION OF THE LANDSCAPE THAT IS HABITABLE FOR THE STUDY SPECIES 'ENERALIZED MODEL
%_ SINGLE PATCH EXTINCTION RATE AS A FUNCTION OF IMMIGRATION #_ SINGLE PATCH COLONIZATION RATE AS A FUNCTION OF IMMIGRATION 2ESCUE EFFECT IMMIGRATION INTO A PATCH LOWERS PATCH EXTINCTION RISK !NTI RESCUE EFFECT IMMIGRATION INTO A PATCH INCREASES PATCH EXTINCTION RISK !LLEE EFFECT COLONIZATION SUCCESS IS A NON LINEAR FUNCTION OF IMMIGRATION ACCELERATING WITH INCREASING IMMIGRATION RATE !NTI !LLEE EFFECT NON LINEAR COLONIZATION SUCCESS DECELERATING WITH INCREASING IMMIGRATION RATE -ODEL WITH TWO DISTINCT HABITATS
HI THE FRACTION OF A LANDSCAPE THAT IS COVERED BY TYPE I HABITAT PATCHES PI THE FRACTION OF THE LANDSCAPE THAT IS BOTH OF HABITAT TYPE I AND OCCUPIED EI EXTINCTION RATE OF TYPE I PATCHES CIJ COLONIZATION ONTO EMPTY PATCHES OF TYPE I DUE TO MIGRANTS GENERATED BY OCCUPIED PATCHES OF TYPE J hI RATE OF INCREASE IN PATCH OCCUPANCY OF SPECIES WHEN IT IS RARE AND ONLY PATCH TYPE I IS PRESENT
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
"OX
4WO SPECIES METAPOPULATION MODEL
. THE NUMBER OF PATCHES OCCUPIED BY SPECIES ." THE NUMBER OF PATCHES OCCUPIED BY BOTH SPECIES 0ATCH STATES %MPTY 4YPE 4YPE 4YPE " M MIGRATION RATE OF SPECIES MIGRANTS FROM A 4YPE PATCH
É
M MIGRATION RATE OF SPECIES MIGRANTS FROM A 4YPE " PATCH #_ COLONIZATION RATE OF AN EMPTY PATCH BY SPECIES IMMIGRANTS
É
#_ COLONIZATION RATE OF A 4YPE PATCH BY SPECIES IMMIGRANTS %_ EXTINCTION RATE OF A 4YPE PATCH %_ EXTINCTION RATE OF SPECIES IN A 4YPE " PATCH
É
"IOLOGICAL CONCLUSIONS FROM ,EVINS MODEL
&AILED INVASIONS CAN ARISE EITHER FROM PROCESSES THAT AFFECT EXTINCTION OR FROM THE DETAILS OF THE PROCESS OF COLONIZATION 4HERE ARE MANY REASONS EXTINCTION RATES MAY BE HIGH IN A NOVEL ENVIRONMENT )F WITHIN EACH PATCH THE INTRINSIC GROWTH RATE R OF THE INVADER IS NEGATIVE IE R SO BIRTHS DEATHS THEN EXTINCTION IS INEVITABLE UNLESS THERE IS VERY RAPID EVOLUTION SEE 'OMULKIEWICZ AND (OLT 4HIS COULD ARISE BECAUSE OF UNFAVORABLE ABIOTIC CONDITIONS OR BECAUSE SUPERIOR COMPETITORS OR EFFECTIVE PREDATORS ARE PRESENT "UT EVEN IF R IF A PATCH HAS A VERY LOW LOCAL CARRYING CAPACITY IT MAY SUFFER HIGH RATES OF EXTINCTION DUE TO DEMOGRAPHIC STOCHASTICITY IF IT HAS A LOW R IT MAY ALSO NOT BE ABLE TO RECOVER RAPIDLY FROM CATASTROPHES AND SO RANDOMLY WALK TO EXTINCTION %NVIRONMENTS WITH FREQUENT CATASTROPHES ARE LIKELY TO GENERATE HIGH EXTINCTION RATES FOR INVASIVE SPECIES SO ALL ELSE BEING EQUAL ARE NOT AS LIKELY TO BE INVADED "UT EQUAL WEIGHT SHOULD BE GIVEN TO CONSTRAINTS ON THE COLONIZATION PROCESS AS POTENTIAL CAUSES OF FAILED INVASIONS )N THE TERMS OF THE BASIC MODEL IF M IS REDUCED SO IS THE LIKELIHOOD OF INVASION 4HE QUANTITY M COMBINES TWO THINGS A PER CAPITA RATE OF EMIGRATION FROM AN OCCUPIED PATCH AND THE NUMBER OF INDIVIDUALS PRESENT THERE AND AVAILABLE TO EMIGRATE 3PECIES THAT ARE SEDENTARY OR PHILOPATRIC ARE LIKELY TO HAVE A LOW M 3UCH SPECIES SHOULD TEND TO BE POOR INVADERS &OR SPECIES WITH EQUAL PER CAPITA RATES OF EMIGRATION THOSE SPECIES WITH THE HIGHEST ABUN DANCE WITHIN OCCUPIED PATCHES CAN GENERATE A HIGH ABUNDANCE OF MIGRANTS AND
+# (ARDING *- -C.AMARA AND 2$ (OLT
SO EXPERIENCE THE HIGHEST COLONIZATION RATE INTO EMPTY PATCHES ,ARGE M SHOULD THUS REmECT BOTH HIGH FECUNDITY AND HIGH SURVIVAL OF EMIGRANTS ACROSS THE MATRIX HABITAT SEPARATING HABITABLE PATCHES 4HE PROBABILITY OF SUCCESSFUL COLONIZATION + ALSO VARIES GREATLY AMONG SPECIES &OR INSTANCE A HIGH + CAN BE EXPECTED IN SPECIES WHERE THE MIGRANTS HAVE HIGH FECUNDITY SO THAT ONE OR A FEW IMMIGRANTS CAN ESTABLISH A SUCCESSFUL POPULATION BY QUICKLY PRODUCING A LARGE NUMBER OF OFFSPRING THEREBY AVOIDING INITIAL DEMOGRAPHIC STOCHASTICITY AND WHEN INDI VIDUALS ARE LONG LIVED "IRTH DEATH PROCESS MODELS EG AS IN -AC!RTHUR AND 7ILSON REVEAL THAT IN COMPARING SPECIES WITH A GIVEN INTRINSIC GROWTH RATE R THE PROBABILITY OF EXTINCTION IS LOWER FOR SPECIES WITH LOWER ABSOLUTE DEATH RATES #ONVERSELY SPECIES WHICH ARE AT RISK OF FREQUENT STOCHASTIC MORTALITY EVENTS ARE LIKELY TO HAVE LOW INTRINSIC COLONIZATION PROPENSITY AND SO HAVE A LOW + )MMIGRANTS ARE LIKELY TO BE UNFAMILIAR WITH THE DETAILS OF LOCAL RESOURCES REFUGES AND MORTALITY RISKS AND IF LEARNING NEW CONDITIONS IS SLOW OR UNRELIABLE IMMI GRANTS MAY BE VULNERABLE TO RAPID ELIMINATION IN NOVEL ENVIRONMENTS /NE MATHEMATICALLY SLIGHT BUT BIOLOGICALLY SIGNIlCANT GENERALIZATION OF THE ,EVINS MODEL SUGGESTED BY ,ANDE AND .EE AND -AY IS TO RECOGNIZE THAT IN A LANDSCAPE NOT ALL EMPTY PATCHES ARE SUITABLE )F WE ASSUME THAT OUT OF 4 PATCHES 5 ARE UNSUITABLE THEN H n54 IS THE FRACTION OF THE LANDSCAPE THAT IS POTENTIALLY OCCUPIABLE BY THE SPECIES 7ORKING BACK THROUGH THE SAME STEPS AS BEFORE WE END UP WITH DXDT +_H X EX 4HE INVASION CRITERION NOW BECOMES +MH E !S NOTED FOR A SOMEWHAT DIFFERENT VERSION OF THE MODEL IN (OLT AND +EITT THIS SIMPLE FORMULATION OF INVASION ENCOMPASSES A GREAT DEAL OF BIOLOGY )N ADDITION TO THE MECHANISMS MENTIONED IN THE PREVIOUS PARAGRAPHS ANOTHER REASON WHY AN INVASION COULD FAIL IS THAT INSUFlCIENT SUITABLE HABITAT IS AVAILABLE %VEN IF EACH SUITABLE PATCH COULD SUSTAIN A POPULATION ON ITS OWN OVER A REASON ABLE TIME SCALE IF THERE ARE TOO FEW OF THEM COLONIZATION MAY NOT BE ABLE TO MATCH EVEN A LOW RATE OF EXTINCTION (OLT AND +EITT SHOW HOW THESE IDEAS PERMIT ONE TO CONSIDER IN A UNIlED FASHION MANY DIFFERENT HYPOTHESES THAT HAVE BEEN PUT FORTH REGARDING THE FACTORS CAUSING DISTRIBUTIONAL RANGE LIMITS 4HE THEORETICALLY BEST INVADER WOULD HAVE LOW EXTINCTION RISK AND HIGH M 4HE THEORETICAL @BEST IS LIKELY TO BE UNFEASIBLE BECAUSE THERE ARE BIOLOGICAL CONSTRAINTS SUCH AS TRADEOFFS BETWEEN LIFE HISTORY TRAITS EG REPRODUCTION AND LONGEVITY IN ANIMALS AND BETWEEN DEVELOPMENT OF VEGETATIVE PROPAGULES AND SEED PRODUCTION IN PLANTS $YNAMIC ,EVINS TYPE METAPOPULATION
4HE ,EVINS MODEL CLARIlES MANY ESSENTIAL FEATURES OF METAPOPULATION DYNAMICS BUT IT RESTS ON QUITE SIMPLE ASSUMPTIONS ABOUT HOW MIGRATION INmUENCES BOTH COLONIZATION AND EXTINCTION (ANSKI 4HE BASIC ,EVINS FRAMEWORK HAS BEEN EXTENDED TO SEVERAL SPECIlC CASES IN DIFFERENT STUDIES INCLUDING FOR EXAMPLE A LIN EAR RESCUE EFFECT (ANSKI 'OTELLI AND +ELLY AND A SPECIlC NONLINEAR !LLEE EFFECT (ANSKI 4HE ,EVINS MODEL WAS RECENTLY GENERALIZED TO ALLOW
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
FOR THESE AND OTHER DYNAMIC INmUENCES FROM MIGRATION ON BOTH COLONIZATION AND EXTINCTION RATES COMPARE &IGS AND (ARDING AND -C.AMARA 4HE GENERALITY IS OBTAINED BY EXPRESSING BOTH COLONIZATION AND EXTINCTION RATES AS FUNCTIONS OF IMMIGRATION RATE AS WE NOW DESCRIBE
&IG !N EXTENSION OF ,EVINS MODEL &IG (ERE THE RATE OF COLONIZATION AND EXTINCTION ARE NOT lXED CONSTANTS BUT CAN BE ANY FUNCTION OF IMMIGRATION RATE _ 4HIS MODEL CAN THEREFORE CAPTURE SEVERAL TYPES OF SINGLE SPECIES DYNAMICS SUCH AS !LLEE EFFECTS RESCUE EFFECTS AND ANTI RESCUE EFFECTS (ARDING AND -C.AMARA
)T IS USEFUL TO THINK OF METAPOPULATION PROCESSES AT TWO SCALES 4HE SMALLEST SCALE IS THE PATCH 4HE SUBPOPULATION INHABITING A PATCH HAS A GIVEN RISK OF LOCAL EXTINCTION %_ THAT MAY BE INmUENCED BY THE RATE OF IMMIGRATION _ TO THE PATCH %MPTY PATCHES ARE COLONIZED AT RATE #_ THAT VERY LIKELY DEPENDS ON _ 'IVEN THESE @LOCAL RATES OF CHANGE THE OVERALL RATE OF CHANGE IN THE PROPORTION X .4 OF PATCHES THAT ARE OCCUPIED IN THE WHOLE METAPOPULATION IS DX #_ n X n %_ X DT
(ARDING AND -C.AMARA (ERE WE AGAIN ASSUME THAT ALL PATCHES ARE POTENTIALLY OCCUPIABLE 4HE ,EVINS MODEL IS THEN A SPECIAL CASE OF THIS MODEL WITH EXTINCTION FUNCTION %_ E AND COLONIZATION FUNCTION #_ +_ !S DESCRIBED BELOW A VARIETY OF BIOLOGICAL PROCESSES CAN BE MIMICKED PHENOMENOLOGICALLY WITH THIS EXTENDED FRAMEWORK $YNAMIC EXTINCTION FUNCTIONS 4HE ORIGINAL ,EVINS EXTINCTION FUNCTION HAS A CONSTANT VALUE E THAT IS INDEPEN DENT OF IMMIGRATION RATE )N A METAPOPULATION IT CAN BE IMPORTANT TO ALLOW THE EXTINCTION RATE OF A PATCH TO DEPEND ON IMMIGRATION INTO THAT PATCH )MMIGRANTS CAN FOR EXAMPLE LOWER PATCH EXTINCTION RISK BY PROVIDING A DEMOGRAPHIC CONTRI BUTION TO DECLINING POPULATIONS OR BY INTRODUCING NEW GOOD GENES EG REDUCING INBREEDING DEPRESSION 3ACCERI ET AL THIS IS THE RESCUE EFFECT "ROWN AND +ODRIC "ROWN (ANSKI &OLLOWING A CATASTROPHE IMMIGRANTS CAN
+# (ARDING *- -C.AMARA AND 2$ (OLT
SPEED THE RECOVERY OF THE POPULATION ALLOWING IT TO MORE RAPIDLY REBOUND FROM DANGEROUSLY LOW DENSITIES $EPENDING ON THE UNDERLYING PROCESSES LEADING TO A RESCUE EFFECT THE EXTINCTION FUNCTION CAN HAVE DIFFERENT SHAPES &IG
&IG )LLUSTRATION OF RESCUE EFFECT FUNCTIONS 4HE RATE OF PER PATCH EXTINCTION CAN SOMETIMES DECREASE AS IMMIGRATION RATE INCREASES 4HREE DIFFERENT TYPES OF RESPONSE TO INCREASED IMMIGRATION ARE ILLUSTRATED
(OWEVER IN OTHER CIRCUMSTANCES IMMIGRATION CAN LEAD TO INCREASED EXTINCTION RISK WE TERM THIS PATTERN AN ANTI RESCUE EFFECT 4HIS CAN FOR EXAMPLE BE DUE TO IMMIGRANTS CARRYING PARASITES OR DISEASES OR BECAUSE IMMIGRANTS CARRY DIFFERENT GENES BREAKING UP LOCALLY ADAPTED BENElCIAL GENE COMBINATIONS 2OLÉN !LVAREZ ET AL )N PREDATOR PREY SYSTEMS INCREASING IMMIGRATION CAN SOMETIMES DESTABILIZE LOCAL INTERACTIONS MAKING EXCURSIONS TO LOW DENSITIES AND HENCE LOCAL EXTINCTIONS MORE LIKELY 3CHÚPS (OLT SEE REVIEW IN (OOPES ET AL 7ITH ALL THESE MECHANISMS INCREASING IMMIGRATION RATE OVER SOME RANGE OF VALUES IS LIKELY TO BOOST LOCAL EXTINCTION RATES $YNAMIC COLONIZATION FUNCTIONS )N ,EVINS MODEL THE COLONIZATION RATE PER PATCH INCREASES LINEARLY WITH THE IMMI GRATION RATE AND HENCE INCREASES LINEARLY WITH THE NUMBER OF OCCUPIED PATCHES
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
(OWEVER COLONIZATION MIGHT TAKE OTHER FORMS AS WELL )T IS COMMON FOR A SPECIES TO HAVE PROBLEMS IN INITIAL ESTABLISHMENT IN A PATCH WHEN THE NUMBER OF IMMI GRANTS IS LOW DUE TO DEMOGRAPHIC SKEWS LACK OF ADULTS OR MALES FOR EXAMPLE DIF lCULTY IN lNDING MATES OR INBREEDING 4HE PHENOMENA OF DISPROPORTIONATELY LOW COLONIZATION SUCCESS WHEN THE IMMIGRATION RATE IS LOW IS AN EXAMPLE OF AN !LLEE EFFECT !LLEE (ANSKI 4HE OPPOSITE WHEN COLONIZATION BY A SINGLE MIGRANT IS MORE SUCCESSFUL WHEN THERE ARE FEW OTHER MIGRANTS IS TERMED AN ANTI !LLEE EFFECT (ARDING AND -C.AMARA )T CAN OCCUR IF MIGRANTS DO NOT SETTLE AT RANDOM BUT AVOID CON SPECIlCS EG TERRITORIALITY SO THAT MIGRANTS ACTIVELY SEEK UNOCCUPIED PATCHES 4HIS LEADS TO A VERY RAPID COLONIZATION INITIALLY BUT AFTER A WHILE MOST PATCHES ARE OCCUPIED AND THE EFFECT SHOULD BECOME LESS IMPORTANT )T IS ALSO CONCEIVABLE THAT IF RESOURCES ARE EXPLOITED WHICH HAVE LOW RATES OF RENEWAL AN INCREASE IN THE NUMBER OF IMMIGRANTS COULD LEAD TO RAPID OVEREXPLOITATION RESOURCE DEPLETION AND THUS A REDUCED PROBABILITY OF SUCCESSFUL ESTABLISHMENT "OTH THESE MECHA NISMS CAN LEAD TO AN ANTI !LLEE EFFECT AT THE METAPOPULATION LEVEL )MPACTS BY RESIDENT GENERALIST PREDATORS UPON COLONIZATION BY AN INVASIVE PREY SPECIES ARE LIKELY TO SHIFT BETWEEN ANTI !LLEE EFFECTS AND !LLEE EFFECTS DEPENDING ON THE QUANTITATIVE DETAILS OF THE PREDATORS FUNCTIONAL RESPONSE AND THE NUMBER OF IMMIGRANTS )F A RESIDENT PREDATOR HAS A TYPE ))) SIGMOIDAL FUNCTIONAL RESPONSE THEN OVER A RANGE OF LOW PREY NUMBERS AN INCREASE IN PREY DENSITY DUE TO AN INCREASING NUMBER OF MIGRANTS LEADS TO AN INCREASE IN THE PER CAPITA MORTALITY RATE INmICTED ON THE PREY EG BECAUSE THE PREDATOR BECOMES INCREASINGLY AWARE OF THE NOVEL PREY WITH INCREASING EXPOSURE TO IT AND SO IS MORE LIKELY TO CAUSE PREY EXTINCTION WITH INCREASING NUMBERS OF COLONISTS 4HIS CAN BE VIEWED AS AN ANTI !LLEE EFFECT WHICH COULD BROADLY DESCRIBE ANY KIND OF NEGATIVE DENSITY DEPEND ENCE OPERATING AT LOW DENSITIES WHICH CAN NEGATIVELY AFFECT COLONIZATION SUCCESS "UT TYPICALLY AT HIGHER PREY DENSITIES MOST PREDATORS HAVE SATURATING FUNCTIONAL RESPONSES EG DUE TO LIMITED HANDLING TIME OR GUT CAPACITY SO THE PER CAPITA MORTALITY RATE EXPERIENCED BY PREY DECLINES WITH INCREASING PREY DENSITY )N THIS RANGE AN INCREASING NUMBER OF MIGRANTS MAY ENHANCE COLONIZATION BY DILUTING THE IMPACT OF PREDATION 3O WHETHER OR NOT A COLONISING SPECIES EXPERIENCES AN !LLEE OR AN ANTI !LLEE EFFECT DUE TO RESIDENT PREDATORS WILL DEPEND UPON BOTH THE PREDATORS FUNCTIONAL RESPONSE AND THE NUMBER OF MIGRANTS 7HO IS A GOOD INVADER IN THE SINGLE SPECIES SYSTEM
4O ANALYSE WHETHER A SPECIES CAN INVADE INTO A PATCHY LANDSCAPE WE SUPPOSE THAT THE SPECIES HAS BEEN INTRODUCED IN A SMALL NUMBER OF PATCHES 7E CAN THEN ASK WHETHER THE NUMBER OF OCCUPIED PATCHES TENDS TO GROW OR DECLINE )N TERMS OF THE GENERALIZED METAPOPULATION MODEL DESCRIBED ABOVE WE ARE CONCERNED WITH WHETHER DXDT WHEN X IS SMALL 4HIS DEPENDS ON THE BEHAVIOUR OF THE COLONIZA TION AND EXTINCTION FUNCTIONS FOR SMALL X AND HENCE SMALL _ 3UPPOSE THAT
+# (ARDING *- -C.AMARA AND 2$ (OLT
#_ 5 +_ FOR SMALL _
AND %_ 5 E FOR SMALL _
4HUS FOR SMALL NUMBERS OF OCCUPIED PATCHES THE METAPOPULATION BEHAVES AS DESCRIBED BY ,EVINS MODEL WITH PARAMETERS + AND E ALTHOUGH IT MAY BEHAVE VERY DIFFERENTLY WHEN THE NUMBER OF OCCUPIED PATCHES INCREASES 7ITH THIS ASSUMPTION APPROXIMATION IS STILL VALID SO THAT THE SPECIES CAN INVADE IF +M E
7HEN DOES AN INVASIVE SPECIES GET ESTABLISHED IN A SINGLE SPECIES METAPOPULATION
&IGURE A F ILLUSTRATE THE EXTINCTION RATE WHITE SURFACE AND COLONIZATION RATE BLACK @HILLS FOR SINGLE SPECIES METAPOPULATIONS )T SHOWS HOW DIFFERENT COMBINATIONS OF #_ AND %_ INmUENCE THE EQUILIBRIA WHERE THE TWO SURFACES MEET $EPENDING ON THE FUNCTIONS #_ AND %_ THERE MAY EXIST AT LEAST ONE NON TRIVIAL EQUILIBRIA IN PATCH OCCUPANCY X SUCH THAT TOTAL COLONIZATION AND EXTINCTION RATES BAL ANCE WHEN A PROPORTION X OF PATCHES ARE OCCUPIED )N SOME CASES THERE MAY BE MORE THAN ONE SUCH EQUILIBRIUM IE FOR A GIVEN M THE TWO RATES ARE EQUAL AT TWO OR THREE DIFFERENT X SEE &IG B C E F (ARDING AND -C.AMARA 4HE EXACT SHAPES OF #_ AND %_ ARE IMPORTANT ALSO FOR THE EXTINCTION RISK OF THE ENTIRE METAPOPULATION AT LOW PATCH NUMBERS &IG 4HE OCCURRENCE OF MULTIPLE EQUI LIBRIA HAS EARLIER BEEN STUDIED IN MORE COMPLEX METAPOPULATION MODELS (ANSKI AND 'YLLENBERG 'YLLENBERG ET AL )F AT LEAST ONE EQUILIBRIUM EXISTS THEN THERE IS AT LEAST ONE STABLE EQUILIBRIUM (ERE BY @STABLE WE MEAN THAT IF X IS INITIALLY CLOSE TO X THEN THE PROPORTION OF OCCUPIED PATCHES WILL TEND TO X OVER TIME )N ,EVINS MODEL THERE IS A UNIQUE EQUILIBRIUM THAT IS STABLE IF +M E &IG A AND THERE IS NO EQUILIBRIUM IF +M ) E 4HUS IN THIS PARTICULAR MODEL A STABLE EQUILIBRIUM EXISTS IF AND ONLY IF THE SPECIES CAN INVADE &OR OTHER SHAPES OF #_ AND %_ IT IS ALSO TRUE THAT IF A SPECIES CAN INVADE THEN THE PROPORTION OF OCCUPIED PATCHES WILL CERTAINLY INCREASE AND TEND TO A STABLE EQUILIBRIUM )N GENERAL HOWEVER THE CONVERSE NEED NOT HOLD AND THE EXISTENCE OF AN EQUILIBRIUM IS NOT EQUIVALENT TO THE ABILITY TO INVADE 4O SEE THIS SUPPOSE THAT THERE IS AN !LLEE EFFECT 4HUS THE PATCH COLONIZATION FUNCTION #_ IS AN ACCELERATING FUNCTION OF _ FOR SMALL _ ,ET THE PATCH EXTINCTION FUNCTION BE AS IN ,EVINS MODEL IE %_ E A CONSTANT 4HEN FOR SUITABLE CHOICE OF E THE TOTAL EXTINCTION RATE EXCEEDS THE TOTAL COLONIZATION RATE FOR SMALL X BUT COLONIZA TION EXCEEDS EXTINCTION IF X IS SOMEWHAT LARGER &IG E 4HUS THE SPECIES CANNOT INVADE HOWEVER IF THE PROPORTION OF PATCHES OCCUPIED WERE ARTIlCIALLY INCREASED SO AS TO EXCEED SOME CRITICAL LEVEL THEN THE PROPORTION WOULD CONTINUE TO INCREASE AND TEND TO A STABLE EQUILIBRIUM
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
&IG ! RANGE OF METAPOPULATIONS WITH DIFFERENT DYNAMICS OF THE MODEL IN &IG 7HITE SURFACES ARE TOTAL EXTINCTION RISKS AND BLACK HILLS TOTAL COLONIZATION RATES A !N ORDINARY ,EVINS METAPOPULATION B ! RESCUE EFFECT MAKES EXTINCTION RISK DECLINE WITH HIGHER MIGRATION RATES C ! DIFFERENT KIND OF RESCUE EFFECT D !NTI RESCUE EFFECT LEADS TO HIGHER EXTINCTION RISK WITH HIGHER MIGRATION RATES E 4HE COLONIZATION FUNCTION IS BELL SHAPED AN !LLEE EFFECT PREVAILS F !N EXAMPLE WITH BOTH A RESCUE AND !LLEE EFFECT
(ETEROGENEOUS LANDSCAPES
(OLT CONSIDERED A GENERALIZATION OF THE STANDARD ,EVINS METAPOPULATION MODEL TO A LANDSCAPE WITH TWO DISTINCT HABITATS ! FRACTION HI OF THE LANDSCAPE IS COMPRISED OF PATCHES OF TYPE I 4HE FRACTION OF HABITAT PATCHES THAT ARE TYPE I AND OCCUPIED BY THE SPECIES IS DENOTED BY PI .ECESSARILY WE HAVE PI ) HI AND HI H ) )F IN THE LATTER CASE THE INEQUALITY HOLDS HI H SOME PATCHES IN THE LANDSCAPE ARE UNSUITABLE FOR OCCUPANCY 5SING THE STANDARD ,EVINS NOTATION EI DENOTES EXTINCTION ON OCCUPIED PATCHES OF TYPE I AND CIJ IS COLONIZATION ONTO EMPTY PATCHES OF TYPE I DUE TO MIGRANTS GENERATED BY OCCUPIED PATCHES OF TYPE J 4HE EQUATION FOR DYNAMICS OF P IS DPDT C P C P H n P n E P A SIMILAR EQUATION DESCRIBES DYNAMICS IN THE SECOND HABITAT TYPE
+# (ARDING *- -C.AMARA AND 2$ (OLT
4HE TOTAL OCCUPANCY BY THE SPECIES IN THE LANDSCAPE IS P P P )F WE SUM THE DYNAMICAL EQUATIONS FOR CHANGE IN OCCUPANCY WE GET AN EXPRESSION FOR DPDT )N GENERAL THIS DOES NOT SIMPLIFY TO A FORM IN JUST P (OWEVER IF ALL THE COLONIZA TION RATES CIJ ARE EQUAL TO A CONSTANT C AND BOTH PATCHES HAVE THE SAME EXTINCTION RATES THE ORIGINAL ,EVINS MODEL EMERGES )N OTHER WORDS ARBITRARY DISTINCTIONS AMONG HABITATS CAN SIMPLY BE IGNORED (OWEVER IF PATCH TYPE INmUENCES EITHER COLONIZATION OR EXTINCTION LANDSCAPE HETEROGENEITY CAN INmUENCE METAPOPULA TION DYNAMICS EG PATCH TYPES DIFFER IN + OR M !LL THE FACTORS MENTIONED ABOVE WHICH INmUENCE COLONIZATION AND EXTINCTION RATES CAN POTENTIALLY SHOW VARIATION AMONG HABITAT TYPES &OR INSTANCE AN INDI VIDUAL BORN IN A HABITAT PATCH OF TYPE I BEFORE EMIGRATING MIGHT BECOME ACCLIMA TIZED TO THE ABIOTIC CONDITIONS IN ITS NATAL SITE EG AS IN PHYSIOLOGICAL ADAPTATION TO THERMAL CONDITIONS AND SO EITHER PREFERENTIALLY SEEK OUT SIMILAR HABITATS WHEN IT DISPERSES OR BE VULNERABLE TO HIGH MORTALITY IF IT SETTLES INTO A DIFFERENT HABITAT LEADING TO FAILED COLONIZATION )F ONLY PATCH TYPE I IS PRESENT THE INITIAL GROWTH RATE OF THE SPECIES WHEN RARE IS hI CII HI n EI AS IN THE STANDARD ,EVINS MODEL 7ITH BOTH PATCH TYPES PRESENT THE ASYMPTOTIC GROWTH RATE OF THE INVADING SPECIES TURNS OUT TO BE h h h 3 ;h n h C C H H= (OLT -ANIPULATING THIS EXPRESSION LEADS TO SEVERAL SIMPLE CONCLUSIONS &IRST A SPE CIES WHICH IS A GENERALIST MAY BE ABLE TO INVADE AND PERSIST BECAUSE IT CAN ENJOY CROSS HABITAT COLONIZATION WHEREAS OTHERWISE SIMILAR HABITAT SPECIALISTS WOULD GO EXTINCT IE EXPERIENCE FAILED INVASIONS 3ECOND SOMETIMES UTILIZING A SECOND HABITAT MAY BE CRUCIAL IN PERMITTING A SPECIES TO PERSIST IN A LANDSCAPE EVEN IF THERE IS NO COLONIZATION AMONG PATCHES OF THIS SECOND TYPE CONDITION IN (OLT 4HIS CAN HAPPEN IF ALL COLONIZATION FROM AND OF THE SECOND HABITAT TYPE IS INTO AND FROM HABITATS OF THE lRST HABITAT TYPE EG BECAUSE PATCHES OF THE SECOND HABITAT TYPE ARE WIDELY SPACED BUT THE SECOND HABITAT TYPE HAS A LOWER EXTINCTION RATE THAN DOES THE PRIMARY HABITAT TYPE 4HIS CAN BE VIEWED AS A KIND OF SPATIAL STORAGE EFFECT )T WOULD BE INTERESTING IN FUTURE WORK TO EXTEND THIS TWO HABITAT MODEL USING THE GENERALIZED APPROACH OF (ARDING AND -C.AMARA #OLONIZATION AMONG SOME HABITATS MAY PERMIT RESCUE EFFECTS EVEN WHILE COLONI ZATION AMONG OTHERS RESEMBLES THE ANTI RESCUE PATTERN )N SUCH CASES THE EXPECT ED DYNAMICS OF INVASION WOULD BE QUITE SENSITIVE TO THE RELATIVE PROPORTIONS OF THE LANDSCAPE OCCUPIED BY THE DISTINCT HABITAT TYPES
).4%2!#4)/.3 7)4( ! .!4)6% 30%#)%3 !N INVASIVE SPECIES CAN INTERACT WITH A NATIVE METAPOPULATION IN THE SAME PATCH NETWORK IN VARIOUS WAYS WITH NET EFFECTS ON THE LIKELIHOOD OF INVASION RANGING FROM POSITIVE TO NEGATIVE &OR INSTANCE WHEN SPECIES COMPETE FOR THE SAME LIM ITING RESOURCE WITHIN PATCHES COMPETITIVE EXCLUSION IS LIKELY -ETAPOPULATION DYNAMICS CAN NONETHELESS PERMIT INVASION BY AN INFERIOR SPECIES IF IT IS SUPERIOR
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
AT COLONIZATION OF EMPTY PATCHES ,EVINS AND #ULVER 4ILMAN 4HIS REQUIRES A TRADEOFF BETWEEN COMPETITION AND COLONIZATION ALLOWING THE INFE RIOR COMPETITOR TO EXPLOIT MORE EFFECTIVELY THE EMPTY HABITAT PATCHES LEFT BY THE SUPERIOR COMPETITOR WHEN IT SUFFERS EXTINCTIONS !MARSEKARE -ETAPOPULATION DYNAMICS CAN ALSO LEAD TO EXCLUSION THAT WOULD OTHERWISE NOT OCCUR (OLT &OR INSTANCE ONE SPECIES CAN DELIMIT A SECOND SPECIES INDI RECTLY BY HOSTING A PATHOGEN THAT IS MORE HARMFUL TO THE SECOND SPECIES (OLT AND ,AWTON !N EXAMPLE IS THE GRADUAL ERADICATION OF THE NATIVE NOBLE CRAY lSH !STACUS ASTACUS IN 3WEDEN WHICH IS BEING REPLACED BY THE .ORTH !MERICAN SIGNAL CRAY lSH 0ACIFASTACUS LENIUSCULUS MEDIATED BY A SHARED INFECTIOUS DISEASE 4HE INVASIVE SPECIES CARRIES A FUNGUS !PHANOMYCES ASTACI TO WHICH IT ITSELF APPEARS TO BE IMMUNE WHEREAS THE NATIVE SPECIES IS SEVERELY IMPACTED BY THE PARASITE "ANGYEEKHUN )N A METAPOPULATION SUCH INDIRECT EXCLUSION MAY OCCUR EVEN IF THE TWO SPECIES OCCUPY DISTINCT HABITAT PATCHES IN THIS EXAMPLE IF FUNGAL SPORES DISPERSE WIDELY THE INVASIVE SPECIES COULD PROVIDE A LANDSCAPE RESERVOIR FOR THE PATHOGEN WHICH CAN ELIMINATE THE NATIVE SPECIES EVEN IN PATCHES WHERE THE INVASIVE SPECIES ITSELF NEVER OCCURS 4HERE CAN ALSO BE FACILITATIVE INTERACTIONS BETWEEN INVASIVE AND RESIDENT SPE CIES )N THE LITERATURE ON SUCCESSION THERE ARE MANY EXAMPLES OF EARLY COLONIZERS FACILITATING INVASION BY LATER COLONISTS EG NITROGEN lXERS MAY NEED TO COLONIZE PRIOR TO OTHER SPECIES #ONNELL AND 3LATYER )N THIS CASE ONE SPECIES ALTERS THE ABIOTIC ENVIRONMENT SO AS TO ENHANCE COLONIZATION OR REDUCE EXTINCTION FOR A SECOND SPECIES -OREOVER ONE SPECIES MAY REQUIRE ANOTHER SPECIES AS A RESOURCE )NVASIONS BY SPECIALIST PREDATORS PARASITES OR HERBIVORES WILL ALMOST ALWAYS DEPEND UPON THE PRESENCE OF THEIR REQUIRED PREY OR HOSTS ! FLEXIBLE MODEL WHICH ALLOWS FOR MANY KINDS OF INTERACTIONS
7E WILL NOW LOOK AT INVASIONS IN WHICH EACH OF TWO SPECIES HAS INTERLINKED META POPULATION DYNAMICS EXTENDING A PHENOMENOLOGICAL METAPOPULATION MODEL OF (ANSKI AND OTHERS &IG TO INCLUDE DIFFERENT TYPES OF COLONIZATION AND EXTINCTION FUNCTIONS AND DIFFERENTIAL MIGRATION RATES 7E USE THIS MODEL TO CLASSI FY DIFFERENT TYPES OF INTERACTIONS BETWEEN AN INVASIVE SPECIES AND A NATIVE SPECIES 7E CONSIDER A METAPOPULATION WITH 4 IDENTICAL PATCHES %ACH PATCH CAN BE IN ONE OF FOUR STATES %MPTY 4YPE WHEN SPECIES IS PRESENT 4YPE WHEN SPECIES IS PRESENT OR 4YPE " WHEN BOTH ARE PRESENT &IG -IGRATION %ACH 4YPE PATCH SENDS OUT SUCCESSFUL SPECIES MIGRANTS AT RATE M %ACH 4YPE PATCH SENDS OUT SUCCESSFUL SPECIES MIGRANTS AT RATE M %ACH 4YPE " PATCH SENDS OUT SUCCESSFUL SPECIES MIGRANTS AT RATE MÉ AND SENDS OUT SUC CESSFUL SPECIES MIGRANTS AT RATE MÉ .OTE THAT THE DIFFERENCE BETWEEN M AND MÉ MEASURES HOW MUCH SPECIES CAN SUPPRESS OR ENHANCE THE MIGRATION RATE OF
+# (ARDING *- -C.AMARA AND 2$ (OLT
&IG 4HE RISK OF EXTINCTION AT LOW PATCH NUMBERS DEPEND ON THE SHAPE OF THE # AND % FUNCTIONS SEE &IG &ROM (ARDING AND -C.AMARA
&IG ! METAPOPULATION MODEL FOR TWO SPECIES 3PECIES IS COMPETITIVELY SUPERIOR AND EXCLUDES SPECIES FROM PATCHES 3PECIES CAN PERSIST IF IT HAS A HIGHER COLONIZATION TO EXTINCTION RATIO THAN SPECIES .EE AND -AY
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
&IG ! METAPOPULATION MODEL SPECIlCALLY DESIGNED TO STUDY INVASIVE SPECIES EQ ! PATCH CAN BE IN ONE OF FOUR STATES EMPTY OCCUPIED BY SPECIES OR SPECIES OR OCCUPIED BY BOTH SPECIES " 4HIS MODEL ALLOWS US TO EXPLORE MANY SORTS OF INmUENCES THAT INVASIVE SPECIES CAN HAVE ON A NATIVE SPECIES 4HE EXTINCTION % AND COLONIZATION RATES # ARE FUNCTIONS OF IMMIGRATION _
SPECIES 3IMILARLY FOR SPECIES THE DIFFERENCE IN MIGRATION PARAMETERS REmECTS INTERSPECIlC IMPACTS ON THE RATE AT WHICH EMIGRANTS ARE EMITTED FROM JOINTLY OCCUPIED PATCHES 4HESE DIFFERENCES COULD OCCUR DUE TO CHANGES IN DENSITY WITHIN PATCHES OR DUE TO CHANGES IN INDIVIDUAL BEHAVIOR IN THE FACE OF THE OTHER SPECIES EG A PREY SPECIES MAY SPEND MORE TIME IN HIDING IN THE FACE OF A PREDATOR AND THUS BE LESS LIKELY TO EMIGRATE FROM PATCHES CONTAINING BOTH PREDATORS AND PREY )NITIALLY WE ASSUME THAT MIGRANTS SETTLE AT RANDOM 3UPPOSE THAT THE NUMBER OF 4YPE AND 4YPE " PATCHES ARE . AND ." RESPECTIVELY 4HEN SPECIES MIGRANTS ARRIVE AT EACH PATCH IN THE ENVIRONMENT AT RATE _ .M ."MÉ 4
4HE RATE OF ARRIVAL OF SPECIES MIGRANTS _ IS SIMILARLY DElNED
#OLONIZATION %ACH EMPTY PATCH IS COLONIZED BY SPECIES MIGRANTS AND HENCE BECOMES A 4YPE PATCH AT RATE #_ %MPTY PATCHES ARE COLONIZED BY SPECIES MIGRANTS AND BECOME 4YPE AT THE RATE #_ %ACH 4YPE PATCH IS COLONIZED BY SPECIES MIGRANTS AND HENCE BECOMES A 4YPE " PATCH AT RATE #_ 3IMILARLY EACH 4YPE PATCH IS COLONIZED BY SPECIES MIGRANTS AND IS CONVERTED TO A 4YPE " PATCH AT THE RATE #_ .OTE THAT WE NEVER HAVE AN EMPTY PATCH SIMULTANEOUSLY COLONIZED BY BOTH SPECIES AND
É
É
+# (ARDING *- -C.AMARA AND 2$ (OLT
%XTINCTION ! 4YPE PATCH CHANGES TO AN EMPTY PATCH AT RATE %_ ! 4YPE PATCH CHANGES TO AN EMPTY PATCH AT RATE %_ ! 4YPE " PATCH WHICH HAS BOTH SPECIES CHANGES TO A 4YPE PATCH WHEN SPECIES GOES EXTINCT AT RATE %_ 3IMILARLY A 4YPE " PATCH CHANGES TO A 4YPE PATCH AT RATE %_ 7E ASSUME THAT IN A PATCH WITH BOTH SPECIES THERE ARE NOT SIMULTANEOUS EXTINCTIONS TAKING 4YPE " PATCHES DIRECTLY BACK TO AN EMPTY STATE )N THIS MODEL THE RATE OF CHANGE OF PATCH STATE DEPENDS ON MIGRATION RATES FROM BOTH THE TWO SINGLE SPECIES AND THE MIXED SPECIES PATCHES 4HE TWO SPECIES CAN THUS INmUENCE EACH OTHER BY ALTERED EXTINCTION AND COLONIZATION RATES BOTH OF WHICH CAN INVOLVE ALTERED MIGRATION RATES SEE &IG
É
É
0OSSIBLE INTERACTIONS BETWEEN SPECIES
.OW CONSIDER INTERACTIONS BETWEEN THE TWO SPECIES &IG )F SPECIES COMPETES WITH SPECIES THEN SPECIES MAY BE ADVERSELY AFFECTED BY THE PRESENCE OF SPECIES IN VARIOUS WAYS )T MAY BE MORE DIFlCULT FOR SPECIES TO COLONISE A PATCH THAT IS ALREADY OCCUPIED BY SPECIES THAN TO COLONISE AN EMPTY PATCH IE #_ #_ )F SPECIES CAN COLONISE A PATCH CURRENTLY OCCUPIED BY SPECIES SO AS TO PRODUCE A PATCH WITH BOTH SPECIES THEN THIS MAY INCREASE THE PROBABILITY THAT SPECIES GOES EXTINCT ON THE PATCH IE %_ %_ 4HE PRESENCE OF SPECIES MAY ALSO REDUCE THE RATE AT WHICH SPECIES SENDS OUT MIGRANTS FROM THE PATCH IE MÉ M 4HIS WILL REDUCE THE IMMIGRATION RATE _ WHICH WILL TEND TO REDUCE THE RATE AT WHICH PATCHES ARE COLONIZED BY SPECIES )F MÉ M THERE IS A POSSIBLE BENElCIAL EFFECT TO SPECIES FOR SPECIES TO ALSO BE PRESENT IN A PATCH 'IVEN A STRONG ANTI RESCUE EFFECT IE INCREASED IMMIGRA TION INCREASES EXTINCTION RATE A REDUCTION IN THE IMMIGRATION RATE _ MAY REDUCE THE RATE AT WHICH SPECIES DIES OUT ON PATCHES 7HETHER COMPETITION FROM SPE CIES IS BENElCIAL OR NOT MAY DEPEND ON THE NUMBER OF PATCHES ALREADY OCCUPIED BY SPECIES &OR EXAMPLE IF THE ANTI RESCUE EFFECT ONLY BECOMES MARKED AT HIGH IMMIGRATION RATES COMPETITION MAY BE DELETERIOUS TO SPECIES WHEN IT IS RARE BUT BENElCIAL WHEN IT IS COMMON )N A SENSE GIVEN METAPOPULATION DYNAMICS AND AN ANTI RESCUE EFFECT A COMPETITOR AS MEASURED BY A REDUCTION IN THE SIZE OF THE MIGRANT POOL GENERATED BY PATCHES MAY DYNAMICALLY BE A MUTUALIST )F INSTEAD OF BEING A COMPETITOR SPECIES IS A PREDATOR THAT BENElTS FROM THE PRESENCE OF PREY SPECIES WE WOULD HAVE #_ #_ %_ %_ AND MÉ M )N THE EXTREME CASE WHERE SPECIES IS A SPECIALIST CONSUMER EG A PARASITE OR PARASITOID THAT IS TOTALLY DEPENDENT ON THE PRESENCE OF SPECIES #_ %_ ' AND M AND THE MODEL REDUCES TO A THREE PATCH SYSTEM SIMILAR TO EPIDEMIOLOGICAL MODELS 4HE DIRECTION OF THE INEQUALITIES FOR THE GROWTH OF SPECIES DEPEND ON THE BIOLOGY OF THE INTERACTION )N A TYPICAL PREDATOR PREY INTERACTION THE INEQUALITIES ARE ALL REVERSED FOR SPECIES
É
É
É
É
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
)N SOME CASES HOWEVER AS NOTED BY (OLT A PREDATOR MAY INSTEAD REDUCE THE RATE OF EXTINCTION OF ITS PREY FOR INSTANCE THE PRESENCE OF THE PREDATOR MAY PREVENT THE PREY SPECIES FROM OVEREXPLOITING ITS OWN RESOURCE BASE !LTHOUGH THIS IS AN INTERESTING POSSIBILITY EG GENERATING ALTERNATIVE LANDSCAPE STATES BELOW WE FOCUS INSTEAD ON MORE CLASSICAL PREDATOR PREY SYSTEMS WHERE THE PREDA TOR IS HARMFUL FOR PREY PERSISTENCE IN A PATCH $YNAMICS OF THE TWO SPECIES METAPOPULATION
7E NOW ANALYSE THE RATES AT WHICH PATCH OCCUPANCY IN THE TWO SPECIES METAPOPU LATION CHANGES OVER TIME $ENOTE THE FRACTION OF PATCHES WITH SPECIES ONLY BY X THE FRACTION WITH SPECIES ONLY BY X AND THE FRACTION WITH BOTH SPECIES PRESENT BY Z 4HE FRACTION OF EMPTY PATCHES IS THUS n X X Z AND THE RATES OF CHANGE OF PATCH OCCUPANCY ARE DX #_ n X X Z n %_ X n #_ X %_ Z DT
DX #_ n X X Z n %_ X n #_ X %_ Z DT
DZ X#_ X#_ n Z%_ %_ DT
É
É
É
É
É
É
É
É
(ERE THE IMMIGRATION RATES CAN BE EXPRESSED IN TERMS OF X X AND Z AS
É
É
_ XM ZM AND _ XM ZM
#RITERIA FOR INVASION )NITIAL INVASION
7E NOW DESCRIBE THE CRITERIA FOR THE INITIAL PHASE OF AN INVASION 7E ASSUME THAT THE NATIVE SPECIES SPECIES CURRENTLY OCCUPIES A PROPORTION X OF ALL PATCHES WHERE THIS PROPORTION IS A STABLE EQUILIBRIUM FOR THE METAPOPULATION WITH JUST SPE CIES PRESENT 7E THEN INTRODUCE THE INVADER SPECIES INTO A FEW PATCHES AND ASK WHETHER THE FREQUENCY OF OCCURRENCE OF THE RARE INVADING SPECIES INCREASES OR DECLINES 3INCE THE INVADING SPECIES IS RARE X AND Z ARE SMALL #ONSEQUENTLY THE RATE AT WHICH SPECIES MIGRANTS ARRIVE AT EACH PATCH _ IS ALSO SMALL 4HUS ALL THAT MATTERS FOR THE INITIAL INVASION ARE THE LIMITING VALUES FOR SMALL _ OF THE COLONIZATION AND EXTINCTION FUNCTIONS FOR SPECIES "Y ANALOGY WITH
+# (ARDING *- -C.AMARA AND 2$ (OLT
&IG /NE EXAMPLE OF HOW INITIAL INVASION RATE IS INmUENCED BY EÉ THE EXTINCTION RISK OF THE INVADER IN TYPE " PATCHES -ODEL STRUCTURE AS IN &IG 4HE THREE CURVES REPRESENT THREE DIFFERENT MÉ MIGRATION RATES FROM TYPE " PATCHES A B C 4HE lGURE IS BASED ON EQUATIONS AND PARAMETER VALUES ARE + X E CÉ +É EÉ M
É
É
EQUATIONS AND WE ASSUME THAT #_ 5 +_ #_ X 5 +_ %_ 5 E AND %_ 5 EÉ FOR SMALL _ $URING THE INITIAL PHASE OF INVASION BY SPECIES THE IMMI GRATION RATE OF SPECIES MIGRANTS CAN BE TAKEN AS CONSTANT AND EQUAL TO ITS VALUE AT THE EQUILIBRIUM OCCUPANCY X OF SPECIES 7E THUS ALSO ASSUME THAT THE RATE AT WHICH A 4YPE PATCH IS CONVERTED TO A 4YPE " PATCH C > #MX IS CONSTANT 3IMILARLY THE RATE AT WHICH A 4YPE " PATCH CONVERTS TO 4YPE EÉ > %MX IS CON STANT 7E NOW SUBSTITUTE THESE EXPRESSIONS INTO EQUATIONS AND EXPRESS _ IN TERMS OF X AND Z EQ AND SINCE X AND Z ARE SMALL IGNORE TERMS INVOLV ING X XZ AND Z 4HE RATE OF CHANGE IN PROPORTION OF INVADED PATCHES EARLY IN THE INVASION PROCESS ARE THEN GIVEN BY THE FOLLOWING LINEARISED EQUATIONS
É
É
DX + n X M n E C X + n X MÉ EÉ Z DT
É
DZ +XM C X +XM n EÉ EÉ Z DT
É
É
É
É
4HESE EQUATIONS CAN BE WRITTEN AS
É
É
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
DX )X *Z DT
DZ *X )Z DT
É
É
WHERE ) + n X M n E CÉ
É É
É
) +XM n EÉ EÉ
É
* +XM CÉ
* + n X M EÉ
É
É
4HE QUANTITY ) IS THE NET RATE AT WHICH A 4YPE PATCH LEADS TO THE PRODUCTION OF 4YPE PATCHES ) IS THE RATE OF COLONIZATION OF EMPTY PATCHES BY MIGRANTS FROM THE 4YPE PATCH IE + n X M MINUS THE RATE OF DISAPPEARANCE OF THE FOCAL 4YPE PATCH AS A RESULT OF EXTINCTION OR COLONIZATION BY SPECIES IE E CÉ SEE EQ 4HE TERM * CAN BE INTERPRETED AS THE RATE OF hCROSSING OVERv THE RATE AT WHICH A 4YPE " PATCH CONTRIBUTES TO THE FORMATION OF 4YPE PATCHES 4HERE ARE TWO WAYS THIS CONTRIBUTION IS MADE 4HE TERM + n X M IS THE RATE AT WHICH MIGRANTS FROM THE 4YPE " PATCH CONVERT EMPTY PATCHES INTO 4YPE PATCHES BY COLONIZATION AND EÉ IS THE RATE AT WHICH THE FOCAL 4YPE " PATCH ITSELF CHANGES TO A 4YPE PATCH AS A RESULT OF THE EXTINCTION OF THE SPECIES OCCUPANTS SEE EQN 3IMILARLY ) IS THE NET RATE AT WHICH A 4YPE " PATCH LEADS TO THE PRODUCTION OF 4YPE " PATCHES 4HE QUANTITY +XM IS THE RATE AT WHICH MIGRANTS FROM THE 4YPE " PATCH COLONISE 4YPE PATCHES AND SO CONVERT THEM TO 4YPE " AND EÉ EÉ IS THE RATE AT WHICH THE 4YPE " PATCH REVERTS TO A PATCH WITH JUST A SINGLE SPECIES PRESENT EQ 4HE CROSS TERM * IS THE NET RATE AT WHICH A SINGLE 4YPE PATCH CONTRIBUTES TO THE FORMATION OF 4YPE " PATCHES !GAIN THERE ARE TWO ELEMENTS TO THIS CONTRIBUTION -IGRANTS FROM THE 4YPE PATCH COLONISE 4YPE PATCHES AND THE PATCH MAY ITSELF BE COLONIZED BY SPECIES SEE EQ ,ET W X Z BE THE TOTAL PROPORTION OF PATCHES IN WHICH SPECIES IS PRESENT 4O ANALYSE WHETHER SPECIES CAN INITIALLY INVADE WE LOOK AT HOW THIS QUANTITY CHANGES OVER TIME 4HE LINEARISED EQUATIONS AND IMPLY THAT WHATEVER THE INITIAL VALUES OF X AND Z THE PROPORTION X W WILL SETTLE DOWN TO AN EQUILIB RIUM VALUE !S THIS EQUILIBRIUM IS APPROACHED
É
É
É
É
DW Ah DT
É
+# (ARDING *- -C.AMARA AND 2$ (OLT
\) * \ WHERE THE RATE OF INITIAL INVASION h IS THE LARGEST EIGENVALUE OF THE MATRIX ! \ \ \* )\ 4HUS SPECIES CAN INVADE THE METAPOPULATION IF h WHILE IF h THE SPE CIES GOES EXTINCT IN THE METAPOPULATION &IGURE ILLUSTRATES HOW INVASION RATE can BE INmUENCED BY THE EXTINCTION RISK OF THE INVADER IN PATCHES OF 4YPE " E É FOR ONE COMBINATION OF PARAMETER VALUES )N THIS CASE INCREASING EXTINCTION RISK IN 4YPE " PATCHES IS VERY COSTLY FOR THE INVADER AND AT TOO HIGH EÉ INVASION EVEN BECOMES IMPOSSIBLE &IG "ELOW WE SHALL DESCRIBE THE EARLY INVASION PROCESS FOR TWO SPECIAL CASES BEFORE CONSIDERING THE GENERAL CRITERIA FOR INVASION
ÉÉ
!N @INVISIBLE INVADER 3UPPOSE THAT THE INVADER SPECIES CANNOT COMPETE FOR PATCHES WITH SPECIES 3PECIlCALLY SPECIES IS UNABLE TO COLONISE PATCHES ALREADY OCCUPIED BY SPECIES AND SPECIES IMMEDIATELY WIPES OUT SPECIES WHEN SPECIES COLONISES A 4YPE PATCH 4HEN THERE EXIST NO PATCHES CONTAINING BOTH SPECIES SO Z SO THAT EQUA TIONS AND REDUCE TO THE SINGLE EQUATION DX )X DT
4HE RATE OF GROWTH OF THE NUMBER OF PATCHES CONTAINING SPECIES IS JUST ) SO INVASION IS POSSIBLE IF ) )F X APPROACHES ZERO THIS EXPRESSION REDUCES TO THE CONDITION FOR INVASION BY A SINGLE SPECIES DISCUSSED EARLIER !S X INCREASES FROM THERE IS A VALUE AT WHICH THE INVADER IS EXCLUDED )N THE SIMPLE ,EVINS MODEL FOR INVASION TO BE POSSIBLE REQUIRES THAT THE INVADER HAVE A HIGHER EQUILIB RIUM PATCH OCCUPANCY WERE IT ALONE THAN DOES THE RESIDENT SPECIES SEE BELOW ! @PARASITE TYPE INVADER .OW SUPPOSE THAT SPECIES IS TOTALLY RELIANT ON THE PRESENCE OF THE NATIVE SPECIES &OR EXAMPLE SPECIES MIGHT BE A PARASITE OR A SPECIALIST PREDATOR OF SPECIES EG PARASITIC WASPS ARE OFTEN OBLIGATE SPECIALISTS ON PARTICULAR HOST SPECIES .OUHUYS AND (ANSKI OR AN OBLIGATE COMMENSAL 3PECIlCALLY ASSUME THAT SPECIES IS UNABLE TO COLONISE EMPTY PATCHES &URTHERMORE ON PATCHES WHERE BOTH SPECIES ARE PRESENT A 4YPE " PATCH IF SPECIES DIES OUT THEN SPECIES IMMEDIATELY DIES OUT AS WELL SO THAT THE PATCH BECOMES EMPTY 4HEN X AND THE RATE OF GROWTH IN THE NUMBER OF PATCHES CONTAINING SPECIES IS JUST ) SINCE EQUATIONS AND REDUCE TO THE SINGLE EQUATION DZ )Z DT
É
É
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
É
4HUS IN THIS SPECIAL CASE INVASION IS POSSIBLE IF ) &ROM WE SEE THAT AN INCREASE IN THE OCCUPANCY BY THE RESIDENT SPECIES TENDS TO FACILITATE INVASION BY SPECIES 'ENERAL CRITERIA FOR INVASION 7E NOW CONSIDER THE GENERAL CASE )T IS EASY TO SHOW THAT IF ) THEN h SO INVASION IS GUARANTEED 4HIS IS NOT SURPRISING EQUATION SHOWS THAT EVEN WHEN COMPETITION BY SPECIES IS AT ITS STRONGEST SPECIES CAN INVADE BY JUST COLONISING EMPTY PATCHES ! FORTIORI IF ) SPECIES CAN INVADE WHATEVER THE FORM OF THE INTERACTION BETWEEN THE TWO SPECIES 3IMILARLY ) IMPLIES h IF THE INVADER WERE ABLE TO SPREAD WHEN RESTRICTED TO PATCHES OCCUPIED BY SPECIES THEN IT IS CERTAINLY A SUCCESSFUL INVADER REGARDLESS OF ITS PERFORMANCE BY ITSELF WHEN CONFRONTED WITH EMPTY PATCHES 4HUS EITHER ) OR ) IS SUFlCIENT TO ENSURE THAT SPECIES CAN INVADE (OWEVER WHEN ) AND ) IT MAY STILL BE POSSIBLE FOR SPECIES TO INVADE BECAUSE 4YPE " AND 4YPE PATCHES TEND TO ENHANCE EACH OTHERS FORMATION )N OTHER WORDS MIGRANTS FROM 4YPE PATCHES MAY COLONISE 4YPE PATCHES AND SO CONVERT THEM TO 4YPE " AND 4YPE MIGRANTS FROM 4YPE " PATCHES MAY COLONISE EMPTY PATCHES AND SO CONVERT THEM TO 4YPE )T IS EASY TO SHOW THAT WHEN ) AND ) SPECIES CAN INVADE h PROVIDED THAT * * ) )
É
É
É
É
É
É
)NVASION IN THE LONG RUN
7E NOW LOOK AT A SPECIAL CASE ILLUSTRATING HOW THE METAPOPULATION SYSTEM CAN DEVELOP IN THE LONG RUN AFTER THE INITIAL INVASION 7E ARE ESPECIALLY INTERESTED IN CHARACTERIZING THE CONDITIONS FOR LONG TERM COEXISTENCE OF THE INVADER AND THE NATIVE SPECIES #ONSIDER THE EXAMPLE WHEN TWO SPECIES CAN ONLY COLONISE EMPTY PATCHES SO THAT THERE ARE NO PATCHES WITH BOTH SPECIES PRESENT 7HO EVER COMES lRST WINS THE PATCH A SO CALLED @LOTTERY MODEL 4HUS THE PRESENCE OF ONE SPECIES REDUCES THE NUMBER OF PATCHES THAT ARE AVAILABLE FOR THE OTHER SPECIES TO OCCUPY .OTE HOWEVER THAT SO FAR AS A SPECIES IS CONCERNED IT IS NOT SIMPLY AS IF THE METAPOPULA TION AS A WHOLE HAD FEWER PATCHES PRESENT 4HIS IS BECAUSE MIGRANTS OF THE SPECIES STILL SETTLE ON PATCHES AT RANDOM SO THOSE MIGRANTS THAT SETTLE ON A PATCH CURRENTLY OCCUPIED BY THE OTHER SPECIES ARE LOST 4HUS THERE IS A DILUTION OF MIGRANTS THAT SETTLE ON EMPTY PATCHES 7HEN THE TWO SPECIES LOCALLY EXCLUDE ONE ANOTHER THE EQUATIONS GOVERNING METAPOPULATION DYNAMICS WHICH ARE NOW JUST EQUATIONS AND REDUCE TO DX #_ n X X n %_ X DT
+# (ARDING *- -C.AMARA AND 2$ (OLT
DX #_ n X X n %_ X DT
&OR SIMPLICITY OF EXPOSITION WE ASSUME THAT WHEN ONLY SPECIES IS PRESENT THERE IS A UNIQUE EQUILIBRIUM LEVEL OF PATCH OCCUPANCY WHICH WE DENOTE BY X 3IMILARLY WHEN SPECIES IS PRESENT ALONE IT HAS A UNIQUE EQUILIBRIUM LEVEL OF PATCH OCCUPANCY X 4O ANALYSE THE ABILITY OF EACH SPECIES TO INVADE WHEN THE OTHER IS PRESENT WE ASSUME THAT #_ 5 +_ AND %_ 5 E FOR SMALL _ AND #_ 5 +_ AND %_ 5 E FOR SMALL _ NOTE THAT THESE FUNCTIONS MAY DEVIATE FROM THIS FORM WHEN _ AND _ ARE NOT SMALL -OTIVATED BY ,EVINS MODEL WE DElNE E E X n AND X n +M + M
È
È
4HESE ARE THE EQUILIBRIUM LEVELS OF SINGLE SPECIES OCCUPANCY WHEN THE ABOVE APPROXIMATIONS FOR SMALL _ AND _ HOLD EXACTLY FOR ALL _ AND _ 7HEN X IS SMALL WE HAVE #_ n X X n %_ X 5 +MX X X 4HUS BY EQUA TION
È
DX X X DT
È
WHEN X IS SMALL
4HAT IS THE INITIAL RATE OF INCREASE IN PATCH OCCUPANCY BY SPECIES IS POSITIVE IF THE PATCH OCCUPANCY IT INITIALLY SEEMS TO AIM TOWARDS IN THE ABSENCE OF SPECIES X IS HIGHER THAN THE CURRENT PATCH OCCUPANCY BY THE OTHER SPECIES X 4HUS IF SPECIES IS AT ITS EQUILIBRIUM OF PATCH OCCUPANCY X SPECIES CAN INVADE IF
È
È
X X
3IMILARLY IF SPECIES IS AT ITS EQULIBRIUM OF PATCH OCCUPANCY X THEN SPECIES CAN INVADE IF
È
X X
)F BOTH EXPRESSIONS AND HOLD ONE WILL SEE ROBUST COEXISTENCE IN THAT EACH SPECIES CAN INCREASE WHEN IT IS RARE AND THE OTHER SPECIES IS AT ITS RESPECTIVE EQUILIBRIUM SEE FURTHER BELOW 4HE DYNAMICS OF THE LOTTERY MODEL WITH ,EVINS FUNCTIONS
)N ANALYSING THE POSSIBILITY FOR COEXISTANCE IT IS OF UTMOST IMPORTANCE TO CONSIDER THE SHAPE OF THE EXTINCTION AND COLONIZATION FUNCTIONS 4HE LOTTERY MODEL OUTLINED
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
ABOVE HAS BEEN SHOWN TO EXCLUDE COEXISTENCE (ANSKI SEE ALSO 3HURIN ET AL (OWEVER THIS CONCLUSION IS BASED ON ASSUMING ,EVINS STATIC FUNCTIONS 7HEN EACH OF THE SINGLE SPECIES METAPOPULATIONS ARE AS IN ,EVINS BASIC MODEL WE HAVE #_ +_ AND %_ E FOR ALL _ AND #_ +_ AND %_ E FOR ALL _ )N THIS SPECIAL CASE XÈ X AND XÈ X )E THE EQUILIBRIUM PATCH OCCUPAN CY IS EQUAL TO WHAT IS EXPECTED BY THE RATE OF INITIAL INVASION 4HUS IF SPECIES IS AT ITS EQUILIBRIUM SPECIES CAN INVADE IF AND ONLY IF X X 3IMILARLY IF SPECIES IS AT ITS EQUILIBRIUM OCCUPANCY THEN SPECIES CAN INVADE IF AND ONLY IF X X 4HUS THE SPECIES WITH THE HIGHEST EQUILIBRIUM PATCH OCCUPANCY WHEN ALONE CAN INVADE THE OTHER AND IT IS NEVER POSSIBLE FOR BOTH SPECIES TO BE ABLE TO INVADE EACH OTHER
&IGURE SHOWS THE METAPOPULATION DYNAMICS IN THE WHOLE OF THE X X PLANE !S CAN BE SEEN THE METAPOPULATION DYNAMICS LEADS TO THE INEVITABLE EXTINCTION OF THE SPECIES WITH THE SMALLEST EQUILIBRIUM PATCH OCCUPANCY ON ITS OWN 4HUS WITH THESE ASSUMPTIONS COEXISTENCE IS NOT POSSIBLE AND THE SPECIES WITH THE LARGEST EQUILIBRIUM OCCUPANCY EXCLUDES THE OTHER (ANSKI P
&IG )N A LOTTERY MODEL PARAMETERISED WITH ,EVINS STATIC FUNCTIONS COEXISTENCE OF SPECIES X AXIS AND SPECIES Y AXIS IS NOT POSSIBLE 4HE PROPORTION OF PATCHES OCCUPIED BY SPECIES WILL CONTINUE TO INCREASE UNTIL SPECIES GOES EXTINCT
+# (ARDING *- -C.AMARA AND 2$ (OLT
4HE LOTTERY MODEL WITH GENERAL FUNCTIONS
4O ANALYSE METAPOPULATION DYNAMICS IN THE GENERAL CASE WHEN THE COLONIZATION AND EXTINCTION RATE CAN HAVE MANY DIFFERENT SHAPES WE CONSIDER HOW THE SIGNS OF DX DX AND VARY IN THE X X PLANE 7HEN SPECIES IS ABSENT X PATCH DT DT OCCUPANCY OF SPECIES INCREASES WITH TIME WHEN OCCUPANCY IS BELOW THE EQUILIB RIUM OCCUPANCY X IE DX X X DT
WHEN X
&ROM CRITERIA AND THE CURVE DX IN THE X X PLANE JOINS THE POINT X TO THE POINT XÈ DT DX 3IMILARLY THE CURVE JOINS THE POINT XÈ TO THE POINT X DT 4HESE CURVES ARE ILLUSTRATED IN &IG 4HE lGURE ALSO SHOWS THE RESULTING METAPOPULATION DYNAMICS &ROM CRITERIA AND AND AS THE lGURE ILLUS TRATES IF XÈ X AND XÈ X THEN EACH SPECIES CAN INVADE THE OTHER AT THE LATTERS EQUILIBRIUM PATCH OCCUPANCY 4HE METAPOPULATION DYNAMICS THEN LEADS TO STABLE CO EXISTENCE OF THE TWO SPECIES 4HE CONDITIONS FOR MUTUAL INVASION CAN BE SATIS lED WHEN THE INITIAL RATE OF INCREASE IN PATCH NUMBERS IS HIGHER THAN WOULD BE EXPECTED FROM ITS EQUILIBRIUM 4HIS PHENOMENON IS LIKELY TO ARISE IF EXTINCTION RATE IS INITIALLY LOWER OR COLONIZATION INITIALLY HIGHER COMPARED TO THE RATE AT HIGHER PATCH OCCUPANCIES 4HIS TYPE OF DISPROPORTIONALLY HIGH INITIAL RATE OF INCREASE IN PATCH OCCUPANCY WILL BE FOUND IN POPULATIONS WITH ANTI RESCUE EFFECTS ANDOR ANTI !LLEE EFFECTS 7HEN SUCH EFFECTS ARE PRESENT THE INITIAL RATE OF INCREASE OF EACH SINGLE SPECIES METAPOPULATION CAN BE HIGH WITHOUT A CORRESPONDINGLY HIGH PATCH OCCUPANCY AT EQUILIBRIUM 4HIS REDUCED EQUILIBRIUM SIZE REDUCES COMPETITION ALLOWING CO EXISTENCE EVEN IN THE LOTTERY MODEL SEE &IG 4HE DYNAMICS AND STABILITY OF A TWO SPECIES SYSTEM DEPEND ON THE EXACT SHAPE OF THE COLONIZATION AND EXTINCTION FUNCTIONS 7E HAVE ILLUSTRATED THIS FOR THE SIMPLE LOTTERY MODEL MORE COMPLEX FORMS OF INTERACTIONS AMONG SPECIES REQUIRE FURTHER ANALYSIS
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
&IG ! LOTTERY MODEL WHICH ALLOWS DIFFERENT SHAPES OF THE # AND % FUNCTIONS CAN HAVE STABLE COEXISTENCE OF TWO SPECIES 4HE INITIAL RATE OF INVASION MUST BE DISPROPORTIONALLY HIGH WHICH CAN BE THE CASE FOR EXAMPLE WHEN THERE IS AN ANTI RESCUE EFFECT
%80,)#)4 30!4)!, 3425#452% !.$ &).)4% .5-"%2 /& 0!4#(%3 4HE FRAMEWORK DESCRIBED ABOVE ASSUMES THE NUMBER OF PATCHES TO BE VERY LARGE (OWEVER IF THE NUMBER OF PATCHES IS LESS THAN ABOUT (ANSKI P SINGLE STOCHASTIC EVENTS OF COLONIZATION AND EXTINCTION BECOME IMPORTANT 4HE RISK THAT ALL PATCHES WILL GO EXTINCT SIMULTANEOUSLY METAPOPULATION EXTINCTION DEPENDS ON THE COMBINATION OF METAPOPULATION SIZE AND THE SHAPE OF THE PER PATCH EXTINCTION FUNCTION &IG ! CONSIDERATION OF THE EFFECTS OF lNITE PATCH NUMBERS IS INEVITABLE WHEN CONSIDERING THE CONSEQUENCES OF EXPLICIT SPACE AND LANDSCAPE STRUCTURE ! VERY ACTIVE AREA OF RESEARCH AT PRESENT IS FOCUSED ON MAKING METAPOPULATION THEORY SPATIALLY EXPLICIT 4HE BASIC IDEA IS THAT IN A METAPOPULATION WITH A lNITE NUMBER OF PATCHES EACH PATCH HAS ITS OWN SPECIlC CHARACTERISTIC AND LANDSCAPE POSITION WHICH IN TURN INmUENCE ITS PROBABILITY OF EXTINCTION AND LIKELIHOOD OF COLONIZATION -ETAPOPULATION DYNAMICS OF THE ENTIRE ENSEMBLE REmECTS BOTH HETE ROGENEITY AMONG PATCHES EG IN AREA WHICH CAN INmUENCE EXTINCTION AND THE SPECIlC LANDSCAPE STRUCTURE AND PATTERN OF CONNECTIVITY OF THE PATCHES 4HE SIZE
+# (ARDING *- -C.AMARA AND 2$ (OLT
AND COMPOSITION OF LOCAL POPULATIONS ALSO INmUENCE INVASION SPEED .EUBERT AND #ASWELL /VASKAINEN AND (ANSKI PROVIDE AN EXCELLENT OVERVIEW OF RECENT THEORY IN THIS AREA AND HERE WE SIMPLY SKETCH SOME OF THE BASIC ISSUES WITH AN EMPHASIS UPON IMPLICATIONS FOR INVASION BIOLOGY -ETAPOPULATION MODELS WITH A SPATIALLY EXPLICIT STRUCTURE PROVIDE IMPORTANT LINKAGES WITH LANDSCAPE ECO LOGY AND WITH APPLIED ISSUES SUCH AS POPULATION VIABILITY ANALYSES /NE BIOLOGICAL ASSUMPTION THAT IS BUILT INTO THE GENERALIZED ,EVINS MODEL WE HAVE CONSIDERED ABOVE IS THAT ALL EMPTY PATCHES ARE ACCESSIBLE TO MIGRANTS EMA NATING FROM ALL OCCUPIED PATCHES )N GENERAL DISPERSAL IS SPATIALLY LIMITED AND SO THIS ASSUMPTION WILL BE VIOLATED 4HIS MAY BE PARTICULARLY IMPORTANT TO CONSIDER IN THE EARLY STAGES OF AN INVASION WHEN A COLONISING SPECIES HAS ESTABLISHED A BEACHHEAD ON JUST ONE OR A FEW SITES &ROM THESE INITIAL SITES WITH LIMITED DISPER SAL THERE MAY BE A SMALL lNITE NUMBER OF EMPTY SITES AVAILABLE FOR COLONIZATION -ATHEMATICALLY THE DYNAMICS CAN BE DESCRIBED AS A -ARKOV CHAIN IN DISCRETE TIME OR -ARKOV PROCESS IN CONTINUOUS TIME %XTINCTION CAN ARISE BECAUSE OF AN ANALOGUE OF DEMOGRAPHIC STOCHASTICITY AT THE METAPOPULATION SCALE %VEN IF INITIAL INVASION IS SUCCESSFUL THE RATE OF INCREASE AND RATE OF SPATIAL SPREAD OF THE COLONISING SPECIES CAN BE DAMPED BECAUSE MANY COLONISTS EMERGING FROM THE CENTER OF THE INVASION SIMPLY MOVE TO PATCHES THAT ARE ALREADY OCCUPIED )N REACTION DIFFUSION STYLE MODELS OF INVASIVE SPECIES HETEROGENEITY IN DISPERSAL RATES SEEMS TO EXERT A PARTICULARLY STRONG EFFECT ON THE OVERALL RATE OF INVASION OF SPECIES 3HIGESADA AND +AWASAKI )N SPATIALLY EXPLICIT LANDSCAPE MODELS THERE CAN BE CRITICAL THRESHOLDS IN HABITAT CONNECTIVITY BELOW WHICH SPECIES ARE LIKELY TO GO EXTINCT EVEN THOUGH A SUBSTANTIAL NUMBER OF PATCHES EXIST WHICH ARE PERFECTLY SUITABLE FOR OCCUPANCY 7ITH 7E MIGHT CALL THIS THE @4ANTALUS EFFECT IN METAPOPULATION ECOLOGY AFTER THE 'REEK LEGEND OF 4ANTALUS WHO WAS TORMENTED BY AN ETERNITY OF HUNGER AND THIRST WITH LUSCIOUS GRAPES AND CLEAN WATER VISIBLE BUT JUST BARELY OUT OF REACH )N GENERAL SPATIALLY EXPLICIT METAPOPULATION MODELS SEEM TO IMPLY THAT LOCALISED DISPERSAL MAKES INVASION MORE DIFlCULT (OWEVER WERE ONE TO PLACE THE GENERALIZED ,EVINS MODEL DISCUSSED ABOVE INTO A SPATIALLY EXPLICIT LANDSCAPE A RICHER ARRAY OF OUTCOMES MIGHT BE OBSERVED &OR INSTANCE WITH !LLEE EFFECTS GIVEN UNIFORM DISPERSAL OVER A LARGE NUMBER OF PATCHES FROM AN INITIAL PROPAGULE TOO FEW INDIVIDUALS MIGHT ENTER ANY GIVEN PATCH TO ENSURE SUCCESSFUL COLONIZATION )F INSTEAD DISPERSAL IS LOCALISED MOST INDIVIDUALS MIGHT ENTER THE SAME RELA TIVELY FEW PATCHES THUS INCREASING THE EFFECTIVE MIGRANT DENSITY IN THOSE PATCHES 4HIS COULD FACILITATE COLONIZATION 7HAT ONE MIGHT OBSERVE IN THIS CASE IS A SUCCESSFUL NUCLEUS OF INITIAL COLONIZATION FOLLOWED BY ACCRETIONARY GROWTH AS NEIGHBORING PATCHES GET SUCCESSFULLY COLONIZED !LTERNATIVELY IF THERE ARE GAPS IN AVAILABILITY OF SUITABLE HABITATS !LLEE EFFECTS COULD LEAD TO CONSTRAINTS ON THE ABILITY OF AN INVASIVE SPECIES TO EXPAND MUCH BEYOND THE SITES OF ITS ORIGINAL COLONIZATION +EITT ET AL /NE COMPLICATION THAT ARISES IN SPATIALLY EXPLICIT METAPOPULATIONS IS THAT IF THERE IS HETEROGENEITY AMONG PATCHES EG IN ATTRIBUTES THAT INmUENCE
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
COLONIZATION SUCH HETEROGENEITY IS LIKELY TO EXHIBIT SPATIAL AUTOCORRELATION 4HIS CAN LEAD TO POPULATION SYNCHRONY WHICH CAN STRONGLY INmUENCE THE PROBABILITY OF REGIONAL EXTINCTION IE A FAILED INVASION #ASWELL AND #OHEN %NGEN ET AL )N GENERAL FOR POPULATION PERSISTENCE THE SIZE OF THE METAPOPULATION SHOULD BE SUBSTANTIALLY GREATER THAN THE SCALE AT WHICH SUCH POPULATION SYN CHRONY IS OBSERVED 7ORKING OUT THE IMPLICATIONS OF SPATIAL AND TEMPORAL AUTO CORRELATION FOR METAPOPULATION DYNAMICS IS AN IMPORTANT AREA FOR FUTURE WORK
%-0)2)#!, 345$)%3 !.$ 4(% 2/,% /& 4(%/29 )N ATTEMPTS TO @TEST PREDICTIONS FROM THEORETICAL MODELS EMPIRICAL METAPOPULA TION BIOLOGISTS ALMOST WITHOUT EXCEPTION WILL REACH THE CONCLUSION THAT THEIR STUDY SYSTEM DOES NOT lT THE ASSUMPTIONS OF THE MODEL /R THEY MIGHT EXPRESS IT THE OTHER WAY AROUND THE MODEL DOES NOT lT THEIR OBSERVATIONS "UT THERE ARE MANY USES OF THEORETICAL MODELS AND NOT ALL MODELS ARE MEANT TO BE TESTED /NE OF THEIR MAIN FUNCTIONS IS AS TOOLS FOR THOUGHT 3UCH MODELS CAN BE USED TO EXPOSE THE LOGIC OF PROCESSES ASSUMED TO BE OPERATING IN PARTICULAR SYSTEMS SHOW ING CLEARLY HOW PREDICTIONS DEPEND ON ASSUMPTIONS 4HEORETICAL MODELS CAN BE USED AS A STARTING POINT TO GENERATE QUESTIONS ABOUT EMPIRICAL SYSTEMS AND AS NEW BIOLOGICAL KNOWLEDGE ABOUT THE DRIVING FORCES OF THAT SYSTEM ARE DISCOVERED NEW SIMPLISTIC GENERAL MODELS CAN BE DEVELOPED OR NEW MORE DETAILED MODELS CAN BE ELABORATED /CCASIONALLY A MODEL MIGHT PREDICT THE BEHAVIOUR OF A SYSTEM "OX ALTHOUGH STOCHASTICITY DUE TO WEATHER AND THE CHAOTIC DYNAMICS OF NATURE WILL MOSTLY HIDE SUCH CORRESPONDENCE (OWEVER MODELS ARE USEFUL IF COR RECTLY HANDLED INCORPORATING MECHANISMS THAT WE THINK ARE IMPORTANT CAN REVEAL THE POTENTIAL BEHAVIOUR OF A SYSTEM *UST AS IN LEARNING ABOUT THE SIMPLE BUILDING BRICKS OF HYDROLOGY AND GAS KINETICS METEREOLOGISTS ALSO LEARN MORE ABOUT THE NATURE OF CURRENTS AND WINDS AND EVEN CLIMATE CHANGE AND YET ARE UNABLE TO PRE DICT THE WEATHER AT A CERTAIN SPOT MORE THAN A FEW DAYS AHEAD SO THE MISMATCH BETWEEN A THEORETICAL MODEL AND EMPIRICAL SYSTEMS IN ECOLOGY RARELY PROVIDES SENSIBLE @TESTS OF THE THEORY ITSELF -ETAPOPULATION THEORY IN THE GENERALIZED FORM PRESENTED HERE IS A PHILOSOPHI CAL TOOL THAT HIGHLIGHTS HOW SPECIES CAN PERSIST DESPITE THE FACT EVERY SINGLE SUB POPULATION FACES A SUBSTANTIAL EXTINCTION RISK )T DOES NOT ATTEMPT TO DESCRIBE THE DETAILED BEHAVIOUR OF A GIVEN REAL SYSTEM AT A GIVEN TIME BUT CAPTURES ESSENTIALS OF FORCES THAT APPLY TO REAL SYSTEMS &OR EXAMPLE 'UTIÏRREZ ET AL STUDIED THE SPATIAL DISTRIBUTION OF FOUR LEPIDOPTERAN BUTTERmY SPECIES "ECAUSE THE FOUR SPECIES ALL HAD THE SAME FAVOURITE HOST PLANT ,OTUS CORNICULATUS THE AUTHORS CLAIMED THIS MUST BE A SYSTEM WHERE THE PREDICTIONS FROM MULTI SPECIES MODELS WOULD BE REALISED (OWEVER IT TURNED OUT THAT ENVIRONMENTAL FACTORS OTHER THAN THE FAVOURITE HOST PLANT DETERMINED THE DISTRIBUTION OF THE FOUR SPECIES FOR EXAMPLE ALTERNATIVE HOST PLANTS DIFFERENCES BETWEEN COASTAL OR INLAND SITES AND VULNERABILITY TO GRAZING /NE OF THE SPECIES
+# (ARDING *- -C.AMARA AND 2$ (OLT
WAS PRESENT IN THE ENTIRE LANDSCAPE AND MIGHT NOT ACT AS A METAPOPULATION AT ALL 4HE STUDY CLAIMS TO HAVE PROVEN THAT THE ASSUMPTIONS OF PHENOMENOLOGICAL MULTI SPECIES METAPOPULATION MODELS ARE UNREALISTIC "UT THESE MODELS CAN ONLY PROVIDE INTERESTING INSIGHTS INTO SYSTEMS WHERE SEVERAL SPECIES ACTUALLY DO COM PETE FOR THE SAME PATCHES AND WHERE COLONIZATION EXTINCTION DYNAMICS AND INTER SPECIlC INTERACTIONS ARE IN FACT MAJOR FORCES AT WORK 4HESE ASSUMPTIONS NEED TO BE ASSESSED AND IT IS NOT CLEAR THAT THE EMPIRICAL SYSTEM OF 'UTIERREZ ET AL PROVIDES A GOOD MATCH TO THE METAPOPULATION ASSUMPTION 7E SUGGEST THAT ON A PRIORI GROUNDS IT IS REASONABLE TO BELIEVE THAT THERE ARE MULTI SPECIES ASSEM BLAGES WHICH QUITE FAITHFULLY MATCH THE ASSUMPTIONS OF METAPOPULATION THEORY EG AQUATIC PREDATORS AND PREY IN PONDS OCCUPY PATCHES WHICH MAY DRY AND SUFFER EXTINCTIONS PARASITES IN THE SAME HOST CAN INTERACT AND ALL GO EXTINCT WHEN THE HOST DIES ETC AND WHERE MULTI SPECIES METAPOPULATION MODELS ARE LIKELY TO PRODUCE SOME INTERESTING INSIGHTS 4HE OLD 0OPPERIAN VIEW THAT HYPOTHESIS MUST BE CONlRMED OR FALSIlED IN CRITICAL TESTS HAS LED TO MUCH CONFUSION AT THE INTERFACE BETWEEN THEORETICAL AND EMPIRICAL METAPOPULATION BIOLOGY 4HEORETICAL MODELS CAN NOT SAY MORE THAN @GIVEN EXACTLY THESE CONDITIONS WE WILL GET THIS OR THAT OUTCOME THEY CAN NOT BE VALIDATED OR FALSIlED IN SYSTEMS WITH OTHER CONDITIONS AND OTHER PREVAILING MECHANISMS )T WOULD BE LIKE TELLING THE METEREOLOGISTS THAT THEY SHOULD BE SKEPTICAL ABOUT THE PROPOSITION @WARM AIR IS LESS DENSE THAN COLD AIR SIMPLY BECAUSE THEY CANNOT ACCURATELY PREDICT TODAYS RAINFALL IN A SPECIlC LOCATION SUCH AS 5LLAPOOL
"OX
"IOLOGICAL CONTROL EXPERIMENT IN A SNAIL METAPOPULATION LIVING IN PONDS IN 'UADELOUPE
"IOMPHALARIA GLABRATA IS A NATIVE SNAIL SPECIES THAT IS THE INTERMEDIATE HOST FOR HUMAN INTESTINAL SCHISTOSOMES A TREMATODE INFECTION ! 6ENEZUELAN SNAIL -ARISA CORNUARIETIS WAS INTRODUCED IN 4HE INVADER DESTROYED LOCAL POPULATIONS OF WATER LILIES THAT ARE IMPORTANT HABITATS FOR THE NATIVE " GLABRATA ! STRONG DECLINE IN PATCH OCCUPANCY IN THE " GLABRATA META POPULATION FOLLOWED IN THE PONDS WHERE THE COMPETITOR WAS INTRODUCED )NTERESTINGLY NEARBY CONTROL PONDS WITHOUT THE INTRODUCED COMPETITOR ALSO HAD DECLINING PATCH OCCUPANCY 0OINTIER ET AL !LTHOUGH THE AUTHORS STATE THAT ENVIRONMENTAL CIRCUMSTANCES MIGHT HAVE CONTRIBUTED TO THE DECLINE OF " GLABRATA IN THE UN INVADED CONTROL PONDS THEY POINT OUT THAT THE OBSERVED PATTERN MATCHES THAT PREDICTED BY SIMPLE THEORETI CAL METAPOPULATIONS MODELS LOWER PATCH OCCUPANCY LEADS TO LOWERED OVERALL COLONIZATION RATE AND THE WHOLE METAPOPULATION NETWORK CAN BE AFFECTED BY THE REMOVAL OF A FEW PATCHES
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
#/.#,53)/. 7E HAVE SUMMARISED SOME ASPECTS OF HOW GENERALIZED METAPOPULATION THEORY IS RELEVANT FOR UNDERSTANDING INVASIONS INTO PATCHY HABITATS 7HEN SPECIES SUR VIVE IN A LANDSCAPE AS A METAPOPULATION IT IS CRITICAL THAT COLONIZATION SUCCESS IS HIGHER THAN THE EXTINCTION RATE OF SUBPOPULATIONS )N CONSERVATION THE WORRY IS OFTEN THAT AN INVADER COMPETES WITH A NATIVE SPECIES 7E HAVE RElNED A TWO SPECIES METAPOPULATION MODEL TO CAPTURE DIFFERENT KINDS OF INTERACTIONS INCLUD ING COMPETITION 4HERE IS A FULL RANGE OF BEHAVIOURS THAT EMERGE DEPENDING ON THE TYPE OF COLONIZATION AND EXTINCTION FUNCTION OF THE INVADER AND THE TYPE OF INmUENCE OF THE NATIVE SPECIES 4HE EXISTENCE OF !LLEE AND ANTI !LLEE EFFECTS OPENS UP A RICH VARIETY OF POSSIBLE DYNAMICAL OUTCOMES 4HE INVASIVE SPECIES BECOMES EXTINCT IF ITS INITIAL SUCCESS IN COLONZING EMPTY PATCHES OR RESISTING EXTINCTION IN OCCUPIED PATCHES AT LOW PATCH NUMBER IS TOO LOW WE HAVE SUGGESTED A NUMBER OF PARTICULAR MECHANISMS THAT CAN LEAD TO SUCH EXCLUSION )F THE INITIAL GROWTH RATE IS POSITIVE IT CAN BECOME ESTABLISHED AND COEXIST SUSTAINABLY WITH THE NATIVE SPE CIES OR FORCE THE LATTER TO GO EXTINCT )F THE INVASIVE SPECIES COMPETES FOR RESOURCES THIS CAN REDUCE PATCH OCCUPANCY FOR THE NATIVE SPECIES AND IF THE NATIVE SPECIES IS VULNERABLE AND HAS AN UNSTABLE EQUILIBRIUM BEYOND WHICH THERE IS NO RETURN THEN EXTINCTION OF THE NATIVE SPECIES CAN BE SUDDEN AND DIFlCULT TO REVERSE 7E PREDICT METAPOPULATION THEORY WILL BECOME SIGNIlCANT MORE RElNED AND APPLIED TO STUDY INVASIVE SPECIES PROBLEMS
!#+./7,%$'%-%.43 +#( WAS FUNDED BY THE 3WEDISH 2ESEARCH #OUNIL 6ETENSKAPSRÍDET AND 2$( BY THE 5NIVERSITY OF &LORIDA &OUNDATION
2%&%2%.#%3 !LLEE 7 # !NIMAL AGGREGATIONS A STUDY IN GENERAL SOCIOLOGY #HICAGO 5NIVERSITY 0RESS #HICAGO !MARSEKARE 0 #OMPETITIVE COEXISTENCE IN SPATIALLY S TRUCTURED ENVIRONMENTS A SYN THESIS %COLOGY ,ETTERS "ANGYEEKHUN % 0ARASITES ON CRAYlSH #HARACTERISATION OF THEIR PATHOGENESIS HOST INTERACTIONS AND DIVERSITY !CTA 5NIVERSITATIS 5PSALIENSIS #OMPHREHENSIVE 3UMMARIES OF 5PPSALA $ISSERTATIONS FROM THE &ACULTY OF 3CIENCE AND 4ECHNOLOGY PAGES "ROWN * ( AND ! +ODRIC "ROWN 4URNOVER RATES IN INSULAR BIOGEOGRAPHY EFFECT OF IMMIGRATION ON EXTINCTION %COLOGY #ASWELL ( AND * #OHEN 2ED WHITE AND BLUE ENVIRONMENTAL VARIANCE SPECTRA AND COEXISTENCE IN METAPOPULATIONS *OURNAL OF 4HEORETICAL "IOLOGY #ONNELL * ( AND 2 / 3LATYER -ECHANISMS OF SUCCESSION IN NATURAL COMMUNITIES
+# (ARDING *- -C.AMARA AND 2$ (OLT
AND THEIR ROLE IN C OMMUNITY STABILITY AND ORGANIZATION !MERICAN .ATURALIST %NGEN 3 2 ,ANDE AND " % 3AETHER 4HE SPATIAL SCALE OF POPULATION mUCTUATIONS AND QUASI EXTINCTION RISK !MERICAN .ATURALIST 'OMULKIEWICZ 2 AND 2 $ (OLT 7HEN DOES EVOLUTION B Y NATURAL SELECTION PREVENT EXTINCTION %VOLUTION 'OTELLI . * AND 7 ' +ELLY ! GENERAL MODEL OF METAPOPULATION DYNAMICS /IKOS 'UTIÏRREZ $ * , ,EØN #ORTÏS 2 -ENÏDEZ 2 * 7ILSON - * 2 #OWLEY AND # $ 4HOMAS -ETAPOPULATIONS OF FOUR LEPIDOPTERAN HERBIVORES ON A SINGLE HOST PLANT ,OTUS CORNICULATUS 'YLLENBERG - ) (ANSKI AND ! (ASTINGS 3TRUCTURED METAPOPULATION MODELS 0AGES IN (ANSKI ) AND - % 'ILPIN EDS -ETAPOPULATION "IOLOGY !CADEMIC 0RESS ,ONDON (ARDING + # AND * - -C.AMARA ! UNIFYING FRAMEWORK FOR METAPOPULATION DYNAMICS !MERICAN .ATURALIST (ANSKI ) $YNAMICS OF REGIONAL DISTRIBUTION THE CORE AND SATELLITE SPECIES HYPOTH ESIS /IKOS (ANSKI ) ! PRACTICAL MODEL OF METAPOPULATION DYNAMICS *OURNAL OF !NIMAL %COLOGY (ANSKI ) -ETAPOPULATION %COLOGY /XFORD 5NIVERSITY 0RESS /XFORD (ANSKI ) AND - 'YLLENBERG 4WO GENERAL METAPOPULATION MODELS AND THE CORE SATELLITE SPECIES HYPOTHESIS !MERICAN .ATURALIST (OLT $ 2 &ROM METAPOPULATION DYNAMICS TO COMMUNITY STRUCTURE 0AGES IN ) (ANSKI AND - % 'ILPIN EDS -ETAPOPULATION "IOLOGY !CADEMIC 0RESS 3AN $IEGO (OLT 2 $ AND * ( ,AWTON !PPARENT COMPETITION AND ENEMY FREE SPACE IN INSECT HOST PARASITOID COMMUNITIES !MERICAN .ATURALIST (OLT 2 $ AND 4 +EITT !LTERNATIVE CAUSES FOR RANGE LIMITS A METAPOPULATIONS PER SPECTIVE %COLOGY ,ETTERS (OLT 2 $ &OOD WEBS IN SPACE /N THE INTERPLAY OF DYNAMIC INSTABILITY AND SPATIAL PROCESSES %COLOGICAL 2ESEARCH (OOPES - & 2 $ (OLT AND - (OLYOAK 4HE EFFECTS OF SPATIAL PROCESSES ON TWO SPECIES INTERACTIONS 0AGE )N -ETACOMMUNITIES 3PATIAL $YNAMICS AND %COLOGICAL #OMMUNITIES EDS - (OLYOAK - ! ,EIBOLD AND 2 $ (OLT 5 OF #HICAGO 0RESS #HICAGO +EITT 4 ( - ! ,EWIS AND 2 $ (OLT !LLEE EFFECTS INVASION PINNING AND SPECIES BORDERS !MERICAN .ATURALIST ,ANDE 2 %XTINCTION THRESHOLDS IN DEMOGRAPHIC MODELS OF TERRITORIAL POPULATIONS !MERICAN .ATURALIST ,EVINS 2 3OME DEMOGRAPHIC AND GENETIC CONSEQUENCES OF ENVIRONMENTAL HETERO GENEITY FOR BIOLOGICAL CONTROL "ULLETIN OF THE %NTOMOLOGICAL 3OCIETY OF !MERICA ,EVINS 2 AND $ #ULVER 2EGIONAL COEXISTENCE OF SPECIES AND COMPETITION B ETWEEN RARE SPECIES 0ROCEEDINGS OF THE .ATL !CADEMY OF 3CIENCES 53!
)NVASIVE SPECIES IN METAPOPULATION SYSTEMS
-AC!RTHUR 2 ( AND % / 7ILSON 4HE THEORY OF ISLAND BIOGEOGRAPHY 0RINCETON 5NIVERSITY 0RESS 0RINCETON .EUBERT - AND ( #ASWELL $EMOGRAPHY AND DISPERSAL CALCULATIONS A ND SENSITIVITY ANALYSIS OF INVASION SPEED FOR STRUCTURED POPULATIONS %COLOGY .EE 3 AND 2 - -AY $YNAMICS OF METAPOPULATIONS HABITAT D ESTRUCTION AND COM PETITIVE COEXISTENCE *OURNAL OF !NIMAL %COLOGY .OUHUYS 3 6 AND ) (ANSKI #OLONISATION RATES AND DISTANCES OF A HOST BUTTERmY AND TWO SPECIlC PARASITOIDS IN A FRAGMENTED LANDSCAPE /VASKAINEN / AND ) (ANSKI -ETAPOPULATION DYNAMICS IN HIGHLY FRAGMENTED LAND SCAPES 0AGES IN ) (ANSKI AND / % 'AGGIOTTI EDITORS %COLOGY 'ENETICS AND %VOLUTION OF -ETAPOPULATIONS %LSEVIER!CADEMIC "URLINGTON 0OINTIER * 0 AND 0 $AVID "IOLOGICAL CONTROL OF "IOMPHALARIA GLABRATA THE INTER MEDIATE HOST OF SCHISTOSOMES BY -ARISA CORNUARIETIS IN PONDS OF 'UADELOUPE LONG TERM IMPACT ON THE LOCAL SNAIL FAUNA AND AQUATIC mORA "IOLOGICAL #ONTROL 2OLÉN !LVAREZ % + *OHANNESSON AND * %RLANDSSON 4HE MAINTENANCE OF A CLINE IN THE MARINE SNAIL ,ITTORINA SAXATILIS THE ROLE OF HOME SITE ADVANTAGE AND HYBRID lTNESS %VOLUTION 3ACCERI ) - +UUSSAARI - +ANKARE 0 6IKMAN 7 &ORTELIUS AND ) (ANSKI )NBREEDING AND EXTINCTION IN A BUTTERmY METAPOPULATION .ATURE 3CHÚPS + %FFECT OF DEFORESTATION ON THE SPATIAL DYNAMICS OF AN ENDANGERED WEEVIL SPECIES 0AGE IN (ABITAT ,OSS (ELSINKI 3EPT (AKAPAINO /Y (ELSINKI 3HIGESADA . AND + +AWASAKI "IOLOGICAL )NVASIONS 4HEORY AND 0RACTICE /XFORD 5NIVERSITY 0RESS /XFORD 3HURIN * " 0 !MARESEKARE * - #HASE 2 $ (OLT - & (OOPES 2 ,AW AND - ! ,EIBOLD !LTERNATIVE STABLE STATES AND REGIONAL COMMUNITY STRUCTURE *OURNAL OF 4HEORETICAL "IOLOGY 3KELLAM * ' 2ANDOM DISPERSAL IN THEORETICAL POPULATIONS "IOMETRIKA 4ILMAN $ 0LANT STRATEGIES AND THE DYNAMICS AND STRUCTURE OF PLANT COMMUNITIES 0RINCETON 5NIVERSITY 0RESS 0RINCETON .* 7ITH + ! 5SING PERCOLATION THEORY TO ASSESS LANDSCAPE CONNECTIVITY AND EFFECTS OF HABITAT FAGMENTATIN 0AGES IN + * 'UTZWILLER EDITOR !PPLYING ,ANDSCAPE %COLOGY IN "IOLOGICAL #ONSERVATION 3PRINGER 6ERLAG .EW 9ORK
#HAPTER EIGHTEEN
#OMPETITION AND THE ASSEMBLY OF INTRODUCED BIRD COMMUNITIES 2 0 $UNCAN AND $ - &ORSYTH
).42/$5#4)/.
! CENTRAL GOAL OF ECOLOGY IS TO UNDERSTAND WHAT DETERMINES THE NUMBER AND IDEN TITY OF SPECIES IN ECOLOGICAL COMMUNITIES /F THE MANY SPECIES THAT COULD POTEN TIALLY OCCUPY AN AREA WHY DO ONLY A PARTICULAR SUBSET OF SPECIES ACTUALLY CO OCCUR AND WHAT DETERMINES THE IDENTITY OF THOSE SPECIES !ND TO WHAT EXTENT ARE THESE PATTERNS THE PRODUCT OF DETERMINISTIC PROCESSES RATHER THAN STOCHASTIC EVENTS -UCH INTEREST HAS FOCUSED ON INTERSPECIlC COMPETITION AS A PROCESS SHAPING CO OCCURRENCE PATTERNS 3TRONG ET AL $IAMOND AND #ASE SOME SPECIES CAPABLE OF JOINING A LOCAL COMMUNITY MAY BE EXCLUDED BY THE PRESENCE OF COM PETITORS )F COMPETITION IS SUFlCIENTLY STRONG AND PERVASIVE ENOUGH TO STRUCTURE ECOLOGICAL COMMUNITIES THEN CERTAIN @ASSEMBLY RULES SHOULD GOVERN HOW COM MUNITIES ARE PUT TOGETHER $IAMOND 7EIHER AND +EDDY )N PARTICU LAR COMPETITION SHOULD BE MORE INTENSE AND COMPETITIVE EXCLUSION MORE LIKELY AMONG SPECIES OF SIMILAR SIZE AND MORPHOLOGY THAT COMPETE FOR SIMILAR RESOURCES )N THESE CIRCUMSTANCES WE EXPECT CO OCCURRING SPECIES TO BE MORPHOLOGICALLY DIF FERENT FROM EACH OTHER AND TO EXHIBIT A PATTERN OF @MORPHOLOGICAL OVERDISPERSION 0IMM -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
20 $UNCAN AND $- &ORSYTH
-ANY STUDIES HAVE ATTEMPTED TO EVALUATE THE IMPORTANCE OF INTERSPECIlC COM PETITION IN SHAPING CO OCCURRENCE PATTERNS BY TESTING FOR MORPHOLOGICAL OVER DISPERSION EG 3TRONG ET AL 'RANT AND !BBOT "OWERS AND "ROWN $IAMOND AND #ASE $AYAN AND 3IMBERLOFF +INGSTON ET AL 3UCH TESTS HAVE GENERALLY INVOLVED COMPARING THE MORPHOLOGICAL PATTERN ING OF SPECIES IN A LOCAL COMMUNITY WITH THAT OF A LARGER POOL OF SPECIES POTENTIALLY CAPABLE OF JOINING THAT COMMUNITY )F SPECIES IN THE LOCAL COMMUNITY EXHIBITED STRONGER MORPHOLOGICAL OVERDISPERSION THAN EXPECTED UNDER A PROCESS OF RANDOM ASSEMBLY FROM THIS LARGER POOL THEN IT WAS CONCLUDED THAT THE LOCAL COMMUNITY WAS STRUCTURED BY COMPETITION #RITICAL TO THE OUTCOME OF SUCH TESTS IS DECIDING WHICH SPECIES TO INCLUDE IN THE LARGER POOL OF SPECIES THAT COULD POTENTIALLY JOIN THE LOCAL COMMUNITY #OLWELL AND 7INKLER 'OTELLI AND 'RAVES )DEALLY ALL SPECIES KNOWN TO HAVE BEEN PRESENT AT SOME STAGE DURING THE PROCESS OF ASSEM BLING THAT COMMUNITY WOULD BE INCLUDED -ISTAKENLY INCLUDING SPECIES THAT WERE NEVER PART OF THE PROCESS EG BECAUSE THEY NEVER REACHED THE SITE CAN BIAS THE OUTCOME OF TESTS FOR OVERDISPERSION #OLWELL AND 7INKLER 5NFORTUNATELY IN MOST SITUATIONS WE DO NOT KNOW HOW LOCAL COMMUNITIES WERE ASSEMBLED AND WHICH SPECIES WERE OR WERE NOT PRESENT DURING THE PROCESS #ONSEQUENTLY EVIDENCE FOR COMPETITIVE EXCLUSION BASED ON TESTS FOR MORPHOLOGICAL OVERDISPER SION IS OFTEN SUBJECT TO UNCERTAINTIES ASSOCIATED WITH CHOOSING THE APPROPRIATE SPECIES POOL 3INCE THE TH CENTURY THERE HAS BEEN A SUBSTANTIAL INCREASE IN THE MOVEMENTS OF PEOPLE AROUND THE GLOBE AND AN ASSOCIATED INCREASE IN THE NUMBERS OF SPECIES TRANSPORTED TO AND RELEASED IN NEW ENVIRONMENTS 7ILLIAMSON -ACK ET AL $UNCAN ET AL !T SOME LOCATIONS T HERE ARE SUFlCIENTLY DETAILED RECORDS THAT WE CAN RECONSTRUCT THE HISTORY OF THESE INTRODUCTIONS )N PARTICULAR THERE ARE EXCELLENT RECORDS DOCUMENTING THE BIRD SPECIES INTRODUCED TO LOCATIONS SUCH AS THE .EW :EALAND AND (AWAIIAN ISLANDS INCLUDING DATA ON THE SPECIES INTRODUCED DATES OF INTRODUCTION WHETHER THEY ESTABLISHED WILD POPULATIONS OR NOT AND MEASURES OF EFFORT SUCH AS THE NUMBERS OF INDIVIDUALS OR THE NUMBERS OF RELEASE EVENTS OF EACH SPECIES INTRODUCED -OULTON AND 0IMM 6ELTMAN ET AL 4HESE RECORDS PROVIDE A REMARKABLE OPPORTUNITY TO TEST HYPOTHESES ABOUT THE FACTORS STRUCTURING ECOLOGICAL COMMUNITIES 0IMM ,OCKWOOD ET AL BECAUSE THEY PROVIDE A NEAR COMPLETE LIST OF THE SPECIES PRESENT DUR ING THE ASSEMBLY PROCESS THUS REDUCING THE UNCERTAINTY ASSOCIATED WITH CHOOSING THE APPROPRIATE SPECIES POOL &URTHERMORE BECAUSE BIRD INTRODUCTIONS TO MANY PLACES INCLUDING (AWAII AND .EW :EALAND OCCURRED DECADES TO CENTURIES AGO THERE SHOULD HAVE BEEN SUFlCIENT TIME FOR THE COMMUNITIES TO REACH COMPOSITIONAL EQUILIBRIUM SPECIES THAT ARE GOING TO BE EXCLUDED BY COMPETITION SHOULD HAVE ALREADY BEEN SO "ECAUSE OF THESE ADVANTAGES RECORDS OF BIRD INTRODUCTIONS HAVE BEEN USED EXTENSIVELY TO TEST FOR PATTERNS CONSISTENT WITH THE OUTCOME OF COMPETITION )N ADDITION TO TESTS FOR MORPHOLOGICAL OVERDISPERSION STUDIES HAVE TESTED FOR @PRIORITY EFFECTS -OULTON BIRDS INTRODUCED AT A LATER DATE IN THE ASSEMBLY PROCESS
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
SHOULD BE MORE LIKELY TO FAIL BECAUSE THEY HAVE TO COMPETE WITH A GREATER DIVERSITY OF ALREADY ESTABLISHED SPECIES AT HIGHER ABUNDANCE 5SING THESE APPROACHES SEV ERAL STUDIES HAVE IDENTIlED PATTERNS CONSISTENT WITH COMPETITION AND ARGUED THAT IT IS AN IMPORTANT PROCESS STRUCTURING INTRODUCED BIRD ASSEMBLAGES -OULTON AND 0IMM -OULTON -OULTON AND 0IMM A B 0IMM -OULTON AND ,OCKWOOD ,OCKWOOD ET AL -OULTON ,OCKWOOD AND -OULTON "ROOKE ET AL -OULTON AND 3ANDERSON ,OCKWOOD ET AL -OULTON ET AL .EVERTHELESS THE RESULTS OF SOME STUDIES HAVE BEEN EQUIVOCAL 3IMBERLOFF -OULTON ET AL $UNCAN AND SEVERAL OBJECTIONS HAVE BEEN RAISED REGARDING THE ANALYSIS AND INTERPRETATION OF THESE DATA 3IMBERLOFF AND "OECKLEN $UNCAN AND "LACKBURN )N PARTICULAR PATTERNS CONSISTENT WITH COMPETITION CAN BE CAUSED BY OR CONFOUNDED WITH VARIATION IN OTHER FAC TORS 3PECIlCALLY $UNCAN SHOWED THAT WHILE PASSERINE BIRDS INTRODUCED TO .EW :EALAND AT A LATER DATE WERE MORE LIKELY TO FAIL A PRIORITY EFFECT CONSISTENT WITH THE OUTCOME OF COMPETITION THIS RESULT WAS CONFOUNDED WITH VARIATION IN INTRODUCTION EFFORT "IRDS INTRODUCED AT A LATER DATE WERE ALSO RELEASED IN SMALLER NUMBERS AND SO WERE MORE LIKELY TO FAIL FOR THAT REASON 3IMILARLY -OULTON ET AL FOUND SIGNIlCANT MORPHOLOGICAL OVERDISPERSION AMONG GAMEBIRDS SUC CESSFULLY INTRODUCED TO .EW :EALAND BUT $UNCAN AND "LACKBURN SHOWED THAT THIS PATTERN COULD NOT HAVE BEEN DUE TO COMPETITION BECAUSE THE DISTRIBUTION OF MOST SPECIES DID NOT OVERLAP IN SPACE OR TIME /UR AIM IN THIS CHAPTER IS TO TRY AND RESOLVE THESE DIFlCULTIES AND TO GAIN GREATER INSIGHT INTO HOW HISTORICAL EVENTS INCLUDING THE TIMING AND EFFORT PUT INTO INTRO DUCTIONS CAN INTERACT WITH A DETERMINISTIC PROCESS COMPETITION TO AFFECT THE OUTCOME OF INTRODUCTIONS AND HENCE THE COMPOSITION AND STRUCTURE OF INTRODUCED SPECIES ASSEMBLAGES 7E INVESTIGATE USING A SIMPLE MATHEMATICAL MODEL HOW THREE FACTORS INTRODUCTION EFFORT THE ABUNDANCE OF A COMPETITOR AND THE STRENGTH OF COMPETITION INTERACT TO DETERMINE THE PROBABILITY THAT AN INTRODUCED SPECIES WILL ESTABLISH IN THE PRESENCE OF A COMPETITOR 7E THEN EXAMINE HOW WELL THE PRE DICTIONS OF THE MODEL ARE SUPPORTED BY DATA USING THE HISTORICAL RECORD OF PASSERINE INTRODUCTIONS TO .EW :EALAND
! -!4(%-!4)#!, -/$%, /& %34!",)3(-%.4 3INCE INTRODUCTIONS TYPICALLY INVOLVE THE RELEASE OF FEW INDIVIDUALS STOCHASTIC PROCESSES CAN PLAY A CRITICAL ROLE IN DETERMINING WHETHER THEY SUCCEED OR FAIL 2ICHTER $YN AND 'OEL ,ANDE 'REVSTAD 7E THEREFORE USED A SIMPLE TWO SPECIES STOCHASTIC BIRTH DEATH MODEL 3"$ 2ENSHAW TO EXPLORE HOW INTERACTIONS BETWEEN THE NUMBER OF INDIVIDUALS RELEASED THE ABUNDANCE OF A PREVIOUSLY ESTABLISHED COMPETITOR AND PER CAPITA STRENGTH OF INTERSPECIlC COM PETITION AFFECT THE PROBABILITY OF A SPECIES ESTABLISHING
20 $UNCAN AND $- &ORSYTH
,ET . BE THE NUMBER OF INDIVIDUALS OF SPECIES RELEASED AT A LOCATION AND LET . BE THE ABUNDANCE OF SPECIES A POTENTIAL COMPETITOR ALREADY PRESENT AT THAT LOCA TION 7E ASSUME THAT BOTH SPECIES HAVE IDENTICAL BIRTH AND DEATH RATES AND THAT INTERSPECIlC COMPETITION IS SYMMETRIC WE ARE PRIMARILY INTERESTED IN HOW DIFFER ENCES IN THE INITIAL POPULATION SIZES OF THE TWO SPECIES AND THE PER CAPITA STRENGTH OF COMPETITION AFFECTS THE PROBABILITY THAT THE INTRODUCED SPECIES ESTABLISHES !SSUMING THAT ISOLATED POPULATIONS GROW SUBJECT TO LOGISTIC GROWTH AND THAT DENSITY DEPENDENCE BOTH WITHIN AND BETWEEN SPECIES AFFECTS ONLY THE DEATH RATE CHANGES IN THE SIZE OF POPULATIONS OF THE TWO SPECIES CAN BE DESCRIBED BY A PAIR OF DIFFERENTIAL EQUATIONS D. ". n $. .B n .D C. E. DT AND D. ". n $. .B n .D C. E. DT WHERE ".I .I B IS THE BIRTH RATE OF SPECIES I WITH B THE INSTANTANEOUS BIRTH RATE AND $.I .ID C.I E.J IS THE DEATH RATE WITH D THE INSTANTANEOUS DEATH RATE C IS A COEFlCIENT REmECTING THE PER CAPITA STRENGTH OF INTRASPECIlC COMPETITION AND E IS A COEFlCIENT REmECTING THE PER CAPITA STRENGTH OF INTERSPECIlC COMPETITION )F THE TWO POPULATIONS ARE AT SIZE . AND . AT A GIVEN TIME THEN THE NEXT EVENT WILL BE ONE OF THE FOLLOWING 2ENSHAW ! BIRTH OF SPECIES TRANSITION . A . WITH PROBABILITY ". 2 . ! DEATH OF SPECIES TRANSITION . A . n WITH PROBABILITY $. 2 . ! BIRTH OF SPECIES TRANSITION . A . WITH PROBABILITY ". 2 . ! DEATH OF SPECIES TRANSITION . A . n WITH PROBABILITY $. 2 . WHERE 2. ". $. ". $. 7E IMPLEMENTED A 3"$ MODEL BY GENERATING TWO INDEPENDENT RANDOM NUM BERS 9 9 ON THE UNIFORM UNIT INTERVAL ; = )F 9 ) ". 2. THEN THE NEXT EVENT WAS A BIRTH OF SPECIES 9 ". 2. AND ) ;". $. = 2. THEN THE NEXT EVENT WAS A DEATH OF SPECIES 9 ;". $. = 2. AND ) ;". $. ". = 2. THEN THE NEXT EVENT WAS A BIRTH OF SPECIES 9 ;". $. ". = 2 . THEN THE NEXT EVENT WAS A DEATH OF SPE CIES
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
4HE TIME BETWEEN EVENTS IS AN EXPONENTIALLY DISTRIBUTED RANDOM VARIABLE SO THAT THE INTER EVENT TIME T WAS SIMULATED AS n ;LOGE9 = T 2. AND THE TIME ADVANCED BY THAT AMOUNT 2ENSHAW 4HIS PROCESS WAS REITER ATED FOR STEPS 7E DElNED SPECIES AS HAVING ESTABLISHED IF IT PERSISTED TO THE END OF THE STEP SIMULATION FOR THE PARAMETER VALUES WE USED POPULATIONS THAT PERSISTED FOR STEPS WERE TYPICALLY mUCTUATING AROUND CARRYING CAPACITY AND WERE LIKELY TO PERSIST FOR MUCH LONGER 4HERE IS STRONG THEORETICAL ,ANDE 'REVSTAD AND EMPIRICAL EVI DENCE )NCHAUSTI AND (ALLEY $RAKE AND ,ODGE THAT ENVIRONMENTAL STOCHASTICITY AFFECTS THE PERSISTENCE OF SPECIES OVER AND ABOVE THE EFFECTS OF DEMO GRAPHIC STOCHASTICITY ALONE (ENCE IN ADDITION TO THE DEMOGRAPHIC STOCHASTICITY MODELLED ABOVE WE ALSO MODELLED ENVIRONMENTAL STOCHASTICITY BY ALLOWING THE DEATH RATE OF EACH SPECIES TO VARY INDEPENDENTLY BETWEEN STEPS ACCORDING TO THE FOLLOWING EQUATION DI D ABS ;. U = WHERE DI IS THE INSTANTANEOUS DEATH RATE OF SPECIES I AND . U IS A RANDOM NOR MAL DEVIATE WITH MEAN AND VARIANCE U 4HIS ACTS TO MODEL DEVIATIONS AWAY FROM SOME MINIMUM INSTANTANEOUS DEATH RATE D WITH LARGER VALUES OF U IMPLYING GREATER VARIATION IN DEATH RATE BETWEEN STEPS AND THUS GREATER ENVIRONMENTAL STOCHASTICITY 4O INVESTIGATE THE GENERAL BEHAVIOUR OF THE MODEL WE HELD PARAMETERS CON STANT AT THE FOLLOWING VALUES IN OUR SIMULATIONS ENVIRONMENTAL STOCHASTICITY U BIRTH RATE B DEATH RATE D AND INTRAPECIlC COMPETITION COEFlCIENT C 7E SET INITIAL VALUES OF . AS AND AND . AS AND AND THE INTERSPECIlC COMPETITION COEFlCIENT E AS AND &OR EACH COMBINATION OF PARAMETER VALUES FOR . . AND E WE RAN THE 3"$ MODEL TIMES AND CALCULATED THE PROPORTION OF THOSE RUNS THAT RESULTED IN SPECIES ESTABLISHING SUCCESSFULLY 4HIS PROPORTION IS AN ESTIMATE OF THE PROBABILITY OF ESTABLISHMENT UNDER THE SET OF CONDITIONS DElNED BY THE PARAMETERS 4HE RESULTS OF OUR SIMULATIONS ARE SUMMARISED IN &IG &IRST THE PROBABILITY OF ESTABLISHMENT INCREASES AS INTRODUCTION EFFORT . THE INITIAL ABUNDANCE OF SPECIES INCREASES 3ECOND WHEN INTERSPECIlC COMPETITION OCCURS IE E THE PROB ABILITY OF ESTABLISHMENT DECLINES AS BOTH THE PER CAPITA COMPETITION COEFlCIENT E AND THE INITIAL ABUNDANCE OF THE COMPETITOR SPECIES . INCREASES -OREOVER THESE THREE FACTORS INTERACT SUCH THAT COMPETITION HAS LITTLE EFFECT ON THE PROBABIL ITY OF ESTABLISHMENT WHEN A COMPETITOR SPECIES OCCURS AT LOW INITIAL ABUNDANCE
20 $UNCAN AND $- &ORSYTH
REGARDLESS OF THE STRENGTH OF COMPETITION (ERE STOCHASTIC EVENTS DOMINATE AND THE NUMBER OF INDIVIDUALS RELEASED IS CRITICAL 7HEN COMPETITOR SPECIES OCCUR AT HIGHER INITIAL ABUNDANCE THE PROBABILITY OF ESTABLISHMENT DEPENDS INCREASINGLY ON THE STRENGTH OF COMPETITION
&IG 2ESULTS OF THE STOCHASTIC BIRTH DEATH MODEL SHOWING THE PROBABILITY OF ESTABLISHMENT AS A FUNCTION OF THE INITIAL ABUNDANCE OF AN INTRODUCED SPECIES . GIVEN A RESIDENT COMPETITOR AT FOUR DIFFERENT ABUNDANCES . THE FOUR PANELS AND WITH THE PER CAPITA STRENGTH OF INTERSPECIlC COMPETITION TAKING SIX VALUES FROM TO SHOWN AS DIFFERENT LINES
4HESE SIMULATION RESULTS HIGHLIGHT TWO PREDICTIONS &IRST THE ABUNDANCE OF A COMPETITOR IN ADDITION TO THE PER CAPITA STRENGTH OF COMPETITION SHOULD BE IMPORTANT
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
IN DETERMINING THE OUTCOME OF AN INTRODUCTION (ENCE WE WOULD EXPECT TO OBSERVE BOTH MORPHOLOGICAL OVERDISPERSION RESULTING FROM THE COMPETITIVE EXCLU SION OF MORPHOLOGICALLY SIMILAR SPECIES AND PRIORITY EFFECTS A HIGHER CHANCE OF FAILURE AMONG LATER INTRODUCTIONS BECAUSE ALREADY RESIDENT COMPETITORS HAVE HAD TIME TO INCREASE IN ABUNDANCE IN INTRODUCED ASSEMBLAGES STRUCTURED BY COMPETI TION 3ECOND THESE FACTORS SHOULD INTERACT SUCH THAT THE INmUENCE OF PER CAPITA STRENGTH OF COMPETITION DEPENDS ON THE RELATIVE ABUNDANCES OF THE INTRODUCED AND COMPETITOR SPECIES AND THE IMPORTANCE OF COMPETITION DEPENDS ON INTRODUC TION EFFORT &IG 4HUS INTER SPECIlC COMPETITION IS PREDICTED TO BE OF MUCH LESS IMPORTANCE IN AFFECTING ESTABLISHMENT WHEN A SPECIES IS INTRODUCED IN SMALL NUMBERS STOCHASTIC PROCESSES DOMINATE OR WHEN THE RESIDENT COMPETITOR OCCURS AT LOW ABUNDANCE 4HE EFFECTS OF COMPETITION SHOULD BE MOST APPARENT WHEN BOTH THE INTRODUCED AND COMPETITOR SPECIES OCCUR AT HIGH ABUNDANCE
#/.&2/.4).' 4(% -/$%, 7)4( $!4! 4(% !33%-",9 /& ).42/$5#%$ 0!33%2).% #/--5.)4)%3 ). .%7 :%!,!.$ $ATA
7E USED HISTORICAL DATA DOCUMENTING THE TIMING AND NUMBERS OF PASSERINE SPECIES INTRODUCED TO FOUR ACCLIMATISATION DISTRICTS IN .EW :EALAND !UCKLAND 7ELLINGTON #ANTERBURY AND /TAGO TO TEST THESE PREDICTIONS 4HE DATA ARE FROM $UNCAN AND LIST THE PASSERINE SPECIES INTRODUCED TO EACH DISTRICT THE YEAR OF INTRODUCTION WHETHER SPECIES ESTABLISHED A WILD POPULATION OR NOT THE YEAR SPECIES WENT EXTINCT IF THEY FAILED TO ESTABLISH AND INTRODUCTION EFFORT MEASURED AS THE NUMBER OF SEPARATE RELEASE EVENTS &OR EACH SPECIES INTRODUCED TO EACH DIS TRICT A TOTAL OF INTRODUCTIONS WE USED THESE DATA AND THE MORPHOLOGICAL DATA DESCRIBED BELOW TO ESTIMATE THE STRENGTH OF INTERSPECIlC COMPETITION THE RELATIVE ABUNDANCE OF THE CLOSEST COMPETITOR AND INTRODUCTION EFFORT 7E OBTAINED MORPHOLOGICAL DATA BY MEASURING MUSEUM SPECIMENS )N ALL CASES WE MEASURED SPECIMENS COLLECTED IN THE COUNTRY WHERE THE SPECIES WAS MOST LIKELY TO HAVE BEEN INTRODUCED FROM AND WHERE POSSIBLE WE MEASURED SPECI MENS COLLECTED AROUND THE TIME THAT INTRODUCTIONS TO .EW :EALAND OCCURRED THE LATE S 4HE COUNTRY OF ORIGIN FOR MOST %UROPEAN SPECIES WAS 5NITED +INGDOM WHILE FOR .ORTH !MERICAN SPECIES WE MEASURED SPECIMENS COLLECTED ON THE WEST COAST OF THE 5NITED 3TATES A LIKELY SOURCE AREA FOR INTRODUCTIONS TO .EW :EALAND &OR ,ONCHURA PUNCTULATA WHICH IS NATIVE TO !SIA WE MEASURED SPECIMENS COL LECTED IN !USTRALIA BECAUSE THIS SPECIES WAS INTRODUCED TO .EW :EALAND FROM THERE 4HOMSON !LL OF THE SPECIMENS WE MEASURED WERE HOUSED IN THE "RITISH -USEUM OF .ATURAL (ISTORY AT 4RING 5+ 7E MEASURED INDIVIDUALS OF EACH SPECIES MALE AND FEMALE EXCEPT FOR FOUR SPECIES WHERE WE MEASURED n INDIVIDUALS WITH APPROXIMATELY EQUAL NUMBERS OF MALES AND FEMALES 7E MEASURED SIX MORPHOLOGICAL CHARACTERS ON
20 $UNCAN AND $- &ORSYTH
EACH INDIVIDUAL THE LENGTH OF THE CULMEN FROM THE BASE OF THE SKULL TO THE TIP OF THE UPPER MANDIBLE THE WIDTH AND DEPTH OF THE BEAK AT THE ANTERIOR MARGIN OF THE NARES THE LENGTH OF THE TARSUS THE LENGTH OF THE WING FROM THE WRIST TO THE TIP OF THE LONGEST PRIMARY AND THE LENGTH OF THE TAIL &OLLOWING 2ICKLEFS AND 4RAVIS AND -OULTON AND 0IMM WE SUM MARISED MORPHOLOGICAL DIFFERENCES AMONG SPECIES USING THE lRST TWO AXES DERIVED FROM A PRINCIPAL COMPONENTS ANALYSIS 0#! BASED ON LOG TRANSFORMED VALUES OF ALL SIX MORPHOLOGICAL CHARACTERS WITH INTRODUCTIONS TO EACH DISTRICT ANALYSED SEPARATELY &IG &OR EACH DISTRICT WE USED THE %UCLIDEAN DISTANCE BETWEEN SPECIES IN THIS MORPHOLOGICAL SPACE TO ESTIMATE HOW MORPHOLOGICALLY SIMILAR SPECIES ARE TO EACH OTHER AND USED THIS AS A MEASURE OF THE STRENGTH OF INTERSPE CIlC COMPETITION
&IG 0LOTS OF THE lRST TWO AXES FROM A PRINCIPAL COMPONENTS ANALYSIS SUMMARISING MORPHOLOGICAL DIFFERENCES AMONG THE PASSERINE SPECIES INTRODUCED TO EACH OF FOUR ACCLIMATISATION DISTRICTS IN .EW :EALAND SEE TEXT 3PECIES THAT ESTABLISHED ARE SHOWN AS OPEN CIRCLES SPECIES THAT FAILED ARE SHOWN AS CLOSED CIRCLES
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
0REVIOUS STUDIES HAVE USED MINIMUM SPANNING TREES COUPLED WITH RANDOMISA TION TESTS TO SEARCH FOR OVERDISPERSION AMONG SUCCESSFULLY ESTABLISHED SPECIES IN MORPHOLOGICAL SPACE EG -OULTON AND 0IMM -OULTON AND ,OCKWOOD ,OCKWOOD ET AL ,OCKWOOD AND -OULTON ,OCKWOOD ET AL (ERE WE ADOPT A REGRESSION APPROACH BECAUSE WE WANT TO SIMULTANE OUSLY CONSIDER THE INmUENCE OF SEVERAL VARIABLES ON ESTABLISHMENT PROBABILITY &OR INTRODUCTIONS TO EACH DISTRICT WE USED THE LOG TRANSFORMED DISTANCE BETWEEN A SPECIES AND ITS CLOSEST NEIGHBOUR IN MORPHOLOGICAL SPACE AS AN ESTIMATE OF THE STRENGTH OF INTERSPECIlC COMPETITION SPECIES WITH A NEAREST NEIGHBOUR MORE SIMILAR IN MORPHOLOGY ARE ASSUMED TO HAVE FACED STRONGER COMPETITION FOR THE SAME RESOURCES ! SPECIES COULD HAVE AS ITS NEAREST NEIGHBOUR ONLY SPECIES THAT WERE PRESENT IN THE SAME DISTRICT AT THE SAME TIME DETERMINED FROM THE YEAR OF INTRODUCTION TO A DISTRICT AND THE YEAR OF EXTINCTION FOR SPECIES THAT FAILED 4HIS AVOIDS A PROBLEM OFTEN PRESENT IN THE USE OF MINIMUM SPANNING TREES WHEREBY ALL SPECIES ARE INCLUDED AS POTENTIAL COMPETITORS EVEN IF THE DISTRIBUTIONS OF SOME SPECIES FAIL TO OVERLAP IN EITHER SPACE OR TIME $UNCAN AND "LACKBURN 4HE LEVEL OF COMPETITION THAT INDIVIDUALS OF A SPECIES EXPERIENCE WILL BE A FUNC TION OF THEIR SIMILARITY TO A COMPETITOR AND THE ABUNDANCE OF THAT COMPETITOR .O SPECIES ABUNDANCE ESTIMATES ARE AVAILABLE FOR THE PERIOD DURING WHICH MOST INTRO DUCTIONS OCCURRED IN .EW :EALAND THE LATE S (OWEVER 4HOMSON OBSERVED THAT INTRODUCED PASSERINES INCREASED RAPIDLY IN ABUNDANCE FOLLOWING ESTABLISHMENT !LTHOUGH LEGISLATION WAS ORIGINALLY PASSED PROTECTING INTRODUCED BIRDS 4HOMSON STATED THAT hWITHIN TEN OR lFTEEN YEARS OF THE COMING IN OF THE BIRDS THEIR NUMBERS INCREASED TO SUCH AN EXTENT THAT THE PROTECTION AFFORDED THEM HAD TO BE TAKEN AWAY AND RESTRICTIVE LEGISLATION IMPOSEDv $URING THIS PERIOD OF RAPID POPULATION INCREASE THE NUMBER OF YEARS ELAPSED SINCE INTRODUCTION SHOULD PROVIDE A REASONABLE INDEX OF RELATIVE ABUNDANCE AT LEAST FOR THOSE SPECIES THAT SUCCESSFULLY ESTABLISHED 7E THEREFORE USED THE TIME DELAY IN YEARS SEPARATING THE INTRODUCTION OF A TARGET SPECIES AND ITS NEAREST COMPETITOR AS AN ESTIMATE OF THAT COMPETITORS RELATIVE ABUNDANCE /UR ASSUMPTION IS THAT THE LONGER THE TIME DELAY THE LONGER A COMPETITORS POPULATION WILL HAVE HAD TO INCREASE AND THE HIGHER ITS ABUNDANCE WILL BE -ODEL DEVELOPMENT AND ANALYSIS
/UR SIMULATIONS PREDICT HOW I NUMBER OF RELEASE EVENTS A MEASURE OF INTRODUC TION EFFORT II LOG TRANSFORMED DISTANCE TO THE NEAREST NEIGHBOUR IN MORPHOLOGI CAL SPACE A MEASURE OF THE PER CAPITA STRENGTH OF INTERSPECIlC COMPETITION AND III TIME DELAY BETWEEN INTRODUCTIONS AN ESTIMATE OF THE RELATIVE ABUNDANCE OF THE CLOSEST COMPETITOR SHOULD INTERACT TO GENERATE PATTERNS IN ESTABLISHMENT SUC CESS &IG 4O SEE HOW WELL THE DATA lT THESE PREDICTIONS WE CONSIDERED HOW WELL A SERIES OF CANDIDATE LOGISTIC REGRESSION MODELS COULD EXPLAIN VARIATION IN ESTAB LISHMENT PROBABILITY FOR PASSERINE INTRODUCTIONS TO .EW :EALAND /UR APPROACH IS TO lT A SERIES OF CANDIDATE MODELS TO THE DATA TO IDENTIFY THE BEST lTTING MODEL AS
20 $UNCAN AND $- &ORSYTH
A BASIS FOR INFERENCE AND THEN TO COMPARE THE RESULTS FROM THAT BEST lTTING MODEL WITH THE SIMULATION RESULTS /UR RESPONSE VARIABLE IS BINARY WHETHER A SPECIES INTRODUCED TO A DISTRICT ESTAB LISHED OR NOT 7E CONSIDERED CANDIDATE LOGISTIC REGRESSION MODELS THAT MIGHT EXPLAIN VARIATION IN ESTABLISHMENT SUCCESS ALL OF WHICH INCLUDED THE NUMBER OF RELEASE EVENTS WHICH WE KNOW IS AN IMPORTANT EXPLANATORY VARIABLE &OURTEEN OF THE MODELS INCLUDED COMBINATIONS OF MORPHOLOGICAL DISTANCE INTRODUCTION DELAY AND POSSIBLE INTERACTIONS BETWEEN THESE VARIABLES THAT CAPTURE THE RANGE OF POSSIBLE OUTCOMES MODELS IN 4ABLE 4HE REMAINING MODELS INCLUDED COMBINATIONS OF MORPHOLOGICAL DISTANCE AND YEAR OF lRST INTRODUCTION 7E CONSIDERED MODELS CONTAINING THE VARIABLE YEAR OF lRST INTRODUCTION BECAUSE SPECIES INTRODUCED A LONG TIME AFTER THEIR CLOSEST COMPETITOR IE A LONG INTRODUC TION DELAY WILL ALSO HAVE A LATER DATE OF INTRODUCTION IN ABSOLUTE TERMS )T HAS BEEN NOTED THAT IN ADDITION TO FACING GREATER COMPETITION LATER INTRODUCTIONS WOULD HAVE FACED ADDITIONAL THREATS INCLUDING A GREATER DIVERSITY AND ABUNDANCE OF INTRODUCED PREDATORS $UNCAN ET AL IN PRESS 7E INCLUDE YEAR OF lRST INTRODUCTION AS A SURROGATE FOR OTHER FACTORS THAT COULD HAVE VARIED THROUGH TIME AND AFFECTED ESTABLISHMENT PROBABILITY 7E DID NOT CONSIDER INTERACTIONS BETWEEN YEAR OF lRST INTRODUCTION AND OTHER VARIABLES BECAUSE WE HAD NO A PRIORI REASON TO THINK THEY SHOULD BE IMPORTANT 7E USED THE SMALL SAMPLE VERSION OF !KAIKES )NFORMATION #RITERION !)#C TO IDENTIFY WHICH OF THE CANDIDATE MODELS BEST lTTED THE DATA "URNHAM AND !NDERSON 4HE BEST lTTING MODEL HAS THE SMALLEST !)#C VALUE AND WE RANKED MODELS FROM BEST TO WORST BASED ON THE DIFFERENCE BETWEEN EACH MODELS !)#C AND THE !)#C OF THE BEST lTTING MODEL 6I VALUES 7E THEN CALCULATED THE !KAIKE WEIGHTS WI SEE "URNHAM AND !NDERSON WHICH PROVIDE A WEIGHT OF EVIDENCE FOR EACH MODEL GIVEN AS AN APPROXIMATE PROBABILITY THAT THE BEST lTTING MODEL IS IN FACT THE BEST OUT OF THE CANDIDATE SET )F THERE IS CLEARLY A SINGLE BEST MODEL AS JUDGED BY THE WEIGHT OF EVIDENCE THEN THAT MODEL CAN BE USED AS A BASIS FOR INFERENCE )N OUR CASE HOWEVER NO SINGLE MODEL PROVIDED A BEST lT TO THE DATA WITH SEVERAL CANDIDATE MODELS PROVIDING A SIMILARLY GOOD lT 2ATHER THAN ARBITRARILY SELECTING ONE OF SEVERAL WELL lTTING MODELS WE USED INFORMATION CONTAINED IN ALL OF THESE MODELS AS A BASIS FOR ROBUST MULTI MODEL INFERENCE 4O DO THIS WE IDENTIlED ALL CANDIDATE MODELS FOR WHICH THE SUM OF THE !KAIKE WEIGHTS FROM LARGEST TO SMALLEST WAS &ROM THIS SET OF BEST lTTING MODELS WE CALCULATED MODEL AVERAGED PARAMETER ESTIMATES WEIGHTING THE PARAMETERS IN EACH MODEL BY THE !KAIKE WEIGHT FOR THAT MODEL AND THEN SUMMED THE WEIGHTED ESTIMATES ACROSS ALL MODELS "URNHAM AND !NDERSON 7E THEN BASED OUR INFERENCE ON THESE MODEL AVERAGED VALUES 2ESULTS
#ANDIDATE MODELS THAT INCLUDED THE VARIABLE @YEAR OF lRST INTRODUCTION INSTEAD OF THE VARIABLE @INTRODUCTION DELAY RECEIVED VIRTUALLY NO SUPPORT MODELS IN
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
4ABLE WEIGHT OF EVIDENCE WI ALL ) IMPLYING THAT VARIATION IN ESTABLISH MENT SUCCESS IS BETTER EXPLAINED BY THE TIME DELAY BETWEEN THE INTRODUCTION OF A TARGET SPECIES AND ITS CLOSEST COMPETITOR RATHER THAN THE ABSOLUTE DATE OF INTRO DUCTION
4ABLE 4HE CANDIDATE MODELS WE CONSIDERED TO EXPLAIN VARIATION IN THE PROBABILITY THAT A PASSERINE SPECIES INTRODUCED TO AN ACCLIMATISATION DISTRICT IN .EW :EALAND ESTABLISHED OR NOT 4HE EXPLANATORY VARIABLES ARE NREL THE NUMBER OF RELEASE EVENTS IN THE DISTRICT A MEASURE OF INTRODUCTION EFFORT DIST THE LOGARITHM OF THE DISTANCE IN MORPHOLOGICAL SPACE FROM THE TARGET SPECIES TO ITS NEAREST NEIGHBOUR A MEASURE OF THE PER CAPITA STRENGTH OF INTERSPECIlC COMPETITION DELAY THE TIME DELAY IN YEARS BETWEEN INTRODUCTION OF THE TARGET SPECIES AND INTRODUCTION OF ITS MORPHOLOGICALLY NEAREST NEIGHBOUR A MEASURE OF THE RELATIVE ABUNDANCE OF THE CLOSEST COMPETITOR YI THE YEAR OF lRST INTRODUCTION -ODEL
%XPLANATORY VARIABLES NREL NREL DIST NREL DELAY NREL DIST DELAY NREL DIST NREL = DIST NREL DELAY NREL = DELAY NREL DIST DELAY NREL = DIST NREL DIST DELAY DIST = DELAY NREL DIST DELAY NREL = DELAY NREL DIST DELAY NREL = DIST DIST = DELAY NREL DIST DELAY NREL = DIST NREL = DELAY NREL DIST DELAY NREL = DELAY DIST = DELAY NREL DIST DELAY NREL = DIST NREL = DELAY DIST = DELAY NREL DIST DELAY NREL = DIST NREL = DELAY DIST = DELAY NREL = DIST = DELAY NREL YI NREL DIST YI NREL DIST YI NREL = DIST
/NLY ONE OF THE MODELS WITH WI DID NOT INCLUDE THE THREE KEY EXPLANATORY VARIABLES IMPLYING THAT ALL THREE VARIABLES WERE IMPORTANT IN EXPLAINING PATTERNS OF ESTABLISHMENT (OWEVER NO SINGLE MODEL CLEARLY PROVIDED A BEST lT TO THE DATA WITH THE TOP lVE MODELS HAVING 6I VALUES IMPLYING THAT EACH HAD hSUBSTANTIALv SUPPORT "URNHAM AND !NDERSON 0ROBABILITY OF ESTABLISHMENT IS PLOTTED AS A FUNCTION OF THE THREE EXPLANATORY VARIABLES BASED ON MODEL AVERAGED
20 $UNCAN AND $- &ORSYTH
PARAMETER ESTIMATES IN &IG 4HE PROBABILITY OF ESTABLISHMENT WAS POSITIVELY RELATED TO INTRODUCTION EFFORT NEGATIVELY WITH INCREASING STRENGTH OF COMPETITION AND NEGATIVELY WITH THE TIME DELAY BETWEEN INTRODUCTIONS
4ABLE #OMPARISON OF THE CANDIDATE MODELS EXPLAINING VARIATION IN THE PROBABILITY THAT A PASSERINE SPECIES INTRODUCED TO AN ACCLIMATISATION DISTRICT IN .EW :EALAND ESTABLISHED OR NOT -ODEL NUMBER CORRESPONDS TO THOSE IN 4ABLE + IS THE NUMBER OF PARAMETERS IN THE MODEL 6I IS THE DIFFERENCE BETWEEN THE !KAIKE )NFORMATION #RITERION !)#C FOR EACH MODEL AND THAT OF THE BEST lTTING MODEL MODEL AND WI ARE THE !KAIKE WEIGHTS -ODEL
LOG LIKELIHOOD
+
!)#C
< < < < < < < < < < < < < < < < <
6I
WI
- WI
$ISCUSSION
4HE RELATIONSHIPS BETWEEN ESTABLISHMENT PROBABILITY AND THE THREE EXPLANATORY VARIABLES REVEALED BY THE DATA FOR PASSERINE INTRODUCTIONS TO .EW :EALAND &IG AGREE REMARKABLY WELL WITH THE FORM OF THE RELATIONSHIPS PREDICTED BY OUR SIMPLE STOCHASTIC BIRTH DEATH MODEL INCORPORATING INTERSPECIlC COMPETITION &IG )N BOTH THE DATA AND THE MODEL THE PROBABILITY OF ESTABLISHMENT INCREASED WITH GREATER INTRODUCTION EFFORT -OREOVER FOR A GIVEN LEVEL OF INTRODUCTION EFFORT ESTABLISHMENT PROBABILITY DECLINED WHEN INTRODUCED SPECIES FACED A COMPETITOR
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
&IG 4HE RELATIONSHIP BETWEEN PROBABILITY OF ESTABLISHMENT AND NUMBER OF RELEASE EVENTS FOR FOUR VALUES OF INTRODUCTION DELAY THE NUMBER OF YEARS AFTER INTRODUCTION OF ITS CLOSEST COMPETITOR THAT A TARGET SPECIES IS INTRODUCED AND FOR FOUR VALUES OF MORPHOLOGICAL DISTANCE THE DISTANCE IN MORPHOLOGICAL SPACE ;&IG = FROM A SPECIES TO ITS NEAREST NEIGHBOUR SHOWN AS DIFFERENT LINES FOR PASSERINE BIRDS INTRODUCED TO FOUR ACCLIMATISATION DISTRICTS IN .EW :EALAND
THAT WAS MORE MORPHOLOGICALLY SIMILAR TO THEM AND DECLINED FURTHER WHEN THAT COMPETITOR HAD BEEN INTRODUCED EARLIER THAN THE TARGET SPECIES ALLOWING TIME FOR THE COMPETITOR TO HAVE ATTAINED HIGHER ABUNDANCE 4HIS AGREEMENT BETWEEN THE RELATIONSHIPS PREDICTED BY THE MODEL AND THOSE OBSERVED IN THE DATA SUGGESTS THAT OUR SIMPLE STOCHASTIC BIRTH DEATH MODEL CAPTURES IMPORTANT FEATURES UNDERPIN NING ESTABLISHMENT SUCCESS IN THIS SYSTEM )N PARTICULAR OUR RESULTS SUGGEST THAT INTERSPECIlC COMPETITION AFFECTED ESTABLISHMENT PROBABILITY FOR PASSERINE SPECIES INTRODUCED TO .EW :EALAND AND THAT THIS ASSEMBLAGE HAS THEREFORE BEEN STRUC TURED BY COMPETITION
20 $UNCAN AND $- &ORSYTH
0ATTERNS CONSISTENT WITH THE OUTCOME OF COMPETITION HAVE BEEN OBSERVED IN BIRD INTRODUCTION DATA WHEN COMPETITION COULD NOT HAVE BEEN A CAUSE OF THOSE PATTERNS -OULTON ET AL $UNCAN AND "LACKBURN AND PATTERNS CON SISTENT WITH COMPETITION HAVE BEEN SHOWN TO BE CONFOUNDED WITH OTHER FACTORS 3IMBERLOFF AND "OECKLEN $UNCAN 7E EMPHASISE THAT WE HAVE ATTEMPTED TO CONTROL FOR THESE EFFECTS lRST BY CONSIDERING ONLY SITUATIONS IN WHICH SPECIES OVERLAPPED IN SPACE AND TIME AND COULD THEREFORE HAVE COMPETED SECOND BY INCORPORATING THE CONFOUNDING EFFECTS OF INTRODUCTION EFFORT INTO OUR MODEL AND ANALYSIS AND THIRD BY SHOWING THAT INCLUDING INTRODUCTION DELAY A COMPETITION EFFECT PROVIDES A BETTER lT TO THE DATA THAN INCLUDING ABSOLUTE DATE OF INTRODUCTION A SURROGATE FOR OTHER VARIABLES THAT MIGHT HAVE CHANGED THROUGH TIME 7HILE HISTORICAL RECORDS OF BIRD INTRODUCTIONS PROVIDE A UNIQUE OPPORTUNITY TO INVESTIGATE THE ROLE OF COMPETITION AND OTHER FACTORS IN STRUCTURING SPECIES ASSEMBLAGES 0IMM ,OCKWOOD ET AL WE STRESS THE NEED TO ACCOUNT FOR SUCH POTENTIALLY CONFOUNDING FACTORS -OREOVER OUR RESULTS HIGHLIGHT THAT THE IMPORTANCE OF COMPETITION RELATIVE TO OTHER FACTORS IN DETERMINING ESTABLISH MENT SUCCESS CAN VARY DEPENDING ON CIRCUMSTANCES #OMPETITION SHOULD BE OF LESS IMPORTANCE IN STRUCTURING A GROUP OF SPECIES ALL INTRODUCED AT THE SAME TIME AND IN LOW NUMBERS BECAUSE STOCHASTIC EVENTS WILL LARGELY DETERMINE WHICH OF THESE SPECIES ESTABLISH AND WHICH FAIL &IG 4HESE RESULTS HAVE IMPORTANT IMPLICATIONS FOR STUDIES THAT ASSESS THE IMPORTANCE OF COMPETITION IN DETERMINING INVASION SUCCESS REGARDLESS OF THE HABITAT OR TAXA CONSIDERED 4HIS IS BECAUSE THE SUPPLY OF INVADING PROPAGULES AND THE ABUNDANCES OF RESIDENT COMPETITORS INVARIABLY DIFFER WIDELY BETWEEN LOCATIONS AND STUDIES AND INTERACTIONS BETWEEN THESE FACTORS INmUENCE THE ROLE THAT COMPETITION PLAYS 3UCH DIFFERENCES MAY CONTRIBUTE TO VARIATION IN THE RELATIVE IMPORTANCE OF COMPETITION THAT IS OBSERVED AMONG EXPERIMENTAL INVASION STUDIES ,EVINE ET AL 4HE CENTRAL MESSAGE OF OUR STUDY IS THAT BOTH STOCHASTIC EVENTS IN THIS CASE MEDIATED BY INTRODUCTION EFFORT AND DETERMINISTIC PROCESSES IN THIS CASE THE OUTCOME OF INTERSPECIlC COMPETITION ARE IMPORTANT IN COMMUNITY ASSEMBLY AND THAT THE TIMING AND SEQUENCE OF INTRODUCTIONS IE HISTORY MATTERS DUE TO PRIOR ITY EFFECTS /UR RESULTS SUGGEST THAT .EW :EALAND WOULD HAVE ENDED UP WITH A DIFFERENT ASSEMBLAGE OF INTRODUCED PASSERINES HAD THE EFFORT PUT INTO INTRODUCING SPECIES BEEN REDISTRIBUTED OR HAD THE SEQUENCE AND TIMING OF INTRODUCTIONS BEEN RESHUFmED 4HE lNDING THAT HISTORICAL CONTINGENCY IS IMPORTANT IN COMMUNITY ASSEMBLY IS NOT NEW AND HAS BEEN DEMONSTRATED REPEATEDLY USING MATHEMATICAL MODELS AND IN LABORATORY SYSTEMS EG 'ILPIN AND #ASE $RAKE ET AL &UKAMI AND -ORIN )NSIGHTS INTO THE ASSEMBLY PROCESS PROVIDED BY HISTORI CAL RECORDS OF BIRD INTRODUCTIONS HINT THAT SUCH EFFECTS COULD BE JUST AS PERVASIVE IN REAL COMMUNITIES
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
!#+./7,%$'%-%.43 4HANKS TO 2OBERT 0RYS *ONES FOR ACCESS TO THE BIRD COLLECTIONS AT 4RING AND THE .EW :EALAND -ARSDEN &UND FOR FUNDING DATA COLLECTION 7E THANK 4IM "LACKBURN 0HILL #ASSEY *ULIE ,OCKWOOD AND AN ANONYMOUS REVIEWER FOR HELPFUL DISCUSSION AND COMMENTS
2%&%2%.#%3 "OWERS - ! AND * ( "ROWN "ODY SIZE AND COEXISTENCE IN DESERT RODENTS CHANCE OR COMMUNITY STRUCTURE %COLOGY "ROOKE 2 + * , ,OCKWOOD AND - 0 -OULTON 0ATTERNS OF SUCCESS IN PASSERIFORM BIRD INTRODUCTIONS ON 3AINT (ELENA /ECOLOGIA "URNHAM + 0 AND $ 2 !NDERSON +ULLBACK ,IEBLER INFORMATION AS A BASIS FOR STRONG INFERENCE IN ECOLOGICAL STUDIES 7ILDLIFE 2ESEARCH "URNHAM + 0 AND $ 2 !NDERSON -ODEL SELECTION AND MULTIMODEL INFERENCE ND EDITION 3PRINGER 6ERLAG .EW 9ORK #OLWELL 2 + AND $ 7 7INKLER ! NULL MODEL FOR NULL MODELS IN BIOGEOGRAPHY 0AGES IN $ 2 3TRONG $ 3IMBERLOFF , ' !BELE AND ! " 4HISTLE EDITORS %COLOGICAL COMMUNITIES CONCEPTUAL ISSUES AND THE EVIDENCE 0RINCETON 5NIVERSITY 0RESS 0RINCETON .* $AYAN 4 AND $ 3IMBERLOFF -OPHOLOGICAL RELATIONSHIPS AMONG COEXISTING HETERO MYIDS AN INCISIVE DENTAL CHARACTER !MERICAN .ATURALIST $IAMOND * AND 4 * #ASE #OMMUNITY ECOLOGY (ARPER AND 2OW .EW 9ORK $IAMOND * - !SSEMBLY OF SPECIES COMMUNITIES IN - , #ODY AND * - $IAMOND EDITORS %COLOGY AND EVOLUTION OF COMMUNITIES (ARVARD 5NIVERSITY 0RESS #AMBRIDGE $RAKE * ! 4 % &LUM ' * 7ITTEMAN 4 6OSKUIL ! - (OYLMAN # #RESON $ ! +ENNY ' 2 (UXEL # 3 ,ARUE AND * 2 $UNCAN 4HE CONSTRUCTION AND ASSEMBLY OF AN ECOLOGICAL LANDSCAPE *OURNAL OF !NIMAL %COLOGY $RAKE * - AND $ - ,ODGE %FFECTS OF ENVIRONMENTAL VARIATION ON EXTINCTION AND ESTABLISHMENT %COLOGY ,ETTERS $UNCAN 2 0 4HE ROLE OF COMPETITION AND INTRODUCTION EFFORT IN THE SUCCESS OF PAS SERIFORM BIRDS INTRODUCED TO .EW :EALAND !MERICAN .ATURALIST $UNCAN 2 0 AND 4 - "LACKBURN -ORPHOLOGICAL OVERDISPERSION IN GAME BIRDS !VES 'ALLIFORMES SUCCESSFULLY INTRODUCED TO .EW :EALAND WAS NOT CASUED BY INTERSPE CIlC COMPETITION %VOLUTIONARY %COLOGY 2ESEARCH $UNCAN 2 0 4 - "LACKBURN AND 0 #ASSEY IN PRESS &ACTORS AFFECTING THE RELEASE ESTAB LISHMENT AND SPREAD OF INTRODUCED BIRDS IN .EW :EALAND IN 7 ' ,EE EDITOR "IOLOGICAL INVASIONS IN .EW :EALAND 3PRINGER 6ERLAG "ERLIN $UNCAN 2 0 4 - "LACKBURN AND $ 3OL 4HE ECOLOGY OF BIRD INTRODUCTIONS !NNUAL 2EVIEW OF %COLOGY %VOLUTION AND 3YSTEMATICS &UKAMI 4 AND 0 * -ORIN 0RODUCTIVITY BIODIVERSITY RELATIONSHIPS DEPEND ON THE HISTORY OF COMMUNITY ASSEMBLY .ATURE
20 $UNCAN AND $- &ORSYTH
'ILPIN - % AND 4 * #ASE -ULTIPLE DOMAINS OF ATTRACTION IN COMPETITION COMMUNI TIES .ATURE 'OTELLI . * AND ' 2 'RAVES .ULL MODELS IN ECOLOGY 3MITHSONIAN )NSTITUTE 0RESS 7ASHINGTON 'RANT 0 2 AND ) !BBOT )NTERSPECIlC COMPETITION ISLAND BIOGEOGRAPHY AND NULL HYPOTHESES %VOLUTION 'REVSTAD & 3 &ACTORS INmUENCING THE CHANCE OF POPULATION ESTABLISHMENT IMPLICA TIONS FOR RELEASE STRATEGIES IN BIOCONTROL %COLOGICAL !PPLICATIONS )NCHAUSTI 0 AND * (ALLEY /N THE RELATION BETWEEN TEMPORAL VARIABILITY AND PERSIS TENCE TIME IN ANIMAL POPULATIONS *OURNAL OF !NIMAL %COLOGY +INGSTON 4 ' *ONES ! :UBAID AND 4 ( +UNZ 2ESOURCE PARTITIONING IN RHINOLO PHOID BATS REVISITED /ECOLOGIA ,ANDE 2 2ISKS OF POPULATION EXTINCTION FROM DEMOGRAPHIC AND ENVIRONMENTAL STO CHASTICITY AND RANDOM CATASTROPHES !MERICAN .ATURALIST ,EVINE * - 0 " !DLER AND 3 ' 9ELENIK ! META ANALYSIS OF BIOTIC RESISTANCE TO EXOTIC PLANT INVASIONS %COLOGY ,ETTERS ,OCKWOOD * , AND - 0 -OULTON %COMORPHOLOGICAL PATTERN IN "ERMUDA BIRDS THE INmUENCE OF COMPETITION AND IMPLICATIONS FOR NATURE PRESERVES %VOLUTIONARY %COLOGY ,OCKWOOD * , - 0 -OULTON AND 3 + !NDERSON -ORPHOLOGICAL ASSORTMENT AND THE ASSEMBLY OF COMMUNITIES OF INTRODUCED PASSERIFORMS ON OCEANIC ISLANDS 4AHITI VER SUS /AHU !MERICAN .ATURALIST ,OCKWOOD * , - 0 -OULTON AND + , "ALENT )NTRODUCED AVIFAUNAS AS NATURAL EXPERIMENTS IN COMMUNITY ASSEMBLY 0AGES IN % 7EIHER AND 0 ! +EDDY EDI TORS %COLOGICAL ASSEMBLY RULES #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE -ACK 2 . $ 3IMBERLOFF 7 - ,ONSDALE ( %VANS - #LOUT AND & ! "AZZAZ "IOTIC INVASIONS CAUSES EPIDEMIOLOGY GLOBAL CONSEQUENCES AND CONTROL %COLOGICAL !PPLICATIONS -OULTON - 0 -ORPHOLOGICAL SIMILARITY AND COEXISTENCE OF CONGENERS AN EXPERI MENTAL TEST WITH INTRODUCED (AWAIIAN BIRDS /IKOS -OULTON - 0 4HE ALL OR NONE PATTERN IN INTRODUCED (AWAIIAN PASSERIFORMS THE ROLE OF COMPETITION SUSTAINED !MERICAN .ATURALIST -OULTON - 0 AND * , ,OCKWOOD -ORPHOLOGICAL DISPERSION OF INTRODUCED (AWAIIAN lNCHES EVIDENCE FOR COMPETITION AND A .ARCISSUS EFFECT %VOLUTIONARY %COLOGY -OULTON - 0 AND 3 , 0IMM 4HE INTRODUCED (AWAIIAN AVIFAUNA BIOGEOGRAPHICAL EVIDENCE FOR COMPETITION !MERICAN .ATURALIST -OULTON - 0 AND 3 , 0IMM A 4HE EXTENT OF COMPETITION IN SHAPING AN INTRO DUCED AVIFAUNA 0AGES IN * $IAMOND AND 4 * #ASE EDITORS #OMMUNITY ECOLOGY (ARPER 2OW .EW 9ORK -OULTON - 0 AND 3 , 0IMM B 3PECIES INTRODUCTIONS TO (AWAII 0AGES IN ( ! -OONEY AND * ! $RAKE EDITORS %COLOGY OF BIOLOGICAL INVASIONS OF .ORTH !MERICA AND (AWAII 3PRINGER .EW 9ORK
!SSEMBLY OF INTRODUCED BIRD COMMUNITIES
-OULTON - 0 AND 3 , 0IMM -ORPHOLOGICAL ASSORTMENT IN INTRODUCED (AWAIIAN PASSERINES %VOLUTIONARY %COLOGY -OULTON - 0 AND * ' 3ANDERSON 0REDICTING THE FATES OF PASSERIFORM INTRODUCTIONS ON OCEANIC ISLANDS #ONSERVATION "IOLOGY -OULTON - 0 * ' 3ANDERSON AND 2 & ,ABISKY 0ATTERNS OF SUCCESS IN GAME BIRD !VES 'ALLIFORMES INTRODUCTIONS TO THE (AWAIIAN )SLANDS AND .EW :EALAND %VOLUTIONARY %COLOGY 2ESEARCH -OULTON - 0 * ' 3ANDERSON AND $ 3IMBERLOFF 0ASSERIFORM INTRODUCTIONS TO THE -ASCARENES )NDIAN /CEAN AN ASSESSMENT OF THE ROLE OF COMPETITION ³COLOGIE 0IMM 3 , 4HE BALANCE OF NATURE #HICAGO 5NIVERSITY 0RESS #HICAGO 2ENSHAW % -ODELING BIOLOGICAL POPULATIONS IN TIME AND SPACE #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 2ICHTER $YN . AND . 3 'OEL /N THE EXTINCTION OF A COLONIZING SPECIES 4HEORETICAL 0OPULATION "IOLOGY 2ICKLEFS 2 % AND * 4RAVIS ! MORPHOLOGICAL APPROACH TO THE STUDY OF AVIAN COM MUNITY ORGANIZATION !UK 3IMBERLOFF $ %XTINCTION SURVIVAL AND EFFECTS OF BIRDS INTRODUCED TO THE -ASCARENES !CTA /ECOLOGICA 3IMBERLOFF $ AND 7 "OECKLEN 0ATTERNS OF EXTINCTION IN THE INTRODUCED (AWAIIAN AVIFAUNA A REEXAMINATION OF THE ROLE OF COMPETITION !MERICAN .ATURALIST 3TRONG $ 2 $ 3IMBERLOFF , ' !BELE AND ! " 4HISTLE %COLOGICAL COMMUNITIES CONCEPTUAL ISSUES AND THE EVIDENCE 0RINCETON 5NIVERSITY 0RESS 0RINCETON 3TRONG $ 2 , ! 3ZYSKA AND $ 3IMBERLOFF 4ESTS OF COMMUNITY WIDE CHARACTER DISPLACEMENT AGAINST NULL HYPOTHESES %VOLUTION 4HOMSON ' - 4HE NATURALISATION OF ANIMALS AND PLANTS IN .EW :EALAND #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 6ELTMAN # * 3 .EE AND - * #RAWLEY #ORRELATES OF INTRODUCTION SUCCESS IN EXOTIC .EW :EALAND BIRDS !MERICAN .ATURALIST 7EIHER % AND 0 ! +EDDY %COLOGICAL ASSEMBLY RULES #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 7ILLIAMSON - "IOLOGICAL )NVASIONS #HAPMAN (ALL ,ONDON
#HAPTER NINETEEN
2OOM FOR ONE MORE %VIDENCE FOR INVASIBILITY AND SATURATION IN ECOLOGICAL COMMUNITIES 3 ! 3MITH AND * " 3HURIN
).42/$5#4)/. )DENTIFYING THE CONTRIBUTIONS OF LOCAL AND REGIONAL PROCESSES IN SHAPING BIO LOGICAL COMMUNITIES IS KEY TO UNDERSTANDING GLOBAL PATTERNS OF SPECIES RICHNESS #ORNELL 'ASTON %COLOGISTS HAVE TYPICALLY FALLEN INTO TWO TRADITIONS TO EXPLAIN VARIATION IN DIVERSITY ONE EMPHASIZING LOCAL PROCESSES SUCH AS COM PETITION PREDATION MUTUALISM AND THE INTERACTION BETWEEN ORGANISMS AND THEIR ENVIRONMENT AND THE OTHER FOCUSED ON SPECIATION EXTINCTION AND DISPERSAL OVER BROAD REGIONAL SCALES 4ERBORGH AND &AABORG #ORNELL #ORNELL AND ,AWTON 2ICKLEFS 4HE LOCAL SCHOOL OF THOUGHT POSITS THAT SPECIES RICHNESS IN COMMUNITIES IS DETERMINED BY PROCESSES THAT INmUENCE DEMOGRAPHIC RATES WITHIN HABITAT PATCHES #HASE AND ,EIBOLD 4HE REGIONAL APPROACH ARGUES THAT DISPERSAL SPECIATION EXTINCTION AND THE HIS TORY OF COMMUNITY ASSEMBLY ARE OF PRIMARY IMPORTANCE IN SHAPING BIOLOGICAL COMMUNITIES 2ICKLEFS #ASWELL AND #OHEN 'ASTON -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY n ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
3! 3MITH AND *" 3HURIN
'ASTON -ORA ET AL &UKAMI 3MITH ET AL 3MITH AND "ERMINGHAM SUBMITTED 4HE CRITICAL DISTINCTION BETWEEN THE TWO APPROACHES HINGES ON WHETHER LOCAL SPECIES RICHNESS IS SATURATED OR WHETHER COMMUNITIES HAVE THE INTRINSIC CAPACITY TO SUPPORT MORE SPECIES THAN THEY ACTUALLY CONTAIN )F THE SUPPLY OF SPECIES THROUGH COLONIZATION OR SPECIATION IS MUCH GREATER THAN THE NUMBER THAT CAN COEXIST DUE TO LOCAL ECOLOGICAL CONSTRAINTS THEN COMMUNI TIES ARE SAID TO BE SATURATED AND UNDER STRONG LOCAL CONTROL #ORNELL AND ,AWTON !LTERNATIVELY IF SPECIATION AND DISPERSAL PROVIDE FEWER SPECIES THAN SITES CAN SUPPORT THEN REGIONAL CONTROL OVER COMMUNITIES IS DOMINANT AND LOCAL RICH NESS IS UNSATURATED 4HE QUESTION OF WHETHER COMMUNITIES ARE NEAR OR FAR FROM SATURATION IS CRITICAL TO OUR UNDERSTANDING OF PATTERNS OF THE DISTRIBUTION AND DIVERSITY OF ORGANISMS 4HE CONCEPT OF SATURATION IS OF FUNDAMENTAL INTEREST TO BOTH COMMUNITY ECOL OGY AND INVASIONS BIOLOGY BECAUSE IT HAS PROFOUND IMPLICATIONS FOR THE INVASIBILITY AND POST INVASION DYNAMICS OF LOCAL COMMUNITIES )NVASIBILITY AND SATURATION ARE RELATED BUT DISTINCT ASPECTS OF COMMUNITIES &OR INSTANCE THERE ARE TWO POTENTIAL OUTCOMES OF SPECIES INTRODUCTIONS IN SATURATED COMMUNITIES &IRST SUCH COMMU NITIES MIGHT RESIST INVASION BY SPECIES INTRODUCED VIA NATURAL OR ANTHROPOGENIC DISPERSAL )N THIS CASE BOTH THE COMPOSITION AND SPECIES RICHNESS OF LOCAL COM MUNITIES ARE IN A STATE OF EQUILIBRIUM AND CHANGE VERY LITTLE WITH THE INTRODUCTION OF NOVEL SPECIES 3ECOND LOCAL COMMUNITIES MIGHT BE BOTH INVASIBLE AND SATURATED WITH SPECIES .EW SPECIES COULD BE ADDED TO LOCAL COMMUNITIES VIA NATURAL COLO NIZATION OR HUMAN INTRODUCTION HOWEVER THESE SPECIES DISPLACE LOCAL RESIDENTS MAINTAINING A CONSTANT NUMBER OF SPECIES "ROWN ET AL 4HEREFORE THE NUMBER OF SPECIES BUT NOT THEIR IDENTITIES WOULD REMAIN CONSTANT OVER TIME !LTERNATIVELY IN UNSATURATED COMMUNITIES DISPERSAL EVENTS OFTEN RESULT IN SUCCESS FUL INVASION WITHOUT CAUSING THE EXTIRPATION OF RESIDENT SPECIES .ET SPECIES RICH NESS INCREASES WITH ENHANCED DISPERSAL BECAUSE THE ADDITION OF NEW SPECIES EXCEEDS THE LOSS OF RESIDENTS ! lNAL POSSIBILITY IS THAT VERY HIGH DISPERSAL RATES RESULT IN hSUPER SATURATIONv AS COMMUNITIES SUPPORT A LARGE NUMBER OF SINK POPULATIONS THAT ARE EXCLUDED LOCALLY IN THE ABSENCE OF DISPERSAL 3HMIDA AND %LLNER -OUQUET AND ,OREAU 0ATTERNS OF COMMUNITY INVASIBILITY AND CHANGES IN SPECIES RICHNESS WITH INCREASED IMMIGRATION RATES AMONG COMMUNI TIES OR THE LENGTH OF EVOLUTIONARY HISTORY CAN THEREFORE BE USED TO EVALUATE THE DEGREES OF SATURATION AND INVASIBILITY OF COMMUNITIES 4HIS CHAPTER ASSESSES THREE LINES OF EVIDENCE FOR SATURATION AND INVASIBILITY IN BIOLOGICAL COMMUNITIES &IRST WE EXAMINE THE OUTCOMES OF FAUNAL EXCHANGES RESULTING FROM RECENT ANTHROPOGENIC MODIlCATION OF THE LANDSCAPE AND PAST GEO LOGIC EVENTS TO EVALUATE THE EFFECT OF ENHANCED IMMIGRATION BETWEEN REGIONS ON SPECIES RICHNESS 3ECOND WE EXAMINE RECENT TRENDS IN THE NUMBERS OF ANTHRO POGENIC SPECIES INVASIONS AND EXTINCTIONS OBSERVED OVER BROAD SPATIAL SCALES 4HE GLOBAL EXPLOSION IN EXOTIC SPECIES INVASIONS SUGGESTS THAT CONTEMPORARY COM MUNITIES ARE CERTAINLY INVASIBLE ,ODGE -OYLE AND ,IGHT 6ITOUSEK ET AL #OHEN AND #ARLTON (OBBS AND -OONEY 2ICCIARDI
%VIDENCE FOR INVASIBILITY AND SATURATION
7HETHER BIOLOGICAL INVASIONS ARE ACCOMPANIED BY DIFFERING NUMBERS OF EXTINC TIONS CAN BE USEFUL FOR EVALUATING WHETHER LOCAL DIVERSITY IN THESE COMMUNITIES IS NEAR OR BELOW SATURATION 3AX AND 'AINES 7E COMPARE THE NUMBER OF SUCCESSFUL INVASIONS VERSUS EXTIRPATIONS IN ORDER TO EVALUATE HOW SPECIES RICHNESS CHANGES WHEN HUMANS INTRODUCE SPECIES 4HIRD WE EXAMINE EXPERIMENTAL SPE CIES INTRODUCTIONS TO EVALUATE THE INVASIBILITY OF LOCAL COMMUNITIES AND COMPARE DEGREES OF SATURATION AMONG DIFFERENT GROUPS OF ORGANISMS )NTENTIONAL INTRODUC TIONS ALLOW US TO ASSESS THE SUCCESS RATE OF COLONIZATION ATTEMPTS AN IMPORTANT ASPECT OF SATURATION AS UNCONTROLLED INTRODUCTIONS DO NOT TELL US HOW MANY INTRO DUCED SPECIES FAIL TO COLONIZE &INALLY WE COMPARE THE EMPIRICAL EVIDENCE FOR SATURATION AND INVASIBILITY WITH THE PREDICTIONS OF FOUR MAJOR THEORETICAL PERSPECTIVES ON BROAD SCALE COMMU NITY STRUCTURE -ODELS OF PATCH DYNAMICS ECOLOGICAL DRIFT EG NEUTRAL MODELS SPECIES SORTING ALONG ENVIRONMENTAL GRADIENTS AND MASS EFFECT SYSTEMS MAKE DIVERGENT PREDICTIONS REGARDING COMMUNITY INVASIBILITY AND SATURATION &AUNAL EXCHANGES PATTERNS OF HUMAN MEDIATED INVASIONS AND EXTINCTIONS AND EXPERI MENTAL INTRODUCTIONS MAY BE USEFUL FOR DISTINGUISHING THE UTILITY OF THE DIFFERENT MODELS FOR DESCRIBING REAL COMMUNITIES 7E SYNTHESIZE DATA AND THEORY PERTAINING TO THE SATURATION OF LOCAL COMMUNITIES AND DISCUSS AVENUES FOR FUTURE RESEARCH
")/4)# ).4%2#(!.'%3 ).6!3)",% !.$ 5.3!452!4%$ #/--5.)4)%3 "IOTIC INTERCHANGES OCCUR WHEN BARRIERS SEPARATING DISTINCT BIOLOGICAL COMMUNI TIES BREAK DOWN ENABLING THE RECIPROCAL EXCHANGE OF RESIDENT SPECIES 2EMOVAL OF DISPERSAL BARRIERS INCREASES THE LIKELIHOOD OF DISPERSAL BETWEEN PREVIOUSLY ISOLATED COMMUNITIES PERMITTING STRONG INFERENCES REGARDING THE IMPORTANCE OF DISPER SAL PER SE IN DETERMINING PATTERNS OF THE DISTRIBUTION AND DIVERSITY OF ORGANISMS (ERE WE USE EVIDENCE FROM CONTEMPORARY AND HISTORIC BIOTIC INTERCHANGES TO ASSESS WHETHER COMMUNITIES ARE SATURATED WITH SPECIES BY DOCUMENTING CHANGES IN SPECIES RICHNESS FOLLOWING REMOVAL OF DISPERSAL BARRIERS -OREOVER BECAUSE THE REGIONAL POOL OF SPECIES CAPABLE OF PARTICIPATING IN CROSS BARRIER EXCHANGES IS OFTEN KNOWN IT IS POSSIBLE TO EVALUATE THE SUCCESS RATE OF COLONIZATIONS IN BOTH DIRECTIONS #ONTEMPORARY BIOTIC INTERCHANGES
#ONTEMPORARY HUMAN MEDIATED BIOTIC INTERCHANGES PROVIDE A POWERFUL TEST FOR SATURATION OF BIOLOGICAL COMMUNITIES OVER MODERATE TO LARGE GEOGRAPHIC SCALES BECAUSE THE OUTCOME CAN BE OBSERVED DIRECTLY WITHOUT RELYING ON THE FOS SIL RECORD "IOTIC INTERCHANGES FOLLOWING THE CONSTRUCTION OF BOTH THE 0ANAMA AND 3UEZ #ANALS ARE WELL DOCUMENTED 0OR 3MITH ET AL AND PROVIDE INSIGHTS INTO THE QUESTION OF COMMUNITY SATURATION )N THE CASE OF THE 0ANAMA #ANAL THE RECENT GEOLOGIC ORIGIN OF THE )STHMUS MILLION YEARS OLD
3! 3MITH AND *" 3HURIN
AND ITS YOUNG FRESHWATER lSH FAUNA "ERMINGHAM AND -ARTIN 0ERDICES ET AL SUGGEST THAT REGIONAL PROCESSES MIGHT BE IMPORTANT IN LIMITING SPE CIES RICHNESS -ESOAMERICAN FRESHWATER lSH ASSEMBLAGES CONTAIN AN ORDER OF MAGNITUDE FEWER SPECIES THAN THEIR PUTATIVE SOURCE POPULATIONS IN NORTHWESTERN 3OUTH !MERICA 3MITH AND "ERMINGHAM UNPUBLISHED DATA SUGGESTING THAT SPE CIATION AND IMMIGRATION MAY BE MORE IMPORTANT IN LIMITING LOCAL DIVERSITY IN THIS SYSTEM #ONSEQUENTLY COMMUNITIES OF FRESHWATER lSHES IN THE 0ANAMA #ANAL REGION MIGHT BE BOTH SUSCEPTIBLE TO INVASION AND UNSATURATED BECAUSE THE PAST SUPPLY OF SPECIES MAY BE LOWER THAN THE NUMBER OF SPECIES THAT THE RIVERS COULD SUPPORT !LTERNATIVELY SPECIES RICHNESS MIGHT REMAIN BELOW THE SPECIATION EXTINC TION EQUILIBRIUM ,OSOS AND 3CHLUTER BECAUSE THE PROCESS OF SPECIATION MAY BE SO SLOW THAT FEW COMMUNITIES EVER APPROACH EVOLUTIONARY EQUILIBRIUM ,OSOS AND 3CHLUTER 2ICKLEFS AND "ERMINGHAM #OMPLETION OF THE 0ANAMA #ANAL IN CREATED A FRESHWATER CORRIDOR BETWEEN THE 2IO #HAGRES ON THE #ARIBBEAN SLOPE AND THE 2IO 'RANDE ON THE 0ACIlC SLOPE OF THE )STHMUS OF 0ANAMA ENABLING THE FRESHWATER lSHES OF PREVIOUSLY ISOLATED DRAINAGE BASINS TO INTERMINGLE 4HREE lSH SPECIES COLONIZED THE 2IO #HAGRES FROM THE 2IO 'RANDE AND lVE SPECIES COLONIZED THE 2IO 'RANDE FROM THE 2IO #HAGRES #OLONISTS REPRESENTED AND OF THE TOTAL SOURCE POOL OF OBLIGATE FRESHWA TER lSH SPECIES IN THE 2IO #HAGRES AND 2IO 'RANDE THAT WERE NOT ALREADY PRESENT IN BOTH BASINS SUGGESTING THAT FRESHWATER lSH COMMUNITIES IN THE 2IO #HAGRES AND 2IO 'RANDE WERE SUSCEPTIBLE TO INVASION 4ABLE .O CASES OF LOCAL EXTIRPATION WERE DOCUMENTED SPECIES RICHNESS FOLLOWING DISPERSAL EVENTS INCREASED BY IN THE 2IO #HAGRES AND IN THE 2IO 'RANDE 3MITH ET AL )N ADDITION COLONISTS BECAME COMMON IN NEWLY INVADED COMMUNITIES ACHIEVING A LEVEL OF DISTRIBUTION AND ABUNDANCE COMPARABLE WITH OR GREATER THAN THAT IN THEIR SOURCE COMMUNITIES 3MITH ET AL 4HE BIOTIC INTERCHANGE THAT OCCURRED FOLLOWING COMPLETION OF THE 3UEZ #ANAL IN WHICH LINKED THE 2ED 3EA AND THE EASTERN -EDITERRANEAN 3EA IS QUALI TATIVELY SIMILAR TO THAT WHICH OCCURRED FOLLOWING THE CONSTRUCTION THE 0ANAMA #ANAL (UNDREDS OF 2ED 3EA MARINE SPECIES COLONIZED THE -EDITERRANEAN VIA THE 3UEZ #ANAL INCLUDING MOLLUSKS AND lSHES 0OR ,ESSEPSIAN MIGRANTS SPECIES THAT COLONIZED THE -EDITERRANEAN FROM THE 2ED 3EA CONSTITUTE APPROXI MATELY OF THE TOTAL SPECIES RICHNESS OF THE ,EVANT "ASIN 0OR -ANY FEWER COLONIZATIONS OF -EDITERRANEAN SPECIES HAVE BEEN RECORDED IN THE 2ED 3EA &IFTY THREE MARINE SPECIES HAVE BEEN REPORTED TO HAVE PARTICIPATED IN THE FAU NAL EXCHANGE 0OR ,ARGE DIFFERENCES IN THE NUMBER OF SUCCESSFUL INVASIONS SUGGEST POTENTIAL DIFFERENCES IN THE INVASIBILITY OF THE TWO COMMUNITIES HOWEVER PASSIVE TRANSPORT BY UNIDIRECTIONAL CURRENTS PARTIALLY EXPLAINS THE OBSERVED ASYM METRY OF INVASION THROUGH THE 3UEZ #ANAL )NVASIONS BY SPECIES MIGRATING THROUGH THE 3UEZ #ANAL HAVE CONTINUED FOR MORE THAN YEARS SINCE THE CANALS CONSTRUCTION WHEREAS NO EXTINCTIONS HAVE BEEN ATTRIBUTED TO INVASIONS FOLLOWING FAUNAL MIXING 0OR 2ATHER A BATHYMETRIC READJUSTMENT OF RESIDENT SPECIES HAS OCCURRED WHEREBY RESIDENT
%VIDENCE FOR INVASIBILITY AND SATURATION
4ABLE 4HE OBLIGATE FRESHWATER lSH ASSEMBLAGES OF THE 2IO 'RANDE AND 2IO #HAGRES DRAINAGE BASINS SAMPLED BY BOTH -EEK AND (ILDEBRAND AND 3MITH ET AL #OLONISTS ARE DENOTED IN BOLD ITALIC TEXT AND @NEW REFERS TO DRAINAGES COLONIZED FOLLOWING COMPLETION OF THE 0ANAMA #ANAL 4HE SPECIES IN 4ABLE ARE ORGANIZED BY THEIR SALINITY TOLERANCE AND THEN BY ALPHABETICAL ORDER OF FAMILY GENUS AND SPECIES NAMES ! NESTED !./6! ANALYSIS OF SPECIES LOG TRANSFORMED ABUNDANCES IN ADJACENT WATERSHEDS WAS PERFORMED IN ORDER TO DETERMINE IF SPECIES WERE MORE SUCCESSFUL IN THEIR NATIVE OR NEWLY COLONIZED DRAINAGES DENOTES VALUES SIGNIlCANT AT P AND o DENOTES VALUES SIGNIlCANT AT P AND THE LOCATION OF THE SYMBOL INDICATES WHETHER THE SPECIES WAS MORE SUCCESSFUL IN ITS NATIVE OR RECENTLY INVADED DRAINAGE 0RIMARY AND SECONDARY FRESHWATER lSHES 2IO 'RANDE 2IO #HAGRES !STYANAX AENEUS NEW !STYANAX RUBERRIMUS "RYCON CHAGRENSIS NEW "RYCON PETROSUS NEW "RYCONAMERICUS EMPERADOR #OMPSURA GORGONAE 'EPHYROCHARAX ATRICAUDATA < (YPHESSOBRYCON PANAMENSIS 0SEUDOCHEIRODON AFlNIS < 2OEBOIDES OCCIDENTALIS NEW 2OEBOIDES GUATEMALENSIS NEW
#YPHOCHARAX MAGDALENAE NEWo (OPLIAS MICROLEPIS 0IABUCINA PANAMENSIS !NCISTRUS CHAGRENSIS NEW
#HAETOSTOMA lSCHERI < (YPOSTOMUS PANAMENSIS < 2INELORICARIA URACANTHA 0IMELODELLA CHAGRESI 2HAMDIA QUELEN "RACHYHYPOPOMUS OCCIDENTALIS 2IVULUS BRUNNEUS < !EQUIDENS COERULEOPUNCTATUS !RCHOCENTRUS PANAMENSIS < 'EOPHAGUS CRASSILABRIS < 6IEJA MACULICAUDA NEW "RACHYRHAPHIS CASCAJALENSIS < "RACHYRHAPHIS EPISCOPI .EOHETERANDRIA TRIDENTIGER 0OECILIA GILLII 0OECILIOPSIS ELONGATA <
3! 3MITH AND *" 3HURIN
SPECIES MAINTAIN THEIR DOMINANCE IN DEEPER COOLER WATER 0OR )NVADERS ALSO CLEARLY PLAY AN IMPORTANT ROLE IN THE COMMUNITY DYNAMICS OF INVADED REGIONS BOTH IN TERMS OF TOTAL CONTRIBUTION TO THE SPECIES RICHNESS AND ABUNDANCE "EN 4UVIA &ISHERIES DATA SUGGEST THAT A LARGE PORTION OF NEW IMMIGRANTS ¾ BELONG TO THE COMMON lSHES OF THE ,EVANT BASIN )T IS IMPORTANT TO NOTE THAT THE 3UEZ #ANAL DATA WAS COLLECTED AT VERY LARGE SPATIAL SCALES THEREFORE MORE SUBTLE EFFECTS OF INVASIONS MAY NOT BE APPARENT "IOTIC INTERCHANGE FOLLOWING COM PLETION OF THE 3UEZ #ANAL PROVIDES STRONG EVIDENCE THAT RECIPROCAL INTERCHANGE INCREASED REGIONAL SPECIES RICHNESS WITHOUT RESULTING IN THE REGIONAL EXTINCTION OF THE RESIDENT FAUNA 0RE HISTORIC BIOTIC INTERCHANGES
"IOTIC INTERCHANGES HAVE OCCURRED FREQUENTLY OVER THE LAST -Y RESULTING FROM CLIMATIC CHANGES AND REARRANGEMENT OF CONTINENTAL LANDMASSES THAT BREAK DOWN BARRIERS TO DISPERSAL 6ERMEIJ A REVIEWED THE OUTCOME OF BIOTIC INTERCHANG ES THAT OCCURRED DURING THE .EOGENE /NE PATTERN THAT CLEARLY EMERGES IS THAT COMMUNITIES ARE INVASIBLE HOWEVER INVADING SPECIES IN MOST CASES ONLY MAKE UP A SMALL PORTION OF THE TOTAL REGIONAL SPECIES POOL IN THE DONOR BIOTA 6ERMEIJ A &OR EXAMPLE BETWEEN OF THE SHALLOW WATER MOLLUSCAN SPECIES IN THE COOL TEMPERATE .ORTH 0ACIlC AND ¾ OF THE REGIONAL SPECIES POOL OF THE .ORTH !TLANTIC PARTICIPATED IN THE TRANS !RCTIC INTERCHANGE 6ERMEIJ B 3IMILAR PATTERNS ARISE IN OTHER INSTANCES OF BIOTIC INTERCHANGES 6ERMEIJ A 4HE LOW APPARENT INVASION RATES FOR SOME PRE HISTORIC BIOTIC INTERCHANGES COULD HOWEVER BE THE RESULT OF THE LARGE SPATIAL SCALE AT WHICH THE DATA HAS BEEN RECORD ED 0ERHAPS MANY SPECIES IN THE DONOR SPECIES POOL ARE NOT ADAPTED TO CONDITIONS IN THE RECIPIENT BIOGEOGRAPHIC REGION 4HE RICHNESS OF THE NATIVE SPECIES POOL MAY THEREFORE OVERESTIMATE THE TRUE NUMBER OF SPECIES CAPABLE OF PARTICIPATING IN THE BIOTIC INTERCHANGE IN QUESTION !LTERNATIVELY THE NATIVE BIOTA MAY REPEL INVASION BY A LARGE PORTION OF THE POTENTIAL INVADERS )N EITHER CASE THE FOSSIL RECORD SUGGESTS THAT COMMUNITIES INVOLVED IN FAUNAL EXCHANGES ADDED SPECIES BUT THAT MANY LIKELY INVASION ATTEMPTS ALSO FAILED 4HE CENTRAL QUESTION PERTAINING TO COMMUNITY SATURATION IS WHETHER BIOTIC INTERCHANGES RESULT IN EXTIRPATION OF RESIDENT SPECIES 4HE CONCEPT THAT THE ARRIVAL OF INVADERS FROM A MORE SOPHISTICATED BIOTA MIGHT LEAD TO THE EXTINCTION OF RESIDENT SPECIES VIA COMPETITIVE DISPLACEMENT HAS A LONG HISTORY 7ALLACE 3IMPSON 7EBB AND -ARSHALL 7EBB -ARSHALL AND #IFELLI 0ATTERNS OF EXTINCTION RESULTING FROM COMPETITIVE DISPLACEMENT WOULD PRESENT STRONG EVIDENCE FOR THE IMPORTANCE OF LOCAL ECOLOGICAL CONTROL OF COMMUNITY MEMBERSHIP 4HE EXCHANGE OF MAMMALS ACROSS THE )STHMUS OF 0ANAMA DUR ING THE 'REAT !MERICAN "IOTIC )NTERCHANGE HAS BEEN CITED AS AN EXAMPLE WHERE INVADING NORTHERN SPECIES DROVE SOUTHERN RESIDENT SPECIES TO EXTINCTION VIA COMPETITIVE DISPLACEMENT -ARSHALL "AKKER (OWEVER WHETHER COMPETITIVE DISPLACEMENT RESULTED IN DIFFERENTIAL RATES OF EXTINCTION BETWEEN
%VIDENCE FOR INVASIBILITY AND SATURATION
.ORTH AND 3OUTH !MERICAN MAMMALS HAS BEEN CONTESTED ,ESSA ET AL -OREOVER THERE ARE MANY INSTANCES OF INVASIONS THAT DID NOT RESULT IN THE EXTINC TION OF RESIDENT SPECIES .O INCREASES IN EXTINCTION RATES OCCURRED FOLLOWING BIOTIC INTERCHANGE IN THE MARINE REALM REGARDING TRANSEQUITORIAL TRANS !RCTIC AND TRANS 0ACIlC INTERCHANGES 6ERMEIJ A B 6ERMEIJ A B ,INBERG OR FOLLOWING THE INVASION OF !FRICAN AND .ORTH !MERICAN MAMMALS INTO !SIA DURING THE -IOCENE AND 0LIOCENE "ARRY ET AL &LYNN ET AL )NVASION EVENTS DURING BIOTIC INTERCHANGES MOST OFTEN ENHANCE THE SPECIES RICHNESS OF RECIPIENT COMMUNITIES "ARRY ET AL &LYNN ET AL 6ERMEIJ A 4HESE PAT TERNS BOLSTER THOSE OF THE CONTEMPORARY INTERCHANGE LITERATURE IN THAT INVASIONS RARELY CAUSE THE GLOBAL EXTINCTION OF RESIDENT SPECIES AND OFTEN RESULT IN INCREASES IN SPECIES RICHNESS AT THE REGIONAL SCALE 4HIS SUGGESTS THAT BIOLOGICAL COMMUNI TIES DO NOT RESIST ALL INVASION ATTEMPTS AND ARE UNDER SATURATED WITH SPECIES 4HE OUTCOMES OF BIOTIC INTERCHANGES EMPHASIZE THE IMPORTANCE OF DISPERSAL IN SET TING AN UPPER LIMIT TO THE NUMBER OF SPECIES COEXISTING IN A GIVEN AREA )N THIS SECTION WE ARGUE THAT THE OUTCOME OF CONTEMPORARY AND HISTORIC BIOTIC INTERCHANGES PROVIDE STRONG EVIDENCE THAT COMMUNITIES ARE BOTH INVASIBLE AND UNSATURATED (OWEVER THE ABOVE EXAMPLES LACK INFORMATION ON THE EFFECTS OF INVASION AT MULTIPLE SPATIAL SCALES )T IS THEREFORE IMPOSSIBLE TO DETERMINE HOW CHANGES IN RICHNESS AT CONTINENTAL OR OCEANIC SCALES ARE REmECTED AT SMALLER LOCAL SCALES )NCREASES IN LARGE SCALE RICHNESS MIGHT BE ACCOMPANIED BY DECREASES AT LOCAL SCALES IF NATIVE SPECIES ARE MUCH REDUCED IN RANGE OR ABUNDANCE )N ADDI TION BETA DIVERSITY OR REGIONAL DISTINCTIVENESS HAS CLEARLY DECLINED IN MANY CASES AS A RESULT OF BIOTIC HOMOGENIZATION -C+INNEY AND ,OCKWOOD 2AHEL 4HE SPATIAL GRAIN AND EXTENT OF OBSERVATION STRONGLY INmUENCES OUR PERCEP TION OF COMMUNITY SATURATION
#/.4%-0/2!29 ")/,/')#!, ).6!3)/.3 #/-0!2).' ).6!3)/. !.$ %84).#4)/. %6%.43 4HE EXPLOSION IN THE NUMBER OF HUMAN MEDIATED INVASIONS CLEARLY ATTESTS THAT CONTEMPORARY BIOLOGICAL COMMUNITIES ARE INVASIBLE ,ODGE -OYLE AND ,IGHT 6ITOUSEK ET AL #OHEN AND #ARLTON (OBBS AND -OONEY 2ICCIARDI 3TUDYING COMMUNITY DYNAMICS FOLLOWING INVASIONS PER MITS INFERENCES ABOUT THE PROCESSES REGULATING SPECIES RICHNESS (ERE WE EXAMINE EVIDENCE FROM A NUMBER OF CONTEMPORARY INVASIONS AND EXTINCTIONS IN DIFFERENT ECOSYSTEMS AND ADDRESS THEIR SIGNIlCANCE FOR THE INVASIBILITY AND SATURATION OF ECOLOGICAL COMMUNITIES 2EGIONAL SCALE PATTERNS
4HE LITERATURE ON CONTEMPORARY ANTHROPOGENIC INVASIONS INDICATES THAT AT BROAD REGIONAL SCALES EG ISLANDS OR ARCHIPELAGOS INVASIONS EXCEED EXTINCTIONS
3! 3MITH AND *" 3HURIN
RESULT ING IN NET INCREASES O F SPECIES RICHNESS #ASE (OBBS AND -OONEY 3AX ET AL 3AX AND 'AINES 4ABLE )NCREASES IN SPECIES RICHNESS VARIED BETWEEN CONTINENTS AND ISLANDS AS WELL AS AMONG TAXA EXHIBITING DIFFERING DEGREES OF DISPERSAL LIMITATION ,ARGER INCREASES IN SPECIES RICHNESS WERE ENCOUN TERED ON ISLANDS AS OPPOSED TO CONTINENTS ESPECIALLY IN THE CASE OF PLANTS WHERE AN ASTOUNDING INCREASE IN SPECIES RICHNESS WAS DOCUMENTED ON OCEANIC ISLANDS 3AX ET AL #OMPARING THE INCREASE IN SPECIES RICHNESS AMONG TAXA INDICATES THAT THE MOST DISPERSAL LIMITED TAXA EXPERIENCED THE LARGEST INCREASES IN SPECIES RICHNESS FOLLOWING HUMAN MEDIATED INVASION EVENTS &OR EXAMPLE INCREASES IN THE SPECIES RICHNESS OF FRESHWATER lSHES AND PLANTS FAR EXCEEDED THOSE OF BIRDS -OST BIRDS CAN DISPERSE OVER MUCH LARGER SPATIAL SCALES THAN FRESHWATER lSHES WHICH DEPEND ON DIRECT CONNECTIONS BETWEEN WATER BODIES AND mOWERING PLANTS WHOSE SEEDS ARE PASSIVELY DISPERSED BY WIND OR ANIMALS 3AX ET AL )T IS THEREFORE NOT SURPRISING THAT DISPERSAL LIMITS THE NUMBER OF lSH AND PLANT SPE CIES FOUND AT THE REGIONAL SCALE TO A GREATER EXTENT THAN IN BIRDS #ONTEMPORARY INVASIONS EXCEED EXTINCTIONS SUPPORTING THE EVIDENCE FROM FAUNAL EXCHANGES THAT COMMUNITIES ARE UNSATURATED ,OCAL SCALE PATTERNS
3TRONG SPECIES INTERACTIONS AT THE LOCAL SCALE MAY NOT MANIFEST THEMSELVES AS SATU RATION AT BROAD REGIONAL SCALES &OR INSTANCE "YERS AND .OONBURG ANA LYZED MODELS WITH STRONG LOCAL INTERACTIONS AND SPATIAL HETEROGENEITY IN RESOURCES 4HEY FOUND THAT HIGH DIVERSITY AT THE REGIONAL SCALE DUE TO BROAD HETEROGENEITY LED TO HIGH INVASIBILITY EVEN THOUGH LOCAL INTERACTIONS GENERATED STRONG BIOTIC RESIS TANCE AT SMALLER SCALES 3TUDIES OF CHANGES IN SPECIES RICHNESS FOLLOWING INVASION EVENTS AT THE LOCAL SCALE MAY THEREFORE PROVIDE MORE POWERFUL TESTS FOR COMMU NITY SATURATION 'IDO AND "ROWN RECORDED CHANGES IN THE SPECIES RICHNESS OF FRESHWATER lSHES IN DRAINAGE BASINS IN .ORTH !MERICA AND FOUND THAT INVASIONS EXCEEDED EXTINCTIONS IN OF CASES -EAN SPECIES RICHNESS OF THE DRAINAGE BASINS INCREASED BY WHILE RICHNESS OF FRESHWATER lSHES IN #ALIFORNIA INCREASED 4ABLE -ARCHETTI ET AL SUGGESTING THAT LOCAL COMMUNITIES WERE NOT RESISTANT TO INVASION OR SATURATED WITH SPECIES )N ADDITION COMPETITION WITH INVADERS HAS RARELY BEEN IMPLICATED AS A CAUSE OF NATIVE SPE CIES EXTINCTIONS $AVIS 2ATHER PREDATION PRESSURE +AUFMAN &RITTS AND 2ODDA AND HABITAT CHANGE EG (AWAIIAN )SLANDS ARE RESPONSIBLE FOR MANY OF THE IMPACTS OF INVADERS ON NATIVES 4HESE RESULTS CONCUR WITH THOSE OF CONTEMPORARY AND PAST BIOTIC INTERCHANGES WHERE INCREASING THE SIZE OF THE AVAIL ABLE REGIONAL SPECIES POOL RESULTED IN NET INCREASES IN SPECIES RICHNESS SEE SECTION !LTERNATIVELY DRAINAGE BASINS MAY CONTAIN MULTIPLE LOCAL POPULATIONS AND CORRESPOND MORE TO THE REGIONAL THAN LOCAL SCALE SO THAT THE SPATIAL EXTENT IS STILL TOO LARGE FOR SATURATION TO BECOME EVIDENT .EVERTHELESS PATTERNS OF INVASIONS AND EXTINCTIONS AT SMALLER SCALES EG DRAINAGES OR ISLANDS PROVIDE NO MORE EVIDENCE FOR SATURATION THAN THOSE OVER BROADER REGIONS
)SLANDS #ALIFORNIA 7ESTERN !USTRALIA 53! #ALIFORNIA 4ENNESSEE 4ENNESSEE #ALIFORNIA #ALIFORNIA #ALIFORNIA
"IRDS
&RESHWATER lSHES
&RESHWATER lSHES
&RESHWATER lSHES
&RESHWATER lSHES
&RESHWATER lSHES
-USSELS
2EPTILES
!MPHIBIANS
"UTTERmIES
<
<
<
3TATE OF #ALIFORNIA
3TATE OF #ALIFORNIA
3TATE OF #ALIFORNIA
%COREGIONS
%COREGIONS
$RAINAGE BASIN
$RAINAGE BASIN
7ESTERN !USTRALIA
3TATE OF #ALIFORNIA
)SLANDS
)SLANDS
7ESTERN !USTRALIA
3TATE OF #ALIFORNIA
7ESTERN !USTRALIA
3TATE OF #ALIFORNIA
)SLANDS
7ESTERN !USTRALIA
3TATE OF #ALIFORNIA
%VIDENCE FOR INVASIBILITY AND SATURATION
7ESTERN !USTRALIA /CEANIC )SLANDS
#ALIFORNIA
"IRDS
,AND "IRDS
7ESTERN !USTRALIA
-AMMALS
"IRDS
/CEANIC )SLANDS #ALIFORNIA
-AMMALS
7ESTERN !USTRALIA
0LANTS
0LANTS
#ALIFORNIA
0LANTS
4ABLE 0ATTERNS OF CHANGES IN SPECIES RICHNESS FOLLOWING INVASION EVENTS $ATA COMPILED FROM (OBBS AND -OONEY 3AX "ROWN AND 'AINES #ASE 'IDO AND "ROWN -ARCHETTI ET AL AND $UNCAN AND ,OCKWOOD 4AXA ,OCATION -EAN .ET )NCREASE OF SAMPLES OF TOTAL PRESENT 32 3PATIAL SCALE IN SPECIES RICHNESS THAT IS INTRODUCED
3! 3MITH AND *" 3HURIN
!33%33).' -%4(/$/,/')#!, ,)-)4!4)/.3 !.$ #/.342!).43 4HERE ARE SEVERAL IMPORTANT CAVEATS TO CONSIDER WHEN INFERRING THE MECHANISMS STRUCTURING COMMUNITIES FROM PATTERNS OF INVASION AND EXTINCTION AT LOCAL AND REGIONAL SCALES &OR EXAMPLE EXTINCTIONS MAY BE MORE DIFlCULT TO DETECT THAN INVASIONS &EW EXTINCTIONS MAY BE RECORDED AS SPECIES THAT ARE NOT OBSERVED CANNOT BE ASSUMED ABSENT WHEREAS INVASIONS ARE UNAMBIGUOUSLY INVASIONS )N ADDITION CHANGES IN SPECIES RICHNESS MAY IGNORE OTHER LARGE EFFECTS ON RANGE OR ABUNDANCE OF NATIVE SPECIES FOLLOWING SPECIES INVASIONS 4HAT IS MANY FORMERLY ABUNDANT WIDESPREAD SPECIES MAY BE REDUCED TO FEW SMALL REMNANT POPULATIONS BY INTERACTIONS WITH INVADERS WITHOUT BECOMING EXTINCT 3UCH CHANGES IN DISTRI BUTION AND ABUNDANCE ARE NOT CAPTURED BY PRESENCEABSENCE DATA %XTINCTIONS CAUSED BY INVADERS MAY ALSO PROCEED SLOWLY AND OCCUR LONG AFTER THE INITIAL COLONIZATION 2ICKLEFS SUGGESTING THAT THERE MAY BE A TIME LAG BETWEEN INVASION AND EXTINCTION EVENTS (OWEVER INVASIONS FOLLOWING THE ELIMI NATION OF DISPERSAL BARRIERS DO NOT RESULT IN MEASURABLY GREATER EXTINCTION RATES OVER EVOLUTIONARY TIME SCALES "ARRY ET AL &LYNN ET AL ,INBERG ET AL .EVERTHELESS EXAMPLES OF INVASIONS THAT LEAD TO MASS EXTINCTION EVENTS ARE WELL DOCUMENTED EG .ILE PERCH IN ,AKE 6ICTORIA +AUFMAN BROWN TREE SNAKE IN 'UAM &RITTS AND 2ODDA AND ZEBRA MUSSELS IN THE 'REAT ,AKES .ALEPA AND 3CHLOESER 6ANDERPLOEG ET AL %LEVATED RATES OF SPECIES INTRODUCTIONS COUPLED WITH LARGE CORRELATED LOSSES OF DIVERSITY HAVE LED TO THE ASSUMPTION THAT EXOTIC SPECIES INTRODUCTIONS ARE ONE OF THE LEADING CAUSES OF SPECIES EXTINCTIONS BUT SEE 'UREVITCH AND 0ADILLA 4HE OBSERVATION THAT EXOTIC SPECIES ARE THE THIRD MOST PREVALENT THREAT TO ENDAN GERED SPECIES THROUGHOUT THE WORLD 3ALA ET AL SUGGESTS THAT MANY EXTINC TIONS RESULTING FROM BIOTIC EXCHANGE ARE STILL TO COME (OWEVER IT HAS OFTEN BEEN DIFlCULT TO IDENTIFY THE ROLE OF EXOTIC INVADERS IN CAUSING SPECIES EXTINCTIONS BECAUSE MOST IMPERILED SPECIES FACE MORE THAN ONE THREAT SIMULTANEOUSLY 'UREVITCH AND 0ADILLA %XPERIMENTS THAT DO NOT SUFFER FROM THE CONFOUNDING EFFECTS OF MULTIPLE ASPECTS OF HUMAN ALTERATION OF THE ENVIRONMENT ARE REQUIRED TO ASSESS THE RELATIVE IMPORTANCE OF INVASIONS AS A CAUSE OF EXTINCTION 2ICCIARDI &INALLY INVASIVE SPECIES HAVE BEEN DOCUMENTED TO PREFERENTIALLY OCCUPY HUMAN DOMINATED LANDSCAPES WHEREAS NATIVE SPECIES HAVE A GREATER AFlNITY FOR NATIVE UNDISTURBED HABITAT $IAMOND AND 6EITECH 3IMBERLOFF 3MALLWOOD #ASE 2AHEL 3AX ET AL $UNCAN ET AL -ANY INVADERS MAY NOT INTERACT WITH RESIDENT SPECIES BECAUSE OF HABITAT PARTI TIONING BETWEEN NATIVE AND INTRODUCED SPECIES THEREFORE COMPLICATING THE USE OF BIOLOGICAL INVASIONS AS TESTS OF COMMUNITY SATURATION )N ADDITION THE HIGH APPARENT INVASIBILITY OF COMMUNITIES MAY BE AS MUCH A PRODUCT OF ANTHROPOGENIC DISTURBANCES THAT WEAKEN BIOTIC RESISTANCE AS HUMAN AIDED DISPERSAL 3EABLOOM ET AL .EVERTHELESS NET INCREASES OF SPECIES RICHNESS AT LOCAL AND REGIONAL SCALES FOLLOWING INVASION EVENTS SUGGEST THAT MANY COMMUNITIES ARE INVASIBLE AND UNSATURATED 4HIS CONCLUSION IS SUPPORTED BY PATTERNS OF PAST AND CONTEM
%VIDENCE FOR INVASIBILITY AND SATURATION
PORARY FAUNAL INTERCHANGE )N THE NEXT SECTION WE REVIEW EXPERIMENTAL STUDIES OF COMMUNITY SATURATION AND COMPARE THEIR RESULTS WITH THOSE OF PATTERNS FROM UNMANIPULATED SYSTEMS
%80%2)-%.4!,,9 34!'%$ ).6!3)/.3 -ACROECOLOGICAL PATTERNS SUGGEST THAT COMMUNITIES ARE BOTH UNSATURATED AND INVASIBLE THAT BIOTIC RESISTANCE TO INVASION IN COMMUNITIES IS WEAK RELATIVE TO DISPERSAL LIMITATION AND THAT NATIVE SPECIES ARE RARELY EXCLUDED FROM COMMUNI TIES BY INTERACTIONS WITH INVADERS 3TOHLGREN ET AL 3AX AND 'AINES 4HIS CONCLUSION HAS IMPORTANT PRACTICAL IMPLICATIONS AS IT SUGGESTS THAT MANAG ING DISPERSAL VECTORS IS MORE EFFECTIVE FOR CONTAINING INVADERS THAN RELYING ON NATIVE COMMUNITIES TO PREVENT THEIR SPREAD (OWEVER THE CONCLUSION THAT SPECIES INTERACTIONS AND BIOTIC RESISTANCE ARE UNIMPORTANT FOR SHAPING COMMUNITIES OR PREVENTING INVASIONS MAY BE INCORRECT &IRST SPECIES INTERACTIONS LIKELY OCCUR AT SCALES MUCH SMALLER THAN THE BROAD REGIONS EG ISLAND CHAINS OR WATERSHEDS THAT ARE THE UNITS OF OBSERVATION FOR BIOGEOGRAPHICAL STUDIES ! NEW COLONIST LIKELY INTERACTS ONLY WITH OTHER SPECIES WITHIN A FAIRLY SMALL NEIGHBORHOOD NOT THE ENTIRE BIOTA OF THE REGION )N ADDITION WHILE INVASIONS ARE OFTEN DRAMATIC AND OBVIOUS FAILED INVASION ATTEMPTS MOSTLY PASS UNOBSERVED 7E DO NOT KNOW WHETHER THE REGIONAL DIFFERENCES IN DIVERSITY THAT REMAIN FOLLOWING WHOLESALE SPECIES INTRODUCTIONS ARE DUE TO ENVIRONMENTAL CONSTRAINTS SPECIES INTERACTIONS OR LACK OF DISPERSAL OPPORTUNITIES FOR SOME SPECIES &INALLY EXTINCTION OF SPECIES MAY BE SLOW RELATIVE TO INVASION 2ICKLEFS AND SOME SPECIES MAY BE GREATLY REDUCED IN ABUNDANCE OR GEOGRAPHIC RANGE BY INVADERS WITHOUT BEING COMPLETELY EXTIRPATED 2EGIONAL DIVERSITY LOSS DUE TO INVADERS MAY THEREFORE BE A WEAK INDI CATOR OF THE IMPORTANCE OF BIOTIC EXCLUSION ,OCAL INTERACTIONS MAY BE DIFlCULT TO DETECT IN MACROECOLOGICAL PATTERNS BUT STILL BE CRITICAL FOR CONSTRAINING INVASIONS 4HE lNAL APPROACH TO ASSAYING COMMUNITY SATURATION AND INVASIBILITY THAT WE DISCUSS IS THROUGH EXPERIMENTAL SPECIES INTRODUCTIONS &IELD MANIPULATIONS OF INVASION OFFER A NUMBER OF INSIGHTS THAT CANNOT BE OBTAINED FROM OBSERVATIONAL DATA &IRST THE RATES OF SUCCESS AND FAILURE CAN BE ACCURATELY CHARACTERIZED AS THE POOL OF INTRODUCED SPECIES IS KNOWN 3ECOND ASPECTS OF THE INVADER POOL EG PROPAGULE LOAD OR TIMING AND RECIPIENT COMMUNITY EG DIVERSITY COMPOSITION PRODUCTIVITY OR DISTURBANCE CAN BE DIRECTLY MANIPULATED 4HESE ALLOW ASSIGN MENT OF THE CAUSES OF INVASION SUCCESS OR FAILURE AND INTERPRETATION OF THE TRAITS OF SPECIES OR COMMUNITIES THAT INmUENCE INVASIVENESS AND INVASIBILITY &IELD EXPERIMENTS ARE ALSO GENERALLY CONDUCTED AT MUCH SMALLER LOCAL SCALES SUCH AS THE NEIGHBORHOOD OF PLANT COMMUNITIES AND MAY THEREFORE BE MORE LIKELY TO REVEAL THE ROLE OF SPECIES INTERACTIONS %FFORTS TO EXPERIMENTALLY TEST COMMUNITY SATURATION ARE INCREASINGLY COMMON !SSAYING INVASIBILITY AT THE COMMUNITY LEVEL INVOLVES INTRODUCING POTENTIALLY INVASIVE SPECIES USUALLY ONES THAT ARE PRESENT REGIONALLY BUT ABSENT LOCALLY 4HE
3! 3MITH AND *" 3HURIN
MAJORITY OF lELD STUDIES OF COMMUNITY SATURATION ARE SEED ADDITIONS IN HERBACEOUS PLANT COMMUNITIES 4ABLE 4URNBULL ET AL REVIEWED THE LITERATURE ON SEED ADDITION EXPERIMENTS AND CONCLUDED THAT APPROXIMATELY OF ALL PLANT SPE CIES SHOW EVIDENCE FOR SEED LIMITATION ! SESSILE GROWTH FORM MAY RENDER TERRES TRIAL PLANTS ESPECIALLY VULNERABLE TO DISPERSAL LIMITATION AS PROPAGULES HAVE ONLY ONE OPPORTUNITY TO lND SUITABLE HABITAT PATCHES 3MALL SCALE VARIABILITY IN LIGHT OR SOIL CONDITIONS MAY CONSTRAIN APPROPRIATE SITES FOR GERMINATION TO A SMALL FRACTION OF THE AVAILABLE HABITAT ! LIMITED NUMBER OF STUDIES HAVE BEEN PERFORMED IN OTHER COMMUNITIES INCLUDING POND ZOOPLANKTON 3HURIN AND LABORATORY STUDIES WITH PROTOZOANS &OX ET AL
4ABLE ! SUMMARY OF EXPERIMENTAL STUDIES OF COMMUNITY SATURATION AND INVASIBILITY 0ERCENT INTRODUCTION SUCCESS IS MEASURED AS THE PROPORTION OF INTRODUCED SPECIES OBSERVED IN THE EXPERIMENTAL SYSTEM AND INCLUDES SUCCESSFUL GERMINATION h)NCREASED LOCAL RICHNESSv INDICATES WHETHER LOCAL RICHNESS WAS GREATER IN THE INTRODUCTION TREATMENT THAN THE CONTROL h2ICHNESS INVASIBILITYv INDICATES WHETHER THE SUCCESS OF INVADERS DECLINED AT HIGHER NATIVE SPECIES RICHNESS AND hDISTURBANCE TREATMENTv INDICATES WHETHER PERTURBATIONS TO THE NATIVE COMMUNITY AFFECTED INVASIBILITY ! DASH INDICATES THAT THE TREATMENT WAS NOT PERFORMED OR THE HYPOTHESIS WAS NOT TESTED 3TUDY "URKE AND 'RIME 4ILMAN 3HURIN :OBEL ET AL &OSTER ,EVINE &OSTER ET AL &ARGIONE ET AL &OSTER AND 4ILMAN -OUQUET ET AL
3YSTEM GRASSLAND GRASSLAND ZOOPLANKTON GRASSLAND GRASSLAND SEDGES GRASSLAND GRASSLAND GRASSLAND GRASSLAND
)NCREASED 2ICHNESS $ISTURBANCE INTRODUCTION LOCAL SUCCESS RICHNESS INVASIBILITY TREATMENT
< 9 . 9 9 9 < 9 9 9
< NEGATIVE NEGATIVE NONE < NEGATIVE POSITIVE NEGATIVE < <
9 < 9 9 9 9 < < < <
4ABLE SUMMARIZES EXPERIMENTS TESTING SATURATION AND REVEALS A NUMBER OF PATTERNS &IRST EVERY EXPERIMENTAL SPECIES ADDITION FOUND THAT SOME SPECIES ARE ABSENT FROM LOCAL COMMUNITIES DUE TO DISPERSAL LIMITATION 4HE INTRODUCTION SUC CESS RATE INTO INTACT RECIPIENT COMMUNITIES RANGED FROM FOR POND ZOOPLANKTON TO MUCH HIGHER IN HERBACEOUS PLANT COMMUNITIES 4HE OBSERVATION
%VIDENCE FOR INVASIBILITY AND SATURATION
THAT ZOOPLANKTON COMMUNITIES APPEAR CLOSER TO SATURATION THAN PLANTS MAY REmECT EITHER BIOLOGICAL OR METHODOLOGICAL DIFFERENCES BETWEEN THE STUDIES :OOPLANKTON MAY BE MORE EFFECTIVE DISPERSERS THAN PLANTS OR MAY BE BETTER ABLE TO lND SUITABLE MICROSITES WITHIN PATCHES EG PONDS BECAUSE THEY ARE MOTILE !LTERNATIVELY THE CRITERION FOR SUCCESSFUL INVASION IN THE PLANT STUDIES WAS TYPICALLY GERMINATION NOT SUCCESSFUL REPRODUCTION OR POSITIVE POPULATION GROWTH -ANY OF THE SEEDLINGS THAT GERMINATED MAY NOT HAVE EVENTUALLY ESTABLISHED THEREFORE THE EXPERI MENTS MAY OVERESTIMATE INVASION SUCCESS (OWEVER A NUMBER OF STUDIES LASTED FOR SEVERAL YEARS AND FOUND THAT INTRODUCED PLANTS PERSISTED 4HE RESULTS OF THE EXPERIMENTS SUPPORT LARGE SCALE PATTERNS INDICATING THAT CONTEMPORARY BIOLOGICAL COMMUNITIES ARE INVASIBLE %XPERIMENTS ALSO INDICATE THAT PLANT COMMUNITIES ARE OFTEN UNSATURATED IN THAT INTRODUCTIONS SIMULATING INCREASED CONNECTIVITY TO THE LARGER REGIONAL SPE CIES POOL ENHANCED LOCAL DIVERSITY 3EVEN OUT OF EIGHT STUDIES FOUND HIGHER SPE CIES RICHNESS IN THE INTRODUCTION TREATMENTS THAN IN THE CONTROLS ALL OF THE PLANT EXPERIMENTS THAT CONTRASTED DIVERSITY IN THE SEED ADDITION TREATMENT WITH THE CON TROL 4ABLE "Y CONTRAST 3HURINS POND ZOOPLANKTON EXPERIMENTS FOUND NO DIFFERENCE IN DIVERSITY BETWEEN INVASION TREATMENTS AND THE CONTROL INDICATING THAT POND ZOOPLANKTON COMMUNITIES MAY BE CLOSER TO REGIONAL SATURATION THAN TERRESTRIAL PLANTS %XPERIMENTAL INTRODUCTIONS INDICATE THAT MANY COMMUNITIES ARE UNSATURATED WITH SPECIES AT BOTH LOCAL NEIGHBORHOOD AND REGIONAL SCALES (OWEVER A NUMBER OF PATTERNS FROM THE EXPERIMENTAL LITERATURE CONTRAST WITH THE INTERPRETATION OF MACRO SCALE PATTERNS AS INDICATING WEAK BIOTIC RESISTANCE AND A DOMINANCE OF DISPERSAL LIMITATION RELATIVE TO SPECIES INTERACTIONS IN STRUCTURING COMMUNITIES EG 3TOHLGREN ET AL 3AX AND 'AINES &IRST A NUMBER OF STUDIES FOUND DECLINING INVASION SUCCESS MEASURED EITHER AS THE PERCENT OCCUR RENCE OF INVASIVE SPECIES OR THEIR OVERALL ABUNDANCE AT HIGHER LOCAL RICHNESS OF RESIDENT SPECIES 4ABLE 4HIS RESULT SUGGESTS THAT ALTHOUGH COMMUNITIES ARE UNSATURATED IN THAT THEY CAN SUPPORT MORE SPECIES LOCAL RICHNESS APPROACHES SATURATION AT HIGH LEVELS IN THAT IT BECOMES INCREASINGLY DIFlCULT FOR ADDITIONAL SPECIES TO INVADE )NCREASING BIOTIC RESISTANCE MOST LIKELY RESULTS FROM GREATER INTENSITY OF LOCAL INTERACTIONS AT HIGH DIVERSITY 4HE INCREASED BIOTIC RESISTANCE AT HIGH DIVERSITY COULD BE THE RESULT OF EITHER STRONGER COMPETITIVE INTERACTIONS AMONG ESTABLISHED SPECIES OR BY THE INHIBITORY EFFECTS OF ESTABLISHED SPECIES ON RECRUITMENT 4ILMAN 3ECOND A NUMBER OF EXPERIMENTS EMPLOYED DISTURBANCE TREATMENTS THAT WEAK ENED INTERACTIONS BETWEEN THE RESIDENT COMMUNITY AND INVADERS #OMPARING INVASIBILITY IN DISTURBED VS INTACT NATIVE COMMUNITIES ILLUSTRATES WHICH SPECIES ARE EXCLUDED FROM THE RECIPIENT COMMUNITY DUE TO INTERACTIONS WITH NATIVES VER SUS INABILITY TO TOLERATE LOCAL ABIOTIC CONDITIONS 3TUDIES EMPLOYING DISTURBANCE TREATMENTS EITHER THROUGH REMOVAL OF NATIVE SPECIES OR ENHANCED PRODUCTIVITY BY NUTRIENT ADDITIONS FOUND THAT INVASIBILITY WAS DRAMATICALLY INCREASED BY ALTER ING THE BIOTIC ENVIRONMENT &OR INSTANCE 3HURIN FOUND THAT REDUCING THE ABUNDANCE OF NATIVE SPECIES ALLOWED FOUR TIMES AS MANY INVADERS TO ESTABLISH
3! 3MITH AND *" 3HURIN
AND TO OBTAIN SIXTEEN TIMES GREATER TOTAL ABUNDANCE 4HESE RESULTS INDICATE THAT ALTHOUGH COMMUNITIES MAY BE INVASIBLE AND UNSATURATED DUE TO DISPERSAL LIMITA TION LOCAL INTERACTIONS MAY STILL BE STRONG ENOUGH TO EXCLUDE A LARGE FRACTION OF POTENTIAL INVADERS AND THAT MANY MORE SPECIES MAY BE EXCLUDED THAN SUCCEED IN INVADING INTACT COMMUNITIES 4HIS CONTRAST ILLUSTRATES THE IMPORTANCE OF lELD EXPERIMENTS !NALYSIS OF PATTERNS OF DIVERSITY FOLLOWING FAUNAL EXCHANGE AND ANTHROPOGENIC INTRODUCTIONS MAY BE INTERPRETED TO INDICATE THAT BIOTIC RESISTANCE SELDOM IF EVER REPELS INVADERS 3TOHLGREN ET AL 3AX AND 'AINES 4HIS CONCLUSION EMPHASIZES SUCCESSFUL INVASIONS OVER FAILURES HOWEVER THE LATTER MAY BE MORE COMMON AND OFTEN OCCUR DUE TO LOCAL INTERACTIONS
-%4!#/--5.)49 02%$)#4)/.3 4HE GLOBAL EXPLOSION IN THE INCIDENCE OF EXOTIC SPECIES REmECTS THE RESULTS OF HUMAN ACTIVITIES THAT INCREASE RATES OF MIGRATION AMONG PREVIOUSLY ISOLATED BIOGEOGRAPH IC REGIONS 7ITHIN REGIONS HOWEVER HUMANS MAY EITHER INCREASE HABITAT CONNEC TIVITY BY ACTING AS DISPERSAL VECTORS OR DECREASE IT THROUGH HABITAT FRAGMENTATION 4HE EFFECTS OF MODIFYING RATES OF DISPERSAL WITHIN REGIONS AND IMMIGRATION FROM OTHER REGIONS ARE QUITE DISTINCT (ERE WE FOCUS ON THE EFFECTS OF INCREASED MOVE MENT RATES AMONG REGIONS PUTTING ASIDE THE QUESTION OF HOW HUMAN INDUCED ENVIRONMENTAL CHANGE AFFECTS DISPERSAL WITHIN REGIONS -ETACOMMUNITY MODELS OFFER DIFFERENT THEORETICAL PREDICTIONS REGARDING THE INVASIBILITY AND SATURATION OF LOCAL COMMUNITIES AND THE OUTCOME OF BIOLOGICAL INVASIONS #OMPARING RESPONSES OF DIVERSITY TO CHANGES IN IMMIGRATION RATES WITH PREDICTED OUTCOMES MAY BE USE FUL FOR EVALUATING DIFFERENT PERSPECTIVES ON BROAD SCALE COMMUNITY STRUCTURE 4HEORETICAL AND EMPIRICAL WORK ON METACOMMUNITIES FALLS UNDER FOUR PARA DIGMS WHICH WE CALL PATCH DYNAMICS NEUTRAL SPECIES SORTING AND MASS EFFECTS ,EIBOLD ET AL #HASE ET AL 4HE FOUR APPROACHES DIFFER IN THEIR ASSUMPTIONS ABOUT RELATIVE RATES OF DISPERSAL THE INTENSITY OF INTERSPECIlC INTERACTIONS AND THE DEGREE OF SPATIAL HETEROGENEITY AMONG HABITATS &IG 0ATCH DYNAMICS THE OLDEST PERSPECTIVE IS REPRESENTED BY ISLAND BIOGEOGRAPHY AND METAPOPULATION ECOLOGY 4HIS APPROACH CONSIDERS HABITATS AS DIVIDED INTO HOMOGENEOUS PATCHES AMONG WHICH SPECIES DISPERSE 4HE SIMPLEST VERSION OF THE PATCH DYNAMICS FRAMEWORK ASSUMES THAT SPECIES ARE INDIFFERENT TO ONE ANOTHERS PRESENCE IN PATCHES HOWEVER SUCH MODELS HAVE BEEN MODIlED TO INCORPORATE LOCAL INTERACTIONS THAT LEAD TO EXCLUSION OR FACILITATION ,EVINS AND #ULVER (ASTINGS $ISPERSAL IN THE PATCH DYNAMICS FRAMEWORK IS SLOW RELATIVE TO DEMOGRAPHIC RATES SO THAT PATCHES ARE EITHER OCCUPIED OR EMPTY BUT LOCAL DYNAM ICS ARE IGNORED .EUTRAL THEORY "ELL (UBBELL REPRESENTS A VARIATION ON PATCH DYNAMICS WHERE ALL INDIVIDUALS ARE IDENTICAL IN ALL RELEVANT TRAITS LOCAL INTERACTIONS ARE STRONG AND LEAD TO PRIORITY EFFECTS AND DISPERSAL IS SPATIALLY CON STRAINED 3PECIES MAY COEXIST IN PATCH DYNAMICS MODELS AT EQUILIBRIUM BY TRADE OFFS IN THEIR ABILITY TO COLONIZE AND COMPETE IN PATCHES ,EVINS AND #ULVER
%VIDENCE FOR INVASIBILITY AND SATURATION
(ASTINGS WHILE COEXISTENCE IN NEUTRAL MODELS IS DETERMINED BY A BALANCE BETWEEN SLOW EXCLUSION AND THE INPUT OF SPECIES EITHER FROM OUTSIDE THE REGION OR THROUGH SPECIATION "ELL (UBBELL 4HE SPECIES SORTING APPROACH POSITS THAT SPECIES DISPERSE SUFlCIENTLY RAPIDLY THAT LOCAL ENVIRONMENTAL CONSTRAINTS LIMIT DISTRIBUTIONS TO A GREATER EXTENT THAN THE SUPPLY OF COLONISTS ,EIBOLD ET AL 4HE SPECIES SORTING VIEW CAN BE CONSIDERED CLASSICALLY NICHE BASED IN THAT SPECIES ARE SELECTED BY THE LOCAL ENVI RONMENT AND SITES CONTAIN MOST OR ALL SPECIES CAPABLE OF COEXISTING UNDER THE PARTICULAR LOCAL CONDITIONS 3PECIES SORTING ASSUMES SUFlCIENTLY FAST DISPERSAL THAT LOCAL INTERACTIONS PLAY A DOMINANT ROLE OVER MOVEMENT OF SPECIES IN CONSTRAIN ING COMMUNITY MEMBERSHIP &INALLY THE MASS EFFECTS OR SOURCE SINK PERSPECTIVE HOLDS THAT DISPERSAL CAN BE SO RAPID THAT POPULATIONS ARE MAINTAINED THAT WOULD OTHERWISE DECLINE TO EXTINCTION IN THE ABSENCE OF INPUT OF INDIVIDUALS FROM OTHER HABITATS 3HMIDA AND %LLNER -ASS EFFECTS MODELS RELY ON HETEROGENEITY IN THE ENVIRONMENT THAT CREATES DIFFERENCES IN lTNESS SUCH THAT SOME HABITATS PRODUCE EXCESS INDIVIDUALS THAT DISPERSE TO POOR QUALITY PATCHES WHERE THEY HAVE NEGATIVE GROWTH RATES 3PECIES SORTING HOLDS THAT DISPERSAL IS FAST RELATIVE TO RATES OF POPULATION EXTINCTION BUT NOT SO RAPID THAT THE INPUT OF INDIVIDUALS IS LARGE RELATIVE TO LOCAL REPRODUCTION "Y CONTRAST MASS EFFECTS SYSTEMS OCCUR WHEN DISPERSAL IS FAST RELATIVE TO LOCAL DEMOGRAPHIC RATES 4HE DIFFERENCES AMONG THE FOUR METACOMMUNITY APPROACHES ARE ILLUSTRATED IN &IG 4HE FOUR METACOMMUNITY PERSPECTIVES MAKE DIVERGENT PREDICTIONS REGARD ING THE INVASIBILITY AND SATURATION OF COMMUNITIES AND THE PREDICTED OUTCOME OF INCREASED IMMIGRATION RATES AMONG BIOGEOGRAPHIC PROVINCES 4ABLE #HASE ET AL &OR EXAMPLE PATCH DYNAMICS MODELS WITHOUT INTERACTIONS PREDICT THAT LOCAL COMMUNITIES ARE ALWAYS INVASIBLE AND UNSATURATED #ONSEQUENTLY INVASIONS FOLLOWING INCREASED IMMIGRATION RATES SHOULD BE COMMONPLACE 0ATCH DYNAMIC MODELS WITH STRONG COMPETITIVE EXCLUSION PREDICT THAT MORE SPECIES CAN ALWAYS BE ADDED REGIONALLY AS LONG AS THEY SHOW SUFlCIENTLY STRONG COMPETITION COLONIZATION TRADEOFFS 4ILMAN (OWEVER THE NECESSARY TRADEOFF BECOMES INCREASINGLY STRINGENT AS REGIONAL RICHNESS INCREASES THEREFORE COMMUNITIES BECOME INCREASINGLY RESISTANT TO INVASION AS MORE SPECIES ARE ADDED TO THE REGION 3HURIN AND !LLEN .EUTRAL MODELS PREDICT THAT SPECIES CAN ALWAYS INVADE LOCAL COMMUNITIES REGARDLESS OF LOCAL DIVERSITY AND THE RATE OF LOCAL DISPERSAL BECAUSE THE DEMOGRAPHIC PROPERTIES OF INDIVIDUALS ARE EQUIVALENT #ONSEQUENTLY RESIDENT SPECIES ARE UNABLE TO EXCLUDE INVADERS FROM LOCAL COMMUNITIES 3PECIES SORTING MODELS PREDICT THAT DISPERSAL IS FREQUENT ENOUGH TO ALLOW LOCAL ASSEMBLY PROCESSES TO REACH THEIR @END POINT TRAJECTORIES AND THAT COMMUNITIES THEREFORE RESIST FURTHER INVASIONS 3OURCE SINK MODELS PREDICT THAT COMMUNITIES BECOME HARDER TO INVADE WITH INCREASING DISPERSAL BEYOND THE MAXIMUM LOCAL RICHNESS POINT ,OCAL RICHNESS PLATEAUS UNDER MODERATE LEVELS OF LOCAL DISPERSAL -OUQUET AND ,OREAU ABOVE WHICH COMMUNITIES BECOME INCREASINGLY DIFlCULT TO INVADE BECAUSE BETTER REGIONAL COMPETITORS DISPERSERS ELIMINATE OTHER SPECIES #HASE ET AL
3! 3MITH AND *" 3HURIN
&IG 4HE RELATIONSHIPS AMONG THE FOUR MAJOR METACOMMUNITY PARADIGMS IN TERMS OF THEIR ASSUMPTIONS ABOUT INTERACTION INTENSITY SPATIAL HETEROGENEITY AND DISPERSAL 0ATCH DYNAMICS MODELS ASSUME SLOW DISPERSAL RELATIVE TO EXTINCTION PROBABILITIES AND EITHER INTERACTIVE EG COMPETITION COLONIZATION TRADEOFFS OR NON INTERACTIVE COMMUNITIES 3PECIES SORTING ASSUMES DISPERSAL IS FAST RELATIVE TO EXTINCTION BUT SLOW RELATIVE TO LOCAL DEMOGRAPHIC RATES HIGH SPATIAL HETEROGENEITY AND STRONG INTERACTIONS .EUTRAL MODELS ASSUME A CONTINUUM OF DISPERSAL RATES STRONG LOCAL INTERACTIONS WITH PRE EMPTIVE COMPETITION AND HOMOGENEOUS PATCHES 3OURCE SINK MODELS ASSUME THAT DISPERSAL IS RAPID RELATIVE TO LOCAL DYNAMICS HIGH SPATIAL HETEROGENEITY IN lTNESS AMONG PATCHES AND STRONG LOCAL INTERACTIONS
-ETACOMMUNITY MODELS ALSO DIFFER IN THEIR PREDICTIONS ABOUT COMMUNITY SATU RATION "OTH NON INTERACTIVE PATCH DYNAMIC MODELS AND NEUTRAL THEORY PREDICT THAT LOCAL DIVERSITY IS NEVER SATURATED AND NEW SPECIES CAN ALWAYS BE ADDED TO LOCAL COMMUNITIES !T HIGH LEVELS OF LOCAL DISPERSAL AND SPECIES RICHNESS HOWEVER NEUTRAL THEORY PREDICTS THAT GREATER IMMIGRATION WILL INCREASE THE RATE AT WHICH COMMUNITY COMPOSITION TURNS OVER IN LOCAL COMMUNITIES DUE TO FASTER EXTINCTION OF RESIDENT SPECIES )F MORE SPECIES ARE ADDED TO LOCAL COMMUNITIES THE AVERAGE POPULATION SIZE OF RESIDENT SPECIES MUST DECREASE UNDER ZERO SUM DYNAMICS RENDERING RARE SPECIES MORE SUSCEPTIBLE TO STOCHASTIC mUCTUATIONS IN POPULATION SIZES )N CONTRAST SPECIES SORTING PATCH DYNAMICS WITH INTERACTIONS AND MASS EFFECTS MODELS ALL PREDICT SATURATION OF DIVERSITY )N INTERACTIVE PATCH DYNAMICS AND MASS EFFECTS MODELS LOCAL COMMUNITIES APPROACH SATURATION WITH INCREASED
%VIDENCE FOR INVASIBILITY AND SATURATION
DISPERSAL BECAUSE IT BECOMES MORE DIFlCULT FOR NEW SPECIES TO SATISFY THE NECES SARY TRADE OFF BETWEEN DISPERSAL ABILITY AND THE POTENTIAL TO EXCLUDE OTHER SPECIES 3HURIN AND !LLEN -OREOVER IN MASS EFFECTS MODELS SOURCE SINK DYNAM ICS BREAKDOWN AT HIGH DISPERSAL RATES AND BETTER REGIONAL COMPETITORS ELIMINATE OTHER SPECIES -OUQUET AND ,OREAU )N PURE SPECIES SORTING MODELS WITHOUT DISPERSAL LIMITATION EXOTIC SPECIES ARE UNLIKELY TO BE ABLE TO INVADE BECAUSE THE COMMUNITY IS COLLECTIVELY WELL ADAPTED TO LOCAL CONDITIONS ,OCAL COMMUNITIES ARE THEREFORE ASSUMED TO BE SATURATED UNDER THE SPECIES SORTING PARADIGM
4ABLE 0REDICTIONS OF THE MAJOR METACOMMUNITY PARADIGMS REGARDING THE INVASIBILITY AND SATURATION OF ECOLOGICAL COMMUNITIES 0ARADIGM )NVASIBLE 3ATURATED 0ATCH DYNAMICS 9ES .O NON INTERACTIVE 0ATCH DYNAMICS WITH STRONG COMPETITIVE EXCLUSION
9ES BUT INCREASINGLY DIFlCULT WITH INCREASING DIVERSITY
9ES INCREASINGLY DIFlCULT AT HIGH DIVERSITY TO SATISFY COLONIZATIONCOMPETITION TRADE OFF
.EUTRAL
9ES
.O BUT COMMUNITY COMPOSITION TURNS OVER MORE RAPIDLY WITH INCREASING SPECIES RICHNESS
3PECIES SORTING
.O
9ES
-ASS EFFECTS
9ES BUT INCREASINGLY DIFlCULT WITH INCREASING DIVERSITY AND FREQUENCY OF LOCAL DISPERSAL
9ES INCREASINGLY DIFlCULT AT HIGH DIVERSITY AND DISPERSAL TO SATISFY COLONIZATION COMPETITION TRADE OFF
0ATTERNS OF INVASIBILITY AND SATURATION FROM THE BIOLOGICAL INVASIONS LITERATURE ARE USEFUL FOR EVALUATING THE ABILITY OF THE FOUR METACOMMUNITY PARADIGMS TO DESCRIBE COMMUNITY STRUCTURE AND DYNAMICS 4HE lNDING THAT MOST COMMUNI TIES ARE INVASIBLE AND UNSATURATED IS CONSISTENT WITH THE PREDICTIONS OF ANY OF THE MODELS ASSUMING DISPERSAL LIMITATION PATCH DYNAMICS NEUTRAL AND MASS EFFECTS
3! 3MITH AND *" 3HURIN
AND CHALLENGES THE PREDICTION OF SPECIES SORTING THAT COMMUNITIES RESIST INVASION BECAUSE THEY ARE SATURATED WITH SPECIES 4HE OBSERVATION OF MANY INTRODUCTIONS AND FEW EXTINCTIONS IS INCONSISTENT WITH MODELS WHERE REGIONAL COEXISTENCE OCCURS THROUGH SPATIAL REFUGIA INTERACTIVE PATCH DYNAMICS AND MASS EFFECTS 4HESE MODELS PREDICT THAT ENHANCED IMMIGRATION CAN RESULT IN LOSS OF DIVERSITY THROUGH GREATER EXCLUSION BY GOOD COMPETITORS THAT ARE WEAK DISPERSERS -OUQUET AND ,OREAU 4HE EXPERIMENTAL RESULT OF DECLINING INVASION SUCCESS WITH INCREAS ING LOCAL DIVERSITY HOWEVER IS INCONSISTENT WITH NEUTRAL AND NON INTERACTIVE PATCH DYNAMICS MODELS BUT CONSISTENT WITH ALL THE OTHER METACOMMUNITY MODELS 4HE DISCREPANCY BETWEEN PATTERNS AT LOCAL VS REGIONAL SCALES COULD REmECT THE RELA TIVE IMPORTANCE OF DIFFERENT MECHANISMS OPERATING AT VARYING SPATIAL SCALES 3PECIES RICHNESS MIGHT BE MORE IMPORTANT IN DETERMINING INVASION SUCCESS AT LOCAL SCALES WHEREAS OTHER ECOLOGICAL FACTORS SUCH AS PROPAGULE PRESSURE OR RESOURCE AVAILABIL ITY MIGHT GOVERN PATTERNS OF COMMUNITY INVASIBILITY AND SATURATION AT COMMU NITY WIDE SCALES ,EVINE +ENNEDY ET AL "YERS AND .OONBURG /NE EXPLANATION FOR THIS PATTERN IS THAT CHANGES IN THE NUMBER OF AVAILABLE RESOURCES AS WELL AS DISTURBANCE OR PROPAGULE PRESSURE CAN CAUSE INVASION SUCCESS TO BECOME POSITIVELY CORRELATED WITH DIVERSITY AT LARGE SCALES BY DECREASING MEAN INTERACTION STRENGTH AMONG COMPETING SPECIES "YERS AND .OONBURG 0ATTERNS IN THE BIOLOGICAL INVASIONS LITERATURE SUGGEST THAT NON INTERACTIVE PATCH DYNAMICS AND NEUTRAL MODELS SUCCESSFULLY PREDICT THE DYNAMICS OF INVA SIONS AND EXTINCTIONS AT LARGE SPATIAL SCALES WHILE FAILING TO INCORPORATE THE MECHANISMS RESPONSIBLE FOR INVASION RESISTANCE WITH INCREASING DIVERSITY AT SMALL SPATIAL SCALES )NTERACTIVE PATCH DYNAMICS AND MASS EFFECTS MODELS ADEQUATELY DESCRIBE PATTERNS AT SMALL AND LARGER SPATIAL SCALES (OWEVER THE PREDICTION OF DECLINING DIVERSITY AT THE HIGHEST LEVELS OF DISPERSAL WAS NOT BORN OUT 4HE INVA SIBILITY AND UNDERSATURATION OF COMMUNITIES IS NOT PREDICTED BY SPECIES SORTING MODELS WITH GLOBAL DISPERSAL OR BY INTERACTIVE PATCH DYNAMICS AND MASS EFFECTS MODELS WITH EXTREMELY HIGH RATES OF DISPERSAL (OWEVER THE DECLINE IN INVASION SUCCESS AT HIGHER DIVERSITY AND THE LARGE EFFECTS OF DISTURBANCE IN WEAKENING BIOTIC RESISTANCE TO INVASION FOUND IN THE EXPERIMENTAL LITERATURE SUPPORTS THE SPECIES SORTING PERSPECTIVE
#/.#,53)/. 2ECONCILING SMALL SCALE MECHANISTIC STUDIES OF THE FACTORS THAT ALLOW OR PRE VENT INVASION WITH BROAD SCALE PATTERNS OF DIVERSITY GAIN AND LOSS REMAINS ONE OF THE MOST PRESSING CHALLENGES IN COMMUNITY ECOLOGY AND INVASION BIOLOGY 4HE UNDER SATURATION OF ECOLOGICAL COMMUNITIES EVIDENT FROM MACRO SCALE PAT TERNS OF INVASION AND EXTINCTION IN FAUNAL EXCHANGES AND CONTEMPORARY INVA SIONS HAS BEEN INTERPRETED AS INDICATING THAT LOCAL INTERACTIONS EXERT RELATIVELY WEAK INmUENCE OVER COMMUNITY STRUCTURE 3TOHLGREN ET AL 3AX AND 'AINES (OWEVER EVEN STRONG LOCAL COMPETITIVE INTERACTIONS CAN PLAY OUT VERY
%VIDENCE FOR INVASIBILITY AND SATURATION
SLOWLY OVER BROAD HETEROGENEOUS LANDSCAPES LEADING TO PATTERNS OF INVASIBIL ITY AND UNSATURATED COMMUNITIES AT REGIONAL SCALES &URTHERMORE EXPERIMENTAL INTRODUCTIONS PROVIDE EVIDENCE THAT LOCAL ECOLOGICAL INTERACTIONS PLAY A MAJOR ROLE IN DETERMINING THE SUCCESS OR FAILURE OF INVASIONS 4HE APPARENT UNSATURATION OF COMMUNITIES DOES NOT THEREFORE LEND SUPPORT TO A STRICTLY DISPERSAL LIMITED NON INTERACTIVE VIEW OF ECOLOGICAL COMMUNITIES $ISPERSAL AND LOCAL INTERACTIONS HAVE LONG BEEN TREATED AS MUTUALLY EXCLUSIVE ALTERNATIVE EXPLANATIONS FOR COMMUNITY STRUCTURE (OWEVER RECENT THEORETICAL WORK HAS REVEALED A NUMBER OF WAYS IN WHICH DISPERSAL AND LOCAL INTERACTIONS CAN JOINTLY REGULATE COMMUNITY STRUCTURE 3HURIN AND !LLEN "YERS AND .OONBURG -OUQUET AND ,OREAU 4HE MOVEMENT OF INDIVIDUALS AMONG PATCHES GIVES COHERENCE TO LOCAL COMPETITIVE INTERACTIONS WITHIN A REGION AND THEREFORE LOCAL COMMUNITY DYNAMICS MAY PLAY THEMSELVES OUT AT REGIONAL SPATIAL SCALES 2ICKLEFS )NDEED THE METACOMMUNITY APPROACH SUGGESTS THAT PROCESSES WHICH HAVE TRADITIONALLY BEEN CONSIDERED LOCAL AND REGIONAL IN NATURE NOW NEED TO BE SEEN AS SPATIALLY LINKED %XTENDING LOCAL COMPETITIVE INTERACTIONS TO A BROAD REGION SLOWS THE TIME SCALE OF COMPETITIVE EXCLUSION TO THAT OF SPECIES PRODUCTION 2ICKLEFS WHICH HAS IMPORTANT IMPLICATIONS FOR INVASIONS BIOLOGISTS 'LOBAL EXTINCTIONS MAY LAG BEHIND THE WAVE OF INVASIONS SO THAT MANY PENDING LOCAL EXTIRPATION EVENTS HAVE NOT YET OCCURRED &INALLY THE LITERATURE ON INVASIONS AND EXTINCTIONS REVEALS THAT THE APPARENT PATTERNS ARE STRONGLY SCALE DEPENDENT )NVASION MAY INCREASE BOTH LOCAL EG 4ABLE AND REGIONAL DIVERSITY 3AX AND 'AINES HOWEVER IT IS APPAR ENT THAT BETA DIVERSITY OR REGIONAL DISTINCTIVENESS IN COMPOSITION IS DECLINING 4HE HOMOGENIZATION OF THE BIOSPHERE IS OCCURRING AT EVER INCREASING RATES -C+INNEY AND ,OCKWOOD 2AHEL 3YNERGISTIC INTERACTIONS AMONG INVADERS LEADING TO BIOLOGICAL MELTDOWNS 3IMBERLOFF AND 6ON (OLLE 2ICCIARDI AND AMONG OTHER HUMAN MEDIATED THREATS TO GLOBAL BIODIVERSITY 3ALA ET AL WILL CERTAINLY INCREASE THE VULNERABILITY OF NATURAL COMMUNI TIES TO THE INTRODUCTION OF EXOTIC SPECIES 4HE CONTINUOUS AND EVER INCREASING RAIN OF PROPAGULES OF EXOTIC SPECIES -AC)SAAC ET AL 'RIGOROVICH ET AL CONTINUES TO EXCEED THE ABILITY OF NATURAL COMMUNITIES TO REPEL THEM $ESPITE DOCUMENTED EVIDENCE THAT LOCAL COMMUNITIES RESIST INVASIONS SECTION MACRO SCALE PATTERNS OF BIOTIC INTERCHANGES AND BIOLOGICAL INVASIONS SECTIONS AND SUGGEST THAT IT IS UNLIKELY THAT LOCAL COMMUNITIES CAN BE MANAGED IN WAYS THAT WILL PREVENT ALL INVASIONS &URTHERMORE INCREASED FREQUENCY OF HUMAN MEDIATED TRANSPORT OF EXOTIC SPECIES COUPLED WITH THE INCREASED VULNERABILITY OF ECOSYSTEMS TO INVASION WILL CERTAINLY INCREASE THE PROBABILITY OF INTRODUCING EXOTIC SPECIES WITH NOVEL ECOLOGICAL FUNCTIONS INTO NAÕVE ECOSYSTEMS 3UCH INVASION EVENTS CLEARLY HAVE DISASTROUS REPERCUSSIONS ON THE SPECIES RICHNESS AS WELL AS THE FUNC TIONING OF LOCAL ECOSYSTEMS +AUFMAN .ALEPA AND 3CHLOESER &RITTS AND 2ODDA 6ANDERPLOEG ET AL )N ORDER TO CURTAIL THE INTRODUCTION OF EXOTIC SPECIES AND PREVENT THEIR SOMETIMES DISASTROUS CONSEQUENCES OUR RESULTS SUGGEST THAT MANAGERS AND POLICY MAKERS ALIKE NEED TO FOCUS EFFORTS ON MANAGING
3! 3MITH AND *" 3HURIN
DISPERSAL VECTORS AND PREVENTING THE ESTABLISHMENT OF EXOTIC SPECIES RATHER THAN RELYING ON INTACT NATIVE COMMUNITIES TO REPEL INVADERS
!#+./7,%$'%-%.43 4HE AUTHORS WOULD LIKE TO THANK 2OD $OCKING *OANNA -ACKENZIE 2 #RAIG -AC,EAN AND -ICHELLE 0ALMER FOR HELPFUL COMMENTS ON A PREVIOUS DRAFT OF THIS MANUSCRIPT 3!3 WAS SUPPORTED BY AN .3%2# 0'3 " !N .3%2# GRANT TO *"3 PROVIDED ADDITIONAL FUNDING
2%&%2%.#%3 "AKKER 2 4 4HE DEER mEES THE WOLF PURSUES INCONGUENCIES IN PREDATOR PREY EVO LUTION 0AGES IN $ &UTUYMA AND - 3LATKIN EDITORS #OEVOLUTION 3INAUER 3UNDERLAND "ARRY * # - % -ORGAN ! * 7INKLER , * &LYNN % ( ,INDAY , , *ACOBS AND $ 0ILBEAM &AUNAL INTERCHANGE AND -IOCENE TERRESTRIAL VERTEBRATES OF SOUTHERN !SIA 0ALEOBIOLOGY "ELL ' .EUTRAL -ACROECOLOGY 3CIENCE "EN 4UVIA ! 4HE IMPACT OF THE ,ESSEPSIAN 3UEZ #ANAL &ISH MIGRATION ON THE EAST ERN -EDITERRANEAN ECOSYSTEM 0AGES IN - -ORAITOU !POSTOLOPOULOU AND 6 +IORTSIS EDITORS -EDITERRANEAN MARINE ECOSYSTEMS 0LENUM 0RESS .EW 9ORK "ERMINGHAM % AND ! 0 -ARTIN #OMPARATIVE MT$.! PHYLOGEOGRAPHY OF NEO TROPICAL FRESHWATER lSHES TESTING SHARED HISTORY TO INFER THE EVOLUTIONARY LANDSCAPE OF LOWER #ENTRAL !MERICA -OLECULAR %COLOGY "ROWN * ( 4 * 6ALONE AND # ' #URTIN 2EORGANIZATION OF AN ARID ECOSYSTEM IN RESPONSE TO RECENT CLIMATE CHANGE 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCE "ROWN * ( 3 + -ORGAN %RNEST * - 0ARODY AND * 0 (ASKELL 2EGULATION OF DIVERSITY MAINTENANCE OF SPECIES RICHNESS IN CHANGING ENVIRONMENTS /ECOLOGIA "URKE - * 7 AND * 0 'RIME !N EXPERIMENTAL STUDY OF PLANT COMMUNITY INVASI BILITY %COLOGY "YERS * % AND % ' .OONBURG 3CALE DEPENDENT EFFECTS OF BIOTIC RESISTANCE TO BIOLOGI CAL INVASIONS %COLOGY #ASE 4 * 'LOBAL PATTERNS IN THE ESTABLISHMENT AND DISTRIBUTION OF EXOTIC BIRDS "IOLOGICAL #ONSERVATION #ASWELL ( AND * % #OHEN ,OCAL AND REGIONAL REGULATION OF SPECIES AREA RELATIONS A PATCH OCCUPANCY MODEL 0AGES IN 2 % 2ICKLEFS AND $ 3CHLUTER EDITORS 3PECIES DIVERSITY IN ECOLOGICAL COMMUNITIES (ISTORICAL AND GEOGRAPHICAL PERSPECTIVES 5NIVERSITY OF #HICAGO 0RESS #HICAGO
%VIDENCE FOR INVASIBILITY AND SATURATION
#HASE * - AND - ! ,EIBOLD %COLOGICAL NICHES LINKING CLASSICAL AND CONTEMPORARY APPROACHES 5NIVERSITY OF #HICAGO 0RESS #HICAGO #HASE * 0 !MARASEKARE + #OTTENIE ! 'ONZALEZ 2 (OLT - (OLYOAK - (OOPES - ,EI BOLD - ,OREAU . -OUQUET * " 3HURIN AND $ 4ILMAN #OMPETING THEO RIES FOR COMPETITIVE METACOMMUNITIES 0AGES IN - (OLYOAK 2 (OLT AND - ,EIBOLD EDITORS -ETACOMMUNITIES )N 0RESS #OHEN ! . AND * 4 #ARLTON !CCELERATING INVASION RATE IN A HIGHLY INVADED ESTUARY 3CIENCE #ORNELL ( 6 3PECIES ASSEMBLAGES OF #YNIPID 'ALL 7ASPS ARE NOT SATURATED !MERICAN .ATURALIST #ORNELL ( 6 5NSATURATED PATTERNS IN SPECIES ASSEMBLAGES THE ROLE OF REGIONAL PROCESSES IN SETTLING LOCAL SPECIES RICHNESS 0AGES IN 2 % 2ICKLEFS AND $ 3CHLUTER EDITORS 3PECIES DIVERSITY IN ECOLOGICAL COMMUNITIES HISTORICAL AND GEOGRAPHICAL PERSPECTIVES 5NIVERSITY OF #HICAGO 0RESS #HICAGO #ORNELL ( 6 5NSATURATION AND REGIONAL INmUENCES ON SPECIES RICHNESS IN ECOLOGICAL COMMUNITIES ! REVIEW OF THE EVIDENCE %COSCIENCE #ORNELL ( 6 AND * ( ,AWTON 3PECIES INTERACTIONS LOCAL AND REGIONAL PROCESSES AND LIMITS TO THE RICHNESS OF ECOLOGICAL COMMUNITIES A THEORETICAL PERSPECTIVE *OURNAL OF !NIMAL %COLOGY $AVIS - ! "IOTIC GLOBALIZATION $OES COMPETITION FROM INTRODUCED SPECIES THREATEN BIODIVERSITY "IOSCIENCE $IAMOND * - AND # 2 6EITCH %XTINCTIONS AND INTRODUCTIONS IN THE .EW :EALAND AVIFAUNA CAUSE AND EFFECT 3CIENCE $UNCAN * 2 AND * , ,OCKWOOD 3PATIAL HOMOGENIZATION OF THE AQUATIC FAUNA OF 4ENNESSEE EXTINCTION AND INVASION FOLLOWING LAND USE CHANGE AND HABITAT ALTERATION 0AGES IN * , ,OCKWOOD AND - , -C+INNEY EDITORS "IOTIC HOMOGENIZATION +LUWER !CADEMIC 0RESS0LENUM 0UBLISHERS .EW 9ORK $UNCAN 2 0 4 - "LACKBURN AND $ 3OL 4HE ECOLOGY OF BIRD INTRODUCTIONS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS &ARGIONE * # 3 "ROWN AND $ 4ILMAN #OMMUNITY ASSEMBLY AND INVASION !N EXPERIMENTAL TEST OF NEUTRAL VERSUS NICHE PROCESSES 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES OF THE 5NITED 3TATES OF !MERICA &OSTER " , #ONSTRAINTS ON COLONIZATION AND SPECIES RICHNESS ALONG A GRASSLAND PRODUCTIVITY GRADIENT THE ROLE OF PROPAGULE AVAILABILITY %COLOGY ,ETTERS &OSTER " , 6 ( 3MITH 4 , $ICKSON AND 4 (ILDEBRAND )NVASIBILITY AND COM POSITIONAL STABILITY IN A GRASSLAND COMMUNITY RELATIONSHIPS TO DIVERSITY AND EXTRINSIC FACTORS /IKOS &OSTER " , AND $ 4ILMAN 3EED LIMITATION AND THE REGULATION OF COMMUNITY STRUC TURE IN OAK SAVANNA GRASSLAND *OURNAL OF %COLOGY &OX * 7 * -C'RADY 3TEED AND / , 0ETCHEY 4ESTING FOR LOCAL SPECIES SATURATION WITH NONINDEPENDENT REGIONAL SPECIES POOLS %COLOGY ,ETTERS &RITTS 4 ( AND ' ( 2ODDA 4HE ROLE OF INTRODUCED SPECIES IN THE DEGRADATION OF ISLAND ECOSYSTEMS ! CASE HISTORY OF 'UAM !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS
3! 3MITH AND *" 3HURIN
&LYNN , * 2 ( 4EDFORD AND 1 :HANXIANG %NRICHMENT AND STABILITY IN THE 0LIOCENE MAMMALIAN FAUNA OF .ORTH #HINA 0ALEOBIOLOGY &UKAMI 4 #OMMUNITY ASSEMBLY ALONG A SPECIES POOL GRADIENT IMPLICATIONS FOR MULTIPLE SCALE PATTERNS OF DIVERSITY 0OPULATION %COLOGY 'ASTON + * 'LOBAL PATTERNS IN BIODIVERSITY .ATURE 'ASTON + * %COLOGY THE HOW AND WHY OF BIODIVERSITY .ATURE 'IDO + " AND * ( "ROWN )NVASION OF .ORTH !MERICAN DRAINAGES BY ALIEN lSH SPE CIES &RESHWATER "IOLOGY 'RIGOROVICH ) ! 2 ) #OLAUTTI % , -ILLS + (OLECK ! ' "ALLERT AND ( * -AC)SAAC "ALLAST MEDIATED ANIMAL INTRODUCTIONS IN THE ,AURENTIAN 'REAT ,AKES RETRO SPECTIVE AND PROSPECTIVE ANALYSES #ANADIAN *OURNAL OF &ISHERIES AND !QUATIC 3CIENCE 'UREVITCH * AND $ + 0ADILLA !RE INVASIVE SPECIES A MAJOR CAUSE OF EXTINCTIONS 4RENDS IN %COLOGY AND %VOLUTION (ASTINGS ! $ISTURBANCE COEXISTENCE HISTORY AND COMPETITION FOR SPACE 4HEORETICAL 0OPULATION "IOLOGY (OBBS 2 * AND ( ! -OONEY "ROADENING THE EXTINCTION DEBATE POPULATION DELETIONS AND ADDITIONS IN #ALIFORNIA AND 7ESTERN !USTRALIA #ONSERVATION "IOLOGY (UBBELL 3 0 4HE UNIlED THEORY OF BIODIVERSITY AND BIOGEOGRAPHY 0RINCETON 5NIVERSITY 0RESS 0RINCETON +AUFMAN , #ATASTROPHIC CHANGE IN SPECIES RICH FRESHWATER ECOSYSTEMS THE LESSONS OF ,AKE 6ICTORIA "IO3CIENCE +EIT 4 ( AND 0 ! -ARQUET 4HE INTRODUCED (AWAIIAN AVIFAUNA RECONSIDERED %VIDENCE FOR SELF ORGANIZATION AND CRITICALITY *OURNAL OF 4HEORETICAL "IOLOGY +ENNEDY 4 ! 3 .AEEM + - (OWE * - ( +NOPS $ 4ILMAN AND 0 2EICH "IODIVERSITY AS A BARRIER TO ECOLOGICAL INVASION .ATURE ,EIBOLD - ! - (OLYOAK . -OUQUET 0 !MARASEKARE * - #HASE - & (OOPES 2 $ (OLT * " 3HURIN 2 ,AW $ 4ILMAN - ,OREAU AND ! 'ONZALEZ 4HE METACOM MUNITY CONCEPT A FRAMEWORK FOR MULTI SCALE COMMUNITY ECOLOGY %COLOGY ,ETTERS ,ESSA % 0 " 6 6ALKENBURGH AND 2 ! &ARINA 4ESTING HYPOTHESES OF DIFFEREN TIAL MAMMALIAN EXTINCTIONS SUBSEQUENT TO THE 'REAT !MERICAN "IOTIC )NTERCHANGE 0ALAEOGEOGRAPHY 0ALAEOCLIMATOLOGY 0ALAEOECOLOGY ,EVINE * - 3PECIES DIVERSITY AND BIOLOGICAL INVASIONS 2ELATING LOCAL PROCESS TO COMMUNITY PATTERN 3CIENCE ,EVINE * - ,OCAL INTERACTIONS DISPERSAL AND NATIVE AND EXOTIC PLANT DIVERSITY ALONG A #ALIFORNIA STREAM /IKOS ,EVINS 2 AND $ #ULVER 2EGIONAL COEXISTENCE OF SPECIES AND COMPETITION BETWEEN RARE SPECIES 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCE ,INBERG $ 2 -ARINE BIOTIC INTERCHANGE BETWEEN THE .ORTHERN AND 3OUTHERN HEMI SPHERES 0ALEOBIOLOGY ,ODGE $ - "IOLOGICAL INVASIONS ,ESSONS FOR ECOLOGY 4RENDS IN %COLOGY AND %VOLUTION
%VIDENCE FOR INVASIBILITY AND SATURATION
,OSOS * " AND $ 3CHLUTER !NALYSIS OF AN EVOLUTIONARY SPECIES AREA RELATIONSHIP .ATURE -AC)SAAC ( * 4 # 4HOMAS # 2OBBINS AND - ! ,EWIS -ODELING SHIPS BALLAST WATER AS INVASION THREATS TO THE 'REAT ,AKES #ANADIAN *OURNAL OF &ISHERIES AND !QUATIC 3CIENCE -ARCHETTI - 0 4 ,IGHT * &ELICIANO 4 !RMSTRONG : (OGAN * 6IERS AND 0 " -OYLE (OMOGENIZATION OF #ALIFORNIAS lSH FAUNA THROUGH ABIOTIC CHANGE 0AGES IN * , ,OCKWOOD AND - , -C+INNEY EDITORS "IOTIC (OMOGENIZATION +LUWER !CADEMIC 0RESS0LENUM 0UBLISHERS .EW 9ORK -ARSHALL , ' 4HE 'REAT !MERICAN "IOTIC )NTERCHANGE AN INVASION INmUENCED CRISIS FOR 3OUTH !MERICAN MAMMALS 0AGES IN - ( .ITECKI EDITOR "IOTIC CRISES IN ECOLOGICAL AND EVOLUTIONARY TIME !CADEMIC 0RESS .EW 9ORK -ARSHALL , ' AND 2 , #IFELLI !NALYSIS OF CHANGING DIVERSITY PATTERNS IN #ENOZOIC LAND MAMMAL AGE FAUNA 3OUTH !MERICA 0ALAEOVERTEBRATA -C+INNEY - , AND * , ,OCKWOOD "IOTIC HOMOGENIZATION A FEW WINNERS REPLACING MANY LOSERS IN THE NEXT MASS EXTINCTION 4RENDS IN %COLOGY %VOLUTION -ORA # 0 - #HITTARO 0 & 3ALE * 0 +RITZER AND 3 ! ,UDSIN 0ATTERNS AND PRO CESSES IN REEF lSH DIVERSITY .ATURE -OUQUET . AND - ,OREAU #OMMUNITY PATTERNS IN SOURCE SINK METACOMMUNITIES !MERICAN .ATURALIST -OUQUET . 0 ,EADLEY * -ERIGUET AND - ,OREAU )MMIGRATION AND LOCAL COM PETITION IN HERBACEOUS PLANT COMMUNITIES A THREE YEAR SEED SOWING EXPERIMENT /IKOS -OYLE 0 " AND 4 ,IGHT "IOLOGICAL INVASIONS OF FRESH WATER EMPIRICAL RULES AND ASSEMBLY THEORY "IOLOGICAL #ONSERVATION .ALEPA & 4 AND $ 7 3CHLOESSER :EBRA MUSSELS "IOLOGY IMPACTS AND CONTROL ,EWIS 0UBLISHERS "OCA 2ATON 0ERDICES ! % "ERMINGHAM ! -ONTILLA AND ) $OADRIO %VOLUTIONARY HISTORY OF THE GENUS 2HAMDIA 4ELEOSTEI 0IMELODIDAE IN #ENTRAL !MERICA -OLECULAR 0HYLOGENETICS AND %VOLUTION 0OR & $ ,ESSEPSIAN -IGRATION 4HE INmUX OF THE 2ED 3EA "IOTA INTO THE -EDITERRANEAN BY WAY OF THE 3UEZ #ANAL 6ERLAG "ERLIN 0OR & $ 4HE LEGACY OF 4ETHYS !N AQUATIC BIOGEOGRAPHY OF THE ,EVANT +LUWER !CADEMIC 0RESS ,ONDON 2AHEL & * (OMOGENIZATION OF lSH FAUNAS ACROSS THE 5NITED 3TATES 3CIENCE 2AHEL & * (OMOGENIZATION OF FRESHWATER FAUNAS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS 2ICCIARDI ! &ACILITATIVE INTERACTIONS AMONG AQUATIC INVADERS IS AN hINVASIONAL MELTDOWNv OCCURRING IN THE 'REAT ,AKES #ANADIAN *OURNAL OF &ISHERIES AND !QUATIC 3CIENCE 2ICCIARDI ! !SSESSING SPECIES INVASIONS AS A CAUSE OF EXTINCTION 4RENDS IN %COLOGY AND %VOLUTION
3! 3MITH AND *" 3HURIN
2ICKLEFS 2 % #OMMUNITY DIVERSITY RELATIVE ROLES OF LOCAL AND REGIONAL PROCESSES 3CIENCE 2ICKLEFS 2 % ! COMPREHENSIVE FRAMEWORK FOR GLOBAL PATTERNS IN BIODIVERSITY %COLOGY ,ETTERS 2ICKLEFS 2 % AND % "ERMINGHAM .ONEQUILIBIRUM $IVERSITY $YNAMICS OF THE ,ESSER !NTILLEAN !VIFAUNA 3CIENCE 3ALA / % & 3 #HAPIN * * !RMESTO % "ERLOW * "LOOMlELD 2 $IRZO % (UMBER 3ANWALD , & (UENNEKE 2 " *ACKSON ! +INZIG 2 ,EEMANS $ - ,ODGE ( ! -OONEY - /ESTERHELD . ,E2OY 0OFF - 4 3YKES " ( 7ALKER - 7ALKER AND $ ( 7ALL 'LOBAL BIODIVERSITY SCENARIOS FOR THE YEAR 3CIENCE 3AX $ & 3 $ 'AINES AND * ( "ROWN 3PECIES INVASIONS EXCEED EXTINCTIONS ON ISLANDS WORLDWIDE ! COMPARATIVE STUDY OF PLANTS AND BIRDS !MERICAN .ATURALIST 3AX $ & AND 3 $ 'AINES 3PECIES DIVERSITY FROM GLOBAL DECREASES TO LOCAL INCREASES 4RENDS IN %COLOGY AND %VOLUTION 3EABLOOM % 7 7 3 (ARPOLE / * 2EICHMAN AND $ 4ILMAN )NVASION COM PETITIVE DOMINANCE AND RESOURCE USE BY EXOTIC AND NATIVE #ALIFORNIA GRASSLAND SPECIES 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES OF THE 5NITED 3TATES OF !MERICA 3HMIDA ! AND 3 %LLNER #OEXISTENCE OF PLANT SPECIES WITH SIMILAR NICHES 6EGETATIO 3HURIN * " $ISPERSAL LIMITATION INVASION RESISTANCE AND THE STRUCTURE OF POND ZOOPLANKTON COMMUNITIES %COLOGY 3HURIN * " AND % ' !LLEN %FFECTS OF COMPETITION PREDATION AND DISPERSAL ON SPE CIES RICHNESS AT LOCAL AND REGIONAL SCALES !MERICAN .ATURALIST 3HURIN * " AND $ 3 3RIVASTAVA .EW PERSPECTIVES ON LOCAL AND REGIONAL DIVERSITY BEYOND SATURATION 0AGES IN - (OLYOAK - ,EIBOLD AND 2 (OLT EDITORS -ETACOMMUNITIES SPATIAL DYNAMICS AND ECOLOGICAL COMMUNITIES 5NIVERSITY OF #HICAGO 0RESS #HICAGO 3IMBERLOFF $ %XTINCTION SURVIVAL AND EFFECTS OF BIRDS INTRODUCED TO THE -ASCA RENES !CTA /ECOLOGIA 3IMBERLOFF $ AND " 6 (OLLE 0OSITIVE INTERACTIONS OF NONINDIGENOUS SPECIES INVA SIONAL MELTDOWN "IOLOGICAL )NVASIONS 3IMPSON ' ' (ISTORY OF THE FAUNA OF ,ATIN !MERICA !MERICAN *OURNAL OF 3CIENCE 3IMPSON ' ' 3PLENDID ISOLATION THE CURIOUS HISTORY OF 3OUTH !MERICAN MAMMALS 9ALE 5NIVERSITY 0RESS .EW (AVEN 3MALLWOOD + 3 3ITE INVASIBILITY BY EXOTIC BIRDS AND MAMMALS "IOLOGICAL #ONSERVATION 3MITH 3 ! AND % "ERMINGHAM 4HE BIOGEOGRAPHY OF LOWER -ESOAMERICAN FRESHWATER lSHES 3UBMITTED TO THE *OURNAL OF "IOGEOGRAPHY 3MITH 3 ! ' "ELL AND % "ERMINGHAM #ROSS #ORDILLERA EXCHANGE MEDIATED BY THE 0ANAMA #ANAL INCREASED THE SPECIES RICHNESS OF LOCAL FRESHWATER lSH ASSEMBLAGES 0ROCEEDINGS OF THE 2OYAL 3OCIETY OF ,ONDON "
%VIDENCE FOR INVASIBILITY AND SATURATION
3TOHLGREN 4 * $ "INKLEY ' 7 #HONG - ! +ALKHAN , $ 3CHELL + ! "ULL 9 /TSUKI ' .EWMAN - "ASHKIN AND 9 3ON %XOTIC PLANT SPECIES INVADE HOTSPOTS OF NATIVE PLANT DIVERSITY %COLOGICAL -ONOGRAPHS 4ERBORGH * 7 AND * &AABORG 3ATURATION AND BIRD COMMUNITIES IN THE 7EST )NDIES !MERICAN .ATURALIST 4ILMAN $ #OMPETITION AND BIODIVERSITY IN SPATIALLY STRUCTURED HABITATS %COLOGY 4ILMAN $ #OMMUNITY INVASIBILITY RECRUITMENT LIMITATION AND GRASSLAND BIODIVER SITY %COLOGY 4ILMAN $ .ICHE TRADEOFFS NEUTRALITY AND COMMUNITY STRUCTURE ! STOCHASTIC THEORY OF RESOURCE COMPETITION INVASION AND COMMUNITY ASSEMBLY 0ROCEEDINGS OF THE .ATIONAL !CADEMY OF 3CIENCES 53! 4URNBULL , ! - * #RAWLEY AND - 2EES !RE PLANT POPULATIONS SEED LIMITED ! REVIEW OF SEED SOWING EXPERIMENTS /IKOS 6ANDERPLOEG ( ! 4 & .ALEPA $ * *UDE % , -ILLS + 4 (OLECK * 2 ,IEBIG ) ! 'RIGOROVICH AND ( /JAVEER $ISPERSAL AND EMERGING ECOLOGICAL IMPACTS OF 0ONTO #ASPIAN SPECIES IN THE ,AURENTIAN 'REAT ,AKES #ANADIAN *OURNAL OF &ISHERIES AND !QUATIC 3CIENCES 6ERMEIJ ' * A )NVASION AND EXTINCTION 4HE LAST THREE MILLION YEARS OF .ORTH 3EAN PELECYPOD HISTORY #ONSERVATION "IOLOGY 6ERMEIJ ' * B 'EOGRAPHICAL RESTRICTION AS A GUIDE TO THE CAUSES OF EXTINCTION THE CASE OF THE COLD NORTHERN OCEANS DURING THE .EOGENE 0ALEOBIOLOGY 6ERMEIJ ' * A 7HEN BIOTAS MEET 5NDERSTANDING BIOTIC INTERCHANGE 3CIENCE 6ERMEIJ ' * B !NATOMY OF AN INVASION THE TRANS !RCTIC INTERCHANGE 0ALEOBIOLOGY 6ITOUSEK 0 - # - $!NTONIO , $ ,OOPE - 2EJMANEK AND 2 7ESTBROOKS )NTRODUCED SPECIES A SIGNIlCANT COMPONENT OF HUMAN CAUSED GLOBAL CHANGE .EW :EALAND *OURNAL OF %COLOGY 7ALLACE ! 2 4HE GEOGRAPHICAL DISTRIBUTION OF ANIMALS (AFNER .EW 9ORK 7EBB 3 $ AND , ' -ARSHALL (ISTORICAL BIOGEOGRAPHY OF RECENT 3OUTH !MERICAN LAND MAMMALS 0AGES IN - ! -ARES AND ( ( 'ENOWAYS EDITORS -AMMALIAN BIOLOGY IN 3OUTH !MERICA 4HE 5NIVERSITY OF 0ITTSBURGH 0ITTSBURGH 7EBB 3 $ ,ATE #ENEZOIC DISPERSALS BETWEEN THE !MERICAS 0AGES IN & ' 3TEHLI AND 3 $ 7EBB EDITORS 4HE 'REAT !MERICAN "IOTIC )NTERCHANGE 0LENUM .EW 9ORK :OBEL - - /TSUS * ,IIRA - -OORA AND 4 -OLS )S SMALL SCALE SPECIES RICHNESS LIMITED BY SEED AVAILABILITY OR MICROSITE AVAILABILITY %COLOGY
#HAPTER TWENTY
4HE BIOGEOGRAPHY OF NATURALIZED SPECIES AND THE SPECIES AREA RELATIONSHIP RECIPROCAL INSIGHTS TO BIOGEOGRAPHY AND INVASION BIOLOGY $ & 3AX AND 3 $ 'AINES
).42/$5#4)/. h(E WHO ADMITS THE DOCTRINE OF THE CREATION OF EACH SEPARATE SPECIES WILL HAVE TO ADMIT THAT A SUFlCIENT NUMBER OF THE BEST ADAPTED PLANTS AND ANIMALS HAVE NOT BEEN CREATED ON OCEANIC ISLANDS FOR MAN HAS UNINTENTIONALLY STOCKED THEM FROM VARIOUS SOURCES FAR MORE FULLY AND PERFECTLY THAN HAS NATUREv #HARLES $ARWIN $ARWIN WAS NOT ARGUING THAT SPECIES INVASION WAS A PREFERABLE CONDITION )NDEED HE ARGUED THAT INTRODUCED SPECIES WERE LIKELY TO DRIVE MANY ISLAND ENDEMICS -7 #ADOTTE ET AL EDS #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
$& 3AX AND 3$ 'AINES
ICS TO EXTINCTION )NSTEAD HE WAS DRAWING ON PATTERNS OF SPECIES INTRODUCTION AND NATURALIZATION TO MAKE INFERENCES ABOUT THE CAPACITY OF ISLANDS TO HOLD MANY MORE SPECIES THAN HAD NATURALLY COLONIZED OR EVOLVED IN SITU $ARWIN WAS CLEARLY A BROAD THINKER AND IN HIS QUEST TO UNDERSTAND THE NATURAL WORLD HE FREQUENTLY DREW UPON FORMS OF EVIDENCE THAT MIGHT BE VIEWED AS hARTIlCIALv OR hUNNATURALv &OR EXAMPLE HE DREW HEAVILY UPON EVIDENCE FROM ARTIlCIAL BREEDING TO BETTER UNDERSTAND THE PROCESS OF NATURAL SELECTION 4HEREFORE IT IS NOT SURPRISING THAT HE DREW UPON EVIDENCE FROM NATURALIZED SPECIES IE INTRODUCED SPECIES THAT FORM SELF SUSTAINING POPULATIONS TO BETTER UNDERSTAND BIOGEOGRAPHIC PRINCIPLES OF THE NATURAL WORLD "ESIDES HIS COMMENTS QUOTED ABOVE HE ALSO USED NATURALIZED SPE CIES NAMELY THEIR KNOWN RATES OF SPREAD TO INFER THAT NATIVE SPECIES WOULD HAVE HAD AMPLE TIME TO DRAMATICALLY ALTER THEIR GEOGRAPHIC RANGES DURING THE LAST GLA CIAL PERIOD 4HESE TWO OBSERVATIONS OF $ARWINS ARE BUT A FEW OF THE MANY POSSIBLE INSIGHTS THAT STUDYING NATURALIZED SPECIES CAN PROVIDE FOR THE lELDS OF BIOGEOGRA PHY AND ECOLOGY )N THIS CHAPTER WE WILL ENDEAVOR TO ACCOMPLISH SEVERAL GOALS &IRST WE REVIEW WORK DONE TO DATE POST $ARWIN THAT EXPLORES INSIGHTS THAT STUDYING NATURALIZED SPECIES CAN PROVIDE TO UNDERSTANDING NATURAL PATTERNS AND PROCESSES 3ECOND IN KEEPING WITH THE THEME OF THIS BOOK WE WILL ATTEMPT TO USE THESE SAME PATTERNS TO BETTER UNDERSTAND NATURALIZED SPECIES THEMSELVES IE TO UNDERSTAND PATTERNS AND PROCESSES RELEVANT TO INVASION BIOLOGY &INALLY WE WILL EXPLORE AN UNDERSTUDIED TOPIC IN THE BIOGEOGRAPHY OF NATURALIZED SPECIES NAMELY THE SPECIES AREA RELA TIONSHIPS OF NATURALIZED SPECIES FOCUSING AMONG OTHER TOPICS ON THE ISSUE QUOTED ABOVE BY $ARWIN IE THE CAPACITY OF ISLANDS TO HOLD ADDITIONAL SPECIES
! 2%6)%7 /& ")/'%/'2!0()# 0!44%2.3 /& .!452!,):%$ 30%#)%3 4HE lELDS OF BIOGEOGRAPHY AND INVASION BIOLOGY SHARE SIMILAR HISTORIES "OTH lELDS HAVE BEEN THE SUBJECT OF STUDY BY MANY OF THE BEST KNOWN ECOLOGISTS EVO LUTIONARY BIOLOGISTS AND NATURALISTS OF THE TH THROUGH TH CENTURIES .OTABLE CONTRIBUTIONS TO "IOGEOGRAPHY HAVE BEEN MADE BY ,INNEAUS "UFFON (OOKER $ARWIN 7ALLACE $ARLINGTON $OBZHANSKY -AYR 'RINNELL %LTON ,ACK 7ILSON AND -AC!RTHUR TO NAME BUT A FEW FOR A MORE COMPLETE LIST SEE ,OMOLINO ET AL #ONTRIBUTORS TO THE lELD OF INVASION BIOLOGY HAVE BEEN NO LESS ILLUSTRIOUS AND IN FACT ARE OFTEN MANY OF THE SAME INDIVIDUALS FOR A TREATMENT OF THIS SUB JECT SEE $AVIS THIS VOLUME $ESPITE THEIR LONG HISTORIES BOTH BIOGEOGRAPHY AND INVASION BIOLOGY HAVE ONLY RELATIVELY RECENTLY GARNERED SUFlCIENT ATTENTION TO WARRANT THE ESTABLISHMENT OF JOURNALS AND SOCIETIES DEDICATED TO THESE TOPICS FOR EXAMPLE THE *OURNAL OF "IOGEOGRAPHY WAS ESTABLISHED IN WHILE THE JOURNAL "IOLOGICAL )NVASIONS WAS ESTABLISHED IN )T IS PERHAPS NOT SURPRISING THEN THAT MOST RESEARCH THAT INTEGRATES THESE TWO lELDS HAS BEEN CONDUCTED IN THE PAST DECADE 7HILE RELATIVELY RECENT THIS BODY OF WORK HAS GREAT POTENTIAL BOTH TO INFORM OUR UNDERSTANDING OF BIOGEOGRAPHIC PATTERNS AND PROCESSES AS WELL AS TO
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
INFORM OUR UNDERSTANDING OF SPECIES INVASIONS (ERE WE REVIEW SEVERAL TOPICS THAT HAVE BEEN PARTICULARLY RELEVANT TO BOTH THESE ENDEAVORS ,ATITUDINAL GRADIENTS IN RICHNESS AND RANGE SIZE
4HE LATITUDINAL GRADIENT IN SPECIES RICHNESS FROM A PEAK IN THE TROPICS TO A MINIMA AT THE POLES IS ONE OF THE MOST GENERAL PHENOMENA IN BIOGEOGRAPHY "ROWN AND ,OMOLINO 3AX )N FACT UNLIKE MOST hGENERALv PATTERNS IN BIOLOGY THERE ARE VERY FEW KNOWN EXCEPTIONS 0ERHAPS THE BEST KNOWN OF THESE EXCEPTIONS IS THAT OF BENTHIC MARINE MACROALGAE WHICH GENERALLY PEAK IN RICHNESS AT MID LATITUDES EG 'AINES AND ,UBCHENCO ,UNING -ID OR HIGH LATITUDE PEAKS IN RICHNESS ALSO OCCUR FOR INDIVIDUAL FAMILIES AND GENERA SUCH AS ICHNEUMO NID WASPS PENGUINS AND PINES "ROWN AND ,OMOLINO 3TEVENS AND %NQUIST )N SPITE OF THESE NOTABLE EXCEPTIONS HOWEVER ALL MAJOR GROUPS OF VERTE BRATES MOST INVERTEBRATE GROUPS VASCULAR AND NON VASCULAR PLANTS AND MANY OTHER TAXONOMIC GROUPS SHOW THIS LATITUDINAL GRADIENT SEE REVIEW IN 7ILLIG ET AL %UROPEAN NATURALISTS lRST PROMINENTLY DESCRIBED THIS PATTERN DURING THE !GE OF %XPLORATION FOR EXAMPLE (UMBOLDT REPRINTED BY (AWKINS ELOQUENTLY DESCRIBES INCREASES IN PLANT RICHNESS AS ONE APPROACHES THE TROPICS 4HE @GRADIENT ITSELF AS OPPOSED SIMPLY TO DIFFERENCES BETWEEN THE TEMPERATE ZONES AND TROPICS BECAME MORE APPARENT AND BETTER CHARACTERIZED AS MORE BIOGEO GRAPHIC DATA BECAME AVAILABLE DURING THE TWENTIETH CENTURY EG &ISCHER 3IMPSON FOR A REVIEW OF THIS TOPIC SEE "ROWN AND 3AX 2ESEARCH DESCRIBING THIS GRADIENT CONTINUES TO THIS DAY EG 7ILLIG ET AL 2ODRIGUERO AND 'ORLA ! SECOND GRADIENT THAT IS NOT AS WELL CHARACTERIZED IS THAT OF VARIATION IN GEOGRAPHIC RANGE SIZE ACROSS LATITUDE 4HE lRST INKLING OF THIS PATTERN IS PRESENT IN THE SEMINAL WORK OF %DUARDO 2APOPORT WHO DEMONSTRATED THAT THE GEOGRAPHIC EXTENT OF MAMMALIAN SUBSPECIES TENDED TO INCREASE WITH INCREASING LATITUDE )T WAS NOT UNTIL HOWEVER THAT 'EORGE 3TEVENS lRST CHARACTERIZED THESE PATTERNS AT THE SPECIES LEVEL SHOWING THAT SPECIES TENDED ON AVERAGE TO HAVE LARGE LATITUDINAL EXTENTS AT HIGHER LATITUDES 3TEVENS CHRISTENED THIS PAT TERN 2APOPORTS RULE AND SET OFF A mURRY OF RESEARCH ON THIS TOPIC GREATLY REVITAL IZING STUDIES OF LATITUDINAL GRADIENTS IN BIOGEOGRAPHY !T PRESENT THE GENERALITY OF THE LATITUDINAL GRADIENT IN SPECIES RANGE SIZE IS MUCH DEBATED EG 'ASTON ET AL BUT THERE IS BROAD AND UNCONTESTED EVIDENCE THAT THIS PATTERN IS ROBUST WITHIN TEMPERATE LATITUDES OF THE .ORTH (EMISPHERE FOR MANY TAXONOMIC GROUPS EG BIRDS MAMMALS CRAYlSH TREES ETC 3TEVENS &RANCE ,ETCHER AND (ARVEY 'ASTON ET AL 7HAT IS ENTIRELY UNCLEAR FOR BOTH THESE GRADIENTS IS WHETHER THERE IS ANY UNI VERSALLY APPLICABLE EXPLANATION FOR THEM /VER THE YEARS A NUMBER OF HYPOTHESES HAVE BEEN PROPOSED TO EXPLAIN THESE GRADIENTS PARTICULARLY THE GRADIENT IN SPECIES RICHNESS 0ERHAPS THE MOST OBVIOUS OF THESE EXPLANATIONS HAS BEEN THE OBSERVATION THAT THERE IS GENERALLY MORE AVAILABLE ENERGY HEAT AND WATER AS ONE APPROACHES
$& 3AX AND 3$ 'AINES
THE TROPICS WHICH COULD PROMOTE OR MAINTAIN HIGHER LEVELS OF BIOLOGICAL DIVERSITY IN TERRESTRIAL ENVIRONMENTS EG 0IANKA NOTE THAT WHILE VARIATION IN AVAIL ABLE WATER IS CLEARLY NOT A LIMITING COMPONENT OF SPECIES RICHNESS IN THE OCEAN THAT VARIATION IN ENERGY AND HEAT MAY BE OF DIRECT IMPORTANCE IN SURFACE WATERS AND OF INDIRECT IMPORTANCE IN THE DEEP SEA WHERE THE LATITUDINAL GRADIENT IN SPE CIES RICHNESS ALSO OCCURS EG 7ILLIG ET AL /THER REASONABLE EXPLANATIONS FOR THE LATITUDINAL GRADIENT IN SPECIES RICHNESS HOWEVER HAVE ALSO BEEN PROPOSED AND MANY OF THESE INVOKE TEMPORALLY EXPLICIT EXPLANATIONS FOR THESE PATTERNS &OR EXAMPLE IT HAS BEEN SUGGESTED THAT LONG TERM STABILITY OF RESOURCE AVAILABILITY OR CONDITIONS HAVE ALLOWED MORE SPECIES TO ACCUMULATE OR BE PRESERVED IN THE TROPICS EG 0IANKA )N TERRESTRIAL ENVIRONMENTS FOR EXAMPLE THE EFFECTS OF ICE AGES AND OTHER CHANGES IN CLIMATE HAVE BEEN REDUCED IN THE TROPICS RELA TIVE TO HIGH LATITUDE REGIONS WHERE GLACIERS HAVE REPEATEDLY CLEARED AWAY MOST FORMS OF LIFE "ROWN AND ,OMOLINO /THER TEMPORALLY EXPLICIT EXPLANATIONS SUGGEST THAT HIGHER SPECIATION RATES AT LOW LATITUDES MAY BE RESPONSIBLE FOR THE RICHNESS GRADIENT EG 2OHDE &OR THE LATITUDINAL GRADIENT IN RANGE SIZE SIMILAR EXPLANATIONS OR LOGICAL CONTINUATIONS OF THESE EXPLANATIONS HAVE BEEN EMPLOYED FOR EXAMPLE GLACIERS OR OTHER FORMS OF ENVIRONMENTAL PERTURBA TION MAY HAVE DIFFERENTIALLY REMOVED SPECIES WITH SMALL GEOGRAPHIC RANGES FROM HIGH LATITUDES "ROWN 3AX 4HE GRADIENT IN RANGE SIZE HAS ALSO BEEN SUGGESTED TO BE A CONSEQUENCE OF THE GRADIENT IN RICHNESS WITH THE ASSUMPTION THAT REGIONS WITH HIGH SPECIES RICHNESS WOULD CAUSE THOSE SPECIES PRESUMABLY BECAUSE OF SOME SORT OF LIMITING BIOTIC INTERACTIONS SUCH AS COMPETITION TO ON AVERAGE HAVE SMALLER GEOGRAPHIC RANGES "ROWN 4HROUGH THE YEARS THE NUMBER OF HYPOTHESES PROPOSED PARTICULARLY FOR THE LATITUDINAL GRADIENT IN SPECIES RICHNESS HAS SWELLED )N 0IANKA CHARACTERIZED SIX PRINCIPLE HYPOTHESES BY 2OHDE CHARACTERIZED MORE THAN HYPOTHESES AND TODAY THERE ARE MORE THAN HYPOTHESES FOR THESE GRADIENTS DESCRIBED IN THE LITERATURE 7ILLIG ET AL 4HE TROUBLE CLEARLY HAS BEEN IN REDUCING THE NUMBER OF EXPLANATIONS (EREIN HOWEVER LIES ONE OF THE PRINCIPAL DIFlCULTIES OF MANY BIOGEOGRAPHIC PURSUITS NAMELY THE DIFlCULTY IN REJECTING HYPOTHESES WHEN MANIPULATIVE EXPERIMENTS ARE IMPOSSIBLE OR NEARLY IMPOSSIBLE TO PURSUE AND THE RELATIVE MERITS OF INDIVIDUAL HYPOTHESES ARE INSTEAD MEASURED AGAINST CORRELATIVE DATA (EREIN ALSO LIES ONE OF THE PRINCIPAL ADVANTAGES OF STUDYING NATURALIZED SPE CIES AS THEIR INTRODUCTION AND SUBSEQUENT NATURALIZATION PROVIDES A MANIPULATION FOR A LARGE UNCONTROLLED @EXPERIMENT ONE THAT WOULD OTHERWISE BE IMPOSSIBLE TO PERFORM AT SUCH LARGE SPATIAL AND TEMPORAL SCALES 3IMILARLY THE OCCURRENCE OF THESE UNCONTROLLED EXPERIMENTS IN MANY REGIONS AND CONTINENTS AROUND THE WORLD PROVIDES THE REPLICATION NEEDED TO DRAW GENERAL INSIGHTS FROM THE @RESULTS OF THESE EXPERIMENTS 4HE SPECIlC ADVANTAGE OF STUDYING NATURALIZED SPECIES WITH RESPECT TO THIS ISSUE IS THAT THE GREAT MAJORITY OF THESE SPECIES HAVE ONLY BEEN PRESENT IN THEIR NATURALIZED RANGES FOR A FEW HUNDRED YEARS AT MOST 4HIS MEANS THAT ANY PATTERNS IN GEOGRAPHIC GRADIENTS IN RICHNESS OR RANGE SIZE OBSERVED IN NATURALIZED SPECIES
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
CANNOT BE DIRECTLY ATTRIBUTABLE TO EFFECTS OF GLACIATIONS OTHER HISTORICAL PROCESSES THAT HAVE DIFFERENTIALLY AFFECTED DIFFERENT LATITUDES OR TO DIFFERENT EVOLUTIONARY RATES OF ACCUMULATION OVER TIME THE POTENTIAL INDIRECT EFFECTS OF THESE PROCESS WILL BE DISCUSSED LATER 4HIS MEANS THAT IF ONE CAN ACCOUNT FOR DIFFERENCES IN PAT TERNS OF INTRODUCTION WE MAY BE ABLE TO LEARN A GREAT DEAL ABOUT WHAT STRUCTURES OR WHAT DOESNT STRUCTURE THE GEOGRAPHIC DISTRIBUTIONS OF SPECIES BY STUDYING PATTERNS OF NATURALIZED SPECIES 4O EXAMINE THESE ISSUES 3AX EXAMINED THE GEOGRAPHIC DISTRIBUTION OF NATURALIZED SPECIES OF SEVERAL TAXONOMIC GROUPS ON SEVERAL CONTINENTS PLANTS IN %UROPE lSHES AND BIRDS IN .ORTH !MERICA AND MAMMALS IN %UROPE .ORTH AND 3OUTH !MERICA 4HIS WORK SHOWS THAT WITHIN CONTINENTAL AREAS OF THE TROPICS FEW SPECIES HAVE INVADED AND THAT THOSE THAT HAVE TEND TO BE HUMAN COMMENSALS WITH VERY LARGE GEOGRAPHIC RANGES WE SHALL RETURN TO THE ISSUE OF FEW INVASIONS WITHIN TROPICAL MAINLAND AREAS IN A SECTION BELOW !T EXTRA TROPICAL LATITUDES HOWEVER WHERE MOST NATURALIZED SPECIES ARE DISTRIBUTED NATURALIZED SPECIES SHOW GEOGRAPHIC PATTERNS OF DISTRIBUTION THAT ARE QUALITATIVELY SIMILAR TO THOSE SHOWN BY NATIVE SPECIES IE RICHNESS PEAKS AT LOW LATITUDES AND DECLINES TOWARD THE POLES WHILE AVERAGE GEOGRAPHIC RANGE SIZE IS SMALLEST AT LOW LATITUDES AND INCREASES TOWARDS THE POLES &IGS AND FOR A DISCUSSION OF THE SMALL IDIOSYN CRASIES IN THESE PATTERNS SEE 3AX 4HESE LATITUDINAL PATTERNS DO NOT APPEAR TO BE DRIVEN EXCLUSIVELY BY PATTERNS OF INTRODUCTION EFFORT PER SE AT LEAST FOR BIRDS BECAUSE THE GREATEST NUMBER OF INTRODUCTION ATTEMPTS FOR BIRDS IN .ORTH !MERICA HAVE BEEN AT HIGH TEMPERATE LATITUDES IE ABOVE DEGREES LATITUDE WHERE HUMAN POPULATIONS ARE LARGEST AND NOT AT LOW TEMPERATE LATITUDES IE BELOW DEGREES WHERE THE NUMBER OF NATURALIZED SPECIES IS GREATEST 4HESE PATTERNS ALSO DO NOT APPEAR TO BE AN INDIRECT CONSEQUENCE OF PATTERNS THAT EXISTED IN NATURALIZED SPECIES NATIVE RANGES SEE 3AX FOR EVIDENCE AND DETAILS 4HIS SUGGESTS THAT LATITUDINAL GRADIENTS IN RICHNESS AND RANGE SIZE CAN FORM RELATIVELY QUICKLY OVER THE ECOLOGICAL TIME OF A FEW HUNDRED YEARS SINCE EXOTIC SPECIES WERE INTRODUCED AND THAT TEMPORALLY DEPENDENT EXPLANATIONS FOR THESE GRADIENTS SUCH AS GLACIA TION EVENTS AND DIFFERENTIAL RATES OF SPECIATION MAY NOT BE NECESSARY TO EXPLAIN THESE PATTERNS 4HIS REPRESENTS A POTENTIALLY SIGNIlCANT CONTRIBUTION TO OUR UNDER STANDING OF THESE GRADIENTS BY PROVIDING A MEANS BY WHICH WE CAN POTENTIALLY REJECT CERTAIN HYPOTHESES AS GENERAL AND NECESSARY EXPLANATIONS )N ADDITION TO LEARNING ABOUT WHAT STRUCTURES BIOGEOGRAPHIC GRADIENTS STUDY ING THESE PATTERNS WITH NATURALIZED SPECIES ALSO PROVIDES INSIGHTS INTO INVASION BIOLOGY )F SPECIES ARE MORE LIKELY TO BECOME ESTABLISHED AT LOW TEMPERATE LATI TUDES THAN HIGH TEMPERATE LATITUDES INDEPENDENT OF DELIBERATE ATTEMPTS AT INTRO DUCTION 3AX THEN REGIONS MAY BE DIFFERENTIALLY SUSCEPTIBLE TO INVASION 4HE EVIDENCE PRESENTED HOWEVER SUGGESTS THAT WE SHOULD ADOPT A MORE COMPLI CATED VISION OF hINVASION SUSCEPTIBILITYv THAN IS GENERALLY USED 4HIS IS BECAUSE DESPITE MORE SPECIES INVADING LOW TEMPERATE LATITUDES THESE NON NATIVE SPECIES TEND TO ACQUIRE SMALL GEOGRAPHIC RANGES )N CONTRAST FEW SPECIES TEND TO INVADE HIGH LATITUDES BUT THE ONES THAT DO TEND TO ACQUIRE LARGE GEOGRAPHIC RANGES
$& 3AX AND 3$ 'AINES
&IG ,ATITUDINAL GRADIENTS IN RICHNESS OF NATURALIZED SPECIES 4HE SPECIES RICHNESS OF NATURALIZED EXOTIC SPECIES IN $ LATITUDINAL BANDS ON CONTINENTS 4HE DASHED LINES INDICATE THE 4ROPIC OF #ANCER OR #APRICORN DIVIDING TROPICAL AND TEMPERATE LATITUDES &ISH DISTRIBUTIONS WERE EXAMINED AT TEMPERATE LATITUDES ONLY 2EPRINTED WITH PERMISSION OF "LACKWELL 0UBLISHING FROM 3AX
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
&IG ,ATITUDINAL GRADIENTS IN GEOGRAPHIC RANGE SIZE OF NATURALIZED SPECIES 4HE MEAN LATITUDINAL EXTENT OF NATURALIZED EXOTIC SPECIES IN $ LATITUDINAL BANDS ON CONTINENTS %RROR BARS REPRESENT OR n ONE STANDARD ERROR 0OINTS WITHOUT ERROR BARS ARE BASED ON A SINGLE SPECIES 4HE DASHED LINES INDICATE THE 4ROPIC OF #ANCER OR #APRICORN DIVIDING TROPICAL AND TEMPERATE LATITUDES 2EPRINTED WITH PERMISSION OF "LACKWELL 0UBLISHING FROM 3AX
$& 3AX AND 3$ 'AINES
4HIS SUGGESTS A TRADEOFF IN SUSCEPTIBILITY OF INVASION BETWEEN REGIONS THAT IS BAL ANCED BETWEEN THE ABSOLUTE NUMBER OF LIKELY INVADERS AND THE ABSOLUTE GEOGRAPH IC EXTENT THOSE INVADERS ARE LIKELY TO ACHIEVE -ANY QUESTIONS REGARDING THESE PATTERNS REMAIN UNANSWERED !RE THESE PATTERNS GENERAL TO ALL CONTINENTS AND ALL TAXONOMIC GROUPS OF NATURALIZED SPE CIES 7ILL THESE PATTERNS CHANGE OVER TIME AS MORE INTRODUCED SPECIES BECOME ESTABLISHED AND AS EXISTING SPECIES CONTINUE TO EXPAND THEIR GEOGRAPHIC RANGES !ND WILL FUTURE RANGE COLLAPSES IN THE GEOGRAPHIC DISTRIBUTION OF SOME NATURAL IZED SPECIES AFFECT THESE PATTERNS !NSWERING THESE QUESTIONS WILL INVOLVE MUCH WORK BUT DOING SO OFFERS THE PROMISE OF GREAT INTELLECTUAL CONTRIBUTIONS TO OUR UNDERSTANDING OF BOTH BIOGEOGRAPHY AND SPECIES INVASIONS )NVASIONS OF HOTSPOTS OF DIVERSITY
)N CONTRAST TO EXPERIMENTAL WORK DONE AT SMALL SPATIAL SCALES AND IN CONTRAST TO THE SUPPOSITION OF %LTON THAT SPECIES RICH AREAS SHOULD BE MORE DIFlCULT TO INVADE THAN SPECIES POOR ONES WORK AT BIOGEOGRAPHIC SCALES HAS GENERALLY SHOWN THAT NATIVE AND NATURALIZED RICHNESS OF SPECIES ARE POSITIVELY CORRELATED ACROSS LANDSCAPES AND REGIONS 4WO PAPERS THAT DREW PARTICULAR ATTENTION TO THIS PHE NOMENON WERE PUBLISHED IN ,ONSDALE EXAMINED PUBLISHED STUDIES OF PLANT RICHNESS FROM AROUND THE WORLD THE SPATIAL EXTENT COVERED BY THESE STUDIES VARIED FROM A FEW SQUARE KILOMETERS TO GREATER THAN A MILLION SQUARE KILOMETERS AND THE REGIONS COVERED INCLUDED ISLANDS AND CONTINENTS TEMPERATE AND TROPICAL AREAS "Y EXAM INING THE mORAS THAT DISTINGUISHED BETWEEN NATIVE AND EXOTIC SPECIES HE WAS ABLE TO SHOW THAT NATIVE AND EXOTIC SPECIES RICHNESS WERE SIGNIlCANTLY POSITIVELY CORRELATED ACROSS THESE SITES EVEN AFTER CONTROLLING FOR DIFFERENCES IN AREA AMONG SITES 4HE TOTAL AMOUNT OF VARIANCE IN THE NUMBER OF EXOTIC SPECIES PREDICTED BY THE NUMBER OF NATIVE SPECIES WAS IMPROVED BY CONSIDERING WHETHER A PARTICULAR SITE WAS AN ISLAND OR A RESERVE HOWEVER EVEN WITHOUT THIS INFORMATION A RELATIVE LY CLEAR AND ROBUST PATTERN HAD BEEN IDENTIlED NATIVE AND EXOTIC RICHNESS WERE POSITIVELY CORRELATED AT BIOGEOGRAPHIC SCALES 3TOHLGREN ET AL COLLECTED lELD DATA ON NATIVE AND EXOTIC PLANT SPECIES AT LOCAL SCALES ACROSS VEGETATION TYPES AND WITHIN BIOMES IN THE WESTERN 53 !T THE SCALE OF VEGETATION TYPES AND BIOMES THEY FOUND A POSITIVE RELATIONSHIP BETWEEN NATIVE AND EXOTIC RICHNESS &URTHER 3TOHLGREN ET AL INDICATED THE OBVIOUS BUT PREVIOUSLY UNARTICULATED OBSERVATION THAT THE AREAS RICHEST IN NATIVE SPECIES WERE IN FACT BEING INVADED BY THE MOST EXOTIC SPECIES 4HIS WORK BY ,ONSDALE AND 3TOHLGREN ET AL HAS SUBSEQUENTLY BEEN CONlRMED AT BIOGEOGRAPHIC SPATIAL SCALES BY SEVERAL OTHER STUDIES -OST OF THIS WORK HAS ALSO BEEN DONE WITH PLANTS 3TADLER ET AL HAVE SHOWN A POSI TIVE CORRELATION BETWEEN NATIVE AND EXOTIC PLANT RICHNESS IN ECOGEOGRAPHIC ZONES OF +ENYA -C+INNEY A FOUND THIS PATTERN IN PROTECTED AREAS OF THE 53 0YSEK ET AL FOUND THIS PATTERN IN NATURE RESERVES OF THE #ZECH 2EPUBLIC
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
$EUTSCHEWITZ ET AL FOUND THIS PATTERN IN REGIONS OF THE $ESSAU DISTRICT OF 'ERMANY AND lNALLY 3TOHLGREN ET AL SHOW THAT NATIVE AND EXOTIC RICHNESS ARE POSITIVELY CORRELATED ACROSS COUNTIES WITHIN 53 3TATES AND ACROSS THE STATES THEMSELVES 7HILE THE FOCUS OF THESE PATTERNS HAS BEEN ON PLANTS AN EXPLORATION OF OTHER GROUPS PARTICULARLY AT LARGE SPATIAL SCALES SHOWS SIMILAR PATTERNS PARTICULARLY WITHIN THE TEMPERATE ZONES &OR EXAMPLE A COMPARISON OF NATIVE AND EXOTIC MAMMALIAN RICHNESS WITHIN DEGREE BANDS OF LATITUDE IN TEM PERATE .ORTH !MERICA REVEALS A STRIKINGLY STRONG POSITIVE RELATIONSHIP BETWEEN NATIVE AND EXOTIC RICHNESS &IG A 3IMILARLY DATA FROM 3AX ET AL SHOWS THAT NATIVE AND EXOTIC BIRD RICHNESS ARE POSITIVELY CORRELATED ON OCEANIC ISLANDS &IG B )N CONTRAST HOWEVER TO THESE POSITIVE CORRELATIONS AT LEAST ONE NEGATIVE CORRELATION BETWEEN NATIVE AND EXOTIC SPECIES AT BIOGEOGRAPHIC SCALES IS KNOWN FROM THE LITERATURE IE FOR FRESHWATER lSHES IN WATERSHEDS OF .ORTH !MERICA 'IDO AND "ROWN 4HERE ARE SOME REASONS WHICH WE WILL RETURN TO LATER THAT WE MIGHT EXPECT ATYPICAL PATTERNS FROM FRESHWATER lSHES $ESPITE THIS EXCEPTION HOWEVER WITH THE EVIDENCE AVAILABLE TO DATE IT APPEARS THAT THE GENERAL PATTERN IS FOR NATIVE AND EXOTIC RICHNESS TO BE CORRELATED ACROSS LARGE AREAS AT LEAST WITHIN A GIVEN REGION ALTHOUGH COMPARISONS OF AREAS ACROSS REGIONS MAY YIELD DIFFER ENT RESULTS A TOPIC WE RETURN TO IN THE SECTION BELOW ON INVASIONS OF MAINLAND TROPICAL AREAS
&IG 0OSITIVE CORRELATION BETWEEN NATIVE AND NATURALIZED SPECIES RICHNESS ! 2ICHNESS OF NATIVE AND NATURALIZED MAMMAL SPECIES IN DEGREE BELTS OF LATITUDE FROM DEGREES IN .ORTH !MERICA 2 P DATA FROM 3TEVENS AND 3AX " 2ICHNESS OF HISTORIC NUMBER OF NATIVE AND CURRENT NUMBER OF NATURALIZED BIRD SPECIES ON OCEANIC ISLANDS 2 P DATA FROM 3AX ET AL
$& 3AX AND 3$ 'AINES
4HIS RELATIVELY SIMPLE OBSERVATION THAT NATIVE AND EXOTIC RICHNESS ARE POSITIVELY CORRELATED ACROSS LARGE AREAS COMES IN CONTRAST WITH MUCH WORK DONE AT EXPERI MENTAL SCALES THAT SHOWS A NEGATIVE RELATIONSHIP BETWEEN NATIVE RICHNESS AND EXOTIC INVASION EG 4ILMAN 3TACHOWICZ ET AL .AEEM ET AL 4HIS EXPERIMENTAL WORK IS CONSISTENT WITH MODELING WORK EG #ASE AND PERHAPS MORE SIGNIlCANTLY WITH THE SUPPOSITION OF %LTON THAT SPECIES RICH AREAS SHOULD BE MORE DIFlCULT TO INVADE THAN SPECIES POOR AREAS ! NUMBER OF STUD IES HAVE ATTEMPTED TO RECONCILE THE DIFFERENCES OBSERVED BETWEEN EXPERIMENTAL AND OBSERVATIONAL STUDIES EG 7ARDLE &RIDLEY ET AL 0ERHAPS THE MOST CONVINCING EXPLANATION FOR THESE DIFFERENCES HAVE BEEN ARTICULATED BY ,EVINE WHO SUGGESTS THAT REGARDLESS OF ANY IMPACT NATIVE RICHNESS MAY HAVE ON SPECIES INVASIONS WHEN ALL ELSE IS EQUAL IN CONTROLLED EXPERIMENTAL SETTINGS THAT THESE IMPACTS WILL BE OUTWEIGHED BY REAL WORLD SPATIAL VARIATION IN ENVIRON MENTAL CONDITIONS SUCH AS NUTRIENT AND ENERGY AVAILABILITY PRECIPITATION AND HABITAT HETEROGENEITY THAT PROMOTE COVARIANCE IN THE RICHNESS OF BOTH NATIVE AND EXOTIC SPECIES 4HIS EXPLANATION BY ,EVINE FOR RECONCILING DIFFERENCES OBSERVED IN OBSERVATIONAL AND EXPERIMENTAL STUDIES SUGGESTS THAT NATIVE AND EXOTIC RICHNESS SHOULD BE EXPECTED TO POSITIVELY COVARY WHENEVER BOTH GROUPS RESPOND SIMILARLY TO ENVIRONMENTAL VARIABLES IE THAT SITE CONDITIONS THAT PROMOTE HIGH NATIVE RICH NESS WILL OFTEN ALSO PROMOTE HIGH EXOTIC RICHNESS /THER EXPLANATIONS FOR A POSITIVE ASSOCIATION BETWEEN NATIVE AND EXOTIC RICHNESS HOWEVER ARE ALSO POSSIBLE /NE ALTERNATIVE EXPLANATION IS THAT INTRODUCTION EFFORTS BY HUMANS IE PROPAGULE PRESSURE OF EXOTIC SPECIES ARE HIGHER IN SPECIES RICH THAN SPECIES POOR ENVIRON MENTS SUCH THAT REGIONS WITH MANY NATIVE SPECIES ARE ALSO THE SAME REGIONS WHERE HUMANS INTRODUCE THE MOST SPECIES &OR THIS TO BE A UNIVERSAL EXPLANATION FOR THESE PATTERNS HOWEVER THE PATTERN OF INTRODUCTION EFFORT BY HUMANS WOULD HAVE TO CONSISTENTLY MATCH NATIVE SPECIES RICHNESS ACROSS REGIONS WHICH SEEMS UNLIKELY TO BE GENERALLY TRUE AND IS DElNITELY NOT THE CASE IN MANY PLACES EG BIRD INTRODUCTION EFFORT IN .ORTH !MERICA DOES NOT MATCH PATTERNS OF NATIVE SPECIES RICHNESS SEE ABOVE ! SECOND ALTERNATIVE EXPLANATION IS THAT THE POSITIVE ASSOCIA TION BETWEEN NATIVE AND EXOTIC RICHNESS ACROSS REGIONS IS DUE TO DIFFERENCES IN THE AREA OF REGIONS COMPARED "ECAUSE OF THE SPECIES AREA RELATIONSHIP LARGE REGIONS SHOULD HAVE MORE NATIVE AND MORE EXOTIC SPECIES (OWEVER WHILE SPECIES AREA RELATIONSHIPS CERTAINLY MAY BE IMPORTANT IN DETERMINING SUCH PATTERNS POSITIVE RELATIONSHIPS BETWEEN NATIVE AND EXOTIC RICHNESS ARE OBSERVED EVEN AMONG EQUAL SIZE AREAS EG 3AX OR WHEN THE EFFECT OF AREA IS CONTROLLED EG ,ONSDALE 'IVEN THAT THESE ALTERNATIVE EXPLANATIONS ARE UNLIKELY TO DRIVE THE POSI TIVE RELATIONSHIP FREQUENTLY OBSERVED BETWEEN NATIVE AND EXOTIC RICHNESS IT SEEMS LIKELY THAT THE OBSERVED RELATIONSHIPS ARE INDEED DUE TO VARIATION IN ENVIRONMEN TAL CHARACTERISTICS SUCH AS ENERGY AND NUTRIENT AVAILABILITY THAT INmUENCE NATIVE AND EXOTIC SPECIES RICHNESS IN SIMILAR WAYS )F ENVIRONMENTAL CHARACTERISTICS ARE DRIVING THE POSITIVE ASSOCIATION BETWEEN NATIVE AND EXOTIC RICHNESS OBSERVED ACROSS SITES THEN THESE PATTERNS HAVE IMPOR
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
TANT IMPLICATIONS FOR CONSERVATION AND ENVIRONMENTAL MANAGEMENT 4HEY SUG GEST THAT SPECIES RICH NATIVE PRESERVES CANNOT BE EXPECTED TO REPEL EXOTIC SPECIES INVASIONS AND THAT APPROPRIATE MANAGEMENT CONTROL EFFORTS FOR EXOTIC SPECIES MUST BE MAINTAINED TO PREVENT THEM FROM BECOMING ESTABLISHED &URTHER WITH RESPECT TO ECOLOGICAL THEORY THESE PATTERNS AND ITS LIKELY EXPLANATION SUGGEST TWO THINGS &IRST THEY SUGGEST THAT EVEN DIVERSE CONTINENTAL AREAS CAN OFTEN SUP PORT MANY ADDITIONAL SPECIES 3ECOND THEY SUGGEST THAT THE RICHNESS OF NATIVE SPECIES WITHIN AN AREA MAY INDICATE THE RELATIVE CAPACITY OF THAT AREA TO SUPPORT SPECIES SINCE SITES RICH IN NATIVE SPECIES HAVE PRESUMABLY INCREASED IN RICHNESS THE MOST WHILE SITES POOR IN NATIVE SPECIES HAVE PRESUMABLY INCREASED IN RICHNESS THE LEAST 4ROPICAL MAINLANDS REGIONS WITH FEW INVADERS
"ECAUSE NATIVE AND EXOTIC RICHNESS ARE POSITIVELY CORRELATED ACROSS SITES AT LARGE SPATIAL SCALES ONE MIGHT SUSPECT THAT TROPICAL REGIONS WHERE THE GLOBAL PEAKS IN NATIVE RICHNESS EXIST ARE ALSO INVADED BY MANY EXOTIC SPECIES .OTHING HOWEVER COULD BE FURTHER FROM THE TRUTH ESPECIALLY IN MAINLAND TROPICAL AREAS WHERE RELATIVELY FEW EXOTICS HAVE GENERALLY INVADED 2EJMANEK 3AX &INE 4HIS MEANS THAT THE GENERALLY POSITIVE CORRELATION BETWEEN NATIVE AND EXOTIC RICHNESS OFTEN BREAKS DOWN WHEN COMPARING ACROSS AREAS IN BOTH TEMPER ATE AND TROPICAL ZONES EG THE STRONG PATTERN DEPICTED IN &IG ! WOULD BREAK DOWN IF TROPICAL POINTS WERE INCLUDED ON THE PLOT .EVERTHELESS WITHIN TROPICAL AREAS THE POSITIVE CORRELATION BETWEEN NATIVE AND EXOTIC RICHNESS CAN STILL HOLD EG IN -EXICAN 3TATES NATIVE AND EXOTIC SPECIES OF mOWERING PLANTS ARE POSITIVELY CORRELATED 2 P DATA FROM 6ILLASE×OR AND %SPINOSA 'ARCIA !LSO UNLIKE TROPICAL MAINLAND ENVIRONMENTS ON TROPICAL ISLANDS MANY EXOTIC SPECIES HAVE BECOME NATURALIZED EG 3AX ET AL 7HY HOWEVER SO FEW EXOTIC SPECIES HAVE BECOME ESTABLISHED IN MAINLAND TROPICAL AREAS IN NOT CLEARLY KNOWN 4WO PRINCIPAL STUDIES TO DATE HAVE PROVIDED EMPIRICAL DATA SHOWING THE CON TRAST BETWEEN THE NUMBER OF EXOTIC SPECIES THAT HAVE BECOME NATURALIZED IN TROPI CAL MAINLAND TROPICAL ISLAND AND TEMPERATE AREAS 2EJMANEK EXAMINED THE NUMBERS OF NATIVE AND EXOTIC PLANTS IN VARIOUS mORAS OF THE WORLD SHOWING THAT THE RELATIVE PROPORTION OF EXOTIC SPECIES AS WELL AS THE ABSOLUTE NUMBER OF EXOTICS AFTER CONTROLLING FOR AREA DECLINES PRECIPITOUSLY WITHIN TROPICAL MAIN LAND REGIONS RELATIVE TO TROPICAL ISLANDS OR TEMPERATE AREAS 3IMILARLY 3AX SHOWS THAT FEW SPECIES OF BIRDS OR MAMMALS HAVE BECOME NATURALIZED ON CONTI NENTS WITHIN THE TROPICS &IG BUT REPORTS THAT MANY HAVE BECOME ESTABLISHED ON TROPICAL ISLANDS AND WITHIN TEMPERATE AREAS 4HUS BOTH STUDIES REPORT QUALI TATIVELY SIMILAR PATTERNS FEW SPECIES HAVE INVADED MAINLAND TROPICAL AREAS WHILE RELATIVELY MANY SPECIES HAVE INVADED TROPICAL ISLANDS AND TEMPERATE AREAS 4HE MECHANISM RESPONSIBLE FOR THIS PATTERN REMAINS ELUSIVE /NE POSSIBILITY HOWEVER IS THAT PATTERNS OF HUMAN DISTURBANCE OR INTRODUCTION EFFORT OF EXOTIC
$& 3AX AND 3$ 'AINES
SPECIES ARE DIFFERENT IN MAINLAND TROPICAL AREAS THEN ELSEWHERE 7HILE EACH REGION DOES OF COURSE HAVE ITS OWN UNIQUE HISTORY SUCH AN EXPLANATION DOES NOT APPEAR TO BE GENERALLY TRUE &OR EXAMPLE MAINLAND -EXICO AND ISLANDS OF THE #ARIBBEAN SHARE SIMILAR HISTORIES OF %UROPEAN COLONIZATION DISTURBANCE SUBSEQUENT POPULA TION GROWTH AND PRESUMABLY INTRODUCTION EFFORTS YET THESE ISLANDS HARBOR MANY MORE NATURALIZED SPECIES OF BIRDS AND MAMMALS THAN MAINLAND -EXICO 3AX !NOTHER POSSIBILITY IS THAT MAINLAND TROPICAL REGIONS ARE RESIS TANT TO INVASION BECAUSE OF A COMBINATION OF BIOTIC AND ABIOTIC FACTORS 2EJMANEK 4HE POTENTIAL ROLE OF ABIOTIC FACTORS HOWEVER IS DIFlCULT TO RECONCILE WITH THE DATA PROVIDED IN 3AX WHICH SHOWS THAT COASTAL AREAS OF TROPICAL CONTI NENTS WHICH PRESUMABLY HAVE VERY SIMILAR ABIOTIC CONDITIONS AS TROPICAL ISLANDS HAVE FEW EXOTIC BIRD OR MAMMAL SPECIES )N LIGHT OF THIS 3AX ARGUES THAT ABIOTIC FACTORS SHOULD NOT BE THE LIMITING VARIABLE IN EXOTIC SPECIES INVASION OF MAINLAND TROPICAL AREAS )NSTEAD HE ARGUES BASED ON THE DIFFERENTIAL PLACEMENT OF NATURALIZED SPECIES LOW LATITUDE RANGE BOUNDARIES ON CONTINENTS AND ISLANDS THAT BIOTIC RESISTANCE WHICH MAY BE STRONGLY CORRELATED WITH SPECIES RICHNESS IS THE PRIMARY FACTOR RESISTING SPECIES INVASIONS OF MAINLAND TROPICAL AREAS /F COURSE IF HIGH SPECIES RICHNESS IN MAINLAND TROPICAL AREAS IS RESULTING IN SOME SORT OF BIOTIC RESISTANCE TO INVASION THEN WHY DOESNT SPECIES RICHNESS CORRELATE WITH INVASION RESISTANCE IN TEMPERATE LATITUDES !T THE MOMENT THERE IS NO CLEAR ANSWER TO THIS QUESTION /NE POSSIBILITY HOWEVER IS THAT SOME THRESHOLD IN SPE CIES RICHNESS MUST BE REACHED WHICH MAY BE MET IN MAINLAND TROPICAL AREAS BEFORE BIOTIC RESISTANCE IS AN EFFECTIVE FORCE IN RESISTING SPECIES INVASIONS 3UCH AN EXPLANATION WOULD BE CONSISTENT WITH THE GREATER APPARENT INVASIBILITY OF TROPICAL ISLANDS AND TEMPERATE AREAS WHERE SPECIES RICHNESS IS REDUCED RELATIVE TO MAIN LAND TROPICAL AREAS 4HE SUGGESTION THAT BIOTIC RESISTANCE IS IMPORTANT IN RESISTING SPECIES INVASION OF MAINLAND TROPICAL AREAS IS ALSO CONSISTENT WITH BIOGEOGRAPHIC HYPOTHESES THAT POSTULATE THAT LOW LATITUDE RANGE BOUNDARIES OF SPECIES OR THE ABILITY OF SPECIES TO EXTEND THEIR GEOGRAPHIC RANGE CLOSER TO THE EQUATOR ARE SET BY BIOTIC INTERAC TIONS WITH OTHER SPECIES EG $OBZHANSKY -AC!RTHUR 4HESE BIOTIC INTERACTIONS ARE ASSUMED TO INCLUDE ALL NEGATIVE PAIRWISE SPECIES INTERACTIONS IE COMPETITION PREDATION AND AMENSALISM BUT WITH RESPECT TO SPECIES INVA SION COULD ALSO INCLUDE MISSING MUTUALISTIC SPECIES 2ICHARDSON ET AL /F COURSE RESEARCH IN ECOLOGY SINCE THE TIME OF -AC!RTHUR HAS HAD A STRONG FOCUS ON THE ROLE OF COMPETITION EG "RUNO ET AL )N SPITE OF THIS WORK IN INVA SION BIOLOGY SUGGESTS THAT COMPETITION ITSELF MAY NOT BE AS IMPORTANT IN AFFECTING SPECIES RICHNESS AS OTHER TYPES OF BIOTIC INTERACTIONS &OR EXAMPLE RECENT WORK BY $AVIS SUGGESTS THAT COMPETITION FROM EXOTIC SPECIES SHOULD RARELY HAVE NEGATIVE CONSEQUENCES ON NATIVE SPECIES RICHNESS &URTHER MOST OF THE NEGATIVE CONSEQUENCES OF EXOTIC SPECIES ON NATIVE RICHNESS HAVE BEEN ASSOCIATED WITH INTRO DUCED PREDATORS AND DISEASES EG BLACK RATS THE BROWN TREE SNAKE AND AVIAN MALARIA EG %BENHARD &RITTS AND 2ODDA 3COTT ET AL )F THIS INFORMATION CAN RECIPROCALLY BE APPLIED TO UNDERSTANDING WHAT PREVENTS SPECIES
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
INVASIONS THEN THIS WORK WOULD SUGGEST THAT PREDATION MEANT HERE IN THE BROAD SENSE OF HERBIVORY PREDATION PARASITISM AND DISEASE COULD LIKELY EXPLAIN WHY MAINLAND TROPICAL AREAS ARE SO DIFlCULT TO INVADE IN THE TROPICS PARTICULARLY THE MAINLAND TROPICS NOT ONLY ARE THERE FOR EXAMPLE MORE MAMMALIAN PREDATORS AND HERBIVORES BUT ALSO GREATER NUMBERS OF PARASITES AND DISEASES EG 7ILLIG ET AL 2ODRIGUERO AND 'ORLA )F PREDATION SENSU LATO IS IMPORTANT IN PREVENTING SPECIES INVASION OF MAINLAND TROPICAL AREAS THEN THIS MAY SUGGEST DEPENDING ON HOW THRESHOLDS OF RICHNESS OF PREDATORS OPERATE THAT PREDATION MAY BE IMPORTANT IN PREVENTING SPECIES INVASION OF OTHER PLACES AS WELL BECAUSE FOR EXAMPLE EVEN IF PREDATION CANNOT PREVENT SPECIES INVASION AT BIOGEOGRAPHIC SCALES IN TEMPERATE AREAS IT MAY STILL BE IMPORTANT AT ECOLOGICAL SPATIAL SCALES )F THIS IS TRUE THEN IT COULD HAVE LARGE IMPLICATIONS FOR ECOLOGICAL THEORY AND EXPERIMENTATION &OR EXAMPLE CURRENTLY IN ECOLOGY MUCH EFFORT IS FOCUSED ON UNDERSTANDING THE ROLE OF RICHNESS IN PREVENTING SPECIES INVASION -UCH OF THIS WORK HOWEVER IS FOCUSED ON THE ROLE THAT RICH NESS OF COMPETITORS MAY HAVE IN PREVENTING SPECIES INVASION EG +ENNEDY ET AL A COMPLIMENT TO THIS WOULD BE INCREASED ATTENTION TO THE ROLE THAT RICHNESS OF PREDATORS INCLUDING HERBIVORES PARASITES AND DISEASES MAY PLAY IN PREVENTING SPECIES INVASION 0ATTERNS OF INVASION ON ISLANDS
7HAT $ARWIN WROTE ABOUT ISLANDS ALMOST YEARS AGO COULDNT BE MORE TRUE TODAY HUMANS HAVE BEEN lLLING ISLANDS hFAR MORE FULLYv THAN HAS NATURE ,IFEFORMS THAT WERE ENTIRELY ABSENT FROM MANY ISLANDS PARTICULARLY OCEANIC ONES SUCH AS TERRESTRIAL MAMMALS AND FRESHWATER lSHES HAVE BEEN INTRODUCED AND BECOME ESTABLISHED IN ABUNDANCE 3IMILARLY LIFEFORMS THAT WERE PRESENT BUT LESS DIVERSE ON ISLANDS THAN IN SIMILAR SIZED AREAS ON CONTINENTS SUCH AS VASCULAR PLANTS HAVE BECOME MUCH MORE SPECIOSE ON ISLANDS TODAY THAN IN THE PAST )N MANY CASES THOSE SPECIES THAT HAVE BEEN INTRODUCED AND BECOME ESTABLISHED HAVE HAD DEVASTATING EFFECTS ON THE NATIVE mORA AND FAUNA CAUSING EXTINCTIONS IN SOME CASES AND REDUCTIONS IN THE ABUNDANCE OF NATIVE SPECIES IN MANY IF NOT ALL CASES .ONETHELESS THE NET EFFECT OF THESE CHANGES HAS BEEN AN INCREASE IN NET RICHNESS FOR MANY GROUPS OF SPECIES ON MANY ISLANDS EG 7ILSON #HOWN ET AL 3AX ET AL 4HE CONSERVATION CHALLENGES POSED BY SUCH PATTERNS ARE SEVERE AND COMPLEX BUT ARE NOT THE FOCUS OF THIS DISCUSSION )NSTEAD HERE WE REPORT ON THE PATTERNS THEMSELVES AND ON WHAT THESE PATTERNS CAN TELL US ABOUT BIOGEOGRAPHY INVASIVE SPECIES AND WHAT WE DO NOT YET UNDERSTAND )SLAND mORAS AND FAUNAS ARE OFTEN DESCRIBED AS BEING OUT OF BALANCE OR NOT HARMONIC WITH MAINLAND BIOTAS "ROWN AND ,OMOLINO 4HIS IS BECAUSE EVENLY REPRESENTATIVE SUBSETS OF THE SUITE OF ORGANISMS FOUND ON CONTINENTS ARE NOT FOUND ON ISLANDS )NSTEAD A DISPROPORTIONATE NUMBER OF SPECIES FOUND ON ISLANDS ARE FROM TAXONOMIC GROUPS THAT ARE LIKELY TO DISPERSE ACROSS OCEAN WATERS 4HIS INCLUDES BIRDS AND INSECTS WHICH CAN OFTEN mY LONG DISTANCES OR BE BLOWN BY
$& 3AX AND 3$ 'AINES
STORMS TO DISTANT LOCALITIES PLANTS WHOSE PROPAGULES CAN BE BLOWN BY THE WIND OR CARRIED BY BIRDS IN THEIR GUTS ON THEIR FEET ETC AND REPTILES WHICH ARE OFTEN ABLE TO SURVIVE EXTENDED VOYAGES WITH LITTLE FOOD OR WATER ON hRAFTSv OF NATURAL VEGETATION THAT HAVE BEEN WASHED OUT TO SEA BY STORMS "Y CONTRAST TAXONOMIC GROUPS THAT ARE NOT LIKELY TO MAKE OR SURVIVE SUCH DISPERSAL EVENTS SUCH AS FRESHWATER lSH TERRESTRIAL MAMMALS AND AMPHIBIANS ARE LIKELY TO BE ABSENT OR DEPAUPERATE ON ISOLATED ISLANDS /VER THE PAST DECADE MUCH HAS BEEN LEARNED ABOUT HOW HUMANS ARE MEDIAT ING CHANGES ON ISLANDS FOR EXAMPLE THE IMPORTANCE OF INTRODUCED PREDATORS AND PATHOGENS IN CAUSING NATIVE SPECIES EXTINCTIONS EG &RITTS AND 2ODDA !TKINSON ET AL THE RELATIVE ROLE OF DIFFERENT ECOLOGICAL CORRELATES IN THE ESTABLISHMENT SUCCESS OF INTRODUCED SPECIES EG $UNCAN ET AL AND HOW THE ESTABLISHMENT OF NOVEL VEGETATION CAN FACILITATE THE COLONIZATION OF OTHER SPE CIES EG (UTTON -UCH HAS ALSO BEEN LEARNED ABOUT HOW THE COMPOSITION AND RICHNESS OF DIFFERENT TAXONOMIC GROUPS ARE CHANGING ON ISLANDS &OR EXAMPLE THERE HAVE BEEN LARGE CHANGES IN THE COMPOSITION OF BIRD SPECIES LARGE INCREASES IN THE TOTAL RICHNESS OF PLANT SPECIES COUPLED WITH SUBSTANTIAL DECLINES IN NATIVE PLANT ABUNDANCE AND LARGE INCREASES IN THE PRESENCE OF TAXA THAT WERE PREVI OUSLY RARE OR ENTIRELY ABSENT ON ISLANDS SUCH AS FRESHWATER lSHES AND NON VOLANT MAMMALS EG 7ILSON 3AX ET AL 7HAT WE DO NOT YET UNDERSTAND IS HOW THE SPECIES RICHNESS OF THESE DIFFERENT TAXONOMIC GROUPS WILL CHANGE IN THE FUTURE OR WHETHER ISLANDS ARE APPROACHING ANY SORT OF MAXIMUM CAPACITY FOR HOLDING ADDITIONAL SPECIES 4HESE ISSUES REQUIRE CONSIDERABLE ADDITIONAL WORK BUT SOME KEY INSIGHTS CAN BE GLEANED BY EXAMINING SPECIES AREA RELATIONSHIPS
30%#)%3 !2%! 2%,!4)/.3()03 /& .!452!,):%$ 30%#)%3 4HE POSITIVE RELATIONSHIP BETWEEN INCREASING AREA AND INCREASING NUMBER OF SPE CIES HAS BEEN KNOWN FOR SOME TIME 7HITTAKER !RRHENIUS HOW EVER WAS THE lRST TO PLOT SPECIES AREA AGAINST SPECIES RICHNESS ON A LOG LOG SCALE $OING THIS LAID THE FOUNDATION FOR COMPARISONS BETWEEN SPECIES AREA RELATIONSHIPS FOR DIFFERENT TAXONOMIC GROUPS AND FOR DIFFERENT SETS OF LOCALITIES BECAUSE SPE CIES AREA RELATIONSHIPS ON LOG LOG PLOTS COMMONLY TAKE A LINEAR FORM SIMPLIFYING COMPARISONS OF SLOPES AND INTERCEPTS HOWEVER SEE ,OMOLINO AND 7EISER FOR A DISCUSSION OF WHEN NON LINEAR PATTERNS ARE EXPECTED 4HE SLOPES AND INTER CEPTS OF LOG LOG SPECIES AREA RELATIONSHIPS CONTAIN INFORMATION ABOUT HOW SPECIES ARE DISTRIBUTED HOW DISPERSAL LIMITED DIFFERENT TAXONOMIC GROUPS ARE AND HOW ISOLATION AND LIMITED AREA AFFECT SPECIES RICHNESS EG 2OSENZWEIG )N SPITE OF THE USEFULNESS OF THESE PATTERNS IN CHARACTERIZING THE DISTRIBUTIONS OF SPECIES THE PRECISE MECHANISMS FOR SPECIES AREA RELATIONSHIPS ARE STILL STRONGLY CONTESTED EG -ATTER ET AL 3PECIES AREA RELATIONSHIP ARE BELIEVED TO BE A CONSE QUENCE OF PATTERNS OF SPECIES ABUNDANCE THE INTERPLAY OF SPECIES ABUNDANCE AND GEOGRAPHIC RANGE DISTRIBUTIONS THE NUMBER OF HABITATS PRESENT AND CONSE
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
QUENTLY THE VARIETY OF SPECIES SUPPORTED PASSIVE SAMPLING OF A LARGER FRACTION OF A REGIONS SPECIES POOL LOWER EXTINCTION RISKS OCCURRING IN LARGER POPULA TIONS A DYNAMIC RELATIONSHIP BETWEEN COLONIZATION AND EXTINCTION AND THE DYNAMICS OF SPECIATION COLONIZATION AND EXTINCTION -ATTER ET AL 0ART OF THE DIFlCULTY IN TEASING THESE DIFFERENT HYPOTHESES APART IS THAT THEY CLEARLY ARE NOT MUTUALLY EXCLUSIVE !DDITIONALLY THE MECHANISMS THAT ARE MOST IMPOR TANT FOR THE SPECIES AREA RELATIONSHIPS MAY VARY ACROSS SPATIAL SCALES FOR EXAMPLE AT THE SMALL SPATIAL SCALES OF MOST ECOLOGICAL STUDIES MECHANISMS LIKE SPECIATION WILL GENERALLY BE RELATIVELY UNIMPORTANT WHEREAS AT LARGER SPATIAL SCALES SPECIA TION MAY BE A VERY IMPORTANT PROCESS )N THIS DISCUSSION WE RESTRICT OUR FOCUS TO SPECIES AREA RELATIONSHIPS OCCURRING AT LARGE SPATIAL SCALES IE AT SPATIAL SCALES THAT EXCEED SEVERAL HECTARES !LTHOUGH THERE IS A RICH LITERATURE ON SPECIES AREA RELATIONSHIPS SEE REVIEWS BY #ONNOR AND -C#OY 2OSENZWEIG AND ,OMOLINO RELATIVELY LITTLE HAS BEEN PUBLISHED ON SPECIES AREA RELATIONSHIPS OF NATURALIZED OR OTHER WISE EXOTIC SPECIES !LTHOUGH IT SEEMS LIKELY THAT SOMEONE HAS EXAMINED A SPE CIES AREA RELATIONSHIP FOR EXOTIC SPECIES PRIOR TO YEARS AGO THE lRST PAPER WE ARE AWARE OF THAT EXPLICITLY DISCUSSES SUCH A RELATIONSHIP IS BY #RAWLEY WHO COMPARED THE SPECIES AREA RELATIONSHIPS OF NATIVE AND EXOTIC PLANT SPECIES -ORE RECENTLY 0YSEK EXAMINED THE SPECIES AREA RELATIONSHIPS OF NATIVE AND EXOTIC SPECIES IN CITIES OF CENTRAL %UROPE /THER SUBSEQUENT STUDIES THAT HAVE CON SIDERED THE RELATIONSHIP BETWEEN AREA AND EXOTIC SPECIES INCLUDE WORK BY #HOWN ET AL ON 3OUTHERN /CEAN )SLANDS BY ,ONSDALE ACROSS SITES FROM AROUND THE WORLD BY -OODY ON THE #HANNEL )SLANDS OF #ALIFORNIA BY -C+INNEY A IN PROTECTED AREAS OF THE 53 BY -C+INNEY B AND 2EJMANEK ON EXOTIC lSHES AND PLANTS IN 53 3TATES BY 0YSEK ET AL A AND B ON EXOTIC PLANTS IN NATURE RESERVES OF CENTRAL %UROPE AND MOST RECENTLY BY 2USSELL ET AL ON THE OFFSHORE ISLANDS OF .EW :EALAND (ERE WE BUILD ON THIS PREVIOUS WORK TO CONSIDER WHAT EXAMINATIONS OF EXOTIC SPECIES AREA RELATIONSHIPS AND THEIR COMPARISONS WITH NATIVE SPECIES AREA RELATIONSHIPS CAN TELL US ABOUT SPECIES INVASION AND ABOUT THE FACTORS THAT LIMIT AND MAINTAIN SPECIES RICHNESS )N PARTICULAR WE FOCUS ON TWO SETS OF ISSUES &IRST WHAT DO CONTRASTS AS WELL AS SIMILARITIES BETWEEN THE FORM OF NATIVE AND EXOTIC SPECIES AREA RELATION SHIPS TELL US ABOUT INVASION AND BIOGEOGRAPHIC PROCESSES 3ECOND HOW DO CHANGES IN SPECIES AREA RELATIONSHIPS FOLLOWING SPECIES INVASIONS INFORM OUR UNDERSTAND ING OF HOW SPECIES RICHNESS HAS CHANGED AND WILL CHANGE IN THE FUTURE AT DIFFERENT SPATIAL SCALES AND IN LOCATIONS THAT VARY IN THEIR DEGREE OF ISOLATION #ONTRASTS AND SIMILARITIES BETWEEN NATIVE AND NATURALIZED SPECIES AREA RELATIONSHIPS
3OME PREVIOUS WORK HAS CONSIDERED THE IMPLICATIONS OF DIFFERENCES IN THE SLOPES OF SPECIES AREA RELATIONSHIPS BETWEEN NATIVE AND EXOTIC SPECIES #RAWLEY FOUND SIGNIlCANT SPECIES AREA RELATIONSHIPS FOR NATIVE AND EXOTIC PLANT SPECIES
$& 3AX AND 3$ 'AINES
WHEN EXAMINING DATA FROM ACROSS REGIONS IN "RITAIN )RELAND EASTERN .ORTH !MERICA AND 7ESTERN !USTRALIA (OWEVER HE FOUND THE SLOPE OF THE SPECIES AREA RELATIONSHIP TO BE STEEPER FOR NATIVE SPECIES WHICH HE SUGGESTED WAS A CONSE QUENCE OF THE HIGHER BETA DIVERSITY OF NATIVE SPECIES )N ANOTHER STUDY 0YSEK FOUND IN CITIES OF CENTRAL %UROPE THAT NEOPHYTES EXOTIC SPECIES THAT HAVE INVADED THE REGION SINCE !$ SHOW A SIGNIlCANTLY STEEPER SPECIES AREA SLOPE THAN DO ARCHAEOPHYTES EXOTICS THAT INVADED PRIOR TO OR NATIVE SPECIES (E SUGGESTED THAT THIS MIGHT BE DUE TO THE POTENTIALLY INHOSPITABLE ENVIRON MENT FOR NEOPHYTES THAT EXISTS OUTSIDE URBAN AREAS IF THIS WERE TRUE CITIES WOULD SERVE AS HABITAT hISLANDSv FOR NEOPHYTES THUS EXPLAINING THEIR STEEPER SPECIES AREA SLOPE AS ISLANDS TYPICALLY EXHIBIT MUCH STEEPER SLOPES THAN COMPARABLE CONTINENTAL REGIONS 2OSENZWEIG 2USSELL ET AL FOUND THE SLOPE OF THE SPECIES AREA RELATIONSHIP FOR EXOTIC MAMMALS ON OFFSHORE ISLANDS OF .EW :EALAND TO BE 4HEY SUGGEST THAT THIS SLOPE WHICH IS SHALLOWER THAN THOSE OFTEN SEEN ON ISLANDS MAY SUGGEST THAT THE INTERACTION BETWEEN AREA AND ISOLATION IS REDUCED FOR THESE MAMMALS SINCE THEIR TRANSPORT AND INTRODUCTION HAS BEEN FACILITATED BY HUMANS /F COURSE INTERPRETING DIFFERENCES BETWEEN THE SLOPES OF DIFFERENT SPECIES AREA RELATIONSHIPS IS NOT A TRIVIAL MATTER AND IS AN ACTIVITY WITH MANY POTENTIAL PITFALLS EG -ARTIN ,OMOLINO .EVERTHELESS WE BELIEVE THAT MAKING SUCH COMPARISONS BETWEEN NATIVE AND EXOTIC RELATIONSHIPS MAY BE EXTREMELY VALUABLE !S THIS CHAPTER HOWEVER IS A lRST ATTEMPT TO SEARCH FOR GENERALITIES FROM COMPARISONS OF MANY NATIVE AND EXOTIC SPECIES AREA RELATION SHIPS WE HERE EXAMINE A TOPIC THAT WE BELIEVE IS MORE READILY TRACTABLE NAMELY A COMPARISON OF NATIVE AND EXOTIC SPECIES AREA RELATIONSHIPS THAT DO AND DO NOT SHOW SIGNIlCANT LINEAR RELATIONSHIPS ON A LOG LOG SCALE !LTHOUGH THE SPECIES AREA RELATIONSHIP IS A VERY GENERAL PATTERN NOT ALL DATA SETS SHOW A SIGNIlCANT RELATIONSHIP BETWEEN THESE VARIABLES &URTHER THE NATIVE AND EXOTIC COMPONENTS OF THESE RELATIONSHIPS MAY NOT BEHAVE IN SIMILAR WAYS &OUR OUTCOMES ARE POSSIBLE IN COMPARISONS OF NATIVE AND EXOTIC SPECIES AREA RELATION SHIPS NATIVES SHOW A SIGNIlCANT LINEAR RELATIONSHIP BUT EXOTICS DO NOT BOTH NATIVES AND EXOTICS SHOW SIGNIlCANT RELATIONSHIPS EXOTICS SHOW A SIGNIlCANT RELATIONSHIP BUT NATIVES DO NOT OR NEITHER NATIVES OR EXOTICS SHOW SIGNIlCANT RELATIONSHIPS !S THE OCCURRENCE OF THE FOURTH OUTCOME IN WHICH NEITHER NATIVES OR EXOTICS SHOW SIGNIlCANT SPECIES AREA RELATIONSHIPS SHOULD BE EXCEEDINGLY RARE WE RESTRICT OUR DISCUSSION HERE TO THE lRST THREE OUTCOMES LISTED ABOVE 3PECIES AREA RELATIONSHIPS FOR NATIVES BUT NOT FOR EXOTICS
7E BEGIN WITH THE SITUATION WHERE NATIVE SPECIES DO AND EXOTIC SPECIES DO NOT SHOW A SIGNIlCANT POSITIVE LINEAR RELATIONSHIP ON A LOG LOG SCALE BETWEEN AREA AND SPECIES RICHNESS 7E ILLUSTRATE THIS WITH PLANT SPECIES IN #ALIFORNIA #OUNTIES 53 3TATES AND -EXICAN 3TATES &IG )N EACH CASE NATIVE SPECIES SHOW A STRONG POSITIVE SPECIES AREA RELATIONSHIP BUT EXOTIC SPECIES DO NOT )T IS IMPORTANT TO NOTE THAT NOT ONLY ARE THE RELATIONSHIPS BETWEEN EXOTIC SPECIES RICHNESS AND AREA NOT
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
SIGNIlCANT BUT THAT THERE IS NO HINT OF A TREND TOWARDS A POSITIVE RELATIONSHIP 'IVEN THE BROAD SPATIAL RANGE EXAMINED NEARLY THREE ORDERS OF MAGNITUDE OF AREA IN EACH CASE AND LARGE NUMBERS OF EXOTIC SPECIES MORE THAN EXOTIC SPE CIES IN EACH CASE IT IS SOMEWHAT SURPRISING THAT EXOTIC SPECIES DO NOT SHOW THE EXPECTED RELATIONSHIP 7E SUGGEST HERE THAT EXOTICS MAY NOT SHOW THE EXPECTED RELATIONSHIP FOR ANY ONE OF THE FOLLOWING THREE REASONS EXOTIC SPECIES ARE INHERENTLY DIFFERENT THAN NATIVE SPECIES AND SHOULD NOT BE EXPECTED TO RESPOND IN SIMILAR WAYS TO AREA AS NATIVE SPECIES THERE ARE A LIMITED NUMBER OF EXOTIC SPECIES WITHIN EACH OF THESE REGIONS SUCH THAT EVEN SMALL SUBREGIONS IE COUN TIES OR STATES COULD HOLD ALL OR MOST OF THE EXOTIC SPECIES IN QUESTION THEREBY MAKING IT UNLIKELY FOR THERE TO BE A SIGNIlCANT RELATIONSHIP AT THE SCALES ANALYZED EXOTIC SPECIES ARE MORE STRONGLY INmUENCED BY THE DISTRIBUTION OF HUMAN POPU LATIONS THAN BY AREA THIS COULD BE TRUE FOR ANY NUMBER OF REASONS SUCH AS A CORRESPONDENCE BETWEEN HUMAN POPULATION SIZE AND INTRODUCTION EFFORT OF EXOTIC SPECIES BETWEEN HUMAN POPULATION DENSITY AND DISTURBANCE WHICH MAY FAVOR EXOTIC SPECIES OR BETWEEN HUMAN POPULATION DENSITY AND CLIMATE MATCHING THAT OCCURS FROM SOURCE AREAS FOR EXOTIC SPECIES WHERE MANY HUMANS HAVE COLONIZED FROM AND EXOTICS ARE LOCALLY ADAPTED AND RECIPIENT AREAS FOR EXOTIC SPECIES WHERE MANY HUMANS NOW RESIDE AND EXOTICS ARE PREADAPTED FOR LOCAL CONDITIONS $ISCRIMINATING AMONG THESE HYPOTHESES IS NOT TRIVIAL AS THEY ARE NEITHER MUTUALLY EXCLUSIVE NOR NECESSARILY EXHAUSTIVE .EVERTHELESS WITH THE DATA AVAIL ABLE TO US WE SHOULD BE ABLE TO DISCRIMINATE AMONG AT LEAST SOME OF OUR STATED
&IG 3PECIES AREA RELATIONSHIPS FOR NATIVE AND EXOTIC SPECIES OF PLANTS 3OLID CIRCLES ARE NATIVE AND EMPTY CIRCLES ARE EXOTIC SPECIES OF VASCULAR PLANTS ! .ATIVES SHOW A POSITIVE LINEAR RELATIONSHIP 2 Z # P WHILE EXOTICS DO NOT SHOW A SIGNIlCANT RELATIONSHIP DATA FROM #ALmORA WWWCALmORAORG " .ATIVES SHOW A POSITIVE LINEAR RELATIONSHIP 2 Z # P WHILE EXOTICS DO NOT SHOW A SIGNIlCANT RELATIONSHIP SEE !PPENDIX FOR A DESCRIPTION OF DATA SOURCES AND METHODS # .ATIVES SHOW A POSITIVE LINEAR RELATIONSHIP 2 Z # P WHILE EXOTICS DO NOT SHOW A SIGNIlCANT RELATIONSHIP NOTE THAT THESE DATA ARE FOR mOWERING PLANTS ONLY DATA FROM 6ILLASE×OR AND %SPINOSA 'ARCIA
$& 3AX AND 3$ 'AINES
HYPOTHESES WITH THE GOAL OF BETTER UNDERSTANDING THE CURIOUS ABSENCE OF SPECIES AREA RELATIONSHIPS FOR THESE EXOTIC SPECIES 4HE lRST HYPOTHESIS THAT OF INHERENT DIFFERENCES BETWEEN NATIVE AND EXOTIC SPECIES SEEMS UNLIKELY THIS IS BECAUSE THE CHARACTERISTICS OF THE NATIVE AND EXOTIC SPECIES IN QUESTION ARE UNLIKELY TO BE SO DIFFERENT THAT THEY SHOULD RESPOND IN COMPLETELY DIFFERENT WAYS TO PHYSICAL OR BIOTIC CHARACTERISTICS OF THE ENVIRONMENT THAT PROMOTE RICHNESS WITH INCREASING AREA SUCH AS INCREASES IN HABITAT DIVERSITY .EVERTHELESS THIS IS A POSSIBILITY AND ONE THAT IS DIFlCULT TO RULE OUT &OR -EXICAN 3TATES THIS DOES NOT APPEAR TO BE THE CASE HOWEVER AS NATIVE AND EXOTIC RICHNESS ARE STRONGLY POSITIVELY CORRELATED ACROSS STATES 2 P &OR #ALIFORNIA #OUNTIES AND 53 3TATES HOWEVER NO SUCH POSITIVE RELATIONSHIP IS APPARENT LEAVING THIS HYPOTHESIS AS A POSSIBILITY FOR THOSE AREAS 4HE SECOND HYPOTHESIS THAT OF EXOTIC SPECIES POOL EXHAUSTION WITHIN INDIVIDUAL SAMPLE UNITS ALSO SEEMS UNLIKELY SINCE A RELATIVELY SMALL FRACTION OF THE TOTAL NUMBER OF EXOTIC SPECIES IN THESE REGIONS ARE PRESENT WITHIN INDIVIDUAL SAMPLE AREAS &OR EXAMPLE BETWEEN CA AND OF THE TOTAL NUMBER OF EXOTIC PLANT SPECIES IN -EXICO ARE FOUND WITHIN INDIVIDUAL STATES SUG GESTING THAT THE NUMBER OF EXOTIC SPECIES PRESENT WITHIN INDIVIDUAL STATES HAS NOT APPROACHED OR EXHAUSTED THE TOTAL POOL OF SPECIES AVAILABLE IN -EXICO NOTE THAT SIMILAR PATTERNS EXIST FOR #ALIFORNIA #OUNTIES AND 53 3TATES 4HE THIRD HYPOTH ESIS WHICH SUGGESTS THAT HUMAN POPULATION DENSITY WILL INmUENCE EXOTIC SPECIES RICHNESS IS STRONGLY SUPPORTED IN #ALIFORNIA #OUNTIES 53 AND -EXICAN 3TATES WHERE IN ALL CASES HUMAN POPULATION DENSITY IS STRONGLY CORRELATED WITH EXOTIC SPECIES RICHNESS &IG $IFFERENTIATING THE PROXIMATE CAUSE OF THIS PATTERN IS DIFlCULT HOWEVER AS INTRODUCTION EFFORT DISTURBANCE OR SOME TYPE OF CLIMATE MATCHING EXPLANATION ALL SEEM CREDIBLE )T IS CURIOUS TO NOTE ADDITIONALLY THAT NATIVE SPECIES EITHER DO NOT SHOW A SIGNIlCANT RELATIONSHIP WITH HUMAN POPULA TION IN #ALIFORNIA #OUNTIES OR SHOW RELATIONSHIPS WHERE LESS VARIANCE IS EXPLAINED RELATIVE TO EXOTIC SPECIES IN 53 AND -EXICAN 3TATES INDICATING THAT HUMAN POPU LATION IS A MUCH BETTER INDICATOR OF EXOTIC THAN NATIVE RICHNESS 3PECIES AREA RELATIONSHIPS FOR NATIVES AND EXOTICS
.ATIVE AND EXOTIC COMPONENTS OF PARTICULAR SPECIES AREA RELATIONSHIPS IE FOR PARTICULAR TAXA ACROSS A PARTICULAR SET OF AREAS CAN BOTH SHOW SIGNIlCANT POSITIVE LINEAR RELATIONSHIPS ON PLOTS OF LOG AREA AND LOG SPECIES RICHNESS 7E ILLUSTRATE THIS HERE WITH TWO EXAMPLES PLANTS ON THE #HANNEL )SLANDS OF #ALIFORNIA AND PLANTS ON OCEANIC ISLANDS &IG " AND # .OTE ALSO THAT PLANTS IN MAINLAND SITES OF #ALIFORNIA SHOW A NON SIGNIlCANT BUT STILL POSITIVE TREND BETWEEN AREA AND EXOTIC SPECIES RICHNESS AND A SIGNIlCANT POSITIVE RELATIONSHIP BETWEEN NATIVE RICHNESS AND AREA &IG ! 3UCH PATTERNS IE WHERE BOTH NATIVE AND EXOTIC SPECIES SHOW POSITIVE RELATIONSHIPS BETWEEN AREA AND RICHNESS CAN BE ARGUED TO BE CONSISTENT WITH THE NULL HYPOTHESIS THAT SPECIES RICHNESS WILL ALWAYS BE INmUENCED BY AREA !S SUCH THESE RESULTS ARE NOT PARTICULARLY SURPRISING BUT NEVERTHELESS OF INTEREST BECAUSE THEY SUGGEST THAT NATIVE AND EXOTIC SPECIES ARE BOTH RESPONDING IN SIMILAR
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
&IG (UMAN POPULATION AND RICHNESS OF NATIVE AND EXOTIC SPECIES 3OLID CIRCLES ARE NATIVE AND EMPTY CIRCLES ARE EXOTIC SPECIES ! %XOTIC SPECIES SHOW A POSITIVE LINEAR RELATIONSHIP 2 P WHILE NATIVES DO NOT SHOW A SIGNIlCANT RELATIONSHIP " %XOTIC AND NATIVE SPECIES SHOW POSITIVE LINEAR RELATIONSHIPS NATURALIZED SPECIES 2 P NATIVES 2 P # %XOTIC AND NATIVE SPECIES SHOW POSITIVE LINEAR RELATIONSHIPS NATURALIZED SPECIES 2 P NATIVES 2 P $ATA SOURCES AS CITED IN &IG FOR PLANTS DATA FOR HUMAN POPULATION SIZE ARE FROM #ALIFORNIA #OUNTIES ESTIMATES HTTPWWWDOFCAGOVHTML$EMOGRAPREPNDAT HTM 53 3TATES ESTIMATES HTTPWWWCENSUSGOVMAINWWWCENHTML AND -EXICAN STATES ESTIMATES HTTPWWWCITYPOPULATIONDE-EXICOHTML
WAYS TO DIFFERENCES IN AREA /N THE #HANNEL )SLANDS HOWEVER THE PATTERNS ARE NOT IDENTICAL THE SLOPES OF THE RELATIONSHIPS ARE SIMILAR NATIVES Z EXOTICS Z BUT THE SLOPE OF THE EXOTIC RELATIONSHIP IS SHALLOWER WHICH IS CONSISTENT WITH #RAWLEYS CONCLUSION THAT BETA DIVERSITY IS REDUCED FOR EXOTIC SPECIES RELATIVE TO NATIVES 4HIS SHALLOWER SLOPE IS ALSO CONSISTENT WITH THE EXPECTATION THAT EXOTIC SPECIES ARE NOT FUNCTIONALLY AS DISPERSAL LIMITED AS NATIVES BECAUSE STEEPER SLOPES ARE GENERALLY CONSIDERED TO BE INDICATIVE OF INCREASED INSULARITY AND ISOLATION EG 2OSENZWEIG 2USSELL ET AL 4HIS CONCLUSION IS STRONGLY SUPPORTED IN THIS CASE BY EXAMINING THE RELATIONSHIP THAT NATIVE AND EXOTIC SPECIES HAVE RESPECTFULLY WITH ISOLATION BY PLOTTING THE RESIDUALS OF LOG AREA AND LOG RICHNESS AGAINST DISTANCE OF EACH ISLAND TO THE MAINLAND IT IS CLEAR THAT THE RICHNESS OF NATIVE SPECIES IS STRONGLY INmUENCED BY ISOLATION WHILE THE RICHNESS OF EXOTIC SPECIES IS NOT &IG )N THIS CASE IT APPEARS THEREFORE THAT BOTH NATIVE AND EXOTIC SPECIES ARE RESPONDING IN SIMILAR WAYS TO AREA BUT ARE DIFFERENTIALLY AFFECTED BY ISOLATION )N CONTRAST TO THIS PATTERN ON THE #HANNEL )SLANDS THE PATTERN ON OCEANIC ISLANDS IS SOMEWHAT DIFFERENT /N OCEANIC ISLANDS BOTH THE SLOPES AND INTERCEPTS OF THE SPECIES AREA RELATIONSHIPS FOR NATIVE AND EXOTIC SPECIES ARE ALMOST IDENTICAL NATIVES Z # EXOTICS Z # 4HIS RESULT IS A CONSE QUENCE OF THE EXTREMELY TIGHT COUPLING BETWEEN NATIVE AND EXOTIC SPECIES RICHNESS
$& 3AX AND 3$ 'AINES
&IG 3PECIES AREA RELATIONSHIPS FOR NATIVE AND EXOTIC SPECIES OF PLANTS 3OLID CIRCLES ARE NATIVE AND EMPTY CIRCLES ARE EXOTIC SPECIES OF VASCULAR PLANTS ! .ATIVES SHOW A POSITIVE LINEAR RELATIONSHIP 2 Z # P WHILE EXOTICS DO NOT SHOW A SIGNIlCANT RELATIONSHIP ALTHOUGH THE TREND IS NEVERTHELESS POSITIVE SEE !PPENDIX FOR A DESCRIPTION OF DATA SOURCES AND METHODS " .ATIVES AND EXOTICS SHOW POSITIVE LINEAR RELATIONSHIPS NATIVES 2 Z # P EXOTICS 2 Z # P DATA FROM *UNAK ET AL # .ATIVES AND EXOTICS SHOW POSITIVE LINEAR RELATIONSHIPS NATIVES 2 Z # P EXOTICS 2 Z # P DATA FROM 3AX ET AL
&IG )SOLATION AND THE RICHNESS OF PLANT SPECIES ON THE #HANNEL )SLANDS OF #ALIFORNIA ! 3IGNIlCANT LINEAR RELATIONSHIP BETWEEN THE DISTANCE OF ISLANDS TO THE MAINLAND AND THE RESIDUALS OF LOG AREA AND LOG NUMBER OF NATIVE SPECIES 2 P " 4HE SAME RELATIONSHIP FOR EXOTIC SPECIES IS NOT SIGNIlCANT $ATA FROM *UNAK ET AL 3EE -OODY FOR A SIMILAR EXAMINATION OF THESE DATA
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
ON THESE ISLANDS LOG NATIVE SPECIES VS LOG EXOTIC SPECIES 2 P #LEARLY BOTH NATIVES AND EXOTICS ARE RESPONDING TO AREA GIVEN THE HIGHLY SIG NIlCANT RELATIONSHIP BETWEEN AREA AND RICHNESS BUT IN THIS CASE IT APPEARS THAT OTHER FACTORS ARE ALSO CONTRIBUTING TO THE TIGHT COUPLING BETWEEN NATIVE AND EXOTIC SPECIES RICHNESS !T THIS POINT THESE OTHER FACTORS ARE UNCLEAR BUT THIS PATTERN IS INTRIGUING AND AT PRESENT MAY BE ONE OF THE MORE IMPORTANT UNEXPLAINED PATTERNS IN SPECIES INVASIONS AND BIOGEOGRAPHY 3PECIES AREA RELATIONSHIPS FOR EXOTICS BUT NOT FOR NATIVES
&INALLY WE CONSIDER SCENARIOS IN WHICH EXOTIC SPECIES SHOW A SPECIES AREA RELA TIONSHIP AND NATIVE SPECIES DO NOT 7E ILLUSTRATE THIS HERE WITH FRESHWATER lSHES IN WATERSHEDS OF TEMPERATE .ORTH !MERICA AND WATERSHEDS OF #ALIFORNIA &IG )N BOTH THESE EXAMPLES EXOTIC SPECIES DElNED HERE AS BEING NON NATIVE TO THE WATERSHEDS IN QUESTION SHOW SIGNIlCANT POSITIVE LINEAR RELATIONSHIPS IN LOG LOG SPACE WHILE NATIVE SPECIES DO NOT 7E BELIEVE THAT THERE ARE TWO PRINCIPAL HYPOTHESES THAT CAN EXPLAIN THESE PATTERNS &IRST FRESHWATER lSHES ARE EXTREMELY DISPERSAL LIMITED AND MAY HAVE HISTORICALLY BEEN UNABLE TO TAKE ADVANTAGE OF LARGE AREAS BECAUSE OF EXTREME BARRIERS TO DISPERSAL )F THE LIKELIHOOD OF lSHES COLONIZING A WATERSHED IS DRIVEN MORE BY THE NATURE AND SEVERITY OF THE DISPERSAL BARRIER THAN BY THE SIZE OF THE WATERSHED THEN NATIVE RICHNESS MAY BE POORLY CORRELATED WITH WATERSHED AREA $ISPERSAL BARRIERS HOWEVER SHOULD NOT BE AS IMPORTANT FOR EXOTIC FRESHWATER lSHES BECAUSE IN MOST CASES THE SPREAD OF THESE SPECIES IS FACILITATED BY DIRECT HUMAN INTRODUCTIONS ! SECOND POTENTIAL EXPLANATION FOR THE DIFFERENCE IN NATIVE AND EXOTIC SPECIES AREA RELATIONSHIPS OF FRESHWATER lSHES IN .ORTH !MERICA AND #ALIFORNIA MAY BE DUE TO RECENT ANTHROPOGENIC CHANGES IN THE ENVIRONMENT &OR EXAMPLE MANY OF THE LARGEST WATERSHEDS IN THE DATABASE OF 53 WATERSHEDS ARE FOUND IN THE WESTERN 53 )N THE WESTERN 53 MANY DAMS HAVE BEEN BUILT AND LACUS TRIAN ENVIRONMENTS CREATED IN REGIONS THAT HISTORICALLY HAD VERY FEW LAKES EG -ARCHETTI ET AL 4HE CREATION OF THESE LAKES MAY HAVE INCREASED THE CAPAC ITY OF THESE REGIONS TO SUPPORT A LARGER VARIETY OF FRESHWATER lSH SPECIES 4HIS PAT TERN IS THEREFORE CONSISTENT WITH THE HYPOTHESIS THAT EXOTIC SPECIES ARE RESPONDING TO CURRENT ENVIRONMENTAL CONDITIONS WHILE NATIVE SPECIES WHICH HAVE NOT HAD SUFlCIENT TIME TO SPECIATE AND lLL THESE NEWLY AVAILABLE HABITATS ARE RESPONDING TO CONDITIONS THAT WERE HISTORICALLY PRESENT )F THIS IS TRUE THEN IT WOULD SUGGEST THAT EXOTIC SPECIES WHEN THEY ARE WIDELY INTRODUCED ACROSS POTENTIAL SUITABLE HABITATS MAY BE A BETTER INDICATOR OF AN AREAS CAPACITY TO SUPPORT SPECIES THAN THE NATIVES THEMSELVES WHICH MAY INSTEAD BE IN A DISPERSAL LIMITED STATE OF DISEQUILIBRIUM BETWEEN ENVIRONMENTAL CAPACITY AND SPECIES RICHNESS #HANGES IN SPECIES AREA RELATIONSHIPS
/NE OF THE MOST PERTINENT ASPECTS OF STUDYING SPECIES AREA RELATIONSHIPS IN TODAYS CHANGING WORLD IS EXAMINING HOW SPECIES AREA RELATIONSHIPS HAVE CHANGED WITH
$& 3AX AND 3$ 'AINES
&IG 3PECIES AREA RELATIONSHIPS FOR NATIVE AND EXOTIC SPECIES OF FRESHWATER lSH ! .ATIVES DO NOT SHOW A SIGNIlCANT RELATIONSHIP DATA FROM 'IDO AND "ROWN " %XOTIC SPECIES SHOW A POSITIVE LINEAR RELATIONSHIP 2 Z # P DATA FROM 'IDO AND "ROWN # .ATIVES DO NOT SHOW A SIGNIlCANT RELATIONSHIP DATA FROM -OYLE AREA ESTIMATES FOR THE WATERSHEDS USED IN THIS ANALYSIS ARE FROM HTTPENDEAVORDESUCDAVISEDUNEWCARA $ %XOTIC SPECIES SHOW A POSITIVE LINEAR RELATIONSHIP 2 Z # – P DATA SOURCES AS CITED ABOVE FOR PANEL #
THE ADDITION OF EXOTIC SPECIES AND THE EXTINCTION OF NATIVES 2OSENZWEIG AND #OLLINS ET AL CONSIDER THIS ISSUE WITH THOUGHT EXPERIMENTS THAT VARY THE NUMBER OF EXOTIC SPECIES EXCHANGED BETWEEN REGIONS TO PREDICT WHAT THE EFFECTS OF EXOTIC SPECIES INTRODUCTIONS WILL BE FOR LOCAL AND GLOBAL SPECIES RICHNESS
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
(ERE WE EXPLORE THE CLOSELY RELATED ISSUE OF HOW SPECIES AREA RELATIONSHIPS HAVE ACTUALLY CHANGED OVERTIME USING EMPIRICAL DATA AND CONSIDER WHAT INSIGHTS THESE CHANGES MAY PROVIDE )N &IG WE HAVE PLOTTED THE TREND LINES OF HISTORIC AND CURRENT SPECIES AREA RELATIONSHIPS OF PLANT SPECIES FOR SEVERAL REGIONS BY @HISTORIC WE MEAN THE NUMBER OF NATIVE SPECIES BELIEVED TO HAVE BEEN PRESENT BEFORE ANY ANTHROPOGENIC EXTINC TIONS OCCURRED AND BY @CURRENT WE MEAN THE NUMBER OF SPECIES PRESENT TODAY WHICH IS THE SUM OF EXTANT NATIVE AND NATURALIZED SPECIES $ATA ON THE NUMBER OF NATIVE EXTIRPATIONS IS AVAILABLE FOR ALL OF THE PLOTTED TREND LINES EXCEPT FOR mORAS FROM MAINLAND SITES IN #ALIFORNIA (OWEVER GIVEN THE EXTREMELY LOW NUMBER OF PLANT SPECIES THAT HAVE BEEN EXTIRPATED FROM COMPARABLE #HANNEL )SLAND SITES MEAN OF FEWER THAN FOUR SPECIES PER ISLAND AND FROM THE OTHER PLANT DATA SETS CONSIDERED HERE IT SEEMS LIKELY THAT THE NUMBER OF SPECIES LOST FROM THE #ALIFORNIA MAINLAND SITES SHOULD ALSO BE RELATIVELY LOW AND SHOULD NOT SIGNIlCANTLY IMPACT THE OBSERVED PATTERNS !LL OF THE PATTERNS PLOTTED SHOW ONE OVERRIDING SIMILARITY IE AN INCREASE IN THE NUMBER OF SPECIES PRESENT ACROSS SITES &IG 4HE MAGNITUDE OF THIS INCREASE HOWEVER IS NOT IDENTICAL BETWEEN REGIONS BUT IS INSTEAD GENERALLY CONSISTENT WITH THE DEGREE OF ISOLATION AND RELATIVE MEAN RICHNESS OF EACH OF THESE REGIONS AVERAGE INCREASE IN RICHNESS ON OCEANIC ISLANDS #HANNEL )SLANDS #ALIFORNIA MAINLAND SITES 53 3TATES AND #ALIFORNIA #OUNTIES NOTE THAT #ALIFORNIA #OUNTIES AND 53 3TATES HAVE SIMILAR MEAN NUMBERS OF NATIVE SPECIES AND RESPECTFULLY BUT THAT THE SPATIAL EXTENT AND EFFECTIVE ISO LATION BETWEEN 53 3TATES IS MUCH HIGHER THAN THAT BETWEEN #ALIFORNIA #OUNTIES 4HESE INCREASES IN SPECIES RICHNESS PARTICULARLY THE POSITIVE CORRELATION BETWEEN ISOLATION AND THE MAGNITUDE OF INCREASED SPECIES RICHNESS IS CONSISTENT WITH THE CHANGES PREDICTED TO OCCUR BY #OLLINS ET AL AND ALSO WITH $ARWINS OBSER VATION THAT HUMANS ARE lLLING UP ISOLATED REGIONS FAR MORE FULLY THAN NATURE HAS DONE !NOTHER PATTERN EVIDENT IN &IG IS THAT WITH THE ESTABLISHMENT OF NATURALIZED SPECIES RELATIVELY LARGE AREAS ARE @CATCHING UP IN TOTAL PLANT RICHNESS WITH THOSE REGIONS THAT HAVE HISTORICALLY BEEN LESS ISOLATED 4HUS THE LARGEST #HANNEL )SLANDS NOW HAVE AS MANY PLANT SPECIES AS WERE HISTORICALLY FOUND ON EQUAL SIZED AREAS OF THE #ALIFORNIA MAINLAND &IG 3IMILARLY LARGE OCEANIC ISLANDS NOW HAVE AS MANY PLANT SPECIES AS WERE HISTORICALLY FOUND WITHIN 53 3TATES OF COMPARABLE SIZE &IG 7HILE COMPARING THE #HANNEL )SLANDS WITH #ALIFORNIA MAINLAND SITES SEEMS REASONABLE IT IS NOT CLEAR HOWEVER TO WHICH LANDMASSES THE LARGEST OCEANIC ISLANDS SHOULD BE COMPARED 4O EXPLORE THIS FURTHER WE CONSIDER THE TWO LARGEST OCEANIC ISLANDS IN OUR DATABASE (AWAII AND .EW :EALAND (AWAIIS CLOS EST CONTINENTAL LAND MASS IS .ORTH !MERICA AND IN FACT (AWAIIS GREATEST NUMBER OF NATURAL COLONISTS ARE BELIEVED TO HAVE COME FROM THE !MERICAN CONTINENTS 6 &UNK PERSONAL COMMUNICATION "ECAUSE (AWAII IS PRESENT AT HIGH TROPICAL LATITUDES THE MOST REASONABLE COMPARISON IN .ORTH !MERICA WOULD SEEM TO BE WITH EQUAL SIZED AREAS OF -EXICO #OMPARING BOTH THE HISTORIC AND CURRENT NUMBER
$& 3AX AND 3$ 'AINES
&IG #HANGE IN SPECIES AREA RELATIONSHIPS FOR PLANTS 4HE DASHED LINES INDICATE THE HISTORIC RELATIONSHIP BETWEEN AREA AND NATIVE SPECIES OF VASCULAR PLANTS 4HE SOLID LINES INDICATE THE CURRENT RELATIONSHIP BETWEEN AREA AND ALL EXTANT SPECIES OF VASCULAR PLANTS NATIVE AND EXOTIC )N ALL CASES THE INTERCEPT OF THESE SPECIES AREA RELATIONSHIPS HAVE SHIFTED UP AND IN SOME CASES THE SLOPE OF THESE RELATIONSHIPS HAVE BECOME MORE SHALLOW
OF PLANT SPECIES IN (AWAII WITH THE NUMBER OF NATIVE SPECIES PRESENT IN -EXICAN 3TATES IT IS CLEAR THAT THE HISTORIC mORA OF (AWAII WAS DEPAUPERATE COMPARED WITH -EXICAN 3TATES (OWEVER THIS DISCREPANCY HAS NOW LARGELY DISAPPEARED #URRENT PLANT RICHNESS IS RELATIVELY CLOSE TO WHAT WOULD BE EXPECTED IF (AWAII WERE A PIECE OF MAINLAND OF .ORTH !MERICA &IG ! .EW :EALANDS CLOSEST CONTINENT IS !USTRALIA AND .EW :EALANDS GREATEST NUMBER OF NATURAL COLONISTS HAVE COME FROM !USTRALIA -C'LONE ET AL #OMPARING PLANT SPECIES IN .EW :EALAND WITH THOSE IN !USTRALIAN 3TATES SHOWS THAT HISTORIC SPECIES RICHNESS OF PLANTS IN .EW :EALAND WAS ONLY MINIMALLY LOWER THAN IN !USTRALIAN 3TATES OF COMPARABLE SIZE AND THAT CURRENT PLANT RICHNESS IS NOW SOMEWHAT GREATER THAN WOULD BE
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
EXPECTED CONSIDERING THE ROLE OF AREA ALONE WERE .EW :EALAND PRESENT ON THE MAINLAND OF !USTRALIA &IG " 4HE LONG TERM IMPLICATIONS OF THESE CHANGES IN RICHNESS ARE DIFlCULT TO ASCERTAIN AS ARE THE LONG TERM TRAJECTORIES OF CONTINUING CHANGES IN SPECIES RICHNESS ON THESE ISLANDS )T IS POSSIBLE THAT NET RICHNESS WILL EVENTUALLY DECREASE IF THERE IS A LONG TIME LAG BEFORE SIGNIlCANT NUMBERS OF NATIVE EXTINCTIONS OCCUR !LTERNATIVELY RICHNESS MAY CONTINUE TO INCREASE IF EXTINCTION RATES REMAIN LOW AND ADDITIONAL SPECIES BECOME ESTABLISHED 2OSENZWEIG #OLLINS ET AL 3AX ET AL 5NDOUBTEDLY ADDITIONAL STUDY WILL HELP TO CLARIFY THIS ISSUE (OWEVER GIVEN THE EVIDENCE AVAILABLE FROM THE SPECIES AREA RELATIONSHIPS CONSIDERED HERE IT APPEARS THAT FURTHER EFFECTIVE DECREASES IN ISOLA TION MEDIATED BY THE INTRODUCTION OF ADDITIONAL EXOTIC SPECIES SHOULD LEAD TO CON TINUED INCREASES IN THE INTERCEPT OF SPECIES AREA RELATIONSHIPS FOR ANY REGION AND TO FURTHER DECREASES IN THE SLOPE OF THOSE RELATIONSHIPS IE TO CONTINUED INCREASES IN RICHNESS FOR INDIVIDUAL AREAS )T IS IMPORTANT TO STRESS THAT THE INCREASES IN RICHNESS DESCRIBED HERE SHOULD NOT BE CONSTRUED AS @GOOD BUT INSTEAD AS EVIDENCE OF THE TYPES OF DIFFERENTIAL IMPACTS THAT HUMANS ARE HAVING ON VARIOUS REGIONS AROUND THE WORLD )NDEED THESE DATA
&IG #HANGE IN SPECIES RICHNESS OF PLANTS ON (AWAII AND .EW :EALAND RELATIVE TO SPECIES AREA RELATIONSHIPS OF NEAREST CONTINENTS %MPTY CIRCLES REPRESENT HISTORIC NUMBER OF NATIVE SPECIES ON CONTINENTS SOLID CIRCLES REPRESENT HISTORIC NUMBER OF NATIVE SPECIES ON ISLANDS AND SOLID SQUARES REPRESENT THE CURRENT EXTANT NATIVE AND NATURALIZED NUMBER OF SPECIES ON ISLANDS ! 4HE HISTORIC RICHNESS OF mOWERING PLANT SPECIES ON (AWAII WAS WELL BELOW THE LINE OF THE SPECIES AREA RELATIONSHIP FOR -EXICAN STATES BUT IS CURRENTLY VERY CLOSE TO THIS LINE " 4HE HISTORIC RICHNESS OF VASCULAR PLANT SPECIES IN .EW :EALAND WAS CLOSE TO BUT BELOW THE LINE OF THE SPECIES AREA RELATIONSHIP FOR !USTRALIAN 3TATES BUT IS CURRENTLY ABOVE THIS LINE
$& 3AX AND 3$ 'AINES
SUGGEST THAT THE MOST ISOLATED AND DISTINCTIVE BIOTAS OF THE WORLD ARE THE ONES BEING MODIlED BY THE LARGEST DEGREE 3UCH MODIlCATIONS LEAD TO AT LEAST TWO TYPES OF BIOTIC HOMOGENIZATION &IRST THEY LEAD TO HOMOGENIZATION OF SPECIES COMPOSI TION AMONG REGIONS AS UNIQUE SPECIES ARE LOST AND COMMON ONES ARE GAINED EG ,OCKWOOD AND -C+INNEY 3ECOND THEY LEAD TO HOMOGENIZATION OF SPECIES RICHNESS AMONG REGIONS IN WHICH VARIATION IN SPECIES RICHNESS AND SPECIES AREA RELATIONSHIPS IS REDUCED 4HE LONG TERM IMPLICATIONS OF BIOTIC HOMOGENIZATION ARE STILL UNKNOWN BUT IT IS CLEAR THAT THE LOSS OF DISTINCTIVE BIOTAS AND THE MODIlCATION OF PATTERNS OF BIODIVERSITY ACROSS THE GLOBE ARE TOPICS WORTHY OF MUCH ADDITIONAL STUDY
#/.#,5$).' 4(/5'(43 7E HAVE ATTEMPTED TO REVIEW AND PRESENT SOME OF THE BASIC PATTERNS OF BIOGEO GRAPHIC DISTRIBUTION OF EXOTIC SPECIES 'IVEN THE LIMITED SCOPE OF A SINGLE BOOK CHAPTER WE WERE NOT ABLE TO REVIEW ALL OF THE MANY PATTERNS THAT HAVE BEEN DESCRIBED TO DATE BUT INSTEAD HAVE FOCUSED ON THOSE PATTERNS THAT WE DEEMED TO BE OF THE GREATEST INTEREST TO ECOLOGISTS (AD WE INSTEAD CHOSEN TO EXPLORE THOSE ISSUES OF GREATEST INTEREST TO EVOLUTIONARY BIOLOGISTS WE WOULD UNDOUBTEDLY HAVE CHOSEN A SLIGHTLY DIFFERENT SET OF TOPICS TO REVIEW &OR EXAMPLE ONE PATTERN THAT IS EXTREMELY INTRIGUING WITH NATURALIZED SPECIES IS THE RAPID EVOLUTION OF CLINES IN BODY SIZE ACROSS LATITUDE THAT QUANTITATIVELY MATCH BUT QUALITATIVELY DIFFER FROM THOSE SEEN IN THE NATIVE RANGE SUGGESTING THAT EVOLUTION CAN SIMULTANEOUSLY OPERATE IN A DETERMINISTIC AND CONTINGENT MANNER (UEY ET AL 'ILCHRIST ET AL 3TILL WE HOPE THAT THE WORK DESCRIBED HERE PROVIDES A GOOD INROAD TO THE GROWING LITERATURE ON THIS TOPIC A LITERATURE THAT PROMISES TO PROVIDE RECIPROCAL INSIGHTS TO ECOLOGICAL AND BIOGEOGRAPHICAL THEORY AS WELL AS TO OUR APPLIED UNDER STANDING OF INVASION BIOLOGY &INALLY WE BELIEVE THAT IF WE AS A SOCIETY ARE GOING TO SUCCESSFULLY LEARN TO UNDERSTAND AND MITIGATE THE ENVIRONMENTAL THREATS POSED BY ANTHROPOGENIC CHANGES TO THE ENVIRONMENT THEN WE MUST EMPLOY ALL AVAILABLE EVIDENCE TO DO SO UNDOUBTEDLY STUDIES OF SPECIES INVASION AT BIOGEOGRAPHIC SCALES CAN DO MUCH TO HELP ACHIEVE THESE GOALS
!#+./7,%$'%-%.43 7E WOULD LIKE TO THANK THE EDITORS OF THIS BOOK FOR GIVING US THE OPPORTUNITY TO WRITE THIS CHAPTER -ANY OF THE IDEAS IN THIS MS BENElTED FROM CONVERSATIONS WITH * "ROWN 4HE QUALITY OF THIS MS HAS BENElTED SIGNIlCANTLY FROM COMMENTS BY $ 0ERAULT - "EALS AND - ,OMOLINO 4HIS IS CONTRIBUTION NUMBER FROM 0)3#/ THE 0ARTNERSHIP FOR )NTERDISCIPLINARY 3TUDIES OF #OASTAL /CEANS ! ,ONG TERM %COLOGICAL #ONSORTIUM FUNDED BY THE $AVID AND ,UCILE 0ACKARD &OUNDATION
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
2%&%2%.#%3 !RRHENIUS / 3PECIES AND AREA *OURNAL OF %COLOGY !TKINSON # 4 2 * $USEK + , 7OODS AND 7 - )KO 0ATHOGENICITY OF AVIAN MALARIA IN EXPERIMENTALLY INFECTED (AWAII !MAKIHI *OURNAL OF 7ILDLIFE $ISEASES "ANKS $ , ! VASCULAR mORA OF THE !GUA 4IBIA -OUNTAINS SOUTHERN #ALIFORNIA 2ANCHO 3ANTA !NA "OTANICAL 'ARDEN /CCASIONAL 0UBLICATION NUMBER #LAREMONT #! "ICKFORD # AND 0 2ICH 6EGETATION AND mORA OF THE ,ANDELS (ILL "IG #REEK 2ESERVE -ONTEREY #OUNTY #ALIFORNIA 3ECOND %DITION 0UBLICATION NUMBER %NVIRONMENTAL &IELD 0ROGRAM 5NIVERSITY OF #ALIFORNIA 3ANTA #RUZ #! "LACKBURN 4 - AND + * 'ASTON 3PATIAL PATTERNS IN THE SPECIES RICHNESS OF BIRDS IN THE .EW 7ORLD %COGRAPHY "OYD 3 $ ! mORA OF THE 'AVILAN (ILLS 7ESTERN 2IVERSIDE #OUNTY #ALIFORNIA -ASTERS OF 3CIENCE 4HESIS 5NIVERSITY OF #ALIFORNIA 2IVERSIDE #! "ROWN * ( -ACROECOLOGY 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), "ROWN * ( AND - 6 ,OMOLINO "IOGEOGRAPHY 3ECOND %DITION 3INAUER !SSOCIATES 3UNDERLAND -! "ROWN * ( AND $ & 3AX 'RADIENTS IN SPECIES DIVERSITY WHY ARE THERE SO MANY SPECIES IN THE TROPICS 0AGES IN - 6 ,OMOLINO $ & 3AX AND * ( "ROWN EDITORS &OUNDATIONS OF "IOGEOGRAPHY CLASSIC PAPERS WITH COMMENTARIES 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), "RUNO * & * * 3TACHOWICZ AND - $ "ERTNESS )NCLUSION OF FACILITATION INTO ECOLOGI CAL THEORY 4RENDS IN %COLOGY AND %VOLUTION #ASE 4 * )NVASION RESISTANCE SPECIES BUILD UP AND COMMUNITY COLLAPSE IN MODEL COMPETITION COMMUNITIES 0AGES IN - % 'ILPIN AND ) (ANSKI EDITORS -ETAPOPULATION DYNAMICS !CADEMIC 0RESS ,ONDON 5+ #HOWN 3 , . * - 'REMMEN AND + * 'ASTON %COLOGICAL BIOGEOGRAPHY OF SOUTHERN OCEAN ISLANDS SPECIES AREA RELATIONSHIPS HUMAN IMPACTS AND CONSERVATION !MERICAN .ATURALIST #OLLINS - $ $ 0 6AZQUEZ AND . * 3ANDERS 3PECIES AREA CURVES HOMOGENIZATION AND THE LOSS OF GLOBAL DIVERSITY %VOLUTIONARY %COLOGY 2ESEARCH #ONNOR % & AND % $ -C#OY 4HE STATISTICS AND BIOLOGY OF THE SPECIES AREA RELATION SHIP !MERICAN .ATURALIST #RAWLEY - * 7HAT MAKES A COMMUNITY INVASIBLE 0AGES IN ! * 'RAY - * #RAWLEY AND 0 * %DWARDS EDITORS #OLONIZATION SUCCESSION AND STABILITY "LACKWELL 3CIENTIlC 0UBLICATIONS /XFORD 5+ $ARWIN # /N THE ORIGIN OF SPECIES -URRAY ,ONDON 5+ $AVIS - ! "IOTIC GLOBALIZATION DOES COMPETITION FROM INTRODUCED SPECIES THREATEN BIODIVERSITY "IOSCIENCE $E .EVERS ' 0EPPERWOOD &LORA 0EPPERWOOD 2ANCH .ATURAL 0RESERVE 3ONOMA #OUNTY #ALIFORNIA #ALIFORNIA !CADEMY OF 3CIENCES 3AN &RANCISCO #!
$& 3AX AND 3$ 'AINES
$EUTSCHEWITZ + ! ,AUSCH ) +UHN AND 3 +LOTZ .ATIVE AND ALIEN PLANT SPECIES RICHNESS IN RELATION TO SPATIAL HETEROGENEITY ON A REGIONAL SCALE IN 'ERMANY 'LOBAL %COLOGY AND "IOGEOGRAPHY $OBZHANSKY 4 %VOLUTION IN THE TROPICS !MERICAN 3CIENTIST $UNCAN 2 0 4 - "LACKBURN AND $ 3OL 4HE ECOLOGY OF BIRD INTRODUCTIONS !NNUAL 2EVIEW OF %COLOGY %VOLUTION AND 3YSTEMATICS %BENHARD 4 )NTRODUCED BIRDS AND MAMMALS AND THEIR ECOLOGICAL EFFECTS 3WEDISH 7ILDLIFE 2ESEARCH %LTON # 3 4HE ECOLOGY OF INVASIONS BY ANIMALS AND PLANTS -ETHUEN AND #O ,4$ ,ONDON 5+ &INE 0 6 ! 4HE INVASIBILITY OF TROPICAL FORESTS BY EXOTIC PLANTS *OURNAL OF 4ROPICAL %COLOGY &ISCHER ! ' ,ATITUDINAL VARIATIONS IN ORGANIC DIVERSITY %VOLUTION &RANCE 2 4HE .ORTH !MERICAN ,ATITUDINAL GRADIENT IN SPECIES RICHNESS AND GEOGRAPHIC RANGE OF FRESHWATER CRAYlSH AND AMPHIPODS !MERICAN .ATURALIST &RIDLEY * $ 2 , "ROWN AND * & "RUNO .ULL MODELS OF EXOTIC INVASION AND SCALE DEPENDENT PATTERNS OF NATIVE AND EXOTIC SPECIES RICHNESS %COLOGY IN PRESS &RITTS 4 ( AND ' ( 2ODDA 4HE ROLE OF INTRODUCED SPECIES IN THE DEGRADATION OF ISLAND ECOSYSTEMS A CASE HISTORY OF 'UAM !NNUAL 2EVIEW OF %COLOGY %VOLUTION AND 3YSTEMATICS 'AINES 3 $ AND * ,UBCHENCO ! UNIlED APPROACH TO MARINE PLANT HERBIVORE INTER ACTIONS "IOGEOGRAPHY !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS 'ASTON + * 4 - "LACKBURN AND * ) 3PICER 2APOPORTS RULE TIME FOR AN EPITAPH 4RENDS IN %COLOGY AND %VOLUTION 'IDO + " AND * ( "ROWN )NVASION OF .ORTH !MERICAN DRAINAGES BY ALIEN lSH SPE CIES &RESHWATER "IOLOGY 'ILCHRIST ' 7 2 " (UEY * "ALANYA - 0ASCUAL AND , 3ERRA ! TIME SERIES OF EVOLUTION IN ACTION A LATITUDINAL CLINE IN WING SIZE IN 3OUTH !MERICAN $ROSOPHILA SUB OBSCURA %VOLUTION 'ROOMBRIDGE " ED 'LOBAL BIODIVERSITY STATUS OF THE %ARTHS LIVING RESOURCES #HAPMAN (ALL ,ONDON 5+ (AWKINS " ! %COLOGYS OLDEST PATTERN 4RENDS IN %COLOGY AND %VOLUTION (UEY 2 " ' 7 'ILCHRIST - , #ARLSON $ "ERRIGAN AND , 3ERRA 2APID EVOLUTION OF A GEOGRAPHIC CLINE IN SIZE IN AN INTRODUCED mY 3CIENCE (UTTON ) "IRDS OF ,ORD (OWE )SLAND PAST AND PRESENT ,ITHOCRAFT 'RAPHICS -ELBOURNE !USTRALIA *UNAK 3 4 !YERS AND 2 3COTT ! mORA OF 3ANTA #RUZ )SLAND 3ANTA "ARBARA "OTANIC 'ARDENS 3ANTA "ARBARA #! +ENNEDY 4 ! 3 .AEEM + - (OWE * - ( +NOPS $ 4ILMAN AND 0 2EICH "IODIVERSITY AS A BARRIER TO ECOLOGICAL INVASION .ATURE ,ATHROP % 7 AND 2 & 4HORNE ! mORA OF THE 3ANTA 2OSA 0LATEAU SOUTHERN #ALIFORNIA 3OUTHERN #ALIFORNIA "OTANISTS 3PECIAL 0UBLICATION NUMBER #LAREMONT #!
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
,ETCHER ! * AND 0 ( (ARVEY 6ARIATION IN GEOGRAPHIC RANGE SIZE AMONG MAMMALS OF THE 0ALEARCTIC !MERICAN .ATURALIST ,EVINE * - 3PECIES DIVERSITY AND BIOLOGICAL INVASIONS RELATING LOCAL PROCESS TO COM MUNITY PATTERN 3CIENCE ,ONSDALE 7 - 'LOBAL PATTERNS OF PLANT INVASIONS AND THE CONCEPT OF INVASIBILITY %COLOGY ,OMOLINO - 6 )NTERPRETATIONS AND COMPARISONS OF CONSTANTS IN THE SPECIES AREA RELATIONSHIP AN ADDITIONAL CAUTION !MERICAN .ATURALIST ,OMOLINO - 6 4HE SPECIES AREA RELATIONSHIP NEW CHALLENGES FOR AN OLD PATTERN 0ROGRESS IN 0HYSICAL 'EOGRAPHY ,OMOLINO - 6 $ & 3AX AND * ( "ROWN &OUNDATIONS OF "IOGEOGRAPHY CLASSIC PAPERS WITH COMMENTARIES 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), ,OMOLINO - 6 AND - $ 7EISER 4OWARDS A MORE GENERAL SPECIES AREA RELATION SHIP DIVERSITY ON ALL ISLANDS GREAT AND SMALL *OURNAL OF "IOGEOGRAPHY ,UNING + 3EAWEEDS THEIR ENVIRONMENT BIOGEOGRAPHY AND ECOPHYSIOLOGY *OHN 7ILEY AND 3ONS )NC .EW 9ORK .9 -AC!RTHUR 2 ( AND % / 7ILSON 4HE 4HEORY OF )SLAND "IOGEOGRAPHY 0RINCETON 5NIVERSITY 0RESS 0RINCETON .* -AC!RTHUR 2 ( 'EOGRAPHIC ECOLOGY PATTERNS IN THE DISTRIBUTION OF SPECIES (ARPER 2OW .EW 9ORK .9 -ARCHETTI - 0 4 ,IGHT * &ELICIANO 4 !RMSTRONG : (OGAN * 6IERS AND 0 " -OYLE (OMOGENIZATION OF #ALIFORNIAS lSH FAUNA THROUGH ABIOTIC CHANGE 0AGES IN * , ,OCKWOOD AND - , -C+INNEY EDITORS "IOTIC (OMOGENIZATION +LUWER !CADEMIC0LENUM 0UBLISHERS .EW 9ORK .9 -ARTIN 4 % 3PECIES AREA SLOPES AND COEFlCIENTS A CAUTION ON THEIR INTERPRETATION !MERICAN .ATURALIST -ATTER 3 & ) (ANSKI AND - 'YLLENBERG ! TEST OF THE METAPOPULATION MODEL OF THE SPECIES AREA RELATIONSHIP *OURNAL OF "IOGEOGRAPHY -C#LINTOCK % 7 +NIGHT AND . &AHY ! mORA OF THE 3AN "RUNO -OUNTAINS 3AN -ATEO #OUNTY #ALIFORNIA 0ROCEEDINGS OF THE #ALIFORNIA !CADEMY OF 3CIENCES FOURTH SERIES -C'LONE - 3 2 0 $UNCAN AND 0 " (EENAN %NDEMISM SPECIES SELECTION AND THE ORIGIN AND DISTRIBUTION OF THE VASCULAR PLANT mORA OF .EW :EALAND *OURNAL OF "IOGEOGRAPHY -C+INNEY - , A )NmUENCE OF SETTLEMENT TIME HUMAN POPULATION PARK SHAPE AND AGE VISITATION AND ROADS ON THE NUMBER OF ALIEN PLANT SPECIES IN PROTECTED AREAS IN THE 53! $IVERSITY AND $ISTRIBUTIONS -C+INNEY - , B $O HUMAN ACTIVITIES RAISE SPECIES RICHNESS #ONTRASTING PATTERNS IN 5NITED 3TATES PLANTS AND lSHES 'LOBAL %COLOGY AND "IOGEOGRAPHY -C+INNEY - , AND ,OCKWOOD * , "IOTIC HOMOGENIZATION A FEW WINNERS REPLAC ING MANY LOSERS IN THE NEXT MASS EXTINCTION 4RENDS IN %COLOGY AND %VOLUTION -OODY ! !NALYSIS OF PLANT SPECIES DIVERSITY WITH RESPECT TO ISLAND CHARACTERISTICS ON THE #HANNEL )SLANDS #ALIFORNIA *OURNAL OF "IOGEOGRAPHY
$& 3AX AND 3$ 'AINES
-OYLE 0 " )NLAND lSHES OF #ALIFORNIA REVISED AND EXPANDED EDITION 5NIVERSITY OF #ALIFORNIA 0RESS "ERKELEY #! .AEEM 3 * - ( +NOPS $ 4ILMAN + - (OWE 4 +ENNEDY AND 3 'ALE 0LANT DIVERSITY INCREASES RESISTANCE TO INVASION IN THE ABSENCE OF COVARYING EXTRINSIC FACTORS /IKOS 0IANKA % 2 ,ATITUDINAL GRADIENTS IN SPECIES DIVERSITY A REVIEW OF CONCEPTS !MERICAN .ATURALIST 0YSEK 0 !LIEN AND NATIVE SPECIES IN CENTRAL %UROPEAN URBAN mORAS A QUANTITATIVE COMPARISON *OURNAL OF "IOGEOGRAPHY 0YSEK 0 6 *AROSIK AND 4 +UCERA 0ATTERNS OF INVASION IN TEMPERATE NATURE RESERVES "IOLOGICAL #ONSERVATION 0YSEK 0 4 +UCERA AND 6 *AROSIK 0LANT SPECIES RICHNESS OF NATURE RESERVES THE INTERPLAY OF AREA CLIMATE AND HABITAT IN A CENTRAL %UROPEAN LANDSCAPE *OURNAL OF "IOGEOGRAPHY 2APOPORT % ( !REOGRAPHY GEOGRAPHIC STRATEGIES OF SPECIES TRANSLATION BY " $RAUSEL 0ERGAMON /XFORD 5+ 2AVEN 0 ( ( * 4HOMPSON AND " ! 0RIGGE &LORA OF THE 3ANTA -ONICA -OUNTAINS #ALIFORNIA 3ECOND %DITION 3OUTHERN #ALIFORNIA "OTANISTS 3PECIAL 0UBLICATION .O 2EJMANEK - 3PECIES RICHNESS AND RESISTANCE TO INVASIONS 0AGES IN ' ( /RIANS 2 $IRZO * ( #USHMAN EDITORS "IODIVERSITY AND ECOSYSTEM PROCESSES IN TROPICAL FORESTS 3PRINGER 6ERLAG "ERLIN 'ERMANY 2EJMANEK - 4HE RICH GET RICHER RESPONSES &RONTIERS IN %COLOGY AND THE %NVIRONMENT 2ICHARDSON $ - . !LLSOPP # - $!NTONIO 3 * -ILTON AND - 2EJMANEK 0LANT INVASIONS THE ROLE OF MUTUALISMS "IOLOGICAL 2EVIEWS 2ODRIGUERO - 3 AND $ % 'ORLA ,ATITUDINAL GRADIENT IN SPECIES RICHNESS OF THE .EW 7ORLD 4RIATOMINAE 2EDUVIIDAE 'LOBAL %COLOGY AND "IOGEOGRAPHY 2OHDE + ,ATITUDINAL GRADIENTS IN SPECIES DIVERSITY THE SEARCH FOR THE PRIMARY CAUSE /IKOS 2OSENZWEIG - , 3PECIES DIVERSITY IN SPACE AND TIME #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 5+ 2OSENZWEIG - , 4HE FOUR QUESTIONS 7HAT DOES THE INTRODUCTION OF EXOTIC SPECIES DO TO DIVERSITY %VOLUTIONARY %COLOGY 2ESEARCH 2USSELL * # - . #LOUT AND " ( -C!RDLE )SLAND BIOGEOGRAPHY AND THE SPE CIES RICHNESS OF INTRODUCED MAMMALS OF THE .EW :EALAND OFFSHORE ISLANDS *OURNAL OF "IOGEOGRAPHY 3AX $ & ,ATITUDINAL GRADIENTS AND GEOGRAPHIC RANGES OF EXOTIC SPECIES IMPLICATIONS FOR BIOGEOGRAPHY *OURNAL OF "IOGEOGRAPHY 3AX $ & 3 $ 'AINES AND * ( "ROWN 3PECIES INVASIONS EXCEED EXTINCTIONS ON ISLANDS WORLDWIDE A COMPARATIVE STUDY OF PLANTS AND BIRDS !MERICAN .ATURALIST 3COTT * - 3 #ONANT AND # VAN 2IPER ))) EDITORS %VOLUTION ECOLOGY CONSERVA TION AND MANAGEMENT OF (AWAIIAN BIRDS A VANISHING AVIFAUNA #OOPER /RNITHOLOGICAL 3OCIETY #AMARILLO #!
"IOGEOGRAPHIC PATTERNS OF NATURALIZED SPECIES
3IMPSON ' ' 3PECIES DENSITY OF .ORTH !MERICAN 2ECENT MAMMALS 3YSTEMATIC :OOLOGY n 3TACHOWICZ * * 2 " 7HITLATCH AND 2 7 /SMAN 3PECIES DIVERSITY AND INVASION RESISTANCE IN A MARINE ECOSYSTEM 3CIENCE 3TADLER * ! 4REFmICH 3 +LOTZ AND 2 "RANDL %XOTIC PLANT SPECIES INVADE DIVERSITY HOT SPOTS THE NATURALIZED mORA OF NORTHWESTERN +ENYA %COGRAPHY 3TEVENS ' # 4HE LATITUDINAL GRADIENT IN GEOGRAPHIC RANGE HOW SO MANY SPECIES COEXIST IN THE TROPICS !MERICAN .ATURALIST 3TEVENS ' # AND " * %NQUIST -ACROECOLOGICAL LIMITS TO THE ABUNDANCE AND DISTRIBUTION OF 0INUS 0AGES IN $ - 2ICHARDSON EDITOR %COLOGY AND BIOGEOG RAPHY OF 0INUS #AMBRIDGE 5NIVERSITY 0RESS #AMBRIDGE 5+ 3TOHLGREN 4 * $ "INKLEY ' 7 #HONG - ! +ALKHAN , $ 3CHELL + ! "ULL 9 /TSUKI ' .EWMAN - "ASHKIN AND 9 3ON %XOTIC PLANT SPECIES INVADE HOT SPOTS OF NATIVE PLANT DIVERSITY %COLOGICAL -ONOGRAPHS 3TOHLGREN 4 * $ 4 "ARNETT AND * 4 +ARTESZ 4HE RICH GET RICHER PATTERNS OF PLANT INVASIONS IN THE 5NITED 3TATES &RONTIERS IN %COLOGY AND THE %NVIRONMENT 4ILMAN $ #OMMUNITY INVASIBILITY RECRUITMENT LIMITATION AND GRASSLAND BIODIVER SITY %COLOGY 6ILLASE×OR * , AND & * %SPINOSA 'ARCIA 4HE ALIEN mOWERING PLANTS OF -EXICO $IVERSITY AND $ISTRIBUTIONS 7ARDLE $ ! %XPERIMENTAL DEMONSTRATION THAT PLANT DIVERSITY REDUCES INVASIBILITY EVIDENCE OF A BIOLOGICAL MECHANISM OR A CONSEQUENCE OF SAMPLING EFFECT /IKOS 7ILLIG - 2 $ - +AUFMAN AND 2 $ 3TEVENS ,ATITUDINAL GRADIENTS OF BIODIVER SITY PATTERN PROCESS SCALE AND SYNTHESIS !NNUAL 2EVIEW IN %COLOGY %VOLUTION AND 3YSTEMATICS 7ILLOUGHBY * 7 ! mORA OF THE 6ACA -OUNTAINS #ALIFORNIA -ASTERS 4HESIS #ALIFORNIA 3TATE 5NIVERSITY 3ACRAMENTO #! 7ILSON + %XTINCT AND INTRODUCED VERTEBRATE SPECIES IN .EW :EALAND A LOSS OF BIODIS TINCTIVENESS AND GAIN IN BIODIVERSITY 0ACIlC #ONSERVATION "IOLOGY
$& 3AX AND 3$ 'AINES
!00%.$)8 $%4!),%$ -%4(/$3 0LANTS IN 53 3TATES
4HE NUMBER OF NATIVE AND NATURALIZED SPECIES OF VASCULAR PLANTS FOR EACH STATE ARE FROM -AC ET AL AND 3TEIN ET AL $ATA ON NUMBER OF EXTINCT OR EXTIRPATED PLANTS FOR EACH STATE WERE COLLECTED FROM REPORTS OF PRIVATE AND PUBLIC STATE AGENCIES PREDOMINATELY THE .ATURAL (ERITAGE 0ROGRAMS OF INDIVIDUAL STATES THE DATA USED IN THESE ANALYSES ARE AVAIL ABLE UPON REQUEST FROM THE AUTHORS )N EACH CASE THE NUMBER OF SPECIES LISTED AS h38v EXTINCT OR EXTIRPATED FROM A STATE OR h3(v PRESENT HISTORI CALLY IN A STATE BUT NO LONGER KNOWN TO OCCUR WERE SUMMED TO PROVIDE THE TOTAL NUMBER OF SPECIES THAT HAVE BEEN EXTIRPATED #OMPLETE DATA FOR -ASSACHUSETS -INNESOTA AND .ORTH $AKOTA WERE UNAVAILABLE SO THESE STATES WERE EXCLUDED FROM THESE ANALYSES !LASKA AND (AWAII WERE ALSO EXCLUDED FROM THESE ANALYSES 0LANTS IN MAINLAND AREAS OF #ALIFORNIA
!VAILABLE mORAS OF PARTICULAR SITES ON THE MAINLAND OF #ALIFORNIA WERE SELECTED TO REPRESENT THE SPAN OF AREAS PRESENT ON THE #ALIFORNIA #HANNEL )SLANDS )N TOTAL NINE SITES WERE USED 4HESE INCLUDED THE mORAS OF THE 3ANTA -ONICA -OUNTAINS 2AVEN ET AL 3AN "RUNO -OUNTAINS -C#LINTOCK ET AL 6ACA -OUNTAINS 7ILLOUGHBY !GUA 4IBIA -OUNTAINS "ANKS 3ANTA 2OSA 0LATEAU ,ATHROP AND 4HORNE 'AVIAN (ILLS "OYD 0ESCADERO -ARSH 7 !NDERSON AND 2 -ORGAN UNPUBLISHED MANUSCRIPT ,ANDELS (ILL "IG #REEK 2ESERVE "ICKFORD AND 2ICH AND 0EPERWOOD 2ESERVE $E .EVERS $ATA ON THE NUMBER OF NATIVE AND NON NATIVE SPECIES ARE FROM THESE SOURCES .O DATA WAS AVAILABLE ON NUMBER OF EXTIRPATED SPECIES
#HAPTER TWENTY ONE
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS - 7 #ADOTTE 4 &UKAMI AND 3 - -C-AHON
).42/$5#4)/. 4HE OVERARCHING GOAL OF THIS VOLUME WAS TO EXAMINE HOW CONCEPTUAL ECOLOGY INFORMS OUR UNDERSTANDING OF SPECIES INVASIONS WHILE SIMULTANEOUSLY VIEWING SPECIES INVASIONS AS POTENTIAL TESTS OF ECOLOGICAL THEORY SEE #HAPTER !S ONE HALF THE PURPOSE OF THE PRESENT VOLUME ATTESTS TO ECOLOGICAL THEORY IS USEFUL FOR CON TEXTUALIZING WHEN AND HOW SPECIES INVADE EG 3HEA AND #HESSON -ORE THAN THIS AND AS THE SECOND HALF OF THIS VOLUMES PURPOSE SPECIES INVASIONS ALLOW US TO SEE HYPOTHESIZED DYNAMICS AND TO TEST MAJOR IDEAS IN ECOLOGY AND EVOLUTION EG ,ODGE 3AX ET AL 4HROUGHOUT THIS VOLUME AUTHORS HAVE EXPLIC ITLY EXPLORED THE ADVANCES IN KNOWLEDGE GAINED BY COMBINING CONCEPTUAL ECOLOGY WITH INVASION ECOLOGY (OWEVER BIOLOGICAL INVASIONS HAVE BEEN STUDIED FOR THEIR OWN SAKE AS THEY ARE CONSIDERED TO BE A MAJOR CONSERVATION RISK 6ITOUSEK ET AL AND AN IMPOR TANT COMPONENT OF INVASIONS STUDIES IS THE STUDY OF HOW NON INDIGENOUS SPECIES ENTER AND PROLIFERATE IN NEW COMMUNITIES ! MULTITUDE OF HYPOTHESES HAVE BEEN CREATED TO EXPLAIN HOW SPECIES INVADE NEW HABITATS )NDERJIT ET AL 9ET THESE HYPOTHESES CAN BE CONSIDERED AS SPECIAL CASES OF MORE GENERAL ECOLOGICAL PHENOMENA OR AS AD HOC EXPLANATIONS lLLING THE VOID WHERE WE LACK A GENERAL THEORY EG ,AKATOS 4HOUGH THE PRIMARY GOAL OF THIS VOLUME HAS BEEN TO COMBINE CONCEPTUAL ECOLOGY AND INVASION BIOLOGY MANY OF THE AUTHORS EXAMINED -7 #ADOTTE ET AL (EDS) #ONCEPTUAL ECOLOGY AND INVASION BIOLOGY – ¥ 3PRINGER 0RINTED IN THE .ETHERLANDS
-7 #ADOTTE 4 &UKAMI AND 3- -C-AHON
ECOLOGICAL THEORY OR PARTICULAR INVASIONS FROM DIFFERENT LEVELS OF ORGANIZATION 7E ORGANIZED THE CHAPTERS INTO THREE GENERAL SCALES OF ORGANIZATION POPULATION COM MUNITY AND BIOGEOGRAPHIC SCALES )NSTEAD OF VIEWING THESE SCALES AS NECESSARILY DISCRETE OR HIERARCHICALLY RELATED IT MAY BE USEFUL TO VIEW THESE PROCESSES AS A CONTINUUM FEEDING BACK INTO ONE ANOTHER &IG )N ORDER TO ADEQUATELY DESCRIBE AND UNDERSTAND INVASIONS WE MUST LOOK TO PROCESSES ALLOWING SPECIES TO OVERCOME I BIOGEOGRAPHICAL BARRIERS IN THE MOVEMENT OF PROPAGULES II ABIOTIC BARRIERS IN ESTABLISHING NEW POPULATIONS AND III BIOTIC BARRIERS IN MAINTAINING HIGHER BIRTH THAN DEATH RATES AND BEING ABLE TO INCREASE NUMBERS AND SPREAD TO NEW LOCALES 4HESE ARE ESSENTIALLY lLTERS SUBSAMPLING POTENTIAL COLONISTS FROM LARGER SPECIES POOLS "ELYEA AND ,ANCASTER 4HE DISPERSAL lLTER LIMITS SPECIES THAT ARE UNLIKELY TO MIGRATE TO THE LOCAL COMMUNITY WHILE THOSE WITH CERTAIN CHARACTERISTICS EG LONG DISTANCE DISPERSAL OR COMMON AGRICULTURAL SEED CONTAMINANTS WILL HAVE A HIGHER PROBABILITY OF COLONIZING AND ABIOTIC lLTERS SELECT CERTAIN SPECIES OR TRAITS AS THOSE WITH A HIGHER CHANGE OF SURVIVING IN THE NEW HABITAT "ELYEA AND ,ANCASTER /BSERVATIONS MADE AT DIFFERENT SCALES OFTEN REQUIRE MECHANISTIC LINKS TO OTHER SCALES OF ORGANIZATION &OR EXAMPLE EXTINCTIONS ARE ULTIMATELY OBSERVED AT A BIOGEOGRAPHIC SCALE BUT THE MECHANISMS LEADING TO EXTINCTION MUST BE OBSERVED AT THE POPULATION LEVEL EG WHAT ELEVATES DEATH RATES OR LOWER BIRTH RATES
&IG 4HE INVASION PROCESS AS A CONTINUUM ACROSS SPATIAL SCALES 4HE RING REPRESENTS THE SCALE OF ORGANIZATION POPULATION COMMUNITY AND BIOGEOGRAPHIC $IRECTIONAL BOXES INDICATE DOMINANT PROCESSES AT EACH SCALE WHICH LEAD INTO ONE ANOTHER 4HE NUMBERED DASHED LINES REFER TO THE FOUR INVASION STEPS OUTLINED IN THIS CHAPTER IMMIGRATION AND ESTABLISHMENT SPECIES INTERACTIONS SPATIAL SPREAD AND LARGE SCALE PATTERNS
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS
%XPLANATORY MECHANISMS SUCH AS THE CAUSES OF EXTINCTION CAN DRAW EXPLICIT LINKS BETWEEN SCALES AND THIS IS WHERE WE SEE OPPORTUNITY TO BETTER UNDERSTAND THE PROCESSES DRIVING INVASIONS AND HOW ECOLOGICAL THEORY INFORMS US ABOUT THESE INVASIONS 4HE SCALES USED IN THIS VOLUME DO NOT NECESSARILY TRANSLATE INTO ECOLOGICALLY RELEVANT SPATIAL SCALES EG M VS M BUT REmECT LEVELS OF ECOLOGICAL PROCESSES AFFECTING SPECIES ABUNDANCE AND DISTRIBUTION 3CALE EXPLICIT APPROACHES CAN TELL US MUCH ABOUT THE NATURE OF ECOLOGICAL PROCESSES EG #ADOTTE AND &UKAMI 2AHBEK &URTHER A NUMBER OF RECENT STUDIES HAVE SHOWN THAT OUR UNDERSTANDING OF THE PROCESSES DRIVING SPECIES INVASIONS ARE AFFECTED BY THE SPATIAL SCALE AT WHICH SPECIES INVASIONS ARE EXAMINED #OLLINGHAM ET AL ,LORET ET AL (AMILTON ET AL .OT ONLY DO ECOLOGICAL PROCESSES APPEAR SCALE CONTINGENT BUT SO DO TEMPORAL DYNAMICS OF INVASIONS &OR EXAMPLE BOTH #OLLINGHAM ET AL AND (AMILTON ET AL SHOW THAT SPECIES INVA SIONS APPEAR TO REACH STASIS OR EQUILIBRIUM IE STOP SPREADING EARLIER AT LARGER OR COARSER SCALES COMPARED TO lNE SPATIAL SCALES )S THERE A MORE GENERAL CONTEXT WITHIN WHICH WE CAN CONCEIVE OF INVASIONS ESPECIALLY ONE THAT LINKS DIFFERENT SCALES -ANY OF THE CHAPTERS IN THIS VOLUME DISCUSS INVASIONS IN TERMS OF SMALL POPULATIONS AVOIDING EXTINCTION 4HERE ARE A NUMBER OF WAYS BY WHICH POPULATIONS AVOID EXTINCTION INCLUDING PROLONGING LIFE SPANS PROTRACTED DORMANCY AND ESPECIALLY INCREASING REPRODUCTIVE RATES AND POPULATION GROWTH RATES &OR EXAMPLE 'ROTKOPP ET AL SHOW THAT TRAITS ASSOCIATED WITH RAPID POPULATION INCREASES HIGH RELATIVE GROWTH RATE SMALL SEED MASS AND SHORT GENERATION TIME WERE THE BEST PREDICTORS OF PINE INVASIONS ONE OF THE MOST AGGRESSIVE GROUPS OF PLANT INVADERS )N THIS CHAPTER WE LOOK AT A SPECIES ABILITY TO INCREASE POPULATION SIZE INTRINSIC RATE OF INCREASE R AS THE PORTAL TO UNDERSTANDING PATTERNS OF INVASIONS AND LINKING SPATIAL SCALES 4HROUGH THE REST OF THIS CHAPTER WE EXPLORE THE PROCESSES AFFECTING R AT DIFFERENT SCALES OF ORGANIZA TION AND BY UNDERSTANDING THE NATURE OF R AND HOW IT DRIVES DYNAMICS AT DIFFERENT SCALES WE BELIEVE THAT LIGHT CAN BE SHED ON THE ULTIMATE CAUSES OF SPECIES INVA SIONS 7HILE UNDERSTANDING THE ECOLOGICAL PROCESSES AFFECTING R APPEAR IMPORTANT FOR UNDERSTANDING THE INVASION PROCESS WE ARE NOT CLAIMING THAT IT ALONE CAN EXPLAIN ALL INVASIONS NOR THAT IT EVEN NECESSARILY BE THE MOST IMPORTANT FACTOR 2ATHER WE WISH TO SHOW HOW A CONCEPTUAL TREATMENT OF A SPECIES TRAIT CAN HELP IN SYSTEMATICALLY UNDERSTANDING DIFFERENT PROCESSES AT DIFFERENT SCALES AND STAGES OF INVASIONS 3TEP IMMIGRATION AND ESTABLISHMENT
3PECIES CLASSIlED AS INVADERS HAVE ONE T HING IN COMMONnTHEY HAVE OVERCOME DISPERSAL AND ABIOTIC BARRIERS AND HAVE ARRIVED IN NEW HABITATS #HAPTERS IN THIS VOLUME ASSUME THAT SPECIES ARE ABLE TO DISPERSE INTO NEW HABITATS THROUGH THEIR OWN ABILITIES OR HUMAN VECTORS
-7 #ADOTTE 4 &UKAMI AND 3- -C-AHON
4HE lRST STAGE IN ANY INVASION IS THE ESTABLISHMENT OF INDIVIDUALS COMMENCING THE NEW POPULATION 4HERE ARE A MULTITUDE OF FACTORS THAT AFFECT THE LIKELIHOOD OF ESTABLISHMENT SUCCESS 4HESE INCLUDE ABIOTIC CONDITIONS COMPOSITION OF RESIDENT SPECIES LIFE HISTORY TRAITS PROMOTING INVASION "AKER AND THE NUMBER OF IMMIGRANTS INITIATING THE POPULATION IE PROPOGULE PRESSURE SEE #ARLTON ,OCKWOOD ET AL 7ARREN ET AL #HAPTER EXPLICITLY CONSIDER THE POPULATION PROCESSES INVOLVED WITH ESTABLISHMENT 4HEY VIEW ESTABLISHMENT AS A PROBABILISTIC PROCESS WHERE THE PROBABILITY OF ESTABLISHMENT 0N IS DETERMINED BY THE INITIAL POPULATION SIZE N AND BIRTH AND DEATH RATES B AND D £ R ¥ N £D ¥N 0N n " " n " n " ¤B ¦ ¤ B ¦ (ERE THE INTRINSIC RATE OF INCREASE R IS SIMPLY B n D %SSENTIALLY POPULATIONS OVERCOME THE RISKS OF SMALL POPULATION SIZES EITHER THROUGH INCREASED PROPAGULE PRESSURE N OR BY RAPIDLY INCREASING POPULATION SIZES BY INCREASING R RELATIVE TO D VIA HIGHER BIRTH RATES 4HE INTERACTION BETWEEN R AND N IS CRITICAL FOR ESTABLISHMENT SEE #HAPTER THEIR &IG 3PECIES WITH EXTREMELY LOW MORTALITY AND THEREFORE HIGH R HAVE A HIGH PROBABILITY OF SUCCESS LARGELY INDEPENDENT OF THE NUMBER OF INITIAL PROGAGULES (OWEVER SPECIES WITH LOW R OR HIGH MORTALITY WILL NEED HIGH NUMBERS OF PROPA GLUES TO ENSURE SUCCESSFUL ESTABLISHMENT 4HESE TWO VARIABLES N AND R ARE IMPORTANT BECAUSE THE ESTABLISHMENT OF A NEW POPULATION IS DETERMINED BY THE PROCESSES AFFECTING SMALL POPULATIONS "Y INCREAS ING IN SIZE EITHER THROUGH IMMIGRATION OR BIRTH A POPULATION CAN BETTER AVOID SOME OF THE PERILS PLAGUING SMALL POPULATIONS #HAPTERS DEAL WITH THE WAYS IN WHICH POPULATIONS OF INVADERS ESTABLISH AND PERSIST #HAPTER "UCKLEY AND -ETCALF AND #HAPTER &RECKLETON ET AL CONSIDER WHAT HAPPENS TO SMALL POPULA TIONS 3TOCHASTICITY DEMOGRAPHIC AND ENVIRONMENTAL AS WELL AS !LLEE EFFECTS CAN BE STRONG FORCES AFFECTING A NEW POPULATIONS ABILITY TO PERSIST "Y UNDERSTANDING HOW STOCHASTICITY AS WELL AS THE ABIOTIC ENVIRONMENT INmUENCE R AT DIFFERENT TIMES AND PLACES RESEARCHERS CAN THEN MAKE LONG TERM PROBABILISTIC PREDICTIONS REGARD ING INVADER PERSISTENCE AND POPULATION GROWTH 3UBSEQUENT POPULATION GROWTH ALSO DEPENDS UPON R SUCH AS IN THE LOGISTIC GROWTH MODEL SEE #HAPTER )N #HAPTER -URRELL SHOWS THAT EVEN THOUGH LOCALIZED INVADER SUCCESS PARTIALLY DEPENDS UPON DISPERSAL RATES VARIATION IN R STILL HAS A LARGE EFFECT ON SUCCESS (OWEVER POPULATIONS ARE NOT ISOLATED ENTITIES SOLELY INTERACTING WITH THEIR ENVIRONMENTS #AN WE THEN INCORPORATE MULTIPLE SPECIES INTO THE NOTION OF INVADER SUCCESS
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS
3TEP SPECIES INTERACTIONS
/NCE SPECIES OVERCOME ABIOTIC AND GEOGRAPHIC BARRIERS AND ESTABLISH IN A NEW HABITAT THEY ARE STILL FACED WITH BIOTIC BARRIERS THE BIOLOGICAL MECHANISMS AFFECT ING THEIR INVASION EG )NDERJIT ET AL AND WILL BE FACED WITH A SUITE OF BIOTIC INTERACTIONS COMPETITION PREDATION PATHOGENS ETC 4HESE INTERACTIONS CAN LEAD TO VERY COMPLEX DYNAMICS 4AKEN ON THEIR OWN #HAPTERS AND APPEAR TO COVER RATHER IDIOSYNCRATIC INTERACTIONS WHICH CAN LEAD TO INDIVIDUAL HYPOTHESES EXPLAINING DIFFERENT TYPES OF INVASION PROMOTING INTERACTIONS 4HIS WOULD SEEM TO GIVE CREDENCE TO THE NOTION THAT WE ARE UNABLE TO GENERATE LAWS IN COMMUNITY ECOLOGY ,AWTON DESPITE THE FACT THAT UNDERSTANDING THE COM MUNITY LEVEL IS WHERE OUR CONSERVATION AND INVASION CONTROL EFFORTS ARE DIRECTED 3IMBERLOFF (OWEVER BASIC ECOLOGICAL THEORY MAY BE THE BEST WAY FOR BIOLOGISTS UNDERSTAND THE IMPORTANT INTERACTIONS AND ECOLOGICAL PROCESSES AFFECTING INVASIONS SUCCESS 3HEA AND #HESSON -OST ECOLOGICAL THEORY THAT EXAMINES THE OUTCOMES OF SPECIES INTERACTIONS EXPLICITLY CONSIDERS THE ROLE OF NEGATIVE INTERACTIONS ON INDIVIDUAL POPULATION GROWTH RATES AND POPULATION PERSISTENCE 7HETHER USING ,OTKA 6OLTERRA TYPE EQUATIONS EG #OURCHAMP AND #AUT #HAPTER WHERE PARAMETERS APPROXIMATE COMPETITIVE INTERACTIONS WITHOUT SPECIFYING A MECHA NISM OR RESOURCE BASED MECHANISTIC APPROACHES EG 4ILMAN #HASE AND ,EIBOLD ECOLOGICAL THEORY HAS THE POTENTIAL TO HELP ECOLOGISTS UNDERSTAND AND POSSIBLY PREDICT THE OUTCOMES OF MULTISPECIES INTERACTIONS 4HERE MAY BE A GENERALIZED WAY TO THINK ABOUT AN INVADERS SUCCESS IN LIEU OF NEGATIVE INTERACTIONS !GAIN WE CAN LOOK TO THE THINGS THAT AFFECT R 4HE PROCESSES AFFECTING A POPULATIONS INTRINSIC RATE OF INCREASE CAN BE VERY COMPLEX YET FOR AN INVADER TO PERSIST ITS LONG TERM GROWTH RATE R MUST BE * &OR SUCCESSFUL INVAD ERS R IS MUCH GREATER THAN AT CERTAIN TIMES AND PLACES #HESSON CONSIDERS THAT THE LONG TERM GROWTH RATE R IS RELATED TO THREE MECHANISMS AS R 5R n 6. 6) WHERE R IS THE EFFECT OF mUCTUATION INDEPENDENT MECHANISMS ON R IE IN THE PRESENCE OF COMPETITORS BUT WITHOUT ENVIRONMENTAL CHANGES 6. IS THE EFFECT OF THE NONLINEAR COMPETITION RESPONSES TO VARIANCE IN RESOURCES AND 6) IS THE STORAGE EFFECT SEE "OX FOR ELABORATIONS OF THESE THREE PARAMETERS 4HE STORAGE EFFECT REPRESENTS A SPECIES ABILITY TO DIMINISH THE EFFECTS OF COMPETITION WHEN THE SPECIES IS NOT FAVORED BY THE ENVIRONMENT #HESSON 3PECIES CAN REDUCE COMPETITIVE INTERACTIONS IN A NUMBER OF WAYS SUCH AS MIGRATING TO REGIONS WITH FREE RESOURCES OR LACKING DOMINANT COMPETITORS CHANG ING THEIR BEHAVIOR TO REDUCE COMPETITIVE OVERLAP OR ENTERING A DORMANT STATE AND RE EMERGING UNDER BETTER CONDITIONS
-7 #ADOTTE 4 &UKAMI AND 3- -C-AHON
"OX 4(% 4(2%% #/-0/.%.43 /& ,/.' 4%2- '2/74( #(%33/. 4HE mUCTUATION INDEPENDENT GROWTH RATE R DEPENDS UPON THE RATE AT WHICH R DECLINES IN RESPONSE TO DECLINING RESOURCES FOR THE INVADER I BI AND THE DIFFERENCE BETWEEN THE AVERAGE lTNESS OF THE INVADER IN ISOLATION K COMPARED TO THAT IN THE PRESENCE OF RESIDENT COMPETITORS KS WHERE K UB WHERE U IS THE PER CAPITA GROWTH RATE IN THE ABSENCE OF RESOURCE LIMITATION 3O THAT R BI K n KS .ONLINEAR COMPETITION RESPONSES 6. DEPENDS UPON TWO ADDITIONAL PROP ERTIES THE DIFFERENCE BETWEEN THE NONLINEAR RESPONSES TO LIMITING RESOURC ES o FOR THE INVADER IN ISOLATION AND WITH COMPETITORS AND THE VARIANCE OF THE LIMITING FACTOR FOR BOTH INVADER AND RESIDENT 6& I 3O THAT 6. BI oI n oS 6& I &INALLY THE STORAGE EFFECT 6L IS THE ABILITY OF A SPECIES TO ALTER POPULATION GROWTH TO AVOID LESS FAVORABLE ENVIRONMENTS WHERE THE INVADER WOULD BE AT A COMPETITIVE DISADVANTAGE BI n l na m 6) N n (ERE l IS THE CORRELATION BETWEEN THE ENVIRONMENTAL RESPONSES BETWEEN DIFFERENT SPECIES n a IS THE BUFFERED POPULATION GROWTH AND m IS THE VARI ANCE IN ENVIRONMENT RESPONSE 3EE #HESSON FOR FURTHER DETAILS
4HE ABILITY FOR SPECIES TO EXHIBIT BEHAVIORAL OR LIFE HISTORY ATTRIBUTES THAT SERVE TO REDUCE THE NEGATIVE EFFECTS OF COMPETITION MAY BE WIDESPREAD 3UCCESSFUL INVA SIVE PLANTS FOR EXAMPLE OFTEN GROW RAPIDLY IN COMPETITION REDUCED SUCCESSIONAL HABITATS 'ROTKOPP ET AL OR HAVE SMALL SEED SIZES #ADOTTE AND ,OVETT $OUST (AMILTON ET AL WHICH SERVE TO HELP PLANTS MOVE FURTHER (OWE AND 3MALLWOOD AND ESTABLISH LONGER SEEDS BANKS THAN LARGE SEEDS 'ROVES
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS
/F COURSE SPECIES INTERACTIONS CAN BE VERY COMPLEX 3PECIES INTERACTIONS MAY PRODUCE DYNAMICS THAT APPEAR CHAOTIC -AY OR UNPREDICTABLE (UISMAN AND 7EISSING 9ET #OURCHAMP AND #AUT #HAPTER $UNCAN AND &ORSYTH #HAPTER AND 3MITH AND 3HURIN #HAPTER SHOW THAT INVASIONS CAN HAVE REGULAR AND UNDERSTANDABLE DYNAMICS IN THE PRESENCE OF MULTIPLE SPECIES INTERAC TIONS #OURCHAMP AND #AUT #HAPTER GO FURTHER TO SHOW HOW COMPETITION AND PREDATION CAN INTERACT TO PROMOTE OR HINDER ANIMAL INVASIONS ON ISLANDS 3TEP SPATIAL SPREAD
$ISPERSAL AND SPREAD IS A CHARACTERISTIC DElNING PROBLEMATIC INVASIONS 3EVERAL CHAPTERS EXPLICITLY EXAMINE WHAT HAPPENS TO POPULATIONS OF INVADERS IN A SPATIAL CONTEXT #HAPTERS -URPHY ET AL ,EWIS ET AL AND (ARDING ET AL 3KELLAMS FORMULATION OF A POPULATIONS SPREAD ACCORDING TO A REACTION DIFFUSION EQUATION HAS BEEN PARAMOUNT TO UNDERSTANDING HOW INVADERS MOVE ACROSS A LANDSCAPE EG +OT ET AL +OT 7ITH #ADOTTE #HAPTER ,EWIS ET AL #HAPTER 3KELLAMS ORIGINAL FORMULATION CAN BE SUMMARIZED AS FOL LOWS SEE #HAPTERS AND FOR MORE ON 3KELLAMS EQUATIONS DX 3R$ DT 4HIS REACTION DIFFUSION MODEL REVEALS THAT THE RATE OF SPREAD IS DEPENDENT UPON TWO SPECIES CHARACTERISTICS THE INTRINSIC RATE OF INCREASE R AND THE DIFFUSION COEF lCIENT $ MEASURED AS DISTANCE OVER TIME &IGURE SHOWS THAT SPECIES WITH LOW R THOUGH THEY MAY HAVE HIGH MOVEMENT RATES WILL NOT SPREAD VERY FAST 3IMILARLY A HIGH R SPECIES WITH LOW MOVEMENT WILL FAIL TO SPREAD RAPIDLY
&IG 4HE VELOCITY OF SPREAD AS INmUENCED BY A DIFFUSION COEFlCIENT $ AND INTRINSIC RATE OF INCREASE R FROM 3KELLAMS REACTION DIFFUSION EQUATION SEE TEXT
-7 #ADOTTE 4 &UKAMI AND 3- -C-AHON
3PREAD MODELS ARE THE LINK BETWEEN POPULATION AND METAPOPULATION DYNAM ICS 3KELLAMS MODEL ASSUMES A UNIFORM ENVIRONMENT WHICH MAY BE A REALISTIC ASSUMPTION AT LARGER SPATIAL SCALES !T INTERMEDIATE SCALES HOWEVER HABITATS ARE OFTEN PATCHY ELICITING METAPOPULATION DYNAMICS ONTO SPECIES SPREAD EG 7OLFF (ANSKI -URPHY ET AL #HAPTER AND (ARDING ET AL #HAPTER USE A METAPOPULATION PERSPECTIVE TO UNDERSTAND DYNAMICS AT LANDSCAPE LEVELS 4HE RATE OF SPREAD USING A METAPOPULATION APPROACH WILL DEPEND UPON TWO PARAMETERS THE RATES OF MIGRATION AND PATCH EXTINCTION ! HIGHER RATE OF MIGRA TION WILL MEAN THAT NEW PATCHES HAVE A HIGHER PROBABILITY OF BEING COLONIZED AND LOWER PATCH EXTINCTION MEANS THAT MORE LOCAL PATCHES WILL ACT AS SOURCES INCREAS ING THE POOL OF POTENTIAL COLONIZERS !S POINTED OUT EARLIER A HIGH R CAN HELP A COLO NIZING POPULATION OVERCOME INHERENT SMALL POPULATION RISKS AND THEREBY REDUCE EXTINCTION PROBABILITIES AND R IS ALSO LIKELY IMPORTANT FOR IMMIGRATION RATE )F WE ASSUME THAT POPULATION SIZE . AT ANY GIVEN TIME IS LARGELY DEPENDENT UPON R AS IN A LOGISTIC EQUATION £ .T ¥ .T .T .T " n " ¤ + ¦ AND WE ASSUME THAT IMMIGRATION INTO EMPTY PATCHES IS SOME FUNCTION OF THE LOCAL DENSITY IN OCCUPIED PATCHES THEN THE PARAMETERS THAT DETERMINE LOCAL DENSITY LIKELY HAVE A FUNCTIONAL RELATIONSHIP WITH MEAN DENSITY AND SOME DISTANCE FUNC TION o RELATED TO THE SPATIAL DISTRIBUTION OF EXTANT POPULATIONS )T d.T o AND WE ASSUME THAT ENVIRONMENTAL VARIATION AFFECTING R IS RANDOM AND NORMALLY DIS TRIBUTED ABOUT SOME MEAN AND CARRYING CAPACITY + IS CONSTANT ACROSS PATCHES THEN R SHOULD CHARACTERIZE CHANGES IN DENSITY ACROSS A LARGER SPATIAL SCALE AND CONSEQUENTLY THE RATE AT WHICH NEW PATCHES ARE COLONIZED 3TEP LARGE SCALE PATTERNS
3PATIAL SPREAD OF INVADERS IS A PROCESS OCCURRING ACROSS SPATIAL SCALES AND EXHIB ITS PATTERNS BEST UNDERSTOOD BY BIOGEOGRAPHY OR MACROECOLOGY 3AX AND 'AINES #HAPTER EXPLORE LARGE SCALE PATTERNS OF SPECIES INVASIONS 4HEY EXAMINE HOW DIFFERENT TAXONOMIC GROUPS OF INVADERS FORM RANGE SIZE AND RICHNESS PATTERNS THROUGH THE LENS OF EXISTING BIOGEOGRAPHICAL THEORY 4O UNDERSTAND THE PROCESSES INmUENCING RANGE SIZE WE CAN STILL APPLY OUR BASIC VARIABLE R 4HROUGH R WE NOT ONLY UNDERSTAND SPECIES SPREAD BUT ALSO THE lNAL RANGE OF DISTRIBUTION (OLT ET AL &RECKLETON ET AL 5SING THE WELL FOUNDED IDEA THAT A SPECIES DISTRIBUTION IS CORRELATED WITH MEAN LOCAL ABUNDANCE EG "ROWN (ANSKI ET AL (OLT ET AL PROVIDES AN IMPORTANT WAY TO CONCEP TUALIZE THESE RELATIONSHIPS ,OCAL EQUILIBRIAL POPULATION DENSITY . OF SPECIES I AT SITE X IS .I X BX n DI U RIX U SO THAT SPECIES WITH HIGHER ABUNDANCES WILL HAVE EITHER LOWER DEATH RATES D OR HIGHER BIRTH RATES B OR BOTH )F WE ASSUME
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS
&IG "IRTH OR DEATH RATE DIFFERENCES ACROSS AND ENVIRONMENT TOP PANEL CAN EITHER LEAD TO RANGE SIZE DIFFERENCES BOTTOM PANEL BETWEEN TWO SPECIES ADAPTED FROM (OLT ET AL
THAT BIRTH RATES DECLINE FROM THE CENTER OF AN ENVIRONMENTAL GRADIENT THEN BIRTH OR DEATH RATE DIFFERENCES BETWEEN SPECIES WILL PREDICT RANGE SIZE &IG &RECKLETON ET AL EXPANDED THIS TO INCLUDE THE MORE REALISTIC SCENARIO WHERE HABITAT SUITABILITY IS PATCHY SIMILAR TO THAT IN METAPOPULATION DYNAMICS 5LTIMATELY THEY SHOW THAT PATCHINESS HAD LITTLE EFFECT ON OVERALL RANGE SIZE )T IS STILL THE DEMOGRAPHIC PARAMETERS BIRTH AND DEATH RATES WITHIN PATCHES THAT CRITI CALLY DETERMINED RANGE SIZE &URTHER (OLT AND +EITT SHOW THAT GRADIENTS IN EXTINCTION AND IMMIGRATION RATES AS WELL AS PATCH AVAILABILITY IN A METAPOPULA TION CAN LIMIT RANGE SIZE
-7 #ADOTTE 4 &UKAMI AND 3- -C-AHON
#/.#,53)/. 4HIS CURSORY EXAMINATION USES A POPULATIONS INTRINSIC RATE OF INCREASE R AS THE VEHICLE TO UNDERSTANDING INVASIONS AT DIFFERENT SCALES 7E SHOW THAT R IS NOT ONLY IMPORTANT FOR LOCAL POPULATION ESTABLISHMENT AND SIZE BUT CAN A LSO HELP US TO UNDERSTAND THE PROCESSES OF SPECIES INTERACTIONS SPATIAL SPREAD AND RANGE SIZES IN INVASIONS ACROSS MULTIPLE SPATIAL SCALES "Y UNDERSTANDING R WE CAN UNDERSTAND THE CHANGES IN LOCAL POPULATIONS OVERTIME THE FACTORS LEAD TO THE SUCCESS OF INVADERS WHEN INTERACTING WITH OTHER SPECIES THE RATE OF SPREAD ACROSS LARGER SPATIAL SCALES AND THE ULTIMATE LIMITS TO THEIR INVENTIVE RANGES /F COURSE OTHER ECOLOGICAL AND EVOLUTIONARY FACTORS will BE IMPORTANT FOR INDIVIDUAL INVASIONS BUT WE SHOW USING R AS AN EXAMPLE THAT by TAKING A CONCEPTUAL APPROACH TO THE ECOLOGICAL FACTORS WE CAN UNDERSTAND THE DYNAMICS OF INVASIONS AT DIFFERENT SCALES OF ORGANIZATION 2%&%2%.#%3 "AKER ( ' 4HE EVOLUTION OF WEEDS !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS "ELYEA , 2 AND ,ANCASTER * !SSEMBLY RULES WITHIN A CONTINGENT ECOLOGY /IKOS "ROWN * ( /N THE RELATIONSHIP BETWEEN ABUNDANCE AND DISTRIBUTION OF SPECIES !MERICAN .ATURALIST #ADOTTE - 7 AND &UKAMI 4 $ISPERSAL SPATIAL SCALE AND SPECIES DIVERSITY IN A HIERARCHICALLY STRUCTURED EXPERIMENTAL LANDSCAPE %COLOGY ,ETTERS #ARLTON * 4 0ATTERN PROCESS AND PREDICTION IN MARINE INVASION ECOLOGY "IOLOGICAL #ONSERVATION #HASE * - AND ,EIBOLD - ! %COLOGICAL .ICHES ,INKING #LASSICAL AND #ONTEMPORARY !PPROACHES 5NIVERSITY OF #HICAGO 0RESS #HICAGO ), #HESSON 0 -ECHANISMS OF MAINTENANCE OF SPECIES DIVERSITY !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS #OLLINGHAM 9 # 7ADSWORTH 2 ! 7ILLIS 3 ' (UNTLEY " AND (ULME 0 % 0REDICTING THE SPATIAL DISTRIBUTION OF ALIEN RIPARIAN SPECIES ISSUE OF SPATIAL SCALE AND EXTENT * !PPL %COL 3UPPL &RECKLETON 2 0 'ILL * ! .OBLE $ AND 7ATKINSON ! 2 ,ARGE SCALE POPULATION DYNAMICS ABUNDANCE OCCUPANCY RELATIONSHIPS AND THE SCALING FROM LOCAL TO REGIONAL POPULATION SIZE *OURNAL OF !NIMAL %COLOGY 'ROTKOPP % 2EJMÉNEK - AND 2OST 4 , 4OWARD A CAUSAL EXPLANATION OF PLANT INVASIVENESS SEEDLING GROWTH AND LIFE HISTORY STRATEGY OF PINE 0INUS SPECIES !MERICAN .ATURALIST 'ROVES 2 ( 7EED ECOLOGY BIOLOGY AND SPREAD 0ROCEEDINGS OF THE &IRST )NTERNATIONAL 7EED #ONTROL #ONGRESS -ELBOURNE !USTRALIA PP (AMILTON - ! " 2 -URRAY - 7 #ADOTTE ' # (OSE ! # "AKER # * (ARRIS AND $ ,ICARI ,IFE HISTORY CORRELATES OF PLANT INVASIVENESS AT MULTIPLE SPATIAL SCALES %COLOGY ,ETTERS
,INKING SCALE DEPENDENT PROCESSES IN INVASIONS
(ANSKI ) -ETAPOPULATION %COLOGY /XFORD 5NIVERSITY PRESS /XFORD 5+ (ANSKI ) +OUKI * AND (ALKKA ! 4HREE EXPLANATIONS OF THE POSITIVE RELATIONSHIP BETWEEN DISTRIBUTION AND ABUNDANCE OF SPECIES )N 2ICKLEFS 2 % AND 3CHLUTER $ EDS 3PECIES DIVERSITY IN ECOLOGICAL COMMUNITIES HISTORICAL AND GEOGRAPHICAL PERSPECTIVES 5NIVERSITY OF #HICAGO 0RESS #HICAGO PP (OLT 2 $ AND +EITT 4 ( !LTERNATIVE CAUSES FOR RANGE LIMITS A METAPOPULATION PERSPECTIVE %COLOGY ,ETTERS (OLT 2 $ ,AWTON * ( 'ASTON + * AND "LACKBURN 4 - /N THE RELATIONSHIP BETWEEN RANGE SIZE AND LOCAL ABUNDANCE BACK TO BASICS /IKOS (OWE ( & AND 3MALLWOOD * %COLOGY OF SEED DISPERSAL !NNUAL 2EVIEW OF %COLOGY AND 3YSTEMATICS (UISMAN * AND 7EISSING & * &UNDAMENTAL UNPREDICTABILITY IN MULTISPECIES COEX ISTENCE !MERICAN .ATURALIST )NDERJIT #ADOTTE - 7 AND #OLAUTTI 2 ) 4HE ECOLOGY OF BIOLOGICAL INVASIONS PAST PRESENT AND FUTURE )N )NVASIVE 0LANTS %COLOGICAL AND !GRICULTURAL !SPECTS ED )NDERJIT "IRKHAUSER PP +OT - %LEMENTS OF -ATHEMATICAL %COLOGY #AMBRIDGE 5NIVERSITY 0RESS .EW 9ORK .9 +OT - ,EWIS - ! AND VAN DEN $RIESSCHE 0 $ISPERSAL DATA AND THE SPREAD OF INVADING ORGANISMS %COLOGY ,AKATOS ) &ALSIlCATION AND THE METHODOLOGY OF SCIENTIlC RESEARCH PROGRAMMES )N #RITICISM AND THE 'ROWTH OF +NOWLEDGE ED ) ,AKATOS AND ! -USGRAVE #AMBRIDGE 5NIVERSITY 0RESS PP ,AWTON * ( !RE THERE GENERAL LAWS IN ECOLOGY /IKOS ,LORET & -ÏDAIL & "RUNDU ' AND (ULME 0 ,OCAL AND REGIONAL ABUNDANCE OF EXOTIC PLANT SPECIES ON -EDITERRANEAN ISLANDS ARE SPECIES TRAITS IMPORTANT 'LOBAL %COLOGY AND "IOGEOGRAPHY ,OCKWOOD * , #ASSEY 0 AND "LACKBURN 4 4HE ROLE OF PROPAGULE PRESSURE IN EXPLAINING SPECIES INVASIONS 4RENDS IN %COLOGY AND %VOLUTION ,ODGE $ - "IOLOGICAL INVASIONS LESSONS FOR ECOLOGY 4RENDS IN %COLOGY AND %VOLUTION -AY 2 - "IOLOGICAL POPULATIONS WITH NONOVERLAPPING GENERATIONS STABLE POINTS STABLE CYCLES CHAOS 3CIENCE 2AHBEK # 4HE ROLE OF SPATIAL SCALE AND THE PERCEPTION OF LARGE SCALE SPECIES RICH NESS PATTERNS %COLOGY ,ETTERS 3AX $ & 3TACHOWICZ * * AND 'AINES 3 $ 3PECIES )NVASIONS )NSIGHTS INTO %COLOGY %VOLUTION AND "IOGEOGRAPHY 3INAUER !SSOCIATES 3UNDERLAND -! 3HEA + AND #HESSON 0 #OMMUNITY ECOLOGY THEORY AS A FRAMEWORK FOR BIOLOGICAL INVASIONS 4RENDS %COL %VOL 3KELLAM * ' 2ANDOM DISPERSAL IN THEORETICAL POPULATIONS "IOMETRIKA
-7 #ADOTTE 4 &UKAMI AND 3- -C-AHON
4ILMAN $ 2ESOURCE COMPETITION BETWEEN PLANKTONIC ALGAE AN EXPERIMENTAL AND THEORETICAL APPROACH %COLOGY 6ITOUSEK 0 - # - $!NTONIO , , ,OOP AND 2 7ESTBROOKS "IOLOGICAL INVASIONS AS GLOBAL ENVIRONMENTAL CHANGE !MERICAN 3CIENTIST 7ITH + ! 4HE LANDSCAPE ECOLOGY OF INVASIVE SPREAD #ONSERVATION "IOLOGY 7OLFF * / 4HE ROLE OF HABITAT PATCHINESS IN THE POPULATION DYNAMICS OF SNOWSHOE HARES %COLOGICAL -ONOGRAPHS
)NDEX !
ALLELOPATHY !LLEN (( !LLENDORF &( !LLIARIA PETIOLATA !LTERNANTHERA PHILOXERIODES !MARANTHUS POWELLII !MARANTHUS RETROmEXUS !MARANTHUS SPP !MMOPHILA ARENARIA !MOEBA PROTEUS !NCISTRUS CHAGRENSIS !NDERSON 0+ !NDREWARTHA (' !NOLIS SAGREI !NOPLOLEPIS LONGIPES !NTENNARIA ROSEA !NTHRISCUS SYLVESTRIS !PERA SPICA VENTI !PHANOMYCES ASTACI !PIS MELLIFERA !RABIDOPSIS SPP !RABIDOPSIS SUECICA !RCHOCENTRUS PANAMENSIS !RCTIUM LAPPA !RCTIUM MINUS !RGYRESTHIA CONJUGELLA !RTEMISIA ABSINTHIUM !RTEMISIA VULGARIS !SILOMAR CONFERENCE ASSEMBLY RULES SEE COMMUNITY ASSEMBLY !STACUS ASTACUS
ABUNDANCE !BUTILON THEOPHRASTI !CACIA DECURRENS !CACIA MELANOXYLON !CACIA NILOTICA !CANTHASTER PLANCI !CER SPP !CHILLEA MILLEFOLIUM !CROPTILON REPENS !DAMS +,2 ADAPTATION ADAPTIVE RADIATION !EQUIDENS COERULEOPUNCTATUS !FRICA AGGREGATION !GRAWAL ! AGRICULTURE !INOUCHE -, !IZEN -! !KAIKES )NFROMATION #RITERION !LEXANDER (- !LLEE EFFECT
!STYANAX AENEUS !STYANAX RUBERRIMUS !USTRALIA !VENA FATUA " "AKER (' "ARBAREA VULGARIS "ASCOMPTE * "AZZAZ &! "ECKSTEAD * BEHAVIOR "ENTON 4' "EVER *$ BIOGEOGRAPHY BIOLOGICAL CONTROL "IOMPHALARIA GLABRATA BIOTIC HOMOGENIZATION BIOTIC INTERCHANGE BIOTIC RESISTANCE "IRCHLER *! "LACKBURN 4- "LANEY #3 "LEPHARISMA JAPONICUM "OLKER " "RACHYHYPOPOMUS OCCIDENTALIS "RACHYRHAPHIS CASCAJALENSIS "RACHYRHAPHIS EPISCOPI "RASSICA NAPUS "RASSICA SPP "RITAIN SEE 5NITED +INGDOM "ROMUS TECTORUM "ROWN !($ "ROWN *(
)NDEX
"RYCON CHAGRENSIS "RYCON PETROSUS "RYCONAMERICUS EMPERADOR "UCKLEY 9- "UFFON ' "UFO MARINUS "URKE -*7 "YERS *% # #ACTOBLASTIS CACTORUM #ADOTTE -7 #ALIFORNIA #AMERON 4# #AMPSURA GORGONAE #ANADA #ANNABIS SATIVA #APSELLA BURSA PASTORIS #ARDAMINE SCHULZII #ARDARIA DRABA #ARDUUS ACANTHOIDES #ARDUUS NUTANS #ARIBBEAN #ARLETON *4 #ASSEY 0 #ASUARINA CUNNUNGHAMIANA #ASWELL ( CAT DOMESTIC CATALYST SPECIES #ENTAUREA DIFFUSA #ENTAUREA MACULOSA #HAETOSTOMA lSCHERI #HAOTIC DYNAMICS #HENOPODIUM ALBUM #HESSON 0, #HILE #HIONOCHLOA PALLENS #HONDRILLA JUNCEA
#HONDRILLA SPP #HOWN 3, #HROMOLAENA ODORATA #HRYSOMELA SPP #IRSIUM ARVENSE #LAUSS -* #LEMENTS &% #LIDEMIA HIRTA #LONAL GROWTH CLUSTERING SEE AGGREGATION COALESCENCE #OLAUTTI 2) #OLLINGHAM 9# #OLLINS -$ COLONIZATION #OLPIDIUM STRIATUM #OMAI , COMMUNITY ASSEMBLY COMMUNITY INVASIBILITY COMMUNITY SATURATION COMPETITION APPARENT NEIGHBORHOOD RELEASE FROM COMPETITION COLONIZATION TRADEOFF CONSERVATION CONCERN CONTACT EXPERIENCE CONTROL OF SPECIES SEE REMOVAL
)NDEX
#ONVOLVULUS ARVENSIS CORAL REEF #RAWLEY -* #REPIS TECTORUM CROWN OF THORNS STARlSH CYCLIC DYNAMICS #YNOGLOSSUM OFlCINALE #YPHOCHARAX MAGDALENAE #YTISUS SCOPARIUS #ZECH 2EPUBLIC $ $AEHLER ## $!NCONA 5 $ARWIN # $ATURA STRAMONIUM $AUCUS CAROTA $AVIS (' $AVIS -! DENSITY DEPENDENCE $ESCURAINIA SOPHIA DETERMINISTIC PROCESSES $EUTSCHEWITZ + DEVELOPMENTAL PATHWAYS $ICKERSON *% $IEKMANN / DIET BREADTH SEE NICHE BREADTH $IPSACUS FULLONUM DISEASE TRIANGLE DISPERSAL BARRIERS
DISTANCE KERNAL LIMITATION LONG DISTANCE SHORT DISTANCE DISTURBANCE DIVERSITY INVASIBILITY SEE SPECIES RICHNESS DIVERSITY HOTSPOT $OBZHANSKY 4 DORMANCY $RAKE *! $RUDE / $UKES *3 $UNCAN 20 $YTHAM # % %CHINOCHLOA CRUSGALLI %CHIUM VULGARE ECOSYSTEM IMPACTS %DWARDS /2 %GLER &% %LLSTRAND . %LTON #3 ENEMY RELEASE ENVIRONMENT NOVEL VARIABILITY EPIDEMIC EPIGENETIC PROCESSES
)NDEX
EPISTEMOLOGY ERADICATION SEE REMOVAL %RUCASTRUM GALLICUM ESCAPE FROM NATURAL ENEMIES SEE NATURAL ENEMIES %SCHSCHOLZIA CALIFORNIA ESTABLISHMENT %UCALYPTUS OBLIQUA %UPHORBIA CYPARISSIAS %UPHORBIA ESULA %UPLOTES PATELLA %UROPE EVOLUTION RAPID EVOLUTIONARY STABLE STRATEGY EXPERIMENTS LABORATORY NATURAL EXTINCTION & &AGOPYRUM TATARICUM &ARGIONE *
FAUNAL INTERCHANGE SEE BIOTIC INTER CHANGE FEEDBACK PROCESS &ICEDULA HYPOLEUCA &ICUS SPP &ICUS LUTEA &ICUS WASP INTERACTION lRE CYCLES &ITTER ! &LORIDA FOOD WEB &ORBES 3! &ORMICA OMNIVORA &OSTER ", FOUNDER EFFECTS &OX '! &RECKLETON 20 &UKAMI 4 &ULMARIS GLACIALIS FUNGI &USARIUM OXYSPORUM ' 'ALEOPSIS TETRAHIT 'ALINSOGA PARVImORA 'ALINSOGA QUADRIRADIATA 'ALIUM MOLLUGO 'ALIUM SPURIUM 'ASCOIGNE *# 'ASKIN *& 'AUSE '& GENERALIST GENETICS QUATITATIVE VARIABILITY GENOTYPE GENERAL PURPOSE INVASIVE GEOGRAPHIC RANGE SIZE
)NDEX
'EOPHAGUS CRASSILABRIS 'EPHYROCHARAX ARTRICAUDATA 'ERMANY 'HALAMBOR #+ 'IDO +" 'LIBERT '3 'OERGEN % 'OOD 2 'OSSYPIUM SPP 'OULSON $ 'RAY ! 'RIME *0 'RINNELL * 'ROTKOPP % 'UTIERREZ $ 'YPSOPHILA PANICULATA ( HABITAT PATCHES (AMILTON -! (ANSKI ) (ARPER *, (AWAII (ELIANTHUS ANNUS (ELIANTHUS ANOMALUS (ELIANTHUS DEBILIS (ELIANTHUS DESERTICOLA (ELIANTHUS PARADOXUS (ELIANTHUS PETIOLARIS (ELIANTHUS TUBEROSUS HERBICIDE HERBICIDE RESISTANCE HERBIVORY HETEROGENEITY ENVIRONMENTAL SPATIAL
)NDEX
TEMPORAL (ETEROPOGON CONTORTUS HETEROZYGOSITY (ODGSON $* (OLCUS LANATUS (OLT 2 (OOKER *$ (OPLIAS MICROLEPIS (ORDEUM JUBATUM HOST PATHOGEN INTERACTION SEE PATHOGENS (OWARD ,/ HUMAN MODIlED INVASIONS HYBRIDIZATION (YPERICUM PERFORATUM HYPER PREDATION (YPHESSOBRYCON PANAMENSIS (YPOCHAERIS RADICATA (YPOSTOMUS PANAMENSIS
)RIS FULVA )RIS HEXAGONA ISLAND BIOGEOGRAPHY ISLANDS * *ORDAN 72 + +AWASAKI + +EANE 2- +EITT 4( +ENDALL "% +LIRONOMOS * +OLBE ** +OT - +OTANEN 0- +RITICOS $ ,
) INVADER SUCCESS INVASIONAL MELTDOWN INVASIVE GENOTYPE SEE GENERAL PUR POSE GENOTYPES )RELAND )RIS BREVICAULIS
,ACK 2 ,ACTUCA SERRIOLA ,ANIUS LUDOVICIANUS LATITUDINAL GRADIENT ,AYCOCK ' ,EE #% ,EVINE *- ,EVINS 2 ,IEBHOLD ! ,INARIA DALMATICA ,INARIA VULGARIS ,INNEAUS # ,IPICUS 2. ,OCKWOOD * ,ODGE $- ,OLIUM RIGIDUM ,OMOLINO -6 ,ONCHURA PUCTULATA
,ONICERA JAPONICA ,ONSDALE 7- ,OTKA 6OLTERRA EQUATIONS SEE MOD ELS ,OTKA 6OLTERRA ,OTUS CORNICULATUS ,OVETT $OUST * ,UNDQUIST ,, ,UPINUS ARBOREOUS ,YTHRUM SALICARIA -AC!RTHUR 2 -AC)SAAC (* -ACK 2. -ADAGASCAR -AIZE MANAGEMENT -ARISA CORNUARIETIS -ARSHALL $2 MASS EFFECTS MASTING SEE SEED SET SYNCHRONIZED -ATRICARIA PERFORATA -ATSUDA ( -AYR % -C'RADY 3TEED * -C+INNEY -, -C,AIN $+ -EDICAGO LUPULINA -EDITERRANEAN -ELALEUCA SPP -ELANDRIUM ALBUM -ELANDRIUM DIOICUM -ELILOTUS ALBA -ELILOTUS OFlCINALIS -ELILOTUS SPP MESOPREDATOR METACOMMUNITY METAPOPULATION
)NDEX
-ETROSIDEROS POLYMORPHA -EXICO MICROBIAL COMMUNITIES -ICROBOTRYUM VIOLACEUM -ICROSTEGIUM VIMINEUM -ITCHELL #% -ITCHELL /LDS 4 MODEL BIRTH DEATH DETERMINSITC ESTABLISHMENT (ASSELL INDIVIDUAL BASED ,OTKA 6OLTERRA LOTTERY METAPOPULATION .ICHOLSON "AILEY POPULATION SPATIAL SPREAD STOCHASTIC -OODY ! -OONEY (! -ORIN 0* MORPHOLOGICAL OVERDISPERSION -OULTON -0 -OUQUET . MUTATION DELETERIOUS RATES MUTUALISM FACULTATION MYCORRHIZAL PLANT INTERACTIONS -YLIUS 3$ -YRICA FAYA -YRIOPHYLLUM SPICATUM
. NATURAL ENEMIES RELEASE FROM SEE ENEMY RELEASE .EOHETERANDRIA TRIDENTIGER .ESLIA PANICULATA .ETHERLANDS 4HE NEUTRAL DYNAMICS .EW :EALAND NICHE BREADTH FUNDAMENTAL REALIZED .ICHOLSON !* .ICOTIANA SPP NITROGEN lXING .OONBURG %' .ORTH !MERICA NUTRIENT CYCLES / /NDATRA ZIBETHICA /NTARIO #ANADA /PERCULINA VENTRICOSA /PUNTIA SPP /RYZA SPP /SENBERG #7 /XALIS CORNICULATA 0 0ACALA 37 0ACIFASTACUS LENIUSCULUS
)NDEX
0ACIlC /CEAN 0ANAMA 0ARAMECIUM CAUDATUM PARASITE 0ARKER " 0ARKER )- PATCH DYNAMICS SEE HABITAT PATCHES 0ATERSON !( PATHOGENS FUNGAL SOIL SPECIALIST VS GENERALIST 0EARSE !3 0ENNISETUM SETACEUM PHENOLOGY PHENOTYPIC PLASTICITY SEE PLASTICITY 0HRAGMITES AUSTRALIS 0HYTOPHTHORA CINNAMONI 0IABUCINA PANAMENSIS 0IANKA %2 0IMELODELLA CHAGRESI 0IMM 3, 0INUS SPP 0LANTAGO LANCEOLATA 0LANTAGO MAJOR PLANT SOIL INTERACTIONS PLASTICITY 0OA ANNUA 0OECILIA GILLII 0OECILIOPSIS ELONGATAL POLLEN SWAMPING POLLINATION 0OLYGONUM CONVOLVULUS 0OLYGONUM SPP POLYPLOIDY 0OPPERIAN SCIENCE
POPULATION DYNAMICS GENETICS POPULATION VIABILITY ANALYSIS 0ORTULACA OLERACEAE 0OTAMOGETON CRISPUS 0OTENTILLA ARGENTEA 0OTENTILLA RECTA 0OWER !' PREDATION SEED PREDICTION PREY SWITCHING PROPAGULE PRESSURE 0ROSOPIS GLANDULOSA 0RUNUS SEROTINA 0SEUDOCHEIRODON AFlNIS 0SEUDOMONAS mOURESCENS 0SIDIUM CATTLEIANUM 0UCCINIA CHONDRILLINA 0UERARIA LOBATA 0YSEK 0 0YTHIUM SPP
)NDEX
RANGE SIZE SEE GEOGRAPHIC RANGE 2ANUNCULUS REPENS 2APOPORT %( 2ASMUSSEN *" RATE OF SPREAD SEE SPATIAL SPREAD REACTION NORMS REACTION DIFFUSION EQUATIONS SEE MODELS SPATIAL SPREAD 2EINHART +/ 2EJMANEK - REMOVAL OF SPECIES RESCUE EFFECT RESOURCE mUCTUATIONS RETICULATE EVOLUTION SEE HYBRIDIZA TION 2EZNICK $. 2HAMDIA QUELEN 2ICCIARDI ! 2ICHARDSON $- 2ICKLEFS 2% 2INELORICARIA URACANTHA 2IVULUS BRUNNEUS 2OBINIA PSEUDOACACIA 2OBINSON *$ 2OEBOIDES GUATEMALANAE 2OEBOIDES OCCIDENTALIS 2OHDE + 2OSENZWEIG -, 2UBUS ALCEIFOLIUS 3
1 1UANTITATIVE TRAIT LOCI 14, 2 RABBIT 2ABINOWITZ $
3APIUM SEBIFERUM 3AX $& 3CHAAL "! 3CHIERENBECK + 3CHRAG !- 3CLEROTINIA SCLEROTIORUM
3#/0% SEED DORMANCY SEE DORMANCY SEED PREDATION SEE PREDATION SEED SET SYNCHRONIZED 3ENECIO CAMBRENSIS 3ENECIO EBORACENCIS 3ENECIO JACOBAEA 3ENECIO VULGRAIS 3ETARIA FABERI 3ETARIA VERTICILLATA 3ETARIA VIRIDIS 3EYCHELLES 3HIGESAD . 3HIMA *3 3HURIN *" 3ILENE ALBA 3ILENE LATIFOLIA 3ILENE NOCTImORA 3ILVERTOWN *7 3IMBERLOFF $ 3INAPIS ARVENSIS 3KELLAM *' SOIL MICROBES SEE MICROBIAL COMMU NITIES 3OL $ 3OLANUM CAROLINENSE 3OLANUM NIGRUM 3OLANUM ROSTRATUM 3OLIDAGO ALTISSIMA 3OLIDAGO GIGANTEA 3ONCHUS ARVENSIS 3ONCHUS ASPER 3ONCHUS OLERACEUS 3ORBUS AUCUPARIA 3ORGHUM HALEPENSE SOURCE SINK DYNAMICS 3OUTH !FRICA 3PALDING 6- 3PARTINA ALTERNImORA 3PARTINA ANGLICA 3PARTINA FOLIOSA 3PARTINA MARITIMA 3PARTINA X TOWNSENDII
)NDEX
SPATIAL INTERACTIONS SPATIAL PATTERNS SPATIAL SCALE SPATIAL SPREAD SEE ALSO MODELS SPATIAL SPREAD SPATIAL STATISTICS SPECIALIST SPECIATION SPECIES RICHNESS AND INVASIBILITY SPECIES SORTING SPECIES AREA RELATIONSHIPS 3PILOGALE GRACILIS STABILITY 3TADLER * 3TEBBINS ', 3TELLARIA MEDIA 3TEVENS '# STOCHASTIC PROCESSES STOCHASTICITY DEMOGRAPHIC ENVIRONMENTAL 3TOHLGREN 4* STORAGE EFFECT 3TRIGOPOS HABROPTILUS 3TURNUS VULGARIS
SUCCESSION 3UEZ #ANAL 3UKOPP ( 3US SCROFA 4 4AMARIX CHINENSIS 4AMARIX GALLICA 4AMARIX PARVImORA 4AMARIX RAMOSISSIMA 4AMARIX SPP 4ARAXACUM OFlCINALE TENS RULE TERMINOLOGY 4ETRAHYMENA PYRIFORMIS 4HLASPI ARVENSE 4HOMSON '- 4ILMAN $ 4RAGOPOGON DUBIUS 4RAGOPOGON MIRUS 4RAGOPOGON MISCELLUS 4RAGOPOGON PORRIFOLIUS 4RAGOPOGON PRATENSIS TRANSPOSABLE ELEMENTS 4RAVIS * 4RAVIS *-* 4RIFOLIUM REPENS 4RIFOLIUM SUBTERRANEUM 4RIPLEUROSPERMUM PERFORATUM 4RITICUM !EGILOPS SPP TROPHIC INTERACTIONS TROPICS 4URNBULL ,! 4YRIA JACOBAEAE 5 5NITED +INGDOM
)NDEX
5NITED 3TATES 5ROCYON LITTERALIS 6 VAN (OLLE " 6AN +LINKEN 2$ 6ERBASCUM THAPSUS 6ERMEIJ '* 6ERTICILLIUM DABLIAE 6ICIA CRACCA 6ICIA SATIVA 6ICIA TETRASPERMA 6ICIA VILLOSA 6IEJA MACULICAUDA 6IOLA ARVENSIS 6IOLA RIVINIANA VIRUSES 6OLTERRA 6 6ULPIA BROMOIDES 7 7ALLACE !2 7ANG -( 7ARMING % 7ATKINSON !2 7ENDEL *& 7ILLIAMS 0! 7ILLIAMSON - 7ILSON %/ 7ODZICKI + 7OLFE ,- 9 9OUNG 72 9UGOSLAVIA : :OBEL -
