Commonness,populationdepletionandconservationbiologyKevinJ.GastonandRi - PDF document

Commonness,populationdepletionandconservationbiologyKevinJ.GastonandRichardA.FullerBiodiversityandMacroecologyGroup,DepartmentofAnimalandPlantSciences,UniversityofShefÞeld,ShefÞeld,S102TN,UKSpeciesconservationpractice,asopposedtoprinciple,generallyemphasizesspeciesatriskofimminentextinc-tion.Thisresultsinprioritylistsprincipallyofthosewithsmallpopulationsand/orgeographicalranges.How- Correspondingauthor:Gaston,K.J.(k.j.gaston@sheffield.ac.uk0169-5347/$Ðseefrontmatter2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.tree.2007.11.001Availableonline26November2007 MountaingrasshopperMelanoplusspretus,salmonOncor-hynchusspp.,passengerpigeonEctopistesmigratoriusblack-tailedprairiedogCynomysludovicianusandbisonBisonbisonhavearguablyreshapedseveralterrestrialandfreshwaterecosystemsinNorthAmerica[10,13,14].Like-wise,coastalmarineecosystemsovermuchofNorthandCentralAmerica,includingcoralreefs,kelpforests,seagrassbedsandestuarinehabitats,havebeenreshapedbythelossofmostpopulationsofformerlyabundantspecies,includingcorals,oystersandvertebrategrazers[15]Researchontherelationshipbetweenbiodiversityandecosystemfunctionhasbegunincreasinglytofocusontheroleofspeciesidentityratherthansimplyspeciesrichnessrichness.Dominantspeciesaregenerallyagreedtocontrib-utedisproportionatelytoecosystemfunctionfunction.Forexample(i)totallossandreductionsindensityofthedominantplantspeciesinanexperimentalnativeprairietallgrassplotreducedproductivity,whereasequivalentlossofrarespecieshadnoshorttermeffecteffect;(ii)simulationsshowthatlevelsofsedimentbioturbationaredisproportionatelyinßuencedbyabundantspeciesofmarinebenthicinvertebratesinvertebrates;(iii)naturaldeclinesandexperimentalremovalofacommondetrital-feedingriverineÞshincreaseddownstreamtransportoforganiccarbonandincreasedprimaryproductionandrespirationrespiration;and(iv)experimentalchangesintheabundanceofdominantgrasslandplantspeciesvariouslyincreasedanddecreasedsusceptibilitytoinvasioninvasion.Theimportanceofcommonspeciesextendstothegeo-graphicalstructuringofassemblages.Recentanalyseshaveshownthat,countertomuchpreviousassumption,commonratherthanrarespeciesaretheprincipaldriversofspatialvariationinspeciesrichness,andofrelationshipsbetweenspeciesrichnessandenvironmentalvariablesvariables.Indeed,increasinglyitseemslikelythatcommonspeciesaredisproportionatelyinßuentialinshapingmanymacroecologicalpatterns.DepletingthecommonTheconservationimportanceofnaturallycommonspecieswouldperhapsbeofonlypassinginterestifsuchspeciestendedtoremainrelativelyunscathedbyhumanactivities.However,anthropogenicthreatshaveimpactedcommonspeciesformillenniamillennia.Eveninthepastfewcenturies,allfourofDiamondÕsDiamondÕsÔevilquartetÕofmajordriversofthreatandextinction(overexploitation,habitatlossanddepletion,introductionofalienspecies,extinctioncas-cades)havereducedtheabundancesandrangesizesofpreviouslycommonspecies.Insomecasesthishasledtohighlevelsofthreatorextinction,butinothersrelativelysmallproportionaldeclineshaveresultedinthelossoflargenumbersofindividuals.Overexploitationhasresultedinenormousdeclinesintheabundancesofmanypreviouslycommonspecies,per-hapsmostnotablythroughlogging,huntingandÞshing.Indeed,theseactivitiesare,toalargeextent,foundedonthepopulationdepletionofsuchspecies,althoughtheyareoftennotexplicitlycouchedintheseterms.ExamplesincludedepletionsofmanycommerciallyexploitedtreesandmarineÞsh(Box2).Suchlossesofcommonspeciesareoftenexpressedinunitsthatobscurethescaleofpopulationdepletion.Forexample,deforestationisprincipallyexp-ressedintermsofarealoggedorvolumeoftimberextracted,andlandingsofmarineÞshesareusuallyexpressedintermsofbiomass,ratherthanlossofindividuals. Box1.CommonspeciescontributeadisproportionatelylargenumberofindividualsandbiomasstoassemblagesDataonthebreedingavifaunaofBritainrevealthattheassemblageisstructuredprimarilybycommonandwidespreadspecies[44].Thecontributiontototalnumberofindividuals(blackline)andbiomass(greyline)isgreatestforthemostcommonspecies,whichdiminishesrapidlyasrarerspeciesareadded(FigureIa).The25%mostabundantspeciesintheassemblage(theupperquartile)comprise95.02%ofallbreedingindividualsand87.64%ofallbreedingbiomass,converselythe25%leastabundantspeciescomprise0.01%ofallbreedingindividualsand0.06%ofallbreedingbirdbiomass.Aweaker,albeitstillmarked,patternisapparentforrangesize(FigureIb),withthe25%mostwidespreadspeciescomprising59.8%ofall1010kmresolutionoccurrencerecords[45]duringthebreedingseason,whereasthe25%mostrestrictedspeciescomprisejust0.91%ofalloccurrencerecords.Aconse-quenceofthischaracteristicofassemblagesisthatthelossofindividuals,biomassandgeographicrangecoveragethatresultsfromagivenproportionaldeclineisgreaterincommonspeciesthaninrareones. FigureI.Cumulativecontributionofprogressivelyrarerspeciestototalnumberofindividualsandbiomass,andoccurrencerecords,forbirdsinBritain. 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Habitatlossanddegradationhavealsousuallyresultedinsubstantialdepletionofpreviouslycommonspecies,althoughagainseldomcouchedintheseterms.Thus,theloss,sincebeforesigniÞcanthumandisturbance,of29%oftheareaofforestandwoodland,49%ofsteppe,savannaandgrassland,74%ofshrubland,and14%oftundra,hotdesertandicedesert,muchofwhichisongoingongoing,directlyreßectsthedepletionofmanyoncecommonspecies,andinevitablyresultedintheseveredepletionofmanyothersthatoccurredwithintheseenvironmentsenvironments.Recentattentionhasfocussedonlossesofcommonspeciesofbirdsasaconsequenceoflossesoftropicalforest,temperategrasslandsandtheintensityofmodernagricul-turalpracticespractices.Depletionsofcommonspeciesasaconsequenceoftheintroductionofalienspeciesarebeingincreasinglydocumented.PerhapsthestarkestexampleconcernstheAmericanchestnut.Historicallycommonandwidelydis-tributedacrossmuchofeasternNorthAmerica,itbecameyetmoreabundantfollowingtheonsetofanthropogenichabitattransformationowingtoitsrapidestablishmentinpreviouslyloggedareas.However,itsfortunesrapidlyreversedandthespecieswasbroughttothebrinkofextinctionacrossmuchofitsformerrangebytwointro-ducedpathogens,rootrotPhytophthoracinnamonichestnutblightCryphonectriaparasiticaparasitica.Knock-oneffectsonecosystemfunctionincludedreductioninleafprocessingandconsumptionrates,anddecreasinggrowthratesandadultbodymassinmacroinvertebratestreamshreddercommunities,becausefast-decayingandnutri-tiousAmericanchestnutleavesoriginallyprovidedthemaininputsintoforestedheadwaterstreamsstreams.Finally,somepreviouslycommonspecieshavebeenseriouslydepletedasaconsequenceofextinctioncascades.Themostobviousexamplesareparasites.thelouseofthepassengerpigeon,wasthoughttohavebecomeextinctbeforeorcontemporaneouslywithitshost.Althoughithassubsequentlybeenfoundonotherhosts,itsnumbersmusthavebeengreatlydiminishedbythelossofonethatisestimatedtohavenumberedformerlyinthebillionsbillions.Ofcourse,threateningprocessescanimpactcommonspeciesinratherdifferentways.Theymightresultinpersistenceoflocalpopulationsatmuchreducedabun-dances(e.g.someformsofoverexploitation),entirelossoflocalpopulations(e.g.outrighthabitatdestruction),orsomecombinationofthetwotwo.Inpractice,however,astheoverallabundanceofaspeciesdeclines,thesetwooutcomestendtobecomemorecloselylinked,withthedependenciesbetweenthepopulationdynamicsoflocalpopulationsmeaningthatreductionsintheirabundancesleadtodecliningoccupancyoccupancy.FormalanalysesareurgentlyrequiredtodeterminewhichintrinsicorextrinsictraitstendtobemoststronglyassociatedwithsigniÞcantdeclinesofcommonspecies,andwhichmightthereforehelpidentifythosespeciesatgreat-estrisk.Althoughtheanswerdoubtlessdependsontheformofthethreateningprocess,obviouscontendersin-cludethat(i)theyareheavilyexploited(e.g.manytreeandÞshspecies);(ii)theyoccurinhabitatsthatarebeinglost;(iii)abundancesarenaturallyhighlyvariablethroughtime(e.g.someinsectandsmallerÞshspecies);(iv)theyhavelowpopulationgrowthrates;and(v)individualsaggregateintorelativelysmallareasatkeypointsintheirlifecycle(e.g.manymigratoryspeciesorthosebreedinginconÞnedareas).Thelastoftheseappearstobeasurpris-inglyfrequenttraitamongcommonspecies,particularlyintemperateregionswithmarkedseasonalßuctuationsinresourceavailability.TheroadtoextinctionDramaticimpactsonecosystemfunctioncanfollowfromdepletionsofcommonspecieswithoutnecessarilythrea-teningtheglobalpersistenceofthosespeciesintheshortterm.Nonetheless,themanydocumentedexamplesofpreviouslycommonspeciesthatarenowlistedasthrea-tenedwithextinction(e.g.big-leavedmahogany Box2.CasestudiesofpopulationdepletionofpreviouslycommonspeciesRockyMountaingrasshopperMelanoplusspretusDuringoutbreaks,thisspeciesmighthavenumberedperhaps15trillionindividuals,andwasdistributedacrossmuchofthewesternUSAbetweentheMississippiandtheRockyMountains,itdestroyedcropsovervastareasanddevastatedplainsfarmingcommunitiesties.However,atothertimes,itwaslargelyrestrictedinrelativelysmall(althoughstilllargeinabsoluteterms)numberstothevalleybottomsoftheRockyMountainregion,whichexperienceddramaticexpansioninagriculturalactivityduringthelate1800s,particularlystockraisingandthegrowingofforagecrops,whichwould,inshortorder,havedestroyedmuchofthebreedinghabitatrequiredbythespecies.Inthespaceofjustafewyears,theRockyMountaingrasshopperwentfrombeingoneofthemostseriousagriculturalpestsinNorthAmericatoextinction.PeruviananchovetaEngraulisringensTheprincipaldirectconsumerofplanktonicproductioninthecoastalwatersofPeru,morethan10milliontonnesofthispelagicfishspecieswereharvestedinsomeyearsbeforethestockcollapsedin1972.ThecollapsewasapparentlybroughtaboutbyacombinationofthelevelofexploitationandnaturalpopulationvariabilityinthePeruvianupwellingsystem.Thedeclinepersistedintothemid-1980s,whenthestockbeganaperiodofincreasetowardsitsearlierlevelsbeforecollapsingagainduringthelatePassengerpigeonEctopistesmigratoriusArguably,atonetimeperhapsthemostnumerousbirdonearth,thisspecieswasdistributedacrossmuchofNorthAmerica,westtotheGreatPlainsandfromsouthernCanadatothenorthernMississippi.Duringautumnandwinter,itwasnomadic,formingvastflocksthatsearchedformastingtrees.However,bytheearly1900s,itwasextinctinthewild,inlargepartfromoverexploitation,withhabitatlossasapotentialcontributingfactorfactor.ÕThelossofthepassengerpigeonmusthavehadprofoundramificationsforforestecosystems,alteringthelivesofpredatorsandprey,shiftingandchangingthepathwaysofnutrientsandenergyinwayswewillneverknowÕknowÕ.SaigaSaigatataricaThisspeciesonceoccurredabundantlyinthesteppegrasslandsandsemi-ariddeserthabitatofsouthernRussiaandCentralAsia.SincethebreakupoftheformerUSSRuncontrolledillegalhuntingforhornsandmeathasledtoacatastrophicfallinnumbersfromoveramilliontoafewtensofthousands,andtohighlyskewedsexratiosthatareresultinginreproductivecollapse,withmostremainingindividualsinKazakhstanKazakhstan.ItislistedasÔCriticallyEndan-geredÕbyIUCN. TRENDSinEcologyandEvolutionVol.23No.1 ,Americanburyingbeetle,AtlanticcodGadusmorhua,white-rumpedGypsbengalensis,harbourporpoisePhocoenapho-,saigaantelopeSaigatataricaandEuropeanbisonBisonbonasus),orhaveactuallybeendriventoextinction(e.g.RockyMountaingrasshopper,passengerpigeonandCarolinaparakeetConuropsiscarolinensis)indicatethatrapidslippageofacommonspeciestorarityorevenextinctionisnotasunlikelyasitmightseem.EltonEltonobservedthatÔTheargumentthataspeciesisinnodangerbecauseitisverycommonisacompletefallacy;butisveryoftenbroughtforwardquitehonestly,especiallybypeoplewhohaveaÞnancialinterestindestroyingtheanimalsÕ.Althoughtherearemanyexamplesofpreviouslycom-monspeciesnowthreatenedwithextinction,fewdataexistontheformofsuchtemporaltrajectories.Highratesofglobalpopulationdeclinecan,however,triggerthelistingofaspeciesasthreatenedwithextinctioninthenearfutureusingthecriteriausedbymanynationalandinternationalconservationagenciesagencies.Somepreviouslycommonspecieshavebeenlistedinthisway(e.g.Atlanticcod,AtlantichalibutHippoglossushippoglossus,haddockanogrammusaegleÞnusandcommonskate),andwesuspectthatmanyothers,particularlyfromhabitatsthathaveexperiencedseverereductionsinextent,couldsimilarlybelisted.Theapproachisprecautionary,basedonthepresumptionthatthedeclinewillcontinue.Muchdebateseems,however,toresultfromabeliefthatinmanysuchinstancesthisisunlikelytobethecase,withthedeclinebeinganticipatedtobecomeshallowerorceaseatlowpopulationlevels.Indeed,manydirectanthropogenicthreatsareprobablydensitydependentoratleastspatiallyvariable,suchthattherateofdeclinedecreasesasthespeciesbecomesrarer(andÔcommerciallyextinctÕ).However,thereisalsothepossibilitythatthehumanvalueattachedtoraritywillleadtocontinuingexploitationatpreviouslyuneconomiclevelslevels.Whichevermechanismprevails,populationdepletionsremainmarked,andaresharedbymanyotherpreviouslyorstillcommonspecies,evenwhentheratesareinsufÞcient,havenotbeenade-quatelydocumentedorarenowtoodistantinthepast,totriggerathreatlistingonthebasisofextinctionrisk,orconcerntaxawhoseriskofextinctionhasyettobeeval-AneedtopayincreasedconservationattentiontocommonspecieshasseveralsigniÞcantimplications,includingtheneedtoidentify,monitorandalleviatesigniÞcantdepletionListingofpopulationdepletionGiventheimportanceofcommonspeciesfornaturalecosystemstructureandfunction,itwouldseemsensibleforconservationtoidentifynotonlythose(typicallyrare)speciesthatareatthegreatestriskofextinction,butalsothosethataresufferingmarkedpopulationdepletionsBox3).Indeed,onemightenvisageacategorizationofspeciesbasedontheirlevelofpopulationdepletionthatinsomewaysmirrorstheexistingIUCN(TheWorldConservationUnion)approachtothreatlisting(www.iucnredlist.org/).Thiswouldentailpayingmoreattentiontothestatusanddynamicsofmanyofthemorecommonspeciesthanistypicallydoneatpresent.How-ever,therearefarfewercommonspeciesthanrareones,andtherangeofparameterspertinenttodepletionlistingwouldbesmallerthanthatconsideredduringthreatlisting(whichcanincludepopulationsize,rangesize,numberofsubpopulations,fragmentationofrangeanddeclinesinpopulationsize,rangesize,habitatornumberofsubpopulations[4]).Thekeyparameterswouldbesomeestimateoftheabsoluteandproportionallevelsofdeclineinnumbersofindividuals.Keyissuesinlistingofpopu-lationdepletionwouldincludehowtodistinguishbe-tweensystematicdepletionandnaturalabundanceßuctuations,particularlywhentryingtodetectrelativelysmallproportionaldeclines,andthebaselineagainst Box3.ExtinctionanddepletioninconservationbiologyFromastartingpointatFigureI,lossofspeciesandindividualsfromanassemblage,ifunchecked,ultimatelyresultinassemblageextinctionat.Thetrajectorytowardassemblageextinctioncanbedescribedasatradeoffbetweenlossofspecies(extinction)andlossofindividuals(depletion).Effectiveconservationdependsonachievingsomebalancebetweenthesetwoprocessestooptimizespeciesrichnessandecosystembiomassatanypointbetween(a)and(b),representedbythebrokenline.Disproportionatelossofspeciesiscommonplaceforexamplethroughhabitatfragmenta-tionthatresultsdisproportionatelyintheextinctionofspecieswithsmallranges,habitatdegradationthatleadstothelossofspecialists,andinvasivespeciesthatdisplacepoorcompetitors.Theseproblemswillbeexacerbatedinareaswherelittleeffectiveprotectionofrarespeciesisachieved.Overexploitation,bycontrast,willresultindisproportionatelossofindividuals,whichleadstodrasticchangesinbiomass,assemblagestructureandecosystemfunction,butcausesspeciesextinctionsrelativelyrarely.Effectiveprotectionofrarespecies,suchasthatachievedthroughmodernconservationprogrammesinwesternEuropeandintheUSA,willfurtherdiminishtherateofspeciesextinctions,whereasrelativelylittleconservationinvestmentisdevotedtomorewidespreadspecies,oftenoutsideprotectedareas,andwhichshowsmallerproportionaldeclines.Thus,becauseoftheemphasisonpreventingextinctions,muchmodernconservationpracticeresultsinatrajectorybiasedtoward(d). FigureI.Extinctionanddepletioninconservationbiology. 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whichtomeasurepopulationdepletions(particularlyforspeciesinhabitatsthatareproductsofhumanactivities;e.g.farmland).Botharealsochallengesinthreatlisting.BiodiversityindicatorsAtpresent,speciesbasedindicatorsofthestateofbiodi-versitytendtobeheavilybiasedagainstcommonspecies.Some,suchastheRedListIndicesaresolelyconcernedwiththreatened,andthereforepredominantlyrare,rare,.Others,suchastheLivingPlanetIndexarebasedonabundance,butweightequallyagivenpro-portionalchangeintheabundanceofcommonandrarespecies,eventhoughtheformermightinvolvenumbersofindividualsseveralordersofmagnitudehigherthanthethe.ThebirdindicatorspresentlyusedintheUKandEuropeareconstructedinasimilarwayandalthoughtheytendtoconcentrateonthemorecommonspecies,thissetofspeciesisbroadlydeÞnedtoincludeallthosethatcanbeeffectivelymonitoredusingstandardÞeldmethodsandgeneralizedschemesschemes.Itwouldalsoseemsensibletouseindicatorsthatreßectoveralllevelsoflossofindividuals,andthusthataredisproportionatelyinßuencedbythedepletionofthepopu-lationsofcommonspecies.Indeed,onemightarguethatexistingdemandforsuchindicatorsisevidencedbythefactthatthetrendsinthosethatweightspeciesequallyhaveonoccasionbeenincorrectlyobservedasdemonstratingover-allchangesinabundance.ProtectedareasandwiderlandscapesFinally,payingattentiontopopulationdepletionsaswellasrisksofextinctionmightchangeperceptionsofthejustiÞca-tionsfor,andtherelativeemphasistobeplacedon,estab-lishingandmaintainingprotectedareasandonschemestoimprovetheenvironmentalqualityofthewiderlandscapematrix.Protectedareaslieattheheartofmanyregionalandglobalconservationstrategies,andtheirestablishmentandmaintenanceabsorbsthebulkoftheglobalconservationbudget[42].Althoughtheyhavebeenarguedtoservethepurposesbothofcapturingasampleofbiodiversity,andofseparatingorbufferingthissamplefromexternalpressures,thefocalspecies(asopposedtootherbiodiversityfeatures)ofthesampletendtoberareandthreatened.CommonspeciesdoubtlessgainimportantconservationbeneÞtfrompro-tectedareas,butonlysmallproportionsofindividualsaretypicallycovered,andinisolationthiswillseldombesufÞ-cienttomaintaintheircommonstatus.Schemestoimprovetheenvironmentalqualityofthewiderlandscapematrix(e.g.agri-environmentschemes,urbangreenspaceplanning)willbeessentialtomaintain-ingnaturallycommonspeciesinthisstate.Inthiscontext,commonspeciesarelikelytorespondwelltoschemesthatchießyfocusondevelopingtheoverallcapacityofthelandscapetomaintainpopulations,onreducingthepro-portionofproductivitythatßowstothehumanpopulationandonmaintainingandbuildingecosystemfunctionandservices.Indeed,onemightarguethatthestateofpopu-lationsofnaturallycommonspeciesmightprovideavalu-ableindicatorofthesuccessofsuchschemes,whichinevitablyconstitutesadauntingchallengegiventhescaleofthehumanenterpriseenterprise.AcknowledgementsK.J.G.holdsaRoyalSociety-WolfsonResearchMeritAward.R.A.F.issupportedbyfundingfromtheEngineeringandPhysicalSciencesResearchCouncil(EPSRC).WearegratefultoK.L.Evans,S.Gaston,F.vanLangevelde,O.Petchey,H.Possinghamandthreeanonymousreviewersforcommentsanddiscussion,P.Johnsonforassistance,andA.Mackenzieforinvaluablesupport.1Mittermeier,R.A.etal.HotspotsRevisited:EarthÕsBiologicallyRichestandMostEndangeredTerrestrialEcoregions,2Mace,G.M.andLande,R.(1991)Assessingextinctionthreats:towardareevaluationofIUCNthreatenedspeciescategories.Conserv.Biol.148Ð1573Mace,G.M.etal.(2007)Prioritizingchoicesinconservation.InTopicsinConservationBiology(Macdonald,D.andService,K.,eds),pp.17Ð34,BlackwellPublishing4IUCN(2001)IUCNRedListCategories,IUCN(TheWorldConservationUnion)5Yachi,S.andLoreau,M.(1999)Biodiversityandecosystemproductivityinaßuctuatingenvironment:Theinsurancehypothesis.Proc.Natl.Acad.Sci.U.S.A.96,1463Ð14686Baillie,J.E.M.etal.,eds(2004)2004IUCNRedListofThreatenedSpecies:AGlobalSpeciesAssessment,IUCN(TheWorldConservationUnion)7Soule,M.E.(1985)Whatisconservationbiology?35,727Ð8Linklater,W.L.(2003)Scienceandmanagementinaconservationcrisis:acasestudywithrhinoceros.Conserv.Biol.17,968Ð9759Gaston,K.J.(1994)Chapman&Hall10Ellison,A.M.etal.(2005)Lossoffoundationspecies:consequencesforthestructureanddynamicsofforestedecosystems.Front.Ecol.Environ.3,479Ð48611Gaston,K.J.etal.(2000)Abundance-occupancyrelationships.J.Appl.37(Suppl.1),39Ð5912Gaston,K.J.(2002)Abundance,occupancyandconservationbiology.InAvianLandscapeEcology:PureandAppliedIssuesintheLarge-scaleEcologyofBirds.Proceedingsofthe2002IALE(UK)Conference(Chamberlain,D.E.andWilson,A.M.,eds),pp.215Ð227,InternationalAssociationforLanscapeEcology(IALE)13Flannery,T.(2001)TheEternalFrontier:AnEcologicalHistoryofNorthAmericaanditsPeoples,WilliamHeinemann14Wilcove,D.S.(2000)TheCondorÕsShadow:TheLossandRecoveryofWildlifeinAmerica,AnchorBooks15Jackson,J.B.C.etal.(2001)HistoricaloverÞshingandtherecentcollapseofcoastalecosystems.293,629Ð63816Grime,J.P.(1998)BeneÞtsofplantdiversitytoecosystems:immediate,Þlterandfoundereffects.J.Ecol.86,902Ð91017Vanni,M.J.etal.(2002)Stoichiometryofnutrientrecyclingbyvertebratesinatropicalstream:linkingspeciesidentityandecosystemprocesses.Ecol.Lett.5,285Ð29318Solan,M.etal.(2004)Extinctionandecosystemfunctioninthemarine306,1177Ð118019Bunker,D.E.etal.(2005)Specieslossandabovegroundcarbonstorageinatropicalforest.310,1029Ð103120Boyero,L.etal.(2006)Leafbreakdownintropicalstreams:theroleofdifferentspeciesinecosystemfunctioning.Arch.Hydrobiol.4,453Ð46621Geider,R.J.etal.(2001)PrimaryproductivityofplanetEarth:biologicaldeterminantsandphysicalconstraintsinterrestrialandaquatichabitats.Glob.ChangeBiol.7,849Ð88222Smith,M.D.andKnapp,A.K.(2003)Dominantspeciesmaintainecosystemfunctionwithnon-randomspeciesloss.Ecol.Lett.6,509Ð23Taylor,B.W.etal.(2006)LossofaharvestedÞshspeciesdisruptscarbonßowinadiversetropicalriver.313,833Ð83624Burke,M.J.W.andGrime,J.P.(1996)Anexperimentalstudyofplantcommunityinvasibility.77,776Ð79025Smith,M.D.etal.(2004)Dominancenotdiversitydeterminesinvasibilityoftallgrassprairie.Oikos106,253Ð26226Jetz,W.andRahbek,C.(2002)Geographicrangesizeanddeterminantsofavianspeciesrichness.297,1548Ð155127Lennon,J.J.etal.(2004)Contributionofrarityandcommonnesstopatternsofspeciesrichness.Ecol.Lett.7,81Ð87 TRENDSinEcologyandEvolutionVol.23No.1 28Rahbek,C.etal.(2006)Predictingcontinental-scalepatternsofbirdspeciesrichnesswithspatiallyexplicitmodels.Proc.R.Soc.Lond.B.Biol.Sci.274,165Ð17429Gaston,K.J.andFuller,R.A.(2007)Biodiversityandextinction:losingthecommonandthewidespread.Prog.Phys.Geog.31,213Ð22530Diamond,J.M.(1984)ÔNormalÕextinctionsofisolatedpopulations.In(Nitecki,M.H.,ed.),pp.191Ð246,UniversityofChicago31KleinGoldewijk,K.(2001)Estimatinggloballandusechangeoverthepast300years:theHYDEdatabase.GlobalBiogeochem.Cycles32Gaston,K.J.etal.(2003)Habitatconversionandglobalavianbiodiversityloss.Proc.R.Soc.Lond.B.Biol.Sci.270,1293Ð130033BirdLifeInternational(2004)StateoftheWorldÕsBirds2004:IndicatorsforourChangingWorld,BirdLifeInternational34Anagnostakis,S.L.(2001)Theeffectofmultipleimportationsofpestsandpathogensonanativetree.Biol.Invasions3,245Ð25435Schorger,A.W.(1955)ThePassengerPigeon:itsNaturalHistoryandBlackburnPress36Hughes,J.B.etal.(1997)Populationdiversity:itsextentand278,689Ð69237Elton,C.S.(1927)AnimalEcology,SidgwickandJackson38Courchamp,F.etal.(2006)Rarityvalueandspeciesextinction:theanthropogenicAlleeEffect.PLoSBiol.4,2405Ð241039Butchart,S.H.M.etal.(2004)Measuringglobaltrendsinthestatusofbiodiversity:RedListindicesforbirds.PLoSBiol.2,2294Ð230440Loh,J.etal.(2005)Thelivingplanetindex:usingspeciespopulationtimeseriestotracktrendsinbiodiversity.Philos.Trans.R.Soc.LondonSer.B360,289Ð29541Gregory,R.D.etal.(2005)DevelopingindicatorsforEuropeanbirds.Philos.Trans.R.Soc.LondonSer.B360,269Ð28842James,A.N.etal.(1999)BalancingtheearthÕsaccounts.323Ð32443Ehrlich,P.R.(1995)Thescaleofthehumanenterpriseandbiodiversityloss.InExtinctionRates(Lawton,J.H.andMay,R.M.,eds),pp.214Ð226,OxfordUniversityPress44Gaston,K.J.andBlackburn,T.M.(2000)PatternandProcessinMacroecology,BlackwellScience45Gibbons,D.W.etal.,eds(1993)TheNewAtlasofBreedingBirdsinBritainandIreland:1988Ð1991,T.&A.D.Poyser46Lockwood,J.A.(2004)Locust:TheDevastatingRiseandMysteriousDisappearanceoftheInsectthatShapedtheAmericanFrontier,47Fuller,E.(2000)ExtinctBirds,OxfordUniversityPress48Mallon,D.P.(2003)Saigatatarica.In:IUCN2006.2006IUCNRedListofThreatenedSpecieswww.iucnredlist.org49Milner-Gulland,E.J.etal.(2001)Dramaticdeclinesinsaigaantelopepopulations.35,340Ð345 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