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Biological Invasions

57513 2003 Kluwer Academic Publishers Printed in the Netherlands Confronting introduced species a form of xenophobia Daniel Simberloff Department of Ecology and Evolutionary Biology University of Tennessee 569 Dabney Hall TN

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Biological Invasions






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BiologicalInvasions179–192,2003.©2003KluwerAcademicPublishers.PrintedintheNetherlands.Confrontingintroducedspecies:aformofxenophobia?DanielSimberloffDepartmentofEcologyandEvolutionaryBiology,UniversityofTennessee,569DabneyHall,TN37996-1610,USA(e-mail:dsimberloff@utk.edu;fax:+1-865-974-3067) anditsactivitieswerestrengthenedin1997bytheestablishmentofagovernmentBiosecurityCouncil(ParliamentaryCommissionerfortheEnvironment2001).In1995,theSouthAfricangovernmentini-tiatedamassivepublicworksproject,theWorkingforWaterProgramme,tograpplewiththeproblemofintroducedplants(McQueenetal.2000).IntheUnitedStates,acknowledgingthatexistinglegalandmanage-mentframeworkshadprovedfartoolax,PresidentClinton’sExecutiveOrder13112of1999mandatedtheformationofafederalNationalInvasiveSpeciesCouncilthatproducedaNationalManagementPlanin2001,therstattemptatacoordinatednationalresponsetotheproblem(NationalInvasiveSpeciesCouncil2001).Othernationshaveproducedini-tialsurveysofthescopeofbiologicalintroductions(e.g.,Sherley2000;Weidema2000;Claudietal.2002),whiletherearerecentsynthesesontheimpactsofintroducedspeciesonlessstudiedenvironmentssuchasmarineecosystems(e.g.,Pederson2000).Popularauthorshavewrittenmanybooksforthelayaudi-enceonthesubjectinthelastdecade,bothsyntheticoverviews(e.g.,Bright1998;Devine1998;Cox1999;Low1999;VanDriescheandVanDriesche2000;Baskin2002)anddetailedaccountsofspecicinvaders(e.g.,Goldschmidt1996;Meinesz1997).Popularmedia–newspapers,newsmagazines,television–nowprominentlyfeatureboththegeneralproblemandthe‘invaderoftheweek’–Formosantermites,snakeheads,killerbees,spottedknapweed,MadagascanhissingDocumentedimpactsofintroducedspeciesaremany.Forconservationists,themainthreatistotheveryexistenceofnativespecies.Forthemostcom-prehensiverosterofthreatenedspeciesintheUnitedStates,includingthoselistedundertheEndangeredSpeciesActandintheNaturalHeritageSystemdatabases,Wilcoveetal.(2000)wereabletodeter-minethecause(s)ofthethreatfor1880ofthenearly2500species.Manyarethreatenedbymorethanonefactor.Introducedspeciesarethesecond-leadingcause(afterhabitatdegradation/loss),causingorcontribut-ingtothethreatto49%ofthesespecies–morethanthenextthreecategories(overexploitation,pol-lution,anddisease)combined.Thereisnocompre-hensiveglobaltabulationofcauses,butexaminationofthreatsforspecicregionsortaxadepictsasimi-larimportanceforintroducedspecies.Forinstance,arecenttabulation(BirdlifeInternational2000)ofthecausesofthreattothe1186birdspeciesbelievedtobeimperiledshowsthreemajorfactors,sometimesworkinginconcert.Habitatdegradation/lossisagaintheleadingcause(1008species),followedbyover-exploitation(367species)andintroducedspecies(343species).Forbirds,directharvest(overexploitation)isbelievedtobeagreaterfactorthanformostothertaxa.Theparticularwaysthatintroducedspeciesthreatentheexistenceofnativespeciesareremarkablydiverse;themainmechanismsarepredation,parasitism,her-bivory,vectoringofpathogens,modicationofcriticalhabitat,hybridization,andcompetition(SimberloffIntroducedspeciesalsothreatentheexistenceofcommunity-levelbiodiversity.Itismoredifculttoassessthequantitativeextentofthisthreat,partlybecausetheclassicationofcommunitiesissomewhatsubjective(Shrader-FrechetteandMcCoy1993)andpartlybecausetheconservationstatusofcommuni-tieshasnotbeenstudiedaswellasthatofmanyspecies(cf.Grossmanetal.1994).Thereareprobablyca.7000–9000vegetationassociationsintheUnitedStatesthatwouldqualify,bymanycriteria,asdis-tinctcommunities,ofwhich4500havebeensodes-ignated(Bryeretal.2000).Ofthese,atleast371arerecognizedasthreatened(Grossmanetal.1994),butthefractionthreatenedbyparticularfactorscan-notyetbeestimated.Itisevident,however,thatentirecommunitiescandisappearbecauseofintro-ducedspecies.Forexample,theAsianchestnutblightfungus(Cryphonectriaparasitica)arrivedinNewYorkonnurserystockinthelatenineteenthcenturyandspreadover100millionhaofeasternNorthAmericainlessthan50years,killingalmostallmaturechestnutsCastaneadentata)(Anderson1974;vonBroembsen1989).Chestnuthadbeenadominanttreeinmanyforests,and,thoughitisnotextinct,largeindividualsareextremelyrare,anditis‘functionallyextinct’inthesensethatitissouncommonthatitnolongerfulllsitspreviousecosystemfunctions.Thiswasmorethanjustastructuralchangeinthecommunity;forexample,chestnutdecomposesveryrapidly,andnutrientcyclingprobablysloweddownsubstantiallyaschestnutswerereplacedbyoaks(K.Cromack,pers.comm.).Severalcommunitytypesdominatedbychestnutsurelydisap-pearedentirely.Morerecently,theredspruce-FraserrforestcommunityofthesouthernAppalachianshasbeeneliminatedfrommostareasandisdeclin-inginallbecauseofattackbytheEuropeanbalsamwoollyadelgid,Adelgespiceae,onFraserrs(fraseri)(Grossmanetal.1994;WearandGreis2002). ThoughFraserrasaspeciesisnotinimminentdan-gerofdisappearing,thecharacteristicforestinwhichitwascodominantwillalmostcertainlynotpersistinsimilarform.Inadditiontothreateningtheexistenceofnativespeciesandcommunities,introducedspecieshavehadmanyotherconsequences,includingsomehighlyinimicaltoagricultureandpublichealth.Forinstance,tworecentlyintroducedAsianmosquitoes(A.japonicus)areamajorfactorinthespreadofWestNilevirusinNorthAmerica(Baskin2002).DamagebyintroducedspeciestoagricultureiswellknownandrecentlysummarizedbyHuberetal.(2002).Otherimpactsarelessheraldedbutcostlyandfar-reaching.Forexample,inNorthAmericazebramussels(Dreissenapolymorpha)clogwaterpipesandthusthreatendrinkingwatersuppliesandcommercialuses;through1994thecostofattemptingtoclearthemwasover$100million(Dextrase2002).Strikingly,justaspolicymakers,managers,scien-tists,andthepublicaregraspingthemagnitudeofintroducedspeciesasanenvironmentalissue,agrow-ingnumberofcriticshaveattackedattemptstocon-trolintroducedspeciesasacovertformofnativism,racism,xenophobia,orworse.Thecriticismisremark-ablydiverse,fromtheeldsofhistory,philosophy,sociology,gardening,landscapearchitecture,andevenpopularculture.Below,Iexaminethehistoryofthiscriticismandattempttoassessitsimplicationsforpolicyonintroducedspecies.Gardenarchitecture,gardening,andtheNazisOnestrandofthiscriticismconcernspreferencesfornativeplantsamonggardenersandlandscapearchi-tects.Theargumentinthisarenaisanoldone.Forinstance,in1882,themostprominentAmericanland-scapearchitect,FrederickLawOlmsted,engagedinaheateddebatewiththebotanistCharlesSpragueSargentaboutintroducedspeciesinaprojectreha-bilitatingandlandscapingtheMuddyRiverbetweenBostonandBrookline(Olmsted1888;Sargent1888;Zaitzevsky1982);OlmstedadvocatedandSargentdeploredtheiruse.TheupshotisthattheBrooklinesideoftheriverwasplantedsolelywithnatives,whiletheBostonsidehadmanyexotics(Zaitzevsky1982).However,thetermsofthedebatewerewhollyaes-thetic,withSargent(1888,p.266)admitting,‘Itisnoteasytoexplainwhycertainplantslookdistinctlyinplaceincertainsituationsandwhyotherplantslookasdistinctlyoutofplace’andclaimingthatnon-indigenousspecies‘inevitablyproduceinharmoniousresults’Olmsted(1888,p.418),concedingthat‘plant-ingfar-fetchedtreeswithlittlediscriminationhasledtodeplorableresults’,wasnotwilling‘totabooalltreescomingfromoverthesea.’Themostdamningchargeagainstanti-introducedspeciesactivitywasarticulatedbytwoGermangardenarchitects,JoachimWolschke-BulmahnandGertGroning(GroningandWolschke-Bulmahn1992,1994;Wolschke-BulmahnandGroning1992;Wolschke-Bulmahn1992,1995,1997a,b).Broadly,theydocumentaNazicampaignto‘cleansetheGermanlandscapeofunharmoniousforeignsubstance[plantspecies]’(R.Tuxen1939,citedbyGroningandWolschke-Bulmahn1992).TheanalogytoHitler’scallfortheGermanvolktobecleansedofforeigncom-ponentsispatent(GroningandWolschke-Bulmahn1992).ThevigorwithwhichtheNazispursuedthisbotanicalobjectiveischilling,especiallyinlightoftheirfrenziedpursuitoftheirhumanobjective.Forinstance,ReinholdTuxen,headoftheReichCentralOfceforVegetationMapping,demandeda‘warofextermination’againstAsianImpatiensparvißoraanalogizingtheghtagainstthis‘Mongolianinvader’tothelargerbattleagainstBolshevism(R.Tuxen1942,citedbyGroningandWolschke-BulmahnHowever,Wolschke-BulmahnandGroningassailnotonlytheNazis.TheytracethisNazistanceback-wardtoperceivedracist,nationalistic,andanti-SemiticviewsofthepioneeringGermanlandscapearchitectWillyLange(1864–1941)andIrishgardendesignerWilliamRobinson(1838–1935)andforwardtopartsofthecurrentnaturegardenandnativeplantmovements.Thechargeofanti-SemitismagainstLangerestsonthelatter’sseeingtheOldTestament,whichgrantedhumansdominionoverothercreatures,asapossibleinspirationfortheformalFrenchandBritishgardendesignsthathewishedtocontrastwithhis‘naturegarden’.AsimilarindictmentoftheanthropocentrismoftheOldTestamentbythehistorianLynnWhite(1967),inhisclassicpaper‘Thehistoricalrootsofourecologiccrisis’,hasnever,tomyknowledge,elicitedachargeofanti-Semitism.ThisfactalonedoesnotexculpateLange,butitsuggeststhathispercep-tionoftheroleoftheOldTestamentneednotspringfromanti-Semitism.Wolschke-Bulmahn’slabelingof RobinsonrestsonhisdescriptionofasceneinapublicparkinParis:Inoneinstancewesawasparrowortwoalightonaman’shand,andpluckilyrootoutcrumbsthatheheldrmlybetweenhisngerandthumb.Hewasanancientandperseveringpersonage,evidentlyoftheJewishpersuasion;andhowevermuchIregrettoadmitit,asafaithfulchroniclerImuststatethatnotonesparrowapproachedwithinteninchesofthehandofaGentile.(Robinson1869,citedbyWolschke-Bulmahn1992)Thewordingofthispassagemayreectaperva-siveanti-Semitismofthetime,butitalsoappearstometoexpressacertainamountofaffection.TherewascertainlyanationalisticcasttosomeofLange’swritings:‘Germanyhasbeenchosentolenditsnametothisstyleinthehistoryofgardensandtobecomeonceagainan“improveroftheworld”’(Lange1922,citedbyWohlschke-Bulmahn1992).However,suchnationalismisnotequivalenttoxenophobia.Ihavebeenunabletondspecicevidenceinthewrit-ingsofeithermanthatindicatesracism.PerhapsWohlschke-Bulmahn(1992,p.198)isadmittingalackofevidencewhenheusesanargumentofguiltbyasso-ciation:‘BothLangeandRobinsonweremembersofaconservativebourgeoisieinwhichattitudeslikenation-alism,biologismandanti-Semitismwerewidespread.’Itisinstructivethatbothmenadvocatedtheuseofintroducedspeciesinparticularcircumstances,thoughbothenthusiasticallyendorsedusingnativeplants.ThehistorianAnneHelmreich(1997)similarlylam-bastesRobinson,notingthat,eventhoughheattimesrecommendedusingintroducedplants,thesewereallfromNorthAmerica,Greece,Spain,Italy,AsiaMinor,andtheAlps.Robinsonhimselfarguedthatplantsfromtheseareas,withclimatessimilartothatofBritain,wouldmorelikelysurvivethanwouldtropicalplants.Helmreich,however,seesthechoiceoftheselocationsasRobinson’sreafrmationofimperialistnotionsofEnglishsuperiority,onthegroundsthateachhadbeenthehomeofagreatempireor,inthecaseofNorthAmerica,athrivingcivilizationsimilartothatofGreatThesesamehistoriansclaimthatbothRobinsonandLangewereinuencedintheirracistattitudesbyillustriousforebears.Wolschke-Bulmahn(1992)notesthatAlexandervonHumboldtinuencedLange.vonHumboldt(1806)rmlybelievedininnatechar-actersofvariouspeoples,relatedtotheirclimaticcon-ditions,aprevailingviewinhistimebutonethatishighlyquestionabletoday.ThisnotionaccordswellwithLange’sideathatnativeplantgardensaresome-howsuitableforthetemperamentsofthenativepeopleofaregion.Helmreich(1997)documentsRobinson’sdebttoAlfredRusselWallace,whomsheindictsasanationalistandimperialist,apparentlyforthispas-sageinalettertohissister,FannySims,in1861:‘Ahillofgorse,orofheath,abankoffoxgloves&ahedgeofwildroses&purplevetchessurpassinanythingIhaveeverseeninthetropics’(Raby2001,p.159).AtvarioustimesWallaceespousedideasofEuropeansuperiorityontheonehandandlackofsuperiorityontheother(Raby2001).However,ratherthananaestheticjudgmentbasedonracistthinking,thispassageabouttherelativebeautyofEnglishplantsmightsimplyhavebeenanexpressionofhomesick-ness.WallacehadbeenintheMalayArchipelagooversevenyearsatthispoint,sufferingconstantdeprivationandoccasionallyseriousillness.oningandWolschke-Bulmahn(1992,1994)andoning(1997)taratleastsomemodernnativeplantenthusiastswiththebrushofNazism.Forexample,referringtoabookonnaturegardensbyU.Schwarz(1980),Groning(1997,p.232),says,Schwarzhadnointerestwhatsoeverinknowingaboutthehistoryofplantcultivationorearliernaturegardenconcepts,suchasthatofWillyLange,whosupportedracistandnationalistideasandworkedactivelytosupportNationalSocialistideasingar-oningandWolschke-Bulmahn(1994)suggestthattheentirehistoryofecology,includingconcernaboutintroducedspecies,isinfectedbyNazism.ThattheNazisopposedintroducedspecies,andthattheyrelatedthisagendatotheircampaigntoridGermany(andperhapstherestoftheworld)ofpeopletheyconsideredforeignandinferior,neednotmeanthateveryonewhoopposesintroducedspeciesdoessoforxenophobic,racistmotives(Dawson1994;Sorvig1994a,b),justaseveryItalianwhostrivestomakethetrainsrunontimeneednotbeaFascist.EvenastheNazisbecameenamoredofnativeplants,Dutchlandscapearchitectsworriedthattheirmovementtousenativeplantsoutofconcernforthelossofnaturalareaswasbeingco-optedbytheNazisfornefariousreasons(Woudstra1997).Theywereatpainstotry,gingerly,todissociatetheirideasfromthoseoftheiroccupiers(Woudstra1997). TheAmericanwriterMichaelPollan(1994)seesanativistideologylurkingbehindincreasingconcernamonggardenersaboutintroducedspecies.Citingtwoleadingnaturalgardeningauthors,KenDruse(1994)andSaraStein(1993),heasks‘AmIimplyingthatnaturalgardeninginAmericaisacrypto-Fascistmove-ment?Ihopenot.Imentionthehistoricalprecedentpartlytosuggestthatthe“newAmericangarden”isneitherasnewnorasAmericanasitsproponentswouldhaveusthink’(p.54).Infact,bothDruse(1994)andStein(1993)explic-itlybasetheiradvocacyofnativespeciesonthethreatposedbyintroducedspeciestonativespeciesandcommunities.Forinstance,Stein(1994,p.37)notes,Inalastexquisiteirony,theburgeoninginter-estingardeningthataccompaniedthemovefromcitytosuburbstimulatedthenurserytradetoimportortotoutNorwaymaple,alderbuckthorn,Japanesebarberry,kudzuvine,Japanesehoney-suckle,Orientalbittersweet,purpleloosestrife,mul-tiorarose,andother‘easy’ornamentalsthataresoinvasiveindamagedhabitatsastoprecludetheirnaturalrecovery.Druse(1994,p.27)similarlyobserves,‘anon-nativecauseextirpation[localextinction]orevenextinctionofanativeplant’.Throughouttheirwritings,bothauthorsconsistentlyemphasizetheconservationconsequencesofintroducedspecies,nottheaestheticones.YetPollan(1994)doubtsthatthereareseriousconsequences,muchlessthattheyaretherealmotivesfortheadvocacyofnativeplantsingardens.ReferringtoDruse(1994),hewrites,‘Heoffersnoscienticproofforthiscontention,leavingthereadertowonderifthedarkeningspecterofalienspeciesinthegardenmighthavelesstodowithecologythanideology’(p.54).Theconservationconsequencesofintroducedspeciesnotedabove,andtheirmagnitude,vindicateDruse’sandStein’sconcern.Itisalsoworthnotingthatneitherauthoropposestheuseofintroducedspeciesinallcircumstances.Stein(1993,p.202)respondsdirectlytothechargethatsheisideologicallymoti-vated:‘Restorationpuristsinsistonremovingallexoticspecieswhethertheyareweedsornot.Ihaven’ttheper-sonalityforethniccleansing.MuchasItakeprideinbeingbotanicallypatriotic,Istopshortofthatdegreeofxenophobia.’Druse(1994)frequentlyemphasizesthattheproblemisnotwithintroducedplantspersebutwiththeirpossibleimpactonnatives.Forexample,laudingthepoliciesoftheDesertBotanicalGarden,heobserves,ThephilosophyofthePhoenixpublicgardenhasfromthestartallowedforcertainnonnativeplants.Butwhentheyarerecommendedforlandscapeuseoutsidethelivingarchive,thecriteriabecomemuchstrictertopreventpossibleinvasionbydisruptiveAestheticsaside,thereisonehard-and-fastrule.Youalwayshavetobeverycareful.(Druse1994,p.108)ThatgroundsforimputingxenophobiatoDruse,Stein,andsomehistoricalguresarequestionabledoesnotmeangardeningandlandscapearchitecturearealwaysfreeofsuchmotives.JensJensenprovidesanexample.Inhisearlycareer,Jensen,aDanishimmi-granttotheUnitedStatesandtheleadingexponentofthePrairieStyleoflandscapearchitecture,didnothes-itatetouseintroducedspecies,includinghighlyinva-siveoneslikeRussianolive(Elaeagnusangustifoliaandtree-of-heaven(Ailanthusaltissima),generallyongroundsofhardiness(cf.Grese1992).Helatercametoopposeintroducedplantsstrenuously,however,andhiswritingsaboutgardens(Jensen1990)adducethreereasonsforthisstance:aesthetic,functional(intro-ducedplantsarelesslikelytothrive),andecological(whentheydothrive,theycanharmnativespeciesandcommunities).Wolschke-Bulmahn(1995,1997a)discountsthelattertwoandseestherstassimplyareectionofxenophobiaandracism.HeisconvincinginsofarasJensen’sownwritingsaboutplantssoclearlymirrorracistpoliticalscreedsthatitishardnottoseeattitudestowardshumanslurkingbehindsomeofhisattitudestowardsplants:ThegardensthatIcreatedmyselfshall,likeanylandscapedesignitdoesnotmatterwhere,beinharmonywiththeirlandscapeenvironmentandtheracialcharacteristicsofitsinhabitants.TheyshallexpressthespiritofAmericaandthereforehavetobefreeofforeigncharacterasfaraspossibletheLatinandtheOrientalcreptandcreepsmoreandmoreoverourland,comingfromtheSouth,whichissettledbyLatinpeople,andalsofromothercentersofmixedmassesofimmigrants.TheGermanicchar-acterofourrace,ofourcitiesandsettlementswasovergrownbyforeign[character].Latinhasspoiledalotandstillspoilsthingseveryday.(Jensen1937,citedinWolschke-Bulmahn1995,1997a)Similarly,NellieDoubleday,anearlytwentiethcenturyAmericangardenwriter,believedthenatural garden‘accordswithourracialtemperament,there-foreitisdestinedtobecomethedominantstyleofgardeninghereforthesamereasonthattheEnglishlanguageprevailsonthiscontinent’(Doubleday1908,citedbyClayton2000).ThisstatementisquiteclosetoapersistentthemeinthewritingsofJensen(1990)–thatdifferentsettings‘lookright’todifferentpeople(races)becausetheenvironmentshapesacertainracialtemperament.Itis,ofcourse,notpoliticallycorrecttodaytosubscribetosuchaquestionableview,thoughitisprobablywidelyheld.Thisfactneednotreduceallindividualaestheticjudgmentsonthesuitabilityofaparticularintroducedspeciestoaformofracismorxenophobia,however,asIdiscussbelow.Chargingnativeplantenthusiastsandinvasionbiolo-gistsandmanagerswithxenophobiahaspracticalcon-sequences.Largesegmentsofthehorticultureindustryhavefoughtmorestringentregulationofimportationofexotics(see,e.g.,Hudson1998),anditisnotsur-prisingthattheyhavecitedsomeoftheabovecriticstoimpugnthemotivesofwould-beregulators.Forexample,theon-linecatalogofJ.L.Hudson,Seedman(1998)citesGroningandWolschke-Bulmahn(1992)incallingrecentcriticsofexotics‘eco-fascists’anddeniesthatintroducedspeciescauseanyenvironmen-talorconservationproblems:‘Tosafeguardthisfreemovement[ofgermplasm]wemustbegintoeducatethepublicconcerningthepseudoscienticfoundationsoftheanti-exoticsmovement,,theiroriginsinanideologyofrace-hatred,andtheiragendaoftotalcontrol’(p.4).Immigrationpolicy,nativism,andintroducedspeciesSeveralauthorsrelateconcernwithintroducedspeciestotheevolutionofimmigrationpolicy,especiallyintheUnitedStates.ThehistorianPhilipPauly(1996a)seesearlyactivityagainstintroducedspeciesintheUnitedStatesaspartofthenativismthatpervadedthisnationduringtheProgressiveEra:‘attitudestowardsforeignpestsmergedwithethnicprejudices:thegypsymothandtheorientalchestnutblightbothtookonandcon-tributedtocharacteristicsascribedtotheirpresumedhumancompatriots’(p.54).Similarly,‘itshouldbeclearthatattitudesaboutforeignandnativeorganismswereintimatelylinked,throughbotheverydayexpe-rienceandanalogiesofpolicy,toviewson“alien”and“native”humans’(Pauly1996a,p.70).Heespe-ciallyindictsscientistsforwhathecharacterizesasTable1.RegulationsandlawsrelatingtohumanimmigrationandintroducedspeciesintheUnitedStates. IntroducedspeciesImmigration Californiastatequarantine1881ChineseExclusionAct1882Californiafruitpestlaw1883BeginningofEllisIslandrestrictions1901LaceyAct1900Nationalquotas1921PlantQuarantineAct1912ImmigrationAct1924 stringentregulationsgoverningspeciesintroductionssincethattime.Inparticular,hechargesearlyAmericanadvocatesofcombatinginvasions,TheodorePalmer,CharlesMarlatt,andLelandHoward,withxenophobicmotivations.Palmer(1899)wasoneofthersttoraisealarmsaboutintroducedanimals.In1899heobservedthatpigs,goats,rabbits,cats,andespeciallythesmallIndianmongoosehadrepeatedlydevastatednativebio-tasintheWestIndiesandPacicislands,andhearguedthattheUnitedStatesshouldtakeresponsibilityforpreventingsuchdevastationintheHawaiianislandsandPuertoRico.Marlatt(1917)similarlywarnedaboutthepotentialimpactofintroducedinsectsandplantpathogenssuchaschestnutblightandwhitepineblisterrust,callingforstringentquarantinelawsontheplantsthatcarriedsuchpests.Howard(1898)wroteaboutthethreatofintroducedinsects.Pauly’sevidenceforthesescientists’nativismrestsontheapproximatesynchronyofanti-immigrationreg-ulationsontheonehandandintroducedspeciesregu-lationsontheother(Table1).Xenophobiacertainlyplayedamajorroleinnativistrhetoricsurroundingtheincreasinglyrestrictiveimmigrationpolicies(Kraut1994;Tomes1998).Thereis,however,nodirectevi-dencethatthemotivationsofthepioneersofUnitedStatesintroducedspeciespolicywereotherthanwhattheystatedthemtobe:concernforthedamagecausedbyintroducedspeciestonativespeciesandcommuni-ties,andtoagriculturalandsilviculturalecosystems.Pauly(1996b,p.677)admitsasmuchwithhisimpli-cationthatallindividualslivingataparticulartimearetaintedbythepopularattitudesofthatperiod:‘ScholarsoftheProgressiveEraarewellawareofthepervasive-nessofprejudicialattitudesatalllevelsofAmericansocietyduringthisperiod.Genteelscientists,however,seldomdisplayedtheirprejudicesinprint.’ItisnoteworthythateachpieceoflegislationinTable1confrontingintroducedspeciesrespondedtospecicdamage.TheCaliforniaquarantinewasimposedafterpressurefromgrowersdevastatedbya waveofintroducedpestinsectspeciesthatdestroyedcrops.Resultsofthisearlyeffortwereambiguous,leadingtotighterrestrictionsinthestatefruitpestlawof1883(whichPalmer(1899)creditedwithhavingkeptthesmallIndianmongoose(HerpestesjavanicusoutofCalifornia).ThefederalPlantQuarantineActof1912,whichPauly(1996a)interpretsasfurtherhinderingplantintroduction,ismoretraditionallyseen(e.g.,SegarraandRawson1999)quitedifferently,asawayforthefederalgovernmenttopre-emptanincreas-ingnumberofstatestatutes.Themainstateinterestwasgenerallytheneedtoprotectnaturalresources,whilethemainfederalinterestwastoprotectinterstateandinternationalcommerce,particularlyofagricul-turalproducts,bysupersedingstatestatutesthatmightimpedecommerce.TheLaceyActof1900wasprimar-ilyaimedatenlistingfederalaidinimplementingstategamelaws,byprohibitinginterstatetransportationofwildlifethatviolatedstatestatutes.Itwasoriginallyinspiredbythedeclineofmanygamebirdspecies.RegulationofintroductionswasaddedatthebehestofAgricultureSecretary,JamesWilson(Pauly1996a),whonotedtheproblemsalreadycausedbyintroducedspeciessuchasthemongooseinHawaiiandtheWestIndies.AlthoughPauly(1996a)seestheLaceyActasdraconian,itwasandremainsaveryweaklawinthisregard(Kurdila1988;Peoplesetal.1992;U.S.Congress1993),astheonlyspeciesforbiddenentryarethefewona‘blacklist’,andthosefewarethosethathavealreadybeenproblematicelsewhere.Inaddition,ithasproveddifculttoaddspeciestothelist.Anyotherspeciescanbeimported,subjecttoquarantineregulationssothatdiseasesarenotinadvertentlyintro-duced.ThisentireapproachhaslargelyfailedtocontrolSeveralcritics(Peretti1998;Sagoff1999;HellerandMatza2000;Subramaniam2001)seethesamedarkmotivesofxenophobia,nativism,andracismatworktodayincurrentenhancedactivityagainstintroducedspeciesintheUnitedStatesandelsewhere.GroningandWolschke-Bulmahn(1992)depictthecurrentmaniafornativeplantsaspartofanativismdrivingarecentwaveofxenophobiainGermany.ThemostcomprehensivecriticinthisveinisanAmericanbiologistandfem-iniststudentofscience,BanuSubramaniam(2001),whoperceivesa‘panic’aboutintroducedspeciesasareectionofaxenophobicsurgetriggeredbyuneaseaboutchangingracial,economic,andgendernorms:Theparallelsintherhetoricsurroundingforeignplantsandthoseofforeignpeoplesarestriking.alienplantsareaccusedof‘crowd(ing)outnativeplantsandanimals,spread(ing)disease,damag(ing)crops,andthreaten(ing)drinkingwatersupplies’(Verrengia1999a).Thexenophobicrhetoricthatsur-roundsimmigrantsisextendedtoplantsandanimals.(p.29)Subramaniamwrotejustbefore9/11,and,inherview,themainmotorofnativistanxietythenwasglobalization;whateverthemeritsofherper-ceptionofawaveofxenophobia,theattacksof9/11havesurelyincreasedpublicconcernaboutfor-eignimmigrantsandvisitorstotheUnitedStates.Andthisconcernhasspreadtotheissueofintroducedspecies.Forexample,thepotentiallinkofintroducedspeciestoecoterrorismandbioterrorismwasrecog-nizedbefore9/11andquicklyreceivednewemphasis(e.g.,Knobleretal.2002;NationalResearchCouncil2002).However,itisimportanttonotethattheverystatementsSubramaniamascribestoxenophobiaare,infact,true–asnotedabove,introducedspecieshavecrowdedoutnativespecies,theyhavebroughtandspreadnewdiseases,theyhavedamagedcrops,andtheydothreatendrinkingwatersupplies.Thisfactdoesnot,ofcourse,demonstratethemotivesofpersonsraisingtheseissues,anymorethandoesthesimilarityinlanguagetothatusedinhistoricandrecentwavesofnativism.Itdoes,however,suggestthepossibilityofnonefarioussubtexttosuchconcerns.Subramaniam(2001)doesnotdenythatintroducedspecieshavemanyharmfulimpacts,butsheviewsnativismratherthantheimpactsasthekeymotivationofpeopleconcernedwiththem:wearelivinginaculturalmomentwheretheanxietiesofglobalizationarefeedingnationalismsthroughxenophobia.Thebattleagainstexoticandalienplantsisasymptomofacampaignthatmisplacesanddisplacesanxietiesabouteconomic,social,political,andculturalchangesontooutsidersandforeigners.(p.34)JonahPeretti(1998),anAmericansocialandscien-ticcritic,alsodetectsarecentwaveofxenophobia(e.g.,California’sproposition187of1994).HedoesnotassailalltheincreasingconcernwithintroducedspeciesintheUnitedStatesasnecessarilywhollymoti-vatedbyxenophobiaandnativism,buthepositsalink.HesuggeststhattheSouthAfricanresponsetointroducedspeciesisutterlycompromisedbyracism, andbecauseoftheheavySouthAfricaninuenceoninternationalprograms,thelatterarealsotainted:AmorerecentandsubtleexampleofthiscanbefoundinSouthAfricainthe1980s.ThisiswheretheinitialproposalfortheScienticCommitteeonProblemsoftheEnvironment’s(SCOPE)invasivespeciesprojectwasproposedSouthAfricansci-entistshavehadagreatdealofinuenceovertheSCOPEproject.Theyhavebeenover-representedatinternationalSCOPEconferencesonbiologicalinvasionandhavepublishedadisproportionatenum-berofarticlesonthesubject.WhyarescientistsfromSouthAfricaespeciallyconcernedwithbio-logicalinvasions?TheanswermaybesimilartotheNaziproclivityforthenaturegarden.LikeNazism,apartheidthinkingisconcernedwithseparatingthepurefromtheimpureItisnotsurprisingthatSCOPE’shard-linebiologicalnativismhasrootsinSouthAfrica.(p.188)ItistruethatSouthAfricanscientistshavebeenheavilyrepresentedbothinSCOPEintroducedspeciesprojectsandintheliteratureonintroducedspeciesgen-erally.Thiswastrueduringapartheidandremainstruetoday.Infact,theSouthAfricanWorkingforWaterProgramme,apost-apartheidinitiative,isoneofthemostcomprehensiveresponsestoproblemsgeneratedbyintroducedspecies.Itisimportanttoconsider,however,thatnega-tiveimpactsofintroducedspeciesaredisproportion-atelyhighinSouthAfrica,fortwomainreasons,onebiologicalandtheotherhuman.Biologically,thekeyproblemisthatSouthAfricahasalargenumberofendemicspecies,manyofthemcharacteristicofthe‘fynbos’plantassociationthatcovers77,000km(MacdonaldandRichardson1986).Thespeciesinthisremarkablydiversecommunityevolvedindrycondi-tionsandadaptedtooccasionalhigh-intensityres.Thedominantnativeplantsareshrubs,nottrees.SouthAfricaalsohasoneofthemostpronouncedintro-ducedplantinvasionsintheworld.About10millionha(8.28%ofthenation)areinvaded.Whentreesandlargeshrubswereintroduced(especiallyspeciesof,andHakea),someprovedtobere-adaptedandhighlyinvasive,spreadingtoproducelarge,impenetrablestandsinmanyplaces,attheexpenseofthenativebiota,particularlyinthepre-viouslytreelessfynbos.Thistreeinvasionhasgreatlyincreasederosion,modiedsandmovements,andchangedreregimesandgeochemicalcycling;alltheseimpactshaveharmedthenativecommunity.However,probablythebiggestimpactisonthehydrologyofadrynation.Theplantinvadersuse6.7%moreofthemeanannualrunoffnationwidethanthenativesdid,withtheanalogousgureforpartsofthefynbosrisingto17%(LeMaitreetal.2000);theimpactonnativebiotaofadryregionofsuchmassivewaterwithdrawalsissevere.Consequencesforgroundwaterhavenotyetbeenquantied.Thiswaterlossisalsoofgreatconsequencetohumanendeavors–agricultureandsilviculture–aswellastoecosystemservicessuchasoodcontrolandsupplyingbasichumanneeds.Itamountstoover200literperpersondailywhenthebasicminimumallowanceis25literdaily(McQueenetal.2000).ThisiswhytheMandelagovernmentinitiatedtheWorkingforWaterMarcSagoff(1999),anAmericanphilosopher,isanothercriticwhoanalogizesthecurrentconcernwithintroducedspecieswithxenophobia,pointingexplic-itlytonativistswhoattemptedtoimpedehumanimmi-gration.Heargues,asdoTsing(1995),HellerandMatza(2000),andSubramaniam(2001),thatthesametraits(suchassexualrobustness,uncontrolledfecundity,aggressiveness,lackadaisicalparentalcare)withwhichnativistsstigmatizehumanimmigrantsareascribedtointroducedspecies.Thecruxofhisargu-mentisthatthereisnothinggenericallywrongwithintroducedspecies–afterall,henotes,somenativespeciesareinvasive,aggressive,andcauseeconomicdamage.Further,hearguesthattheeconomiccostsattributedtointroducedspecies,asaclass,donotout-weighthebenetsofintroducedspecies(suchasfoodplants),asaclass,andthatanyaestheticjudgmentabouttheirsuitabilitycanonlybesubjective.Thus,anygenericpleaagainstintroducedspeciesmustbexenophobic.Iagreeinpartwiththispoint,andIwilldiscussitinclosing.Africanizedbees,racism,andthesexualconnectionAheraldedinvasionthatepitomizesthecontrastinginterpretationsofconcernaboutintroducedspeciesisthatofApismelliferascutellata,theAfricanizedhon-eybee(NationalInvasiveSpeciesCouncil2003a).In1957,26queensofthisAfricansubspeciesescapedfromcaptivityinBrazil,andhybridsofthissubspeciesandtheEuropeansubspecies(previouslyintroduced) havespreadnorthatca.500km/year.Despiteamas-siveattempttoforestalltheirarrivalwithabee-free‘MaginotLine’inMexico,theyreachedtheUnitedStates(Texas)in1990andsubsequentlybecameestab-lishedinCalifornia(1995)andothersouthwesternstates.Thesubjectofmanystoriesinthepopularmedia,theyhavebeentermed‘killerbees’becausetheyarefarmoreaggressivethantheEuropeansubspecies–theyreacttodisturbancemuchmorequickly,chasevictimsforgreaterdistances,andmassandstinginmuchgreaternumbers.Thoughtheycausefarfewerdeathsthandogorsnakebites(JohnstonandSchmidt2001),thebeesdomeritthe‘killer’sobriquet.Theyhavekilledover1000peo-plesinceescapingcaptivity(SmithsonianInstitution2003),including175inMexicobetween1988and1995alone,and10intheUnitedStatesthrough1998.Inaddition,vastlymorestungindividualshaverequiredmedicalattention.Becausemanyofthedeathsentailhundredsofstings,theyarebelievedtobeexcruciating.Africanizedbeesalsostinglivestock,butthereisnotallyofdamagetodate.Otherconcernsincludewhethertheywillinterferewithcroppollinationservicesand/ordepresstheapiarytrade.Brazilianhoneyproductionplummetedinthewakeoftheinvasionbutrecoveredasbeekeepersacquiredexperiencedealingwiththesemoreaggressivebees.AnnaTsing(1995,p.127),anAmericananthropol-ogist,seesadifferentmotiveforthegreatpublicityandalarm:‘Inordertomakesenseofthisnewalienhazard,however,itseemsimportanttothinkaboutthelong-termsignicanceofraceandnationinU.S.beeculture.’Inherview,thefearhasaracistorigin,resonatingwithracialfear.DescribingthearrivaloftheAfricanizedbeesinCalifornia,shenotesthattheypenetrated‘man-agedapiariesproperlyreservedfor“European”bees.Thenewspaperswentwild.Thistime,briey,themulattoswouldberemovedanddestroyedforaEuropeans-onlyCalifornia’(Tsing1995,p.113).Theracismin‘bee-panic’sheattributestoparticularaspectsofhumanracism:NorthAmericanbeekeepingderivesfromalongEuropeantraditioninwhichbeeshavebeen,ifany-thing,emblematicofdomesticity.Honeybeesaredevotedtotheirhomeinahive;busy,theyworkhard;helpful,theycooperatewithinanaturaldivisionoflabor;loyal,theyprotecttheirhomealtruistically;parental,theyprovisiontheirbrood;frugal,theysaveupafulllarder.(Tsing1995,p.116)Inshort,theseEuropeanbeesarethequintessentialfamilyorganisms,justasWASPspresumablyformthequintessentialhumanfamily.TheAfricanizedbees,whicharefarlessdomesticatedtowardshumans,arealsofarlessdomestic:theytendtoabscondathigherratesthanEuropeanbees.Worse,fromthestand-pointoffamilysanctity,AfricanizedbeeshybridizewithEuropeans:‘FromtheperspectiveofthosewhoseknowledgebeginswiththeunmarkedEuropean-originhoneybee,Africanbeesarepotentialrapists’(Tsing1995,p.128).TheAmericanlmmakerMichaelMoorehasrecentlytakenupTsing’sthemesasacentralmetaphorinhisscathingindictmentoftheviolenceofUnitedStatesculture,‘BowlingforColumbine’(2002).HeinterweavesnewsclipsandeducationallmsaboutAfricanizedbees(includingoneextendedsequencewithaleadingauthorityonthistopic,Justin.O.Schmidt)withmanyshortclipsofyoungAfrican-Americanmenbeingarrestedandrestrainedbypolice.TheconstantjuxtapositionandthecontextofthelmimplythatthefearofbothAfricanizedbeesandAfrican-Americanmenisgeneratedbyracismratherthanbytheiractivities.EvenTsing’spointthattheultimatefearissexualiscleartoviewers:‘Withtrickycutting,Mooreevenmakesaconvincingargu-mentthatmediafrenzyoverKillerBeeswasapieceofinferentialracism,paranoiathatthemoreaggres-sive“Africanized”beesmightmatewithourmeekandrespectable“European”bees’(Fienberg2002).Subramaniam(2001)believesthatantipathytowardsintroducedspeciesisalsopartofageneralizedfearofthefertilityofoversexedimmigrantwomen:Oneoftheclassicmetaphorssurroundingimmi-grantsistheover-sexualizedfemale.Foreignwomenaretypicallyassociatedwithsuperfertility–reproductiongoneamuck.(p.31)Thisrhetoricofuncontrollablefertilityandrepro-ductionisanotherhallmarkofhumanimmi-grants.Repeatedly,alienplantsarecharacterizedasaggressive,uncontrollable,prolic,invasiveandexpanding.(p.30)TheparticularintroducedspeciesSubramaniamchoosestoexemplifythisfear–the‘Canada’thistleCirsiumarvense),anativeofEurope–wouldseemtoundercuthercasesomewhat,asIdonotbelievethatCanadianwomenarestereotypedasoversexedornotablyfertile.However,thekeypointisthatatleast onereasonthisplantisabhorredinNorthAmericacouldsimplybethestatedreason:itismajoragri-culturalpest(ontheU.S.FederalNoxiousWeedList)becauseofmillionsofdollarsofdamageannually,anditalsothreatensthelocalexistenceofspeciesinanum-berofnaturalplantcommunitiesofprairies,savannas,meadows,barrens,glades,andsanddunes(UnitedStatesDepartmentofAgriculture2003).Areintroducedspeciesuglyorunnatural?Asnotedabove,theearlylandscapearchitectureandgardenliteratureisrifewithassertionsthatnativespeciesareaestheticallypleasingandintroducedspeciesaresomehowaestheticallydiscordant,whilemuchofthemodernnaturegardenliteraturestressesthreatstonativespeciesandcommunities,asdoinva-sionbiologistsandpolicymakers.Icontendthatcon-cernwitharealthreattotheveryexistenceofnativespeciesandcommunitiesneedhavenoconnectiontonativism,racism,andxenophobia,nordoattemptstopreventeconomiccoststovarioushumanendeavors,suchasagricultureandsilviculture.However,anaspectofthiscontentionbearsfurtherdiscussion.Thefactsthatearlyactivistsinthecampaigntolimitspeciesintroductions,suchasPalmerandMarlatt,citedonlyecological,agricultural,andsilviculturalthreats,thattheirdescriptionsandpredictionswereval-idated,andthattheynowhereusedracistorxenophobicterms,doesnoteliminatethepossibilitythat,eitherconsciouslyorsubconsciously,theyweremotivatedatleastpartlybyracismorxenophobia.Afterall,Pauly(1996b)arguesthatsuchattitudeswerecompletelyper-vasiveintheUnitedStatesatthattime,butthateducatedscientistswerecarefulnottodisplaytheirprejudices,particularlyinprint.Theassumptionthatitisdifculttodisentangleindividualmotivationfromlargerculturalandinstitutionalcurrentsunderpinsmuchofmodernhistoriography(cf.Tosh1991,p.114;Applebyetal.1994,p.306).Iwouldonlysay,however,thatIfeeltheburdenofproofshouldbeontheaccuserwhenclaimsofracismandxenophobiaareadvanced(cf.MarinelliAseconddifcultissueiswhetheranaestheticpref-erencefornativespecies,particularlynativeplants,cantrulybeuninfectedbynativismandxenopho-bia.Someofthosewhobasedtheirconcernonaes-thetics(e.g.,Humboldt,Doubleday,Jensen)explicitlyappealedtoasenseofpsychologicalwell-beingasso-ciatedwithnativevegetation,thustothenotionthattheenvironment,includingthebioticenvironment,hasshapedthepsychologyofdifferentnationalgroupsdif-ferently,atleasttotheextentofmoldingaestheticpref-erences.Thoughnowhighlypoliticallycharged,thiswasandperhapsstillisawidelyheldidea.Athoroughtreatmentisbeyondthescopeofthispaper;sufceittosaythatatleastsomewhocriticizedintroducedspeciesonthesegrounds(e.g.,Jensen)adoptedter-minologysosimilartothatofcontemporarynativistsandxenophobesthatitisdifculttobelievethetwosentimentswereunlinkedintheirminds.Mostappealstoaestheticsasanargumentagainstintroducedspeciesdonotrelateaestheticpreferencestogrouppsychol-ogy,nordotheyusetheterminologyofracismorxenophobia.However,theyareunconvincingexactlybecauseaestheticappealissofranklyamatteroftaste.Perhapsthispointismoststrikinglymadebynot-ingthatadvocatesofintroducedspecies(e.g.,Cronon1991;Pollan1994;Pauly1996a)alsoappealtoaesthet-ics,seeinggreatbeautyinmixturesofintroducedandnativespecies.Further,asindicatedbySagoff(1999),manypeoplehavegrownupsurroundedbyspeciesthatwereintroducedbeforetheywereborn,and,forthem,whateveraestheticisassociatedwithasenseofplacemayattachtothosespeciesaswell.Inshort,aestheticsisobviouslytoosubjectiveabasisforpolicyonintroducedspecies.Onevariantofthisaestheticargumentissubtler–thecontentionthatintroducedspeciesaresome-how‘unnatural’,sotheirpresenceisanoffenseagainstnature.Forinstance,thisthreadrunsthroughgarden/landscapearchitecturewritingsfromSargentthroughStein,evenwhenadifferentpoint,suchasenvironmentalsuitabilityorprotectionofnativespecies,isstressed.Theviewthatintroducedspeciesareunnaturaliseasilyassailed(e.g.,Pauly1996a;Gould1998;Peretti1998),usuallybyappealtotheworksofthehistorianWilliamCronon(1983,1996a),whohasdepictedtheenormousimprintofnativeAmericansbeforethearrivalofEuropeans.CrononthusquestionswhetheranypartofNorthAmericaqual-iesas‘natural’or‘wilderness’ifthesetermsaremeanttomean‘unaffectedbyhumans.’Theargumentthengoesthat,ifwecannotsaythathumanshadnotalready‘tampered’withnaturebeforeEuropeansgottoNorthAmerica,howcanweassailintroducedspecies,eventhosebroughtbyhumans,onthegroundsthattheyaresomehowunnatural?Cronon’sviewsonwildernessandnatureareextremelycontroversialandhavebeenbothadoptedassupportbyopponentsofenvironmentalism (e.g.,Budiansky1995)andcastigatedasanti-environmentalist(seeCronon1996b).WithoutaddressingthecogencyofCronon’srebuttal(1996b),whichassertsthathisprofoundquestioningabouttherelationshipofhumanstonatureandwildernesswasmeanttostrengthentheenvironmentalmovement,Ibelievehisargumentsdoimpugnappealsagainstintroducedspeciesbasedontheargumentthattheyareunnatural.Hemarshalsstrongsupportingevidenceforhiscontentionthattheconceptofnatureisahumanconstruct.Ifthisisso,viewsofwhatisnaturalarepersonaljudgmentsjustasaesthetictastesare.Insum,Ibelievethestrongestethicalbases,andpos-siblytheonlyethicalbases,forconcernaboutintro-ducedspeciesarethattheycanthreatentheexistenceofnativespeciesandcommunitiesandthattheycancausestaggeringdamage,reectedineconomicterms,tohumanendeavors.Thissaid,ImustaddresswhatIbelieveisaredherringintroducedbyaphilosopher(Sagoff1999)andtwoecologists(Slobodkin2001;Rosenzweig2001).Thisisthenotionthatcurrentconcernwithintroducedspeciesisfocussedonallintroducedspeciesandfoundedonthenotionthatintroducedspeciesaregenerically‘bad’andnativespecies‘good’.Althoughsomeextremeadherentsofanaestheticstancefavoringnativespeciesdoubtlessholdsuchaview,invasionbiologistsdonot,andthemanyrecentgovernmentandinternationalactivitiesonintroducedspeciesexplicitlyrecognizetheenormousbenetsofsomeintroducedspecies.The1992RioConventiononBiologicalDiversity(article8h)calledfordealingnotwithallintroducedspecies,but‘withthosealienspecieswhichthreatenecosystems,habi-tats,orspecies’.PresidentClinton’sExecutiveOrder13112aimednottoforbidintroductionofallspecies,but‘topreventtheintroductionofinvasivespeciesandprovidefortheircontrolandtominimizetheeco-nomic,ecological,andhumanhealthimpactsthatinva-sivespeciescause’(NationalInvasiveSpeciesCouncil2003b).By‘invasive’,theExecutiveOrdermeans‘analienspecieswhoseintroductiondoesorislikelytocauseeconomicorenvironmentalharmorharmtohumanhealth’(NationalInvasiveSpeciesCouncil2003b).Similarly,reviewsoftheissue(e.g.,Simberloff2000;Huberetal.2002)rarelyfailtonotethegreatbenetsconferredbysomeintroducedspecies.Thus,noneofthesubstantialeffortsformoreeffec-tivecontrolofintroducedspeciesaimtopreventallintroductionsortoremoveallestablishedintroducedspecies.Theytargetintroducedspeciesthatarelikelytocauseecological,economic,orpublichealthproblems.Agoodanalogyistosyntheticchemicals.Thoughweknowfullwellthatcarcinogensthatoccurnat-urallyinfoodsaremoreabundantinhumandietsthansyntheticcarcinogens(NationalResearchCouncil1996),weintheUnitedStatesaresurelygladtohavetheToxicSubstancesControlActof1976,underwhichtheEnvironmentalProtectionAgencytracksandteststhousandsofnewchemicalssynthesizedeachyeartondtheonesthatcausecancer.Unfortunately,attemptstopredictwhichspecies,amongasuiteofpotentialintroductions,arelikelytobeproblematichavehadverymixedsuccess(Macketal.2000).Becausethestakesaresohigh,anditisfarmoredifcult(oftenimpossible)toremoveintro-ducedspeciesoncetheyareestablishedthantokeepthemoutintherstplace,the‘innocentuntilprovenguilty’philosophythathasguidednationalandinter-nationalpolicyuntilnow(see,e.g.,NationalResearchCouncil2000)isinadequateandshouldbereplacedwithaphilosophyof‘guiltyuntilproveninnocent’(Panettaetal.1994;Macketal.2000).Inpractice,ofcourse,thisapproachcouldnotrequireproof,butratherrigorousexpertassessmentofallproposedintro-ductions;currently,inmostnations,suchassessmentisnotrigorousandis,inanyevent,restrictedonlytospeciesforwhichthereisalreadysomesuspicionofathreat,oftenanagriculturalone.TheNewZealandBiosecurityActof1993(ParliamentaryCommissionerfortheEnvironment2001)includedtherstnationallawthatdoesnotpresupposeinnocence.AcknowledgementsIthankLouiseE.Robbinsforcontinuingdialogueonthistopic,ToddCampbell,WilliamCronon,andMaryTebofordiscussiononcertainpoints,andNathanSanders,JustinSchmidt,EvanSugden,andMichaelTurelliforhelpfulinformation.ReferencesAndersonTW(1974)ThechestnutpollendeclineasatimehorizoninlakesedimentsineasternNorthAmerica.CanadianJournalofEarthScience11:678–685ApplebyJ,HuntLandJacobM(1994)TellingtheTruthaboutHistory.Norton,NewYork 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