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1、6.1ExoticandEndangeredSpeciesWhenyouhearsomeonebubblingenthusiasticallyaboutanexoticspecies,youcansafelybetthespeakerisn’tanecologist.Thisisanameforaresidentofanestablishedcommunitythatwasdeliberatelyoraccidentallymovedfromitshomerangeandbecameestablishedelsewher
2、e.Unlikemostimports,whichcan’ttakeholdoutsidetheirhomerange,anexoticspeciespermanentlyinsinuatesitselfintoanewcommunity.Sometimestheadditionsareharmlessandevenhavebeneficialeffects.Moreoften,theymakenativespeciesendangeredspecies,whichbydefinitionareextremelyvuln
3、erabletoextinction.Ofallspeciesontherareorendangeredlistsorthatrecentlybecameextinct,closeto70percentowetheirprecariousexistenceordemisetodisplacementbyexoticspecies.Twoexamplesareincludedheretoillustratetheproblem.Duringthe1800s,BritishsettlersinAustraliajustcou
4、ldn’tbondwiththekoalasandkangaroos,sotheystartedtoimportfamiliaranimalsfromtheirhomeland.In1859,inwhatwouldbethestartofawholesaledisaster,anorthernAustralianlandownerimportedandthenreleasedtwodozenwildEuropeanrabbits(Oryctolaguscuniculus).Goodfoodandgoodsporthunt
5、ing—thatwastheidea.Anidealrabbithabitatwithnonaturalpredatorswasthereality.Sixyearslater,thelandownerhadkilled20,000rabbitsandwasbesiegedby20,000more.Therabbitsdisplacedlivestock,evenkangaroos.NowAustraliahas200to300millionhippityhoppingthroughthesouthernhalfofth
6、ecountry.Theyovergrazeperennialgrassesingoodtimesandstripbarkfromshrubsandtreesduringdroughts.Youknowwherethey’vebeen;theytransformgrasslandsandshrublandsintoerodeddeserts.Theyhavebeenshotandpoisoned.Theirwarrenshavebeenplowedunder,fumigated,anddynamited.Evenwhen
7、all-outassaultsreducedtheirpopulationsizeby70percent,therapidlyreproducingimportsmadeacomebackinlessthanayear.Didtheconstructionofa2,000-mile-longfenceprotectwesternAustralia?No.Rabbitsmadeittotheothersidebeforeworkersfinishedthefence.In1951,governmentworkersintr
8、oducedamyxomavirusbywayofmildlyinfectedSouthAmericanrabbits,itsnormalhosts.Thisviruscausesmyxomatosis.ThediseasehasmildeffectsonSouthAmericanrabbitsthatcoevolv