Examples of positive (+) and unintended negative (−) roles of non-native species that were intentionally introduced for conservationpurposes.∗PurposeExampleReferenceHabitat, shelter, andfood for nativespecies+American shad (Alosa sapidissima) introducedinto the Columbia River Basin and California as aforage fish for Pacific salmonidsPetersen et al. 2003+non-native crayfish introduced across NorthAmerica to provide forage for recreational fishes(e.g., largemouth bass [Micropterus salmoides])Kats & Ferrer 2003−introduced non-native crayfish resulted in declinesof several native amphibian taxaKats & Ferrer 2003Catalysts for nativespecies+non-native trees planted on abandoned pastures tofacilitate restoration of native tree restorationspecies in Puerto RicoLugo 1997+non-native cattle maintain early-successionalvegetation that favors native fishes and reptilesBrown & McDonald 1995;Tesauro & Ehrenfeld 2007−removal of cattle may result in proliferation ofnon-native grasses, which would have detrimentaleffects on the vulnerable (IUCN Red List) nativeskink (Cyclodina whitakeri)Norton 2009+non-native black locust (Robinia pseudoacacia)provides cover and restores soil fertility on minedlandsAshby 1987+European legume gorse (Ulex europaeus) acts as anurse plant for native forest regeneration in NewZealand in old fields once livestock grazing stopsSullivan et al. 2007−plant succession under European legume gorsefollows a different trajectory resulting in lowerspecies richness of native forest speciesSullivan et al. 2007Taxon substitution+Aldabra giant tortoise (Aldabrachelys gigantea)replaces the ecological role of extinct giantCylindraspistortoises in the Mascarene IslandsGriffiths & Harris 2010Ecosystem services+non-nativeChrysolinabeetles control invasive St.John’s wort (Hypericum perforatum) in Australiaand North AmericaMorrison et al. 1998−failed biocontrol of non-native cane beetle(Dermolepida albohirtum) through introductionof non-native cane toad (Bufo marinus) inAustraliaLever 2001Preservation ofspecies+species are transplanted to islands outside theirhistorical range to mediate threats from non-nativepredators or transplanted poleward to mediateconcerns about species’ ability to shift theirdistributions in response to changing climateJolly & Colbourne 1991;Fontenot et al. 2006;Richardson et al. 2009;Willis et al. 2009∗Negative roles listed here are not exhaustive and include only those that directly oppose the listed positive roles. Many of the non-native specieslisted have other negative effects on conservation objectives.substituted the herbivory and seed-dispersal functions ofnative tortoises that recently became extinct (Griffithset al. 2010).In other cases the substitute roles provided by non-native species have been more serendipitous (Table 1).
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