Our Livini' Resources — Non-native S/tecies 



441 



1990). Wild pigs were reported primarily in the 

 southeastern United States, California, and 

 Hawaii; despite their status as game in most 

 areas, they pose serious threats to native plant 

 communities and rare plant species by their for- 

 aging and digging (Singer 1981; Stone and 

 Loope 1987). Wild horses {Eqiiiis caballus) are 

 primarily present in the western United States 

 and on the barrier islands of the east coast. 

 Although they may damage native vegetation, 

 wild horses are generally protected as part of 

 the historic scene. 



After maminals. non-native fish were listed 

 most often as problem non-native species. For 

 all areas combined, we received 272 reports 

 representing a total of 40 non-native fish 

 species. Non-native trout (introduced to aug- 

 ment local fisheries) and common carp 

 (Cyprinus carpio) were reported most. 

 Introduced trout include species from other 

 parts of the United States (e.g.. eastern brook 

 trout, Salvelinus fontinaUs. introduced in many 

 areas of the West) and species from other areas 

 of the world (primarily European brown trout. 

 Salmo tnitta). Introduced trout may decimate 

 susceptible native fish populations, lead to the 

 loss of native varieties through interbreeding, 

 and deplete amphibians and aquatic inverte- 

 brates in waters originally without fish (Taylor 

 et al. 1984; Larson and Moore 1985). Most 

 areas reporting problems or threats from 

 non-native trout are in the western United States 

 (Figure). Carp have been introduced in waters 

 throughout much of the United States, but most 

 areas reporting them as serious pests were wet- 

 land-management districts and wildlife refuges 

 along the Mississippi. Missouri, and Columbia 

 river systems. 



We received 245 reports of non-native birds 

 from survey respondents. Although many bird 

 species have been introduced into the United 

 States (Table 1 ). many failed to become estab- 

 lished or remained restricted to areas where 

 introduced. Only 19 species were reported as 

 causing significant damage. European starling 

 (Stumits vulgaris) and rock dove (common 

 pigeon, Coliimha livia) were reported most 

 often, primarily in developed areas. 



Only three non-native amphibian species 

 and four non-native reptiles were reported. 

 The.se species (e.g.. marine toad. Biifo iiiarinus) 

 are primarily a problem in tropical and subtrop- 

 ical areas of southern Florida and Hawaii and 

 some U.S. territories. 



Seventy-three of the species identified in the 

 surveys had been targeted for control or eradi- 

 cation. Feral cats were the subject of the great- 

 est number of management projects (138 areas). 

 Seventy-eight areas were conducting or had 

 completed projects to control wild pigs, while 

 60 areas listed management for feral dogs, 41 



for wild horses, 35 for cows {.Bos laiinis). and 

 35 for feral burros (Eqiius asimis). 



Non-mammalian species were less often tar- 

 gets for control. Thirty-four areas, primarily 

 U.S. Fish and Wildlife Service areas, listed con- 

 trol or eradication programs for carp. Other fish 

 subject to control were introduced rainbow trout 

 (Oncorliynchus mykiss: 22 areas) and brook 

 trout (20 areas) in streams in western North 

 America. Fewer projects were listed for birds. 

 European starlings were the target of most con- 

 trols ( 15 areas). A few areas listed control pro- 

 jects for non-native invertebrates. Most com- 

 mon were fire ants (Soleiiopsis spp.. 14 areas) 

 and gypsy moths (Lymantria dispar; 9 areas). 



This survey highlights widespread and seri- 

 ous concerns about the effects of introduced 

 species on native plant and animal communi- 

 ties. Geographically, this was true for areas 

 across most of the United States except Alaska, 

 where survey respondents generally reported 

 few problems with non-native species, possibly 

 because of the extreme climate of that area. 

 Even there, however, non-native species can be 

 a serious threat in local areas; some nesting 

 waterfowl and seabirds on island wildlife 

 refuges are severely affected by predation from 

 introduced Arctic foxes (Alopex kigopiis). 



Some of the greatest adverse impacts of 

 non-native species have been in freshwater 

 communities and on islands. Introduced fish 

 have caused calamitous changes in the Great 

 Lakes, decimating both the natural community 

 of the lakes and the commercial fishery that 

 depends on these inland seas (Lawrie 1970; Eck 

 and Wells 1987). Adverse effects of introduced 

 fish, especially predaceous species, on native 

 tlsh. amphibians, and invertebrates are a recur- 

 rent pattern (Taylor et al. 1984; Moyle 1986). 

 Introduced brown trout, in particular, are seri- 

 ous predators on native salmonids in the United 

 States. In spite of their small size, introduced 

 western mosquitofish {Gambiisia affinis) may 

 eliminate other small, native fishes through 

 competition or predation; they may also prey 

 heavily on the young of food and game fish and 

 also on aquatic amphibian larvae (Meffe et al. 

 1983). 



Non-native species introduced to islands 

 have caused the greatest hami to terrestrial plant 

 and animal communities. Areas specifically 

 responding to our surveys included the national 

 seashores on the barrier islands of the east coast 

 and Gulf of Mexico, the National Park Service 

 on the California Channel Islands, and national 

 parks and wildlife refuges on the Hawaiian 

 Islands. It is generally considered that long-iso- 

 lated island plants and animals are poorly adapt- 

 ed to cope with introduced predators, competi- 

 tors, and disease organisms, and all of these 

 island areas have suffered serious damage from 





Feral dog 



Non-native trout 



Wild horse 



Figure. Distribution of several 

 non-native animal species on pub- 

 lic lands as reported by land man- 

 agers responding to mail surveys: 

 feral cat, wild pig. feral dog. non- 

 native trout, carp, and wild horse. 



