Our Liviiifi RcsiHirces — Nim-natire Species 



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Case Studies 



Spectacled Caiman 



The spectacled caiman has been estabUshed 

 in southern Florida for about 30 years (Eihs 

 1980). There are few pubUshed accounts of this 

 species in Florida, but one (Ellis 1980) indicat- 

 ed that these animals eat fish, amphibians, and 

 mammals. This information, coupled with the 

 species" ability to tolerate crowding in bodies of 

 water and relatively rapid maturation, suggests 

 that impacts on native alligators (Alligator inis- 

 sissippiensis) might be expected (CM. Sekerak, 

 University of South Florida, personal communi- 

 cation). Studies in the species" native range (J. 

 Dixon. Texas A&M University, personal com- 

 munication), however, suggest that the specta- 

 cled caiman does not co-occur with larger 

 species of crocodilians. perhaps because of their 

 predation on the smaller caimans. Since the 

 American alligator reaches a larger size than the 

 spectacled caiman, it is possible that the 

 American alligator will deter the caiman from 

 substantially expanding its range. 



Marine Toad 



The marine toad, native to the tropical New 

 World, is widely introduced and now has a vir- 

 tually circumtropical range (Zug and Zug 

 1979). Populations were originally established 

 for insect control, but the species itself became 

 a pest. Information from Australia (Tyler 1989) 

 indicates that ingestion of marine toads, 

 because they have highly toxic skin glands, 

 results in deaths of native reptiles, birds, and 

 mammals. Observations on Guam, where the 

 marine toad has been established since 1937 

 (McCoid 1993), indicate that poisonings of pet 

 dogs and cats by biting or mouthing marine 

 toads are relatively common (R. Dorner. 

 Marianas Veterinary Clinic, personal communi- 

 cation). On Guam, the island-wide decline of a 

 large varanid lizard is attributed to its predation 

 on the introduced toad (McCoid et al. 1994). In 

 Florida, where the marine toad has been estab- 

 lished since 1955. poisonings of pets (Ashton 

 and Ashton 1988) and declines of nadve 

 amphibians in areas of co-occurrence with the 

 marine toad are reported (J. Rossi. Jacksonville 

 University, personal communication). In a labo- 

 ratory situation, a native toad {Biifo ameri- 

 canus) was behaviorally dominated and exclud- 

 ed from feeding by marine toads (Boice and 

 Boice 1970). There is a literature survey on the 

 marine toad that includes information on 

 extralimital populations (Lawson 1987). 



African Clawed Frog 



Despite initial fears of the effect of the 



African clawed frog on aquatic California ver- 

 tebrates (St. Amant 1975). a subsequent study 

 (McCoid and Fritts 1980a) indicated that these 

 fears may be unwarranted because the only ver- 

 tebrates found in stomach analyses were imma- 

 ture African clawed frogs and an introduced fish 

 species. Other studies (McCoid and Fritts 

 1980b. 1993) characterize populations as living 

 primarily in temporary and artificial bodies of 

 water, where most native aquatic vertebrates are 

 expected to be absent. Recently, populations in 

 southern California may have declined because 

 of drought (McCoid et al. 1993). Although 

 African clawed frogs have been established in 

 California since the mid-1960"s (McCoid and 

 Fritts 1980b). impacts on native invertebrates, 

 their primary food source, are unassessed. 



Bullfrog 



Although precise dates of introductions of 

 the bullfrog into many areas of western Noi1h 

 America are not well known (Bury and Whelan 

 1984). the earliest introduction occurred in 

 1896 (Hayes and Jennings 1986). Impacts on 

 native ranid frogs, however, are well document- 

 ed and may account for range restrictions of 

 native ranids (Moyle 1973; Hayes and Jennings 

 1986: Stuart and Painter 1993). Recent infor- 

 mation indicates that the Mexican garter snake 

 is also declining because of predation by bull- 

 frogs {see Rosen and Schwalbe, this section). 



Brown Tree Snake 



Since the introduction of the brown tree 

 snake on Guam about 40 years ago. the snake 

 has reached enormous densities (Rodda et al. 

 1992) and is implicated in the demise of the 

 entire native forest-dwelling bird community 

 (Savidge 1987) and some of the larger lizard 

 species (Rodda and Fritts 1992). Additional 

 impacts include disniption of electrical power 

 (Fritts et al. 1987). predation on domesticated 

 animals (Fritts and McCoid 1991). and human 

 health risks (Fritts et al. 1990, 1994). There are 

 several overviews of the brown tree snake prob- 

 lem on Guam (Fritts 1988; McCoid 1991: also 

 see Fritts and Rodda, this section). 



Discussion and Summary 



Exotic species of reptiles and amphibians 

 are established in the following areas of the 

 United States (Table): Florida (30 species), 

 Hawaii ( 12), Guam (9), Commonwealth of the 

 Northern Mariana Islands (8), California (6), 

 Louisiana (5). Puerto Rico (5). Texas (4), and 

 Arizona (3). All other areas combined have 9 

 species. Many of these introductions are due to 

 released or escaped pets. 



