J24 



Reptiles and Amphihuiiis — Our Livui^ Resources 



Amphibians 



by 



R. Bruce Bury 



P. Stephen Corn 



C. Kenneth Dodd, Jr. 



Roy W. McDiannid 



Norman J. Scott, Jr. 

 National Biological Service 



Amphibians are ecologically important in 

 most freshwater and terrestrial habitats in 

 the United States: they can be numerous, func- 

 tion as both predators and prey, and constitute 

 great biomass. Amphibians have certain physio- 

 logical (e.g., permeable skin) and ecological 

 (e.g.. complex life cycle) traits that could justi- 

 fy their use as bioindicators of environmental 

 health. For example, local declines in adult 

 amphibians may indicate losses of nearby wet- 

 lands. The aquatic breeding habits of many ter- 

 restrial species result in direct exposure of egg. 

 larval, and adult stages to toxic pesticides, her- 

 bicides, acidification, and other human-induced 

 stresses in both aquatic and terrestrial habitats. 

 Reported declines of amphibian populations 

 globally have drawn considerable attention 

 ("Bury ct al. 19S(); Bishop and Petit 1992; 

 Richards et al. 1993; Blaustein 1994; Pechmann 

 and Wilbur 1994). 



Approximately 230 species of amphibians, 

 including about 140 salamanders and 90 anu- 

 rans (frogs and toads) occur in the continental 

 United States. Because of their functional 

 importance in most ecosystems, declines of 

 amphibians are of considerable conservation 

 interest. If these declines are real, the number of 

 listed or candidate species at federal, state, and 

 local levels could increase significantly. 

 Unfortunately, because much of the existing 

 infomiation on status and trends of amphibians 

 is anecdotal, coordinated monitoring programs 

 are greatly needed. 



Faunal Comparisons 



North American amphibian species exhibit 

 two major distributional patterns, endemic and 



- Dis|unct populations of same species 



O 01 concern or stale-protected 



■ Federally protected 



A Extirpated US. population of Tarahumara frog (Rana tarahumarae) 



Figure. Distribution of U.S. endemic amphibian species 

 to be more broadly dispersed. 



widespread. Endemic species (Figure) tend to 

 have small ranges or are restricted to specific 

 habitats (e.g., species that occur only in one 

 cave or in rock talus on a single mountainside). 

 Declines are documented best for endemic 

 species, partly because their smaller ranges 

 make monitoring easier. Populations of 

 endemics are most susceptible to loss or deple- 

 tions because of localized activities (Bury et al. 

 1980; Dodd 1991). Examples of endemic 

 species affected by different local impacts 

 include the Santa Cruz long-toed salamander 

 {Anibystoiiia mucrodactylum croceiim) in 

 California, the Texas blind salamander 

 (Typhlomolge rathbuni) in Texas, and the Red 

 Hills salamander {Pluieognatluis hubrichti) in 

 Alabama; these three species are listed as feder- 

 ally threatened or endangered. 



The number of endemic species that have 

 suffered losses or are suspected of having 

 severe threats to their continued existence has 

 increased in the last 15 years (Table). In pail, 

 the increa.se reflects descriptions of new species 

 with restricted ranges, but the accelerating pace 



Table. The number of amphibian species showing docu- 

 mented or perceived dechnes in 1980 (Bury et al. 1980) 

 and 1994. 



those west of the 100th meridian tend 



of habitat alteration is the primary threat. 



The ranges of most endemics in the western 

 states (26 species) are widely dispersed across 

 the landscape. In contrast, endemics in the east- 

 em and southeastern states (25 species) tend to 

 be clustered in centers of endemism, such as in 

 the Edwards Plateau (Texas), Interior (Ozark) 

 Highlands (Arkansas, Oklahoma), Atlantic 

 Coastal Plain (Texas to Virginia), and uplands 

 or mountaintops in the Appalachian Mountains 

 (West Virginia to Georgia). 



Widespread species often are habitat gener- 

 alists. Many were previously common, but have 

 shown regional or rangewide declines (Hine et 

 al. 1 98 1; Com and Fogelman 1984; Hayes and 

 Jennings 1986; Table). Reported declines of 

 widespread species often lack explanation, per- 

 haps because these observations have only 

 recently received general attention or because 

 temporal and spatial variations in population 

 sizes of many amphibians are not well under- 

 stood. Some reports are for amphibians in rela- 

 tively pristine habitats where human impacts 

 are not apparent. 



A few examples of declines in widespread 

 species illustrate the threats they face across the 

 country: 



