A Biogeographic Study of Amphibians in Tennessee

Range maps and descriptive, taxonomic, and habitat information are provided for 20 species of frogs and 41 species of salamanders. The environmental setting of Tennessee is described in terms of geology, physiography, climate, drainages, soils, vegetation, and ecoregions. For the purposes of the analyses, a grid cell pattern containing 122 sampling units is used, and the amphibian fauna is organized into three faunal groups. These groups are frog species, salamander species, and all species grouped together as amphibians. The results of a G-test for the frequency distribution of range limits fitted to a Poisson distribution suggest a clumped dispersion pattern for each faunal group. Using the coefficient of Jaccard, cluster analyses of distribution data delineate three areas of faunal homogeneity for frogs, nine for salamanders, and six for all amphibians. Coefficients of correlation of similarity matrices are calculated and indicate that (1) the geographic distribution patterns of both frogs and salamanders are most closely correlated with the patterns of climate, soils, and physiography; and (2) when compared to frogs, salamander distributions exert a larger influence on the determination of amphibian areas of homogeneity. An analysis of the faunal composition of areas of homogeneity in terms of past dispersal patterns of their component species reveals that frog areas are dominated by species that dispersed from southeastern, southwestern, and southern centers of dispersal while salamander areas are dominated by species with an Appalachian Highland center of dispersal. Simple correlation and stepwise multiple regression analyses of the relationships between frog, salamander, and amphibian species densities and values for 17 environmental variables indicate that frogs and salamanders exhibit diametrically different responses to a majority of the environmental gradients studied. Modified by historical factors, aspects of the evolutionary time, ecological time, and spatial heterogeneity theories are used to tentatively explain these density gradients. Frog and salamander faunas of Tennessee exhibit significantly different biogeographic patterns. This is evident in both a study of areas of faunal homogeneity and an analysis of species densities. Results from analyses of total amphibian fauna obscure the unique characteristics of each faunal group.