Quantifying amphibian range fragmentation in the southeastern United States

The southeastern United States is home to the highest amphibian species richness in North America. An often overlooked component of research on factors that drive amphibian geographic distributions is description of species range shape. Broad-scale range disjunction has implications for phylogeography, ecology, and conservation, but descriptions of fragmentation are usually based on subjective visual assessment of range maps. Here, we describe a method for objectively quantifying range fragmentation and use this method to describe the patterns of amphibian species range shapes in the Southeast. Species ranges varied widely in degree of fragmentation, from completely contiguous to highly fragmented, and degree of isolation of range fragments. Incorporating ecological niche models added information about fine-scale habitat fragmentation. Although 12 species had ranges with either high or moderate fragmentation, the only area where range fragments of more than two of the 12 species overlapped was the Appalachian Highlands, suggesting that range fragmentation in the Southeast is driven by multiple biogeographic processes.