This project will provide empirical tests of the major explanations for limits on species' range using a salamander endemic to the eastern United States. Most species' geographic distributions are not explained by obvious barriers to dispersal or limits on environmental tolerances, making understanding range limits a central question in ecological and evolutionary biology. In addition, understanding the factors that limit ranges is an urgent priority for conservation as climate change, exotic species invasions, and habitat alterations influence the ranges of the majority of Earth's species. With a better understanding of the mechanisms limiting species? ranges, species at risk of extinction due to global climate change can be identified. In turn, management can focus on targeting locations for protected areas or choosing species for managed translocation. Overall, the proposed research should have broad basic, as well as practical, implications because interest in species' range limits is widespread throughout the ecological, evolutionary, and conservation community.
Although range limit hypotheses are well-grounded in theory, empirical tests have lagged behind. This integrative approach will provide an understanding of the mechanisms that limit species' geographic distributions and lead to a framework for predicting species? extinction risk. The streamside salamander (Ambystoma barbouri) has a restricted continuous range in Kentucky, Ohio, and Indiana. Within the species' range, edge populations generally have lower genetic diversity and effective population sizes than populations in the center of the distribution which may prevent geographic expansion at the range edges. This study will use a combination of population genomics, landscape genetics, and an experimental field study to determine (1), if asymmetric gene flow from core to edge constrains local adaptation and range expansion, and (2) if increased habitat resistance at the species edge prevents range expansion. It is expected that these multiple hypotheses may all contribute to range limits, at least to some extent.