Assessing the relative influence of abiotic and biotic impacts to range limits in two terrestrial salamander species (Plethodon glutinosus and Plethodon mississippi)

My research investigated the impact of abiotic factors and species interactions on the geographic distribution of two terrestrial salamander species, Plethodon glutinosus (Northern Slimy Salamander) and P. mississippi (Mississippi Slimy Salamander) at different spatial scales. I addressed the influence of ecological factors such as climate and topography on the relative strength of competitive interactions at broad and local scales. Often these factors are studied as independent determinants of species range limits therefore, my research was designed to address how interactions between different ecological factors affected populations across geographic space. The novelty of my research was the methodological approach used. To my knowledge, this is the first use of ecological niche modeling in conjunction with fine scaled studies of competitive interactions to empirically test the influence of ecological factors on the relative strength of competitive interactions.At broad spatial scales the cost of competitive interactions for P. glutinosus and P. mississippi was found to increase at the range margin relative to the interior of the range. However, along the range margin, the influence of climate and species interactions did not vary in a predictable manner. It is likely that interactions between microclimatic conditions, habitat structure, and land cover are stronger constraints on species interactions at the range margin than broad scale climate patterns. Subtle alterations in aggressive behavior, due to the introduction of a non-native congener, had little impact in local scale distribution. This is likely due to habitat structure and local abiotic conditions at the site of introduction.Overall the distributions of P. glutinosus and P. mississippi are shaped by multiple interactions between abiotic and biotic factors that differ in their relative strength at different spatial scales across geographic space. My work demonstrates the importance of considering interactions among various ecological causes of range limits and the spatial scale of investigation.