Examining Head-shape Differences and Ecology in Morphologically Similar Salamanders at Their Zone of Contact

Studying morphological features in addition to ecological characteristics of co-occurring species can provide insight into interactions between species. Determining factors that influence interactions between species provides a framework for understanding evolution in natural environments. Plethodontid salamanders are model taxa frequently used to study species interactions in regard to competition, coexistence, and exclusion. Past studies have suggested that P. ventralis and P. websteri exhibit character displacement in color and may competitively interact when in sympatry. We studied P. ventralis and P. websteri at a sympatric location in Jefferson County, Alabama and compared this population to allopatric populations of each species to identify whether these species differed in morphology and diet, which are indicators for interspecific competition. We found that P. ventralis and P. websteri differed in head shape, in general, and that head shape differed among populations within species. However, we did not find significant shifts within species between allopatric and sympatric locations, which would have indicated character displacement or convergence. Furthermore, species did not differ in diet at any of the studied locations. Interestingly, we discovered that variation in head shape among locations of both species, regardless if the location was allopatric or sympatric, was significant. This result reiterates the importance of including population variation in the context of character displacement and competition. Results of this study can be placed in a robust theoretical context developed from numerous studies of salamander interactions and, thus, lead to a greater understanding of population variation, competition, and species interactions between ecologically similar species.