Community structure and distributions of two terrestrial salamanders : a pluralistic approach
A goal of evolutionary ecology is to understand the forces that generate ecological communities and maintain species boundaries. Although the effects of particular biotic and abiotic forces have been well studied, much less is known about how these forces interact to influence the evolution of community structure. Here, I report an example of compensatory abiotic and biotic factors limiting the distribution of two terrestrial salamanders and effectively maintaining community structure. The distribution of the wide-ranging Plethodon cinereus completely surrounds the range of P. hubrichti, thus it was believed that P. hubrichti was geographically restricted as a result of interspecific competition from P. cinereus. Using a combination of morphological analysis, resource use (food) data, climatic data, and ecological-niche modeling, I found no evidence to support the hypothesis that biotic interactions with P. cinereus have restricted the range of P. hubrichti. I found no partitioning of food resources in sympatry and no evidence of sympatric morphological divergence. Conversely, there was significant evidence supporting the hypothesis that abiotic forces affected the distribution of P. hubrichti. There was a significant association between local environmental variables and average population morphology, as well as significant morphological convergence of the two species in sympatry, both consistent with adaptation to the local environment. Additionally, ecological niche modeling accurately predicted the range of P. hubrichti, lending further support to this hypothesis. Most notably, even though ecological niche modeling predicted that the ecologically-viable range of P. cinereus included nearly 90% of the range of P. hubrichti, it is absent from nearly this entire region. Combined with the prior behavioral research (where P. hubrichti was the more aggressive of the two), these results strongly suggest that biotic interactions with P. hubrichti negatively impact and restrict the distribution of P. cinereus. This finding is the converse of what was predicted based upon the species distributions alone. This study provides a concrete example of how both biotic and abiotic forces interact to maintain joint species distributions and influence community structure. It also stresses the need for a pluralistic approach to community ecology as well as species' distributions that integrate multiple data sets.