The importance (or lack thereof) of niche divergence to the maintenance of a northern species complex: the case of the long-toed salamander (Ambystoma macrodactylum Baird).

The relative importance of ecological vs. non-ecological factors for the origin and maintenance of species is an open question in evolutionary biology. Young lineages--such as the distinct genetic groups that make up the ranges of many northern species--represent an opportunity to study the importance of ecological divergence during the early stages of diversification. Yet, few studies have examined the extent of niche divergence between lineages in previously glaciated regions and the role of ecology in maintaining the contact zones between them. In this study, we used tests of niche overlap in combination with ecological niche models to explore the extent of niche divergence between lineages of the long-toed salamander (Ambystoma macrodactylum Baird) species complex and to determine whether contact zones correspond to (divergent) niche limits. We found limited evidence for niche divergence between the different long-toed salamander lineages, substantial overlap in the predicted distribution of suitable climatic space for all lineages and range limits that are independent of niche limits. These results raise questions as to the importance of ecological divergence to the development of this widespread species complex and highlight the potential for non-ecological factors to play a more important role in the maintenance of northern taxa.