Abstract
It has been suggested that both niche-based and neutral mechanisms are important for biological communities to evolve and persist. For communities in extreme and isolated environments such as caves, theoretical and empirical considerations (low species turnover, high stress, strong convergence owing to strong directional selection) predict neutral mechanisms and functional equivalence of species. We tested this prediction using subterranean amphipod communities from caves and interstitial groundwater. Contrary to expectations, functional morphological diversity within communities in both habitats turned out to be significantly higher than the null model of randomly assembled communities. This suggests that even the most extreme, energy-poor environments still maintain the potential for diversification via differentiation of niches.