Niche partitioning and phylogenetic distance of rotifer species revealed by the four-year temporal dynamics in a small mountain lake

We examined the realized niche space of rotifer species in Lake Hataya Ohnuma, a mountain lake, based on the population and genetic data over four years to test whether the degree of niche overlap among rotifer species was related to their genetic or phylogenetic distances. In this lake, 11 genetically distinct rotifer species occurred abundantly during the study period. Some of the species occurred in the same seasons and overlapped strongly in their temporal niche space, while others did not. Analyses showed that phylogenetic distance among the rotifer species was significantly and positively correlated with temporal niche overlap, suggesting that genetically similar species occupy different temporal niche spaces, probably as a result of avoiding competitive interactions. Although most pairs of species that showed significant partitioning in their realized niche often occurred in the same environmental ranges in terms of seston P and chlorophyll-a concentrations and water stagnation conditions, the range of temperatures in which each of these two species occurred was significantly less overlapping. These results suggest that the current or past competitive interactions play a crucial role in determining the structure of the rotifer community and its temporal dynamics, and that water temperature is the most important niche axis partitioning the realized niche among the rotifer species.