Isotopic and dietary niches as indicators for resource partitioning in the gleaner bats Myotis bechsteinii, M. nattereri, and Plecotus auritus

The n-dimensional ecological niche summarizes all living requirements of a species. According to the competition and niche theory, co-occurring species have to differ in at least one dimension to live in stable coexistence. Measuring the overall ecological niche within natural ecosystems is probably impossible but methods that describe several dimensions at once like the isotopic niche are good approximations. However, the impact of each factor contributing to the isotopic niche might be difficult to estimate. The dietary niche, as one part of the isotopic niche, can be examined with high resolution using molecular techniques. In this study we aimed to improve our understanding of species coexistence. We outlined the importance of the isotopic and dietary niches in the context of resource partitioning using the bat species Myotis bechsteinii, Myotis nattereri, and Plecotus auritus of the gleaner guild as examples. The dietary and isotopic niches were estimated with stable isotope analysis and molecular fecal analysis. We tested (i) how distinct the occupied dietary niches of members of the same guild are and (ii) how similar the dietary and isotopic niches are to each other. While the inter-specific overlap was high for the dietary niche, no overlap could be observed for the isotopic niche. In general, the isotopic niche can describe a more complete picture of the ecological niche, while the dietary niche provides highly detailed information. The combination of both niches might advance our understanding of stable species coexistences.