Habitat selection as a major resource partitioning mechanism between the two sympatric sibling bat species Myotis myotis and Myotis blythii

Abstract

1. Ecomorphological studies have described local bat communities as densely‐packed species assemblages arising from non‐deterministic processes. Together with the observation that insectivorous bats readily exploit patchy, often unlimited trophic resources, this has even led to the claim that partitioning of niche space may be absent. However, the paucity of data on resource exploitation per se among bat guilds rarely allows these assertions to be verified. In particular, the mechanisms allowing the co‐existence of similar species have proved difficult to determine. 2. As a subset of an insectivorous guild, the vespertilionid bats Myotis myotis and M. blythii offer an opportunity to examine this question. Genetically closely‐related, they are morphologically almost identical. Yet, as established by faecal analysis, they exploit distinct trophic niches, preying upon ground‐ and grass‐dwelling prey taxa, respectively. The distinct habitat requirements of their basic prey suggest that ecological segregation may stem primarily from a differential allocation of foraging space. 3. The present study tests the hypothesis that sympatric M. myotis and M. blythii segregate spatially to an extent which prevents competitive interference. I performed radio‐tracking on Swiss sympatric populations. Using multivariate analyses and randomized contingency table procedures, I looked for (i) habitat overlap and overall inter‐specific differences in habitat choice, and (ii) the habitat preferences exhibited by individuals when foraging within their own feeding areas. 4. Primary foraging habitats were largely species‐specific. Not only were they spatially segregated, but they also differed structurally. All habitats selected by M. myotis offered a high accessibility to ground‐dwelling prey (freshly‐cut meadows, mown grass in intensively cultivated orchards, forests without undergrowth), whereas grassland predominated in all habitats of M. blythii (steppe, unmown meadows, pastures). This corroborates the predictions drawn from dietary niches. 5. This study shows that refined mechanisms of resource partitioning, not predictable by the study of morphological characters or echolocation alone, may still account for the organization of parts of insectivorous bat guilds. It also supports the view that habitat selection may prove to be a major mode of resource allocation amongst similar insectivorous bats, particularly for species exploiting limited food supplies.