Island bat diets: does it matter more who you are or where you live?

Abstract

Differences in body size, echolocation call frequency and location may result in diet partitioning among bat species. Comparisons between island populations are one way to evaluate these competing hypotheses. We conducted a species-level diet analysis of three Rhinolophus and one Hipposideros species on the Philippine islands of Cebu, Bohol and Siquijor. We identified 655 prey (MOTUs) in the guano from 77 individual bats. There was a high degree of overlap among species' diets despite differences in body size and call frequency. For example, the diet of the 3g-Hipposideros pygmaeus (mean CF=102kHz) exhibited a diet overlap higher than expected by chance with all three Rhinolophus species, even the 13g-Rhinolophus inops (mean CF=54kHz). We observed more convergence in diet between Rhinolophus species and H.pygmaeus than between Rhinolophus species themselves, which may be explained by the broad diet of H.pygmaeus. There was less dietary overlap between Rhinolophus virgo from two islands than between R.virgo and congeners from Cebu. These data suggest that location causes convergence in diet, but specific species characteristics may drive niche specialization. The complex interplay between location and the perceptual ability of each species leads to a situation where simple explanations, for example body size, do not translate into predictable prey partitioning. In particular, our observations raise interesting questions about the foraging strategy and adaptability of the tiny H.pygmaeus.