Trophic Niche Differentiation in Rodents and Marsupials Revealed by Stable Isotopes.

Tropical rainforestssupport the greatest diversity of small mammalsin the world, yet we have little understanding about the mechanisms that promote the coexistence of species. Diet partitioning can favor coexistence by lessening competition, and interspecific differences in body size and habitat use are usually proposed to be associated with trophic divergence. However, the use of classic dietary methods (e.g. stomach contents) is challenging in small mammals, particularly in community-level studies, thus we used stable isotopes ( δ13Cand δ15N) to infer about trophic niche. We investigated i) how trophic nicheis partitioned among rodent and marsupialspecies in three Atlantic forest sites and ii) if interspecific body size and locomotor habit inequalities can constitute mechanisms underlying the isotopic nichepartitioning. We found that rodents occupied a broad isotopic nichespace with species distributed in different trophic levels and relying on diverse basal carbon sources (C3 and C4 plants). Surprisingly, on the other hand, marsupialsshowed a narrow isotopic niche, both in δ13Cand δ15Ndimensions, which is partially overlapped with rodents, contradicting their description as omnivoresand generalists proposed classic dietary studies. Although body mass differences did not explained the divergence in isotopic values among species, groupsof species with different locomotor habit presented clear differences in the position of the isotopic nichespace, indicating that the use of different forest strata can favor trophic nichepartitioning in small mammalscommunities. We suggest that anthropogenic impacts, such as habitat modification (logging, harvesting), can simplify the vertical structure of ecosystems and collapse the diversity of basal resources, which might affect negatively small mammalscommunities in Atlantic forests.