Understanding the spatial variations in the diets of two Sturnira bats (Chiroptera: Phyllostomidae) in Argentina

Frugivorous phyllostomid bats are a diverse group and one of the major partners of fleshy-fruited plants in seed dispersal mutualisms. The first step towards comprehension of mechanisms shaping the structure of highly diverse phyllostomids assemblages is to gather information about diet composition and to study the variations in the use of fruits across space. Herein we tested whether frugivorous phyllostomids changes the use of its fruits where fruit offer may change with the altitude and latitude. Particularity, using 1,525 dietary records from 20 sites, we evaluated the spatial use of Solanum, Piper and other fruits by two syntopic and similar species of Sturnira bats from Northwestern Argentina. The relationship between dietary compositions and spatial variables was studied through Dirichlet statistical regressions. Additionally, we constructed predictive models of diets in function of latitude and altitude by estimating the parameters of Dirichlet distributions, and compared then their behavior. Both bats showed spatial changes in the diets. However, in taking into account the overall pattern of predicted diets throughout the space, inter-specific differences were detected. While both species increased the use of Solanum with altitude, only Sturnira erythromos showed a meaningful altitudinal and latitudinal response concerning to the use of Piper and other fruits or Solanum, respectively. Our predictive models for diets enable us to split the space into two sectors, one characterized by a high dietary overlap and another with the salient feature of dissimilar preference towards the subsidiary resources. These findings call for a model of spatial segregation, acting at a regional scale, as a hypothetical mechanism allowing the coexistence of both species.