Specialization and omnivory in diverse mammalian assemblages

Phyllostomid bats form some of the most speciose mammalian assemblages known, with more than 70 species estimated to co-occur on one site. These species encompass a dietary spectrum that ranges across several trophic levels, and many show morphological specializations for their dietary behaviour (e.g., long tongues in nectar-feeding bats). However, previously reported diets have varied among studies including assignments of species to feeding ensembles. In this study we present data that demonstrate that phyllostomid bats are opportunistic omnivores despite their specializations. We analyzed the diet of 67 phyllostomid bat species from the Neotropics based on both fecal analyses and nitrogen isotope ratios in wing tissue and found that most species complemented their primary diet with nutrients from many different food sources. From these new dietary data, we were unable to distinguish meaningful feeding ensembles of species based on diet. Thus, we argue that interspecific competition is not restricted to species within an ensemble but seems instead to occur across the entire assemblage. Our results suggest that phyllostomid species have specialized successively on distinct diets during their radiation without sacrificing their capability to exploit a variety of food types. The combination of morphological and behavioural specialization on the one hand and opportunistic omnivory on the other might promote the high diversity of phyllostomid bat assemblages.