Trophic Ecology of an Assemblage of Leaf-Litter Amphibians and Reptiles from Costa Rica

      Niche-assembly models for community ecology indicate that partitioning of a resource base among syntopic species can account for coexistence.  Diet has been identified as one of the most important resource bases divided among syntopic species.  To understand interspecific and intraspecific variation in trophic niche relations of a diverse assemblage of terrestrial frog and lizards in Costa Rica, I examined gut samples from 940 individuals of 17 species of frogs and lizards in this assemblage.  All age classes were sampled, and samples came from every month of the year, eliminating age-class or seasonal biases present in other studies.  All species showed strong ontogenetic shifts in preferred prey size except for Dendrobates pumilio, which is characterized by exceptionally low variation in body size and strong diet specialization.  Strength of the ontogenetic shift in preferred prey size was significantly correlated with range in standard length, indicating that ontogenetic shifts in prey types may be common in generalist species.  Several generalist species showed ontogenetic shifts in prey type, generally species with large variation in body size.  No clear pattern in proportion of empty stomachs or prey types utilized emerged with respect to seasonality, suggesting that wet-dry seasonality has no strong effect on feeding patterns at this wet forest site.  Apart from a well-developed ant-specialist trophic guild comprised exclusively of frogs, similar patterns exist in feeding between lizards and frogs within this assemblage. Comparisons to Monte Carlo null models indicates that there is significant structure in use of dietary resources within this assemblage; species in this assemblage are not using prey resources independently of other species in the assemblage.  Values for symmetric niche overlap were higher between lizards than between frogs, but niche overlap between frogs and lizards was similar to that between frogs.  This study provides support for considerable intraspecific variation within the trophic niche with respect to ontogeny and seasonality, and suggests that diverse lineages (anurans and lizards) show remarkable convergence with respect to patterns of resource use.