Trophic structure of frog assemblages in coastal habitats in southern Brazil

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We evaluated the hypothesis that contrasting environmental conditions in a coastal wetland and nearby sand dunes results in frog assemblages with divergent trophic structures. We predicted that the more productive habitat (wetland) would have higher diversity of primary producers and frogs with larger trophic niches and greater interspecific dietary overlap when compared to the less‐productive dune habitat. Stomach content analysis (SCA) and stable isotope analysis (SIA) were used to compare frog trophic ecology in the two habitats. We compared trophic niche size (Shannon’s index) and overlap (Pianka’s index; isotopic ellipse area, SEA c ). Bayesian isotope mixing models were used to estimate relative contributions of basal production sources to frog biomass in each habitat. Estimates indicated that wetland frogs assimilated material from diverse basal sources (suspended particulate organic matter (POM), C 3 plants, periphyton), whereas frogs inhabiting dunes assimilated material mostly originating from C 3 plants. Both SCA and SIA revealed less trophic overlap among frogs from the sand dunes compared with those from the wetland. Dietary overlap was greater than expected at random for frogs in both the wetland and dunes. Mean overlap among isotopic ellipses (SEAc) of all frogs at each habitat was higher in the wetland (0.14‰) than in the dunes (0.04‰). These findings corroborate our prediction that trophic structure in the wetland is more complex than in the sand dunes. Also, as expected, we observed greater isotopic niche segregation among frogs in the sand dunes, a potential mechanism that reduces competition for limited food resources.