Trophic positions and niche segregation of two anuran species in the ecosystem of a forest lake

Abstract

Different species of amphibians often breed in the same water bodies and their diets overlap. Theoretically, this might lead to a competitive elimination of either one but there are multispecies temporal larval communities persisting over the years. We hypothesized that larvae of two common European anuran species segregate their trophic niches despite their omnivorous habits and possible similarity of trophic levels. We assessed interspecific differences in food assimilation at larval and postmetamorphic stages of two anurans in an ecosystem of forest lake and an adjacent terrestrial ecosystem using a stable isotope approach. Trophic level of tadpoles of both species corresponded to those of some benthic invertebrate predators. Trophic positions of postmetamorphic juveniles corresponded to those of terrestrial invertebrate predators. The unpredictable decrease of δ15N values in anuran tissues during the transition from aquatic to terrestrial habitats corresponded to the differences between aquatic and terrestrial isotopic baselines whereas dynamics of normalized δ15N confirmed an increase in their trophic level. Finally, we detected a strong segregation of trophic niches of the two species at both larval and postmetamorphic stages. The described niche separation provides an important prerequisite for decreasing possible intraspecific competition and promoting long-term co-existence of these syntopic anurans.