Neotropical regions host an astonishing variety of Amphibian species, often sharing very narrow ecological niches. Trophic specialization, as well as spatial and temporal differentiation in resource use, allow sympatric species to minimize competition. However, closely related species, constrained by similar physiology and behavior, often use resources in a similar way, reducing the scope for coexistence. 

A recently accepted paper, that will be published in the next issue of Acta Herpetologica, studied the diet and the trophic niche overlap of four syntopic Amphibian species in the Reserva Biológica Lami José Lutzenberger, in South Brasil. The study focus on 109 Physalaemus frogs (8 P. biligonigerus, 9 P. cuvieri, 74 P. gracilis and 18 P. henseli) collected as by-catch in entomological pitfall traps filled with 70° ethanol, from November 2014 to January 2016. Each frog was dissected and its gastrointestinal content was analyzed under stereomicroscope to reconstruct the trophic niche of each species. 

The analysis of the percentage of different prey types in the diet of the studied species showed food specialization for P. biligonigerus and P. cuvieri; in addition, P. gracilis was found to present considerable trophic selectivity. P. henseli, on the other hand, showed a wider trophic niche, suggesting a more generalist diet. The four Physalaemus species considered in the study showed high degrees of trophic niche overlap, ranging from 71% between P. biligonigerus and  P. henseli, to 96% between P. biligonigerus and P. cuvieri.

Ants and isopoda were found to represent the most important elements in the diet of the four frog species: both groups of prey are social insects with very large nests. Moreover, ants are often unpalatable for many predators. By concentrating their trophic preference on such very abundant resources, Physalaemus species are therefore able to minimize competition, in spite of their phylogenetic proximity and of their similar physiological adaptations.

The full study is available here 

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