Diet, Density, Biomass, and Prey Consumption through Ontogeny of a Dominant Frog Species at Different Distances from Streams in a Tropical Rainforest

Some amphibian species are highly abundant in riparian areas, with high numbers of both froglets and adults. These two age classes commonly have different diets. Studying how dietary differences are associated with ontogeny and the spatial distribution of frogs with respect to water bodies contributes to understanding the role of amphibians in trophic webs and in the biological dynamic of riparian ecosystems. We analyzed the diet, density, and mass of Craugastor berkenbuschii, a leaf-litter frog abundant in riparian areas in tropical forest in southern Mexico. We also estimated the number and biomass of prey consumed per area in relation to distance to streams (near: 0–15 m, far: 45–60 m) and body size. We found no differences in any diet variable between the two distances to streams, but diet composition changed with ontogeny. As snout–vent length increased, the number of prey consumed decreased and stomach content mass and mean prey length increased. Frog density and mass were higher near the streams than farther from the streams. The proportion of large and medium-sized frogs did not vary by distance to the streams, but the proportion of small frogs was marginally higher near the streams. Close to the streams, small frogs consumed a higher estimated invertebrate number per area than did medium-sized frogs, and these in turn more than large frogs. However, farther from the streams, large and medium-sized frogs preyed on a higher number of invertebrates per area than small frogs. Invertebrate biomass consumed did not differ among size classes at either of the distances, but both invertebrate number and biomass consumed by the species were higher near the streams than farther from them. The finding that prey number consumed decreased as frog size increased, together with the strong affinity of the species—particularly of small frogs—to streams, had an effect on estimates of invertebrate consumption. These results implied a higher consumption of invertebrates near than farther from the streams, and a greater impact of small than large frogs on invertebrate numbers in riparian environments.