Zoophagy in the Larvae of Ibero-Maghrebian Spade-foot Toads

摘要

The ecological role of anuran larvae is usually defined as a primary consumer. Recent studies have shown, however, that some grazing-rasping species consume animal matter on a regular basis. We investigated zoophagy in two species of Spade-foot Toads (Pelobates cultripes and Pelobates varaldii). The larvae of both species showed no specific morphological adaptations for macrophagy but are very large and inhabit invertebrate-rich ponds under prolonged summer drought conditions. We hypothesized that both species would consume animals having high nutritional value, and that there would be no difference between the two species in terms of the animals consumed, because tadpoles are broad dietary generalists. We also hypothesized that the consumption of animals would vary during development based on the size limitations of the oral cavity. Examination of the intestinal contents of P. varaldii and P. cultripes indicated that they had consumed a wide range of invertebrates, as predicted. Differences in the composition of animals between the two species might be attributable to variability in the composition of invertebrate assemblages among ponds. We provide the first evidence of consumption by taxa within Pelobates of aquatic species of Insecta (Coleoptera, Diptera, Ephemeroptera, and Odonata), Collembola (Sminthuridae and Poduridae), large Branchiopoda (Anostraca, Notostraca, and Spinicaudata), and Gastropoda (Physidae and Planorbidae). We also found a correlation between the diversity of animals consumed and the ontogenetic variation in size in both Pelobates species. These findings support the hypothesis that grazing-rasping tadpoles have an omnivorous role in aquatic trophic webs.