Is trophic differentiation of green frogs in Pelophylax ridibundus - P. esculentus - P. lessonae population systems in South Banat, Serbia related to habitat suitability?

Abstract

Population systems comprising all three frog taxa from the complex are rare and in Serbia are recorded only along the Danube river. This study suggests green frogs’ trophic differentiation from three localities adjacent to nature preserves with different levels of anthropogenic pressures in South Banat is related to their habitat suitability (HS). Diet and habitat suitability differences were recorded across all localities which have habitat characteristics conforming to typical green frogs’ habitats. Samples from 221 adult frogs were obtained and a total of 1477 prey items were identified. Insects dominated the diet for all three taxa with 88% of relative abundance (Hymenoptera 28%; Coleoptera 18%; and Lepidoptera 17%), with 12% being other small invertebrates – spiders, crustaceans and molluscs. Rank abundance curves suggest that frogs acquired prey opportunistically, in line with previous studies and optimal foraging theory predictions. Low trophic differentiation was present with localityspecific prey dominating the ordination. Observed patterns were better explained by HS values than by taxon-specific characteristics. The locality Jaruga, with river-like features, surrounded by orchards and Nera river floodplain forests, had the highest HS value, with moth larvae being the dominant prey. A slightly lower HS was measured on the Stevanove ravnice locality, a mosaic landscape along the Danube river - open steppe-like pastures and hydrophytic vegetation under accelerated eutrophication where hymenopteran and dipteran prey dominated. The locality Danube-Tisa-Danube canal, a completely anthropogenically altered locality with a clover-planted causeway and severe tourist pressure, had the lowest HS values and dominance of beetles. Managers could use such results when devising new mechanisms of adaptive habitat management which optimize the presence and abundance of important species. Prey dependence on locality structure with different anthropogenic and zoogenic pressure heightens the importance of prey availability which frogs can acquire according to their habitat preferences and bionomic constraints.