Diet patterns of water green frogs (Pelophylax esculentus complex) in mixed population systems in Serbia

Population systems in which all three taxa of the Pelophylax esculentus complex coexist are rare and in Serbia can only be found along the Danube. Although several studies describe the diet in populations with only one taxon, there is a lack of data from mixed populations. We studied the diet in mixed populations of edible frogs at three sites for three years. We collected gut contents from 221 adult frogs using the stomach flushing method and identified 1,477 prey items. The diet consisted mainly of insects (88%). For all three taxa, the most frequently consumed prey groups were Hymenoptera (28%), Coleoptera (18%), Lepidoptera (17%) and Diptera (11%). Larger prey (in terms of length and volume) was mainly consumed by P. ridibundus, followed by P. esculentus. The smallest prey were mainly consumed by P. lessonae. However, P. ridibundus consumed fewer prey items than P. lessonae. No significant difference was found between the taxa in the staple diet, while there were differences in the less abundant prey categories, especially between P. ridibundus and P. lessonae. The narrowest trophic niche width was observed in P. lessonae, followed by P. esculentus, and the widest in P. ridibundus. Our results suggest that the diet of the three taxa is diverse and consists of a large number of invertebrate groups. However, the diet was locality-specific, with the dominance of different prey groups in different localities depending on habitat characteristics. These results confirm our expectation that the frogs of the Pelophylax esculentus complex follow an opportunistic foraging strategy, as predicted by optimal foraging theory.