Population density and food analysis of Bombina variegata and Rana graeca

BY : RIKA BISA, SPYROS SFENTHOURAKIS, STELLA FRAGUEDAKIS-TSOLIS and BASIL CHONDROPOULOS Section of Animal Biology, Department of Biology, University of Patras, Panepistimioupoli 265 00 Rio, Greece

Abundance and diet of Bombina variegata and Rana graeca were investigated from August 2004 to August 2005 in two permanent mountain water bodies (Zesto River and Prioni Nazeti Stream) situated in the National Park of Northern Pindos (Greece). At Zesto, we recorded high population densities for both anuran species, while at Nazeti population density was high only for R. graeca. In the diet of B. variegata and of R. graeca, a large variety of prey taxa was identified in the stomach contents, suggesting that they are opportunistic predators. However, at both sites, the study species principally consumed five prey groups, i.e. ants, spiders, flies, terrestrial beetles and aquatic insect larvae. A comparison of prey size consumed by adults revealed that B. variegata feeds on smaller prey than R. graeca. Furthermore, intraspecific differences based on prey size were obtained for adults and sub-adults of R. graeca. In this study we found that prey size is a possible factor of niche partitioning for anuran species.