Out in the Cold: Trophic Resource Use by the Common Frog (Rana temporaria) Populations Inhabiting Extreme Habitats

We studied trophic resource use and availability in three populations of the common frog (Rana temporaria): one from the subarctic (Kilpisjärvi, Finland), and two (alpine and low-altitude valley populations) from the Retezat Mountains (Southern Carpathians, Romania). We used stomach flushing to sample consumed prey, and estimated prey availability using pitfall traps and netting. In addition, we analyzed the geographical pattern of feeding based on published records covering the entire range of the species. Feeding intensity varied, both spatially and according to frog size. Adults consumed prey of higher richness and more prey items than juveniles. There was latitudinal variation in prey consumption, with populations from extreme habitats (alpine and arctic) having the highest prey richness. This high feeding plasticity partly explains why Rana temporaria is widespread and reaches high altitudes and latitudes in Europe.