Responses in the diet composition of the common frog (Rana Temporaria) to the stochastic gradation of autumnal moth (Epirrita autumnata) larvae

Abstract

We studied the feeding ecology of the common frog Rana temporaria in a population located at the subarctic taiga-tundra frontier in Finland over two consecutive years (2002, 2003). In the summer of 2003, an unexpected gradation of autumnal moth (Epirrita autumnata) larvae occurred at our study site. This situation allowed us to study the changes in the diet composition of the same common frog population between a presumably average and an extraordinary year with respect to the gradation of one of the prey species. We found clear evidence for the opportunistic feeding behaviour of common frogs in a natural population, as reflected by the mass appearance of Epirrita autumnata larvae in the frogs' stomach content in 2003. Further, our results draw attention to the fact that a one-year study on the feeding ecology of an opportunistic species can result in flawed conclusions.