Changes in the Food Niche during Postmetamorphic Ontogeny of the Frog Pseudacris triseriata

The food niche and foraging strategies of the chorus frog Pseudacris triseriata were investigated by examining the prey/predator size relationship as it relates to prey availability, and they were found to be dynamic from metamorphosis to adulthood. Snout to vent length of the frogs proved to be a good predictor of the mean size of prey taken. Relative availability of the different sized prey items in the environment was estimated from samples of potential prey obtained by suction sampling. This availability information was used in addition to the data on stomach contents to describe the foraging strategies of the different size classes of frogs. It was found that small frogs (- 17.0 mm) ate prey as they were encountered in the environment, and that large frogs (>23.1 mm) selected larger prey which were rarer in the community. Intermediate sized frogs (between 17.1 and 23.0 mm) were characterized by an intermediate pattern. Intermediate frogs consumed large numbers of prey per unit time, and the possibility that this facilitated rapid growth is discussed. The mean maximum prey size increased with increasing frog size, but leveled off for the largest size classes, whereas mean minimum prey size continued to increase with increasing frog size. The large frogs were selective in their diet as they apparently chose the more optimal (in terms of benefits and costs of pursuit, capture and consumption) sized prey while they discriminated against the smaller prey. This ontogenetic pattern of foraging strategies is somewhat unique among predators for which there exists information in the literature, and it is suggested that the small body size (<30 mm) of P. triseriata relative to the size of their prey (terrestrial arthropods) allows this pattern.