Diet of the Cascades frog (Rana cascadae) as it relates to prey availability in the Klamath Mountains of Northwest California.

Frogs in the family Ranidae are considered generalist predators that consume prey as it is encountered in the environment. However, few studies have attempted to quantify the types and relative amounts of prey available to these frogs so a thorough understanding of their foraging ecology as it relates to prey availability is lacking. This study examined the diet of R. cascadae as it relates to prey availability in a Klamath Mountain basin in northern California during their active season of 2007. Based on the analysis of 275 stomach samples, Rana cascadae consumed 3052 prey items from 110 invertebrate taxa confirming that this species is a generalist predator. However, an Index of Relative Importance indicated that five prey categories were most important in the diet: Acrididae, Aranae, Formicidae, insect larvae, and Tipulidae. Differences in diet were detected between sexes, life stages, and seasons. Adult females consumed more Acrididae in the summer than males or Juveniles. Adult male and juvenile frogs showed selection for insect larvae and Tipulid flies during the summer. In the spring adult females and juveniles also selected Tipulid flies and adult males selected Elaterid beetles. All life-stages and both sexes appeared to avoid very small prey Shifts in prey use with changes in ontogeny were documented, with frogs consuming more large prey and less small prey as they grew.