Diet of the American Bullfrog Lithobates catesbeianus Naturalized on Okinawajima, Ryukyu Archipelago, Japan

Abstract

The diet of the nonnative American Bullfrog Lithobates catesbeianus occurring in Ogimi Village of Okinawajima, Ryukyu Archipelago, is investigated. Seventy two of 89 frogs (nine adults, five subadults, and 58 juveniles) captured had food items in its stomach. We identified a total of 64 taxa from 253 food items. Our analyses show that (1) the diet consists mainly of terrestrial prey, (2) mollusks and vertebrates are the essential prey groups for adults and subadults, and (3) odonates, mollusks, and arachnids are the main prey for juveniles. Such dietary habits are quite different from those of several conspecific nonnative populations in mainland Japan and other regions. Part of this is most likely related to the absence of the frog’s favorite prey, nonnative American crayfish Procambarus clarkii, in the study area. We also confirm the predation of a poisonous newt Cynops ensicauda popei (Salamandridae) and several aquatic insects by this frog and present some implications for these results.