Gut Check: Predatory Ecology of the Invasive Wrinkled Frog (Glandirana rugosa) in Hawai‘i

Invertebrates constitute the most diverse Pacific island animal lineages and have correspondingly suffered the most devastating extinction rates. Losses of native invertebrate lineages have been driven largely by ecosystem changes brought about by loss of habitat and direct predation by introduced species. Although Hawai‘i notably lacks native terrestrial reptiles and amphibians, both intentional and unintentional anthropogenic releases of herpetofauna have resulted in establishment of more than two dozen species of frogs, toads, turtles, lizards, and a snake. Despite well-known presence of nonnative predatory species in Hawai‘i, ecological impacts remain unstudied for a majority of these species. In this study, we evaluated diet of the Japanese wrinkled frog, Glandirana rugosa, an intentional biocontrol release in the Hawaiian Islands in the late nineteenth century. We collected live frogs on O‘ahu and used museum collections from both O‘ahu and Maui to determine exploited diet composition. These data were then compared with a published dietary analysis from the native range in Japan. We compiled and summarized field and museum distribution data from O‘ahu, Maui, and Kaua‘i to document current range of this species. Gut content analyses suggest that diet composition in the Hawaiian Islands is significantly different from that in its native Japan. In the native range, dominant taxonomic groups by volume were Coleoptera (beetles), Lepidoptera (moths, butterflies), and Formicidae (ants). Invasive frogs in Hawai‘i exploited mostly Dermaptera (earwigs), Amphipoda (landhoppers), and Hemiptera (true bugs). In Hawai‘i this species also exploited endemic insects (~4% total volume, 7 genera) and snails (14 snails in three endemic genera). Our results suggest the need for more in-depth assessment of ecological impacts of G. rugosa and other established herpetofauna in Hawai‘i to improve our ability to prevent and manage ecological damage and ultimately restore diverse island ecosystems.