Diet composition of post-metamorphic bullfrogs (Rana catesbeiana) in the Zhoushan Archipelago, Zhejiang Province
舟山群岛变态后牛蛙的食性研究

Bullfrogs (Rana catesbeiana) are listed as one of the 100 worst invasive alien species in the world. They are generalist predators and thus may affect native species through predation. However, in previous diet studies, the food contents of bullfrogs were mostly examined at a single site. From June 30 to August 11 in 2005, we examined the diet composition of post-metamorphic bullfrogs on eight islands (Daishan, Liuheng, Xiushan, Fodu, Taohua, Xiashi, Cezi, and Putuoshan) in the Zhoushan Archipelago, Zhejiang Province, with the stomach flushing method. A total of 391 bullfrogs were measured during the study period, including 113 adults and 278 juveniles. Analyses of stomach contents showed that, for adult bullfrogs, the most important prey items (by diet volume) overall were Decapoda, Coleoptera, Odonata, Mesogastropoda, Raniformes, and Cypriniformes; while for juvenile bullfrogs, they were Decapoda, Coleoptera, Cypriniformes, Odonata, Or- thoptera, Hymenoptera, Lepidoptera larvae, Mesogastropoda, and Raniformes. Moreover, prey size and diet volume increased with the body size of both adult and juvenile bullfrogs. The diet composition of primary preys of bullfrogs was significantly different among different islands. The results indicate that bullfrogs exert different predatory influences on native fauna at different sites, and that bullfrogs are generalist predators with extensive ecological impacts on native fauna.