舟山群岛变态后牛蛙的食性研究

牛蛙(Ranacatesbeiana)是极其危险的外来入侵种,对当地生物类群的捕食是其主要的危害机制,但目前有关其食性的研究均只局限于一个研究地点。为了全面评估牛蛙对当地生物类群的捕食影响,2005年6月30日至8月11日期间,作者采用洗胃法对舟山群岛8个岛屿(岱山、六横、秀山、佛渡、桃花、虾峙、册子和普陀山)变态后牛蛙的食性进行了研究。共采集到变态后的牛蛙391只,包括牛蛙成体113只和亚成体278只。食性分析结果表明:(1)按食物体积计算,成年牛蛙以十足目、鞘翅目、蜻蜓目、中腹足目、蛙形目和鲤形目为主要食物,亚成体牛蛙以十足目、鞘翅目、鲤形目、蜻蜓目、直翅目、膜翅目、鳞翅目幼虫、中腹足目和蛙形目为主要食物;成体和亚成体牛蛙胃中食物的平均大小均随其体长增加而增大;(2)不同岛屿上的牛蛙在主要食物类型构成上存在差异。这表明牛蛙在不同地方对不同生物类群造成的捕食危害是不一样的,充分反映了其生态危害的广泛性。

Diet composition of post-metamorphic bullfrogs (Rana catesbeiana) in the Zhoushan Archipelago, Zhejiang Province

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.