Bullfrog Lithobates catesbeianus (Amphibia: Ranidae) tadpole diet: description and analysis for three invasive populations in Uruguay

Abstract

The North American bullfrog, Lithobates catesbeianus is a dangerous invasive species that has been introduced worldwide for commercial and ornamental purposes. Although studies of the bullfrog’s effects on invaded communities have been carried out, they have focused mostly on post-metamorphic stages. However, considering the experimental evidence and its ecological attributes, the L. catesbeianus tadpole could also have significant impact on invaded communities. The aim of this study was to perform a detailed qualitative and quantitative exploration of the L. catesbeianus larval diet. Gut content was studied and compared for three invaded locations in Uruguay (Departments of Canelones, Soriano and Cerro Largo). Although microscopic algae (Spirogyra spp., Euglena spp., Closterium spp., Volvox spp. and Scenedesmus spp.) were the most frequent prey, the diet was also made up of small invertebrates (especially rotifers) and eggs. Statistically significant differences in diet richness and prey identity were found among the three study sites, probably due to local conditions. One common feature among the three locations was the ingestion of prey with high protein levels, filamentous algae and animal prey. The high frequency of high-protein prey could explain the substantial growth rate of these larvae. Native tadpoles appear to have a much poorer diet than bullfrogs. We can thus assume that the L. catesbeianus larvae will be a major competitor and a potential predator for native communities. We propose that L. catesbeianus tadpoles may have significant effects on invaded communities, and should be considered in future research and managements plans.