Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina

Abstract

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high and probably has an impact on their prey. Freshwater crabs are the main items in the diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.

Keywords:

• American bullfrog
• Amphibian
• Argentina
• invasive population
• Lithobates

Acknowledgements

We thank E. Espejo for housing and logistical support. Special thanks to J. López for a critical review and suggestions that improved this work, to R. Rhymer and F. Hertel for English correction and to the anonymous reviewers for comments that helped improve this manuscript. We thank the Provincial Fauna Office of San Juan for permission (SA and DS 1300-4736-2011) to conduct our research.

Additional information

Funding

This research was partially supported by a post-graduate fellowship from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) awarded to E. Sanabria.