American bullfrog (Lithobates catesbeianus) distribution, impact on native amphibians and management priorities in San Carlos, Uruguay

Abstract

Biological invasions are a major cause of biodiversity and ecosystem services loss. However, information on distribution and impacts is limited for many alien species, restricting the development of local management measures. The aim of this study is: to identify the current situation of the American bullfrog (Lithobates catesbeianus) invasion focus in San Carlos (Maldonado, Uruguay); to evaluate its impacts on native anurans; and to provide management tools. Between 2017 and 2019, 75 permanent ponds were sampled, finding an expanding bullfrog population (occupying 32 ponds, in 16.5 km2). Results show that native anuran richness was lower in the invaded ponds. Observed impacts were greater for the aquatic frogPseudis minuta, probably due to greater encounter rates with the invader. The abundance of tadpoles was also lower in the invaded ponds. The local pond network was explored using graph theory, evaluating its topological role and centrality. In this network, a list of priority ponds was generated to prevent local bullfrog expansion. Given the relatively small size of this population, eradication seems feasible. Focusing on the key nodes could prevent further expansion, by using spatial prioritization to organize the recommended management of the pond network.