Amphibian richness patterns in Atlantic Forest areas\ud invaded by American bullfrogs

The relationship between invasion success and native biodiversity is central to biological invasion research. New theoretical and analytical approaches have revealed that spatial scale, land-use factors and community assemblages are important predictors of the relationship between community diversity and invasibility and the negative effects of invasive species on community diversity. In this study we assess if the abundance of Lithobates catesbeianus, the American bullfrog, negatively affects the richness of native amphibian species in Atlantic Forest waterbodies in Brazil. Although this species has been invading Atlantic Forest areas since the 1930s, studies that estimate the invasion effects upon native species diversity are lacking. We developed a model to understand the impact of environmental, spatial and species composition gradients on the relationships between bullfrogs and native species richness. We found a weak positive relationship between bullfrog abundance and species richness in invaded areas. The path model revealed that this is an indirect relationship mediated by community composition gradients. Our results indicate that bullfrogs are more abundant in certain amphibian communities, which can be species-rich. Local factors describing habitat heterogeneity were the main predictors of amphibian species richness and composition and bullfrog abundance. Our results reinforce the important role of habitats in determining both native species diversity and potential invasibility.This study was supported by IGRE Associação Sócio Ambientalista and received grants from Fundação o Boticário de Proteção a Natureza (0835_20092) and the Rufford Small Grants Foundation. The Conselho Nacional de Desenvolvimento Científico provided a student fellowship to CB and a grant (Proc. 476789/2009-5) and fellowship (Procs. 305473/2008-5, 307001/2011-3) to TG. The Fundação de Amparo à Pesquisa do Estado de São Paulo provided a grant to TG (Proc. 2012/10000-5). ICMBio granted a collection permit for this study (Proc. 23009-1). This manuscript benefited from comments by Sandra Hartz, Célio Haddad, Márcio Borges-Martins, Adriano Sanches Melo, and three anonymous reviewers. We are thankful to all rural owners who granted access to study sites and the Parque Nacional da Serra do Itajaí for logistical support. We also thank S. Declerck for sharing the nested MEM function, V.F. Caorsi for her help with laboratory procedures, and D. Borges-Provette for help with the literature for tadpole identification