The enemy within: consequences of the invasive bullfrog on native anuran populations

The bullfrog, Lithobates catesbeianus, is one of the most important invasive anurans, affecting especially native anurans due to their similar habits. Here we used a hierarchical co-occurrence model fit in a Bayesian framework to investigate the effects of the bullfrog on two native frog species from southern Brazil, testing the hypothesis that bullfrog presence changes the activity of native species and their relationship with habitat. We found that both occupancy and detection probabilities of native species were similar with bullfrog presence or absence at a site. However, we observed changes in activity and microhabitat use preferences of both native species when the bullfrog was present, suggesting that the presence of the invasive species altered the behavior of the native species. Changes induced by invasive species can result in severe long-term consequences for native species since niche differentiation may not mediate the ability of species to persist together indefinitely.