Endemic amphibians cornered in headwaters by trout invasion in a mountain range in Argentina

The Sierras Pampeanas Centrales, one of the most important extra-Andean mountain systems of Argentina, harbour endemic and threatened amphibian species. In the past century, two alien predatory fish species (brook trout and rainbow trout) were introduced into rivers and streams of the area where amphibian species breed. We hypothesized that the presence of trout would adversely affect the distribution of native amphibians in streams of the area. To test this hypothesis, the habitat requirements of trout and native amphibians were compared, and the effect of trout presence on amphibian occurrence was evaluated. Transects (n= 126) were surveyed along rivers and streams in high-altitude grasslands of the area, and the occurrences of trout and amphibians and habitat variables were recorded. The habitat requirements of each species were compared using multivariate methods. Generalized linear mixed models were used to evaluate whether the occurrence of amphibians depends on trout, habitat variables or both. The distribution of each species between streams orders was assessed. The results showed that the presence of trout was the main factor conditioning the distribution of two endemic amphibian species (Boana cordobaeandOdontophrynus achalensis) in basins of the study area. This threat needs to be incorporated urgently into action plans to guide conservation efforts towards the management of trout populations.