Joint effects of rising temperature and the presence of introduced predatory fish on montane amphibian populations

Amphibian populations in montane habitats are often subjected to high thermal variability, which may exacerbate anthropogenic impacts such as the introduction of exotic species. Here, we present data from two experiments exploring the joint effects of rising temperatures and the presence of waterborne cues from an exotic predatory fish on the short- and long-term antipredatory responses (i.e. activity and time to metamorphosis respectively) of Rana iberica and Salamandra salamandra larvae from two montane amphibian populations. We found some evidence of a cumulative effect of an increase in temperature and the presence of predators. Although predator recognition was not precluded at rising temperatures, we observed an increase in larval activity in warmer water, which might negatively affect survival by favoring prey detectability by predators. We also observed a strong quadratic effect of temperature and a joint effect of temperature and predators on larval development: at intermediate temperatures, larvae exposed to exotic trout cues had greatly accelerated metamorphosis. These results suggest that warmer conditions might be particularly harmful for larvae in montane wetlands enduring the presence of exotic predators.