Varying Thermal Dependence of Life History Traits Predicts Responses to Environmental Change in Aquatic Amphibian Larvae

ABSTRACT Many organisms respond to environmental changes through plastic modifications of their phenotypes. While phenotypic plasticity has been extensively studied in response to single factors in laboratory settings, organisms in nature face the combined effects of diverse biotic and abiotic stressors. These multistressor effects complicate predictions about the impact of environmental changes on population dynamics. One approach to improving predictive accuracy is to identify common mechanistic links to variations in life‐history traits. In this study, we examined how biotic and abiotic stressors influence life‐history variation, using predictions based on the differing thermal sensitivities of differentiation and growth rates in aquatic amphibian larvae and their subsequent impact on the behaviour of terrestrial juveniles. Using a mesocosm experiment, we exposed larvae of two sympatric newt species, Ichthyosaura alpestris and Lissotriton vulgaris , to combinations of a biotic factor (the presence of heterospecifics) and an abiotic factor (simulated drying). Our results revealed that simulated drying increased the availability of high water temperatures, thereby shortening the larval period as predicted by the high thermal sensitivity of differentiation rates. The presence of heterospecifics, not drying regime, increased the size at emergence in the larger species, I. alpestris , consistent with the relatively low thermal sensitivity of growth rates. The impact of drying carried over to the terrestrial juveniles, affecting their covered distance in both taxa, while the presence of heterospecifics influenced maximum voluntary speed during exploratory behaviour in I. alpestris juveniles. This suggests that the additive effects of biotic and abiotic factors on subsets of life‐history and behavioural traits combine at the individual level, depending on species identity. Future research should focus on the interplay between ecologically‐realistic thermal conditions and species interactions within pond larval assemblages to understand the impact of environmental changes on amphibian population dynamics.