Stochastic variation in temperature and food availability impacts growth, but not metabolic rate and exploration in a juvenile amphibian

Abstract

A substantial proportion of environmental variation is stochastic. While environmental stochasticity plays a key role in the evolution of phenotypic strategies, its short-term effects within generations remain poorly understood. These short-term organismal responses are especially relevant in the context of ongoing climate change, characterized by increasing unpredictability of weather conditions that are manifested directly through stochastic temperature fluctuations and can indirectly cause unpredictable food supply. We investigated how stochastic fluctuations in temperature and food supply affect the growth rate, resting metabolic rate (RMR) and exploratory behaviour in juvenile Alpine newts (Ichthyosaura alpestris). Additionally, we quantified among-individual variation in acute thermal reaction norms (10–20°C) for RMR and exploration to assess their potential role in population-level responses to environmental stochasticity. Exposure to a stochastic food supply reduced growth rate, measured as increases in both body mass and total length. Stochastic temperature fluctuations decreased body mass growth but accelerated growth in total length. Both types of environmental stochasticity had negligible effects on population-mean thermal reaction norms for RMR and exploration. However, the intercepts (both traits) and slopes (exploration only) of these norms varied substantially among individuals. Stochastic food supply and temperature impacted growth depending on measured trait. The observed consistent among-individual variation in thermal reaction norms for RMR and exploration suggests a population-level capacity to cope with environmental unpredictability. Our results show that stochastic environmental variation influences ectotherm phenotypes even over short timescales. A mechanistic understanding of climate change impacts on ectotherm life histories, population dynamics and species interactions will require increased attention to this underexplored component of environmental variation. Read the free Plain Language Summary for this article on the Journal blog.