Impacts of behaviour and acclimation of metabolic rate on energetics in sheltered ectotherms: a climate change perspective

Abstract

Many ectothermic organisms counter harsh abiotic conditions by seeking refuge in underground retreats. Variations in soil hydrothermal properties within these retreats may impact their energy budget, survival and population dynamics. This makes retreat site choice a critical yet understudied component of their strategies for coping with climate change. We used a mechanistic modelling approach to explore the implications of behavioural adjustments and seasonal acclimation of metabolic rate on retreat depth and the energy budget of ectotherms, considering both current and future climate conditions. We used a temperate amphibian, the alpine newt (Ichthyosaura alpestris), as a model species. Our simulations predict an interactive influence of different thermo- and hydroregulatory strategies on the vertical positioning of individuals in underground refuges. The adoption of a particular strategy largely determines the impact of climate change on retreat site choice. Additionally, we found that, given the behavioural thermoregulation/hydroregulation and metabolic acclimation patterns considered, behaviour within the retreat has a greater impact on ectotherm energetics than acclimation of metabolic rate under different climate change scenarios. We conclude that further empirical research aimed at determining ectotherm behavioural strategies during both surface activity and inactivity is needed to understand their population dynamics and species viability under climate change.

Keywords: energy budget; hydroregulation; mechanistic niche modelling; retreat site choice; thermoregulation.

Figure 1.

Simulated retreat depths (cm below ground) of a model ectotherm (terrestrial newt) using various thermo- and hydroregulatory strategies (a–d) in winter and (e–h) in summer under current climate conditions (a,b,e,f) and under different climate change scenarios (c,d,g,h). The width of each violin indicates relative time spent at a given depth. Data plotted with transparency show the uncertainty associated with different climate change scenarios (see Material and methods for details on the scenarios considered).

Figure 2.

Simulated cumulative mandatory energy use change of various thermo- and hydroregulatory strategies, with or without acclimation of standard metabolic rates, with respect to the same strategy under the current climate in a model ectotherm (terrestrial newt) hidden in a burrow. Individuals were simulated adopting strategies involving vertical movements in the substrate up to 2 m (a–d) and up to 50 cm (e–h) during winter (a,b,e,f) and summer (c,d,g,h). Note that the depicted cumulative energy use change represents the total change during the whole simulated period (i.e. all summer or winter hours in the simulation).