COS 126-5 - A trait-based approach to thermal niches: linking movement and metabolism to predict thermal tolerances of terrestrial invertebrates

Background/Question/Methods

The survival of animals under global warming strongly depends on their individual thermal niches. Previous studies have used physiological traits like respiration and aerobic performance or the isotherms that limit the geographic distribution of species to derive thermal niches. However, it is impossible to empirically measure these traits for the plethora of ectothermic species worldwide, which calls for a mechanistic approach to thermal niches grounded in fundamental trait-based processes that is more generalizable across species. The individual thermal niche results from the balance between energy loss and gain. Active movement is an important component of this energetic balance as it affects not only energy gain via food intake but also energy loss via activity metabolism.

Results/Conclusions

Here, we develop a novel trait-based approach for how thermal niches arise from temperature-dependent movement. Therefore, we used image-based tracking to quantify the unimodal responses of the movement speed of Carabid beetles to temperature. We used these empirical data to parameterize a mathematical model based on metabolic and predator-prey theory for net energy gain to derive a general mechanistic concept of thermal niches. Our modeling results show that energy loss and energy gain both initially increase with temperature with feeding rates exceeding energy loss via metabolism. Feeding rates, however, decrease again at higher temperatures, resulting in less energy gain than loss and potential starvation at a specific thermal limit. By simultaneously accounting for the thermal response of basal and field metabolism, the model therefore provides a mechanistic derivation of the commonly observed left-skewed thermal performance curves of individual and population growth rates and the thermal response of fitness. Additionally, we illustrated how our approach can be used to project changes in net energy gain under current and future climatic conditions across broad geographic scales. Overall, this trait-based approach allows a relatively rapid and cost-effective assessment of climate change vulnerability for a wide range of animal taxa on broad geographic scales.