A framework for modelling thermal load sensitivity across life

Pieter Arnold, Daniel W.A. Noble, Adrienne Nicotra, Michael R. Kearney, Enrico Rezende, Samuel Andrew, Veronica Briceno, Lauren Buckley, Keith Allen Christian , Susana Clusella-Trullas, Sonya Geange, Lydia Guja, Octavio Jimenez Robles, Ben Kefford, Vanessa Kellermann, Andrea Leigh, Renee Marchin, Karel Mokany, Joanne Bennett

Forecasts of vulnerability to climate warming require an integrative understanding of how species are exposed to, are damaged by, and recover from thermal stress in natural environments. The sensitivity of species to temperature depends on the frequency, duration, and magnitude of thermal stress. Thus, there is a generally recognised need to move beyond physiological metrics based solely on critical thermal limits and integrate them with natural heat exposure regimes. Here we propose the Thermal Load Sensitivity (TLS) framework, which integrates biophysical principles for quantifying exposure with physiological principles of the dynamics of damage and repair processes in driving sublethal impacts on organisms. Building upon the established Thermal Death Time (TDT) model, which integrates both the magnitude and duration of stress, the TLS framework attempts to disentangle accumulation of damage and subsequent repair processes that alter responses to thermal stress. With the aid of case studies and reproducible simulation examples, we discuss how the TLS framework can be applied to enhance our understanding of the ecology and evolution of heat stress responses. These include assessing thermal sensitivity across diverse taxonomic groups, throughout ontogeny, and for modular organisms, as well as integrating additional stressors in combination with temperature. We identify critical research opportunities, knowledge gaps, and new ways of integrating physiological measures of thermal sensitivity to improve forecasts of thermal vulnerability.