COS 20-3 - A unified model of individual death leads for integrating temperature variation into population dynamics .

Abstract: Forecasting extinction risk in response to climate change is one of ecology's more pressing challenges. Recent progress has been made documenting thermal performance curves (TPCs) for a wide variety of taxa and these have been used to identify risk indicators like ‘thermal safety margins’ and estimates of ‘warming tolerance’ based upon their match to current and/or future conditions. While fruitful, these approaches have faced criticism over their many simplifying assumptions and weaknesses, including perhaps most notably, that they cannot differentiate how extreme events such as heat-waves impact extinction risk. As species are becoming increasingly exposed to heat stress because of climate and habitat change, this is a critical challenge that can be met by integrating better assumptions about physiological responses into population dynamics based estimates of extinction risk.



The use of population dynamics as a component of risk assessment requires a number of key innovations that, when addressed, have highlighted gaps in our understanding of how temperature impacts vital rates of birth, death, and their response to density dependence. In addition, recent work has shown that extrapolating these relationships from ‘permissive’ to ‘stressful’ temperatures is unacceptable given that fundamentally different physiological processes operate in these ranges. To overcome these challenges, we introduce a unified framework for modeling the temperature-dependence of per-capita death rates that is based upon the contributions of metabolism and proteome degradation, modulated by a dynamic heat-shock response. We analyze this model and find the heat-shock response provides a critical connection between temperature’s effect on death rates in the permissive and stressful temperature ranges. By incorporating a stochastic birth-death framework, we extend the model to quantify the risk of extinction posed by transient heat events that vary in their magnitude, duration, and frequency.