Bridging physiological responses to population outcomes under variable thermal stress

Embedding thermal tolerance metrics into population dynamics offers a promising toolkit for understanding the impacts of stressful heat events, but the time-dependence of thermal stress rarely factors into such assessments. Within organisms, heat causes damage that alternatively accumulates under stressful temperatures and is repaired under permissive ones. While risk under exclusively stressful temperatures is well characterized by thermal death time models, resilience to fluctuating temperatures is less clear. Understanding how this damage accumulation within organisms scales up to affect population thermal tolerance is a necessary step for predicting population dynamics and extinction risk. We address this gap by embedding a model of organismal stress and recovery into population dynamics, yielding time-dependent thermal performance curves of population growth rates. By parameterizing this novel framework with existing data from Drosophila melanogaster, we explore how integrating thermal stress across biological scales shapes the consequences of organismal stress on population outcomes under realistic thermal fluctuations.