Adapted Yet at Risk: The Paradox of Thermotolerant Species in a Warming World

Assessing the persistence capacity of poor-dispersal species under climate change requires integrating knowledge of both physiological sensitivity (e.g., thermal tolerance metrics) and projected climatic exposure. While warm-adapted species in climatically buffered habitats could persist longer, and heat-sensitive species in rapidly warming regions might face higher extinction risk, such a simplistic dichotomy of "winners" and "losers" often fails to reflect the complexity of real-world systems. Drawing on recent literature on ectotherm thermal tolerance, we argue here that thermotolerant species generally inhabit regions with historically high thermal variability, where intense climatic shifts are often projected. This leads to a paradox where heat-tolerant species are experiencing similar or even higher climate stress than heat-sensitive ones. In addition, multiple methodological challenges in estimating thermal limits, accounting for behavioral, physiological, and evolutionary capacities, and predicting exposure to novel climatic conditions complicate assessments of persistence capacity. We advocate for a shift toward more mechanistic methodological frameworks for assessing thermal tolerance, and for the incorporation of climatic variability at biologically relevant spatial and temporal scales, thereby enabling more accurate forecasts of species' responses to climate change. Such a refined approach is essential to inform effective climate-adaptive biodiversity conservation strategies, especially for taxa with limited capacity to track shifting climates.