Thermal Tolerance and Climate Vulnerability of Tropical Ectotherms: A Review of Physiological Limits, Behavioural Buffering, and Conservation Implications

Abstract

Ectothermic animals, which make up the great majority of animal diversity, depend on environmental temperature for nearly all physiological functions and are therefore directly exposed to climate warming. This review synthesises published evidence on the thermal physiology of ectotherms to evaluate why tropical species are widely considered disproportionately vulnerable despite the smaller magnitude of warming projected at low latitudes. We examine (1) the conceptual framework of thermal performance curves, critical thermal limits, and thermal safety margins; (2) latitudinal and habitat-related patterns in heat tolerance; (3) the capacity of behavioural thermoregulation, physiological plasticity, and evolutionary adaptation to buffer warming; and (4) observed and projected ecological consequences. The literature shows that upper thermal limits vary little across latitude and are strongly conserved phylogenetically, whereas lower limits are flexible. Tropical ectotherms typically live closer to their thermal optima and possess narrow thermal safety margins. Acclimation of heat tolerance is generally modest, and behavioural buffering depends on the availability of cool microhabitats, linking physiological vulnerability directly to habitat structure. Sublethal effects, including elevated metabolic costs, restricted activity time, and heat-induced fertility loss, may drive population decline well before lethal limits are reached. We identify methodological limitations in current vulnerability assessments and propose conservation priorities centred on microhabitat retention, elevational connectivity, and integration of physiological data into conservation planning.