ectothermy

Ectothermy is a mode of thermoregulation in which an animal's body temperature is determined largely by the external environment rather than by internal metabolic heat production. Ectotherms rely on heat exchange with surroundings to warm up or cool down. By contrast, endotherms generate significant heat through metabolism and maintain relatively stable body temperatures independent of the environment.

Ectotherms include many vertebrates such as reptiles, amphibians, and fish, as well as most invertebrates. Their body temperatures tend to coincide with ambient temperatures, though many species regulate their exposure using behavior and microhabitats—basking in sunlight to raise temperature, seeking shade or burrowing to avoid heat, or altering activity patterns with the time of day or season.

Metabolic consequences: ectotherms generally have lower resting metabolic rates than endotherms and require less food for maintenance. This can support large numbers of individuals in resource-sparse environments, but it also links activity, growth, and reproduction to external temperatures. Extreme cold or heat can limit performance, distribution, and life-history timing.

Ecology and evolution: ectothermy is common across major animal groups and is particularly successful in stable or moderate climates and variable habitats such as deserts, tropical forests, and aquatic systems. Evolutionarily, it reflects trade-offs between energy efficiency and environmental dependence.

Contemporary relevance: climate change and habitat alteration influence ectotherm physiology and distributions, expanding suitable range in some regions while increasing exposure to thermal stress in others. Understanding ectothermy informs studies of ecology, physiology, and conservation.