ektotherm

Ektotherm, also spelled ectotherm, is an animal whose body temperature largely depends on external heat sources rather than internal metabolic heat production. Ektothermy is common among many aquatic and terrestrial species and contrasts with endothermy, in which heat is generated metabolically to maintain a relatively constant body temperature.

Ektotherms obtain heat by basking in sunlight, absorbing heat from water or substrate, and seeking shade or burrows to regulate temperature. They often adjust their activity to environmental conditions, becoming more active at favorable temperatures and limiting activity when conditions are too hot or cold. Some lineages exhibit specialized strategies such as regional heat retention in certain tissues, but the general pattern is reliance on external heat sources.

The group includes most fishes, amphibians, reptiles, and many invertebrates. This strategy reduces energetic demands and can support survival in habitats where food resources are scarce or irregular. However, it also makes activity, growth, and reproduction highly dependent on ambient temperatures, and can limit geographic distribution and seasonal activity in extreme climates.

Ecological implications of ektothermy include strong links between thermal environments and species distributions, life history timing, and behavior. Climate change can alter the availability of suitable temperatures, affecting activity patterns and range shifts. Overall, ektothermy represents a widespread evolutionary strategy that emphasizes energy efficiency and environmental reliance across diverse taxa.