ektothermy

Ektothermy, sometimes spelled ectothermy or ektothermy, is a mode of thermoregulation in which an organism relies largely on external heat sources to determine body temperature. In contrast to endothermy, ectotherms do not maintain a constant internal temperature through metabolic heat production, and their body temperature often tracks the environment.

Body temperature in ectotherms tends to vary with ambient conditions and is strongly linked to activity and metabolism. Many species regulate heat behaviorally, basking in sunlight, seeking shade, moving between microhabitats, or altering activity patterns. Some exhibit regional heterothermy, warming specific parts of the body, or, in certain groups, localized heat production.

Major groups that are predominantly ectothermic include reptiles (such as snakes, lizards, and turtles), amphibians (frogs and salamanders), many fishes, and most invertebrates. Birds and mammals are typically endothermic, maintaining relatively stable internal temperatures, while some aquatic and terrestrial taxa show mixed or context-dependent thermoregulation.

Ecological and evolutionary implications of ectothermy include lower baseline energy requirements and the ability to exploit environments with variable resources, but reduced performance in cold conditions and limited sustained activity without heat. Ektothermy is common across many lineages and interacts with climate, life history, and habitat use.