ectotherm

Ectotherm, also called ectothermic animal, is an animal whose body temperature is largely determined by external environmental conditions rather than by internal metabolic heat production. In contrast to endotherms, which generate substantial metabolic heat to maintain a relatively constant body temperature, most ectotherms have lower metabolic rates and rely on the surrounding environment to regulate temperature. The term is often used interchangeably with poikilotherm, though in practice there is variation: ectothermy describes reliance on environmental heat, while poikilothermy refers to fluctuating body temperature.

Major ectotherm groups include reptiles (lizards, snakes, turtles, crocodilians), amphibians (frogs, salamanders), many fish, and invertebrates such as mollusks, crustaceans, and insects.

Thermoregulation is primarily behavioral. Ectotherms seek sun or shade, bask on warm surfaces, or retreat to shelters to regulate heat. Some species adjust posture or skin coloration to absorb or reflect heat. Metabolic rates generally rise with temperature, influencing growth, development, and activity when conditions allow and slowing them during cold periods.

Temperature also influences life history traits, such as development rate and, in some reptiles, incubation temperature determining offspring sex. Geographic distribution and seasonal activity are tightly linked to climate and microhabitats. Ectotherms can be vulnerable to extreme weather and climate change but may thrive where endotherms face energy costs.

Overall, ectothermy is a major strategy for energy efficiency in many environments, shaping species distributions, behavior, and ecological interactions.