Ectothermic

Ectothermic describes organisms whose body temperature is largely determined by the external environment rather than produced internally. In most ectotherms, temperature control is achieved primarily through behavioral means such as basking in the sun to heat up, seeking shade or burrowing to avoid heat, and adjusting posture to maximize or minimize heat gain. Many ectotherms also change their activity pattern with season or time of day, remaining inactive at extreme heat or cold.

Physiologically, metabolic rate in ectotherms is strongly temperature dependent. Higher ambient temperatures generally raise metabolic rate, digestion, growth, and locomotion, while cold slows these processes. Because they do not expend energy to maintain a constant body temperature, ectotherms typically require less energy overall than endotherms of similar size, but their activity is limited by environmental temperatures and by the availability of external heat sources.

Ecologically, ectothermy shapes habitat use and geographic distribution, favoring environments with reliable thermal opportunities. They are found across many groups, including reptiles, amphibians, fishes, and many invertebrates. They often exhibit a range of strategies to cope with temperature variation, such as nocturnality, microhabitat selection, and seasonal dormancy.

Some species show regional endothermy, warming specific tissues to support high-speed swimming or sustained activity in cooler water, but most of the body temperature tracks the surroundings. Understanding ectothermy helps explain the physiology, behavior, and ecology of a large portion of animal diversity.