Ektotermie

Ektotermie, or ectothermy, is a form of thermoregulation in which an organism's body temperature is largely determined by external environmental temperatures. Ectotherms rely on ambient heat sources such as sunlight, warm substrates, or warm air, and use behavioral strategies (basking, seeking shade, changing posture) to regulate their body temperature. Because their heat comes from outside, their body temperature tends to fluctuate with the environment, a condition also described as poikilothermy.

Common ectotherms include reptiles, amphibians, fish, and many invertebrates. In contrast to endotherms, most ectotherms have lower metabolic rates and require less food energy. This allows survival in habitats where food is scarce, but can limit activity, growth, and geographic distribution in cold or variable climates. Temperature strongly affects physiological processes such as digestion, locomotion, and reproduction, and peak performance occurs within a species-specific optimal temperature range.

In practical terms, ectothermy shapes ecology and behavior: activity patterns, habitat choice, and seasonal life histories are dictated by environmental temperatures. Ectotherms can be highly sensitive to climate and microhabitat temperature variation, making them vulnerable to extreme weather and climate change.

Evolutionary note: Ectothermy represents a major contrast to endothermy, where body temperature is maintained largely by metabolic heat production. Endothermy evolved independently in birds and mammals. Many major animal groups remain predominantly ectothermic.