ectothermie

Ectothermie is a physiological strategy in which an organism's body temperature is determined largely by external heat sources rather than internal metabolic heat production. Ectotherms include most reptiles, amphibians, fish, and many invertebrates. This contrasts with endothermy, where stable body temperature is maintained primarily by metabolic heat, as in birds and mammals. Some discussions distinguish ectothermy from poikilothermy, a broader term for organisms whose body temperature varies with the environment; in practice, ectothermy emphasizes reliance on external heat rather than a fixed internal thermostat.

In ectotherms, body temperature generally tracks ambient conditions and is strongly influenced by environmental temperature. Metabolic rate tends to rise with warmth, increasing activity and growth, but slows in cold conditions. Because they do not expend large energy on internal heating, many ectotherms have lower maintenance costs, but their performance is limited by external temperatures and seasonality. They commonly use behavioral strategies—basking to warm up, seeking shade or burrows to avoid heat, and selecting microhabitats with favorable temperatures.

Ecological and evolutionary implications: Ectothermy shapes where species live, how fast they grow, and how they respond to climate change. Temperature shifts can alter distributions and life-history traits; warming may move ranges toward higher latitudes or elevations and increase vulnerability during heat waves. Some pelagic fishes and sharks show regional endothermy and are exceptions to the general pattern. Overall, ectothermy forms a major life-history strategy across many taxa.