Ektotermi

Ektotermi, or ectothermy, is a mode of thermoregulation in which an animal's body temperature is determined largely by external heat sources rather than by internal metabolic heat production. The term derives from Greek words meaning outside heat. In ectotherms, metabolic heat production is typically insufficient to maintain a constant internal temperature, though some species can raise their body temperature through behavioral heating or use of microhabitats.

Most ectotherms are poikilothermic, meaning their body temperature fluctuates with ambient conditions. However, many display a degree of temporal or spatial thermoregulation, maintaining activity within a restricted temperature range by seeking sun, shade, or different microhabitats. Ektotermi is common across a broad range of organisms, including reptiles (snakes, lizards, turtles), amphibians (frogs, salamanders), most fish, and many invertebrates such as insects and crustaceans.

Ectothermy has important ecological and physiological consequences. The energy cost of heat production is low, enabling persistence in environments with limited resources, but ectotherms depend on environmental temperatures for activity, growth, and reproduction. They often use behavioral strategies such as basking, burrowing, nocturnal activity, or seasonal dormancy (hibernation and estivation) to cope with temperature variability. The distribution and daily activity patterns of ectotherms are closely tied to climate, solar exposure, and microhabitat structure.

In contrast to endotherms, ectotherms rely less on metabolic heat and more on environmental heat to regulate body temperature. This distinction underpins broad differences in physiology, life history, and ecological niches among major animal groups.