poikilotherm

Poikilotherm is a term in biology for an animal whose body temperature changes with ambient temperature. They are contrasted with homeotherms, which keep a relatively constant internal temperature through metabolic heat production and regulation. Poikilotherms usually exhibit limited internal thermoregulation; their body temperature tracks the environment within a small range around their core.

Metabolic rate in poikilotherms is strongly temperature-dependent: as temperature increases, their metabolism and activity typically increase; at low temperatures, they slow down or become inactive. This temperature sensitivity affects behavior, performance, growth, and distribution.

Coping strategies are largely behavioral: seeking shade or sun, burrowing, changing aquatic depth, moving to warmer or cooler microhabitats. Some species display physiological adjustments such as acclimation, enabling enzyme systems to function over a range of temperatures. A subset can enter states of torpor or hibernation, reducing metabolic rate to survive unfavorable conditions, though these states are examples of heterothermy.

Poikilothermy is common in many taxonomic groups, including most fish, amphibians, reptiles, and invertebrates. It is advantageous in low-energy lifestyles and in environments where constant heat production is costly, but it can limit activity and geographic range in climates with extreme temperatures.

Etymology: from Greek poikilos, varied, and therme, heat.