Poikiliothermie

Poikilothermy is a thermoregulatory strategy in which an animal's internal body temperature varies with the surrounding environment rather than being kept constant by metabolic heat production. In poikilotherms, core temperature tends to rise and fall with ambient temperature, and metabolic rates often respond markedly to environmental conditions.

Most poikilotherms are ectotherms that rely on external heat sources to regulate body temperature. They regulate exposure to heat or cold primarily through behavior: basking in sunlight to warm up, seeking shade or burrowing to cool down, and shifting activity patterns with the seasons. Some species may display limited physiological adjustments to temperature, such as changes in enzyme activity, but do not maintain a constant internal temperature.

Taxonomic distribution: Poikilothermy is widespread among invertebrates and many vertebrate lineages, including most fishes, amphibians, and reptiles. Birds and mammals are predominantly homeothermic, maintaining stable body temperatures through metabolic heat production.

Ecological and evolutionary implications: The poikilothermic strategy reduces energetic costs and can support growth and reproduction when temperatures are favorable, but it makes survival and performance highly dependent on environmental conditions. Temperature influences digestion, locomotion, and development, and climate change can shift species distributions and life cycles.