Ectotherma

Ectotherma refers to a broad category of animals whose internal body temperature is largely determined by external conditions rather than by metabolic heat production. The term is used to describe ectothermy, the general principle by which most reptiles, amphibians, fishes, and many invertebrates regulate their physiology. Ectotherms rely on environmental heat sources such as sunlit surfaces, warm substrates, or shelter in warm microhabitats to raise their body temperature, and may seek cooler areas to prevent overheating. Their metabolic rate and activity often depend strongly on ambient temperature, with many processes accelerating with warmth and slowing in cold conditions.

Common examples include snakes, lizards, frogs, salamanders, most fishes, and many invertebrates. Some groups display flexible strategies, including nocturnal activity, basking, burrowing, or color changes to adjust heat absorption. In contrast to endotherms, ectotherms generally require less energy for temperature regulation but may have slower growth or development at low temperatures.

Ecologically, ectothermy shapes species’ distributions, activity patterns, and responses to climate. Temperature-dependent factors can influence growth rates, reproduction, and sex determination in some reptiles. Evolutionarily, ectothermy is ancestral for vertebrates; endothermy arose in the lineages leading to birds and mammals. In modern usage, Ectotherma is sometimes used informally to refer to all ectothermic animals, but it is not a formal taxonomic clade and is distinct from endothermic groups.