Practice question

Poikilothermic animals have body temperatures that vary appreciably over time, often approaching the temperature of their surroundings. Most obtain much of their heat externally and therefore are also ectothermic. A lizard may warm in sunlight and cool in shade; a fish’s body temperature generally follows the surrounding water. This dependence reduces the energetic cost of producing metabolic heat, so food requirements are often lower than in similarly sized endotherms. It does not mean poikilotherms passively accept every temperature. Behavioural thermoregulation—basking, burrowing, changing posture, selecting water depth, or shifting activity time—can keep body temperature within a preferred range. They are not all mammals; mammals are predominantly endothermic, although some enter heterothermic states. Nor do poikilotherms necessarily have narrow tolerances: some are eurythermal and others stenothermal. “Match” should thus be read as strong thermal coupling to the environment, not exact equality at every moment. Their physiological rates, including digestion, locomotion, and development, commonly accelerate with warming up to an optimum and then decline as temperatures approach harmful limits.