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An ectotherm (from the Greek ἐκτός (ektós) "outside" and θερμός (thermós) "heat"), more commonly referred to as a "cold-blooded animal", [1] is an animal in which internal physiological sources of heat, such as blood, are of relatively small or of quite negligible importance in controlling body temperature. [2]
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature as its own body temperature, thus avoiding the need for internal thermoregulation.
Warm-blooded is an informal term referring to animal species whose bodies maintain a temperature higher than that of their environment. In particular, homeothermic species (including birds and mammals) maintain a stable body temperature by regulating metabolic processes. Other species have various degrees of thermoregulation.
Because many homeothermic animals use enzymes that are specialized for a narrow range of body temperatures, hypothermia rapidly leads to torpor and then death. Additionally, homeothermy obtained from endothermy is a high energy strategy [ 5 ] and many environments will offer lower carrying capacity to these organisms.
In addition, mesotherm body temperatures tend to rise as body size increases (a phenomenon known as gigantothermy [3]), unlike endotherms. This reflects the lower surface area to volume ratio in large animals , which reduces rates of heat loss.
The body temperatures of many small birds (e.g. hummingbirds) and small mammals (e.g. tenrecs) fall dramatically during daily inactivity, such as nightly in diurnal animals or during the day in nocturnal animals, thus reducing the energy cost of maintaining body temperature. Less drastic intermittent reduction in body temperature also occurs in ...
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In horses, the lower critical temperature is 5 °C while the upper critical temperature depends on the definition used. [10] Their thermoneutral zone is roughly 5–30 °C (41–86 °F). [11] In mice, the lower critical temperature and upper critical temperature can be the same, creating a thermoneutral point instead of a thermoneutral zone.