Cold-blooded organisms (called poikilotherms - "of varying temperature") maintain their body temperatures in ways different from mammals and birds. The term is now outdated in scientific contexts. Cold-blooded creatures were, initially, presumed to be incapable of maintaining their body temperatures at all. Cold-blooded animals are now called ectotherms, a term which signifies that their heat (therm) comes from outside (ecto) of them; the term cold-blooded is misleading.
Advances in the study of how creatures maintain their internal temperatures (termed: Thermophysiology) have shown that many of the earlier notions of what the terms "warm-blooded" and "cold-blooded" mean, were far from accurate (see below: Definitions). Today scientists realize that body temperature types are not a simple matter of black and white. Most creatures fit more in line with a graded spectrum from one extreme (cold-blooded) to another (warm-blooded).
In biology, a warm-blooded animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature. This involves the ability to cool down or produce more body heat. Warm-blooded animals mainly control their body temperature by regulating their metabolic rates (e.g. increasing their metabolic rate as the surrounding temperature begins to decrease).
Both the terms "warm-blooded" and "cold-blooded" have fallen out of favor with scientists, because of the vagueness of the terms, and due to an increased understanding in this field. Body temperature types do not fall into simple either/or categories. Each term may be replaced with one or more variants (see: Definitions of warm-bloodedness). Body temperature maintenance incorporates a wide range of different techniques that result in a body temperature continuum, with the traditional ideals of warm-blooded and cold-blooded being at opposite ends of the spectrum.
Warm-blooded vs.Cold blooded
Advantages of a fast metabolism
The overall speed of an animal's metabolism increases by a factor of about 2 for every 10 C° rise in temperature (limited by the need to avoid hyperthermia). Warm-bloodedness does not provide greater speed than cold-bloodedness - cold-blooded animals can move as fast as warm-blooded animals of the same size and build. But warm-blooded animals have much greater stamina than cold-blooded creatures of the same size and build, because their faster metabolisms quickly regenerate energy supplies (especially ATP) and break down muscular waste products (especially lactate). This enables warm-blooded predators to run down cold-blooded prey, warm-blooded prey to outrun cold-blooded predators (provided they avoid the initial charge or ambush) and warm-blooded animals to be much more successful foragers.
Advantages of homeothermy
Enzymes have strong temperature preferences and their efficiency is much reduced outside their preferred ranges. A creature with a fairly constant body temperature can therefore use enzymes which are efficient at that temperature. Another advantage of a homeothermic animal would be its ability to maintain its constant body temperature even in freezing cold weather. A poikilotherm must either operate well below optimum efficiency most of the time or spend extra resources making a wider range of enzymes to cover the wider range of body temperatures.
Disadvantages of warm-bloodedness
Because warm-blooded animals use enzymes which are specialised for a narrow range of body temperatures over-cooling rapidly leads to torpor and then death. Also, the energy required to maintain the homeothermic temperature comes from food - this results in homeothermic animals needing to eat much more food than poikilothermic animals.
Shivering and fat-burning to maintain temperature are very energy-intensive, for example:
in winter many small birds lose one third of their body weight overnight.
in general a warm-blooded animal requires 5 to 10 times as much food as a cold-blooded animal of the same size and build, so cold-blooded animals are better at surviving famines and barren environments.
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