Homeothermy, homothermy or homoiothermy is

thermoregulation 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 ...

that maintains a stable internal body temperature regardless of external influence. This internal

body temperature 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 ...

is often, though not necessarily, higher than the immediate environment (from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

ὅμοιος ''homoios'' "similar" and θέρμη ''thermē'' "heat"). Homeothermy is one of the three types of thermoregulation in

warm-blooded Warm-blooded is an informal term referring to animal species which can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The onl ...

animal species. Homeothermy's opposite is

poikilothermy A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...

. A poikilotherm is an organism that does not maintain a fixed internal temperature but rather fluctuates based on their environment and physical behaviour. Homeotherms are ''not'' necessarily

endotherm An endotherm (from Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions inste ...

ic. Some homeotherms may maintain constant body temperatures through behavioral mechanisms alone, ''i.e.'', behavioral thermoregulation. Many reptiles use this strategy. For example, desert lizards are remarkable in that they maintain near-constant activity temperatures that are often within a degree or two of their lethal critical temperatures.

Evolution

Pros

Enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

s have a relatively narrow temperature range at which their efficiencies are optimal. Temperatures outside this range can greatly reduce the rate of a reaction or stop it altogether. A creature with a fairly constant body temperature can therefore specialize in enzymes which are efficient at that particular temperature. A

poikilotherm A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...

must either operate well below optimum efficiency most of the time, migrate, hibernate or expend extra resources producing a wider range of enzymes to cover the wider range of body temperatures. However, some environments offer much more consistent temperatures than others. For example, the tropics often have seasonal variations in temperature that are smaller than their diurnal variations. In addition, large bodies of water, such as the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

and very large

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s, have moderate temperature variations. The waters below the ocean surface are particularly stable in temperature.

Cons

Because many homeothermic animals use enzymes that are specialized for a narrow range of body temperatures,

hypothermia Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe h ...

rapidly leads to

torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the time ...

and then death. Additionally, homeothermy obtained from endothermy is a high energy strategy and many environments will offer lower

carrying capacity The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as t ...

to these organisms. In cold weather the energy expenditure to maintain body temperature accelerates starvation and may lead to death.

References

{{Reflist Animal physiology Human homeostasis Thermoregulation

Evolution

Pros

Cons

See also

References