An ectotherm (from the Greek ἐκτός (ektós) "outside" and θερμός (thermós) "hot"), is an organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature.[1] Such organisms (for example frogs) rely on environmental heat sources,[2] which permit them to operate at very economical metabolic rates.[3] Some of these animals live in environments where temperatures are practically constant, as is typical of regions of the abyssal ocean and hence can be regarded as homeothermic ectotherms. In contrast, in places where temperature varies so widely as to limit the physiological activities of other kinds of ectotherms, many species habitually seek out external sources of heat or shelter from heat; for example, many reptiles regulate their body temperature by basking in the sun, or seeking shade when necessary in addition to a whole host of other behavioral thermoregulation mechanisms. For home captivity as pet, reptile owners can use a UVB/UVA light system to assist the animals' basking behaviour.[4]

In contrast to ectotherms, endotherms rely largely, even predominantly, on heat from internal metabolic processes, and mesotherms use an intermediate strategy.

In ectotherms, fluctuating ambient temperatures may affect the body temperature. Such variation in body temperature is called poikilothermy, though the concept is not widely satisfactory and the use of the term is declining. In small aquatic creatures such as Rotifera, the poikilothermy is practically absolute, but other creatures (like crabs) have wider physiological options at their disposal, and they can move to preferred temperatures, avoid ambient temperature changes, or moderate their effects.[1][5] Ectotherms can also display the features of homeothermy, especially within aquatic organisms. Normally their range of ambient environmental temperatures is relatively constant, and there are few in number that attempt to maintain a higher internal temperature due to the high associated costs.[6]

Basking turtles
Pseudemys turtles (shown here basking for warmth) are ectothermic.
Lizard Thermoregulation
The red line represents the air temperature. The purple line represents the body temperature of the lizard. The green line represents the base temperature of the burrow. Lizards are ectotherms and use behavioral adaptations to control their temperature. They regulate their behavior based on the temperature outside; if it is warm they will go outside up to a point and return to their burrow as necessary.
Junonia lemonias DSF by Kadavoor
Junonia lemonias is basking under the sun.


Various patterns of behavior enable certain ectotherms to regulate body temperature to a useful extent. To warm up, reptiles and many insects find sunny places and adopt positions that maximise their exposure; at harmfully high temperatures they seek shade or cooler water. In cold weather, honey bees huddle together to retain heat. Butterflies and moths may orient their wings to maximize exposure to solar radiation in order to build up heat before take-off.[1] Gregarious caterpillars, such as the Forest Tent caterpillar and fall webworm, benefit from basking in large groups for thermoregulation.[7][8][9][10][11] Many flying insects, such as honey bees and bumble bees, also raise their internal temperatures endothermally prior to flight, by vibrating their flight muscles without violent movement of the wings (see insect thermoregulation). Such endothermal activity is an example of the difficulty of consistent application of terms such as poikilothermy and homiothermy.[1]

In addition to behavioral adaptations, physiological adaptations help ectotherms regulate temperature. Diving reptiles conserve heat by heat exchange mechanisms, whereby cold blood from the skin picks up heat from blood moving outward from the body core, re-using and thereby conserving some of the heat that otherwise would have been wasted. The skin of bullfrogs secretes more mucus when it is hot, allowing more cooling by evaporation.

During periods of cold, some ectotherms enter a state of torpor, in which their metabolism slows or, in some cases, such as the wood frog, effectively stops. The torpor might last overnight or last for a season, or even for years, depending on the species and circumstances.

Pros and cons

A 1.8m southern black racer basking in the Inverness, Florida sunshine on a cool morning.

Ectotherms rely largely on external heat sources such as sunlight to achieve their optimal body temperature for various bodily activities. Accordingly, they depend on ambient conditions to reach operational body temperatures. In contrast, endothermic animals, as a rule, maintain nearly constant high operational body temperatures largely by reliance on internal heat produced by metabolically active organs (liver, kidney, heart, brain, muscle) or even by specialized heat producing organs like brown adipose tissue (BAT). Also, as a rule, ectotherms have lower metabolic rates than endotherms at a given body mass. As a consequence, endotherms generally rely on higher food consumption, and commonly on food of higher energy content. Such requirements may limit the carrying capacity of a given environment for endotherms as compared to its carrying capacity for ectotherms.

Because ectotherms depend on environmental conditions for body temperature regulation, as a rule, they are more sluggish at night and in early mornings. When they emerge from shelter, many diurnal ectotherms need to heat up in the early sunlight before they can begin their daily activities. In cool weather the foraging activity of such species is therefore restricted to the day time in most vertebrate ectotherms, and in cold climates most cannot survive at all. In lizards, for instance, most nocturnal species are geckos specialising in "sit and wait" foraging strategies. Such strategies do not require as much energy as active foraging and do not, as a rule, require hunting activity of the same intensity. From another point of view, sit-and-wait predation may require very long periods of unproductive waiting. Endotherms cannot, in general, afford such long periods without food, but suitably adapted ectotherms can wait without expending much energy. Endothermic vertebrate species are therefore less dependent on the environmental conditions and have developed a higher variability (both within and between species) in their daily patterns of activity.[12]

Contrast between thermodynamics and biological terminology

Possible confusion can arise from the difference in the terminology of physics and biology. Whereas the thermodynamic terms "exothermic" and "endothermic" respectively refer to processes that give out heat energy and processes that absorb heat energy, in biology the sense is effectively inverted. The metabolic term "ectotherm" refers to organisms that rely largely on external heat to achieve a full working temperature, and "endotherm" refers to organisms that produce heat from within as a major factor in controlling their bodily temperature.



  1. ^ a b c d Davenport, John. Animal Life at Low Temperature. Publisher: Springer 1991. ISBN 978-0412403507
  2. ^ Jay M. Savage; with photographs by Michael Fogden and Patricia Fogden. (2002). The Amphibians and Reptiles of Costa Rica: a Herpetofauna Between Two Continents, Between Two Seas. Chicago, Ill.: University of Chicago Press. p. 409. ISBN 978-0-226-73538-2.
  3. ^ Milton Hildebrand; G. E. Goslow, Jr. Principal ill. Viola Hildebrand. (2001). Analysis of vertebrate structure. New York: Wiley. p. 429. ISBN 978-0-471-29505-1.CS1 maint: Multiple names: authors list (link)
  4. ^ "Best Reptile UVA/UVB Light Bulbs (Reviewed + Best Deals From Amazon) – BuddyGenius". 4 January 2018. Archived from the original on 17 January 2018. Retrieved 6 May 2018.
  5. ^ Lewis, L; Ayers, J (2014). "Temperature Preference and Acclimation in the Jonah Crab, Cancer borealis". Journal of Experimental Marine Biology and Ecology. 455: 7–13. doi:10.1016/j.jembe.2014.02.013.
  6. ^ Willmer, Pat; Stone, Graham; Johnston, Ian. Environmental Physiology of Animals. Hoboken: Wiley, 2009. Ebook Library. Web. 01 Apr. 2016.
  7. ^ McClure, Melanie; Cannel, Elizabeth; Despland, Emma (June 2011). "Thermal ecology and behaviour of the nomadic social forager Malacosoma disstria". Physiological Entomology. 36 (2): 120–127. doi:10.1111/j.1365-3032.2010.00770.x.
  8. ^ Schowalter, T. D.; Ring, D. R. (2017-01-01). "Biology and Management of the Fall Webworm, Hyphantria cunea (Lepidoptera: Erebidae)". Journal of Integrated Pest Management. 8 (1). doi:10.1093/jipm/pmw019. Archived from the original on 2017-11-15.
  9. ^ Rehnberg, Bradley (2002). "Heat Retention by webs of the fall webworm Hyphantria cunea (Lepidoptera: Arctiidae): infrared warming and forced convective cooling". Journal of Thermal Biology: 525–530.
  10. ^ LOEWY, KATRINA. "LIFE HISTORY TRAITS AND REARING TECHNIQUES FOR FALL WEBWORMS (HYPHANTRIA CUNEA DRURY) IN COLORADO" (PDF). Journal of the Lepidopterists' Society. Archived (PDF) from the original on 2018-05-06.
  11. ^ Hunter, Alison F. (2000-11-01). "Gregariousness and repellent defences in the survival of phytophagous insects". Oikos. 91 (2): 213–224. doi:10.1034/j.1600-0706.2000.910202.x. ISSN 1600-0706.
  12. ^ Hut RA, Kronfeld-Schor N, van der Vinne V, De la Iglesia H (2012). In search of a temporal niche: environmental factors. Progress in Brain Research. 199. pp. 281–304. doi:10.1016/B978-0-444-59427-3.00017-4. ISBN 9780444594273. PMID 22877672.

Basking may refer to:

Basking in reflected glory, associating oneself with successful other such that their success becomes one's own

Basking Ridge, New Jersey, unincorporated area in Bernards Township in the Somerset Hills region of Somerset County, New Jersey

Basking Ridge (NJT station), New Jersey Transit station in Bernards Township, New Jersey

Basking shark, Cetorhinus maximus, is the second largest living fish, after the whale shark

Basking, behaviour used to raise body temperature, exhibited by some animals (see ectotherm)


Bradyaerobic is a term used in biology that describes an animal that has low levels of oxygen consumption.By necessity a bradyaerobic animal can engage in short low or high low-level aerobic activities, followed by brief anaerobically powered bursts of energy. Bradyaerobes can be sprinters, but not long distance animals.


Bradymetabolism refers to organisms with a high active metabolism and a considerably slower resting metabolism. Bradymetabolic animals can often undergo dramatic changes in metabolic speed, according to food availability and temperature. Many bradymetabolic creatures in deserts and in areas that experience extreme winters are capable of "shutting down" their metabolisms to approach near-death states, until favorable conditions return(see hibernation and estivation).

Several variants of bradymetabolism exists. In mammals, the animals normally have a fairly high metabolism, only dropping to low levels in times of little food. In most reptiles, the normal metabolic rate is quite low, but can be raised when needed, typically in short bursts of activity in connection with capturing prey.


Ecto may refer to:

"an ecto", colloquial abbreviation for an ectomorph body type in Somatotype and constitutional psychology

Ecto (album) is an album by songwriter Happy Rhodes

Ecto (software) is a weblog client for Macintosh and Windows

The rare crafting material Ecto from MMORPG Guild Wars

Ecto is with the outer external


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 set free by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production. Examples include special-function muscular exertion such as shivering, and uncoupled oxidative metabolism such as within brown adipose tissue.

Only birds and mammals are extant universally endothermic groups of animals. Certain lamnid sharks, tuna and billfishes are also endothermic.

In common parlance, endotherms are characterized as "warm-blooded". The opposite of endothermy is ectothermy, although in general, there is no absolute or clear separation between the nature of endotherms and ectotherms.

Exergonic process

An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs free energy change is negative (∆G < 0). "Exergonic" (from the prefix exo-, derived for the Greek word ἔξω exō, "outside" and the suffix -ergonic, derived from the Greek word ἔργον ergon, "work") means "releasing energy in the form of work". In thermodynamics, work is defined as the energy moving from the system (the internal region) to the surroundings (the external region) during a given process.

All physical and chemical systems in the universe follow the second law of thermodynamics and proceed in a downhill, i.e., exergonic, direction. Thus, left to itself, any physical or chemical system will proceed, according to the second law of thermodynamics, in a direction that tends to lower the free energy of the system, and thus to expend energy in the form of work. These reactions occur spontaneously.

A chemical reaction is also exergonic when spontaneous. Thus in this type of reactions the Gibbs free energy decreases. The entropy is included in any change of the Gibbs free energy. This differs from a exothermic reaction or a endothermic reaction where the entropy is not included. The Gibbs free energy is calculated with the Gibbs–Helmholtz equation:


T = temperature in kelvins (K)
ΔG = change in the Gibbs free energy
ΔS = change in entropy (at 298 K) as ΔS = Σ{S(Product)} − Σ{S(Reagent)}
ΔH = change in enthalpy (at 298 K) as ΔH = Σ{H(Product)} − Σ{H(Reagent)}

A chemical reaction progresses only spontaneously when the Gibbs free energy decreases, in that case the ΔG is negative. In exergonic reactions the ΔG is negative and in endergonic reactions the ΔG is positive:



equals the change in the Gibbs free energy after completion of a chemical reaction.
Exothermic reaction

An exothermic reaction is a chemical reaction that releases energy through light or heat. It is the opposite of an endothermic reaction.Expressed in a chemical equation: reactants → products + energy.

Exothermic Reaction means "exo" (derived from the greek word: "έξω", literally translated to "out") meaning releases and "thermic" means heat. So the reaction in which there is release of heat with or without light is called

exothermic reaction.


Gigantothermy (sometimes called ectothermic homeothermy or inertial homeothermy) is a phenomenon with significance in biology and paleontology, whereby large, bulky ectothermic animals are more easily able to maintain a constant, relatively high body temperature than smaller animals by virtue of their smaller surface area to volume ratio. A bigger animal has proportionately less of its body close to the outside environment than a smaller animal of otherwise similar shape, and so it gains heat from, or loses heat to, the environment much more slowly.The phenomenon is important in the biology of ectothermic megafauna, such as large turtles, and aquatic reptiles like ichthyosaurs and mosasaurs. Gigantotherms, though almost always ectothermic, generally have a body temperature similar to that of endotherms. It has been suggested that the larger dinosaurs would have been gigantothermic, rendering them virtually homeothermic.

Greenland shark

The Greenland shark (Somniosus microcephalus), also known as the gurry shark, grey shark, or by the Kalaallisut name eqalussuaq, is a large shark of the family Somniosidae ("sleeper sharks"), closely related to the Pacific and southern sleeper sharks. The distribution of this species is mostly restricted to the waters of the North Atlantic Ocean and Arctic Ocean.

It has the longest known lifespan of all vertebrate species (estimated to be between 300–500 years), and is among the largest extant species of shark. As an adaptation to living at depth, it has a high concentration of trimethylamine N-oxide in its tissues, which causes the meat to be toxic. Greenland shark flesh treated to reduce toxin levels is eaten in Iceland as a delicacy known as kæstur hákarl.


Heterothermy or heterothermia (from Greek ἕτερος heteros "other" and θέρμη thermē "heat") is a physiological term for animals that vary between self-regulating their body temperature, and allowing the surrounding environment to affect it. In other words, they exhibit characteristics of both poikilothermy and homeothermy.


Homeothermy or homothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This internal body temperature is often, though not necessarily, higher than the immediate environment (from Greek ὅμοιος homoios "similar" and θέρμη thermē "heat"). Homeothermy is one of the three types of thermo regulation in warm-blooded animal species. Homeothermy's opposite is poikilothermy.

Homeotherms are not necessarily endothermic. 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.


Kleptothermy is any form of thermoregulation by which an animal shares in the metabolic thermogenesis of another animal. It may or may not be reciprocal, and occurs in both endotherms and ectotherms. Its most common form is huddling.


A mesotherm (from Greek μέσος mesos "intermediate" and thermē "heat") is a type of animal with a thermoregulatory strategy intermediate to cold-blooded ectotherms and warm-blooded endotherms.

Nashville Zoo at Grassmere

The Nashville Zoo at Grassmere is a zoological garden and historic plantation farmhouse located 6 miles (9.7 km) southeast of Downtown Nashville. As of 2014, the zoo was middle Tennessee's top paid attraction and contained 6,230 individual animals, encompassing 339 species. The zoo's site is approximately 188 acres (76 ha) in size. It is an accredited member of the Association of Zoos and Aquariums.


A poikilotherm () is an animal whose internal temperature varies considerably. It is the opposite of a homeotherm, an animal which maintains thermal homeostasis. While the term in principle can apply to all organisms, it is generally only applied to animals, and mostly to vertebrates. Usually the fluctuations are consequence of variation in the ambient environmental temperature. Many terrestrial ectotherms are poikilothermic.

However some ectotherms remain in temperature-constant environments to the point that they are actually able to maintain a constant internal temperature (i.e. are homeothermic). It is this distinction that often makes the term "poikilotherm" more useful than the vernacular "cold-blooded", which is sometimes used to refer to ectotherms more generally.

Poikilothermic animals include types of vertebrate animals, specifically some fish, amphibians, and reptiles, as well as a large number of invertebrate animals. The naked mole-rat is the only mammal that is currently thought to be poikilothermic.


A stenotherm (from Greek στενός stenos "narrow" and θέρμη therme "heat") is a species or living organism only capable of living or surviving within a narrow temperature range.

The opposite is a eurytherm, an organism that can function at a wide range of different body temperatures.


Tachyaerobic is a term used in biology to describe the muscles of large animals and birds that are able to maintain high levels or physical activity because their hearts make up at least 0.5-0.6 percent of their body mass and maintain high blood pressures. A reptile displaying equal size to a tachyaerobic mammal does not have the same capabilities. Tachyaerobic animals' hearts beat more quickly, produce more oxygen, and distribute blood at a quicker rate than reptiles.

The use of tachyaerobic muscles is important to animals such as giraffes that need blood circulated through a large body size quickly.


Thermolabile refers to a substance which is subject to destruction, decomposition, or change in response to heat. This term is often used to describe biochemical substances.For example, many bacterial exotoxins are thermolabile and can be easily inactivated by the application of moderate heat.

Enzymes are also thermolabile and lose their activity when the temperature rises.

Loss of activity in such toxins and enzymes is likely due to change in the three-dimensional structure of the toxin protein during exposure to heat.

In pharmaceutical compounds, heat generated during grinding may lead to degradation of thermolabile compounds.

This is of particular use in testing gene function. This is done by intentionally creating mutants which are thermolabile. Growth below the permissive temperature allows normal protein function, while increasing the temperature above the permissive temperature ablates activity, likely by denaturing the protein.

Thermolabile enzymes are also studied for their applications in DNA replication techniques, such as PCR, where thermostable enzymes are necessary for proper DNA replication. Enzyme function at higher temperatures may be enhanced with trehalose, which opens up the possibility of using normally thermolabile enzymes in DNA replication.


Warm-blooded animal species can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The only known living homeotherms are birds and mammals, though ichthyosaurs, plesiosaurs and dinosaurs are believed to have been homeotherms. Other species have various degrees of thermoregulation.

Animal body temperature control varies by species, so the terms "warm-blooded" and "cold-blooded" (though still in everyday use) suggest a false idea of there being only two categories of body temperature control, and are no longer used scientifically.

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