The ectotherms They are animals whose body temperature depends directly and mainly on the ambient temperature. This implies that little or none of your body temperature is due to metabolism. Therefore, to maintain their temperature within a physiologically appropriate range, they must gain or dissipate heat from the medium..
The opposite condition of being ectothermic is being endothermic. All birds and mammals are categorized as endotherms. All aquatic amphibians and invertebrates, as well as the vast majority of reptiles (excluding birds), and terrestrial fish and invertebrates, are categorized as ectotherms..
All plants could also be considered ectotherms, although this qualification is alien to botany. From a thermal perspective, plants are called macrotherms if they live in warm environments (> 18 ° C every month), mesotherms if they live in temperate environments (> 22 ° C, warmest month; 6-18 ° C, coldest month ), or microtherms if they live in cold environments.
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Endotherms are animals whose body temperature is regulated internally by their metabolism and not externally by the environment. In general, endotherms are homeothermic, that is, they have relatively constant body temperature, in contrast to poikilotherms, which have highly variable body temperature.
Ectotherms are also often called poikilotherms (from the Greek: poikilos, changing; thermos, heat). In one case, the temperature dependence of the medium is emphasized. In the other, the variability of body temperature. The first term is preferable because ectotherms can be homeotherms if the temperature of the medium is constant..
Endotherms and ectotherms are also often called, respectively, warm and cold-blooded animals. This use is not recommended because there are ectotherms that keep their body temperature as high as that of many endotherms. Of these animals it cannot be said that they are cold-blooded.
Heterotherms are ectotherms that are partially homeotherms. During periods of activity, they can generate metabolic heat to keep the body temperature of at least part of your body constant. However, during periods of inactivity, they drop their body temperature depending on that of the environment, just like other ectotherms..
Regional heterotherms are endotherms whose body temperature varies substantially between parts of the body..
The endothermic condition makes animals independent of environmental temperature, allowing them to occupy cold terrestrial environments, to remain permanently active to take advantage of feeding and reproductive opportunities, as well as to escape predators.
In the circumpolar regions there are no reptiles, and amphibians and insects are not very diverse and abundant. In these regions it is advantageous and even necessary to be endothermic.
However, endotherms make a very high energy investment to regulate their temperature. By not making this investment, ectotherms have food requirements up to 17 times lower than endotherms of similar body mass.
For this reason, reptiles (excluding birds), amphibians and fish can exploit ecological niches, reserved for organisms with low energy consumption, not available for birds and mammals..
Once they have been able to warm their bodies sufficiently using external heat sources, ectotherms can develop activity levels as high as those of birds and mammals..
The low energy budget of ectotherms allows them: 1) to specialize in scarce foods, increasing their diversity; 2) be successful in environments, such as deserts, in which there is not enough food for most endotherms; 3) have a high reproductive efficiency in relation to food consumption.
Ectotherms raise their body temperature by exposing themselves to direct sunlight (heliothermia) or by coming into contact with substrates (example: rocks) that have been heated by the sun. They lower their body temperature by taking refuge in the shade or by coming into contact with relatively cold substrates.
Their bodies lack thermal insulation (example: feathers, fur), which facilitates heat exchange with the environment.
Among the strategies they can use to regulate the heating produced by sunlight are: 1) direct the orientation (perpendicular, parallel, oblique) of the body with respect to the sun's rays; 2) darken or lighten the color of your skin through the action of chromatophores. Both strategies are particularly common in reptiles..
Ectothermic fish cannot sun themselves to warm themselves, but they can regulate their body temperature by choosing masses or layers of water that have a certain temperature. This often allows them to maintain a constant body temperature (homeothermia) for long periods of time..
Ectotherms can also regulate their temperature through vascular adjustments (altering peripheral circulation), exposing the inner surface of the mouth to air, or losing water through evaporation (tolerating some dehydration). The pineal organs of ectotherms appear to act as light dosimeters for thermoregulation.
Circumpolar and alpine ectotherms face, respectively, ambient temperatures below freezing during winter, or at night.
To survive extreme cold, these animals employ two strategies: 1) avoid freezing their extracellular body fluids, keeping these fluids in a liquid state at temperatures down to -58 ° C (which is known as supercooling); 2) tolerate freezing (down to -3 ° C) of such fluids.
In the first strategy, observed in fish and insects, the blood plasma does not freeze because it contains antifreeze solutes (sugars, such as fructose; derivatives of sugars, such as glycerol; glycoproteins).
In the second strategy, observed in amphibians, the blood plasma is frozen, but the death of the cells does not occur because they contain antifreeze solutes (low molecular weight compounds, glycerol). Although there is freezing of extracellular fluids, there is no freezing of intracellular fluids. If there is, they die.
Ectothermic marine predators (sharks and other fish) are rare at high latitudes, where they are replaced by endothermic marine predators (marine mammals, penguins, auks). In cold waters, ectothermic predators cannot match the activity levels of endothermic predators.
There are primarily ectothermic animals that are heterothermic, that is, they manifest a certain degree of endothermy, either temporary or regional..
Some arctic insects are strict ectotherms when on the ground. However, in order to take flight, these insects must previously warm up the muscles that move the wings, which they achieve by moving them repeatedly. During flight, these insects are effectively endotherms. They even need to dissipate heat so as not to overheat.
When they are coiled around their eggs incubating them, female Indian pythons raise their body temperature by shivering. In this way, they heat the eggs, facilitating the development of embryos and accelerating hatching..
Sharks of the Lamnidae family, swordfish or tunas are regional heterotherms. The transfer of heat generated by the musculature through blood countercurrent mechanisms allows them to raise the temperature of the brain, viscera and other muscles. This improves their aerobic swimming capacity and makes them more effective predators..
Crocodiles, such as Crocodylus porosus, they are the largest terrestrial ectotherms. Its optimal body temperature is 30-33 ºC, which, like other reptiles, keep moving between sunny and shady places. A particular strategy for crocodiles to reduce their body temperature is to keep their mouth wide open for hours..
The European Viper, Viper berus, it is a poisonous snake whose distribution reaches the Arctic Circle. To allow the incubation of the eggs at low temperatures, this snake is viviparous. During the summer, to maintain adequate body temperatures for predation and reproduction, these snakes expose themselves as much as they can to sunlight.
In Alaska, the amphibian Sylvatica frog survives temperatures down to -16 ° C. This is due to high concentrations of antifreeze substances present in your blood during winter. These substances include glucose and urea. To reduce icing, this frog also dehydrates during winter.
Arctic fish of the Gadidae family and Antarctic fish of Nototheniidae have independently evolved essentially identical cryoprotective substances (glycoproteins). This represents a remarkable case of adaptive convergence to face similar climatic conditions..
The bee (Apis mellifera) and other social insects are homeothermic in their nests. To this end: 1) they are placed in thermally favorable places and structured to favor passive heating and cooling; 2) they flap their wings in coordination to heat them through muscle thermogenesis, or to cool them through air circulation and evaporation.
The mosquitos (Aedes, Anopheles) Are ectotherms adapted to hot climates. They are lethal because they transmit diseases such as malaria, yellow fever, chikungunya, dengue and Zika. Due to climate change, by 2050 they will have expanded their distribution in temperate zones, exposing 50% of humans to these diseases.
In Alaska, the beetle Cucujus clavipes, Thanks to the antifreeze solutes of its hemolymph, it resists winter temperatures of -58 ° C. In the laboratory, it has been established that this beetle could withstand temperatures below -150 ºC, which do not exist on Earth..
At these temperatures, the body fluids of this insect reach the state of vitrification.
In their adult form, tapeworms, such as Taenia solium (had beef) and Taeniarhynchus saginatus (pork tapeworm), are intestinal parasites that, because they lack a digestive system, are totally dependent on the human host for their nutrition.
Inside the intestine, these tapeworms maintain their constant temperature (37 ºC), which is why they are homeotherms..
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