Ectothermy

The evidence for ectothermy is also weak, although it has been claimed by some researchers that the absence of nasal passages large enough to house respiratory turbinate bones is the 'Rosetta Rock' that demonstrates dinosaurian ectothermy.

From: Encyclopedia of Geology , 2005

Endotherm☆

Marta G. Labocha , Jack P. Hayes , in Encyclopedia of Ecology (Second Edition), 2019

Energetic Influence of Endotherms on Ecosystems

Endothermy is more energetically costly than ectothermy. Because endotherms employ more free energy than ectotherms, the same amount of food can maintain a larger population of similar-sized ectotherms than endotherms. Moreover, xc% or more of the energy assimilated by endotherms is converted to heat, then merely a small percentage of the nutrient energy fatigued from the ecosystem by endotherms is converted to biomass (i.e., to grow tissue or produce offspring). In other words, endotherms have lower product efficiency than ectotherms.

Because of the high energetic toll of endothermy, endothermic carnivores require higher prey densities than ectothermic carnivores. In systems with low primary productivity they volition be absent or rare. Even folivorous endotherms may exist absent in habitats with extremely low productivity.

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Heterotrophic Energy Flows

Kenneth A. Nagy , in Encyclopedia of Energy, 2004

three.5 Rates of Feeding

Feeding rates that are really achieved in the field are influenced non only by intrinsic factors, such equally endothermy or ectothermy, activeness level, reproductive status, and digestive physiology, only as well by extrinsic factors, such every bit flavor, food availability, competitive and social interactions with other individuals of the same or other species, and reduction of feeding opportunities due to the presence of predators or inclement ecology conditions (e.g., excessive midday heat, darkness, rainstorms). Over a period of several days or weeks, animals are usually able to compensate for short-term difficulties in getting food and are able to obtain approximately plenty food to maintain energy balance. Trunk size is the nigh important determinant of feeding charge per unit; bigger animals consume more food than do smaller animals. Still, this is non a 1-to-i human relationship. An animal weighing ten times more than another creature does not swallow 10 times more food each twenty-four hours; rather, it eats merely approximately 5 to half-dozen times more, in accordance with the scaling of metabolic rate. When differences in body mass are deemed for, feeding rates still vary by more than 25 times among species during their activeness seasons. For example, a representative insectivorous lizard that weighs 100 g consumes about 0.seven one thousand of food (dry thing intake [DMI]) per mean solar day, whereas a typical 100-g bird living in a marine habitat consumes about eighteen k of dry out affair per day ( Tabular array Ii). Both may be living in the same seashore habitat, eating a like diet (arthropods), and maintaining the same body temperature during the day, merely the cadger'south metabolic energy expenditures over a 24-h period are just about iv% those of the bird, and so the cadger's food needs are proportionately lower as well. Within diverse groups of endothermic vertebrates, there is a 230% variation in feeding rates amongst same-sized animals. Desert-dwelling mammals and birds have relatively depression feeding rates, and marine birds have relatively high feeding rates. Desert mammals and birds are known to have lower metabolic rates (basal and field) than do related species living in other habitats, so their food requirements should be correspondingly lower. The high feeding rates of herbivorous mammals, relative to other mammals, most likely result in function from their depression MEE (Tabular array I), meaning that relatively more than plant food must be eaten to obtain a given daily rate of metabolizable energy intake.

Table II. Feeding Rates of Wild Vertebrates, Summarized in Allometric Equations Derived from Field Measurements of Energy Metabolism, for Diverse Groups of Mammals, Birds, and Reptiles

Animate being group a b Expected feeding charge per unit (g dry matter/day) for a 100-g animal
Eutherian mammals (58 species) 0.299 0.767 10.2
Marsupial mammals (twenty species) 0.483 0.666 ten.4
Herbivorous mammals (26 species) 0.859 0.628 15.five
Desert mammals (25 species) 0.192 0.806 7.9
Birds (95 species) 0.638 0.685 xv.0
Passerine birds (39 species) 0.630 0.683 xiv.6
Desert birds (15 species) 0.407 0.681 9.4
Marine birds (36 species) 0.880 0.658 eighteen.two
Reptiles (55 species) 0.011 0.920 0.77
Herbivorous reptiles (9 species) 0.033 0.717 0.91
Insectivorous lizards (27 species) 0.011 0.914 0.73

Note. The equations have the following course: y=axb , where y=feeding rate (in grams dry matter consumed per day), x=body mass (in grams), a is the intercept at body mass=1 g, and b is the allometric gradient.

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Thermoregulation in Animals: Some Fundamentals of Thermal Biology☆

Udo Gansloßer Gianna Jann , in Encyclopedia of Environmental (Second Edition), 2019

Evolutionary Considerations

This already leads to the question of phylogenetic development of thermoregulation. In society to understand this tradition, it may exist helpful to look at some taxa that are somewhere in between ecto- and endothermy. Some insects, for example, large, nocturnal moths (Sphingidae), bees, dragonflies or wasps, are able to regulate thoracic and in some cases also abdominal temperature. However, this endothermy is only achieved when they are active, they perform wing-movements, called shivering, decoupled from flying. Moths at least, due to their hairy scales, have values of thermal conductance like to birds and mammals, and they tin keep large differences between Ta and Tb (some Due north American moths tin fly at a core trunk temperature of around 30°C at Ta   =   0°C). Notwithstanding, these small animals cannot reach continuous endothermy like to same-sized vertebrates if they are not active day and night (which insects are non).

Larger species in the continuum between ecto- and endothermy are found among fish. Bluefin tuna (Thunnus thymnus) of 200–350   kg tin can uphold temperature differences of upwardly to twenty°C. In these fish, reverse to "cold- bodied" species, we find large amounts of cherry (=   aerobic) skeletal muscles near the body core (along the vertebral column) instead of under the peel. Besides a high BMR, and a countercurrent rut-exchanger in the circulatory organisation are further characteristics of these endothermic fish. Besides scarlet skeletal muscles, endothermic fish also have local estrus sources in stomach, gut and liver tissue. Besides (again kept upwardly by retia mirabilia   =   countercurrent heat exchangers) in the eyes and the brain of warm-blooded fish such as Mako sharks (Isurus oxyrhynchus) there is a temperature difference to the environment of >   5°C. Nevertheless, in that location are no heat generating tissues in the sharks, heads, instead warm blood from abdominal crimson muscles is transported directly to the middle and encephalon regions. In some bony fish (e.chiliad., Swordfish, Xiphias gladius) contrary to sharks, eye muscles are working as local heat sources, the whole complex of heater muscles, brain and eyes is thickly isolated in fat, and temperature differences of up to 14°C tin exist upheld between brain and surrounding water.

There is besides prove for mechanisms of physiological and behavioral temperature command in these fish. Also some python snakes and Leatherback turtles (Dermochelys coriacea) are able to obtain a certain command over their body temperatures.

Thus, the question of when and why endothermy could evolve has to be approached very broadly. The adaptive value of real endothermy and effective thermoregulation could take been to allow a decrease in torso size at a constant body temperature. This would not only take immune an increase in activity, but besides an increase in reproduction. However, endothermy too is plush, and thus certain preconditions had to be met before achieving it. On the biochemical level, changes in membrane permeability for ions, are discussed as necessary preconditions for increasing metabolic rates. On the organismic level, it seems plausible at least in the evolution of mammals to assume that the large (upward to 250   kg) therosaurus reptiles, the ancestors of mammals, had, due to their large size, accomplished a sure caste of thermal independence, and that a whole array of morphological and physiological changes (development of isolating fur, increasing efficiency of ventilation by developing a bony palate and diaphragm, etc.) then immune the transition from big reptile (with then chosen inertial homeothermy, which means they merely were as well large to lose enough heat for existence poikilotherms) to small mammal with an active, regulatory endothermy.

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Physiological Ecology

B.Yard. McNab , in Encyclopedia of Ecology, 2008

Physiological ecology deals with the adjustments, that is, the adaptations that organisms make to the physical and biological environments in which they alive. They include the modification of rates of metabolism; the differential employ of ectothermy and endothermy; the ability to remainder salt and water budgets in terrestrial and aquatic environments; the adjustment of gas exchange in hypoxic, hyperbaric, and hypobaric environments; and the evolution of photosynthesis relative to h2o availability and the gas composition of the atmosphere. Geographical distributions may be express by common cold in montane and polar environments, water presence or absence in terrestrial regions, and the abundance of oxygen and carbon dioxide in aquatic and terrestrial environments, every bit well equally the presence and the absence of competitors and selective food types. Many aspects of physiological ecology are associated with the ability to maintain an adequate internal physiological land, which ultimately must be paid for by the acquisition of resources from the environment and by acceptable energy expenditures. If this cannot exist accomplished while maintaining a standard physiological country, many species reduce energy expenditure, such as entering torpor, but ofttimes with consequences for their life history, as with a reduction in reproductive output.

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Reptiles, Biodiversity of

F. Harvey Pough , in Encyclopedia of Biodiversity (2nd Edition), 2013

Glossary

Ancestral

Describes a grapheme or character state of the organism being considered that retains the primitive condition for its evolutionary lineage.

Derived

Describes a character or character state of the organism being considered that has changed from the ancestral status for its evolutionary lineage.

Ectothermy

Deriving the energy needed to raise body temperature from sources outside the body.

Endothermy

Deriving the energy needed to raise body temperature from within the body – i.e., from metabolic rut production.

Heliothermic

Regulating body temperature primarily by moving betwixt sun and shade.

Operative temperature

A measure of environmental temperature that combines the furnishings of heat exchange via radiation, convection, with metabolic heat production, and evaporative estrus loss.

Paraphyletic

A taxonomic grouping of animals that does not run into the cladistic criterion of including the most recent common ancestor and all its descendants.

Sis group

The evolutionary lineage nigh closely related to the one existence discussed.

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Vertebrates, Overview

Carl Gans , Christopher J. Bong , in Encyclopedia of Biodiversity (Second Edition), 2001

Glossary

Chordate

A member of the group Chordata. The Chordata includes the about recent common ancestor of tunicates and cephalochordates and all of that antecedent's descendants. Tunicates, lancelets, hag-fishes, and vertebrates are all chordates.

Ectoderm

An embryonic tissue that provides the hereafter exterior layer of the fauna.

Ectothermy

A method of body temperature control in which the animal utilizes external sources for gaining and giving up oestrus, thus achieving temperature command without affecting metabolic rate.

Endothermy

A method of torso temperature control in which the animal modifies its metabolic rate to achieve the desired torso temperature.

Neural crest

An embryonic tissue intermediate between neurectoderm and ectoderm, with cells migrating widely to their last destination. This tissue gives rise to anterior skeletal elements, many portions of the futurity head and pharynx, and all pigment cells. Sometimes also referred to as mesectoderm.

Neurectoderm

An embryonic tissue that gives rise to the central tube of the nervous system.

Notochord

A strong, flexible, longitudinal rod running along the middorsal portion of the chordate body. It is situated dorsal to the coelom and ventral to the central tube of the nervous organisation.

Pharynx

The inductive portion of the gastrointestinal tract, characterized by lateral buds that provide skeletal back up for the gill region.

Tuberculum interglenoideum

An inductive projection of the commencement (cervical) vertebra in salamanders. The tuberculum interglenoideum bears articular facets that insert into the foramen magnum of the skull and provide additional joint points betwixt the skull and the vertebral cavalcade.

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Reptiles, Biodiversity of

F. Harvey Pough , in Encyclopedia of Biodiversity, 2001

2.C. Active Reptiles and the Development of Endothermy

In an ecological context, the generalization that reptiles are ectotherms with low metabolic rates and depression levels of activity applies to extant species, although some modifications of that characterization volition be addressed in subsequent sections. In an evolutionary context, yet, the generalization is obviously simulated because birds are reptiles and they are endotherms with high metabolic rates. Clearly the reptilian lineage has a capacity for endothermy that is barely expressed in nonavian reptiles. An examination of the development of endothermy explains that dichotomy and emphasizes how tightly anatomical and physiological characteristics are linked to thermal ecology.

Ectothermy is the ancestral status for vertebrates, and the derived condition of whole-torso endothermy has evolved at least twice, in mammals and in birds. In a broader view, regional endothermy has evolved independently in sharks, tunas, and billfishes, and whole-body endothermy may have been characteristic of pterosaurs (flying archosaurian reptiles of the Mesozoic) and some lineages of dinosaurs.

Ectotherms and endotherms have very unlike relationships to their concrete environments: Ectotherms rely primarily on behavioral thermoregulation to raise their body temperatures considering they have depression metabolic rates, and the absence of insulation facilitates uptake of estrus from the surround. In dissimilarity, endotherms use internal heat production from high metabolic rates to regulate body temperature, and they require insulation to retain metabolic heat in their bodies.

The evolutionary transition from ectothermy to endothermy is impeded by a Catch-22—adding insulation to an ectotherm impedes its behavioral thermoregulation, but in the absenteeism of insulation any heat produced by increasing its resting metabolic rate is lost to the environment. The solution to this paradox lies in finding a basis for the evolution of insulation or the evolution of an increased metabolic rate that does not depend on the preexisting occurrence of the other character.

Mammals are the sis group of reptiles (including birds) and the common ancestor of mammals and reptiles was ectothermal. Thus, the evolution of endothermy in the mammalian lineage may provide a model for the evolution of endothermy amidst reptiles. Anatomical changes seen in the fossil record of predatory synapsids, the sister grouping of mammals, strongly support the hypothesis that the initial stride in the evolution of mammalian endothermy was selection for increased locomotor capacity. These changes include the development of a cursorial body course, changes in the rib cage that suggest the presence of a diaphragm, and increased surface area in the nasal passages to warm and humidify large volumes of air. Increasing levels of locomotor activity require an increase in metabolic rate, and internal oestrus production would create a selective value for insulation (see Pough et al., 1999, Chapters 4 and xix, for details and references).

Some features of the fossil record of birds suggest that a similar scenario can be applied to the evolution of avian endothermy, but others announced to contradict that interpretation. Like the predatory synapsids, the pocket-sized maniraptoran dinosaurs that form the sister group of birds appear to have been armada-footed predators that pursued their casualty. That estimation suggests that these dinosaurs may have evolved the metabolic capacity for endothermy just as synapsids did, and if the recent written report of feathers in fossil dinosaurs is right, information technology would support that interpretation. However, 2 lines of evidence cast doubt on the hypothesis that the dinosaurian precursors of birds had high metabolic rates. Test of an excellently preserved specimen of the minor dinosaur Sinosauropteryx suggests that information technology had simple septate lungs that were ventilated by a pistonlike movement of the liver like those of living crocodilians. Lungs of this sort would non support high rates of oxygen consumption. That interpretation is supported past CAT scans of the nasal passages of dinosaurs that reveal no trace of modifications of the nasal passages to warm and humidify large volumes of air (meet Pough et al., 1999, Chapter 13, for details and references).

This evolutionary perspective emphasizes intricate interconnections amidst the anatomical and physiological characters of extant reptiles and their ecology and behavior, as well as the evolutionary chapters for breaking those links. An examination of living reptiles reveals additional connections amid anatomy, physiology, ecology, and behavior.

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Thermoregulation, Performance, and Energetics

Laurie J. Vitt , Janalee P. Caldwell , in Herpetology (Third Edition), 2009

Synthesis

Water balance, respiration, thermoregulation, and energetics are tightly linked in ectothermic vertebrates. For amphibians, rates of water loss can be extremely high, and most species select microhabitats that minimize water loss. Such microhabitats are usually relatively cool or enclosed. Almost amphibians take in large amounts of water and produce dilute urine, although there are some notable exceptions. 1 outcome of action at depression temperatures and of ectothermy in general is that metabolic rates are low (no metabolic cost of heat production). For many reptiles, activeness occurs at high trunk temperatures, but during periods of inactivity, trunk temperatures are much lower. Reptiles in general take in much less h2o than amphibians and are capable of retaining more of what they take in. As a result, they produce relatively concentrated urine, often including uric acid equally a concentrated waste material product. Similar amphibians, metabolic rates of reptiles are low because at that place is no toll of estrus production (with a few exceptions); however, overall, reptilian metabolic rates are higher than those of amphibians. Because nearly all energy caused is directed into low-cost maintenance, growth, reproduction, and storage, amphibians and reptiles can occur at high densities in environments that limit densities of homeothermic vertebrates that expend much of their ingested energy on heat production. Amphibians and reptiles can also persist through long periods of energy shortages.

Although the interplay between temperature, water economy, and energetics is well documented from a physiological perspective, the correlated evolution of these of import physiological traits is just beginning to be appreciated. The evolutionary history of geckos in the genus Coleonyx exemplifies the possibilities an evolutionary approach to the interplay betwixt water economy, temperature, and metabolism can accept in agreement physiological processes. The antecedent of Coleonyx in North America appears to have had relatively depression torso temperature (26°C), high evaporative water-loss rate (2.5 mg/g/hr), and a low standard metabolic rate (0.07 mg/g/hour) and lived in a relatively moist, forested habitat. Two extant species, C. mitratus and C. elegans, retain these characteristics, and they are members of the earliest lineage (Fig. seven.27). During the evolutionary history of Coleonyx, species moved into more arid environments, ultimately into the deserts of Due north America. Correlated with that shift are increases in body temperatures (above 31.0°C), reductions in evaporative water loss (< 0.1 mg/1000/60 minutes), and increases in standard metabolic rate (> 0.xv mg/g/hr). In this instance, the fix of predictions based on a shift from mesic to xeric habitats holds true, indicating that these are indeed adaptations to life in specific environments. Finally, this example points to the importance of maintaining physiological homeostasis for amphibians and reptiles occupying diverse environments.

Figure 7.27. An hypothesis of physiological–ecological character country evolution in lizards in the genus Coleonyx. Four equally parsimonious hypotheses were found based on physiological data lonely, but when coupled with biogeographic information, the other three were rejected. EWLR = evaporative water-loss charge per unit, TP = temperature preference, SMR = standard metabolic charge per unit, H = high, Fifty = low. Solid bars indicate acquisition of a new state, and crosshatched bars indicate independent evolution of a derived state. The genera Eublepharis, Hemitheconyx, and Holodactylus make up the outgroup. Presumably, a shift occurred in the selective regime (SR) from an energy-rich to an energy-poor microhabitat during the evolutionary history of Coleonyx.

 Adjusted from Punch and Grismer, 1992.

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H2o Residual AND THE PHYSIOLOGY OF THE AMPHIBIAN TO AMNIOTE TRANSITION

Karen L.M. Martin , Kenneth A. Nagy , in Amniote Origins, 1997

CONCLUSION

Gans and Pough (1982, p. 8 ) wrote, "Nosotros advise that the absenteeism of a unifying morphological scheme, rather than beingness an incidental by-production, is an of import aspect of the reptilian grade. The lives of Recent reptiles are shaped by a set up of shared characteristics that need not produce obvious structural features." The features they propose as definitive are physiological features: The amniotic egg, ectothermy, depression metabolic rate (compared with endotherms), reliance on anaerobiosis for action, and behavioral temperature regulation. We propose that a similar case may be fabricated for the traits that unite the "amphibian" course: Great morphological diversity with no obvious unifying morphological characters, simply physiological features that set them apart from the bony fishes and from the reptiles. These features include increased variability or relaxed regulation of body hydration levels, high cutaneous permeability to water, relatively low body temperatures for activity, and extremely low metabolic requirments. Pough (1983) described amphibians every bit being "well known for their mostly quiescent and inconspicuous lifestyles and for their low almanac use of free energy." Bartholomew (1982, p. 344) noted "nowadays-day members of the form Amphibia are morphologically different from the Paleozoic forms which were transitional between fish and reptiles. Even so, they demonstrate clearly the loftier level of success with which animals are sometimes able to exploit a harsh and demanding environment, despite physiological adjustments that announced at showtime glance to exist small-scale and ineffective."

Initially nosotros stated that one of the basic issues in comparison amphibians and reptiles is their water budget, and that this affects the whole fauna's physiology in a variety of means. The synergistic effects of providing a dry out outer surface are the possibility of warmer trunk temperatures, higher metabolism, and increased activity and growth rates. This could pb to increased tolerance of high temperatures but perhaps decreased tolerance of low temperatures.

What are the advantages of remaining an amphibian, and not completing the transition to country? The low energy strategy enables amphibians to survive with a very brusk growing season (Pough, 1983). The geographic range may exist limited only by the duration of development from larva to developed for hibernation or aestivaton (Pinder et al., 1992). Some species of the desert or in the arctic may be inactive as much as half dozen–10 months of the year, a life-style that does agree a sure appeal. With a very low metabolic rate, amphibians can survive on a limited nutrient source. Adult Rana muscosa can survive an eight month inactive period with only 4–half-dozen% torso fat (Bradford, 1983). In addition, adults and larvae do not compete for food; therefore, more members of the population may be supported at one time in the same habitat. Temperature choice past habitat is reflected in the biogeography of extant amphibians, which extend to college altitude and latitude than reptiles; amphibians show greater tolerance to colder climates than reptiles (Pinder et al., 1992). Amphibians tin be agile at much cooler torso temperatures than reptiles (Hutchison and Dupre, 1992); for example, there are observations of frogs swimming under water ice (as practise some turtles) and salamanders walking in snow. Several species of frogs tolerate being frozen during winter (Storey and Storey, 1986). By becoming inactive, amphibians can tolerate broad fluctuations in internal conditions during drought or very cold conditions.

By releasing the constraints of the hydric niche, the primeval amniotes increased body temperature and metabolic rate, simply in so doing may take limited themselves to a more than narrow thermal niche. In essence, the reptile past comparing has a higher metabolism and a more than narrowly regulated, homeostatic internal milieu that enables it to be more than active than an amphibian in a much wider range of terrestrial habitats. In this fashion, reptiles take obtained greater independence from the hydric environment by means of a more fixed internal milieu than was the case in anamniote tetrapods.

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Thermoregulation in Animals

U. Ganslosser , in Encyclopedia of Ecology, 2008

Adaptation to Cold Seasons

In temperature-conformic ectotherms that are generally unable to increase their temperatures by internal ways, torpor or hibernation in wintertime or estivation in hot, dry summers (the latter being shown, for example, by lungfish or desert snails) is superficially similar to torpor in endotherms; however, external energy sources are needed to end this country. In insects, a special course of arrested development chosen diapause, triggered by combination of hormonal, photoperiodic, and nutritional factors, is a common strategy. Heterotherm animals are also characterized by changing their body temperatures and basal metabolism according to external conditions. Torpor is characterized by a low body temperature and depression BMR. In and so far, it is probably a variation of temperature conformity instead of regulation. All the same, there is an important deviation betwixt heterothermy and ectothermy: heterotherms are capable of increasing torso temperatures (more often than not by increasing BMR) by their ain, internal ways, whereas ectotherms need some external source of warmth or other free energy for this waking upwardly. Thermoregulation is never totally switched off during torpor; instead, the set bespeak for the onset of thermoregulatory activities is only temporarily lowered. Heterothermy has long been regarded equally a primitive character of animals non all the same set for real homeothermy, but information technology is a finely tuned adaptive strategy.

Torpor is further divided by the regularity and seasonality of its occurrence and triggering mechanisms. Long torpor, generally hibernation, is often extended for several months and is characterized by a lowering of body temperatures nether ten   °C, and metabolic rate is about 5% of BMR during agile phases. Still, even deep hibernating torpor in all species studied and then far is interrupted past curt periods of activity at normal body temperature, and these intervals are internally triggered.

Big mammals, such as bears, also get into torpor. However, this is only shallow torpor; with a reduction of their trunk temperatures past near 5   °C, center rates and metabolic rates are reduced by up to 30%. Nevertheless, hibernating bears can stay in their dens for several months, and their energy needs are covered by burning fat. Some other physiological adaptations, such as recycling urea into essential amino acids, and well-nigh probably also calcium storage and recycling, have been developed in these big carnivores as well. Large bears are non the only carnivores capable of larger torpor. Raccoons and raccoon dogs, at least in parts of their range, too enter torpor for several weeks.

Brusk-term torpor of several days or even daily torpor is much more widespread also among larger mammals – both American and European badgers enter daily or short-term torpors, with torso temperatures of about 28   °C. Daily or short-term torpor, in general, reduces trunk temperatures to c. x–thirty   °C; metabolic rates are reduced to values of nigh 30%. Most mammal species entering daily torpor are small and nocturnal such as pocket-sized marsupials (dasyurids, petaurids, and didelphids), mouse lemurs, hedgehogs, tenrecs, shrews, or bats. However, in most all these taxa (except primates), we also detect species exhibiting deep torpor with torso temperatures around 5   °C and durations of 10 days to several months (marsupials: Cercatetus nanus, a burramyid, reaches values of 2% of its normal BMR for several weeks, European hedgehog: energy of about 4% normal rate, T b c. 5   °C for at least ten days, bats: Myotis −2 to +5   °C T b, energy most 1% BMR, etc.). Heterothermy among birds is dissimilar in several aspects: it generally occurs during the night, T b is lowered by c. 5   °C, it also occurs in rather large species such every bit turkey vultures, just, and this is a phenomenon whose adaptive significance is however unclear, energetic demand is mostly higher than BMR. Only few species, such as some members of Colibri, tend to reduce T b to values below 18   °C, some below 10   °C, and merely one species of bird, a nightjar from Due north America, Phalaenoptilus nuttallii, goes into torpor for several days in a row, and besides reaches a T b as low every bit six   °C. It is not yet totally articulate, neither for birds nor for mammals, which physiological mechanisms are responsible for reawakening. One hypothesis assumes a combination of depression blood pressure and accumulation of toxic metabolic products in the blood to cleanse the blood from these waste products, another assumes a biological clock (possibly even the circadian one which is likewise beingness slowed by lower torso temperatures). In any example, the end of a torpor phase is accomplished past active warming, the velocity of which mostly depends on body size: small-scale animals of nigh 10   1000 trunk weight can gain nearly 1   °C per min, species of about 1   kg only accomplish 0.5   °C min−1, and species over x   kg are real wearisome wakers, with increases of about 0.one   °C min−1. This is a constraint on the capability for deep torpor in large species.

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