Editing Endotherm (section)

==Pros and cons of an endothermic metabolism==
The major advantage of endothermy over ectothermy is decreased vulnerability to fluctuations in external temperature. Regardless of location (and hence external temperature), endothermy maintains a constant core temperature for optimal enzyme activity.

Endotherms control body temperature by internal homeostatic mechanisms. In mammals, two separate homeostatic mechanisms are involved in thermoregulation—one mechanism increases body temperature, while the other decreases it. The presence of two separate mechanisms provides a very high degree of control. This is important because the core temperature of mammals can be controlled to be as close as possible to the optimal temperature for enzyme activity.

The overall rate of an animal's [[metabolism]] increases by a factor of about two for every {{convert|10|C-change|F-change|0|abbr=on}} rise in [[temperature]], limited by the need to avoid [[hyperthermia]]. Endothermy does not provide greater speed in movement than ectothermy (cold-bloodedness)—ectothermic animals can move as fast as warm-blooded animals of the same size and build when the ectotherm is near or at its optimal temperature, but often cannot maintain high metabolic activity for as long as endotherms. Endothermic/homeothermic animals can be optimally active at more times during the diurnal cycle in places of sharp temperature variations between day and night and during more of the year in places of great [[season]]al differences of temperature. This is accompanied by the need to expend more energy to maintain the constant internal temperature and a greater food requirement.<ref>{{cite book | vauthors = Campbell NA, Reece JB |year=2002 |title=Biology |url=https://archive.org/details/biologyc00camp |url-access=registration |edition=6th |publisher=Benjamin/Cummings |page=[https://archive.org/details/biologyc00camp/page/845 845] |isbn=978-0-8053-6624-2 }}</ref>  Endothermy may be important during reproduction, for example, in expanding the thermal range over which a species can reproduce, as embryos are generally intolerant of thermal fluctuations that are easily tolerated by adults.<ref>{{cite journal | vauthors = Farmer CG | title = Parental Care: The Key to Understanding Endothermy and Other Convergent Features in Birds and Mammals | journal = The American Naturalist | volume = 155 | issue = 3 | pages = 326–334 | date = March 2000 | pmid = 10718729 | doi = 10.1086/303323 | s2cid = 17932602 }}</ref><ref>{{cite journal | vauthors = Farmer CG | title = Reproduction: the adaptive significance of endothermy | journal = The American Naturalist | volume = 162 | issue = 6 | pages = 826–840 | date = December 2003 | pmid = 14737720 | doi = 10.1086/380922 | s2cid = 15356891 }}</ref> Endothermy may also provide protection against [[fungal]] infection. While tens of thousands of fungal species infect insects, only a few hundred target mammals, and often only those with a compromised [[immune system]]. A recent study<ref>{{cite journal | vauthors = Robert VA, Casadevall A | title = Vertebrate endothermy restricts most fungi as potential pathogens | journal = The Journal of Infectious Diseases | volume = 200 | issue = 10 | pages = 1623–1626 | date = November 2009 | pmid = 19827944 | doi = 10.1086/644642 | doi-access = free }}</ref>
suggests fungi are fundamentally ill-equipped to thrive at mammalian temperatures. The high temperatures afforded by endothermy might have provided an evolutionary advantage.

[[Ectotherms]] increase their body temperature mostly through external heat sources such as [[sunlight]] energy; therefore, they depend on environmental conditions to reach operational body temperatures. Endothermic animals mostly use internal heat production through metabolic active organs and tissues (liver, kidney, heart, brain, muscle) or specialized heat producing tissues like [[brown adipose tissue]] (BAT). In general, endotherms therefore have higher metabolic rates than ectotherms at a given body mass. As a consequence they also need higher food intake rates, which may limit abundance of endotherms more than ectotherms.

Because ectotherms depend on environmental conditions for body temperature regulation, they typically are more sluggish at night and in the morning when they emerge from their shelters to heat up in the first sunlight. Foraging activity is therefore restricted to the daytime (diurnal activity patterns) in most vertebrate ectotherms. In lizards, for instance, only a few species are known to be nocturnal (e.g. many geckos) and they mostly use 'sit and wait' foraging strategies that may not require body temperatures as high as those necessary for active foraging. Endothermic vertebrate species are, therefore, less dependent on the environmental conditions and have developed a high variability (both within and between species) in their diurnal activity patterns.<ref name =Hut>{{cite book|vauthors=Hut RA, Kronfeld-Schor N, van der Vinne V, De la Iglesia H |chapter=In search of a temporal niche |title=The Neurobiology of Circadian Timing|year=2012|volume=199|pages=281–304|pmid=22877672|doi=10.1016/B978-0-444-59427-3.00017-4|series=Progress in Brain Research|isbn=978-0-444-59427-3 }}</ref>

It is thought that the evolution of endothermia was crucial in the development of [[Eutheria|eutherian]] mammalian species diversity in the Mesozoic period. Endothermia gave the early mammals the capacity to be active during nighttime while maintaining small body sizes. Adaptations in [[photoreception]] and the loss of UV protection characterizing modern eutherian mammals are understood as adaptations for an originally nocturnal lifestyle, suggesting that the group went through an evolutionary bottleneck (the [[Nocturnal bottleneck|nocturnal bottleneck hypothesis]]). This could have avoided predator pressure from diurnal reptiles and dinosaurs, although some predatory dinosaurs, being equally endothermic, might have adapted a nocturnal lifestyle in order to prey on those mammals.<ref name=Hut/><ref>{{cite journal | vauthors = Gerkema MP, Davies WI, Foster RG, Menaker M, Hut RA | title = The nocturnal bottleneck and the evolution of activity patterns in mammals | journal = Proceedings. Biological Sciences | volume = 280 | issue = 1765 | pages = 20130508 | date = August 2013 | pmid = 23825205 | pmc = 3712437 | doi = 10.1098/rspb.2013.0508 }}</ref>