View source for Nearctic realm

{{Short description|Biogeographic realm encompassing temperate North America}}
{{For|the thoroughbred racehorse|Nearctic (horse)}}
{{more footnotes|date=November 2013}}
[[Image:Ecozone Nearctic.svg|thumb|320px|The Nearctic realm (in green)]]

The '''Nearctic realm''' is one of the eight [[biogeographic realm]]s constituting the Earth's land surface.

The Nearctic realm covers most of [[North America]], including [[Greenland]], [[Central Florida]], and the highlands of [[Mexico]]. The parts of North America that are not in the Nearctic realm include most of coastal Mexico, southern Mexico, [[southern Florida]], coastal central [[Florida]], [[Central America]], [[Bermuda]] and the [[Caribbean]] islands. Together with [[South America]], these regions are part of the [[Neotropical realm]].

==Major ecological regions==
[[File:Terrestrial ecoregions USA CAN MEX.svg|thumb|right|600px|Ecoregions of the Nearctic realm, color-coded by [[ecoregion]]. Note that much of the coast, south, and southwest Mexico and the southern half of Florida in the United states are considered part of the [[Neotropic realm]].]]

The [[World Wildlife Fund]] (WWF) divides the Nearctic into four [[bioregion]]s, defined as "geographic clusters of ecoregions that may span several habitat types, but have strong biogeographic affinities, particularly at taxonomic levels higher than the species level (genus, family)".

===Canadian Shield===
The [[Canadian Shield]] bioregion extends across the northern portion of the continent, from the [[Aleutian Islands]] to [[Newfoundland and Labrador|Newfoundland]]. It includes the Nearctic's [[Arctic Tundra|arctic tundra]] and [[boreal forest]] ecoregions.

In terms of [[floristic province]]s, it is represented by part of the Canadian Province of the [[Circumboreal Region]].

===Eastern North America===

The Eastern North America bioregion includes the [[temperate broadleaf and mixed forests]] of the Eastern United States and southeastern Canada, the [[Great Plains]] [[temperate grasslands, savannas, and shrublands|temperate grasslands]] of the central U.S. and south-central Canada, the [[temperate coniferous forest]]s of the southeastern U.S., including [[central Florida]]. In terms of [[floristic province]]s, it is represented by the [[North American Atlantic Region]] and part of the Canadian Province of the [[Circumboreal Region]].

===Western North America===
The Western North America bioregion includes the temperate coniferous forests of the coastal and mountain regions of southern Alaska, western Canada, and the western U.S. from the [[West Coast of the United States|Pacific Coast]] and [[Northern California]] to the [[Rocky Mountains]] (known as the [[Cascadia (bioregion)|Cascadian bioregion]]), as well as the cold-winter intermountain [[deserts and xeric shrublands]] and temperate grasslands and shrublands of the [[Western U.S.]]

In terms of [[floristic province]]s, it is represented by the [[Rocky Mountain Floristic Region|Rocky Mountain region]].

===Northern Mexico===
The Northern Mexico bioregion includes the mild-winter to cold-winter deserts and xeric shrublands, warm temperate and subtropical pine and [[Madrean pine–oak woodlands|pine-oak forests]], and Mediterranean climate ecoregions of the [[Mexican Plateau]], [[Baja California peninsula]], and the [[southwestern U.S.]], bordered to the south by the [[Neotropical]] [[Trans-Mexican Volcanic Belt]].<ref>{{Cite web |title=Ecoregions 2017 © |url=https://ecoregions.appspot.com/ |access-date=2023-01-25 |website=ecoregions.appspot.com}}</ref> This region also includes the only [[subtropical dry broadleaf forest]] in the Nearctic realm, the [[Sonoran–Sinaloan transition subtropical dry forest]].

In terms of [[floristic province]]s, it is represented by the [[Madrean Region]].

==History==
Although North America and South America are presently joined by the [[Isthmus of Panama]], these continents were separated for about 180 million years, and evolved very different plant and animal lineages. When the ancient supercontinent of [[Pangaea]] split into two about 180 million years ago, North America remained joined to [[Eurasia]] as part of the supercontinent of [[Laurasia]], while South America was part of the supercontinent of [[Gondwana]]. North America later split from Eurasia. North America has been joined by land bridges to both [[Asia]] and South America since then, which allowed an exchange of plant and animal [[species]] between the continents, the [[Great American Interchange]].

A former land bridge across the [[Bering Strait]] between Asia and North America allowed many plants and animals to move between these continents, and the Nearctic realm shares many plants and animals with the [[Palearctic]]. The two realms are sometimes included in a single [[Holarctic realm]].

Many large animals, or [[megafauna]], including [[horse]]s, [[camel]]s, [[tapir]]s, [[mammoth]]s, [[mastodon]]s, [[ground sloth]]s, sabre-tooth cats (''[[Smilodon]]''), [[Tremarctinae|short-faced bears]] and the [[American cheetah]], became extinct in North America at the end of the [[Pleistocene]] epoch (ice ages) in what is called the [[Quaternary extinction event]].

==Flora and fauna==

===Flora and fauna that originated in the Nearctic===
Mammals originally unique to the Nearctic include:
* Order [[Primate]]s – the first primate/proto-primate, ''[[Purgatorius]]'', originated in the [[Danian|Early Paleocene]] of the Nearctic.
* Family [[Canidae]] – [[dog]]s, [[Wolf|wolves]], [[fox]]es, and [[coyote]]s.
* Family [[Camelidae]] – [[camel]]s and their South American relatives including the [[llama]]. Now extinct in the Nearctic
* Family [[Equidae]] – [[horse]]s, [[donkey]]s and their relatives. Now only found in the Nearctic as feral horses.
* Family [[Tapiridae]] – [[tapir]]s now extinct in the Nearctic.
* Family [[Antilocapridae]] – last survivor of which is the [[pronghorn]].
* Subfamily [[Tremarctinae]] (short-faced [[bear]]s) – including the giant short-faced bear (''[[Arctodus|Arctodus simus]]''). The only surviving member of the group is the [[spectacled bear]] (''Tremarctos ornatus'') of South America. 

===Flora and fauna endemic to the Nearctic===
Two [[mammal]] families are endemic to the Nearctic, the pronghorns ([[Antilocapridae]]) and the mountain beaver ([[Aplodontiidae]]).<ref>{{cite web | url=https://www.guwsmedical.info/mammals/nearctic.html | title=Nearctic - Mammals | date=22 July 2021 }}</ref> The Holarctic has four endemic families of birds: [[Loon|divers]] (Gaviidae), [[grouse]] (Tetraoninae), [[auk]]s (Alcidae), and the [[waxwing]]s (Bombycillidae). The scarab beetle families [[Pleocomidae]] and [[Diphyllostomatidae]] ([[Coleoptera]]) are also endemic to the Nearctic. The fly species ''[[Cynomya cadaverina]]'' is also found in high numbers in this area.

Plant families endemic or nearly endemic to the Nearctic include the  [[Crossosomataceae]], [[Simmondsiaceae]], and [[Limnanthaceae]].

==See also==
* [[List of ecoregions in Canada (WWF)]]
* [[List of ecoregions in Mexico|List of ecoregions in Mexico (WWF)]]
* [[List of ecoregions in the United States (WWF)]]

== References ==
{{Reflist}}
* Abell, R.A. et al. (2000). ''Freshwater Ecoregions of North America: A Conservation Assessment'' Washington, DC: Island Press, [https://books.google.com/books?id=IpDmnEWoA2oC Freshwater Ecoregions of North America: A Conservation Assessment].
* Flannery, Tim (2001). ''The Eternal Frontier: an Ecological History of North America and its Peoples''. Grove Press, New York.
* Ricketts, Taylor H., Eric Dinerstein, David M. Olson, Colby J. Loucks, et al. (1999). ''Terrestrial Ecoregions of North America: a Conservation Assessment''. Island Press, Washington DC., [https://books.google.com/books?id=DRl_RhheUhQC Terrestrial Ecoregions of North America: A Conservation Assessment].

==External links==
* [https://web.archive.org/web/20150107214750/http://wwf.panda.org/about_our_earth/ecoregions/maps/ Map of the ecozones]
* [http://www.nearctica.com/ Nearctica, The Natural World of North America]
* {{Cite NIE|wstitle=Nearctic Region|short=x}}

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{{Biomes}}
{{Nearctic tropical and subtropical dry broadleaf forest ecoregions}}
{{Nearctic tropical and subtropical coniferous forest ecoregions}}
{{Nearctic temperate broadleaf and mixed forest ecoregions}}
{{Nearctic temperate coniferous forest ecoregions}}
{{Nearctic boreal forest/taiga ecoregions}}
{{Nearctic tropical and subtropical grassland, savanna, and shrubland ecoregions}}
{{Nearctic temperate and subtropical grassland, savanna, and shrubland ecoregions}}
{{Nearctic tundra ecoregions}}
{{Nearctic mediterranean forest, woodland, and scrub ecoregions}}
{{Nearctic desert and xeric shrubland ecoregions}}
{{Nearctic mangrove ecoregions}}
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[[Category:Nearctic realm| ]]
[[Category:Biogeographic realms]]