Nearctic ecozone
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2008-06-17T17:55:21Z
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{{For|the thoroughbred racehorse|Nearctic (horse)}}
The '''Nearctic''' is one of the eight [[Terrestrial ecoregion|terrestrial]] [[ecozone]]s dividing the Earth's land surface.
[[Image:Ecozone Nearctic.svg|thumb|The Nearctic Ecozone]]
The Nearctic ecozone covers most of [[North America]], including [[Greenland]] and the highlands of [[Mexico]]. Southern Mexico, southern [[Florida]], [[Central America]], and the [[Caribbean]] islands are part of the [[Neotropic]] ecozone, together with [[South America]].
==Major ecological regions==
The [[World Wide Fund for Nature]] (WWF) divides the Nearctic into four '''Bioregions''', 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]] 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 United States and south-central Canada, and the [[Temperate coniferous forests]] of the southeastern United States.
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 United States from the Pacific to the [[Rocky Mountains]], as well as the cold-winter intermountain [[deserts and xeric shrublands]] and temperate grasslands and shrublands of the western United States.
In terms of [[floristic province]]s, it is represented by the [[Rocky Mountain Region]].
===Northern Mexico===
The Northern Mexico bioregion includes the mild-winter to cold-winter deserts and xeric shrublands of northern Mexico and the southwestern United States, including the [[Chihuahuan Desert|Chihuahuan]], [[Sonoran Desert|Sonoran]], and [[Mojave Desert|Mojave]] deserts, as well as the [[Mediterranean climate]] [[California chaparral and woodlands]] and the warm temperate and subtropical pine and pine-oak forests, including the [[Arizona Mountains forests]] and the [[Sierra Madre Occidental pine-oak forests|Sierra Madre Occidental]], [[Sierra Madre Oriental pine-oak forests|Sierra Madre Oriental]], and [[Sierra Juarez and San Pedro Martir pine-oak forests|Sierra Juarez and San Pedro Martir]] pine-oak forests.
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 ecozone shares many plants and animals with the [[Palearctic]]. The two ecozones are sometimes included in a single '''[[Holarctic]]''' ecozone.
Many large animals, or [[megafauna]], including [[horse]]s, [[camel]]s, [[mammoth]]s, [[mastodont]]s, [[ground sloth]]s, sabre-tooth cats (''[[Smilodon]]''), the giant short-faced [[bear]] (''Arctodus simius''), and the [[cheetah]], became extinct in North America at the end of the [[Pleistocene]] epoch (ice ages), at the same time the first evidence of humans appeared, in what is called the [[Holocene extinction event]]. Previously, it was believed that the megafaunal extinctions were caused by the changing climate, but many scientists now believe that while the climate change contributed to these extinctions, the primary cause was hunting by newly-arrived humans or, in the case of some large predators, extinction resulting from prey becoming scarce. The [[American bison]] (''Bison bison''), [[brown bear]] or grizzly bear (''Ursus arctos''), and [[elk]] or wapiti (''Cervus canadensis'') entered North America around the same time as the first humans, and expanded rapidly, filling ecological niches left empty by the newly-extinct North American megafauna.
==Flora and fauna==
===Flora and fauna that originated in the Nearctic===
Animals originally unique to the Nearctic include:
*Family ''[[Canidae]]'', [[dog]]s, [[Wolf|wolves]], [[Fox|foxes]], and [[coyote]]s
*Family ''[[Camelidae]]'', [[camel]]s and their South American relatives including the [[llama]]. The last North American Camelids went extinct during the last ice age.
*Family ''[[Equidae]]'', [[horse]]s and their relatives.
*Family ''[[Antilocapridae]]'', which includes the [[pronghorn]]
*Tremarctine, or short-faced, [[bears]], including the extinct giant short-faced bear (''Arctodus simius''). The last remaining member of the group is the [[spectacled bear]] (''Tremarctos ornatus'') of South America.
*The now-extinct [[American cheetah]] (''Miracinonyx'')
===Flora and fauna endemic to the Nearctic===
One [[bird]] family, the wrentits (''Timaliinae''), is endemic to the Nearctic region. The Holarctic has four endemic families: [[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.
Plants families endemic or nearly endemic to the Nearctic include [[Crossosomataceae]], [[Simmondsiaceae]], and [[Limnanthaceae]].
==Nearctic Terrestrial Ecoregions==
{{Nearctic tropical and subtropical dry broadleaf forests}}
{{Nearctic tropical and subtropical coniferous forests}}
{{Nearctic temperate broadleaf and mixed forests}}
{{Nearctic temperate coniferous forests}}
{{Nearctic boreal forests/taiga}}
{{Nearctic tropical and subtropical grasslands, savannas, and shrublands}}
{{Nearctic temperate and subtropical grasslands, savannas, and shrublands}}
{{Nearctic tundra}}
{{Nearctic mediterranean forests, woodlands, and shrub}}
{{Nearctic deserts and xeric shrublands}}
{{Ecozones}}
{{Terrestrial_biomes}}
==External links==
*{{commons|Nearctic}}
*[http://www.panda.org/about_wwf/where_we_work/ecoregions/maps/index.cfm Map of the ecozones]
*[http://www.nearctica.com/ Nearctica, The Natural World of North America]
==References==
* 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.
[[Category:Ecozones]]
[[Category:Biogeography]]
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[[pl:Kraina nearktyczna]]
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