Nearctic realm

For the thoroughbred racehorse, see Nearctic (horse).

The Nearctic realm

The Nearctic realm is one of the eight biogeographic realms 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, and the Caribbean islands. Together with South America, these regions are part of the Neotropical realm.

Major ecological regions

The World Wildlife Fund (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. It includes the Nearctic's arctic tundra and boreal forest ecoregions.

In terms of floristic provinces, 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 of the central United States and south-central Canada, the temperate coniferous forests of the southeastern United States, including central Florida. In terms of floristic provinces, 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 Coast and Northern California to the Rocky Mountains (known as the Cascadian bioregion), 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 provinces, 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, warm temperate and subtropical pine and pine-oak forests, and Mediterranean climate ecoregions of the Mexican Plateau, Baja California peninsula, and the southwestern United States, bordered to the south by the Neotropical Trans-Mexican Volcanic Belt. 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 provinces, 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 horses, camels, tapirs, mammoths, mastodons, ground sloths, sabre-tooth cats (Smilodon), 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 Primates – the first primate/proto-primate, Purgatorius, originated in the Early Paleocene of the Nearctic.
• Family Canidae – dogs, wolves, foxes, and coyotes.
• Family Camelidae – camels and their South American relatives including the llama. Now extinct in the Nearctic
• Family Equidae – horses, donkeys and their relatives. Now only found in the Nearctic as feral horses.
• Family Tapiridae – tapirs now extinct in the Nearctic.
• Family Antilocapridae – last survivor of which is the pronghorn.
• Subfamily Tremarctinae (short-faced bears) – including the giant short-faced bear (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

One bird family, the wrentits (Timaliinae), is endemic to the Nearctic region. Two mammal families are endemic to the Nearctic, the pronghorns (Antilocapridae) and the mountain beaver (Aplodontiidae). The Holarctic has four endemic families: divers (Gaviidae), grouse (Tetraoninae), auks (Alcidae), and the waxwings (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.

Nearctic terrestrial ecoregions

Nearctic tropical and subtropical dry broadleaf forests ecoregions
Sonoran–Sinaloan transition subtropical dry forest	Mexico

Nearctic tropical and subtropical coniferous forests ecoregions
Bermuda subtropical conifer forests	Bermuda

Nearctic temperate broadleaf and mixed forests ecoregions
Allegheny Highlands forests	United States
Appalachian mixed mesophytic forests	United States
Appalachian–Blue Ridge forests	United States
Central U.S. hardwood forests	United States
East Central Texas forests	United States
Eastern forest–boreal transition	Canada, United States
Eastern Great Lakes lowland forests	Canada, United States
Gulf of St. Lawrence lowland forests	Canada
Middle Atlantic coastal forests	United States
Mississippi lowland forests	United States
New England–Acadian forests	Canada, United States
Northeastern coastal forests	United States
Ozark Mountain forests	United States
Sierra Madre Occidental pine–oak forests	Mexico, United States
Sierra Madre Oriental pine–oak forests	Mexico, United States
Southeastern mixed forests	United States
Southern Great Lakes forests	Canada, United States
Upper Midwest forest–savanna transition	United States
Western Great Lakes forests	Canada, United States
Willamette Valley forests	United States

Nearctic temperate coniferous forests
Alberta Mountain forests	Canada
Alberta-British Columbia foothills forests	Canada
Arizona Mountains forests	United States
Atlantic coastal pine barrens	United States
Blue Mountains forests	United States
British Columbia mainland coastal forests	Canada, United States
Cascade Mountains leeward forests	Canada, United States
Central and Southern Cascades forests	United States
Central British Columbia Mountain forests	Canada
Central Pacific coastal forests	Canada, United States
Colorado Rockies forests	United States
Eastern Cascades forests	Canada, United States
Fraser Plateau and Basin complex	Canada
Florida scrub	United States
Great Basin montane forests	United States
Haida Gwaii	Canada
Klamath-Siskiyou forests	United States
Middle Atlantic coastal forests	United States
North Central Rockies forests	Canada, United States
Northern California coastal forests	United States
Northern Pacific coastal forests	Canada, United States
Northern transitional alpine forests	Canada
Okanagan dry forests	Canada, United States
Piney Woods forests	United States
Puget lowland forests	Canada, United States
Sierra Juárez and San Pedro Mártir pine–oak forests	Mexico
Sierra Nevada forests	United States
South Central Rockies forests	United States
Southeastern conifer forests	United States
Wasatch and Uinta montane forests	United States

Nearctic boreal forests/taiga ecoregions
Alaska Peninsula montane taiga	United States
Central Canadian Shield forests	Canada
Cook Inlet taiga	United States
Copper Plateau taiga	United States
Eastern Canadian forests	Canada
Eastern Canadian Shield taiga	Canada
Interior Alaska–Yukon lowland taiga	Canada, United States
Mid-Continental Canadian forests	Canada
Midwestern Canadian Shield forests	Canada
Muskwa–Slave Lake forests	Canada
Newfoundland Highland forests	Canada
Northern Canadian Shield taiga	Canada
Northern Cordillera forests	Canada
Northwest Territories taiga	Canada
South Avalon–Burin oceanic barrens	Canada, France (Saint Pierre and Miquelon)
Southern Appalachian spruce–fir forest	United States
Southern Hudson Bay taiga	Canada
Yukon Interior dry forests	Canada

Nearctic tropical and subtropical grasslands, savannas, and shrublands ecoregions
Western Gulf coastal grasslands	Mexico, United States

Nearctic temperate grasslands, savannas, and shrublands ecoregions
California Central Valley grasslands	United States
Canadian aspen forests and parklands	Canada, United States
Central and Southern mixed grasslands	United States
Central forest–grasslands transition	United States
Central tall grasslands	United States
Columbia Plateau	United States
Edwards Plateau savanna	United States
Flint Hills tall grasslands	United States
Montana valley and foothill grasslands	United States
Nebraska Sand Hills mixed grasslands	United States
Northern mixed grasslands	Canada, United States
Northern short grasslands	Canada, United States
Northern tall grasslands	Canada, United States
Palouse grasslands	United States
Texas blackland prairies	United States
Western short grasslands	United States

Nearctic tundra ecoregions
Alaska–St. Elias Range tundra	Canada, United States
Aleutian Islands tundra	United States
Arctic coastal tundra	Canada, United States
Arctic foothills tundra	Canada, United States
Baffin coastal tundra	Canada
Beringia lowland tundra	United States
Beringia upland tundra	United States
Brooks–British Range tundra	Canada, United States
Davis Highlands tundra	Canada
High Arctic tundra	Canada
Interior Yukon–Alaska alpine tundra	Canada, United States
Kalaallit Nunaat high arctic tundra	Greenland
Kalaallit Nunaat low arctic tundra	Greenland
Low Arctic tundra	Canada
Middle Arctic tundra	Canada
Ogilvie–MacKenzie alpine tundra	Canada, United States
Pacific Coastal Mountain icefields and tundra	Canada, United States
Torngat Mountain tundra	Canada

Nearctic Mediterranean forests, woodlands, and scrub ecoregions
California coastal sage and chaparral	Mexico, United States
California interior chaparral and woodlands	United States
California montane chaparral and woodlands	United States

Nearctic deserts and xeric shrublands ecoregions
Baja California desert	Mexico
Central Mexican matorral	Mexico
Chihuahuan Desert	Mexico, United States
Colorado Plateau shrublands	United States
Columbia Plateau shrublands	Canada, United States
Great Basin shrub steppe	United States
Gulf of California xeric scrub	Mexico
Meseta Central matorral	Mexico
Mojave Desert	United States
Snake–Columbia shrub steppe	United States
Sonoran Desert	Mexico, United States
Tamaulipan matorral	Mexico
Tamaulipan mezquital	Mexico, United States
Wyoming Basin shrub steppe	United States

Nearctic mangroves ecoregions
Northwest Mexican Coast mangroves	Mexico

See also

• List of ecoregions in Canada (WWF)
• List of ecoregions in Mexico (WWF)
• List of ecoregions in the United States (WWF)

References

• Abell, R.A. et al. (2000). Freshwater Ecoregions of North America: A Conservation Assessment Washington, DC: Island Press, 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., Terrestrial Ecoregions of North America: A Conservation Assessment.

External links

• Map of the ecozones
• Nearctica, The Natural World of North America
• "Nearctic Region" . New International Encyclopedia. 1905.