Nearctic

The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.

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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.

Although North America and South America are presently joined by the Isthmus of Panama, these continents were separated for tens of millions of years, and evolved very different plant and animal lineages. When the ancient supercontinent of Pangaea split into two 200 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 horses, camels, mammoths, mastodonts, ground sloths, 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 Wapiti or Red Deer (Cervus elaphus) 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.

One bird family, the wrentits (Timaliinae), is endemic to the Nearctic region. The Holarctic has four endemic families: divers (Gaviidae), grouse (Tetraoninae), auks (Alcidae), and the waxwings (Bombycillidae).

Animals originally unique to the Nearctic include:

Family Canidae, dogs, wolves, foxes, and coyotes
Family Camelidae, camels and their South American relatives including the llama.
Family Equidae, horses 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 cheetah (Acinonyx jubatus) evolved in North America and later spread to Eurasia.

Plants originally unique to the Nearctic include families:

Nearctic Terrestrial Ecoregions

Tropical and subtropical dry broadleaf forests
Sonoran-Sinaloan transition subtropical dry forest(Mexico)

Tropical and subtropical coniferous forests
Bermuda subtropical conifer forests (Bermuda) Sierra Madre Occidental pine-oak forests (Mexico, United States) Sierra Madre Oriental pine-oak forests (Mexico, United States)

Temperate broadleaf and mixed forests
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) Mississippi lowland forests (United States) New England-Acadian forests (Canada, United States) Northeastern coastal forests (United States) Ozark Mountain forests (United States) Southeastern mixed forests (United States) Southern Great Lakes forests (United States) Upper Midwest forest-savanna transition (United States) Western Great Lakes forests (Canada, United States) Willamette Valley forests (United States)

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 Mexican Volcanoes forests (Mexico) Central Pacific coastal forests (Canada, United States) Colorado Rockies forests (United States) Eastern Cascades forests (Canada, United States) Fraser Plateau and Basin complex (Canada) Great Basin montane forests (United States) 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) Okanogan dry forests (Canada, United States) Piney Woods forests (United States) Puget lowland forests (Canada, United States) Queen Charlotte Islands (Canada) Sierra Juarez and San Pedro Martir pine-oak forests (Baja California, Mexico) Sierra Nevada forests (United States) South Central Rockies forests (United States) Southeastern conifer forests (United States) Wasatch and Uinta montane forests (United States)

Boreal forests/taiga
Alaska Peninsula montane taiga (United States) Central Canadian Shield forests (Canada, United States) 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, United States) 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) Southern Hudson Bay taiga (Canada) Yukon Interior dry forests (Canada)

Tropical and subtropical grasslands, savannas, and shrublands
Western Gulf coastal grasslands (Mexico, United States)
Temperate grasslands, savannas, and shrublands
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) 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 (Canada, United States)

Tundra
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)

Mediterranean forests, woodlands, and shrub
California chaparral and woodlands (Mexico, United States)

Deserts and xeric shrublands
Baja California desert (Mexico) Central Mexican matorral (Mexico) Chihuahuan desert (Mexico, United States) Colorado Plateau shrublands (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) Wyoming Basin shrub steppe (United States)