|
The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface
(see map ).
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 from since then, which allowed an exchange of plant
and animal species between the continents.
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,
mastodons, 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 (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 became
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 ecoregions |
|
Sonoran-Sinaloan transition subtropical dry forest (Mexico)
|
|
| Tropical and Subtropical Coniferous Forests ecoregions |
|
Bermuda subtropical conifer forests (Bermuda)
Sierra Madre Occidental pine-oak forests (Mexico)
Sierra Madre Oriental pine-oak forests (Mexico)
|
|
| 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)
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 ecoregions |
|
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 Madre Occidental forests (Mexico;
southeast Arizona, US)
Sierra Madre Oriental 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)
|
|
| Boreal
Forests/Taiga ecoregions |
|
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 ecoregions |
|
Western Gulf coastal grasslands (Mexico,
United States)
|
| 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)
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 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)
|
|
| Mediterranean Forests, Woodlands, and Shrub ecoregions |
|
California chaparral and
woodlands (Mexico, United States)
|
|
| Deserts and Xeric Shrublands ecoregions |
|
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 (Mexico)
|
External links
|