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EspañolNEARCTIC ECOZONE
(Redirected from Nearctic)
''For the thoroughbred racehorse see Nearctic (horse).''
The 'Nearctic' is one of the eight terrestrial ecozones dividing the Earth's land surface.
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.
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)."
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.
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, and the Temperate coniferous forests of the southeastern United States.
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.
The Northern Mexico bioregion includes the mild-winter deserts and xeric shrublands of northern Mexico and the southwestern United States, including the Chihuahuan, Sonoran, and 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, Sierra Madre Oriental, and Sierra Juarez and San Pedro Martir pine-oak forests.
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 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 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.
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. The last North American Camelids went extinct during the last ice age.
★ 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 now-extinct American cheetah (''Miracinonyx'')
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'').
Plants families endemic or nearly endemic to the Nearctic include Crossosomataceae, Simmondsiaceae, and Limnanthaceae.
★ Map of the ecozones
★ Nearctica, The Natural World of North America
★ 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.
''For the thoroughbred racehorse see Nearctic (horse).''
The 'Nearctic' is one of the eight terrestrial ecozones dividing the Earth's land surface.
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 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.
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, and the Temperate coniferous forests of the southeastern United States.
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.
Northern Mexico
The Northern Mexico bioregion includes the mild-winter deserts and xeric shrublands of northern Mexico and the southwestern United States, including the Chihuahuan, Sonoran, and 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, Sierra Madre Oriental, and Sierra Juarez and San Pedro Martir pine-oak forests.
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 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 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'', dogs, wolves, foxes, and coyotes
★ Family ''Camelidae'', camels and their South American relatives including the llama. The last North American Camelids went extinct during the last ice age.
★ 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 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: divers (''Gaviidae''), grouse (''Tetraoninae''), auks (''Alcidae''), and the waxwings (''Bombycillidae'').
Plants families endemic or nearly endemic to the Nearctic include Crossosomataceae, Simmondsiaceae, and Limnanthaceae.
Nearctic Terrestrial Ecoregions
External links
★ Map of the ecozones
★ 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.
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