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TheNearctic realm is one of the eightbiogeographic realms constituting the Earth's land surface.
The Nearctic realm covers most ofNorth America, includingGreenland,Central Florida, and the highlands ofMexico. The parts of North America that are not in the Nearctic realm include most of coastal Mexico, southern Mexico,southern Florida, coastalcentral Florida,Central America, and theCaribbean islands. Together withSouth America, these regions are part of theNeotropical realm.
TheWorld Wildlife Fund (WWF) divides the Nearctic into fourbioregions, 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)."
TheCanadian Shield bioregion extends across the northern portion of the continent, from theAleutian Islands toNewfoundland. It includes the Nearctic'sarctic tundra andboreal forest ecoregions.
In terms offloristic provinces, it is represented by part of the Canadian Province of theCircumboreal Region.
The Eastern North America bioregion includes thetemperate broadleaf and mixed forests of the Eastern United States and southeastern Canada, theGreat Plainstemperate grasslands of the central United States and south-central Canada, thetemperate coniferous forests of the southeastern United States, includingcentral Florida. In terms offloristic provinces, it is represented by theNorth American Atlantic Region and part of the Canadian Province of theCircumboreal Region.
The Western North America bioregion includes thetemperate coniferous forests of the coastal and mountain regions of southern Alaska, western Canada, and the western United States from thePacific Coast andNorthern California to theRocky Mountains (known as theCascadian bioregion), as well as the cold-winter intermountaindeserts and xeric shrublands and temperate grasslands and shrublands of theWestern United States.
In terms offloristic provinces, it is represented by theRocky Mountain region.
The Northern Mexico bioregion includes the mild-winter to cold-winter deserts and xeric shrublands, warm temperate and subtropical pine andpine-oak forests, and Mediterranean climate ecoregions of theMexican Plateau,Baja California peninsula, and thesouthwestern United States, bordered to the south by theNeotropicalTrans-Mexican Volcanic Belt.[1] This region also includes the onlysubtropical dry broadleaf forest in the Nearctic realm, theSonoran–Sinaloan transition subtropical dry forest.
In terms offloristic provinces, it is represented by theMadrean Region.
Although North America and South America are presently joined by theIsthmus of Panama, these continents were separated for about 180 million years, and evolved very different plant and animal lineages. When the ancient supercontinent ofPangaea split into two about 180 million years ago, North America remained joined toEurasia as part of the supercontinent ofLaurasia, while South America was part of the supercontinent ofGondwana. North America later split from Eurasia. North America has been joined by land bridges to bothAsia and South America since then, which allowed an exchange of plant and animalspecies between the continents, theGreat American Interchange.
A former land bridge across theBering 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 thePalearctic. The two realms are sometimes included in a singleHolarctic realm.
Many large animals, ormegafauna, includinghorses,camels,tapirs,mammoths,mastodons,ground sloths, sabre-tooth cats (Smilodon),short-faced bears and theAmerican cheetah, became extinct in North America at the end of thePleistocene epoch (ice ages) in what is called theQuaternary extinction event.
Mammals originally unique to the Nearctic include:
Onebird family, thewrentits (Timaliinae), is endemic to the Nearctic region. Twomammal families are endemic to the Nearctic, the pronghorns (Antilocapridae) and the mountain beaver (Aplodontiidae).[2] The Holarctic has four endemic families:divers (Gaviidae),grouse (Tetraoninae),auks (Alcidae), and thewaxwings (Bombycillidae). The scarab beetle familiesPleocomidae andDiphyllostomatidae (Coleoptera) are also endemic to the Nearctic. The fly speciesCynomya cadaverina is also found in high numbers in this area.
Plant families endemic or nearly endemic to the Nearctic include theCrossosomataceae,Simmondsiaceae, andLimnanthaceae.
| Sonoran–Sinaloan transition subtropical dry forest | Mexico |
| Bermuda subtropical conifer forests | Bermuda |
| Western Gulf coastal grasslands | Mexico,United States |
| 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 |
| California coastal sage and chaparral | Mexico,United States |
| California interior chaparral and woodlands | United States |
| California montane chaparral and woodlands | United States |
| Northwest Mexican Coast mangroves | Mexico |
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