Abiogeographic realm is the broadestbiogeographic division of Earth's land surface, based on distributional patterns ofterrestrial organisms. They are subdivided intobioregions, which are further subdivided intoecoregions.A biogeographic realm is also known as "ecozone", although that term may also refer to ecoregions.
The realms delineate large areas of Earth's surface within which organisms have evolved in relative isolation over long periods of time, separated by geographic features, such asoceans, broaddeserts, or highmountain ranges, that constitutenatural barriers to migration. As such, biogeographic realm designations are used to indicate general groupings of organisms based on their shared biogeography. Biogeographic realms correspond to thefloristic kingdoms ofbotany orzoogeographic regions ofzoology.
From 1872,Alfred Russel Wallace developed a system of zoogeographic regions, extending theornithologistPhilip Sclater's system of six regions.[1]
Biogeographic realms are characterized by the evolutionary history of the organisms they contain. They are distinct frombiomes, also known as major habitat types, which are divisions of the Earth's surface based onlife form, or the adaptation of animals, fungi, micro-organisms and plants to climatic,soil, and other conditions. Biomes are characterized by similarclimax vegetation. Each realm may include a number of different biomes. Atropical moist broadleaf forest in Central America, for example, may be similar to one in New Guinea in its vegetation type and structure, climate, soils, etc., but these forests are inhabited by animals, fungi, micro-organisms and plants with very different evolutionary histories.[citation needed]
The distribution of organisms among the world's biogeographic realms has been influenced by the distribution oflandmasses, as shaped byplate tectonics over thegeological history of Earth.
The "biogeographic realms" of Udvardy[2] were defined based on taxonomic composition. The rank corresponds more or less to thefloristic kingdoms andzoogeographic regions.
The usage of the term "ecozone" is more variable. Beginning in the 1960s, it was used originally in the field ofbiostratigraphy to denote intervals of geologicalstrata with fossil content demonstrating a specific ecology.[3] In Canadian literature, the term was used by Wiken[4] in macro-levelland classification, with geographic criteria (seeEcozones of Canada).[4][5] Later, Schultz[6] would use it with ecological and physiognomical criteria, in a way similar to the concept ofbiome.
In theGlobal 200/WWF scheme,[7] originally the term "biogeographic realm" in Udvardy sense was used. However, in a scheme ofBBC,[8] it was replaced by the term "ecozone".
TheWorld Wildlife Fund scheme[8][7][9] is broadly similar toMiklos Udvardy's system,[2] the chief difference being the delineation of the Australasian realm relative to the Antarctic, Oceanic, and Indomalayan realms. In the WWF system, the Australasia realm includesAustralia,Tasmania, the islands ofWallacea,New Guinea, theEast Melanesian Islands,New Caledonia, andNew Zealand. Udvardy's Australian realm includes only Australia and Tasmania; he placesWallacea in the Indomalayan Realm, New Guinea, New Caledonia, and East Melanesia in the Oceanian Realm, and New Zealand in the Antarctic Realm.
| Biogeographic realm | Area | Lands included | |
|---|---|---|---|
| million square kilometres | million square miles | ||
| Palearctic | 54.1 | 20.9 | The bulk ofEurasia andNorth Africa. |
| Nearctic | 22.9 | 8.8 | Greenland and most ofNorth America. |
| Afrotropic | 22.1 | 8.5 | Trans-Saharan Africa,Madagascar andArabia. |
| Neotropic | 19.0 | 7.3 | South America,Central America, theCaribbean,South Florida and theFalkland Islands. |
| Australasia | 7.6 | 2.9 | Australia,Melanesia,New Zealand,Lesser Sunda Islands,Sulawesi,Maluku Islands and the neighbouring islands. The northern boundary of this zone is known as theWallace Line. |
| Indomalaya | 7.5 | 2.9 | TheIndian subcontinent,Southeast Asia,southern China and most of theGreater Sunda Islands. |
| Oceania | 1.0 | 0.39 | Polynesia (except New Zealand),Micronesia, and theFijian Islands. |
| Antarctic | 0.3 | 0.12 | Antarctica,Alexander Island,South Georgia and the South Sandwich Islands. |
ThePalearctic andNearctic are sometimes grouped into theHolarctic realm.
Following the nomenclatural conventions set out in theInternational Code of Area Nomenclature, Morrone[10] defined the next biogeographic kingdoms (or realms) and regions:
The applicability of Udvardy scheme[2] to most freshwater taxa is unresolved.[11]
Thedrainage basins of the principal oceans and seas of the world are marked by continental divides. The grey areas areendorheic basins that do not drain to the ocean.[citation needed]
According to Briggs[13] and Morrone:[14]
According to the WWF scheme:[15]
