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A biogeographic realm is the broadest biogeography division of Earth's land surface, based on distributional patterns of terrestrial organisms. They are subdivided into , which are further subdivided into . A biogeographic realm is also known as "ecozone", although that term may also refer to ecoregions.
From 1872, Alfred Russel Wallace developed a system of zoogeographic regions, extending the ornithology Philip Sclater's system of six regions.
Biogeographic realms are characterized by the evolutionary history of the organisms they contain. They are distinct from , also known as major habitat types, which are divisions of the Earth's surface based on life form, or the adaptation of animals, fungi, micro-organisms and plants to climatic, soil, and other conditions. Biomes are characterized by similar climax community. Each realm may include a number of different biomes. A tropical 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.
The distribution of organisms among the world's biogeographic realms has been influenced by the distribution of , as shaped by plate tectonics over the geological history of Earth.
The usage of the term "ecozone" is more variable. Beginning in the 1960s, it was used originally in the field of biostratigraphy to denote intervals of geological stratum with fossil content demonstrating a specific ecology. In Canadian literature, the term was used by Wiken in macro-level regionalisation, with geographic criteria (see Ecozones of Canada). Later, Schultz would use it with ecological and physiognomical criteria, in a way similar to the concept of biome.
In the Global 200/WWF scheme, originally the term "biogeographic realm" in Udvardy sense was used. However, in a scheme of BBC, it was replaced by the term "ecozone".
| Palearctic realm | The bulk of Eurasia and North Africa. | |
| Nearctic realm | Greenland and most of North America. | |
| Afrotropic | Trans-Saharan Africa, Madagascar and Arabia. | |
| Neotropic | South America, Central America, the Caribbean, South Florida and the Falkland Islands. | |
| Australasia | Australia, Melanesia, New Zealand, Lesser Sunda Islands, Sulawesi, Maluku Islands and the neighbouring islands. The northern boundary of this zone is known as the Wallace Line. | |
| Indomalaya | The Indian subcontinent, Southeast Asia, southern China and most of the Greater Sunda Islands. | |
| Oceanian realm | Polynesia (except New Zealand), Micronesia, and the Fiji. | |
| Antarctic realm | Antarctica, Alexander Island, South Georgia and the South Sandwich Islands. |
The Palearctic realm and Nearctic realm are sometimes grouped into the Holarctic realm.
The of the principal oceans and seas of the world are marked by continental divides. The grey areas are that do not drain to the ocean.
According to the WWF scheme:
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