A continent- or subcontinent-sized area, separated from other biogeographical realms by physical barriers to plant and animal migration, such as major mountain ranges, and oceans: for example, the Afrotropical Biogeographic Realm, which contains one of the highest levels of biodiversity on Earth (see Udvardy (1975) IUCN Occ. Paper 18). Each biogeographic realm may include a number of different biomes. The use of ecozone for biogeographic realm is a fairly recent development; see J. Schultz (2005).