The concept of biomes and biogeographic realms
Major terrestrial biomes of the world as per the World Wildlife Fund (WWF) classification
To understand distribution and biotic components of different Biomes
Biomes are large geographical regions of earth which have characteristics types of biotic communities that are shaped by the climate of the region. On the basis of global analysis for conservation of terrestrial ecosystems, Olson et al. (2001) unified the biome concept. The terrestrial world has been divided into 14 biomes and eight biogeographic realms. Nested within14 biomes are 867 ecoregions that reflect finer regional-scale patterns of ecological organization that are shaped by local geography and climate, being different from one another by the unique collections of ecosystems and species assemblages that have evolved there (Hoekstra et al. 2005). The Biome Classification System has been developed by The Nature Conservancy and the World Wildlife Fund (WWF). This classification is being used by the National Geographic Society (www.nationalgeographic.com/) and the Millennium Ecosystem Assessment (www.millenniumassessment.org/). WWF defines an ecoregion as a "large unit of land or water containing a geographically distinct assemblage of species, natural communities, and environmental conditions". According to Olson et al. (2001), the 14 terrestrial biomes/ Major Habitat Types show the diverse types of organisms that are adapted to life on land, ranging from mangrove forests by the sea to the alpine meadows of the Himalayas. Biomes represent broad habitat and vegetation types and span across biogeographic realms. For example, the tundra biome is found in both Palearctic and Nearctic realms. Biomes are useful units for assessing global biodiversity and ecosystem services because they stratify the globe into ecologically meaningful and contrasting classes The eight biogeographic realms and the 14 major biomes (major habitats) are listed in Table 22.1 and illustrated in Fig.22.1. Each biogeographic realm contains a range of major biomes. The Indo-Malayan, Oceanic, and Neotropical realms are dominated by tropical forest and grassland biomes (Fig. 22.1). The polar realms (Palearctic, Nearctic) contain higher proportions of tundra and boreal forest. The Afrotropics are dominated by tropical grasslands. Oceania is composed mostly of low, tropical islands and is dominated by tropical forest and tropical grassland biomes.