The current distribution of plants and animals reflects a long evolutionary response to the changing climate and configuration of continents and oceans. Biomes are defined by the plants and animals adapted to the environmental conditions found in them. Like other physical systems, the geography of world biomes is highly dependent on climate. Recent climate change has already made small changes in the distribution of some plants and animals. If climate change continues into the future, the distribution of Earth biomes could be quite different.
Biogeographical realms are geographical regions out of which assemblages of plants and animals evolved and dispersed. The Nearctic realm includes most of North America and Greenland. THe Nearctic realm possesses a great diversity of biomes including the tundra, grassland, deciduous and coniferous forest, chaparral, and desert biomes. The Nearctic realm has been separated from Neotropical by deserts, and until recently, an absence of a land bridge between them. The Palaearctic realm stretched across Europe, most of Asia, the Mediterranean, North Africa. It is very similar to the Nearctic in terms of the diversity of biomes including tundra, grassland, deciduous and coniferous forest, chaparral, and desert biomes. The Neotropical realm found throughout most of central and South America is dominated by tropical forests, savannas, and deserts. The Afrotropical realm is inhabited by tropical forests, savannas, and deserts and is found in Africa south of the Sahara. The Australian (or Australasian) realm has a desert core, surrounded by tropical forest and savanna. The Australian realm boasts a unique variety of plants and animals as they have evolved in isolation from outside influence. Pouched marsupial mammals, like the Kangaroo, are found in the Australian realm. The Indomalayan realm includes much of southeast Asia and is nearly exclusively tropical forest. It was isolated from the Palaearctic by the Himalayan Mountains. The Indomalayan realm was previously separated by a sea lane that has subsequently been closed by continental drift. The Antarctic realm exhibits a diverse set of ecosystems from temperate forest and grassland in New Zealand to tundra and ice sheets in Antarctica. Many of New Zealand's mammals are like those frequenting Antarctic shores. The Oceanian realm includes tropical islands of the Pacific ocean and dominated by tropical forests. Physical barriers are often the most imposing barriers to diffusion.
In "The Fundamentals of Biogeography", a biome was defined as a large stable terrestrial ecosystem. Classification of biomes vary, and no one system dominates biogeography studies. Five principal biomes, forest, savanna, grassland, desert and tundra are distinguished on the basis of unique plant and animal communities are recognized in this book. Within each biome may be several formation classes that are vegetation units defined on the basis of the dominate plants in a terrestrial ecosystem. For instance, the forest biome includes the tropical rain forest, seasonal forest and shrub, Mediterranean woodland, Midlatitude broadleaf deciduous and mixed forests, broadleaf evergreen, and marine west coast forest to name a few.