The term biogeographic realm refers to an area of land that contains relatively similar living organisms. In most cases, the organisms living within these biogeographic realms have been isolated from the rest of the organisms around the world and have, therefore, experienced distinct evolutionary processes. In other words, each realm corresponds to a specific evolutionary history. Biogeographic realms are further divided into ecoregions, which are, in turn, divided into biomes. This article takes a closer look at each of the 8 biogeographic realms: Antarctic, Oceania, Indo-Malaya, Australasia, Neotropic, Afrotropic, Nearctic, and Palearctic.
Antarctic Biogeographic Realm
The Antarctic biogeographic realm covers a total area of 0.12 million square miles, making it the smallest of all the realms. The Antarctic biogeographic region is located in the Southern Ocean and is comprised of the area surrounding the South Pole, including: Antarctica, the islands above the Antarctic tectonic plate, the ice in the waters, and the ocean itself. All of these different components make up 20% of the Southern Hemisphere. Because of the freezing temperatures here, just under 1% of the Antarctic is actually exposed land. This realm is home to plant species such as: lichens, mosses, Antarctic hair grass, and microfungis. Additionally, some animals species may be found here, depending on the time of year. These animal species include: penguins, whales, squid, albatross, seals, and Antarctic petrels.
Oceania Biogeographic Realm
The Oceania biogeographic realm covers a total area of 0.39 million square miles, making it the second smallest of all the realms. The Oceania biogeographic region is located in the Pacific Ocean, in a region referred to as Asia Pacific. It is comprised of a number of islands, including: the US state of Hawaii, a part of Japan, the Juan Fernandez Islands, the Cocos Islands, and the Campbell islands (to name a few). Although it covers a larger area than the Antarctic realm, Oceania actually has the smallest land area of all the biogeographic realms on earth. It has a permanent human population of over 40 million individuals. Geographically, Oceania is known for its large amounts of coral reef, the most famous of which is the Great Barrier Reef. Because of the isolated nature of the islands within this realm, each location has very unique plant and animal life.
Indo-Malayan Biogeographic Realm
The Indo-Malayn biogeographic realm stretches across the southern reaches of East Asia, the greater part of South Asia, and the area known as Southeast Asia. It covers a total area of 2.9 million square miles, which includes: the Indian subcontinent, parts of southern China, Indonesia, and the Phillipines (as well as other locations). This realm is primarily covered in tropical and subtropical forests that have been further divided into 3 bioregions: Indochina, Indian subcontinent, and Munda Shelf and the Philippines. The Indo-Malayan biogeographic realm is home to a number of endemic species, both plant and animal. Some examples of endemic species found here include: fairy bluebirds, gibbons, treeshrews, Kitti’s long-nosed bat, and Philippine creepers. Other large mammals that can be found in the Indo-Malayan realm are the leopard, tiger, orangutang, Indian rhinoceros, Asian elephant, and water buffalo.
Australasian Biogeographic Realm
The Australasian biogeographic realm covers a total area of 2.9 million square miles, making it the same size as the Indo-Malayan realm. It includes New Guinea, New Zealand, Tasmania, Australia, and the eastern region of the Indonesian archipelago. Australia is considered the most environmentally diverse country within this realm as it is made up of desert, rainforest, grasslands, and mountains. The Australasian realm sits between the Antarctic realm and the Indo-Malayan realm; it is separated from the Asia realm by the Wallace Line. Because of this position, some of the plant and animal species of this realm can also be found in the Indo-Malyan and Antarctic realms as well. Researchers believe this is because all three realms once made up the Gondwana supercontinent. In fact, New Guinea, Tasmania, and Australia continued to be connected long after the dissolution of Gondwana and today, are only separated by relatively shallow waters.
Neotropical Biogeographic Realm
The Neotropical biogeographic realm covers an entire area of 7.3 million square miles and is made up of the tropical regions of the Americas. It includes all of South America, Central America, the Caribbean, the Yucatan Peninsula of Mexico, the southern region of the US state of Florida, and a small part of the southern tip of the US state of Texas. The plant and animal species of this realm are distinct from those found in North America, which is why the two regions are characterized separately. This difference in species occurred because of the two realms were physically separated until between 2 and 3 million years ago. Interestingly, the Neotropical biogeographic realm has more tropical rainforest coverage than any other realm. It is further divided into 8 ecological regions.
Afrotropical Biogeographic Realm
The Afrotropical realm covers a total area of 8.5 million square miles and is made up of southwestern Pakistan, southern Iran, the southern regions of the Arabian Peninsula, the area south of the Sahara Desert in Africa, the island of Madagascar, and the islands in the western part of the Indian Ocean. The majority of this realm has a tropical climate, although it is diverse in ecological habitats, including: deserts, highlands, savannahs, and forests (coastal, montane, and lowland). It is home to over 200 endemic fish species, 12 endemic plant families, 7 endemic bird families, and 3 endemic mammal families. Additionally, the Afrotropical realm is home to 2 gorilla species and 2 chimpanzee species, which belong to the Hominidae genus along with humans.
Nearctic Biogeographic Realm
The Nearctic biogeographic realm covers a total area of 8.8 million square miles, making it the second largest of all the realms. It encompasses the US (including most of Texas and northern Florida), Canada, Greenland, and the highland regions of Mexico. This realm is further divided into 4 ecological regions including: eastern, western, southwestern (which includes the northern part of Mexico), and the Canadian Shield. Each of these regions has distinct environmental habitats that support a diverse range of plant and animal species. Animal families that originated and continue to thrive in this realm include: canines (dogs, wolves, coyotes), equine (horses and donkeys), and antelopes. Some of the animal families that originated here are now extinct, although their relatives inhabit the Neotropical realm.
Palearctic Biogeographic Realm
The Palearctic biogeographic realm covers a total area of 20.9 million square, making it the largest of all the realms. It is made up of the area north of the Saharan Desert in Africa, the area north of the Himalayan Mountains in Asia, the northern region of the Arabian Peninsula, and the entire area of Europe. It is further divided into 7 ecoregions, which contain boreal forests, Mediterranean climates, coastal deserts, river basins, and mountainous terrain. The Palearctic is home to several endemic animal families, including: red pandas, mouse-like hamsters, and accentor birds.