Ecozones

The boundary between Australasia and Indomalaya follows the Wallace Line, named after the naturalist Alfred Russel Wallace who noted the differences in fauna between the islands either side of the line. The Islands to the west, including Java, Bali, Borneo, and the Philippines share a similar fauna with East Asia, including tigers, rhinoceros, and apes. During the ice ages, sea levels were lower, exposing the continental shelf that links these islands to one another and to Asia, and allowed Asian land animals to inhabit these islands.

To the East, Australia and New Guinea are distinguished by marsupial mammals, including kangaroos, possums, and wombats. The last remaining monotreme mammals, the echidnas and the platypus, are endemic to Australasia. Prior to the arrival of humans about 50,000 years ago, only about one-third of Australasian mammal species were placental.

Millions of years ago, Antarctica was part of the ancient supercontinent of Gondwanaland and had a warmer, wetter climate supporting a distinct community of woody vascular plants known as the Antarctic flora. By 30-35 million years ago Antarctica was isolated geographically and climatically and the much colder climate caused the Antarctic flora to died out in Antarctica.

Today Antarctic krill is the keystone species of the Southern Ocean, and is an important food organism for whales, seals, Leopard Seals, fur seals, Crabeater Seals, squid, icefish, penguins, albatrosses and many other birds.

With the exception of the southern tip the Afrotropic zone is exclusively tropical. To the north a belt of deserts, including the Sahara, separate the Afrotropic from the Palearctic ecozone, which includes northern Africa and temperate Eurasia.

Endemic fauna of the Afrotropics includes the cichlids of the East African Great Lakes which harbour more than two-thirds of the 2,000 species in the family, ostriches, guineafowl and several families of passerines. Africa also contains three endemic orders of mammals: aardvarks, Afrosoricida (tenrecs and golden moles) and elephant shrews. The East-African plains are dominated by large mammals. Four species of Great Apes (Hominidae) are endemic to Africa: both species of Gorilla and both species of Chimpanzee. Humans and their ancestors originated in Africa.

Bounded by mountain ranges to the north and the Wallace line to the south east the Indomalayan ecozone was historically dominated by forests.

Large mammals characteristic of Indomalaya include leopards, tigers, water buffalos, Asian Elephants, Indian Rhinoceros, Javan Rhinoceros, Malayan Tapir, orangutans, and gibbons. Indomalaya has three endemic bird families with Pheasants, pittas, Old World babblers, and flowerpeckers also being characteristic of the region.

Although currently joined to South America for 180 million years the two continents where separated and therefore evolved very different plant and animal lineages.

A number of large animals, including horses, camels, mammoths, mastodonts, ground sloths, sabre-tooth cats, the giant short-faced bear, and the cheetah, became extinct in North America at the same time the first evidence of humans appeared. The American bison, brown bear or grizzly bear, and elk entered North America around the same time as the first humans, and expanded rapidly, filling ecological niches left empty by the newly-extinct North American megafauna.

The Neotropic includes more tropical rainforest than any other ecozone, including the vast Amazon Rainforest. Prior to the formation of the Isthmus of Panama two to three million years ago North and South America where separate land masses.

The Neotropic ecozone includes 31 endemic bird families (over twice the number of any other ecozone) including rheas, curassows, toucans and hummingbirds. Mammal groups unique to the Neotropics include anteaters, sloths, armadillos, New World monkeys, and rodents such as capybaras, guinea pigs, and chinchillas.

Oceania is composed mostly of volcanic high islands and Coral atolls that arose from the sea in geologically recent times. Because the islands of Oceania have never been connected by land to a continent, the flora and fauna of the islands have all reached the islands via the ocean. On reaching the islands the flora and fauna evolved to life on the islands; for example a number of birds evolved into flightless species due to the lack of predators.

A number of islands have indigenous lizards, including geckoes and skinks, whose ancestors probably arrived on floating rafts of vegetation washed out to sea by storms. However, amphibians who are intolerant to salt water are absent. With the exception of bats, which live on most of the island groups, there are few if any indigenous mammal species in Oceania.

The largest of the ecozones the Paleartic is a predominately a temperate region encompasing Europe, Asia north of the Himalaya foothills, northern Africa, and the northern and central parts of the Arabian Peninsula. The ecozone is bounded by the tundra and the vast "boreal forest" known as the taiga in the north and deserts to the south. South of the taiga is a belt of Temperate broadleaf and mixed forests and Temperate coniferous forests. Although this European-Siberian region is characterized by shared plant and animal species it does share similarities with the the temperate and boreal regions of the Nearctic ecoregion of North America. Eurasia and North America were often connected by the Bering land bridge, and as a result have similar mammal and bird fauna, with many Eurasian species having moved into North America (including the Brown Bear, Red Deer, American Bison, and Reindeer), and fewer North American species having moved into Eurasia.

The lands bordering the Mediterranean Sea in southern Europe, north Africa, and western Asia are home to the Mediterranean basin ecoregions, which together constitute world's largest and most diverse mediterranean climate region of the world, with generally mild, rainy winters and hot, dry summers. The Mediterranean basin's mosaic of Mediterranean forests, woodlands, and shrub are home to 13,000 endemic species.