Indomalayan realm
The Indomalayan realm is one of the eight biogeographic realms.[1] It extends across most of South and Southeast Asia and into the southern parts of East Asia.
"Oriental region" redirects here. Not to be confused with Oriental (Morocco).
Also called the Oriental realm by biogeographers, Indomalaya spreads all over the Indian subcontinent and Southeast Asia to lowland southern China, and through Indonesia as far as Sumatra, Java, Bali, and Borneo, east of which lies the Wallace line, the realm boundary named after Alfred Russel Wallace which separates Indomalaya from Australasia. Indomalaya also includes the Philippines, lowland Taiwan, and Japan's Ryukyu Islands.
Most of Indomalaya was originally covered by forest, and includes tropical and subtropical moist broadleaf forests, with tropical and subtropical dry broadleaf forests predominant in much of India and parts of Southeast Asia. The tropical forests of Indomalaya are highly variable and diverse, with economically important trees, especially in the families Dipterocarpaceae and Fabaceae.
History[edit]
The flora of Indomalaya blends elements from the ancient supercontinents of Laurasia and Gondwana. Gondwanian elements were first introduced by India, which detached from Gondwana approximately 90 MYA, carrying its Gondwana-derived flora and fauna northward, which included cichlid fish and the plant families Crypteroniaceae and possibly Dipterocarpaceae. India collided with Asia 30-45 MYA, and exchanged species. Later, as Australia-New Guinea drifted north, the collision of the Australian and Asian plates pushed up the islands of Wallacea, which were separated from one another by narrow straits, allowing a botanic exchange between Indomalaya and Australasia. Asian rainforest flora, including the dipterocarps, island-hopped across Wallacea to New Guinea, and several Gondwanian plant families, including podocarps and araucarias, moved westward from Australia-New Guinea into western Malesia and Southeast Asia.
Flora[edit]
The subfamily Dipterocarpoideae comprises characteristic tree species in Indomalaya's moist and seasonally dry forests, with the greatest species diversity in the moist forests of Borneo.[2] Teak (Tectona) is characteristic of the seasonally dry forests of the Indomalaya, from India through Indochina, Malaysia, and the Philippines. Tropical pitcher plants (Nepenthes) are also characteristic of Indomalaya, and the greatest diversity of species is in Sumatra, Borneo, and the Philippines.
The tropical forests of Indomalaya and Australasia share many lineages of plants, which have managed over millions of years to disperse across the straits and islands between Sundaland and New Guinea. The two floras evolved in long isolation, and the fossil record suggests that Asian species dispersed to Australasia starting 33 million years ago as Australasia moved northwards, and dispersal increased 12 million years ago as the two continents approached their present positions. The exchange was asymmetric, with more Indomalayan species spreading to Australasia than Australasian species to Indomalaya.[3]
Fauna[edit]
Two orders of mammals, the colugos (Dermoptera) and treeshrews (Scandentia), are endemic to the realm, as are families Craseonycteridae (Kitti's hog-nosed bat), Diatomyidae, Platacanthomyidae, Tarsiidae (tarsiers) and Hylobatidae (gibbons). Large mammals characteristic of Indomalaya include the leopard, tigers, water buffalos, Asian elephant, Indian rhinoceros, Javan rhinoceros, Malayan tapir, orangutans, and gibbons.
Indomalaya has three endemic bird families, the Irenidae (fairy bluebirds), Megalaimidae and Rhabdornithidae (Philippine creepers). Also characteristic are pheasants, pittas, Old World babblers, and flowerpeckers.
Indomalaya has 1000 species of amphibians in 81 genera, about 17 of global species. 800 Indomalayan species, or 80%, are endemic. Indomalaya has three endemic families of amphibians, Nasikabatrachidae, Ichthyophiidae, and Uraeotyphlidae. 329, or 33%, of Indomalayan amphibians are considered threatened or extinct, with habitat loss as the principal cause.[4]
More information is available under Indomalayan realm fauna.