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.
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.
Major ecological regions
The World Wildlife Fund (WWF) divides Indomalayan realm into three bio-regions, which it defines as "geographic clusters of eco-regions that may span several habitat types, but have strong biogeographic affinities, particularly at taxonomic levels higher than the species level (genus, family)".
Indian subcontinent
The Indian subcontinent bioregion covers most of India, Bangladesh, Nepal, Bhutan, and Sri Lanka and eastern parts of Pakistan. The Hindu Kush, Karakoram, Himalaya, and Patkai ranges bound the bioregion on the northwest, north, and northeast; these ranges were formed by the collision of the northward-drifting Indian subcontinent with Asia beginning 45 million years ago. The Hindu Kush, Karakoram, and Himalaya are a major biogeographic boundary between the subtropical and tropical flora and fauna of the Indian subcontinent and the temperate-climate Palearctic realm.
Indochina
The Indochina bioregion includes most of mainland Southeast Asia, including Myanmar, Thailand, Laos, Vietnam, and Cambodia, as well as the subtropical forests of southern China.
Sunda Shelf and the Philippines
Malesia is a botanical province which straddles the boundary between Indomalaya and Australasia. It includes the Malay Peninsula and the western Indonesian islands (known as Sundaland), the Philippines, the eastern Indonesian islands, and New Guinea. While the Malesia has much in common botanically, the portions east and west of the Wallace Line differ greatly in land animal species; Sundaland shares its fauna with mainland Asia, while terrestrial fauna on the islands east of the Wallace line are derived at least in part from species of Australian origin, such as marsupial mammals and ratite birds.
History
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
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
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.
Indomalayan ecoregions
| Andaman Islands rain forests | India |
| Borneo lowland rain forests | Brunei, Indonesia, Malaysia |
| Borneo montane rain forests | Brunei, Indonesia, Malaysia |
| Borneo peat swamp forests | Brunei, Indonesia, Malaysia |
| Brahmaputra Valley semi-evergreen forests | India |
| Cardamom Mountains rain forests | Cambodia, Thailand, Vietnam |
| Chao Phraya freshwater swamp forests | Thailand |
| Chao Phraya lowland moist deciduous forests | Thailand |
| Chin Hills–Arakan Yoma montane forests | Myanmar, India |
| Christmas and Cocos Islands tropical forests | Australia |
| Eastern Highlands moist deciduous forests | India |
| Eastern Java–Bali montane rain forests | Indonesia |
| Eastern Java–Bali rain forests | Indonesia |
| Greater Negros–Panay rain forests | Philippines |
| Hainan Island monsoon rain forests | China |
| Himalayan subtropical broadleaf forests | Bhutan, India, Nepal |
| Irrawaddy freshwater swamp forests | Myanmar |
| Irrawaddy moist deciduous forests | Myanmar |
| Jiang Nan subtropical evergreen forests | China |
| Kayah–Karen montane rain forests | Myanmar, Thailand |
| Lower Gangetic Plains moist deciduous forests | Bangladesh, India |
| Luang Prabang montane rain forests | Laos |
| Luzon montane rain forests | Philippines |
| Luzon rain forests | Philippines |
| Malabar Coast moist forests | India |
| Maldives–Lakshadweep–Chagos Archipelago tropical moist forests | British Indian Ocean Territory, India, Maldives |
| Meghalaya subtropical forests | India |
| Mentawai Islands rain forests | Indonesia |
| Mindanao montane rain forests | Philippines |
| Mindanao–Eastern Visayas rain forests | Philippines |
| Mindoro rain forests | Philippines |
| Mizoram–Manipur–Kachin rain forests | Bangladesh, India, Myanmar |
| Myanmar coastal rain forests | Myanmar |
| Nansei Islands subtropical evergreen forests | Japan |
| Nicobar Islands rain forests | India |
| North Western Ghats moist deciduous forests | India |
| North Western Ghats montane rain forests | India |
| Northern Annamites rain forests | Laos, Vietnam |
| Northern Indochina subtropical forests | China, Laos, Myanmar, Thailand, Vietnam |
| Northern Khorat Plateau moist deciduous forests | Laos, Thailand |
| Northern Thailand-Laos moist deciduous forests | Laos, Thailand |
| Northern Triangle subtropical forests | Myanmar |
| Northern Vietnam lowland rain forests | Vietnam |
| Orissa semi-evergreen forests | India |
| Palawan rain forests | Philippines |
| Peninsular Malaysian montane rain forests | Malaysia, Thailand |
| Peninsular Malaysian peat swamp forests | Malaysia, Thailand |
| Peninsular Malaysian rain forests | Indonesia, Malaysia, Singapore, Thailand |
| Red River freshwater swamp forests | Vietnam |
| South China Sea Islands | disputed between China, Malaysia, Philippines, Taiwan, Vietnam |
| South China–Vietnam subtropical evergreen forests | China, Vietnam |
| South Taiwan monsoon rain forests | Taiwan |
| South Western Ghats moist deciduous forests | India |
| South Western Ghats montane rain forests | India |
| Southern Annamites montane rain forests | Cambodia, Laos, Vietnam |
| Southwest Borneo freshwater swamp forests | Indonesia |
| Sri Lanka lowland rain forests | Sri Lanka |
| Sri Lanka montane rain forests | Sri Lanka |
| Sulu Archipelago rain forests | Philippines |
| Sumatran freshwater swamp forests | Indonesia |
| Sumatran lowland rain forests | Indonesia |
| Sumatran montane rain forests | Indonesia |
| Sumatran peat swamp forests | Indonesia |
| Sundaland heath forests | Indonesia |
| Sundarbans freshwater swamp forests | Bangladesh, India |
| Taiwan subtropical evergreen forests | Taiwan |
| Tenasserim–South Thailand semi-evergreen rain forests | Malaysia, Myanmar, Thailand |
| Tonle Sap freshwater swamp forests | Cambodia, Vietnam |
| Tonle Sap–Mekong peat swamp forests | Cambodia, Vietnam |
| Upper Gangetic Plains moist deciduous forests | India |
| Western Java montane rain forests | Indonesia |
| Western Java rain forests | Indonesia |
| Central Deccan Plateau dry deciduous forests | India |
| Central Indochina dry forests | Cambodia, Laos, Thailand, Vietnam |
| Chota-Nagpur dry deciduous forests | India |
| East Deccan dry evergreen forests | India |
| Irrawaddy dry forests | Myanmar |
| Khathiar–Gir dry deciduous forests | India |
| Narmada Valley dry deciduous forests | India |
| Northern dry deciduous forests | India |
| South Deccan Plateau dry deciduous forests | India |
| Southeastern Indochina dry evergreen forests | Cambodia, Laos, Thailand |
| Southern Vietnam lowland dry forests | Vietnam |
| Sri Lanka dry-zone dry evergreen forests | Sri Lanka |
| Himalayan subtropical pine forests | Bhutan, India, Nepal, Pakistan |
| Luzon tropical pine forests | Philippines |
| Northeast India–Myanmar pine forests | Myanmar, India |
| Sumatran tropical pine forests | Indonesia |
| Eastern Himalayan broadleaf forests | Bhutan, India, Nepal |
| Northern Triangle temperate forests | Myanmar |
| Western Himalayan broadleaf forests | India, Nepal, Pakistan |
| Eastern Himalayan subalpine conifer forests | Bhutan, India, Nepal |
| Western Himalayan subalpine conifer forests | India, Nepal, Pakistan |
| Terai–Duar savanna and grasslands | Bhutan, India, Nepal |
| Rann of Kutch seasonal salt marsh | India, Pakistan |
| Kinabalu montane alpine meadows | Malaysia |
| Deccan thorn scrub forests | India, Sri Lanka |
| Indus Valley desert | India, Pakistan |
| Northwestern thorn scrub forests | India, Pakistan |
| Thar desert | India, Pakistan |
| Godavari–Krishna mangroves | India |
| Indochina mangroves | Cambodia, Malaysia, Thailand, Vietnam |
| Indus River Delta–Arabian Sea mangroves | Pakistan |
| Myanmar coast mangroves | Myanmar, India, Malaysia, Thailand |
| Sunda Shelf mangroves | Brunei, Indonesia, Malaysia |
| Sundarbans mangroves | Bangladesh, India |
See also
- Ecoregions of India
- Ecoregions of the Philippines
- Mainland Southeast Asia (the Indochinese Peninsula)
- Malesia
- Sundaland
Bibliography
References
- Indomalayan realm Archived 2022-10-06 at the Wayback Machine biologyonline.com. Retrieved 29 August 2021
- Appanah, Simmathiri and Jennifer M. Turnbull, eds. (1998). A Review of Dipterocarps: Taxonomy, ecology and silviculture. Center for International Forestry Research, 1998.
- Ebach, Malte C. (2017). Handbook of Australasian Biogeography. CRC Press, Jan 6, 2017.
- Bain, R.H., Biju, S.D., Brown, R.M., Das, I., Diesmos, A.C., Dutta, S.K., Gower, D.J., Inger, R.F., Iskandar, D.T., Kaneko, Y., Neng, M.W., Lau, Meegaskumbura, M., Ohler, A., Papenfuss, T., Pethiyagoda, R., Stuart, B.L., & Wilkinson, M. (2008). Amphibians of the Indomalayan Realm.