The Indomalayan realm is one of the eight biogeographic realms.[ Indomalayan realm biologyonline.com. Retrieved 29 August 2021] It extends across most of South Asia and Southeast Asia and into the southern parts of East Asia.
Also called the Oriental realm by biogeography, 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 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
Australia 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
and
, 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.
[Appanah, Simmathiri and Jennifer M. Turnbull, eds. (1998). A Review of Dipterocarps: Taxonomy, ecology and silviculture. Center for International Forestry Research, 1998.] 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.[Ebach, Malte C. (2017). Handbook of Australasian Biogeography. CRC Press, Jan 6, 2017.]
Fauna
Two orders of mammals, the
(Dermoptera) and
(Scandentia), are endemic to the realm, as are families Craseonycteridae (Kitti's hog-nosed bat),
Diatomyidae, Platacanthomyidae, Tarsiidae (
) and Hylobatidae (
). Large mammals characteristic of Indomalaya include the
leopard,
,
Bubalus,
Asian elephant, Indian rhinoceros,
Javan rhinoceros,
Malayan tapir,
, and
.
Indomalaya has three endemic bird families, the Irenidae (), Megalaimidae and Rhabdornithidae (Philippine creepers). Also characteristic are , pittas, Old World babblers, and .
Indomalaya has 1000 species of 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.[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. [2]]
More information is available under Indomalayan realm fauna.
Indomalayan ecoregions
, or major habitat types, as defined by Olson & Dinerstein, et al. (2001).
[Olson, D. M., Dinerstein, E., Wikramanayake, E. D., Burgess, N. D., Powell, G. V. N., Underwood, E. C., D'Amico, J. A., Itoua, I., Strand, H. E., Morrison, J. C., Loucks, C. J., Allnutt, T. F., Ricketts, T. H., Kura, Y., Lamoreux, J. F., Wettengel, W. W., Hedao, P., Kassem, K. R. (2001). Terrestrial ecoregions of the world: a new map of life on Earth. Bioscience 51(11):933–938, [3] .]
]]
See also
-
Ecoregions of India
-
Ecoregions of the Philippines
-
Mainland Southeast Asia (the Indochinese Peninsula)
-
Malesia
-
Sundaland
Bibliography
-
Wikramanayake, E., E. Dinerstein, C. J. Loucks, D. M. Olson, J. Morrison, J. L. Lamoreux, M. McKnight, and P. Hedao. 2002. Terrestrial ecoregions of the Indo-Pacific: a conservation assessment. Island Press, Washington, DC, USA, [4].
