Indomalayan realm

Indomalayan realm
Name	Indomalayan realm
Area km2	7,000,000
Continents	Asia
Countries	India; Bangladesh; Myanmar; Thailand; Laos; Cambodia; Vietnam; Malaysia; Singapore; Brunei; Indonesia; Philippines; Nepal; Bhutan; Sri Lanka; Pakistan
Biomes	Tropical and subtropical moist broadleaf forests; tropical dry forests; montane forests; mangroves; freshwater; peat swamp

Indomalayan realm The Indomalayan realm is a major biogeographic region of South and Southeast Asia encompassing portions of the Asian mainland and many continental and insular islands. It links the faunal and floral provinces associated with Himalaya, Indian subcontinent, Malay Peninsula, Sumatra, Borneo, and parts of the Philippines, while abutting the Palearctic realm and the Australasian realm. The realm has been central to studies by figures and institutions such as Alfred Russel Wallace, Charles Darwin, Ernst Mayr, Julian Huxley, and the International Union for Conservation of Nature.

Definition and Boundaries

Biogeographic delineations of the Indomalayan realm appear in works by Wallace and in schemes used by the World Wildlife Fund and the Biogeographic realms (WWF) classification, with boundaries defined against the Palearctic realm in the northwest and the Australasian realm across the Wallace Line and Lydekker's Line. Political entities overlapping the realm include India, Pakistan, Bangladesh, Nepal, Bhutan, Sri Lanka, Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, Singapore, Brunei, Indonesia, and the Philippines. Notable geographic landmarks that mark transitions include the Himalaya, the Arakan Mountains, the Isthmus of Kra, the Sunda Shelf, and the Sahul Shelf.

Biogeography and Ecoregions

The realm comprises multiple WWF ecoregions such as Tropical and subtropical moist broadleaf forests, Tropical and subtropical dry broadleaf forests, Montane grasslands and shrublands, Mangroves, and Freshwater ecoregions. Prominent named ecoregions include the Eastern Himalayan broadleaf forests, Indochina mangroves, Peninsular Malaysian rain forests, Borneo lowland rain forests, Sundaic lowland rain forests, Sri Lanka dry-zone dry evergreen forests, and Western Ghats montane rain forests. Island biogeography concepts developed from studies of Sumatra, Java, Borneo, Sulawesi, and Luzon influenced theoretical work by Robert MacArthur and E.O. Wilson. The region’s freshwater basins such as the Ganges River, Mekong River, Irrawaddy River, and Salween River host distinct ichthyofaunal assemblages noted in monographs by the International Union for Conservation of Nature and regional universities.

Flora and Fauna

Floral assemblages include diverse families and genera like Dipterocarpaceae, Fagaceae, Lauraceae, Rubiaceae, and endemic taxa recorded in floras such as those of Flora of British India and the Flora Malesiana. Characteristic trees include species of Shorea, Dipterocarpus, and Hopea in lowland rain forests, while montane zones support Rhododendron and Ericaceae assemblages. Faunal highlights span iconic mammals such as Bengal tiger, Indian elephant, greater one-horned rhinoceros, Sumatran orangutan, Bornean orangutan, Malayan tapir, Asian black bear, and Clouded leopard, and avifauna including Great hornbill, Indian peafowl, Sri Lanka junglefowl, and migratory species recorded at Bhitarkanika and Morecambe Bay-style shorebird sites. Herpetofauna and ichthyofauna include taxa like King cobra, Gharial, Asian arowana, and numerous endemic freshwater fishes described by institutions such as the Natural History Museum, London and the Smithsonian Institution.

Geological and Climatic History

Tectonic collision of the Indian Plate with the Eurasian Plate uplifted the Himalaya and shaped monsoon dynamics studied in journals like Nature and Science. Sea-level oscillations during the Pleistocene exposed the Sunda Shelf connecting islands such as Borneo, Sumatra, and Java with the mainland, influencing dispersal discussed by Wallace and later by Heaney (biogeographer). Climatic drivers such as the Indian monsoon, East Asian monsoon, and interglacial cycles influenced vegetation shifts recorded in pollen studies by researchers at University of Cambridge, University of Oxford, and National University of Singapore. Volcanism on islands including Krakatoa, Mount Tambora, and Mount Merapi also affected biotic turnover and cultural history examined in works about the 1815 eruption of Mount Tambora.

Human Influence and Land Use

Human societies from ancient polities like the Maurya Empire, Gupta Empire, Srivijaya, Majapahit, and kingdoms of Ayutthaya and Khmer Empire shaped landscapes through agriculture, wet-rice cultivation, and trade networks recorded along Maritime Silk Road routes. Colonial enterprises by British Empire, Dutch East India Company, French Indochina, and Spanish Philippines restructured resource extraction, plantation economies (rubber, oil palm) and introduced species leading to ecological change noted in economic histories at Harvard University and University of California, Berkeley. Contemporary land use involves cities such as Mumbai, Delhi, Bangkok, Jakarta, Kuala Lumpur, and Manila expanding into former forested areas, while regional development projects like Three Gorges Project-style dams and corridors affect hydrology and connectivity.

Conservation and Threats

Conservation initiatives include protected areas such as Kaziranga National Park, Manas National Park, Royal Chitwan National Park, Taman Negara, Gunung Leuser National Park, and transboundary programs supported by World Wildlife Fund, Convention on Biological Diversity, and regional NGOs like Wildlife Conservation Society. Major threats comprise habitat loss from logging, conversion to oil palm plantations, illegal wildlife trade involving species protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora, invasive species, and climate change impacts documented by Intergovernmental Panel on Climate Change. Conservation science involving landscape restoration, community forestry, and payments for ecosystem services has been advanced in case studies from Kerala, Sabah, Aceh, Annamite Range, and Western Ghats.

Category:Biogeographic realms