The Indo-Malaysian Realm
The Indo-Malaysian Zoogeographic Realm is comprised primarily of the tropical parts of South and South East Asia although extending some degrees north in places into the subtropical zone, particularly in northern India. It includes most of the Indian subcontinent south of the Himalayas together with most of Indochina, the Malay Peninsula, and the islands of the Sunda Archipelago. Biogeographically it is divided among the Oriental, Sundaic, and Wallacean zoogeographic regions. Most of it was originally covered by tropical moist and dry forests, with a few scattered areas of savanna and desert. Its evolution was greatly affected by ice-age sealevel changes. At the height of the last glacial age, the oceans were hundreds of metres lower than at the present time. Lands like Indonesia and the Philippines, and perhaps New Guinea and Australia as well, were not as widely separated as today. At least Indonesia was certainly connected with the mainland and with the Philippines as late as about 18,000 years ago. These climatic oscillations, with long warm, interglacial stages between the cold periods, as well as the rise and fall of the oceans, had a tremendous impact on animal distribution patterns and migrations, and this is still going on. When sea levels dropped during the Pleistocene Bali was connected to both Java and Sumatra as well as to the Asian mainland, but the deep water of the Lombok Strait continued to keep the rest of the Sunda Islands isolated. The Lombok Strait lies to the immediate west of the island, marking the passage of the biogeographical division between the prolific fauna of the Indomalayan ecozone and the distinctly different, but similarly prolific, fauna of Australasia – this distinction is known as the ‘Wallace Line’ (or ‘Wallace’s Line’) and is named after Alfred Russel Wallace, the person to comment on the division between the two regions as well as on the abrupt boundary between the two biomes.
Geologically speaking, the Indo-Malaysian Realm combines elements of the ancient supercontinents of Laurasia and Gondwana. Gondwanian elements were first introduced by what is now India, which detached from Gondwana approximately 90 million years ago, carrying its flora and fauna northward before colliding with Asia between 45 and 30 million years ago. Later, as what are now Australia and New Guinea drifted north, the collision of their plates pushed up the islands of the Wallacean Region, which were separated from one another by narrow straits, thereby allowing periodic exchanges of plants and animals. All told, the Indo-Malaysian Realm remains one of the richest areas for vertebrate diversity on Earth.
Species and subspecies
The Asian or Asiatic elephant (Elephas maximus) is the world’s second largest land animal. At least three subspecies are found sporadically across South and South East Asia.
The Asiatic lesser one-horned rhinoceros (Rhinoceros sondaicus) is divided into three subspecies that historically occurred throughout South East Asia from eastern India and southern China to Indonesia.
The Asiatic two-horned rhinoceros (Dicerorhinus sumatrensis) is similarly divided into three subspecies that historically occurred across South and South East Asia, including the islands of Sumatra, Borneo and Java.
The wild Asiatic buffalo or water buffalo (Bubalus arnee) was once widespread and common across southern Asia from Mesopotamia to Indochina and Indonesia. Habitat destruction, hunting, and diseases (particularly rinderpest) transmitted from domestic cattle have caused a considered decline, and the species is now found only in a few wet grassland, swamp and riverine areas of India, Nepal, Bhutan, Thailand, Cambodia, and possibly Myanmar. Unfortunately, many of these surviving populations are thought to have interbred with feral or domestic water buffalo (B. bubalus).
The banteng (Bos javanicus) is a type of wild cattle that was historically widespread in the forests and grasslands of South East Asia, but which has declined in most parts of its range due to habitat destruction and heavy hunting pressure. Three subspecies inhabit the Indo-Malaysian Realm.
Carpenter’s white-handed gibbon (Hylobates lar carpenteri) is confined to northern and north-eastern Thailand, where it is threatened by hunting and habitat destruction.
The macaques (Macaca) are a group of large, grounddwelling monkeys. Many are declining due to hunting and habitat destruction. The long-tailed macaque (M. fascicularis) is widespread across South East Asia where it is divided into at least 10 subspecies. The nominate form (M. f. fascicularis) occurs in Cambodia, Vietnam, the Malay Peninsula, the Philippines, Borneo, Sumatra, Java, Bali, Sumba, Timor and on a number of smaller islands. The northern pig-tailed macaque (M. leonina) ranges throughout much of mainland South East Asia, in a variety of habitats. The stump-tailed macaque (M. arctoides) is found in south-western China (Guangdong, Guangxi, Guizhou, and Yunnan), north-eastern India (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura), Laos, northern Myanmar, Thailand, Vietnam, and north-western peninsular Malaysia. It has been introduced to Hong Kong.
The Bengal slow loris (Nycticebus bengalensis) is a small, nocturnal prosimian that remains widespread within the Indian subcontinent and Indochina, including the Malay Peninsula, but is everywhere threatened by habitat destruction, hunting for use in ‘traditional medicine’ and collection for the pet trade.
The sun bear (Helarctos malayanus) is the world’s smallest bear species, and gets its name from the yellowish crescent patch on its chest. Two subspecies are found in the forests of South East Asia. The Malayan sun bear (H. m. malayanus) still ranges widely across Indo-China from north-eastern India to Sumatra, but has been extirpated from most of the areas it formerly inhabited. The main threats are loss of habitat and hunting for use in ‘traditional medicine’.
The nominate form of the Asiatic black bear (Ursus thibetanus thibetanus) is still found widely from north-eastern India (Assam) and Nepal through Indochina to the Malay Peninsula, but is everywhere threatened by hunting for use in ‘traditional medicine’.
The fishing cat (Prionailurus viverrinus) is a medium-sized wild cat found in widely scattered populations across South and South East Asia, where it favours wetlands. It has been extirpated over most of its historical range due to habitat destruction and human persecution.
Pocock’s wild dog (Cuon alpinus fumosus) is found widely but patchily in Mongolia, southern China (Szechuan), Myanmar, Thailand, Laos, Cambodia, Vietnam, peninsular Malaysia and Java, but is everywhere threatened by loss of habitat, depletion of its prey base and human persecution.
The greater hog badger (Arctonyx collaris) is found widely but patchily in South East Asia from southern China (Yunnan) to the Malay Peninsula, where it is threatened by hunting and trapping.
The large-spotted civet (Viverra megaspila) is a rarely seen species found widely but patchily in southern China, Cambodia, Laos, Myanmar, Thailand, Vietnam, and peninsular Malaysia.
The Sunda pangolin (Manis javanica) is an arboreal species still found throughout much of South East Asia from Myanmar and Vietnam to Java. It is everywhere seriously threatened, however, by overcollection for use as food and in Chinese ‘traditional medicine’.
The Asian small-clawed otter (Aonyx cinereus) continues to have a very wide distribution extending from South Asia, through South East Asia to Sumatra, Borneo, and Palawan in the Philippines. The species has undergone considerable declines, however, due to hunting and loss of habitat, and has been extirpated from many areas. The escape of captive specimens in England in recent years has resulted in an introduced population there.
The hairy-nosed otter (Lutra sumatrana) is the rarest and least-known of Asian otters. Once thought to be extinct due to overhunting, it has been rediscovered in a number of areas across South East Asia (Thailand, Vietnam, Cambodia, and Sumatra), with an additional record from northern Myanmar. There are also historical records from Borneo, peninsular Malaysia, Laos, and north-eastern India.
The smooth-coated otter (Lutrogale perspicillata) is divided into three subspecies. The nominate form (L. p. perspicillata) remains widespread in South and South East Asia, but is everywhere threatened by loss of habitat, pollution, and hunting.
Temminck’s flying squirrel (Petinomys setosus) is found patchily throughout much of South East Asia in northern Myanmar, Thailand, the Malay Peninsula, Sumatra, and northern Borneo. It is everywhere threatened by loss of habitat.
The greater marmoset rat (Hapalomys longicaudatus) is known from a few scattered localities in southern Myanmar, western Thailand, and the Malay Peninsula.
The lesser ranee mouse (Haeromys pusillus) is known only from a few specimens collected on Palawan and Calauit in the Philippines and from northern Borneo.
The white-collared fruit bat (Megaerops wetmorei) is found widely but patchily in south-western peninsular Malaysia, central Sumatra, northern Borneo, and Mindanao in the Philippines. The tailless fruit bat (M. kusnotoi) is currently confined to two disjunct areas in eastern and western Java, although there is evidence to suggest that the species formerly occurred on Bali and Lombok as well. Both are threatened by loss of habitat.
Andersen’s flying fox (Pteropus speciosus) is known for certain only from Mindanao and the Sulu Islands in the Philippines, as well as from the Talaud Islands and two small islands off the south-eastern coast of Borneo. The goldenmantled flying fox (P. pumilus) is widespread within the Philippines, occurring as well on Miangas (Palmas) Island off the north-eastern coast of Borneo. Both are threatened by loss of habitat, hunting,, and human persecution.
The Javan slit-faced bat (Nycteris javanica) is a forest and cave-dependent species known sporadically from Java, Nusa Penida, and the Kangean Islands of Indonesia.
Thomas’ woolly bat (Kerivoula flora) has a highly disjunct range in north-eastern Borneo, Bali, and in the Lesser Sunda Islands (Sumbawa, Sumba, and Flores). It is threatened by loss of habitat.
The slender-billed vulture (Gyps tenuirostris) and the white-rumped vulture (G. bengalensis) were both historically widespread and common in mainland South and South East Asia. Populations began to decline during the latter half of the nineteenth century owing to loss of habitat, but in recent years have all but collapsed due to poisoning and human persecution. Both are now largely confined to parts of India, Myanmar, and Cambodia.
The red-headed vulture (Sarcogyps calvus) was once similarly widespread and abundant in South and South East Asia from the Himalayas to southern peninsular Malaysia, but has undergone a massive and rapid decline mainly due to poisoning, habitat destruction and human persecution.
The spot-billed pelican (Pelecanus philippensis) nested in huge numbers throughout South and South East Asia in the late nineteenth century. One colony alone on the Sittaung River, in what was then southern Burma, was described in 1877 as covering 300 km2 and containing millions. Immense numbers still bred in the area in 1910, but by 1939 all the birds had completely disappeared due to deforestation and human disturbance. Similar declines were noted elsewhere, but the species is now well-protected and still numbers between 13,000 and 18,000 overall.
The milky stork (Mycteria cinerea) is found widely but sporadically in Cambodia, Peninsular Malaysia and on the islands of Sumatra, Sulawesi, Buton, Java, Bali, and Sumbawa in Indonesia, where it primarily inhabits mangroves, tidal mudfields, rice fields, and swamps. It is seriously threatened by intense hunting pressure at its nesting colonies as well as by human disturbance and loss of its coastal habitat.
Two subspecies of white-necked stork (Ciconia episcopus) occur patchily throughout much of Asia where they are everywhere threatened by hunting and habitat destruction. The nominate form (C. e. episcopus) is found from India through Indochina to the Philippines, the Malay Peninsula and northern Sumatra. The Sundaic white-necked stork (C. e. neglecta) is found in southern Sumatra, Java, Sulawesi and the Lesser Sunda Islands.
The lesser adjutant (Leptoptilos javanicus) is a type of stork found widely in wetland areas across South and South East Asia, but is everywhere threatened by hunting and habitat destruction.
The white-shouldered ibis (Pseudibis davisoni) historically occurred widely, if patchily, from south-western China to Borneo, but is now restricted to northern and eastern Cambodia, extreme southern Laos, and a small area of Borneo (East Kalimantan, Indonesia). Based on its significant declines it has been described as the most seriously threatened large waterbird in South East Asia.
The black-bellied tern (Sterna acuticauda) historically occurred throughout southern Asia from Pakistan to Vietnam but has been wholly or entirely extirpated in South East Asia due to loss of habitat and the overcollection of eggs. The surviving population, thought to be less than 10,000, is now confined to the vicinity of large rivers on the Indian subcontinent.
The white-winged wood duck (Asarcornis scutulata) was historically widely distributed in the wetlands of South East Asia, but has undergone an astonishing decline over the last century. Today a total of perhaps 1000 birds survive in isolated pockets scattered from India to Sumatra.
The masked finfoot (Heliopais personatus) is an aquatic, grebe-like bird found very patchily from north-eastern India and Bangladesh through South East Asia to Sumatra and perhaps Java. In 2016 the total population was estimated at between 1000 and 2500.
The green peafowl (Pavo muticus) was historically widespread and common throughout much of South East Asia but has been extirpated from most of its former range by loss of habitat and hunting for its meat and feathers. Populations are now confined to southern China (Yunnan), parts of Myanmar, Thailand, Laos, Cambodia and Vietnam, and the island of Java.
The yellow-crested cockatoo (Cacatua sulphurea) historically ranged throughout a relatively wide area of Indonesia, with an additional, introduced population on Hong Kong. It is now seriously threatened by trapping for the international cagebird trade, with over 100,000 having been illegally exported from Indonesia between 1980 and 1992 alone. Several subspecies will be discussed in more detail below.
The sunset lorikeet (Trichoglossus forsteni) was, as a species, historically found in the western Lesser Sunda Islands and smaller islands to the north, where it has suffered serious declines due to overcollection for the cage-bird trade. Mitchell’s sunset lorikeet (T. f. forsteni) is known from a few areas on Bali and Lombok.
The grey imperial pigeon (Ducula pickeringii) is confined to a scattering of small islands in the southern Philippines and off the northern coasts of Borneo and Sulawesi, where it is threatened by habitat destruction and hunting.
The straw-headed bulbul (Pycnonotus zeylanicus) was, up until the late twentieth century, common throughout the Malay Peninsula and Indonesia but has suffered massive declines primarily due to trapping for the cage-bird trade. It is now most likely extirpated from Thailand, Myanmar, Java and a few smaller islands, surviving only in peninsular Malaysia, Singapore, and parts of Borneo and Sumatra.
The great slaty woodpecker (Mulleripicus pulverulentus) is the largest species of woodpecker that is certain to exist today. While still found across a large part of the Indian subcontinent and South East Asia it is everywhere threatened by the destruction of its preferred habitat (old-growth forests), and is hunted in some areas.
The Siamese crocodile (Crocodylus siamensis) is among the most threatened of all crocodilians. Historically found over much of mainland South East Asia as well as in Indonesia, it was heavily hunted for its hide and by the 1990s virtually extinct in the wild. The situation has not changed much since, with only small wild populations scattered in remote areas of Vietnam, Cambodia, Laos, Thailand and Indonesia (Borneo and Java). The species is very common in captivity, however, particularly in crocodile farms.
The Asian giant tortoise (Manouria emys) is divided into two subspecies found patchily in South East Asia. The southern Asian giant tortoise (M. e. emys) occurs in the Malay Peninsula and parts of Sumatra and Borneo, where it has suffered considerable declines due to loss of habitat and collection for use as food.
The elongated tortoise (Indotestudo elongata) remains widespread in India (Tripura, Jalpaiguri, East Bengal, and Bihar), Nepal, Bangladesh, Myanmar, Laos, Thailand, Cambodia, Vietnam, peninsular Malaysia, and southern China, but is everywhere declining due to mass harvesting for food and overcollection by the international pet trade.
The frog-faced softshell turtle (Pelochelys cantorii), one of the world’s largest extant freshwater turtles, historically occurred across much of southern Asia from India and Indochina to Sumatra, Borneo, Java and the Philippines. The species has disappeared from most of this range due to hunting and habitat destruction.
The black-rayed softshell turtle (Amyda cartilaginea) remains fairly widespread from north-eastern India through South East Asia to Java and Borneo, but is everywhere threatened by overcollection for use as food.
The Malayan flat-shelled turtle (Notochelys platynota) remains widespread in South East Asia but has suffered serious declines due to overharvesting for food.
The South East Asian box turtle (Cuora amboinensis) is divided into at least four subspecies. The Burmese box turtle (C. a. lineata) is confined to parts of Myanmar, where it is seriously threatened by overcollection for use as food and in ‘traditional medicine’.
The sunburst turtle (Heosemys spinosa) is found widely but patchily inMyanmar, theMalay Peninsula (including Singapore), Borneo and the Philippines,where it has been seriously reduced in number by overcollection for Asian food markets.
The black marsh turtle (Siebenrockiella crassicollis) is found patchily in South East Asia, including the islands of Sumatra, Java and Borneo, where it is threatened by overharvesting.
Two species of roofed turtle (Batagur) are among the most seriously endangered chelonians in the world. The northern roofed turtle (B. baska) continues to survive in India, Bangladesh, Cambodia, and parts of Indonesia and Malaysia, having been extirpated from Myanmar, Thailand, Vietnam, and Singapore. The southern roofed turtle (B. affinis) occurs in Cambodia, Sumatra, and the Malay Peninsula.
The yellow-headed temple turtle (Heosemys annandalii) is found in Cambodia, Laos, the Malay Peninsula, Vietnam and possibly Myanmar, where it has been greatly reduced in number due to overcollection for Asian food markets.
The Burmese python (Python bivittatus) is found in northeastern India (where it is known only from two small, disjunct areas), through Nepal and southern China (including the island of Hainan) and throughout most of mainland South East Asia. It is absent from the Malay Peninsula, Borneo and Sumatra, but occurs on Java, Bali, Sumbawa and possibly Lombok as well as in southern Sulawesi. Although widely distributed it is everywhere declining due to overcollection for its meat and leather, as well as by loss of habitat. The species has been introduced and established in southern Florida, USA via the pet trade, where it has become a serious threat to the native fauna.
The king cobra (Ophiophagus hannah) remains relatively common across South and South East Asia, but is threatened by loss of habitat. As the world’s largest venomous snake, it is also highly persecuted by humans.
Boulenger’s cross frog (Oreophryne monticola) is known only from the mountains of Bali and Lombok in Indonesia. Volcanic activity is a particular threat on the latter island. The Tasan frog (Alcalus tasanae) is known only from a few disjunct areas of western and southern Thailand but may occur as well in southern Myanmar.
The giant freshwater whipray (Urogymnus polylepis), one of the world’s largest freshwater fish, was historically found in large rivers and estuaries across southern and South East Asia, including the island of Borneo and possibly western Java. Overfishing and habitat destruction have since reduced it to a few disjunct localities.
The longnose marbled whipray (Fluvitrygon oxyrhyncha) is a very rare species known only from a few specimens collected from Cambodia, Thailand, southern Vietnam and Borneo. The white-edge whipray (F. signifer) is found widely but patchily in Thailand, peninsular Malaysia, Sumatra and Borneo.
The Asian bony-tongues (Scleropages) are long-bodied fish that inhabit blackwater rivers, forested swamps and wetlands throughout much of South East Asia, although in very low densities. The Sunda bony-tongue (S. formosus) occurs in the Mekong drainage of Vietnam and Cambodia, as well as in south-eastern Thailand, the Malay Peninsula, Borneo, and Sumatra, with an additional introduced population on Singapore. It is threatened by overcollection for the international aquarium trade and habitat destruction. The Burmese bony-tongue (S. inscriptus) is known only from captive individuals that may have been either wild-caught or farm-bred. The species has been reported from the Great Tenasserim River drainage of peninsular Myanmar and from Pedu Lake, western Malaysia, with further anecdotal reports from rivers on the Andaman coast of Thailand.
Jullien’s golden carp (Probarbus jullieni) historically occurred in the Mekong, Chao Phraya and Mae Klong River drainages of Thailand, Vietnam, Cambodia and Laos, as well as the Pahang, Terengganu and Perak rivers of peninsular Malaysia. The species has become rare or extirpated in many areas due to loss of habitat and damming, although it is also being bred commercially in Thailand and Laos, where it is considered a delicacy.
The giant sharkminnow (Osteochilus schlegelii) is found patchily in Indochina, peninsular Malaysia, Sumatra, and Borneo.
Anthropogenic effects on the flora and fauna
In recent historical time (i.e. ad since 1500), the Indo-Malaysian Realm as a whole has lost at least 57 species/19subspecies of vertebrates. Among the extinct forms 9 species/6 subspecies are mammals, 3 species/13 subspecies are birds, 6 species are reptiles, 20 species are amphibians, and 19 species are freshwater fishes. Another 24 species/3 subspecies are possibly extinct, and 3 species/2 subspecies are currently extinct in the wild.
In addition, there are 1965 species/159 subspecies currently threatened with extinction (that is to say, either Critically Endangered, Endangered, or Vulnerable according to the IUCN Red List, as well as certain forms either listed as Data Deficient or Not Assessed but which are clearly at some risk of extinction). Of these, 417 species/107 subspecies are mammals, 289 species/40 subspecies are birds, 330 species/12 subspecies are reptiles, 390 species are amphibians, and 539 species are freshwater fishes.