Sundaland-at-the-Last-Glacial-Maximum-showing-the-modern-distribution-of-land-in-dark

Sundaland (also called Sundaica or the Sundaic region) is a biogeographical region of

Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

corresponding to a larger landmass that was exposed throughout the last 2.6 million years during periods when sea levels were lower. It includes

Bali Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller o ...

Borneo Borneo () is the List of islands by area, third-largest island in the world, with an area of , and population of 23,053,723 (2020 national censuses). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda ...

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

, and

Sumatra Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

, and their surrounding small islands, as well as the

Malay Peninsula The Malay Peninsula is located in Mainland Southeast Asia. The landmass runs approximately north–south, and at its terminus, it is the southernmost point of the Asian continental mainland. The area contains Peninsular Malaysia, Southern Tha ...

Mainland Southeast Asia Mainland Southeast Asia (historically known as Indochina and the Indochinese Peninsula) is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to th ...

Extent

The area of Sundaland encompasses the

Sunda Shelf Geology, Geologically, the Sunda Shelf () is a south-eastern extension of the continental shelf of Mainland Southeast Asia. Major landmasses on the shelf include the Indonesia, Indonesian islands of Bali, Borneo, Java, Madura Island, Madura, an ...

, a tectonically stable extension of Southeast Asia's continental shelf that was exposed during

glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

s of the last 2 million years. The extent of the Sunda Shelf is approximately equal to the 120-meter

isobath A bathymetric chart is a type of isarithmic map that depicts the submerged bathymetry and physiographic features of ocean and sea bottoms. Their primary purpose is to provide detailed depth contours of ocean topography as well as provide the si ...

. In addition to the Malay Peninsula and the islands of Borneo, Java, and Sumatra, it includes the

Java Sea The Java Sea (, ) is an extensive shallow sea on the Sunda Shelf, between the Indonesian islands of Borneo to the north, Java to the south, Sumatra to the west, and Sulawesi to the east. Karimata Strait to its northwest links it to the South Ch ...

, the

Gulf of Thailand The Gulf of Thailand (), historically known as the Gulf of Siam (), is a shallow inlet adjacent to the southwestern South China Sea, bounded between the southwestern shores of the Indochinese Peninsula and the northern half of the Malay Peninsula. ...

, and portions of the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan island, Taiwan and northwestern Philippines (mainly Luz ...

. In total, the area of Sundaland is approximately 1,800,000 km². The area of exposed land in Sundaland has fluctuated considerably during the past recent 2 million years; the modern land area is approximately half of its maximum extent. The western and southern borders of Sundaland are clearly marked by the deeper waters of the

Sunda Trench The Sunda Trench, earlier known as and sometimes still indicated as the Java Trench, is an oceanic trench located in the Indian Ocean near Sumatra, formed where the Australian- Capricorn plates subduct under a part of the Eurasian plate. It is l ...

– some of the deepest in the world – and the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

. The eastern boundary of Sundaland is the

Wallace Line The Wallace Line or Wallace's Line is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace and named by the English biologist Thomas Henry Huxley. It separates the biogeographic realms of Asia and 'Wallacea', a ...

, identified by

Alfred Russel Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was an English naturalist, explorer, geographer, anthropologist, biologist and illustrator. He independently conceived the theory of evolution through natural selection; his 1858 pap ...

as the eastern boundary of the range of Asia's land

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

fauna, and thus the boundary of the

Indomalayan The Indomalayan realm is one of the eight biogeographic realms. 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 Ind ...

and

Australasian realm The Australasian realm is one of eight biogeographic realms that is coincident with, but not (by some definitions) the same as, the geographical region of Australasia. The realm includes Australia, the island of New Guinea (comprising Papua Ne ...

s. The islands east of the Wallace line are known as

Wallacea Wallacea is a biogeography, biogeographical designation for a group of mainly list of islands of Indonesia, Indonesian islands separated by deep-water straits from the Asian and Australia (continent), Australian continental shelf, continental ...

, a separate biogeographical region that is considered part of

Australasia Australasia is a subregion of Oceania, comprising Australia, New Zealand (overlapping with Polynesia), and sometimes including New Guinea and surrounding islands (overlapping with Melanesia). The term is used in a number of different context ...

. The Wallace Line corresponds to a deep-water channel that has never been crossed by any land bridges. The northern border of Sundaland is more difficult to define in bathymetric terms; a phytogeographic transition at approximately 9ºN is considered to be the northern boundary. Greater portions of Sundaland were most recently exposed during the last glacial period from approximately 110,000 to 12,000 years ago. When the sea level was decreased by 30–40 meters or more, land bridges connected the islands of Borneo, Java, and Sumatra to the Malay Peninsula and mainland Asia. Because the sea level was 30 meters or more lower throughout much of the last 800,000 years, the current status of Borneo, Java, and Sumatra as islands has been a relatively rare occurrence throughout the Pleistocene. In contrast, the sea level was higher during the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58 Sundaland was partially submerged starting around 18,000 years ago and continuing until about 5000 BC. During the

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered m ...

the sea level fell by approximately 120 meters, and the entire Sunda Shelf was exposed.

Modern climate

All of Sundaland is within the

tropics The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

; the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

runs through central Sumatra and Borneo. Like elsewhere in the tropics, rainfall, rather than temperature, is the major determinant of regional variation. Most of Sundaland is classified as perhumid, or everwet, with over 2,000 millimeters of rain annually; rainfall exceeds

evapotranspiration Evapotranspiration (ET) refers to the combined processes which move water from the Earth's surface (open water and ice surfaces, bare soil and vegetation) into the Atmosphere of Earth, atmosphere. It covers both water evaporation (movement of w ...

throughout the year and there are no predictable dry seasons like elsewhere in Southeast Asia. The warm and shallow seas of the Sunda Shelf (averaging 28 °C or more) are part of the Indo-Pacific Warm Pool/

Western Pacific Warm Pool The Tropical Warm Pool (TWP) or Indo-Pacific Warm Pool is a mass of ocean water located in the western Pacific Ocean and eastern Indian Ocean which consistently exhibits the highest water temperatures over the largest expanse of the Earth's surface ...

and an important driver of the

Hadley circulation The Hadley cell, also known as the Hadley circulation, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward near the tropopause at a height of above the Earth's surface, cooling and des ...

and the

El Niño-Southern Oscillation EL, El or el may refer to: Arts and entertainment Fictional entities * El, a character from the manga series ''Shugo Chara!'' by Peach-Pit * Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things'' * El, fami ...

(ENSO), particularly in January when it is a major heat source to the atmosphere. ENSO also has a major influence on the climate of Sundaland; strong positive ENSO events result in droughts throughout Sundaland and tropical Asia.

Modern ecology

The high rainfall supports closed canopy evergreen forests throughout the islands of Sundaland, transitioning to deciduous forest and savanna woodland with increasing latitude. The remaining primary (unlogged) lowland forest is known for giant

dipterocarp Dipterocarpaceae is a family of flowering plants with 22 genera and about 695 known species of mainly lowland tropical forest trees. Their distribution is pantropical, from northern South America to Africa, the Seychelles, India, Indochina, Indo ...

trees and

orangutan Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Classified in the genus ...

s; after logging, forest structure and community composition change to be dominated by shade intolerant trees and shrubs. Dipterocarps are notable for mast fruiting events, where tree fruiting is synchronized at unpredictable intervals resulting in predator satiation. Higher elevation forests are shorter and dominated by trees in the oak family. Botanists often include Sundaland, the adjacent

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

and

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

in a single

floristic province A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both re ...

Malesia Malesia is a biogeographical region straddling the Equator and the boundaries of the Indomalayan and Australasian realms. It is a phytogeographical floristic region in the Paleotropical kingdom. It was first recognized as a distinct region ...

, based on similarities in their flora, which is predominantly of Asian origin. During the last glacial period, sea levels were lower and all of Sundaland was an extension of the Asian continent. As a result, the modern islands of Sundaland are home to many Asian mammals including

elephants Elephants are the Largest and heaviest animals, largest living land animals. Three living species are currently recognised: the African bush elephant (''Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian ele ...

monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes. Thus monkeys, in that sense, co ...

ape Apes (collectively Hominoidea ) are a superfamily of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and Europe in prehistory, and counting humans are found global ...

tiger The tiger (''Panthera tigris'') is a large Felidae, cat and a member of the genus ''Panthera'' native to Asia. It has a powerful, muscular body with a large head and paws, a long tail and orange fur with black, mostly vertical stripes. It is ...

tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...

s, and

rhinoceros A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...

. The flooding of Sundaland separated species that had once shared the same environment. One example is the river threadfin ('' Polydactylus macrophthalmus'', Bleeker 1858), which once thrived in a river system now called "North Sunda River" or "Molengraaff river". The fish is now found in the Kapuas River on the island of Borneo, and in the Musi and Batanghari rivers in Sumatra.

Selective pressure Evolutionary pressure, selective pressure or selection pressure is exerted by factors that reduce or increase reproductive success in a portion of a population, driving natural selection. It is a quantitative description of the amount of change oc ...

(in some cases resulting in

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

) has operated differently on each of the islands of Sundaland, and as a consequence, a different assemblage of mammals is found on each island. However, the current species assemblage on each island is not simply a subset of a universal Sundaland or Asian fauna, as the species that inhabited Sundaland before flooding did not all have ranges encompassing the entire Sunda Shelf. Island area and number of terrestrial mammal species are related, with the largest islands of Sundaland (Borneo and Sumatra) having the highest diversity.

Ecoregions

;

Tropical and subtropical moist broadleaf forests Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature (WWF). Description TSMF is generally found in la ...

* Eastern Java–Bali rain forests (

) *

Eastern Java–Bali montane rain forests Eastern or Easterns may refer to: Transportation Airlines *China Eastern Airlines, a current Chinese airline based in Shanghai * Eastern Air, former name of Zambia Skyways *Eastern Air Lines, a defunct American airline that operated from 192 ...

(

). * Western Java montane rain forests (

) * Western Java rain forests (

) *

Borneo lowland rain forests The Borneo lowland rain forests is an ecoregion, within the tropical and subtropical moist broadleaf forests biome, of the large island of Borneo in Southeast Asia. It supports approximately 15,000 plant species, 380 bird species and several mamm ...

(

) *

Borneo montane rain forests The Borneo montane rain forests is an ecoregion on the island of Borneo in Southeast Asia. It includes montane tropical and subtropical moist broadleaf forests, also known as a cloud forests. The ecoregion is partly in East Malaysia (Sabah and S ...

(

) *

Borneo peat swamp forests The Borneo peat swamp forests ecoregion, within the tropical and subtropical moist broadleaf forests biome, are on the island of Borneo, which is divided between Brunei, Indonesia and Malaysia. Location and description Peat swamp forests occur ...

(

) * Mentawai Islands rain forests (

Mentawai Islands Mentawai may refer to: * Mentawai Islands, Indonesia ** Mentawai Strait ** Mentawai people, ethnic group of Indonesia ** Mentawai language, their Austronesian language {{dab Language and nationality disambiguation pages ...

) *

Peninsular Malaysian montane rain forests The Peninsular Malaysian montane rain forests is an ecoregion on the Malay Peninsula. It occupies the mountainous spine of the peninsula in Malaysia and southernmost Thailand. It is in the tropical and subtropical moist broadleaf forests biome. ...

(

) *

Peninsular Malaysian peat swamp forests A peninsula is a landform that extends from a mainland and is only connected to land on one side. Peninsulas exist on each continent. The largest peninsula in the world is the Arabian Peninsula. Etymology The word ''peninsula'' derives , . ...

(

) *

Peninsular Malaysian rain forests The Peninsular Malaysian rain forests is an ecoregion on the Malay Peninsula and adjacent islands. It is in the tropical and subtropical moist broadleaf forests biome. Geography The ecoregion covers most of the southern Malay Peninsula in Malay ...

(

Anambas Islands Anambas Islands Regency () is an island regency (Indonesia), regency in the Riau Islands, Riau Islands Province, Indonesia, located in the Natuna Sea. The regency consists of 255 islands, including five List of outlying islands of Indonesia, out ...

) * Southwest Borneo freshwater swamp forests (

) * Sumatran freshwater swamp forests (

) *

Sumatran lowland rain forests The Sumatran lowland rain forests ecoregion (WWF ID: IM0158) covers the lowland forests running the length of the island of Sumatra in Indonesia. The region is one of exceptionally high biodiversity, similar to Borneo and New Guinea islands. Man ...

(

Nias Nias (, Nias: ''Tanö Niha'') is an island located off the western coast of Sumatra, Indonesia. Nias is also the name of the archipelago () of which the island is the centre, but also includes the Batu Islands to the southeast and the small ...

Bangka Island Bangka is an island lying east of Sumatra, Indonesia. It is administered under the province of the Bangka Belitung Islands, being one of its namesakes alongside the smaller island of Belitung across the Gaspar Strait. The 9th largest island in ...

) *

Sumatran montane rain forests The Sumatran montane rain forests ecoregion (WWF ID: IM0159) covers the mountainous elevations (greater than 1,000 meters) of the Barisan Mountains Range that runs the length of the southwestern side of the island of Sumatra in Indonesia. The eco ...

(

) * Sumatran peat swamp forests (

) *

Sundaland heath forests The Sundaland heath forests, also known as ''Kerangas'' forest, is a type of tropical moist forest found on the island of Borneo, which is divided between Brunei, Indonesia, and Malaysia, as well as on the Indonesian islands of Belitung and Ban ...

(

) ;

Tropical and subtropical coniferous forests Tropical and subtropical coniferous forests are a tropical forest habitat (ecology), habitat type defined by the World Wide Fund for Nature. These forests are found predominantly in North America, North and Central America and experience low level ...

* Sumatran tropical pine forests (

) ;

Montane grasslands and shrublands Montane grasslands and shrublands are a biome defined by the World Wildlife Fund. The biome includes high elevation grasslands and shrublands around the world. The term "montane" in the name of the biome refers to "high elevation", rather than t ...

Kinabalu montane alpine meadows Mount Kinabalu (Dusun language, Dusun: ''Gayo Ngaran'' or ''Nulu Nabalu'', ) is the highest mountain in Malaysia and Borneo. With a height of , it is the List of islands by highest point, third-highest peak of an island on Earth, List of South ...

(

) ;

Mangroves A mangrove is a shrub or tree that grows mainly in coastal saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen and remove sal ...

Sunda Shelf mangroves The Sunda Shelf mangroves ecoregion, in the mangrove biome, are on the coasts of the islands of Borneo and eastern Sumatra in Malaysia and Indonesia. They are home to the proboscis monkey. As well as being an important habitat for terrestrial an ...

(

Riau Islands The Riau Islands () is a provinces of Indonesia, province of Indonesia consisting of a group of islands located in the western part of the country. It was established in 2002 after being separated from the neighboring Riau Province. The capit ...

)

History

Early research

The name "Sunda" goes back to antiquity, appearing in

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

's ''Geography'', written around 150 AD. In an 1852 publication, English navigator

George Windsor Earl George Windsor Earl (10 February 1813 – 9 August 1865) was an English navigator, colonial administrator, and author of works on the Indian Archipelago. He coined the term 'Indu-nesian', later adopted as the name for Indonesia. The word's e ...

advanced the idea of a "Great Asiatic Bank", based in part on common features of mammals found in Java, Borneo and Sumatra. Explorers and scientists began measuring and mapping the seas of Southeast Asia in the 1870s, primarily using

depth sounding Depth sounding, often simply called sounding, is measuring the depth of a body of water. Data taken from soundings are used in bathymetry to make maps of the floor of a body of water, such as the seabed topography. Soundings were traditional ...

. In 1921 Gustaaf Molengraaff, a Dutch geologist, postulated that the nearly uniform sea depths of the shelf indicated an ancient

peneplain In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final (or ...

that was the result of repeated flooding events as ice caps melted, with the peneplain becoming more perfect with each successive flooding event. Molengraaff also identified ancient, now submerged, drainage systems that drained the area during periods of lower sea levels. The name "Sundaland" for the peninsular shelf was first proposed by Reinout Willem van Bemmelen in his ''Geography of Indonesia'' in 1949, based on his research during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. The ancient drainage systems described by Molengraaff were verified and mapped by Tjia in 1980 and described in greater detail by Emmel and Curray in 1982 complete with

river delta A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

s and backswamps.''The physical geography of Southeast Asia'' by Avijit Gupta, 2005, , page 403

Data types

The climate and ecology of Sundaland throughout the Quaternary has been investigated by analyzing

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

l ''δ''¹⁸O and pollen from cores drilled into the ocean bed, ''δ''¹⁸O in

speleothem A speleothem (; ) is a geological formation made by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depen ...

s from caves, and ''δ''¹³C and ''δ''¹⁵N in bat guano from caves, as well as species distribution models, phylogenetic analysis, and community structure and species richness analysis.

Climate

Perhumid climate has existed in Sundaland since the early

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

; though there is evidence for several periods of drier conditions, a perhumid core persisted in Borneo. The presence of fossil coral reefs dating to the late Miocene and early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58

Palynological Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...

evidence from Sumatra suggests that temperatures were cooler during the late Pleistocene; mean annual temperatures at high elevation sites may have been as much as 5 °C cooler than present. Most recent research agrees that Indo-Pacific

sea surface temperature Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

s were at most 2-3 °C lower during the

. Snow was found much lower than at present (approximately 1,000 meters lower) and there is evidence that glaciers existed on Borneo and Sumatra around 10,000 years before present. However, debate continues on how precipitation regimes changed throughout the Quaternary. Some authors argue that rainfall decreased with the area of ocean available for evaporation as sea levels fell with ice sheet expansion. Others posit that changes in precipitation have been minimal and an increase in land area in the Sunda Shelf alone (due to lowered sea level) is not enough to decrease precipitation in the region. One possible explanation for the lack of agreement on hydrologic change throughout the Quaternary is that there was significant heterogeneity in climate during the Last Glacial Maximum throughout Indonesia. Alternatively, the physical and chemical processes that underlie the method of inferring precipitation from ''δ''¹⁸O records may have operated differently in the past. Some authors working primarily with pollen records have also noted the difficulties of using vegetation records to detect changes in precipitation regimes in such a humid environment, as water is not a limiting factor in community assemblage.

Ecology

Sundaland, and in particular Borneo, has been an evolutionary hotspot for

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

since the early

due to repeated immigration and

vicariance Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

events. The modern islands of Borneo, Java, and Sumatra have served as refugia for the flora and fauna of Sundaland during multiple glacial periods in the last million years, and are serving the same role at present.

Savanna corridor theory

Dipterocarp Dipterocarpaceae is a family of flowering plants with 22 genera and about 695 known species of mainly lowland tropical forest trees. Their distribution is pantropical, from northern South America to Africa, the Seychelles, India, Indochina, Indo ...

trees characteristic of modern Southeast Asian tropical rainforest have been present in Sundaland since before the

. There is also evidence for

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...

vegetation, particularly in now submerged areas of Sundaland, throughout the last glacial period. However, researchers disagree on the spatial extent of savanna that was present in Sundaland. There are two opposing theories about the vegetation of Sundaland, particularly during the last glacial period: (1) that there was a continuous savanna corridor connecting modern mainland Asia to the islands of Java and Borneo, and (2) that the vegetation of Sundaland was instead dominated by tropical rainforest, with only small, discontinuous patches of savanna vegetation. The presence of a savanna corridor—even if fragmented—would have allowed for savanna-dwelling fauna (as well as early humans) to disperse between Sundaland and the

Indochinese Mainland Southeast Asia (historically known as Indochina and the Indochinese Peninsula) is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to th ...

biogeographic region; emergence of a savanna corridor during glacial periods and subsequent disappearance during interglacial periods would have facilitated speciation through both

(

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

) and

geodispersal In biogeography, geodispersal is the erosion of barriers to gene flow and biological dispersal (Lieberman, 2005.; Albert and Crampton, 2010.). Geodispersal differs from vicariance, which reduces gene flow through the creation of geographic barrie ...

. Morley and Flenley (1987) and Heaney (1991) were the first to postulate the existence of a continuous corridor of savanna vegetation through the center of Sundaland (from the modern Malay Peninsula to Borneo) during the last glacial period, based on palynological evidence. Using the modern distribution of primates, termites, rodents, and other species, other researchers infer that the extent of tropical forest contracted—replaced by savanna and open forest —during the last glacial period. Vegetation models using data from climate simulations show varying degrees of forest contraction; Bird et al. (2005) noted that although no single model predicts a continuous savanna corridor through Sundaland, many do predict open vegetation between modern Java and southern Borneo. Combined with other evidence, they suggest that a 50–150 kilometer wide savanna corridor ran down the Malay Peninsula, through Sumatra and Java, and across to Borneo. Additionally, Wurster et al. (2010) analyzed stable carbon isotope composition in bat guano deposits in Sundaland and found strong evidence for the expansion of savanna in Sundaland. Similarly, stable isotope composition of fossil mammal teeth supports the existence of the savanna corridor. In contrast, other authors argue that Sundaland was primarily covered by tropical rainforest. Using species distribution models, Raes et al. (2014) suggest that Dipterocarp rainforest persisted throughout the last glacial period. Others have observed that the submerged rivers of the Sunda Shelf have obvious, incised meanders, which would have been maintained by trees on river banks. Pollen records from sediment cores around Sundaland are contradictory; for example, cores from highland sites suggest that forest cover persisted throughout the last glacial period, but other cores from the region show pollen from savanna-woodland species increasing through glacial periods. And in contrast to previous findings, Wurster et al. (2017) again used stable carbon isotope analysis of bat guano, but found that at some sites rainforest cover was maintained through much of the last glacial period. Soil type, rather than long-term existence of a savanna corridor, has also been posited as an explanation for species distribution differences within Sundaland; Slik et al. (2011) suggest that the sandy soils of the now submerged seabed are a more likely dispersal barrier.

Paleofauna

Before Sundaland emerged during the late Pliocene and early Pleistocene (~2.4 million years ago), there were no mammals on Java. As sea level lowered, species such as the dwarf elephantoid ''Sinomastodon bumiajuensis'' colonized Sundaland from mainland Asia. Later fauna included tigers, Sumatran rhinoceros, and Indian elephant, which were found throughout Sundaland; smaller animals were also able to disperse across the region.

Human migrations

According to the most widely accepted theory, the ancestors of the modern-day

Austronesian Austronesian may refer to: *The Austronesian languages *The historical Austronesian peoples The Austronesian people, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples who have settled in Taiwan, maritime Sout ...

populations of the Maritime Southeast Asia and adjacent regions are believed to have migrated southward, from the East Asia mainland to

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

, and then to the rest of

Maritime Southeast Asia Maritime Southeast Asia comprises the Southeast Asian countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. The terms Island Southeast Asia and Insular Southeast Asia are sometimes given the same meaning as ...

. An alternative theory points to the now-submerged Sundaland as the possible cradle of Austronesian languages: thus the "Out of Sundaland" theory. However, this view is an extreme minority view among professional archaeologists, linguists, and geneticists. The Out of Taiwan model (though not necessarily the Express Train Out of Taiwan model) is accepted by the vast majority of professional researchers. A study from

Leeds University The University of Leeds is a public research university in Leeds, West Yorkshire, England. It was established in 1874 as the Yorkshire College of Science. In 1884, it merged with the Leeds School of Medicine (established 1831) and was renamed ...

and published in ''

Molecular Biology and Evolution ''Molecular Biology and Evolution'' (''MBE'') is a monthly peer-reviewed scientific journal published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. It publishes work in the intersection of molecular bi ...

'', examining

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the D ...

lineages, suggested that shared ancestry between Taiwan and Southeast Asian resulted from earlier migrations. Population dispersals seem to have occurred at the same time as sea levels rose, which may have resulted in migrations from the

Philippine The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

Islands to as far north as Taiwan within the last 10,000 years. The population migrations were most likely to have been driven by

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

— the effects of the drowning of an ancient continent. Rising sea levels in three massive pulses may have caused flooding and the submerging of the Sunda continent, creating the

and South China Seas and the thousands of islands that make up

and the

today. The changing sea levels would have caused these humans to move away from their coastal homes and culture, and farther inland throughout southeast Asia. This forced migration would have caused these humans to adapt to the new forest and mountainous environments, developing farms and domestication, and becoming the predecessors to future human populations in these regions. Genetic similarities were found between populations throughout Asia and an increase in genetic diversity from northern to southern latitudes. Although the Chinese population is very large, it has less variation than the smaller number of individuals living in Southeast Asia, because the Chinese expansion occurred fairly recently, from the mid to late-Holocene.

Stephen Oppenheimer Stephen Oppenheimer (born 1947) is a British Pediatrics, paediatrician, geneticist, and writer. He is a graduate of Balliol College, Oxford and an honorary fellow of the Liverpool School of Tropical Medicine. In addition to his work in medicin ...

locates the origin of the

Austronesians The Austronesian people, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples who have settled in Taiwan, maritime Southeast Asia, parts of mainland Southeast Asia, Micronesia, coastal New Guinea, Island Melanesi ...

in Sundaland and its upper regions. From the standpoint of

historical linguistics Historical linguistics, also known as diachronic linguistics, is the scientific study of how languages change over time. It seeks to understand the nature and causes of linguistic change and to trace the evolution of languages. Historical li ...

, the home of the

Austronesian languages The Austronesian languages ( ) are a language family widely spoken throughout Maritime Southeast Asia, parts of Mainland Southeast Asia, Madagascar, the islands of the Pacific Ocean and Taiwan (by Taiwanese indigenous peoples). They are spoken ...

is the main island of Taiwan, also known by its unofficial Portuguese name of Formosa; on this island the deepest divisions in Austronesian are found, among the families of the native

Formosan languages The Formosan languages are a geographic grouping comprising the languages of the indigenous peoples of Taiwan, all of which are Austronesian. They do not form a single subfamily of Austronesian but rather up to nine separate primary subfamili ...

References

Selected faunal references in Borneo

* Abdullah MT. 2003. Biogeography and variation of ''Cynopterus brachyotis'' in Southeast Asia. PhD thesis. The University of Queensland, St Lucia, Australia. * Corbet, GB, Hill JE. 1992. The mammals of the Indomalayan region: a systematic review. Oxford University Press, Oxford. * Hall LS, Gordon G. Grigg, Craig Moritz, Besar Ketol, Isa Sait, Wahab Marni, Abdullah MT. 2004. Biogeography of fruit bats in Southeast Asia. Sarawak Museum Journal LX(81):191–284. * Karim, C., A.A. Tuen, Abdullah MT. 2004. Mammals. Sarawak Museum Journal Special Issue No. 6. 80: 221–234. * * * Wilson DE, Reeder DM. 2005. Mammal species of the world. Smithsonian Institution Press, Washington DC.

External links

Review of Oppenheimer's Eden in the East, about Sundaland
{{Borneo Historical continents Biogeography Continental shelves Historical geology Indomalayan realm Malesia Prehistoric Indonesia