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Wallacea is a biogeographical designation for a group of mainly Indonesian islands separated by deep-water
strait A strait is an oceanic landform connecting two seas or two other large areas of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly, it is a narrow ocean chan ...
s from the Asian and Australian continental shelves. Wallacea includes
Sulawesi Sulawesi (), also known as Celebes (), is an island in Indonesia. One of the four Greater Sunda Islands, and the world's eleventh-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu ...
, the largest island in the group, as well as Lombok, Sumbawa,
Flores Flores is one of the Lesser Sunda Islands, a group of islands in the eastern half of Indonesia. Including the Komodo Islands off its west coast (but excluding the Solor Archipelago to the east of Flores), the land area is 15,530.58 km2, and t ...
, Sumba,
Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, ...
,
Halmahera Halmahera, formerly known as Jilolo, Gilolo, or Jailolo, is the largest island in the Maluku Islands. It is part of the North Maluku province of Indonesia, and Sofifi, the capital of the province, is located on the west coast of the island. Ha ...
, Buru, Seram, and many smaller islands. The islands of Wallacea lie between the Sunda Shelf (the
Malay Peninsula The Malay Peninsula ( Malay: ''Semenanjung Tanah Melayu'') is a peninsula 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 ar ...
,
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 sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...
,
Borneo Borneo (; id, Kalimantan) is the third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java, west of Sulawesi, and e ...
,
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...
, and
Bali Bali () is a 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 neighbouring islands, notably Nusa Penida, Nusa Lembongan, and ...
) to the west, and the Sahul Shelf including
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
and
New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torres ...
to the south and east. The total land area of Wallacea is .


Geography

Wallacea is defined as the series of islands stretching between the two continental shelves of Sunda and Sahul, but excluding the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
. Its eastern border (separating Wallacea from Sahul) is represented by a
zoogeographical Zoogeography is the branch of the science of biogeography that is concerned with geographic distribution (present and past) of animal species. As a multifaceted field of study, zoogeography incorporates methods of molecular biology, genetics, mor ...
boundary known as
Lydekker's Line Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...
, while the Wallace Line (separating Wallacea from Sunda) defines its western border. The Weber Line is the midpoint, at which Asian and Australian fauna and flora are approximately equally represented. It follows the deepest
strait A strait is an oceanic landform connecting two seas or two other large areas of water. The surface water generally flows at the same elevation on both sides and through the strait in either direction. Most commonly, it is a narrow ocean chan ...
s traversing the
Indonesian Archipelago The islands of Indonesia, also known as the Indonesian Archipelago ( id, Kepulauan Indonesia) or Nusantara, may refer either to the islands comprising the country of Indonesia or to the geographical groups which include its islands. History ...
. The Wallace Line is named after the
Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peopl ...
naturalist
Alfred Russel Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British natural history, naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution thro ...
, who recorded the differences between mammal and bird fauna between the islands on either side of the line. The islands of
Sundaland Sundaland (also called Sundaica or the Sundaic region) is a biogeographical region of South-eastern Asia corresponding to a larger landmass that was exposed throughout the last 2.6 million years during periods when sea levels were lower. It ...
to the west of the line, including Sumatra, Java, Bali, and Borneo, share a mammal fauna similar to that of East Asia, which includes tigers, rhinoceros, and apes; whereas the mammal fauna of Lombok and areas extending eastwards are mostly populated by marsupials and birds similar to those in Australasia. Sulawesi shows signs of both. During the ice ages, sea levels were lower, exposing the Sunda shelf that links the islands of Sundaland to one another and to Asia and allowing Asian land animals to inhabit these islands. The islands of Wallacea have few land mammals, land birds, or freshwater fish of continental origin, which find it difficult to cross open ocean. Many species of birds, reptiles, and insects were better able to cross the straits, and many such species of Australian and Asian origin are found there. Wallacea's plants are predominantly of Asian origin, and botanists include Sundaland, Wallacea, and New Guinea as the floristic province of Malesia. Similarly, Australia and New Guinea to the east are linked by a shallow continental shelf, and were linked by a land bridge during the ice ages, forming a single continent that scientists variously call
Australia-New Guinea The continent of Australia, sometimes known in technical contexts by the names Sahul (), Australia-New Guinea, Australinea, Meganesia, or Papualand to distinguish it from the country of Australia, is located within the Southern and Easte ...
, Meganesia, Papualand, or Sahul. Consequently, Australia, New Guinea, and the Aru Islands share many
marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...
mammals, land birds, and freshwater fish that are not found in Wallacea.


Biota and conservation issues

Although the distant ancestors of Wallacea's flora and fauna may have been from Asia or Australia-New Guinea, Wallacea is home to many
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
species. There is extensive autochthonous
speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution withi ...
and proportionately large numbers of endemics; it is an important contributor to the overall mega-
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity'') ...
of the Indonesian archipelago. Fauna species include the endemic
anoa Anoa, also known as dwarf buffalo and ''sapiutan'', are two species of the genus ''Bubalus'' endemic to the island of Sulawesi in Indonesia: the mountain anoa (''Bubalus quarlesi'') and the lowland anoa (''Bubalus depressicornis''). Both live ...
(dwarf buffalo) of Sulawesi and the
babirusa The babirusas, also called deer-pigs ( id, babi rusa), are a genus, ''Babyrousa'', in the swine family found in the Indonesian islands of Sulawesi, Togian, Sula and Buru. All members of this genus were considered part of a single species un ...
(deer pig). Maluku shows a degree of species similarity with Sulawesi, but with fewer flora and fauna. Smaller mammals including primates are common.
Seram Island Seram (formerly spelled Ceram; also Seran or Serang) is the largest and main island of Maluku province of Indonesia, despite Ambon Island's historical importance. It is located just north of the smaller Ambon Island and a few other adjacent is ...
is noted for its butterflies and birdlife including the Moluccan king parrot. Wallacea was originally almost completely forested, mostly tropical moist broadleaf forests, with some areas of tropical dry broadleaf forest. The higher mountains are home to montane and subalpine forests, and mangroves are common in coastal areas. According to Conservation International, Wallacea is home to over 10,000 plant species, of which approximately 1,500 (15%) are endemic. Endemism is higher among terrestrial vertebrate species; of 1,142 species found there, almost half (529) are endemic. 45% of the region retains some sort of forest cover, and only 52,017 km2, or 15 percent, is in a pristine state. Of Wallacea's total area of 347,000 km2, about 20,000 km2 are protected. Wallacea is home to 82 threatened and six critically endangered species of terrestrial vertebrates.


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. Description TSMF is generally found in large, discon ...
: * Banda Sea Islands moist deciduous forests ( Kai Islands, Tanimbar Islands, Babar Islands, Leti Islands, eastern Barat Daya Islands) * Buru rain forests ( Buru) *
Halmahera rain forests The Halmahera rain forests is a tropical moist forest ecoregion in Indonesia. The ecoregion includes the island of Halmahera and neighboring islands, including Bacan, Morotai, the Obi Islands, Ternate, Tidore, Gebe, and many smaller islands. ...
(
Halmahera Halmahera, formerly known as Jilolo, Gilolo, or Jailolo, is the largest island in the Maluku Islands. It is part of the North Maluku province of Indonesia, and Sofifi, the capital of the province, is located on the west coast of the island. Ha ...
, Morotai, Obi Islands, Bacan Island) * Seram rain forests ( Seram, Banda Islands,
Ambon Island Ambon Island is part of the Maluku Islands of Indonesia. The island has an area of and is mountainous, well watered, and fertile. Ambon Island consists of two territories: the city of Ambon to the south and various districts (''kecamatan'') o ...
,
Saparua Saparua is an island east of Ambon Island in the Indonesian province of Maluku; the island of Haruku lies between Saparua and Ambon. The main port is in the south at Kota Saparua. The island of Maolana is located near its southwestern side and ...
, Gorong archipelago) * Sulawesi lowland rain forests (Sulawesi, Banggai Islands, Sula Islands,
Sangihe Islands The Sangihe Islands (also spelled "Sangir", "Sanghir" or "Sangi") – id, Kepulauan Sangihe – are a group of islands which constitute two regencies within the province of North Sulawesi, in northern Indonesia, the Sangihe Islands R ...
, Talaud Islands) * Sulawesi montane rain forests (Sulawesi)
Tropical and subtropical dry broadleaf forests The tropical and subtropical dry broadleaf forest is a habitat type defined by the World Wide Fund for Nature and is located at tropical and subtropical latitudes. Though these forests occur in climates that are warm year-round, and may receive ...
: * Lesser Sundas deciduous forests (Lombok, Sumbawa,
Komodo Komodo may refer to: Computers * Komodo Edit, a free text editor for dynamic programming languages * Komodo IDE an integrated development environment (IDE) for dynamic programming languages * Komodo (chess), a chess engine People * Komo ...
, Flores, Alor) * Sumba deciduous forests (Sumba) *
Timor and Wetar deciduous forests The Timor and Wetar deciduous forests is a tropical dry forest ecoregion in Indonesia and East Timor. The ecoregion includes the islands of Timor, Wetar, Rote, Savu, and adjacent smaller islands. Geography Timor, Wetar, Rote, and Savu are pa ...
(
Timor Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, ...
, Wetar)


Distribution between Asia and Australia

Australia may be isolated by sea, but technically through Wallacea, it can be zoologically extended. Australian Early-Middle Pliocene rodent fossils have been found in Chinchilla Sands and Bluffs Down in Queensland, but a mix of ancestral and derived traits suggest murid rodents made it to Australia earlier, maybe in the Miocene, over a forested archipelago, i.e. Wallacea, and evolved in Australia in isolation. Australia's rodents make up much of the continent's placental mammal fauna and include various species from stick-nest rats to
hopping mice A hopping mouse is any of about ten different Australian native mice in the genus ''Notomys''. They are rodents, not marsupials, and their ancestors are thought to have arrived from Asia about 5 million years ago. All are brown or fawn, fadin ...
. Other mammals invaded from the east. Two species of cuscus, the
Sulawesi bear cuscus The Sulawesi bear cuscus, also known as the Sulawesi bear phalanger (''Ailurops ursinus''), is a species of arboreal marsupial in the family Phalangeridae that is endemic to Sulawesi and nearby islands in Indonesia. It lives in tropical moist lo ...
and the
Sulawesi dwarf cuscus The Sulawesi dwarf cuscus (''Strigocuscus celebensis'') is a species of arboreal marsupial in the family Phalangeridae that is endemic to Sulawesi and nearby islands in Indonesia. It inhabits tropical moist lowland forest and is nocturnal, foliv ...
, are the westernmost representatives of the Australasian marsupials. The tectonic uplift of Wallacea during the collision between Australia and Asia 23 million years ago allowed the global dispersal of
passerine A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by th ...
birds from Australia across the Indonesian islands. Bustards and megapodes must have somehow colonized Australia.
Cockatiel The cockatiel (; ''Nymphicus hollandicus''), also known as weiro (also spelt weero), or quarrion, is a medium-sized parrot that is a member of its own branch of the cockatoo family endemic to Australia. They are prized as household pets and c ...
s similar to those from Australia inhabit Komodo Island in Wallacea. A few species of ''
Eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as ...
'', a predominant genus of trees in Australia, are found in Wallacea: '' Eucalyptus deglupta'' on Sulawesi, and '' E. urophylla'' and '' E. alba'' in East Nusa Tenggara. For land snails Wallacea and Wallace's Line do not form a barrier for dispersal.


References

Regions of Southeast Asia


External links

{{Portal, Indonesia, Oceania
Conservation International: Wallacea

Too Many Lines; The Limits of the Oriental and Australian Zoogeographic Regions
George Gaylord Simpson, Proceedings of the American Philosophical Society, Vol. 121, No. 2 (Apr. 29, 1977), pp. 107–120
Wallacea Research Group
Biogeography Australasian realm Ecoregions of Asia Maritime Southeast Asia