Wallacea is a
biogeographical
Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...
designation for a group of mainly
Indonesian islands
* See also: Names of Indonesia
, location = Southeast Asia and Oceania
, waterbody =
* Indian Ocean
* Pacific Ocean
, total_islands = ± 17,000–18,000 islands
, major_islands =
, area_km2 = 8,300,000
, area_footnotes =
, rank =
, length_ ...
separated by deep-water
straits from the
Asian and
Australian continental shelves. Wallacea includes
Sulawesi, the largest island in the group, as well as
Lombok
Lombok is an island in West Nusa Tenggara province, Indonesia. It forms part of the chain of the Lesser Sunda Islands, with the Lombok Strait separating it from Bali to the west and the Alas Strait between it and Sumbawa to the east. It is ...
,
Sumbawa,
Flores,
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, al ...
,
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.
H ...
,
Buru
Buru (formerly spelled Boeroe, Boro, or Bouru) is the third largest island within the Maluku Islands of Indonesia. It lies between the Banda Sea to the south and Seram Sea to the north, west of Ambon and Seram islands. The island belongs to ...
,
Seram
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 ...
, and many smaller islands. The islands of Wallacea lie between the
Sunda Shelf
Geologically, the Sunda Shelf is a south-eastern extension of the continental shelf of Mainland Southeast Asia. Major landmasses on the shelf include the Bali, Borneo, Java, Madura, and Sumatra, as well as their surrounding smaller island ...
(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 are ...
,
Sumatra,
Borneo
Borneo (; id, Kalimantan) is the List of islands by area, 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 Isl ...
,
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 Nu ...
) to the west, and the
Sahul Shelf including
Australia 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 Torr ...
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, 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
straits traversing the
Indonesian Archipelago.
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, 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
Malesia is a biogeographical region straddling the Equator and the boundaries of the Indomalayan and Australasian realms, and also a phytogeographical floristic region in the Paleotropical Kingdom. It has been given different definitions. ...
.
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, 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 a ...
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 els ...
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 (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 until ...
(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 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 tropical and subtropical dry broadleaf forest is a habitat (ecology), 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-roun ...
. The higher mountains are home to montane
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...
and subalpine forests, and mangrove
A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in several ...
s are common in coastal areas. According to Conservation International
Conservation International (CI) is an American nonprofit environmental organization headquartered in Crystal City, Arlington, Virginia.
CI's work focuses on science, policy and partnership with businesses, governments and communities. The or ...
, 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, disco ...
:
* Banda Sea Islands moist deciduous forests ( Kai Islands, Tanimbar Islands
The Tanimbar Islands, also called ''Timur Laut'', are a group of about 65 islands in the Maluku province of Indonesia. The largest and most central of the islands is Yamdena; others include Selaru to the southwest of Yamdena, Larat and Ford ...
, Babar Islands
The Babar Islands ''(''Indonesian: ''Kepulauan Babar)'' are located in Maluku Province, Indonesia between latitudes 7 degrees 31 minutes South to 8 degrees 13 minutes South and from longitudes 129 degrees 30 minutes East to 130 degrees 05 minutes ...
, Leti Islands, eastern Barat Daya Islands)
*Buru rain forests
Buru (formerly spelled Boeroe, Boro, or Bouru) is the third largest island within the Maluku Islands of Indonesia. It lies between the Banda Sea to the south and Seram Sea to the north, west of Ambon and Seram islands. The island belongs to Ma ...
(Buru
Buru (formerly spelled Boeroe, Boro, or Bouru) is the third largest island within the Maluku Islands of Indonesia. It lies between the Banda Sea to the south and Seram Sea to the north, west of Ambon and Seram islands. The island belongs to ...
)
* Halmahera rain forests (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.
H ...
, Morotai
Morotai Island ( id, Pulau Morotai) is an island in the Halmahera group of eastern Indonesia's Maluku Islands (Moluccas). It is one of Indonesia's northernmost islands.
Morotai is a rugged, forested island lying to the north of Halmahera. It ha ...
, Obi Islands, Bacan Island)
*Seram rain forests
The Seram rain forests is a tropical moist forest ecoregion in Indonesia. The ecoregion includes the island of Seram and neighboring islands.
Geography
Seram is the largest island in the ecoregion, with an area of 17,100 km². The ecoregion inc ...
(Seram
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 ...
, Banda Islands
The Banda Islands ( id, Kepulauan Banda) are a volcanic group of ten small volcanic islands in the Banda Sea, about south of Seram Island and about east of Java, and constitute an administrative district (''kecamatan'') within the Centr ...
, 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, 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, Flores, Alor)
* Sumba deciduous forests (Sumba)
* Timor and Wetar deciduous forests (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, al ...
, Wetar
Wetar is a tropical island which belongs to the Indonesian province of Maluku and is the largest island of the Maluku Barat Daya Islands (literally ''Southwest Islands'') of the Maluku Islands. It lies east of the Lesser Sunda Islands, which i ...
)
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
Placental mammals ( infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguish ...
fauna and include various species from stick-nest rats to hopping mice. Other mammals invaded from the east. Two species of cuscus
Cuscus ( or ) is the common name generally given to the species within the four genera of Australasian possum of the family Phalangeridae with the most tropical distribution:
* '' Ailurops''
* '' Phalanger''
* '' Spilocuscus''
* '' Strigocuscus ...
, 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, foli ...
, are the westernmost representatives of the Australasian marsupials.
The tectonic uplift
Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal t ...
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. Cockatiels 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 plant, flowering trees, shrubs or Mallee (habit), mallees in the Myrtaceae, myrtle Family (biology), family, Myrtaceae. Along with several other genera in the Tribe (biology) ...
'', 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