View source for Wallacea

{{Short description|Biogeographical region}}
{{Distinguish|Wallachia|Wallacia (disambiguation){{!}}Wallacia|Wallasea Island{{!}}Wallasea}}
{{For|the insect genus|Wallacea (beetle)}}
[[Image:Indonesia Wallacea.svg|thumb|upright=1.6|Wallacea is the group of islands within the red area. The [[Max Carl Wilhelm Weber|Weber Line]] in blue has been used to separate Wallacea into a western part pertaining to [[Asia]] and an eastern part pertaining to [[Oceania]].]]
[[Image:Map of Sunda and Sahul.svg|upright=1.6|thumb|The [[Sunda Shelf|Sunda]] and [[Sahul Shelf|Sahul]] shelves. Wallacea is the area in between.]]

'''Wallacea''' {{IPAc-en|w|Q|'|l|ei|s|i|@}} is a [[biogeography|biogeographical]] designation for a group of mainly [[list of islands of Indonesia|Indonesian islands]] separated by deep-water [[strait]]s from the [[Asia]]n and [[Australia (continent)|Australian]] [[continental shelf|continental shelves]]. Wallacea includes [[Sulawesi]], the largest island in the group, as well as [[Lombok]], [[Sumbawa]], [[Flores]], [[Sumba]], and [[Timor]]. The islands of Wallacea lie between the [[Sunda Shelf]] (the [[Malay Peninsula]], [[Sumatra]], [[Borneo]], and [[Java (island)|Java]]) to the west, and the [[Sahul Shelf]], including [[Australia]], [[New Guinea]], and [[Maluku islands]] to the south and east. The total land area of Wallacea is {{Convert|347000|km2|abbr=on}}.<ref name="Myers-etal">{{Cite journal
 | last1 = Myers | first1 = N.
 | last2 = Mittermeier | first2 = R. A.
 | last3 = Mittermeier | first3 = C. G.
 | last4 = Da Fonseca | first4 = G. A
 | last5 = Kent | first5 = J.
 | title = Biodiversity hotspots for conservation priorities
 | year = 2000 | journal = Nature | volume = 403 | issue = 6772 | pages = 853–857
 | url = http://wedocs.unep.org/bitstream/handle/20.500.11822/18446/Biodiversity_hotspots_for_conservation_priorit.pdf | access-date = 15 September 2019
 | doi = 10.1038/35002501 | pmid = 10706275
 | bibcode = 2000Natur.403..853M
 | s2cid = 4414279
 }}<!-- {{Harvnb|Myers|Mittermeier|Mittermeier|Da Fonseca|2000|loc=Table 1, p. 854}} --></ref>

==Geography==
Wallacea is defined as the series of islands stretching between the two continental shelves of [[Sunda Shelf|Sunda]] and [[Sahul Shelf|Sahul]], but excluding the [[Philippines]]. Its eastern border (separating Wallacea from Sahul) is represented by a [[zoogeography|zoogeographical]] boundary known as [[Lydekker Line]], while the [[Wallace Line]] (separating Wallacea (Bali and Sulawesi) from Sunda (Borneo and Java)) defines its western border.<ref name=Kealy2015>{{cite journal|title=Islands under the sea: a review of early modern human dispersal routes and migration hypotheses through Wallacea|journal=The Journal of Island and Coastal Archaeology|volume=11|issue=3|pages=364–84|year=2015|doi=10.1080/15564894.2015.1119218|url=https://www.researchgate.net/publication/287798057|last1=Kealy|first1=Shimona|last2=Louys|first2=Julien|last3=o'Connor|first3=Sue|s2cid=129964987}}</ref><ref name=New2002>{{Cite journal|last=New|first= T.R.|title=Neuroptera of Wallacea: a transitional fauna between major geographical regions|journal=Acta Zoologica Academiae Scientiarum Hungaricae|volume=48|issue=2|pages=217–27|year=2002|url=http://actazool.nhmus.hu/48Suppl2/newwallace.pdf}}</ref> 

The [[Max Carl Wilhelm Weber|Weber Line]] is the midpoint, at which Asian and Australian fauna and flora are approximately equally represented. It follows the deepest [[strait]]s traversing the [[list of islands of Indonesia|Indonesian Archipelago]].

The Wallace Line is named after the [[Wales|Welsh]] 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]] to the west of the line, including Sumatra, Java, 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.<ref name=Wallace1869>{{cite book|last=Wallace|first=Alfred Russel|author-link=Alfred Russel Wallace|title=The Malay Archipelago|chapter=Physical Geography|pages=23–30|publisher=Harper & Brothers|location=New York|year=1869|chapter-url=https://archive.org/stream/malayarchipelag05wallgoog#page/n42/mode/2up}}</ref>

During the ice ages, sea levels were lower, exposing the Sunda shelf that links the islands of Sundaland to one another and to Asia<ref>{{Cite web|title=Pleistocene Sea Level Maps|date=12 January 2011|publisher=[[Field Museum of Natural History|The Field Museum]]|url=http://www.fieldmuseum.org/research_collections/zoology/zoo_sites/seamaps/mapindex1.htm|access-date=15 September 2019|archive-date=17 March 2009|archive-url=https://web.archive.org/web/20090317193810/http://www.fieldmuseum.org/research_collections/zoology/zoo_sites/seamaps/mapindex1.htm}}</ref> 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 [[oceanic dispersal|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 Moluucca-New Guinea-Australia as the [[phytochorion|floristic province]] of [[Malesia]].{{cn|date=October 2022}}

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 (continent)|Australia-New Guinea]], Meganesia, Papualand, or Sahul. Consequently, Australia, New Guinea, and the [[Aru Islands Regency|Aru Islands]] share many [[marsupial]] mammals, land birds, and freshwater fish that are not found in Wallacea.<ref name=New2002/>

==Biota and conservation issues==
[[File:Wallacea.png|thumb|upright=1.35|A map of Wallacea, bordered by the Wallace and Lydekker lines.]]

Although the distant ancestors of Wallacea's flora and fauna may have been from Asia or Australia-New Guinea, Wallacea is home to many [[endemism|endemic]] species. There is extensive [[wikt:autochthonous|autochthonous]] [[speciation]] and proportionately large numbers of endemics; the area is an important contributor to the overall mega-[[biodiversity]] of the Indonesian Archipelago.<ref>{{cite report|title=Report on Biodiversity and Tropical Forests in Indonesia|editor1-last=Rhee|editor1-first=S.|editor2-last=Kitchener|editor2-first=D.|editor3-last=Brown|editor3-first=T.|editor4-last=Merrill|editor4-first=R.|editor5-last=Dilts|editor5-first=R.|editor6-last=Tighe|editor6-first=S.|pages=3–2|url=https://pdf.usaid.gov/pdf_docs/pnada949.pdf|archive-url=https://web.archive.org/web/20061004022349/http://pdf.usaid.gov/pdf_docs/PNADA949.pdf|archive-date=October 4, 2006}}</ref>

Fauna includes the [[Lowland anoa|lowland]] and [[mountain anoa]], or dwarf buffalo (''[[Bubalus]]'' sp.), and the babirusa, or "deer-pig" (''[[Babirusa|Babyrousa]]'' sp.), both found on Sulawesi, among other islands. Maluku shares a number of similar species with Sulawesi, albeit with fewer total, given the differences in size between the two islands—Sulawesi has at least 4,000 recorded terrestrial plant and animal species,<ref>{{Cite web |title=Observations - iNaturalist |url=https://www.inaturalist.org/observations?place_id=7529&subview=map |access-date=20 March 2024 |website=[[iNaturalist]]}}</ref> while Maluku has just over 1,000, by comparison. Sulawesi is home to over 2,000 [[invertebrate]] species (with over 1,000 known species of [[arthropod]], not including nearly 900 [[Lepidoptera|lepidopterans]]), 100 species of [[Reptile|reptiles]] and [[Amphibian|amphibians]], and 288 bird species. Maluku has around 70 reptile and amphibian, 250 avian, and over 550 invertebrate species. [[Seram Island]] is particularly noted for its [[Butterfly|butterflies]] and birds, including the [[Moluccan king parrot]]. Smaller mammals, including some [[Carnivora|carnivorans]] (such as [[Civet|civets]]), [[Marsupial|marsupials]] (such as the [[Common spotted cuscus|cuscus]]), [[Primate|primates]] and [[Rodent|rodents]] are common throughout the region.  

A large portion of the waters surrounding Wallacea are part of the [[Coral Triangle]], considered to be the richest [[coral reef]] and marine ecosystems on earth, with the highest number of species, adding to the total [[biodiversity]] of the region. 

Wallacea was originally almost completely forested, mostly [[tropical and subtropical moist broadleaf forests|tropical moist broadleaf forests]], with some areas of [[tropical and subtropical dry broadleaf forests|tropical dry broadleaf forest]]. The higher mountains are home to [[Montane forest|montane]] and [[subalpine]] forests, and [[mangrove]]s 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.<ref name="Myers-etal"/>

Endemism is higher among terrestrial vertebrate species; out of 1,142 species described there, almost half (529) were endemic. 45% of the region retains some sort of forest cover, though only 52,017&nbsp;km<sup>2</sup> (15%) is in a pristine state. Of Wallacea's total 347,000 km<sup>2</sup>-area, about 20,000 km<sup>2</sup> are protected.<ref name="Myers-etal"/>

==Ecoregions==
[[Tropical and subtropical moist broadleaf forests]]:
* [[Sulawesi lowland rain forests]] (Sulawesi, [[Banggai Islands Regency|Banggai Islands]], [[Sangihe Islands]], [[Talaud Islands]])
* [[Sulawesi montane rain forests]] (Sulawesi)

[[Tropical and subtropical dry broadleaf forests]]:

* [[Lesser Sundas deciduous forests]] (Lombok, Sumbawa, [[Komodo Island|Komodo]], Flores, [[Alor Island|Alor]], [[Bali]])
* [[Sumba deciduous forests]] (Sumba)
* [[Timor and Wetar deciduous forests|Timor deciduous forests]] ([[Timor]])

==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 [[Bluff Downs fossil site|Bluffs Down]] in Queensland, but a mix of ancestral and derived traits suggest [[Muridae|murid]] rodents made it to Australia earlier, maybe in the Miocene, over a forested archipelago, i.e. Wallacea, and evolved in Australia in isolation.<ref>{{Cite book
 | last1 = Archer | first1 = M.
 | last2 = Hand | first2 = S. J.
 | last3 = Godthelp | first3 = H.
 | chapter = Patterns in the history of Australia's mammals and inferences about palaeohabitats | pages = 80–103
 | title = History of the Australian Vegetation: Cretaceous to Recent
 | editor-last = Hill | editor-first = R. S.
 | year = 2017 | publisher = University of Adelaide Press
 | chapter-url = https://www.adelaide.edu.au/press/system/files/media/documents/2019-04/uap-australian-vegetation-ebook.pdf | access-date = 15 September 2019
 | isbn = 978-1-925261-47-9 | jstor = 10.20851/j.ctt1sq5wrv.10
 }}<!-- {{Harvnb|Archer|Hand|Godthelp|2017|loc=Muridae (rodents), pp. 99–100}} --></ref> 

[[List of Australian rodents|Australia's rodents]] make up much of the continent's [[placental mammal]] fauna and include various species from [[stick-nest rat]]s to [[hopping mice]]. Other mammals invaded from the east. Two species of [[cuscus]], the [[Sulawesi bear cuscus]] and the [[Sulawesi dwarf cuscus]], are the westernmost representatives of the Australasian marsupials.<ref>{{Cite journal
 | last1 = Rowe | first1 = K. C.
 | last2 = Reno | first2 = M. L.
 | last3 = Richmond | first3 = D. M.
 | last4 = Adkins | first4 = R. M.
 | last5 = Steppan | first5 = S. J.
 | title = Pliocene colonization and adaptive radiations in Australia and New Guinea (Sahul): multilocus systematics of the old endemic rodents (Muroidea: Murinae)
 | year = 2008 | journal = Molecular Phylogenetics and Evolution | volume = 47 | issue = 1 | pages = 84–101
 | url = https://www.bio.fsu.edu/steppan/Rowe_MPE_2008.pdf | access-date = 19 April 2019
 | doi = 10.1016/j.ympev.2008.01.001 | pmid = 18313945
 | bibcode = 2008MolPE..47...84R
 }}<!-- {{Harvnb|Rowe|Reno|Richmond|Adkins|2008|p=88}} --></ref>

The [[tectonic uplift]] of Wallacea during the collision between Australia and Asia {{Circa}} 23 million years ago allowed the global dispersal of [[passerine]] birds from Australia across the Indonesian islands.<ref>{{Cite journal
 | last1 = Moyle | first1 = R. G.
 | last2 = Oliveros | first2 = C. H.
 | last3 = Andersen | first3 = M. J.
 | last4 = Hosner | first4 = P. A.
 | last5 = Benz | first5 = B. W.
 | last6 = Manthey | first6 = J. D.
 | last7 = Travers | first7 = S. L.
 | last8 = Brown | first8 = R. M.
 | last9 = Faircloth | first9 = B. C.
 | title = Tectonic collision and uplift of Wallacea triggered the global songbird radiation
 | year = 2016 | journal = Nature Communications | volume = 7 | article-number = 12709
 | url= | doi = 10.1038/ncomms12709 | pmid = 27575437
 | pmc = 5013600
 | bibcode = 2016NatCo...712709M
 }}<!-- {{Harvnb|Moyle|Oliveros|Andersen|Hosner|2016|loc=Discussion, p. 4}} --></ref> [[Bustards]] and [[megapode]]s must have somehow colonized Australia. [[Cockatiel]]s similar to those from Australia inhabit Komodo Island in Wallacea.{{cn|date=October 2022}}

A few species of ''[[Eucalyptus]]'', a predominant genus of trees in Australia, are found in Wallacea: ''[[Eucalyptus deglupta]]'' on Sulawesi, and ''[[Eucalyptus urophylla|E. urophylla]]'' and ''[[Eucalyptus alba|E. alba]]'' in East Nusa Tenggara.<ref>{{Cite report
 | last1 = Pramono | first1 = I. B.
 | last2 = Pudjiharta | first2 = A.
 | chapter = Research experiences on Eucalyptus in Indonesia
 | title = Reports submitted to the regional expert consultation on eucalyptus | volume = II
 | year = 1996 | publisher = Food and Agriculture Organization, Regional Office for Asia and the Pacific, Bangladesh }}</ref> For land snails Wallacea and Wallace's Line do not form a barrier for dispersal.<ref name="Hausdorf2019">{{Cite journal | doi = 10.1093/zoolinnean/zly031| title = Beyond Wallace's line – dispersal of Oriental and Australo-Papuan land-snails across the Indo-Australian Archipelago| journal = Zoological Journal of the Linnean Society| volume = 185| issue = 1| pages = 66–76| year = 2019| last1 = Hausdorf | first1 = B.}}</ref>

== See also ==
* {{Portal inline|Indonesia}}
* {{Portal inline|Oceania}}

==References==
{{Reflist}}

==External links==
{{Commons cat|Wallacea}}
* [https://web.archive.org/web/20040404233653/http://www.biodiversityhotspots.org/xp/Hotspots/wallacea/ Conservation International: Wallacea]
* George Gaylord Simpson (Apr. 29, 1977), [https://www.jstor.org/pss/986523 "Too Many Lines; The Limits of the Oriental and Australian Zoogeographic Regions"], ''Proceedings of the American Philosophical Society'', Vol. 121, No. 2, pp.&nbsp;107–120. {{Jstor|986523}}
* [https://web.archive.org/web/20090905165443/http://www.wallacea.info/ Wallacea Research Group]

[[Category:Wallacea| ]]
[[Category:Australasian realm]]
[[Category:Biogeography]]
[[Category:Ecoregions of Asia]]
[[Category:Indomalayan realm]]
[[Category:Maritime Southeast Asia]]
[[Category:Regions of Indonesia]]
[[Category:Regions of Southeast Asia]]