Wallacea

Wallacea is defined as the series of islands stretching between the two continental shelves of Sunda and Sahul, but excluding the Philippines. Its eastern border (separating Wallacea from Sahul) is represented by a zoogeographical boundary known as Lydekker's Line, while the Wallace Line (separating Wallacea from Sunda) defines its western border.{{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}}{{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}}

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 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, 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.{{cite book|last=Wallace|first=Alfred Russel|authorlink=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}}

During the ice ages, sea levels were lower, exposing the Sunda shelf that links the islands of Sundaland to one another and to Asia{{Cite web|title=Pleistocene Sea Level Maps|date=12 January 2011|publisher=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|url-status=dead}} 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.{{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-New Guinea, Meganesia, Papualand, or Sahul. Consequently, Australia, New Guinea, and the Aru Islands share many marsupial mammals, land birds, and freshwater fish that are not found in Wallacea.

File:Wallacea.png

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 species. There is extensive autochthonous speciation and proportionately large numbers of endemics; the area is an important contributor to the overall mega-biodiversity of the Indonesian Archipelago.{{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|url-status=dead|archive-date=October 4, 2006}}

Fauna includes the lowland and mountain anoa, or dwarf buffalo (Bubalus sp.), and the babirusa, or "deer-pig" (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,{{Cite web |title=Observations - iNaturalist |url=https://www.inaturalist.org/observations?place_id=7529&subview=map |access-date=20 March 2024 |website=iNaturalist}} 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 lepidopterans), 100 species of reptiles and 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 butterflies and birds, including the Moluccan king parrot. Smaller mammals, including some carnivorans (such as civets), marsupials (such as the cuscus), primates and 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 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; 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 km² (15%) is in a pristine state. Of Wallacea's total 347,000 km²-area, about 20,000 km² are protected.

Tropical and subtropical moist broadleaf forests:

• 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 (Halmahera, Morotai, Obi Islands, Bacan Island)
• Seram rain forests (Seram, Banda Islands, Ambon Island, Saparua, 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:

• Lesser Sundas deciduous forests (Lombok, Sumbawa, Komodo, Flores, Alor)
• Sumba deciduous forests (Sumba)
• Timor and Wetar deciduous forests (Timor, Wetar)

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.{{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 = 9781925261479 | jstor = 10.20851/j.ctt1sq5wrv.10

}}

Australia's rodents make up much of the continent's placental mammal fauna and include various species from stick-nest rats 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.{{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

}}

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.{{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 | issue = 12709

| pages = 12709

| url= | doi = 10.1038/ncomms12709 | pmid = 27575437

| pmc = 5013600

| bibcode = 2016NatCo...712709M

}} Bustards and megapodes must have somehow colonized Australia. Cockatiels 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 E. urophylla and E. alba in East Nusa Tenggara.{{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 }} For land snails Wallacea and Wallace's Line do not form a barrier for dispersal.{{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.}}

• {{Portal inline|Indonesia}}
• {{Portal inline|Oceania}}

{{Reflist}}

{{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. 107–120. {{Jstor|986523}}
• [https://web.archive.org/web/20090905165443/http://www.wallacea.info/ Wallacea Research Group]

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