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Wallace Line

October 21, 2023

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 T.H. Huxley that separates the biogeographical realms of Asia and 'Wallacea', a transitional zone between Asia and Australia also called the Malay Archipelago and the Indo-Australian Archipelago. To the west of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origins is present. Wallace noticed this clear division in both land mammals and birds during his travels through the East Indies in the 19th century.

Wallace's Line delineates Australian and Southeast Asian fauna. The probable extent of land at the time of the Last Glacial Maximum, when the sea level was more than 110 m (360 ft) lower than today, is shown in grey. The deep water of the Lombok Strait between Bali and Lombok formed a water barrier even when lower sea levels linked the now-separated islands and landmasses on either side.

The line runs through Indonesia, such as Makassar Strait between Borneo and Sulawesi (Celebes), and through the Lombok Strait between Bali and Lombok, where the distance is strikingly small, only about 35 kilometers (22 mi), but enough for a contrast in species present on each island. The complex biogeography of the Indo-Australian Archipelago is a result of its location at the merging point of four major tectonic plates and other semi-isolated microplates in combination with ancient sea levels. Those caused the isolation of different taxonomic groups on islands at present relatively close to each other. Wallace's line is one of the many boundaries drawn by naturalists and biologists since the mid-1800s intended to delineate constraints on the distribution of the fauna and flora of the archipelago.[1]

Historical context Edit

 
The original drawing of the line in Wallace's paper

One of the earliest descriptions of the biodiversity in the Indo-Australian Archipelago dates back to 1521 when Venetian explorer Pigafetta recorded the biological contrasts between the Philippines and the Maluku Islands (Spice Islands) (on opposite sides of the Wallace's Line) during the continuation of the voyage of Ferdinand Magellan, after Magellan had been killed on Mactan. Later on, the English navigator G.W. Earl published his observations in faunal differences between the islands in the Indo-Australian archipelago. In 1845[2] G.W. Earl described how shallow seas connected islands on the west (Sumatra, Java, etc.) with the Asian continent and with similar wildlife, and islands on the east such as New Guinea were connected to Australia and were characterized by the presence of marsupials. German naturalist S. Müller proposed similar ideas to Earl's concerning the faunal boundaries in his work between 1839 and 1845,[citation needed] followed by the English ornithologist Philip Sclater who outlined in 1858 the divergence of the bird species in each region.

These early investigations assisted Wallace in developing his theories about the biogeography which he stated publicly in his 1859 paper after extensively traveling the region.[1] He proposed a line to the east of Bali since "all the islands eastward of Borneo and Java formed part of an Australian or Pacific continent, from which they were separated."[3]

The proposal of the line, however, was not the main objective of Wallace's endeavours: His primary purpose was in fact to understand the geological phenomena and the colonization events that caused the boundaries in faunal distribution in the region through the development of his theories of evolution and biogeography.[1] Wallace's studies in Indonesia demonstrated the emerging theory of evolution, at about the same time as J.D. Hooker and Asa Gray published essays also supporting Darwin's hypothesis.[4]On the other hand, the lack of knowledge of tectonic plates, and the uncertainty about biodiversity in the Philippines, left Wallace with some contradicting points he had to deal with concerning his theory on biogeography.[1] In fact, Wallace did not include the Philippines in his 1859 paper, and the determination of a line in honor of his name was suggested by T.H. Huxley (1868).[5][6] Huxley studied the distribution of gallinaceous birds in the archipelago, and noticed that species in the Philippines were remarkably distinct from those in the Asiatic realm. Based on that, he re-drew Wallace's boundary placing the Philippines on the west side of the division and named it “Wallace's line”, although Wallace himself had refused to place the Philippines in the west.[1]

Because of the complexity of the geographical landscape and the differences in diversity of organisms around the archipelago, continuous attempts to characterize faunal and botanical boundaries were carried out after Wallace. Some of them are

  • Scatler line (1894)
  • Lydekker's line (1896)
  • Pelseneer's faunal balance (1904)
  • Mayr's faunal balance (1944)

In addition, several smaller transition sub-regional boundaries were also proposed.[1]

More recent work assessing biodiversity assemblages, phylogeny, and using computer-based geospatial tools to analyze previous boundaries have led to patterns of division similar to those proposed through the 19th century, although some special cases not explained before are reinforced by these modern analyzes. Rueda et al. (2013),[full citation needed] for instance, evaluated the distribution of land mammals, birds, and amphibians in Wallace's realms and concluded that the boundaries suggested by Wallace remain valid. Ali et al. (2020), in a different attempt, studied the fauna of Christmas Island and indicated that most of the ancestral colonizers of the island's land mammals and amphibians disappeared from the Lombok Strait. Therefore, they propose a re-conformation of the Wallace's line so that the Christmas Island would be sited on the Australasian side of the biogeographical divide, instead of the oriental side.[1]

Biogeography Edit

 
The Wallacea region situated between the Wallace Line (after Ernst Mayr or Thomas Henry Huxley) and the Lydekker Line

Understanding of the biogeography of the region centers on the relationship of ancient sea levels to the continental shelves. Wallace's line is visible geographically when the continental shelf contours are examined. It figures as a deep-water channel that separates the southeastern edge of the Sunda Shelf from the Sahul Shelf. The Sunda Shelf links Borneo, Bali, Java, and Sumatra underwater to the mainland of southeastern Asia, while the Sahul Shelf connects Australia to New Guinea and their adjacent islands.[7]

During the Pliestocene, when the ocean levels were up to 120 metres (390 ft) lower, islands became connected, but never uniting Asia with Australia. Consequently, for over 50 million years, deep water between those two large continental shelf areas created a barrier that kept the flora and fauna of Australia separated from those of Asia. It can reasonably be concluded it was an ocean barrier preventing species migration because the physical aspects of the separated islands are very similar.[7] Thus, the Wallacea region consists of islands that remained isolated on their respective continental land masses, with only those organisms capable of crossing the straits between islands populating them.[8]

Alternatively, "Weber's line" runs through this transitional area (to the east of center), at the tipping point between Asian species against those with Australian origins.[8]

Zoogeography Edit

The distributions of many bird species follow the limits of the line, since many birds do not cross even the shortest stretches of open ocean water. Among mammals, bats have distributions that can cross the line, but larger terrestrial mammals are generally limited to one side or the other. On the Australian side, many species of marsupials are present, and some monotremes, alongside native rodents—although the occurrence of rodents in this case is derived from more recent colonization events.[1]

By contrast, to the Asian side, marsupials are excluded, and placental mammals such as apes, cats, elephants, monkeys, rhinoceroses, and other species are found.[1] Exceptions to this include macaques, pigs, and tarsiers on Sulawesi.

Other groups of plants and animals show differing patterns, but the overall pattern is striking and reasonably consistent. Flora do not follow the Wallace Line to the same extent as fauna, since their colonization events differ in their ability to spread across bodies of water. One genus of plants that does not cross the line is the Australasian genus Eucalyptus, except for one species, E. deglupta, which naturally occurs on the island of Mindanao in the Philippines.[3]

See also Edit

References Edit

  1. ^ a b c d e f g h i Ali, Jason R.; Heaney, Lawrence R. (June 2021). "Wallace's line, Wallacea , and associated divides and areas: History of a tortuous tangle of ideas and labels". Biological Reviews. 96 (3): 922–942. doi:10.1111/brv.12683. ISSN 1464-7931. PMID 33502095. S2CID 231764849.
  2. ^ Earl, G.W. (1845). On the physical geography of south-eastern Asia and Australia. G.W. Earl.
  3. ^ a b Wallace 1863, pp. 217–234
  4. ^ Bowler, P.J. (1989). Evolution: The history of an idea (Rev. ed.). Berkeley, California: University of California Press. ISBN 0-520-06385-6. OCLC 17841313.
  5. ^ Huxley, Thomas Henry (January 1868). "December 10, 1868". Proceedings of the Zoological Society of London. 36 (1): 622–637. doi:10.1111/j.1469-7998.1868.tb00455.x. ISSN 0370-2774.
  6. ^ Camerini, J.R. (December 1993). "Evolution, biogeography, and maps: An early history of Wallace's line". Isis. 84 (4): 700–727. doi:10.1086/356637. ISSN 0021-1753. PMID 8307726. S2CID 15219070.
  7. ^ a b Newton, Alfred (1874). Zoology. London, UK: Society for Promoting Christian Knowledge.
    "Zoology by Alfred Newton, M.A., F.R.S. ... 1874". Bibliographical notice. Annals and Magazine of Natural History (book review). 4. 15 (88): 285. April 1875. doi:10.1080/00222937508681077. ISSN 0374-5481.
  8. ^ a b Mayr, Ernst (March 1944). "Wallace's line in the light of recent zoogeographic studies". The Quarterly Review of Biology. 19 (1): 1–14. doi:10.1086/394684. ISSN 0033-5770. S2CID 33245177.

Sources Edit

Further reading Edit

  • Abdullah, M.T. (2003). Biogeography and variation of Cynopterus brachyotis in Southeast Asia (Ph.D. thesis). St. Lucia, Australia: The University of Queensland.
  • Dawkins, Richard (2004). "Chapter 14   Marsupials". The Ancestor's Tale. Weidenfeld & Nicolson. ISBN 0-7538-1996-1.
  • Hall, L.S.; Grigg, Gordon G.; Moritz, Craig; Ketol, Besar; Sait, Isa; Marni, Wahab; Abdullah, M.T. (2004). "Biogeography of fruit bats in Southeast Asia". Sarawak Museum Journal. LX (81): 191–284.
  • Simpson, G.G. (29 April 1977). "Too many lines: The limits of the oriental and Australian zoogeographic regions". Proceedings of the American Philosophical Society. 121 (2): 107–120. JSTOR 986523.
  • van Oosterzee, Penny (1997). Where Worlds Collide: The Wallace line.
  • Wilson, D.E.; Reeder, D.M. (2005). Mammal Species of the World. Washington, DC: Smithsonian Institution Press.

External links Edit

 
Wikimedia Commons has media related to Wallace Line.
  • "Wallacea Research Group" (main).
  • "Map of Wallace's, Weber's, and Lydekker's lines". Diving. Starfish. Switzerland.
  • "Pleistocene sea level maps". Field Museum. Chicago, Illinois.
  • "Wallacea - a transition zone from Asia to Australia, specially rich in marine life and on land". Diving. Starfish. Switzerland.

October 21, 2023
wallace, line, wallace, line, wallace, line, faunal, boundary, line, drawn, 1859, british, naturalist, alfred, russel, wallace, named, english, biologist, huxley, that, separates, biogeographical, realms, asia, wallacea, transitional, zone, between, asia, aust. 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 T H Huxley that separates the biogeographical realms of Asia and Wallacea a transitional zone between Asia and Australia also called the Malay Archipelago and the Indo Australian Archipelago To the west of the line are found organisms related to Asiatic species to the east a mixture of species of Asian and Australian origins is present Wallace noticed this clear division in both land mammals and birds during his travels through the East Indies in the 19th century Wallace s Line delineates Australian and Southeast Asian fauna The probable extent of land at the time of the Last Glacial Maximum when the sea level was more than 110 m 360 ft lower than today is shown in grey The deep water of the Lombok Strait between Bali and Lombok formed a water barrier even when lower sea levels linked the now separated islands and landmasses on either side The line runs through Indonesia such as Makassar Strait between Borneo and Sulawesi Celebes and through the Lombok Strait between Bali and Lombok where the distance is strikingly small only about 35 kilometers 22 mi but enough for a contrast in species present on each island The complex biogeography of the Indo Australian Archipelago is a result of its location at the merging point of four major tectonic plates and other semi isolated microplates in combination with ancient sea levels Those caused the isolation of different taxonomic groups on islands at present relatively close to each other Wallace s line is one of the many boundaries drawn by naturalists and biologists since the mid 1800s intended to delineate constraints on the distribution of the fauna and flora of the archipelago 1 Contents 1 Historical context 2 Biogeography 3 Zoogeography 4 See also 5 References 6 Sources 7 Further reading 8 External linksHistorical context Edit nbsp The original drawing of the line in Wallace s paperOne of the earliest descriptions of the biodiversity in the Indo Australian Archipelago dates back to 1521 when Venetian explorer Pigafetta recorded the biological contrasts between the Philippines and the Maluku Islands Spice Islands on opposite sides of the Wallace s Line during the continuation of the voyage of Ferdinand Magellan after Magellan had been killed on Mactan Later on the English navigator G W Earl published his observations in faunal differences between the islands in the Indo Australian archipelago In 1845 2 G W Earl described how shallow seas connected islands on the west Sumatra Java etc with the Asian continent and with similar wildlife and islands on the east such as New Guinea were connected to Australia and were characterized by the presence of marsupials German naturalist S Muller proposed similar ideas to Earl s concerning the faunal boundaries in his work between 1839 and 1845 citation needed followed by the English ornithologist Philip Sclater who outlined in 1858 the divergence of the bird species in each region These early investigations assisted Wallace in developing his theories about the biogeography which he stated publicly in his 1859 paper after extensively traveling the region 1 He proposed a line to the east of Bali since all the islands eastward of Borneo and Java formed part of an Australian or Pacific continent from which they were separated 3 The proposal of the line however was not the main objective of Wallace s endeavours His primary purpose was in fact to understand the geological phenomena and the colonization events that caused the boundaries in faunal distribution in the region through the development of his theories of evolution and biogeography 1 Wallace s studies in Indonesia demonstrated the emerging theory of evolution at about the same time as J D Hooker and Asa Gray published essays also supporting Darwin s hypothesis 4 On the other hand the lack of knowledge of tectonic plates and the uncertainty about biodiversity in the Philippines left Wallace with some contradicting points he had to deal with concerning his theory on biogeography 1 In fact Wallace did not include the Philippines in his 1859 paper and the determination of a line in honor of his name was suggested by T H Huxley 1868 5 6 Huxley studied the distribution of gallinaceous birds in the archipelago and noticed that species in the Philippines were remarkably distinct from those in the Asiatic realm Based on that he re drew Wallace s boundary placing the Philippines on the west side of the division and named it Wallace s line although Wallace himself had refused to place the Philippines in the west 1 Because of the complexity of the geographical landscape and the differences in diversity of organisms around the archipelago continuous attempts to characterize faunal and botanical boundaries were carried out after Wallace Some of them are Scatler line 1894 Lydekker s line 1896 Pelseneer s faunal balance 1904 Mayr s faunal balance 1944 In addition several smaller transition sub regional boundaries were also proposed 1 More recent work assessing biodiversity assemblages phylogeny and using computer based geospatial tools to analyze previous boundaries have led to patterns of division similar to those proposed through the 19th century although some special cases not explained before are reinforced by these modern analyzes Rueda et al 2013 full citation needed for instance evaluated the distribution of land mammals birds and amphibians in Wallace s realms and concluded that the boundaries suggested by Wallace remain valid Ali et al 2020 in a different attempt studied the fauna of Christmas Island and indicated that most of the ancestral colonizers of the island s land mammals and amphibians disappeared from the Lombok Strait Therefore they propose a re conformation of the Wallace s line so that the Christmas Island would be sited on the Australasian side of the biogeographical divide instead of the oriental side 1 Biogeography Edit nbsp The Wallacea region situated between the Wallace Line after Ernst Mayr or Thomas Henry Huxley and the Lydekker LineUnderstanding of the biogeography of the region centers on the relationship of ancient sea levels to the continental shelves Wallace s line is visible geographically when the continental shelf contours are examined It figures as a deep water channel that separates the southeastern edge of the Sunda Shelf from the Sahul Shelf The Sunda Shelf links Borneo Bali Java and Sumatra underwater to the mainland of southeastern Asia while the Sahul Shelf connects Australia to New Guinea and their adjacent islands 7 During the Pliestocene when the ocean levels were up to 120 metres 390 ft lower islands became connected but never uniting Asia with Australia Consequently for over 50 million years deep water between those two large continental shelf areas created a barrier that kept the flora and fauna of Australia separated from those of Asia It can reasonably be concluded it was an ocean barrier preventing species migration because the physical aspects of the separated islands are very similar 7 Thus the Wallacea region consists of islands that remained isolated on their respective continental land masses with only those organisms capable of crossing the straits between islands populating them 8 Alternatively Weber s line runs through this transitional area to the east of center at the tipping point between Asian species against those with Australian origins 8 Zoogeography EditThe distributions of many bird species follow the limits of the line since many birds do not cross even the shortest stretches of open ocean water Among mammals bats have distributions that can cross the line but larger terrestrial mammals are generally limited to one side or the other On the Australian side many species of marsupials are present and some monotremes alongside native rodents although the occurrence of rodents in this case is derived from more recent colonization events 1 By contrast to the Asian side marsupials are excluded and placental mammals such as apes cats elephants monkeys rhinoceroses and other species are found 1 Exceptions to this include macaques pigs and tarsiers on Sulawesi Other groups of plants and animals show differing patterns but the overall pattern is striking and reasonably consistent Flora do not follow the Wallace Line to the same extent as fauna since their colonization events differ in their ability to spread across bodies of water One genus of plants that does not cross the line is the Australasian genus Eucalyptus except for one species E deglupta which naturally occurs on the island of Mindanao in the Philippines 3 See also Edit nbsp Indonesia portal nbsp Evolutionary biology portal nbsp Geography portalAustralasian realm One of the Earth s eight biogeographic realms Australia continent One of Earth s seven main divisions of land Wallacea Biogeographical regionReferences Edit a b c d e f g h i Ali Jason R Heaney Lawrence R June 2021 Wallace s line Wallacea and associated divides and areas History of a tortuous tangle of ideas and labels Biological Reviews 96 3 922 942 doi 10 1111 brv 12683 ISSN 1464 7931 PMID 33502095 S2CID 231764849 Earl G W 1845 On the physical geography of south eastern Asia and Australia G W Earl a b Wallace 1863 pp 217 234 Bowler P J 1989 Evolution The history of an idea Rev ed Berkeley California University of California Press ISBN 0 520 06385 6 OCLC 17841313 Huxley Thomas Henry January 1868 December 10 1868 Proceedings of the Zoological Society of London 36 1 622 637 doi 10 1111 j 1469 7998 1868 tb00455 x ISSN 0370 2774 Camerini J R December 1993 Evolution biogeography and maps An early history of Wallace s line Isis 84 4 700 727 doi 10 1086 356637 ISSN 0021 1753 PMID 8307726 S2CID 15219070 a b Newton Alfred 1874 Zoology London UK Society for Promoting Christian Knowledge Zoology by Alfred Newton M A F R S 1874 Bibliographical notice Annals and Magazine of Natural History book review 4 15 88 285 April 1875 doi 10 1080 00222937508681077 ISSN 0374 5481 a b Mayr Ernst March 1944 Wallace s line in the light of recent zoogeographic studies The Quarterly Review of Biology 19 1 1 14 doi 10 1086 394684 ISSN 0033 5770 S2CID 33245177 Sources EditWallace A R 1862 1863 On the physical geography of the Malay archipelago Proceedings of the Royal Geographical Society of London 7 5 205 212 doi 10 2307 1799061 ISSN 1478 615X JSTOR 179906 Wallace A R 1863 On the physical geography of the Malay archipelago Journal of the Royal Geographical Society of London 33 217 234 doi 10 2307 1798448 ISSN 0266 6235 JSTOR 1798448 via Internet Archive archive org Further reading EditAbdullah M T 2003 Biogeography and variation ofCynopterus brachyotisin Southeast Asia Ph D thesis St Lucia Australia The University of Queensland Dawkins Richard 2004 Chapter 14 Marsupials The Ancestor s Tale Weidenfeld amp Nicolson ISBN 0 7538 1996 1 Hall L S Grigg Gordon G Moritz Craig Ketol Besar Sait Isa Marni Wahab Abdullah M T 2004 Biogeography of fruit bats in Southeast Asia Sarawak Museum Journal LX 81 191 284 Simpson G G 29 April 1977 Too many lines The limits of the oriental and Australian zoogeographic regions Proceedings of the American Philosophical Society 121 2 107 120 JSTOR 986523 van Oosterzee Penny 1997 Where Worlds Collide The Wallace line Wilson D E Reeder D M 2005 Mammal Species of the World Washington DC Smithsonian Institution Press External links Edit nbsp Wikimedia Commons has media related to Wallace Line Wallacea Research Group main Map of Wallace s Weber s and Lydekker s lines Diving Starfish Switzerland Pleistocene sea level maps Field Museum Chicago Illinois Wallacea a transition zone from Asia to Australia specially rich in marine life and on land Diving Starfish Switzerland Retrieved from https en wikipedia org w index php title Wallace Line amp oldid 1176963425, wikipedia, wiki, book, books, library,

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