ECOZONES AND BIOGEOGRAPHY: WALLACE’S LINE

June 16, 2010 at 7:53 pm | Posted in Asia, Development, Earth, History, Third World | Leave a comment

spin-globe.gif

books-globe.gif

globe-purple.gif

history.gif

world.gif

compass.gif

loudspeaker.gif

globeinmoney.jpg

Ecozones and Biogeographic Boundaries:

Wallace’s Line and Lydekker’s Line

Wallace’s line comes between Australian and Southeast Asian fauna. The deep water of the Lombok Strait between the islands of Bali and Lombok formed a water barrier even when lower sea levels linked the now-separated islands and landmasses on either side.

The Wallace Line (or Wallace’s Line) is a boundary that separates the ecozones of Asia and Wallacea (which is a transitional zone between Asia and Australia). West of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origin are present. The line is named after Alfred Russel Wallace, who noticed this clear dividing line during his travels through the East Indies in the 19th century. The line runs through Indonesia, between Borneo and Sulawesi (Celebes); and through the Lombok Strait between Bali (in the west) and Lombok (in the east). Antonio Pigafetta had also recorded the biological contrasts between the Philippines and the Maluku Islands (Spice Islands) (situated on opposite sides of the line) in 1521 during the continuation of the voyage of Ferdinand Magellan (after Magellan himself had been killed on Mactan).

The distance between Bali and Lombok is small, a matter of only about 35 kilometers. The distributions of many bird species observe the line, since many birds refuse to cross even the smallest stretches of open ocean water. Some bats have distributions that cross the Wallace Line, but other mammals are generally limited to one side or the other; an example of an exception is the Crab-eating Macaque. Other groups of plants and animals show differing patterns, but the overall pattern is striking and reasonably consistent.

Biogeography

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 can be seen as a deep-water channel that marks the southeastern edge of the Sunda Shelf linking Borneo, Bali, Java, and Sumatra underwater to the mainland of southeastern Asia. Australia is likewise connected via the shallow ocean over the Sahul Shelf to New Guinea, and the related biogeographic boundary known as Lydekker’s Line, which separates the eastern edge of Wallacea and the Australian region, has a similar origin. During ice age glacial advances, when the ocean levels were up to 120 m lower, both Asia and Australia were united with what are now islands on their respective continental shelves as continuous land masses, but the deep water between those two large continental shelf areas was — for a period in excess of 50 million years — a barrier that kept the flora and fauna of Australia separated from that of Asia. Wallacea consists of islands that were never recently connected by dry land to either of the continental land masses, and thus was populated by organisms capable of crossing the straits between islands. “Weber’s Line” runs through this transitional area (rather to the east of centre), at the tipping point between dominance by species of Asian vs. Australian origin.[1]

References

· van Oosterzee, Penny (1997). Where Worlds Collide: the Wallace Line.

· Pleistocene Sea Level Maps

· Wallacea – a transition zone from Asia to Australia, specially rich in marine life and on land.

· Dawkins, Richard (2004). The Ancestor’s Tale. Weidenfeld & Nicolson. ISBN 0-7538-1996-1. Chapter 14 – Marsupials.

Borneo

· Abdullah, M. T. (2003). Biogeography and variation of Cynopterus brachyotis in Southeast Asia. PhD thesis. The University of Queensland, St Lucia, Australia.

· Hall, L. S., Gordon G. Grigg, Craig Moritz, Besar Ketol, Isa Sait, Wahab Marni and M. T. Abdullah (2004). “Biogeography of fruit bats in Southeast Asia“. Sarawak Museum Journal LX(81):191-284.

· Wilson D. E., D. M. Reeder (2005). Mammal species of the world. Washington DC: Smithsonian Institution Press.

1. Mayr, E. (1944), “Wallace’s Line in the Light of Recent Zoogeographic Studies”, The Quarterly Review of Biology 19 (1): 1–14, http://www.jstor.org/stable/2808563

links

· 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

· Map of Wallace’s, Weber’s and Lydekker’s lines

Ecozones and Biogeographic Boundaries:

Wallace’s Line and Lydekker’s Line

banknotes.jpg

TrackBack URI


Entries and comments feeds.

%d bloggers like this: