著者

野尻 亘 Wataru Nojiri 桃山学院大学経済学部

出版者

桃山学院大学総合研究所

雑誌

桃山学院大学人間科学 = HUMAN SCIENCES REVIEW, St. Andrew's University (ISSN:09170227)

巻号頁・発行日

no.37, pp.63-99, 2009-10-20

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Alfred Russel Wallace observed the distribution and boundaries of animals inhabiting the Malay Archipelago. The distribution of marsupials in the Australian region is a prominent feature of the area. In Borneo, however, the mammals do not include marsupials. The many parrots of the Australian region are rare in the Oriental region. The birds of the Oriental region do not migrate to Lombok Island, and these are not seen on Celebes or islands further to the east. The Lombok Strait were regarded as the dividing line between these two zoogeographic regions. The boundary between the zoogeographical regions, crossing the Lombok Strait indicated by Wallace was later to be called "Wallace's line" by Thomas Henry Huxley. Later, Mayr conducted further studies on Wallace's line, asserting that differences in the faunas of Bali and Lombok were not due to crustal movements in the Tertiary period, as Wallace had asserted, but rather to sea levels changes in the Pleistocene glacial epoch. During that time, sea levels were 70-100m lower, but because the Lombok Strait is a deepwater strait, the land on either side was not connected. In addition to this, Simpson points out that the eastern end of the Sunda shelf, which is the Asian continental shelf, is Wallace's line, while the West end of the Sahul shelf, which is the Australian continental shelf, is Lydekker's line. The area between these is known as the "Wallacea" transitional zone. Currently, "Wallacea" is believed to have been formed when the Australian continental crust broke off from the Antarctic at the end of the Cretaceous and collided with the southeastern border of the Eurasian continental crust during the mid Miocene. After the collision of these continental plates, there were violent movements in the crust and fault activity. Subsequently, the animals of the both continents migrated to islands, repeating cycles of either evolution or extinction, eventually creating today's diverse distribution of organisms. In other words, modern interpretation of Wallace's line differs greatly from past interpretation. Wallace and other traditional biogeographers believed that Wallace's line is the boundary created by isolation by geographical barriers. At the present time, Wallace's line is explained by collisions along the borders of the earth's plates. In other words, Wallace's line was the "frontier" where different types of species living on different plates were exposed to each other and interacted when the plates collided.