华莱士线

地理

The Wallace Line (or Wallace's Line) is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace that separates the ecozones of Asia and Wallacea, 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 is present. The line is named after Alfred Russel Wallace, who noticed this clear division 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 and Lombok. Antonio Pigafetta had also recorded the biological contrasts between the Philippines and the Maluku Islands (Spice Islands) (on opposite sides of the line) in 1521 during the continuation of the voyage of Ferdinand Magellan, after Magellan had been killed on Mactan.

The distance between Bali and Lombok is small, about 35 kilometres (22 mi). The distributions of many bird species observe the line, since many birds do not cross even the smallest stretches of open ocean water. Some bats have distributions that cross the line, but other mammals are generally limited to one side or the other; 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.

Flora do not follow the Wallace Line to the same extent as fauna.[1]

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 metres (390 ft) 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 over 50 million years, a barrier that kept the flora and fauna of Australia separated from those of Asia. Wallacea consists of islands that were never recently connected by dry land to either of the continental land masses, and thus were populated by organisms capable of crossing the straits between islands. "Weber's Line" runs through this transitional area (to the east of centre), at the tipping point between dominance by species of Asian against those of Australian origin.[2]

Map of Wallacea, bordered by the Wallace and the Lydekker Line

The boundary between Sundaland and Wallacea follows the Wallace Line, named after the naturalist Alfred Russel Wallace who noted the differences in mammal and bird fauna between the islands either side of the line. The Islands of Sundaland to the west of the line, including Sumatra, Java, Bali, and Borneo, share a similar mammal fauna with East Asia, including tigers, rhinoceros, and apes, whereas those from Lombok and eastward are mostly populated by marsupials and birds similar to those in Australasia. Sulawesi shows signs of both.[1] During the ice ages, sea levels were lower, exposing the Sunda shelf that links these islands to one another and to Asia,[2] and allowed Asian land animals to inhabit these islands. The islands of Wallacea have few land mammals, land birds, or freshwater fish of continental origin, who find it difficult to cross open ocean. Many bird, reptile, and insect species 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 Malaya.

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, 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. The line dividing Wallacea from Australia–New Guinea is called Lydekker's Line. The Philippines is usually considered a separate region from Wallacea.[3] The Weber Line is the midpoint where Asian and Australian fauna and flora are approximately equally represented, and follows the deepest straits traversing the Indonesian Archipelago.

Although the distant ancestors of Wallacea's plants and animals 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; it is an important contributor to the overall mega-biodiversity of the Indonesian

archipelago.[4] Because many of the islands are separated from one another by deep water, there is tremendous species diversity among the islands as well.[citation needed]

Fauna species include the endemic anoa (dwarf buffalo) of Sulawesi and the babirusa (deer pig). Maluku shows a degree of species similarity with Sulawesi but with fewer flora and fauna. Smaller mammals including primates are common. Seram is noted for its butterflies and birdlife including the Amboina King Parrot.

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 1500 (15%) are endemic.[citation needed] Endemism is higher among terrestrial vertebrate species; of 1142 species found there, almost half (529) are endemic. 45% of the region retains some sort of forest cover, and only 52,017 km2, or 15 percent, is in pristine state. Of Wallacea's total area of 347,000 km2, about 20,000 km2 are protected.

Wallacea is home to 82 threatened and six critically endangered species of terrestrial vertebrates.

对南洋群岛进行研究的先驱是英国的博物学家华莱士，他在南洋群岛的考察研究取得了丰硕的成果。华莱士的一个重要成果是考察使他产生了进化的思想，最终几乎和达尔文

同时提出进化论，并于1858年在林耐学会上同时宣读了他和达尔文有关生物进化的论文。

华莱士的另一个重要成果是对动物的地理分布的研究和修正，成为了动物地理学的奠基人。华莱士发现在龙目海峡两侧的龙目岛和巴厘岛，望加锡海峡两侧的苏拉威西岛和加

里曼丹岛的动物区系有很大差异，海峡以西的巴厘岛和加里曼丹岛上的动物是典型的东洋

界动物，以东则出现一下西边无法见到的袋貂、葵花鹦鹉、冢雉等大洋洲界物种，同时物

种也比西边贫乏。这条分界线后来被命名为华莱士线，代表大洋洲界动物的最西界。后来

英国另一个博物学家和进化论者赫胥离将华莱士线进行了修正，将巴拉旺岛以外的菲律宾

群岛划到了线的东侧，这个修正线代表物种丰富的大陆型动物群和物种贫乏的岛屿型动物

群的分界（加里曼丹岛等虽然为岛屿，但是动物群的大陆性很强，以前曾长期是亚洲大陆

的一部分，拥有猩猩、长臂猿等最高等的哺乳动物）。