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Invasive species are a serious threat to the native biodiversity of Australia and are an ongoing cost to Australian agriculture. Numerous species arrived with European colonisation of Australia and steadily since then. Management and the prevention of the introduction of new invasive species are key environmental and agricultural policy issues for the Australian federal and state governments. The management of weeds costs A$3.5 billion yearly. == Causes == Both geologic and climatic events helped to make Australia's fauna unique.〔Egerton, pp. 14, 20.〕 Australia was once part of the southern supercontinent Gondwana,〔Egerton, p. 20.〕 which also included South America, Africa, India and Antarctica. Gondwana began to break up 140 million years ago (MYA); 50 MYA Australia separated from Antarctica and was relatively isolated until the collision of the Indo-Australian Plate with Asia in the Miocene era 5.3 MYA. As Australia drifted, it was isolated from evolutionary pressures in the rest of the world, with its species being more primitive and less competitive than the mainland fauna. This phenomenon is not uncommon in geological history of the world - it resulted in the great American interchange, where more developed fauna of the North America, which was connected to Eurasia via Beringia, replaced many species of the more isolated South American fauna. Other examples of island isolation include Madagascar, New Zealand, Socotra, the Galapagos and Mauritius. The placental mammals made their reappearance in Australia in the Pleistocene, as Australia continued to move closer to Indonesia, both bats and rodents appearing reliably in the fossil record. The geographic isolation of Australia created a sharp division between Australian fauna and Asian fauna at the Wallace line. Dingoes probably arrived in Australia between 4,600 and 5,400 years ago, long after the first humans, spread rapidly across the continent and probably contributed to the extinction of even more native species. The current period of invasive species introduction began in 1788 with the arrival of the first European settlers. Because the population density in Australia has historically been very low and there are large tracts of uninhabited land, it is very difficult for people to manage even large feral animals like camels, horses, donkeys and water buffalos. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Invasive species in Australia」の詳細全文を読む スポンサード リンク
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