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island restoration
The ecological restoration of islands, or island restoration, is the application of the principles of ecological restoration to islands and island groups. Islands, due to their isolation, are home to many of the world's endemic species, as well as important breeding grounds for seabirds and some marine mammals. Their ecosystems are also very vulnerable to human disturbance and particularly to introduced species, due to their small size. Island groups such as New Zealand and Hawaii have undergone substantial extinctions and losses of habitat. Since the 1950s several organisations and government agencies around the world have worked to restore islands to their original states; New Zealand has used them to hold natural populations of species that would otherwise be unable to survive in the wild. The principal components of island restoration are the removal of introduced species and the reintroduction of native species.
==Islands, endemism and extinction==
Isolated islands have been known to have greater levels of endemism since the 1970s when the theory of Island biogeography, formulated by Robert MacArthur and E.O. Wilson was developed. This higher occurrence of endemism is because isolation limits immigration of new species to the island, allowing new species to evolve separately from others on the mainland. For example, 71% of New Zealand's bird species (prior to human arrival) were endemic. As well as displaying greater levels of endemism, island species have characteristics that make them particularly vulnerable to human disturbance.
Many island species evolved on small islands, or even restricted habitats on small islands. Small populations are vulnerable to even modest hunting, and restricted habitats are vulnerable to loss or modification of said habitat. More importantly, island species are often ecologically naive, that is they have not evolved alongside a predator, or have lost appropriate behavioural responses to predators. This often resulted in flightlessness, or unusual levels of tameness. This made many species susceptible to hunting (it is thought, for example, that moas were hunted to extinction in a few short generations) and to predation by introduced species. Some, such as the dodo, are thought to have become extinct because of the pressure of both humans and introduced animals. One estimate of birds in the Pacific islands puts the extinctions at 2000 species. Between 40 to 50% of the bird species of New Zealand have become extinct since 200 AD.
The field of island restoration is usually credited with having been started in New Zealand in the 1960s, but other smaller projects, such as the restoration of Nonsuch Island in Bermuda (which began in 1962) have been going on for almost as long. Nevertheless, the program undertaken by the Department of Conservation (DOC) is one of the largest in the world. It began on Cuvier Island, where ecologists removed stock, goats, feral cats and finally, in 1993, Pacific rats. The success of the project resulted in similar projects around New Zealand. The advantages to the DOC were considerable; in addition to protecting species endemic to smaller islands, like the magenta petrel, islands near the mainland, once restored, could act as habitat for species of birds that were unable to survive on the mainland. Species like the takahe, where the remaining wild population was at considerable risk from feral cats and dogs, could be moved to these islands to safeguard the species.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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