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Alien species

Protected areas: Asia and the Pacific

Note: number of protected areas includes those in IUCN categories I-VI

Source: compiled from UNEP-WCMC 2001b

Introduced species have long been recognized as a threat to indigenous species, particularly species endemic to single countries or small islands. For example, native plants on the main islands of New Zealand compete with a range of introduced plants and are heavily affected by introduced terrestrial mammals, among which brush-tailed possums (from Australia) are a particular threat. Tens of millions of New Zealand dollars were spent annually on possum control in the 1990s to reduce habitat loss and control bovine tuberculosis which can be passed from possums to domestic cattle (MFE 1997). New Zealand birds, reptiles and amphibians are also under pressure from introduced predators such as stoats, rats and cats but much emphasis is now given to invasive species control programmes on small islands, where long-term control may be feasible. The robin Petroica traversi was formerly widespread in the Chatham Islands but had been much reduced by the late 19th century. By the 1970s, the species was restricted to Little Mangere Island, where the remaining patch of forest was being destroyed by invasive plants. A conservation programme has now resulted in a population of some 200 birds, all descended from a single pair (MFE 1997).

The brown tree snake Boiga irregularis spread widely through Guam, from the 1950s onward, after being accidentally introduced in military aircraft. It has had a severe impact on the native bird fauna, one species of which is believed to be extinct, one is extinct in the wild and one has been assessed as critically endangered. Molluscs in Moorea (Society Islands, French Polynesia) provide a striking example of the potential impacts of introduced species. A carnivorous snail from Florida, Euglandina rosea, was introduced to control numbers of the giant African land snail Achatina fulica that had become an agricultural pest after itself being introduced to the island. The introduced carnivore subsequently preyed heavily on the endemic native snails in the genus Partula, all seven species of which are now extinct in the wild - although they survive in captivity (Wells 1995).