Over the past 400 years, around half of all animal extinctions have occurred on islands. Island species are often only present in relatively small numbers, putting them at greater risk, and the limited habitat available to them means they cannot easily disperse elsewhere. This also means that island species are particularly vulnerable to the effects of climate change, such as rising temperature and sea levels, extreme weather events, and fires.
Island species are also vulnerable to the introduction of invasive species, as they have typically evolved in isolation with limited competition. Many island species also lack the adaptations to cope with introduced predators. As humans have travelled the world they have introduced large numbers of non-native species to islands, sometimes with devastating consequences, and on some islands the alien species now outnumber the native ones.
The other main risks to island species are natural disasters, habitat destruction, tourism development, overexploitation and pollution. These pressures show their impacts on islands before they would be visible on larger land masses.
Island species at risk
Although once widespread throughout Southeast Asia, today the Bornean orangutan is restricted to the island of Borneo. Currently, the main threat to this species is the loss of forest habitat. In the past 20 years, 80 percent of this species’ habitat has been lost to illegal logging, gold mining and conversion to permanent agriculture such as oil palm plantations.
The Juan Fernández petrel faces its greatest threats on its tiny breeding island, where numerous introduced species are causing extensive damage to the natural ecosystem.
The Lord Howe Island stick-insect was believed Extinct due to predation by introduced black rats until it was rediscovered surviving on a single island outcrop known as Ball’s Pyramid.