The story of Macquarie Island, halfway between New Zealand and Antarctica, is the go-to tale illustrating the devastating effects of invasive species. Before 1810, the island was uninhabited, but an amazing variety of sea birds flourished there. Several species of penguins used it as a mating ground because there were no land predators. Then Macquarie Island was claimed as a base for British sealing ships, and both seals and penguins were hunted to near extinction. The ships brought rats, who settled in and ate seabird eggs. The rats became so numerous that cats were brought in for rat control. However, the cats found seabirds easier to catch, and the cats multiplied while seabirds died out.
At the same time, rabbits were introduced to Macquarie Island so that sailors would have something to eat besides penguins, and they took over the island as well, damaging the grassland and native vegetation. Seabirds suffered further, and some species went extinct. By the 1980s, conservationists were ready to do something about Macquarie Island. Read up on the measures they took, some more successful than others, at Amusing Planet.
(Image credit: Hullwarren)