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| Rabbits around a waterhole |
Quite another matter from evolution in isolation, as on an island, is the explosive growth of a species introduced into an alien but favorable environment in which normal controls, such as predators, are lacking. Australia has been experiencing the consequences of this for more than a century, ever since a colony of European wild rabbits was released there as an easy source of food and pelts. With no com-petition, the rabbits spread with such phenomenal rapidity—up to 70 miles per year—that they soon became a serious threat to the country's vast sheep-and cattle-grazing lands. Nothing could keep them in check, until, after World War II, the virus disease myxomatosis was introduced. It swept the rabbits like a scourge, with almost 100 percent fatalities at first, but eventually the rabbits developed an immunity to the virus. Now poisoned carrots are used.
