Effort to Remove Species Creates More Problems

Jan. 12, 2009 -- The eradication program on Macquarie Island, lying halfway between Australia and Antarctica, is a cautionary tale about the complex web of ecosystems, its authors say.

In the early 19th century, cats were introduced to Macquarie Island, where they swiftly became feral.

In 1878, rabbits were brought in by seal hunters, according to the paper, which appears on Tuesday in the Journal of Applied Ecology, published by the British Ecological Society.

By the late 1960s, the rabbit population had become so large, and so destructive of vegetation, that the Australian authorities used the Myxoma virus -- which causes the disease myxamotosis among rabbits -- to control their numbers.

As a result, the rabbits dwindled, from a peak of 130,000 in 1978 to 20,000 in the 1980s, and the vegetation recovered.

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The downside: the cats, which had been tucking into the rabbits for food, turned to Macquarie's native burrowing birds for sustenance.

Fearing that the birds would get wiped out, the authorities returned to the island in 1985 to launch a cat eradication program.

The cats were all killed in 2000, but myxamotosis had failed to do the same to the rabbits. Without their feline predators, the rabbit population surged anew and in just half a dozen years has inflicted enormous damage, in some places stripping the ground bare.

In ecologists' terms, this is an example of "trophic cascades" -- when a species' abundance is significantly reduced or increased, the change resonates along the food chain.