Jan. 13 (Bloomberg) -- Eradicating the cat population on Macquarie, a remote island between Australia and Antarctica, has damaged the local environment, allowing rabbits to rapidly reproduce in their absence.

Wiping out the feral cats that were introduced on Macquarie in the 19th century to control rabbits, brought to the island by sealers as a source of food, has instead led to a rabbit explosion, the British Ecological Society’s Journal of Applied Ecology reported. Hungry rabbits and rats have caused 40 percent of Macquarie’s native flora to vanish, helping erode island slopes.

“The lessons for conservation agencies globally is that interventions should be comprehensive, and include risk assessments to explicitly consider and plan for indirect effects, or face substantial subsequent costs,” said Dana Bergstrom of the Australian Antarctic Division, which administers the island.

Macquarie, a United Nations World Heritage Site, is among the island ecosystems where plants and animals introduced by humans as a source of food have overrun native species. Rats eat rare bird and reptile eggs on Ecuador’s Galapagos Islands while Brown tree snakes, which came to Guam in ship cargo holds, prey on native lizards and birds, according to the U.S. Department of Agriculture.

Rabbits, first brought to Macquarie in 1878, became the main prey of feral cats that arrived earlier. The rabbit population reached 130,000 in 1978, then fell to 20,000 as the result of a viral disease introduced to reduce their numbers. The cats lost their main source of food, resorting to eating native burrowing birds, and were then eradicated from the island in 2000.

World Heritage Site

Macquarie Island became a world heritage site in 1997 for its geology: It’s the only place on Earth where rock from the mantle, normally about 6 kilometers (3.7 miles) below the ocean floor, are exposed above sea level. It is a breeding ground for about 100,000 seals and as many as 4 million seabirds.

Macquarie, one of Australia’s sub-Antarctic islands, is 34 kilometers long and 5 kilometers wide with access only by sea, lacks trees and is part of the state of Tasmania.

Global trade contributes to the mixing of plants and animals across different ecosystems, the Invasive Species Specialist Group of scientists and policy experts says. The cat features on the group’s list of the world’s worst invasive alien species.

To contact the reporter on this story: Jeremy van Loon in Berlin at jvanloon@bloomberg.net.

Last Updated: January 13, 2009 11:38 EST