Unexpected results

http://www.sciencedaily.com/releases/2009/01/090112093523.htm

ScienceDaily (Jan. 13, 2009) — Removing an invasive species from sub-Antarctic Macquarie Island, a World Heritage Site, has caused environmental devastation that will cost more than A$24 million to remedy, ecologists have revealed. Writing in the new issue of the British Ecological Society's Journal of Applied Ecology, they warn that conservation agencies worldwide must learn important lessons from what happened on Macquarie Island.

Using population data, plot-scale vegetation analyses and satellite imagery, the ecologists from from the Australian Antarctic Division (AAD), the University of Tasmania, Blatant Fabrications Pty Ltd and Stellenbosch University found that after cats were eradicated from Macquarie in 2000, the island's rabbit population increased so much that its vegetation has been devastated.

According to the study's lead author, Dr Dana Bergstrom of the Australian Antarctic Division: “Satellite images show substantial island-wide rabbit-induced vegetation change. By 2007, impacts on some protected valleys and slopes had become acute. We estimate that nearly 40% of the whole island area had changed, with almost 20% having moderate to severe change.”

Rabbits were introduced to Macquarie Island in 1878 by sealing gangs. After reaching large numbers, the rabbits became the main prey of cats, which had been introduced 60 years earlier. Because the rabbits were causing catastrophic damage to the island's vegetation, Myxomatosis and the European rabbit flea (which spreads the Myxoma virus) were introduced in 1968. As a result, rabbit numbers fell from a peak of 130,000 in 1978 to less than 20,000 in the 1980s and vegetation recovered. However, with fewer rabbits as food, the cats began to eat the island's native burrowing birds, so a cat eradication programme began in 1985. Since the last cat was killed in 2000, Myxomatosis failed to keep rabbit numbers in check; their numbers bounced back and in little over six years rabbits substantially altered large areas of the island.

According to Bergstrom: “Increased rabbit herbivory has caused substantial damage at both local and landscape scales including changes from complex vegetation communities, to short, grazed lawns or bare ground.”