Green Times

Global warming will threaten the survival of koalas by making the eucalyptus leaves on which they feed toxic, scientists warned on Wednesday.Australia’s most endearing marsupial is already under threat from a severe drought and loss of habitat as housing encroaches on woodland.

But higher temperatures and increased carbon dioxide could shut down their food supply, leaving them to starve to death.

New research shows that the level of toxicity in the leaves of eucalyptus saplings rises, and their nutrient content falls, when they are exposed to higher levels of carbon dioxide.

“What currently may be good koala habitat may well become, over a period of not so many years at the rate that carbon dioxide concentrations are rising, very marginal habitat,” said Ian Hume, Emeritus Professor of Biology at Sydney University, who carried out the research.

“I’m sure we’ll see koalas disappearing from their current range even though we don’t see any change in tree species or structure of the forests.”

The koala’s ecological niche is precarious enough as it is - eucalyptus leaves have so little nutritional value that the animals have to sleep for 20 hours a day to conserve energy.

The animals are also notoriously fussy eaters - of Australia’s more than 600 species of eucalypt trees, koalas will only browse on the leaves of about 25.

The animals would be unable to adapt to the greater toxicity of gum tree leaves, Prof Hume said after presenting his findings at an Academy of Science conference in Canberra. “I don’t think they’ve got enough time to do that, nowhere near enough time to do that,” he said.

Forced to descend to the ground in search of trees with more nutritious leaves, the slow-moving marsupials would be more vulnerable to being hit by cars and attacked by predators such as dingoes and domestic dogs.

Marsupial physiologist Hugh Tyndale-Biscoe said the grim prognosis was speculative but credible. “It’s a very precarious existence and the distribution of koalas tends to shift,” he said.

“They basically sleep for 20 hours a day and then they’ve got four hours to do everything else - occasionally eat a leaf and maybe once a year go after another koala [to mate]”.
Source: Telegraph, UK