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Climate Change Threatens Koala Bears

May 7, 2008

Sydney University researchers reported Wednesday that rising levels of carbon dioxide pollution are threatening Australia’s Koala population.

The scientists said carbon dioxide in the atmosphere was sapping nutrients away from the eucalyptus leaves the animals feed on, and that the toxicity levels of the leaves correlate with the amount of carbon dioxide in the air.

The research was led by Ian Hume, emeritus professor of biology at Sydney University, who presented the findings Wednesday to the Australian Academy of Science in Canberra. Hume said the carbon dioxide content alters the balance of nutrients and “Ëœanti-nutrients’ in the leaves. Anti-nutrients are substances that either obstruct digestion of nutrients or are toxic.

An increase in carbon dioxide promotes the production of carbon-based anti-nutrients in the trees, such that overall the leaves become toxic to koalas, Hume explained. Some species of eucalyptus have high protein content, but the protein becomes indigestible by koalas once it is bound by anti-nutrients such as tannins.

At current levels, global carbon dioxide emissions will result in a visible reduction in Australia’s koala population within 50 years, Hume said, adding that the koalas would only eat the leaves of 25 out of Australia’ 600 eucalyptus species.   Growing toxicity levels in the trees could further reduce the number of species the koalas find palatable, he said.

“Koalas produce one young each year under optimal conditions, but if you drop the nutritional value of the leaves, it might become one young every three or four years,” Hume told the Associated Press.

Marsupial physiologist Hugh Tyndale-Biscoe said Hume’s predictions of declining koala numbers were credible, although speculative. While koalas had already vanished from some parts of Australia, he said, they remain abundant in other areas and are not likely to be eliminated by climate change.

“Eucalyptus leaves already have little nutritional value, and koalas have adapted to their poor diet by sleeping to conserve energy,” he said.

“It’s a very precarious existence,” Tyndale-Biscoe 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.

The spread of farms and suburbs has already displaced Koala’s from the most nutritious trees on the most fertile land, he said.

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