Rising carbon dioxide levels are depleting nutrients from Australia's eucalyptus leaves, the sole food source for koalas, scientists warned Wednesday.
A team of researchers at the University of Sydney, led by digestive physiology expert Ian Hume, discovered that exposing eucalyptus plants to increased levels of carbon dioxide reduces the amount of available nutrients and increases the amount of toxins in the leaves.
"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," lead researcher Professor Ian Hume said.
"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."
When asked how long it would take for koalas to be affected, he said: "I would've thought a few years ago when we first did these experiments that you might see something in a hundred years.
"But at the rate at which things are going, I suspect that we might see changes within our lifetimes," Prof Hume said.
Hume, who presented his findings Wednesday at an Australian Academy of Science event in Canberra, noted that rising temperatures – another effect of increased atmospheric CO2 – can also affect the growth of the plants.
Koalas are notoriously picky eaters: Of Australia's 600 eucalyptus species, the stout tree-dwelling mammals will dine on only 25 species. The leaves have so little nutritional value and require so much energy to digest that koalas must sleep for 18 to 22 hours each day. Hume said that it is very unlikely that koalas would be able to adapt their diet to the changed nutritional value of the plants.
They may be forced to travel in search of more nutritious meals, increasing their risk of being hit by cars or eaten by dogs or dingoes.
Zoologists say that Koalas are already under grave threats from extreme drought, wildfires, and urban sprawl.