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Professor Ian Hume and his students from the University of Sydney have been researching the effects of CO2 increases and temperature rises on eucalypts. He presented some of their findings on Wednesday at the Australian Academy of Science in Canberra.

Professor Hume's group have shown, in the laboratory, that increases in CO2 affect the level of nutrients and 'anti-nutrients' (things that are either toxic or interfere with the digestion of nutrients) in eucalyptus leaves. Anti-nutrients in eucalypts are built from carbon and an increase in carbon dioxide levels will favour the production of anti-nutrients over nutrients.

Koalas are fussy about the species of eucalyptus that they eat as different species contain different ratios of nutrients to anti-nutrients. Some eucalyptus species may have high protein content, but anti-nutrients such as tannins bind the protein so it can't be used by the koala.

Professor Hume said:
"If there is a significant rise in CO2 concentration in the atmosphere, which we're already seeing, that's going to push the ratio of nutrients to anti-nutrients even lower by increasing the concentration of these carbon-based anti-nutrients.

"What currently may be good koala habitat may well become, over a period of not so many years at the rate that CO2 concentrations are rising, very marginal habitat...

"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."

Changes in eucalyptus nutrient content may force koalas to travel in search of more nutrient-rich species. With habitats fragmented by roads and agriculture, more koalas will travel by land, which increases their risk of being hit by vehicles or eaten by predators.

Higher temperatures could also affect eucalyptus species. Some are so sensitive to temperature that even a one degree shift in mean annual temperature will affect them. These sensitive species could then be out-competed by others which are less sensitive to temperature.

If these less temperature sensitive species aren't suitable for koala feed then "we're not seeing anything in terms of the forest disappearing, but in terms of nutritional habitat, it has disappeared."

When asked if koalas could adapt to changes in nutrient levels, he said: "I don't think they've got enough time to do that, nowhere near enough time to do that."

Professor Hume's group have been studying the four marsupials that eat eucalyptus leaves with the koala being the most highly specialised. The others are the greater glider, common ringtail possum, and common brushtail possum.

By comparing the responses all four species make to dietary changes, a larger picture of the state of the environmental system can be formed.