"What we're seeing, essentially, is that the staple diet of these animals is being turned to leather," Australian National University science professor Bill Foley was quoted as saying in the Weekend Australian.

"Life is set to become extremely difficult for these animals."

Increased carbon dioxide reduced nitrogen and other nutrients in eucalyptus leaves and boosted tannins, a naturally occurring toxin, greenhouse experiments by James Cook University researcher Ivan Lawler found.

This sharply reduced the levels of protein in the leaves, requiring koalas and other animals to eat more nutritionally-poor eucalyptus leaves to survive.

"The food chain for these animals is very finely balanced, and a small change can have serious consequences," the newspaper quoted Dr Lawler as saying.

Koalas and greater gliders, a large gliding possum, depend entirely on eucalyptus leaves for food. Some other marsupials, including brushtail and ringtail possums and many wallaby species, feed extensively on the leaves.

Many insect species also feed exclusively on the leaves.

(Reporting by Michael Byrnes; Editing by Sanjeev Miglani)