Australian scientists believe that changes in the climate over the next century may be disastrous for several species of marsupial - animals with pouches.

The scientists, from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), are concerned about two tree kangaroos and five species of possum.

The animals are now found only on cool tropical peaks in northern Australia.

Trapped by changing climate

CSIRO says they are the last representatives of an extraordinarily rich fauna that flourished there over the last 20 million years, when rainforests covered much of Australia.

One researcher, John Kanowski, said: "The possums and tree kangaroos are essentially temperate animals that have become isolated in the high misty mountains of the tropics.

"They are tree-dwelling, cool-adapted, and very territorial in their behaviour. They may be highly susceptible to global warming."

Where do you go when the mountain tops become too hot ?

The CSIRO team believes that a two-degree global warming which occurred between 5,000 and 3,500 years ago caused a major wave of extinctions.

That, it believes, is the reason why these marsupial species retreated to the mountain tops.

And Mr Kanowski thinks that the climate changes expected in the next 50 or 100 years could be even more devastating for the animals that have so far managed to survive.

"For one thing, the atmosphere is becoming richer in carbon dioxide (CO2), and this makes the leaves on which these animals subsist tougher and less digestible", he says.

The trees themselves are deficient in nutrients, because the pockets of rainforest left after human destruction now grow mostly on poor, thin soil about as nutritious as sand.

Poisoned by their food

"Because the leaves are poor in nutrients, the animals need to eat more to survive," says Mr Kanowski.

And that conceals a further threat, because the leaves contain natural substances - phenolics, alkaloids and cyanide-forming compounds - to protect the trees against over-browsing.

"That means the animals' intake of natural plant toxins is higher too, so they may be gradually poisoned by their own diet."

Loss of one species will affect the whole ecosystem

John Kanowski says understanding the animals' physiology is the key to predicting their response to climate change and alterations to their habitat.

"We think they need cool conditions, not only to keep their body temperatures down, but also to provide the dew they drink."

"If the cool, wet forest retreats, the animals have no choice but to go with it."

There is also concern that the extinction of the animals might affect the rainforest itself.

"These animals have been part of the rainforest for millions of years", says John Kanowski.

"Along with insects, they perform an important task in "mowing" the forest.