Australia's Koalas at risk from climate change
By ROD McGUIRK,
AP
Posted: 2008-05-07 05:26:32
CANBERRA, Australia (AP) - Koalas are threatened by the rising level
of carbon dioxide pollution in the atmosphere because it saps
nutrients from the eucalyptus leaves they feed on, a researcher said
Wednesday.
Ian Hume, emeritus professor of biology at Sydney University, said he
and his researchers also found that the amount of toxicity in the
leaves of eucalyptus saplings rose when the level of carbon dioxide
within a greenhouse was increased.
Hume presented his research on the effects of carbon dioxide on
eucalyptus leaves to the Australian Academy of Science in Canberra on
Wednesday.
The researchers found that carbon dioxide in eucalyptus leaves affects
the balance of nutrients and "anti-nutrients" - substances that are
either toxic or interfere with the digestion of nutrients.
An increase in carbon dioxide favors the trees' production of carbon-
based anti-nutrients over nutrients, so leaves can become toxic to
koalas, Hume said.
Some eucalyptus species may have high protein content, but anti-
nutrients such as tannins bind the protein so it cannot be digested by
koalas.
Hume estimated that current levels of global carbon dioxide emissions
would result in a noticeable reduction in Australia's koala population
in 50 years due to a lack of palatable leaves.
Out of more than 600 eucalyptus species in Australia, koalas will only
eat the leaves of about 25, Hume said. Changing the toxicity levels in
the trees could further reduce the varieties that 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 said.
Hugh Tyndale-Biscoe, a marsupial physiologist, described Hume's
predictions of declining koala numbers as speculative but credible.
Eucalyptus leaves already have little nutritional value, he said, and
koalas have adapted to their poor diet by sleeping to conserve energy.
"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.
Tyndale-Biscoe said koalas had already disappeared from parts of
Australia but remained plentiful in others and were unlikely to be
wiped out by climate change. They already have been displaced from the
most nutritious trees on the most fertile land by the spread of farms
and suburbs, he said.
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