Saturday, July 16, 2005

Australia's Ancient Animals: Burned?

` (As part of my ongoing posts from my inbox.)

Fire Starters blamed for Australian extinctions by Michael Hopkin.

` Ah, yes, it has been long thought that climate change was the main culprit behind the extinction of Australia's grand ecosystems, rich with megafauna (really big animals) and other interesting things. And now, it's being challenged.

[Gifford]Miller and his colleagues say they have found evidence that many animals changed their eating habits soon after humanity's arrival, and that those that were unable to adapt to new foods died out.

The researchers studied preserved eggshell fragments from Lake Eyre, Port Augusta and the Darling-Murray Lakes in southern Australia. Some of the eggs came from the emu (Dromaius novaehollandiae), which survives as a species today; others belonged to the similar, but extinct bird Genyornis newtoni.

Miller's team reconstructed the birds' diets over the past 140,000 years by studying the levels of radioactive carbon isotopes in the eggshells. They found that Dromaius shifted from nutritious grasses, which the team identified by its distinctive levels of radioactive carbon, to less nutritious shrubs and trees around 45,000 years ago.

A similar trend was seen in wombat teeth, the researchers report in this week's Science. But Genyornis showed much less variation in its diet, which may explain why it failed to adapt and survive into the present.

The change in diet is down to man's extensive burning of grasslands, to clear passageways, open up hunting grounds or signal over long distances, Miller argues.

"Our evidence suggests that the enterprise of the first colonists altered ecosystems at their lowest level: the vegetation," Miller says. "And as vegetation changed, those animals with flexible dietary tolerances were able to adjust to the changed food sources, whereas those with more specialized dietary needs became extinct."

The researchers add that no climate shift is known to have occurred in Australia during the time of that extinction. So they argue that humanity, rather than climate, caused a change in vegetation, and widespread extinctions.
` That's pretty neat. If this is true, it will help to disspell certain annoying people's idealized notions about 'noble savages' and whatnot. Aw, most civilizations have been destructive, some more than others.
` Still, nobody knows how close Miller is to being onto something, but I'm sure Nature will let us know in the future.

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