30/09/2017

Change In Weather Patterns Led To Mainland Tasmania Tiger Extinction, Researchers Say

ABC RadioBrett Williamson

DNA from 50 thylacines has been used to identify their primary cause of extinction. (Supplied: University of Adelaide)
Researchers believe they have discovered what killed off mainland populations of the Tasmanian tiger — and their cause of death might surprise you. Associate Professor Jeremy Austin from the University of Adelaide has been comparing the genetics of mainland and Tasmanian thylacines for 10 years.
"We know they must have been separated about 10,000 years ago when sea levels rose and cut Tasmania off from the mainland," he said.
At the SA Museum you can see a preserved thylacine. (ABC Radio Adelaide: Brett Williamson)
Tasmanian thylacines survived until 1936, but mainland thylacines were last recorded in Aboriginal cave art dating back to middle Palaeolithic times.
However, Dr Austin's radio carbon dating of thylacine bones revealed pockets of the species survived until 3,000 to 8,000 years ago in southern parts of Australia.

So what killed them?
Three theories have previously been prominent:
  • The introduction of dingoes to mainland Australia approximately 4,000 years ago;
  • A possible change in Aboriginal hunting techniques pressuring the population; and, more recently
  • A rapid change in climatic conditions.

Last thylacine 'Benjamin' in captivity at Beaumaris Zoo Hobart in 1933

Dr Austin's research, with the help of PhD student Lauren White, has confirmed the main cause of thylacine extinction was a dramatic change in mainland Australia's weather patterns.
"About the same time as dingoes arrived and human populations intensified, we also had the onset of El Niño Southern Oscillation (ENSO)," he said.
"The climate in Australia went from relatively stable to suddenly very unstable.
"It's very clear that the [Tasmanian population] went through a population crash around the same time the species went extinct on the mainland.
"The fact that those things happened around the same time suggests to us it must have been one thing in both of those populations.
"The only thing that is common is climate change, because dingoes weren't in Tasmania and human intensification wasn't occurring.
"Climate change started the decline, then something on the mainland — either dingoes or humans — pushed the species all the way to extinction."
Dr Austin said DNA sampled from remains showed no evidence of contributing disease or bacterial infections.

Are thylacines still alive?
Sightings are a semi-regular occurrence now.


A trio of Tasmanians say they've got footage of a Tasmanian tiger (ABC News)

But Dr Austin is pretty convinced about whether or not thylacines still exist in Tasmania or on the mainland.
"For a population of thylacines to survive, there would have to be hundreds of them in a relatively confined geographical location," he said.
"Not a single animal has ever been shot, trapped, hit by a car or been killed in any other way that a body has been put forward.
"They are extinct and we need to learn the lesson from that.
"There are hundreds of other animals and birds in Australia that could use our help as opposed to spending a lot of time looking up dark alleys at blurry images of foxes or dogs or kangaroos which might, if you squint hard enough, look like a thylacine."
Dr Austin's research was published today in the Journal of Biogeography.

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