Humans killed off Australia's giant beasts

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Humans killed off Australia's giant beasts

Post by klr » Sat Mar 24, 2012 11:02 pm

Not exactly out of the blue, but more evidence for what has long since been suspected.

http://www.bbc.co.uk/news/science-environment-17488447
Scientists have linked a dramatic decrease in spores found in herbivore dung to the arrival of humans in Australia 41,000 years ago

Humans hunted Australia's giant vertebrates to extinction about 40,000 years ago, the latest research published in Science has concluded.

The cause of the widespread extinction has provoked much debate, with climate change being one theory.

However, scientists studied dung samples from 130,000 and 41,000 years ago, when humans arrived, and concluded hunting and fire were the cause.

The extinction in turn caused major ecological changes to the landscape.

The scientists looked at pollen and charcoal from Lynch's Crater, a sediment-filled volcanic crater in Queensland that was surrounded by tropical rainforest until European settlement.

They found Sporormiella spores, which grow in herbivore dung, virtually disappeared around 41,000 years ago, a time when no known climate transformation was taking place.

At the same time, the incidence of fire increased, as shown by a steep rise in charcoal fragments.

It appears that humans, who arrived in Australia around this time, hunted the megafauna to extinction, the scientists said.

The megafauna included three-metre tall giant kangaroos and marsupial lions, as well as giant birds and reptiles.

Susan Rule of the Australian National University in Canberra and her colleagues concluded that vegetation also changed with the arrival of humans.

Mixed rainforest was replaced by leathery-leaved, scrubby vegetation called sclerophyll.

But these changes to the landscape took place after the animal extinctions, indicating that they were the result of the extinction and not its cause, they said.

Human-lit fire - deliberately targeted and more frequent than lightning - had a devastating effect of plants that had previously been protected.

"Any climate change at those times was modest and highly unlikely to affect the outcome," author Matt McGlone wrote in Science.

Lead research author Chris Johnson, from the School of Zoology at the University of Tasmania, said the research raised further questions about the ecological impact of the extinction.

"Big animals have big impacts on plants. It follows that removing big animals should produce significant changes in vegetation."

The removal of large herbivores altered the structure and composition of vegetation, making it more dense and uniform, he said.

"Getting a better understanding of how environments across Australia changed as a result of megafaunal extinction is a big and interesting challenge, and will help us to understand the dynamics of contemporary Australian ecosystems."

'Utter havoc'

Dr John Alroy, from the Department of Biological Sciences, Faculty of Science at Macquarie University, New South Wales, said the debate about whether humans contributed to widespread extinction should "be over now".

"But it has dragged on for nearly a half-century now because the idea that stone age hunters could cause such utter havoc across three entire continents over very short time spans strikes many people as incredible.

"Like it or not, though, it's the truth, and it's time for us to all confront it."

However, Gavin Prideaux, a lecturer in vertebrate palaeontology in the School of Biological Sciences at Flinders University, South Australia, said further research was necessary.

He said the latest study "supports a mounting number of studies that have argued that climate change was not primarily responsible for the Late Pleistocene extinctions in other parts of the continent.

"To test the inferences from this paper we might look at similar lake records from other regions of Australia and seek fossil deposits in the northeast that preserve bones of the giant animals themselves."
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Re: Humans killed off Australia's giant beasts

Post by mistermack » Sat Mar 24, 2012 11:39 pm

The abbo's won't like being blamed for mass extinctions, as all we hear lately is how aboriginal people learned to live in harmony with nature, showing big respect to all creatures.

Having said that, I would have some doubts about humans directly having such a big effect. What level of human population would be needed, and where's the evidence that humans existed in such numbers?

I could however see an indirect effect. Humans brought dogs with them, and they might have bred in vast numbers, if the indigenous animals had no defence. It could have been the dogs that caused the havoc.

Somehow, that seems more likely than humans causing the problem. Dogs can have huge litters every year, and the population could balloon very quickly. Humans take a long long time to flourish, as we are so slow to breed.
It's different now, with medical care and food storage, and low infant mortality.
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Re: Humans killed off Australia's giant beasts

Post by Gawdzilla Sama » Sat Mar 24, 2012 11:42 pm

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Re: Humans killed off Australia's giant beasts

Post by JimC » Sat Mar 24, 2012 11:51 pm

It wasn't me! :?
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Re: Humans killed off Australia's giant beasts

Post by klr » Sat Mar 24, 2012 11:54 pm

JimC wrote:It wasn't me! :?
Nope, you were far too busy with gin and equations to notice the mounting pile of skeletons in the back garden. :toetap:
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Re: Humans killed off Australia's giant beasts

Post by JimC » Sun Mar 25, 2012 12:00 am

On a more serious note, it is probably true that Aborigines in recent times had evolved (culturally) to be extremely efficient and ecologically responsible hunter gatherers. However, when they first arrived, it would be no surprise that they acted just like the first Amerinds, who also caused megafaunal extinctions. Then the learning curve would set in, just a little too late for the Diprotodons and others...

Also, as mistermack has already said, the dogs they brought with them probably had an impact...
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Re: Humans killed off Australia's giant beasts

Post by Ayaan » Sun Mar 25, 2012 12:01 am

It's possible that they did it by running herds off of cliffs, much like Native Americans did before they acquired horses and learned how to hunt from horseback.
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Re: Humans killed off Australia's giant beasts

Post by Gawdzilla Sama » Sun Mar 25, 2012 12:02 am

Ayaan wrote:It's possible that they did it by running herds off of cliffs, much like Native Americans did before they acquired horses and learned how to hunt from horseback.
Saw a video called "Death of the Megabeasts" where they posited fires, deliberately set, in the bush.
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Re: Humans killed off Australia's giant beasts

Post by Blind groper » Sun Mar 25, 2012 11:34 pm

mistermack wrote:Having said that, I would have some doubts about humans directly having such a big effect. What level of human population would be needed, and where's the evidence that humans existed in such numbers?

I could however see an indirect effect. Humans brought dogs with them, and they might have bred in vast numbers, if the indigenous animals had no defence. It could have been the dogs that caused the havoc.
.
Not dogs.
The dingo arrived in Australia about 5,000 years ago - apparently an Asian dog. The megafauna extinctions were more like 45,000 years ago.

Humans may have arrived in Australia as early as 55,000 years ago. if so, that gave them 10,000 years to get more numerous, and to develop techniques for bumping off the big beasts. Aboriginals today have no big beasts left to kill, so those hunting methods were probably lost tens of thousands of years ago.

I also have a personal theory that one contributing factor was lack of fear. The dodo in Mauritious apparently had no fear of the people killing it. Penguins in Antarctica today have no fear of humans. Perhaps the vulnerable megafauna in Australia, when they first met human hunters, had no fear, and let the hunters get too close.

Did you know that the easiest animal to kill for food in Australia, the koala, tastes utterly foul! The result of eating all those nasty gum leaves. That is probably the only reason humans did not wipe them out 50,000 years ago.
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Re: Humans killed off Australia's giant beasts

Post by mistermack » Mon Mar 26, 2012 12:13 am

Definitely not dogs then.

Maybe the human population did grow big enough to cause extinctions, and then shrink back a bit when the megafauna disappeared. The fear of humans idea is tempting, but you would think that they would develop that, over time. It's normally communicated down the generations, rather than inherited, in higher animals, so you would think it could evolve and spread fairly quickly.

But there don't appear to be any other candidates for the extinctions, so it probably was humans.
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Re: Humans killed off Australia's giant beasts

Post by Clinton Huxley » Mon Mar 26, 2012 8:09 am

'Stralia today is a narrow perimeter of squalid beach-front bars surrounding a blasted, desolate interior - anyone know what it was like 50K years ago when the first chaps arrived?
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Re: Humans killed off Australia's giant beasts

Post by Svartalf » Mon Mar 26, 2012 8:40 am

JimC wrote:It wasn't me! :?
Yeah, right, like you didn't know that making them giant kangs drink gin would be bad for them.
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Re: Humans killed off Australia's giant beasts

Post by shiner » Mon Mar 26, 2012 9:38 am

Perhaps it was a combination of ; Human hunters, Human fire, and Global warming.
Is Global warming a new thingy, or a newly discovered thingy?? We only have a few hundred years of accurate data, so how can we know what the temperatures were 45000 years ago.
Any "evidence" we have is guesstimations. A couple of degrees celcius either way can make a big difference to vegetation. Its called Evolution I thinksm.
In the quote in the OP it is mentioned that no dramatic climate change was known to be taking place 45000 yr ago. I beg to differ, humans were establishing themselves, oh , and megafauna were dissappearing. Thats pretty dramatic, I reckon. :smoke:

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Re: Humans killed off Australia's giant beasts

Post by Blind groper » Mon Mar 26, 2012 8:31 pm

Shiner

Our scientific tools are better than that.
We can pick up major climate changes no trouble at all. And the time of the extinctions was a time of minimal, if any, climate change. Since those large beasties had lived through 9 glacial and interglacial periods, we can assume they are not that sensitive to climate change.
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Re: Humans killed off Australia's giant beasts

Post by Faithfree » Mon Mar 26, 2012 9:07 pm

What I find telling is that the 'megafauna' die out in different continents and islands at different times, but always shortly after humans arrived. For example, in New Zealand the megafauna (multiple species of moa) died out only a thousand or less yeas ago, shortly after the Maori arrived. Interesting, there is one place where all the megafauna still thrive, Africa, where humans and the megafauna evolved together.
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