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Tuesday 23 June 2009

RAPID ROUNDUP: Humans to blame for extinction of Giant Kangaroo (PNAS) - Experts respond

Embargo lifted 7am AEST Tuesday 23 June 2009

Australian research suggests human hunting is to blame for the extinction of the largest kangaroo ever to evolve. There has been ongoing debate about whether climate change or human arrival was the major cause of the demise of Australia’s megafauna. The new study, to be published in the journal Proceedings of the National Academy of Sciences of the USA, suggests that human hunting was to blame.

Led by palaeontologist Dr Gavin Prideaux of Flinders University in South Australia, it examined the dietary habits of the giant Kangaroo, Procoptodon goliah, and found that the animal would have fed largely on saltbush shrublands. This suggests that landscape burning and changes in the climate are unlikely to have brought about its demise, because saltbush shrublands carry fire poorly and thrive in dry conditions, leaving human hunting as the most likely explanation.

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Professor Tim Flannery is Professor of Environmental and Life Sciences at Macquarie University

“This careful, fine-grained study of a single megafaunal species has revealed more about ecology and extinction of Procoptodon goliah than all previous research combined. It's just the sort of study that promises to give us a definitive answer to the vexed question of what killed off the world's megafauna. Given our lamentable ignorance of many other megafaunal species, however, for now it must be regarded as just another very solid brick in a strongly building argument that human hunting, rather than climate, was the cause.”

Professor Richard ‘Bert’ Roberts is from the School of Earth and Environmental Sciences, University of Wollongong

"This study neatly ties up several loose threads in the long-running extinction debate. What pushed the Australian megafauna over the edge into oblivion? The weight of evidence is now tipped heavily in favour of hunting by humans. Through detailed reconstructions of the diet of the largest of the now-extinct giant kangaroos that once graced Australia, Gavin Prideaux and colleagues convincingly show that vegetation burning and increased aridity were not the immediate cause of extinction of this ‘whopper hopper’. Their conclusions echo those found late last year for the Tasmanian megafauna, which were also probably extinguished by early human hunters.

By independently reaching the same conclusion for two very different environments – the mountainous rainforests of Tasmania and the dry rangelands of inland Australia – the mystery is no longer whether humans were ultimately responsible for the disappearance of the giant marsupials, but how they did it. As Barry Brook (University of Adelaide) and Chris Johnson (James Cook University) have elegantly demonstrated, it takes only a modest level of hunting of juveniles to drive slow-breeding animals, such as the Australian megafauna, inexorably towards extinction in a few hundred years. So it’s little wonder that direct traces of hunting remain elusive, given the low off-take of animals required to exterminate them and the brief overlap between the first human arrivals on this continent and the last of our magnificent megafauna."

"Prideaux and colleagues have done a terrific job of reconstructing the ecology of this giant species of kangaroo, from the few bones and teeth that are all that remain of it. We now know what plants it ate; how it moved and how it fed; that it needed to drink often; but that it was adapted for efficient long-distance travel so could range out far from waterholes and feed on dry open plains. I think they are right that this new understanding rules out fire or climate change as causes of its extinction, and that the real cause was hunting.

But I actually think the main importance of this paper is in helping to show how dramatically the ecology of Australia changed when people first came here. Procoptodon goliah emerges from this study as a specialist kangaroo of saltbush plains. Probably, every other major vegetation type in Australia had its own specialized large herbivores that helped maintain the continent's ecological balance. With their extinction 45 000 years ago, a great part of the complexity of Australian ecology disappeared. We are only just beginning to comprehend the scale of this loss."

Dr John Magee is from the Department of Earth and Marine Sciences at the Australian National University

“This study has made a major contribution to elucidating the cause of extinction of the Australian megafauna, a research question that has polarised debate for more than 150 years. Much of that debate has been waged between opposing entrenched positions and has very often consisted of opinion-based arguments. One way out of this impasse is through autecological studies of individual megafaunal species. Autecology is the study of the interactions of a single species with its environment and aims to elucidate the requirements, the life history, and the behavior of the species. With extant animals this can be achieved by experimentation and direct measurement, but is much more difficult with extinct species.

The results obtained by this study provide strong support for the role of humans in the extinction of P. goliah and point to a specific mechanism. But most importantly they follow on from carbon-isotopic palaeodiet studies of the extinct giant flightless bird Genyornis newtoni, by our own research group, in establishing convincing data-based evidence for resolving the likely cause of extinction for an element of the megafauna. Similar autecological studies of other elements of the megafauna are urgently required to fully resolve the megafaunal extinction debate. The results so far challenge those who believe that the extinction is climate driven to find real data to support that argument.”

Dr Judith Field is a Senior Research Associate in Microscopy and Archaeology at the University of Sydney

“I think the most obvious problem with this paper is the giant leap of logic in demonstrating that the Procoptodon was arid adapted and therefore can’t have died out during times of LGM stress, so therefore people were responsible. This is entirely unsubstantiated nonsense. Why can’t these guys present this interesting (dietary) information without entering into the realms of fantasy by attributing a human cause?

My understanding is that there are no Procoptodon remains co-occurring with an archaeological record on the continent. So why are humans suddenly responsible? It is not clear when Procoptodon became extinct and it may well have disappeared long before humans arrived. The fossil record is so sparse that providing good chronologies from well contextualized remains is a priority, we can agree on that much. Though in this work, palaeontologists are short on context and big on using any dates they can find.

There is still no clear picture of the extinction process and certainly no evidence that it was an event around 46,000 years ago.. This is a construct not supported by any data. Most megafauna cannot be placed within 100,000 years of human arrival. Attributing a human cause to the disappearance of Procoptodon is still made in the absence of any supporting evidence. I applaud the detailed work on establishing diet etc for this species but any proposal that humans were involved is made entirely in the absence of any empirical evidence.”