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Post by Surroundx on Feb 7, 2015 10:54:40 GMT 10
Hydrological transformation coincided with megafaunal extinction in central AustraliaAbstract Central to the debate over the extinction of many of Australia's last surviving megafauna is the question: Was climate changing significantly when humans arrived and megafauna went extinct? Here we present a new perspective on variations in climate and water resources over the last glacial cycle in arid Australia based on the study of the continent's largest lake basin and its tributaries. By dating paleoshorelines and river deposits in the Lake Eyre basin, we show that major hydrological change caused previously overflowing megalakes to enter a final and catastrophic drying phase at 48 ± 2 ka just as the giant bird, Genyornis newtoni, went extinct (50–45 ka). The disappearance of Genyornis and other megafauna has been previously attributed to "ecosystem collapse" coincident with the spread of fire-wielding humans. Our findings suggest a climate-driven hydrological transformation in the critical window of human arrival and megafaunal extinction, and the results call for a re-evaluation of a human-mediated cause for such extinctions in arid Australia. Source: geology.gsapubs.org/content/early/2015/02/02/G36346.1.abstract
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Post by mingle on Feb 7, 2015 12:08:33 GMT 10
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Post by Ian Thomas on Feb 7, 2015 15:26:49 GMT 10
Good posts, dudes. Think I know someone who'll be interested.  If the 2nd one (lakes dried out) is right then humans round those parts should have gone extinct too? |
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Post by Surroundx on Feb 7, 2015 16:02:48 GMT 10
"Simultaneous extinction of Genyornis at all sites during an interval of modest climate change implies that human impact, not climate, was responsible." The paper I posted implies that in fact the climate change during this time was not so modest. So it more constitutes a revision of the evidence, rather than an outright contradiction for want of a better phrase. |
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Post by dennisw on Feb 7, 2015 20:16:29 GMT 10
A report that I read sometime ago and did not retain the link suggested that it was geological upheaval that closed a link between Lake Eyre and Spencer Gulf that caused the aridity in inland Australia. It was proposed to make the reopening of a link the next major work following the Snowy River Scheme but subsequent governments have shelved the idea preferring to spend the money on urban projects that gain votes.
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Post by molloch on Feb 7, 2015 20:17:14 GMT 10
I can't get the full paper at the moment, but it sounds like they are looking a dates for when the lakes last dried out, not that they couldn't have exhibited this behaviour before. They most likely have discussed this so will be interesting to read the whole thing.
Also, Genyornis is found in a number of regions, regions where we don't see such a dramatic effect in climate change (see the second paper). We'd need to show that these areas underwent the same kind of stress as those in the central basin, and there is no evidence of this yet.
I don't believe there is a lot of concrete evidence for humans in the centre of Australia circa 50kya, so not sure of the effect on humans - it wouldn't have been good for local populations, but how rapidly it happened and whether they could have migrated to wetter climates - who knows. Again, we don't know the effect on the rest of the country. There is good evidence that human occupation and culture continue through the period 50-45kya, so I don't expect it wiped them out continent-wide.
The answer to the MF extinctions, IMHO, will be multi faceted. The megafauna survived severe climate events in the past, relatively unscathed. Numerous species have survived human occupation of Australia since. It's likely that the combination of stress from humans and stress from environmental changes (due to fires and removal of key populations) and stress from climate would have ultimately combined to tip the scales - the straw that broke the Driprotodon's back. It will never be as simple as one cause in isolation - but you could argue that without human involvement the megafauna would have survived. You could say the same about the climate factor, but they had survived climate changes in the past.
I'll grab a copy of the full paper on Monday and see what they say.
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Post by molloch on Feb 7, 2015 20:19:03 GMT 10
A report that I read sometime ago and did not retain the link suggested that it was geological upheaval that closed a link between Lake Eyre and Spencer Gulf that caused the aridity in inland Australia. It was proposed to make the reopening of a link the next major work following the Snowy River Scheme but subsequent governments have shelved the idea preferring to spend the money on urban projects that gain votes. Yeah, but we've already established that there isn't any evidence for that. There was no upheaval and the models don't show that there would be any such effect. |
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Post by Ian Thomas on Feb 27, 2015 20:16:30 GMT 10
The Conversation's got a story on it. Got an idea there's a thread deep down in this board about giant dust spikes at just that time - 50k? There's your smoking gun. Will try finding it, might merge the threads |
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Post by saggitarius on Mar 2, 2015 11:49:27 GMT 10
I can recall a scientific theory floated in the 1970s to dig a channel or pipeline from the ocean to Lake Eyre to create an inland sea. The economic benefit was touted that arid areas of outback NSW would get more rainfall and be able to grow sustainable crops, better pasture and even timber plantations.
There was not much opposition at the time because the greenies were not organised and were more worried about flooding Lake Pedder in Tassie. The idea didn't have legs because I think the boom times were over thanks to Gough and Co running the bank dry and big business didn't want to back it either.
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Post by molloch on Mar 2, 2015 15:35:02 GMT 10
Everything I have read says that there would be a local effect around the basin, but not much change to rainfall. Also, the level of evaporation would be high and salinity would increase, possibly to the point of blocking the channel. A recent paper, from last year, suggested that we would need to reduce evaporation to the point of floating plastic balls on the lake surface or covering it with a large mat. Doesn't seem very practical. The idea has been going a lot longer than 1970, it was floated as soon as the Lake was discovered. Hope, 2004, did a thorough review and produced some detailed models. The paper is available online and is worth a read: www.cawcr.gov.au/staff/pxh/Hope2004.pdfSee Also: Badescu, V., Cathcart, R.B., Bolonkin, A.A., Paulescu, M. and Gravila, P. (2013) Macro-engineering Australia's Lake Eyre with imported seawater. International Journal of Environment and Sustainable Development 12: 264-284 |
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Jolly Green Giant Effin Wombat
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Post by Jolly Green Giant Effin Wombat on Mar 2, 2015 22:03:27 GMT 10
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Post by Ian Thomas on Mar 4, 2015 4:36:04 GMT 10
Emperor penguins went down to 3 colonies in the last ice age. If they'd all died we'd be talking about 'cyclical climate change' wiping out a megafauna penguin.
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Jolly Green Giant Effin Wombat
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Post by Jolly Green Giant Effin Wombat on Mar 4, 2015 12:36:32 GMT 10
Since we know almost nothing about the ecology or feeding behaviour of Diprotodontids it's impossible to say whether they would have been favoured or restricted by climate change in one direction or another.
Numerous examples can be drawn from the current AGW debate of species that have benefited from warming, indeed the research shows that plant growth has increased worldwide as a result of rising c dioxide levels.
For all we know Diprotodontids and related species may have increased in number as temperatures rose. The fossil record gives us earliest and latest dates for Megafauna species, but is much less reliable when it comes to estimates of their abundance.
That's why I'm always deeply suspicious of these left-lurking ideas that invading aborigines had no effect on their Terra Nullis. The fashionable urban myth of blacks living in harmony with their environment is peddled mainly by idealistic apologists for invading hordes who had no more sympathy for their new surroundings than did the Anglo Europeans thousands of years later.
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Post by Surroundx on Mar 5, 2015 0:04:00 GMT 10
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Post by Surroundx on Mar 5, 2015 23:19:26 GMT 10
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Post by Surroundx on Mar 9, 2015 0:18:26 GMT 10
A new paper entitled Late Pleistocene and Holocene mammal extinctions on continental Africa gives a good review of the extinctions from that continent, which are higher than one might expect given the abundance of large mammal taxa still present today: "It is now clear that the magnitude of large mammal extinctions on continental Africa over the last ~100,000 yrs is substantial. In terms of the number of extinct taxa that are securely dated to this time frame, the African extinctions exceed those in Europe and Asia (Grayson, 2007; Louys et al., 2007), match those from Australia (Wroe and Field, 2006; Field et al., 2008; Faith and O'Connell, 2011; Wroe et al., 2013), and are surpassed only by the losses in the Americas (Grayson, 1991, 2007; Cione et al., 2009; Faith and Surovell, 2009). Nevertheless, Africa remains the “fortunate anomaly” (Koch and Barnosky, 2006:221) in the sense that the majority of its large mammals survived the extinctions, in contrast to the situation in the Americas or Australia. The African extinctions can be broadly characterized as involving the loss of species that are grazers or prefer open habitats. Where good extinction chronologies and paleoenvironmental records are available, these losses are readily accounted for by environmental change. In the broader temporal context, these losses represent the more recent examples of a long-term environmentally-driven extinction process over the last million years. Taken together, there is little reason to believe that humans played a major role in African extinctions." Source: www.academia.edu/5176153/Late_Pleistocene_and_Holocene_mammal_extinctions_on_continental_Africa |
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Post by Ian Thomas on Mar 14, 2015 20:27:56 GMT 10
Good catch. Got an idea the humans-dunnit school reckon African mf did not die out because they had a long time to adapt to humans hunting them and knew their tricks. Whereas mf in North America went down like 9 pins when they met humans for the first time. Turns out African mf died off too, so where does that leave overkill?
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Post by johannes on Mar 16, 2015 23:17:53 GMT 10
This list includes animals that were undoubtly exterminated by humans - Quagga, Blue Antilope - and some Eurasian species - Stephanorhinus, deer, Auerochs - that only had a small foothold in some parts of the Maghreb. Otherwise, it mainly documents loss of diversity on the species level (and telling an Ass from a Zebra, or a Zebra from another Zebra, from one single bone or tooth is problematic, to say the least), but no loss of whole genera, or families; perhaps with the exception of Elephas and Syncerus*. This can't be compared with the loss of whole guilds of megaherbivores and the predators depending on them that can be found in Australia or the Americas.
*but remember that there are (feral?) Water Buffalos in Maroc, and Elephas could be found as far west as the Levant in historic times
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Post by johannes on Mar 17, 2015 21:55:12 GMT 10
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Post by Ian Thomas on Mar 19, 2015 10:02:00 GMT 10
This list includes animals that were undoubtly exterminated by humans - Quagga, Blue Antilope - and some Eurasian species - Stephanorhinus, deer, Auerochs - that only had a small foothold in some parts of the Maghreb. Otherwise, it mainly documents loss of diversity on the species level (and telling an Ass from a Zebra, or a Zebra from another Zebra, from one single bone or tooth is problematic, to say the least), but no loss of whole genera, or families; perhaps with the exception of Elephas and Syncerus*. This can't be compared with the loss of whole guilds of megaherbivores and the predators depending on them that can be found in Australia or the Americas.
*but remember that there are (feral?) Water Buffalos in Maroc, and Elephas could be found as far west as the Levant in historic times Sis bangs on about the north-south effect, The higher the latitude the more likely spp were to die out in the Pleistocene extinctions. The Americas have a narrow neck at Panama which leaves nowhere for big animals to go. But Africa and Sundaland had a big land area with good habitat, so more survivors. Downside with Sunda was it sunk underwater but there's still high biodiversity left over on the islands. |
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Post by johannes on Mar 24, 2015 21:18:02 GMT 10
Speaking of Pleistocene megafauna and land bridges, why did Elasmotheres never made it to America, and ground sloths to Eurasia? Did those monsters actively prevent each other's distribution?  |
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Post by Ian Thomas on Mar 31, 2015 6:16:31 GMT 10
Speaking of Pleistocene megafauna and land bridges, why did Elasmotheres never made it to America, and ground sloths to Eurasia? Did those monsters actively prevent each other's distribution? No idea but they all sound like pretty good questions.  |
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Post by Ian Thomas on Mar 31, 2015 6:18:22 GMT 10
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: 
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