Posts
That is the conclusion reached by Brian Huntley and colleagues of Durham University, UK, as reported by BBC (sorry but I cannot find a more direct reference at this time).
According to the British scientists, after running several models for the extinction of mammoth and other megafauna of the Ice Age, the model that is most plausible is that they went extinct because of loss of grasslands and not human hunters' pressure.
During the height of the ice age, mammoths and other large herbivores would have had more food to eat. But as we shifted into the post-glacial stage, trees gradually displaced those herbaceous ecosystems and that much reduced their grazing area.
Update (Aug 19):
Found the relevant paper:
Judy R. M. Allen et al., Last glacial vegetation of northern Eurasia. Quaternary Science Reviews, 2010. Pay per view.
There is also an alternative news article at Science Daily (typically a literal transcription from the press release) that uses maybe less absolute terms than the BBC one:
The change from productive grasslands across large areas of northern Eurasia, Alaska and Yukon to less productive tundra-like habitats had a huge effect on many species, particularly on the large herbivores like the woolly rhinoceros and woolly mammoth. Mammoths and other mega-mammals found it increasingly difficult to find food. We believe that the loss of food supplies from productive grasslands was the major contributing factor to the extinction of these mega-mammals.
25 comments:
Doesn't really make sense. mammoths had survived several earlier forest expansions. And elephants survive quite well in forested regions today. Seems the article is yet another attempt to show ancient humans were somehow more conservation-concious than we are today. I'd be very surprised to find Paleolithic humans were any less greedy or destructive than we are today, granted the improved methods of destruction we now possess.
Well, as I have not been able to find the paper (which anyhow is probably behind paywall) I cannot argue easily in favor or against the paper. The article however seems to state that they are very sure of their conclusions after comparing models.
I do not know if ancient humans were more conservation-conscious but certainly most modern hunter-gatherers have some sort of that consciousness (they do not go on rampage, they experience the kill emotionally and sometimes religiously and they are much more aware in general of Nature, in which they feel immersed and not alienated as we do).
What really matters is if ancient humans were able to cause such destruction, which I doubt. You may also notice that temperate and boreal forests are not as productive as tropical ones, not by far, and that mammoths fed much like reindeer anyhow and belonged totally to the open plains.
However there may be convergent pressures.
Check the update anyhow.
Thanks for the link. I'm still unconvinced. From the Science Daily link:
"Woolly mammoths retreated to northern Siberia 14,000 years ago whereas they had roamed and munched their way across many parts of Europe, including the UK, for most of the previous 100,000 years or more".
So is he claiming that over that 100,000 years climate had remained constant? Besides which I'm fairly sure the woolly mammoth is older than just 100,000 years. But further on we reach the main message:
"This new evidence of massive habitat change linked to climatic change is, according to experts, a parable for modern times ... This is a model for what may happen as a result of rapid climate change over the next century linked to human activity. It is food for thought in these times of global warming and human-induced habitat change. There may well be a lesson to learn."
And this bit is very interesting:
"Five species formerly present in Europe, northern Asia, Alaska and Yukon that became globally extinct as grassland diminished:
Woolly mammoth
Cave lion
Giant deer
Woolly rhino
Cave bear
Five species that survived as grassland diminished:
Brown bear
Elk (moose)
Reindeer
Saiga antelope
Musk ox"
So there seems to have been no shortage of grassland for the musk ox and the saiga.
"So is he claiming that over that 100,000 years climate had remained constant?"
Constantly colder than present it was (ref.). The Ice Age had irregularities but was all the time between 4 and 8 degrees colder than today and that meant that at no time forests expanded before the Epipaleolithic period.
This is critical to understand, I believe.
"So there seems to have been no shortage of grassland for the musk ox and the saiga".
Not sure what you mean. Obviously the needs of mammoths and woolly rhinos were different from those of ruminants. Similarly in Africa today elephants and rhinoceros face today much more intense threats than gazelles, gnus or buffaloes. Each species have their own characteristics. It is noticeable that in general the extinct species were unusually large animals, which need greater caloric input per individual.
Other grassland animals that survived were obviously horse, wolf and even such large beasts as bison and auroch. But you do notice in the archaeological record in many regions that, as forest expanded, large game practically disappeared being replaced by forest game such as deer or boar. Some of the survivors anyhow are at risk (saiga, bison, brown bear, wolf) while the auroch went extinct in Roman or early Medieval times. But that's really a post-Neolithic development.
"Obviously the needs of mammoths and woolly rhinos were different from those of ruminants".
Quite. Elephants and rhinos tend to be browsers rather than being obligate grazers. So open grassland would hardly be their favoured habitat in the first place.
"But you do notice in the archaeological record in many regions that, as forest expanded, large game practically disappeared being replaced by forest game such as deer or boar".
And it's obviously very easy to come to the wrong conclusion from that correlation. Surely the expansion of forest was a consequence of the elimination of browsers rather than the expansion of forest CAUSING the extinction of browsers. A connection the authors obviously failed to take into consideration.
"Similarly in Africa today elephants and rhinoceros face today much more intense threats than gazelles, gnus or buffaloes".
Mainly because of habitat destruction through clearing of forest for farming and firewood (as well as poaching of course).
"The Ice Age had irregularities but was all the time between 4 and 8 degrees colder than today and that meant that at no time forests expanded before the Epipaleolithic period".
And forest expansion at that time is probably as much to do with the absence of megafauna as being the cause of their extinction. I have certainly often read that the Sub-Arctic environment before the Epipaleolithic is usually classified as being 'mosaic vegetation', a variety of habitats within each region, rather than being the monocultures we see today in Northern Eurasia and North America.
"Surely the expansion of forest was a consequence of the elimination of browsers rather than the expansion of forest CAUSING the extinction of browsers".
I don't think this claim can stand. While this might be the case if warming did not happen, warming alone fully justifies the expansion of forests, which were "waiting for their opportunity" in what is now the Mediterranean basin in the case of Europe. In turn the Mediterranean basin lost forest cover.
This process had happened before, in each glacial cycle as far as I know. However it is possible that, in this case, human hunter pressure was the straw that broke the mammoth's back.
"Mainly because of habitat destruction through clearing of forest for farming and firewood".
No. Elephants and rhinos in Africa are mostly savanna dwellers (there are some species/subspecies in jungle but these are not the main focus). The difference is in their naturally occurring numbers (rhinos) and their dramatically huge needs (elephant). Gnus can do with much less and feed much larger numbers in a smaller territory. Gnus are not and will probably be not at risk. Same for mainstream species of zebras, gazelles and buffaloes. They can just sustain large numbers in relatively small areas. Elephants need much more and that is an objective problem in conservation efforts.
"I have certainly often read that the Sub-Arctic environment before the Epipaleolithic is usually classified as being 'mosaic vegetation', a variety of habitats within each region, rather than being the monocultures we see today in Northern Eurasia and North America".
I have no idea of what you mean. 'Subartic' is a vague term, as is 'mosaic vegetation' without a context. If by this you mean that some forested patches existed in Moravia even in the LGM, you might want to recall that Moravia is rugged terrain and not the usual flatlands. If you are thinking of the Franco-Cantabrian region, again that's not your typical subartic area but a peculiar Oceanic one. Mostly the European flatlands south of the ice sheet's edge, were, as one may expect successive belts of taiga, tundra and cold steppe. This last environment was the one that favored human habitation somewhat.
"I don't think this claim can stand".
But I'm obviously not the only one to suggest that. Here's someone who agrees with me, although another disagrees later in the article (but his arguments don't stack up for me):
http://www.gi.alaska.edu/ScienceForum/ASF20/2020.html
"This process had happened before, in each glacial cycle as far as I know".
And didn't affect the mammoths' survival. So, as you say, 'human hunter pressure was the straw that broke the mammoth's back'.
"Elephants and rhinos in Africa are mostly savanna dwellers (there are some species/subspecies in jungle but these are not the main focus)".
Maju, even those 'savanna dwellers' are browsers, not grazers, although so-called 'white' rhinos tend to graze more than do black rhinos. They don't live in open grassland. They prefer 'mosaic vegetation'.
"Mostly the European flatlands south of the ice sheet's edge, were, as one may expect successive belts of taiga, tundra and cold steppe".
Not so when megafauna were present, evidently. Here is a link to enlighten you:
http://rspb.royalsocietypublishing.org/content/276/1667/2509.full
From the article:
"In several parts of the world, palaeoecological studies suggest that extinct megafauna once maintained vegetation openness, and in wooded landscapes created mosaics of different structural types of vegetation with high habitat and species diversity. Following megafaunal extinction, these habitats reverted to more dense and uniform formations".
Some other comments from the article:
"African elephants (Loxodonta africana) maintain open conditions in savannah by suppressing woody regeneration (Dublin et al. 1990), and create grassy openings in forests and thickets (Owen-Smith 1999; R. M. Cowling 2009, personal communication)"
"Vera (2000) argued that large herbivores in lowland temperate Europe once maintained shifting mosaics of grassland, thicket and tall forest. Herbivory converted stands of tall forest into open parkland or grassland by suppressing woody regeneration; these open areas would be invaded by thickets of thorny scrub resistant to browsing, which, in turn, provided patchy refuges where seedlings of palatable trees could re-establish; emergent trees then shaded out understorey scrubs and grew into forest stands destined to repeat the cycle".
"Without large herbivores, these mosaics reverted to uniform closed forest with lower species diversity".
The article then goes on to look at several separate regions.
A better link for that last article (pdf):
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684593/pdf/rspb20081921.pdf
Thanks for the links, Terry. They are indeed interesting and enrich the debate with different viewpoints and data.
Sincerely, I find difficult to believe that human foragers caused mass extinctions alone but may have been a contributing factor along others.
I just can't believe that it was the extinction what caused climate change, because we can easily see that the Ice Age cycles are very much regular since long before humankind and regardless of extinctions, with an approximate period of some 100,000 years.
Warming happened alone (for whatever reasons behind the glacial cycle, not well understood afaik but possibly astronomical or related to the North Atlantic Conveyor's dynamics) and this drove forests northwards in the "temperate zone", what created a major pressure against grassland herbivores.
Mammoths, as far as we know, were grass eaters, unlike their less specialized tropical cousins. The same was surely true of the woolly rhinoceros.. but also of so many smaller species that did survive. It's not probable that the steppe landscape is created by herbivores but by climatic conditions, otherwise extinction and reduction of habitat would have caused forestation in modern steppes and that is not the case.
But I can accept that human pressure was a co-factor, the extra load that inclined the scales against some species already weakened by naturally occurring, cyclical, global warming.
It's worth reminding here that mammoths are known to have got very low genetic diversity, surely a signature of past bottlenecks, maybe in other warm periods that they did survive but not without difficulties.
"It's not probable that the steppe landscape is created by herbivores but by climatic conditions, otherwise extinction and reduction of habitat would have caused forestation in modern steppes and that is not the case".
Low rainfall can prevent forest from forming and so allow grassland to develop. Intermittent fire is also an effective preventer of forest formation. So the whole environmental conditions have changed with the extinction of megafauna and the presence of humans.
"Warming happened alone (for whatever reasons behind the glacial cycle, not well understood afaik but possibly astronomical or related to the North Atlantic Conveyor's dynamics) and this drove forests northwards in the 'temperate zone', what created a major pressure against grassland herbivores".
We have to remember that the environmental conditions were probably much different in the Pleistocene than they are at present. And I don't just mean in the simple shift in climate zones. If it was simply a matter of warming or cooling climate zones would simply change latitude and altitude. It's not as simple as that. You will probably find this link interesting too;
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-41XM80M-F&_user=10&_coverDate=01%2F31%2F2001&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1437277094&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1956411c28183cd85b2ba79a4127bae3
I can read it only with difficulty (it's too small) but presumably the authors' claim is for greater latitudinal distribution of species than at present.
"Mammoths, as far as we know, were grass eaters, unlike their less specialized tropical cousins".
I find that difficult to accept because modern elephants are hardly 'specialized' in their diet. And I assume the same was true of mammoths. Certainly a trunk is not a very efficient tool for collecting grass, even if that trunk belongs to a mammoth.
"I just can't believe that it was the extinction what caused climate change, because we can easily see that the Ice Age cycles are very much regular since long before humankind and regardless of extinctions, with an approximate period of some 100,000 years".
I agree that 'Ice Age cycles are very much regular since long before humankind' but what is so different about the Pleistocene/Holocene warming is that it caused so many extinctions, but previous ones didn't, certainly not on the same scale. Besides which the extinctions don't everywhere coincide with worldwide climate change, merely local change. Leaving open the strong possibility that the connection does indeed run 'the extinction what caused climate change'.
"If it was simply a matter of warming or cooling climate zones would simply change latitude and altitude".
That's what they essentially do. However warming/cooling also bring changes in humidity which are more irregular (but in general warmer tends to mean more humid and colder means dryer - because less water evaporates overall).
"You will probably find this link interesting too"...
Not really: it's a mere abstract (pay per view article) with a very technical text.
Also you could link it using the uch shorter DOI reference (right click on the DOI link above the abstract and select 'copy link location', then paste): http://dx.doi.org/10.1016/S0277-3791(00)00125-6
Or, even better, you can embed a link in text using HTML as follows:
[a href=LINK ]TEXT[/a]
but replace the [] with <>.
"I can read it only with difficulty (it's too small)"...
If you mean letter type, you can surely zoom in with your browser (in Firefox it is in View>Zoom, allowing also for only changing text size while keeping page size).
"... presumably the authors' claim is for greater latitudinal distribution of species than at present".
I do not understand that, even if it would make sense because most of the time it's been colder and interglacial climate is therefore a relatively brief cyclical anomaly that would cause southern vegetation to spread northwards for the interlude.
What they seem to talk about anyhow is about local variations in the context of Beringia.
"I find that difficult to accept because modern elephants are hardly 'specialized' in their diet".
Mammoths are not "modern elephants". Their head was specialized for herbaceous feeding by means of "verticalization".
"Certainly a trunk is not a very efficient tool for collecting grass"...
Hands are not the most efficient tool for collecting grass, one could argue as well (trunk and hands are functionally similar) but still there are monkeys specialized in eating grass and nothing else in the Ethiopian highlands.
"I agree that 'Ice Age cycles are very much regular since long before humankind'"...
Cool. Guess that then we can agree that this last interglacial we live in was not or mostly not caused by human activities.
"... but what is so different about the Pleistocene/Holocene warming is that it caused so many extinctions, but previous ones didn't, certainly not on the same scale".
It is possible but I'd like to read a comparative research. In any case, we would be talking about an extra human factor favoring extinctions along naturally-occurring climate change, but never of a human-made climate change.
"Mammoths are not 'modern elephants'".
No. But near enough to being so. They're more closely related to Asian elephants than to African elephants. The several mammoth species were basically simply varieties of Indian elephant.
"most of the time it's been colder and interglacial climate is therefore a relatively brief cyclical anomaly that would cause southern vegetation to spread northwards for the interlude".
It's not as simple as that. All paleobotanists' research on the period I have read stress the presence of combinations of plants not present together today. At the time warm and cold-loving plants often grew together. Presumably small patches of trees provided micro-climates where species requiring warmer conditions could survive. And the evidence has been known and widely accepted for years. Way back in 1989 Neil Roberts claims as much in his book 'The Holocene'. A short review:
http://www.amazon.com/Holocene-Environmental-History-Neil-Roberts/dp/0631186387
And Cox and Moore in 1985 claimed the same:
http://www.amazon.com/Biogeography-Ecological-Evolutionary-Barry-Cox/dp/1405118989
Unfortunately in neither case do reviwers refer to the relevant sections. You'll have to read the books yourself. Anyway the link I posted says much the same thing.
"In any case, we would be talking about an extra human factor favoring extinctions along naturally-occurring climate change"
Possibly, but maybe not. Many people seem desperate to exclude humans as a cause of megafauna extinctions, for some reason or other. But in fact their presence is the only thing different about the climate warming of 10-15,000 years ago.
"Guess that then we can agree that this last interglacial we live in was not or mostly not caused by human activities".
Probably we can agree. But it is also possible that the vegetation change led to the warming.
But back to the original post:
"But as we shifted into the post-glacial stage, trees gradually displaced those herbaceous ecosystems and that much reduced their grazing area".
It seems quite likely from all paleobotanists research on the vegetation distribution before that change that the spread of trees was not the 'cause' of the megafauna extinction, but the 'consequence' of it.
From the link I posted several days ago:
"In several parts of the world, palaeoecological studies suggest that extinct megafauna once maintained vegetation openness, and in wooded landscapes created mosaics of different structural types of vegetation with high habitat and species diversity".
"Such extinctions might have triggered the following three general types of change to vegetation. Loss of open vegetation and habitat mosaics. Vegetation that had been kept open by herbivory should have been replaced by dense or closed formations, and mosaics that had been maintained by herbivore pressure should have given way to uniform or zonal vegetation patterns".
"Vera (2000) argued that large herbivores in lowland temperate Europe once maintained shifting mosaics of grassland, thicket and tall forest".
"High densities of large herbivores on flood plains at the Last Interglacial are evidenced by pollen of herb species characteristic of disturbed ground, and a high abundance and diversity of dung beetles".
"Miller et al. (2005) found evidence of a major reorganization of vegetation coincident with megafauna extinction across the semi-arid southern mainland of Australia. Stable isotope analysis showed that before 50 ka, emus and wombats had broad diets consisting of a mixture of C4 (subtropical and arid grasses) and C3 plants (shrubs, trees and temperate grasses), with a wide range of values among individual samples suggesting heterogeneous foraging environments. By 45 kyr, their diets had contracted to C3 plants only. Miller et al. (2005) argued that this reflected a habitat change from a mosaic of trees, shrubs and grassland to a more uniform shrub steppe. Climate cannot account for this change".
"The wide range of body sizes, morphologies (including two arboreal kangaroos) and feeding modes in this assemblage indicates a more diverse vegetation than now, probably a mosaic of woodland, shrubland and grassland, with a high proportion of plants with palatable leaves and fleshy fruits. The present-day vegetation is a uniform chenopod shrub steppe (in which the existence of tree kangaroos is unimaginable). The climate experienced by the Middle Pleistocene community was evidently similarly arid to today, so climate change cannot explain the gross simplification of the ecosystem (Prideaux et al. 2007)".
"During most of the Pleistocene, the unglaciated expanses of northern Eurasia and North America were covered by a vast, low steppe of grasses, forbs and sedges (Zimov et al. 1995; Goetcheus & Birks 2001; Guthrie 2001; Yurtsev 2001; van Geel et al. 2007). This ‘mammoth steppe’ was dry but botanically diverse, and it supported a high biomass of woolly mammoths, bison, horses and other large herbivores. From ca 13 ka, it was replaced by waterlogged habitats of wet mossy tundra, shrub tundra and taiga or deciduous forest, with reduced plant diversity (Guthrie 2001; Kienast et al. 2001; Willerslev et al. 2003, 2008; Edwards et al. 2005)".
"Kienast et al. (2008) used plant macrofossils to reconstruct in detail plant communities from the Last Interglacial at a site in northeast Siberia. They found a species-rich mosaic of dry steppe vegetation (composed of forbs, sedges and grasses) interspersed with patches of shrub tundra and thickets, arctic herbfields, wetlands and pioneer communities composed of species typical of dry, disturbed sites. A high abundance in the ancient community of grazing-tolerant plants, as well as spores of dung fungi, indicates a strong impact of large herbivores".
And so on. Perhaps you might like to read the link again.
From the link I posted several days ago:
"In several parts of the world, palaeoecological studies suggest that extinct megafauna once maintained vegetation openness, and in wooded landscapes created mosaics of different structural types of vegetation with high habitat and species diversity".
"Such extinctions might have triggered the following three general types of change to vegetation. Loss of open vegetation and habitat mosaics. Vegetation that had been kept open by herbivory should have been replaced by dense or closed formations, and mosaics that had been maintained by herbivore pressure should have given way to uniform or zonal vegetation patterns".
"Vera (2000) argued that large herbivores in lowland temperate Europe once maintained shifting mosaics of grassland, thicket and tall forest".
"High densities of large herbivores on flood plains at the Last Interglacial are evidenced by pollen of herb species characteristic of disturbed ground, and a high abundance and diversity of dung beetles".
"Miller et al. (2005) found evidence of a major reorganization of vegetation coincident with megafauna extinction across the semi-arid southern mainland of Australia. Stable isotope analysis showed that before 50 ka, emus and wombats had broad diets consisting of a mixture of C4 (subtropical and arid grasses) and C3 plants (shrubs, trees and temperate grasses), with a wide range of values among individual samples suggesting heterogeneous foraging environments. By 45 kyr, their diets had contracted to C3 plants only. Miller et al. (2005) argued that this reflected a habitat change from a mosaic of trees, shrubs and grassland to a more uniform shrub steppe. Climate cannot account for this change".
"The wide range of body sizes, morphologies (including two arboreal kangaroos) and feeding modes in this assemblage indicates a more diverse vegetation than now, probably a mosaic of woodland, shrubland and grassland, with a high proportion of plants with palatable leaves and fleshy fruits. The present-day vegetation is a uniform chenopod shrub steppe (in which the existence of tree kangaroos is unimaginable). The climate experienced by the Middle Pleistocene community was evidently similarly arid to today, so climate change cannot explain the gross simplification of the ecosystem (Prideaux et al. 2007)".
"During most of the Pleistocene, the unglaciated expanses of northern Eurasia and North America were covered by a vast, low steppe of grasses, forbs and sedges (Zimov et al. 1995; Goetcheus & Birks 2001; Guthrie 2001; Yurtsev 2001; van Geel et al. 2007). This ‘mammoth steppe’ was dry but botanically diverse, and it supported a high biomass of woolly mammoths, bison, horses and other large herbivores. From ca 13 ka, it was replaced by waterlogged habitats of wet mossy tundra, shrub tundra and taiga or deciduous forest, with reduced plant diversity (Guthrie 2001; Kienast et al. 2001; Willerslev et al. 2003, 2008; Edwards et al. 2005)".
"Kienast et al. (2008) used plant macrofossils to reconstruct in detail plant communities from the Last Interglacial at a site in northeast Siberia. They found a species-rich mosaic of dry steppe vegetation (composed of forbs, sedges and grasses) interspersed with patches of shrub tundra and thickets, arctic herbfields, wetlands and pioneer communities composed of species typical of dry, disturbed sites. A high abundance in the ancient community of grazing-tolerant plants, as well as spores of dung fungi, indicates a strong impact of large herbivores".
And so on. Perhaps you might like to read the link again.
If it's a species that diverged, as it did, several Ice Ages ago, maybe 4 million years ago, then mammoths were not "simply varieties of Indian elephant".
[Paleobotanists]"stress the presence of combinations of plants not present together today".
Maybe but are we going to go crazy about that?
"Many people seem desperate to exclude humans as a cause of megafauna extinctions"...
And some people seem anxious about defining each extinction as being caused by humans and nothing else. You are that kind and I know that.
"But it is also possible that the vegetation change led to the warming".
No. Warming happened regularly per the 'Ice Age clock' it has some other reason. Why do you even insist? I know why: because you want to believe that. But don't bother: it's not the way you wish.
"... the spread of trees was not the 'cause' of the megafauna extinction, but the 'consequence' of it".
Again not, because it had happened before.
"If it's a species that diverged, as it did, several Ice Ages ago, maybe 4 million years ago, then mammoths were not 'simply varieties of Indian elephant'".
How about 'basically varities of Indian elephant' then?
http://www.google.co.nz/imgres?imgurl=http://www.sanparks.org/parks/kruger/elephants/images/elephant-evolution.jpg&imgrefurl=http://www.sanparks.org/parks/kruger/elephants/about/evolution.php&h=317&w=500&sz=36&tbnid=N5u3cPLXiEb7eM:&tbnh=82&tbnw=130&prev=/images%3Fq%3Delephant%2Bevolution&zoom=1&hl=en&usg=__-qT5lblFa1rH_P3rgpBUL3f7Hro=&sa=X&ei=MYpzTNXNL4LmsQOkouzKCA&ved=0CCMQ9QEwAA
Note that African elephants separated from Indian elephants some time before mammoths separated from Indian elephants. So we basically have two sorts of elephant: African and Asian.
"Maybe but are we going to go crazy about that?"
Yes. Because it tells us the Pleistocene mammoth-steppe was far more productive and varied than are environments at such latitudes are today. And warm-loving plants survived well to the north of where they survive today, even though the climate is much warmer today. The ecology was different.
"And some people seem anxious about defining each extinction as being caused by humans and nothing else. You are that kind and I know that".
I'm certainly not claiming humans wiped out the dinosaurs. However don't you find it rather amazing that megafauna died out in various regions of the world at almost exactly the same time as humans arrived in those regions? There has to be some sort of cause and effect surely? Or is it just complete coincidence?
"Warming happened regularly per the 'Ice Age clock' it has some other reason".
Quite possibly. But only once did it wipe out megafauna, and sometimes megafauna died out without any corresponding warming. So we're back to the claim of the post: that expansion of forest led to megafauna extinction. Definitely not the case. Megafauna extinction led to the expansion of forest, independent of climate warming.
"Again not, because it had happened before".
You complain about me not providing links, but why shopuld I bother? You don't read them. The link definitely said that in places the vegetation definitely changed before the warming. Go back and read again. I'm sick of having to extract the relevant points from the link.
So we're left with the same old problem: what killed the megafauna? Not the expansion of forest.
"However don't you find it rather amazing that megafauna died out in various regions of the world at almost exactly the same time as humans arrived in those regions?"
I do not find that claim proven. Large herbivores certainly survived in Europe after the arrival of humans in general and of H. sapiens in particular. They also did in Siberia, for instance, and in India and SE Asia, and probably many other places.
"The link definitely said that in places the vegetation definitely changed before the warming".
The abstract? I don't think so. Maybe you have access to the full paper?
"I'm sick of having to extract the relevant points from the link".
It's a courtesy practice and also a way to make sure others understand exactly your point. It's not like you can get sick by mere copy-pasting the relevant sentences, right?
"I do not find that claim proven. Large herbivores certainly survived in Europe after the arrival of humans in general and of H. sapiens in particular. They also did in Siberia, for instance, and in India and SE Asia, and probably many other places".
But megafauna survived only for a short period.
"The abstract? I don't think so. Maybe you have access to the full paper?"
I linked to the full paper, but you are obviously uncomfortable with the conclusions so you didn't read it. You believe in some 'Noble Savage' myth. Here's the link again:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684593/pdf/rspb20081921.pdf
"It's not like you can get sick by mere copy-pasting the relevant sentences, right?"
Actually I do get sick of it. I don't really have much spare time. But I'll look again for the relevant bit.
Finally I'd like to point out some inconsistencies. Earlier on, when it suited your position, you claimed mammoths were only about 100,000 years old:
"Woolly mammoths retreated to northern Siberia 14,000 years ago whereas they had roamed and munched their way across many parts of Europe, including the UK, for most of the previous 100,000 years or more".
Thsi date suited your position that mammoths had not lived through any significant climate change. But now you're claiming:
"If it's a species that diverged, as it did, several Ice Ages ago, maybe 4 million years ago, then mammoths were not 'simply varieties of Indian elephant'".
Are you now claiming that over that whole perion the climate was, 'Constantly colder than present it was (ref.). The Ice Age had irregularities but was all the time between 4 and 8 degrees colder than today and that meant that at no time forests expanded before the Epipaleolithic period'. We also come up a gainst another problem for forest being the cause of the mammoths' downfall. Several subspecies lived way south of the Boreal zone until they too dissappeared about the time humans arrived.
"Well-resolved vegetation histories might also reveal an abrupt change in steppe/tundra vegetation immediately following mega herbivore extinction. Distinguishing this against the background of climate instability of this time is difficult, but Hu et al.'s (2002) detailed vegetation history from Nimgun Lake in southwestern Alaska may be a case where this is possible. This record shows evidence of warming effects on arctic vegetation from 15 ka to 13 ka, but with an especially sharp transition at 13.6 ka consisting of a sudden rise in birch Betula and decline of sedges, along with other indicators of increased moisture and vegetation cover. Hu et al. (2002) interpreted this change as being due to a sharp increase in temperature that is recorded in the oxygen isotope record from the Greenland ice sheet, but that took place 1000 years earlier. The change coincides more closely with mammoth extinction at 13.6 kyr (ago) (Guthrie 2006; Solow et al. 2006). Perhaps the effects of climate warming on vegetation were initially damped by mammoths and other large herbivores, and were only fully realized with their extinction (Hu et al. suggested that the main effect of the temperature increase on local climate and vegetation was via raised sea level, which lagged temperature)".
And let's remember the Wrangel Island mammoths. They survived until around 4000 years ago, when they became extinct. Did expanding forest deal to them too?
"But megafauna survived only for a short period".
Figure 2 (Johnson's paper): people arrived everywhere but America and caused no noticeable extinctions. All extinctions are concentrated in the interglacial periods and not just the last one but also the previous one, when human interference must have been minimal.
The only period open to discussion would be the one between 20 and 12 Ka ago. This one is not coincident with human expansions (except in America) but may have been one of increased technological effectiveness maybe.
"I linked to the full paper, but you are obviously uncomfortable with the conclusions so you didn't read it".
I meant the paper on the floral changes.
"You believe in some 'Noble Savage' myth".
IDK, I think that people are sensible and intelligent animals, who, in hunter-gatherer conditions, can only cause that much impact normally and tend to attain certain balance with their environment, just as we see in all the groups that have survived till recently in such conditions. I also think that they were too lazy and scattered to cause those extinctions you claim but that Johnson's data clearly rejects.
"Earlier on, when it suited your position, you claimed mammoths were only about 100,000 years old:
"Woolly mammoths retreated to northern Siberia 14,000 years ago whereas they had roamed and munched their way across many parts of Europe, including the UK, for most of the previous 100,000 years or more"."
That writing style does not look like mine. It must be a quote or whatever. I would not use the word "whereas" for instance and it's unlikely that I wrote "roamed" either nor that I would emphasize their presence in Britain using the political acronym "UK" in a prehistory context.
"Are you now claiming that over that whole perion the climate was, 'Constantly colder than present it was (ref.). The Ice Age had irregularities but was all the time between 4 and 8 degrees colder than today and that meant that at no time forests expanded before the Epipaleolithic period'".
I stand by that sentence I wrote before, yes. Why?
Is it because of the interglacial periods? They separate one Ice Age from another one, just for the record.
"We also come up a gainst another problem for forest being the cause of the mammoths' downfall. Several subspecies lived way south of the Boreal zone until they too dissappeared about the time humans arrived".
Uh? I don't understand what you mean, sorry.
You insist in species disappearing when humans arrive but that is against what your own link (Johnson) states.
...
"This record shows evidence of warming effects on arctic vegetation from 15 ka to 13 ka, but with an especially sharp transition at 13.6 ka consisting of a sudden rise in birch Betula and decline of sedges, along with other indicators of increased moisture and vegetation cover".
It's possible it means some sudden transition from commonality to extinction of some key animal. But please notice the radical change in that animal's densities it must have happened in few centuries for it to have an impact. Because it's not mere extinction what matters but also loss of numbers and therefore of efficiency of the species in whatever they do in the ecology. If a species' numbers are cut by half it may have as much impact as extinction of the remaining half.
On the other side, this relatively sudden changes are registered elsewhere and are generally understood as being part of the global warming process at the end of the Ice Age, which certainly included global sudden changes, specially a very radical and definitory warming spike at that time more or less.
"The change coincides more closely with mammoth extinction at 13.6 kyr (ago)".
Probably was a decisive factor in mammoth extinction, no doubt.
"And let's remember the Wrangel Island mammoths. They survived until around 4000 years ago, when they became extinct. Did expanding forest deal to them too?"
No. Maybe it was inbreeding or overpopulation in a too small space? I really can't tell but I'm pretty sure that they do not have the mobility of polar bears in arctic waters.
"Figure 2 (Johnson's paper): people arrived everywhere but America and caused no noticeable extinctions".
Not true. Australia for a start but I'll come back to the subject in my next post later.
"All extinctions are concentrated in the interglacial periods and not just the last one but also the previous one"
What extinction are you talking about there.
"Uh? I don't understand what you mean, sorry".
Again, I'll come back to that soon.
"It's possible it means some sudden transition from commonality to extinction of some key animal. But please notice the radical change in that animal's densities it must have happened in few centuries for it to have an impact".
And what on earth might have caused that extinction, or reduction in numbers?
"Maybe it was inbreeding or overpopulation in a too small space?"
And 'maybe' it was the arrival of humans?
"On the other side, this relatively sudden changes are registered elsewhere and are generally understood as being part of the global warming process at the end of the Ice Age"
OK. Let's concede for now that it is actually possible for anyone to convince themselves that climate change alone wiped out the mammoths. But, as Julien said on his blog, 'The key thing about reconstructing processes in prehistory is to develop scenarios that make sense of all the available lines of evidence without giving one ... undue primacy'.
So, even with the concession above climate warming could only be responsible for the demise of the woolly mammoth.
""Uh? I don't understand what you mean, sorry".
Further south, in both North America and Eurasia, other mammoth species existed that almost certainly had already become adapted to warmer climates. So why didn't these mammoths simply move north as the woolly mammoths retreated?
In North America possibly three species were available for such a northward movement (although the three may actually have been a single species).
http://en.wikipedia.org/wiki/Columbian_Mammoth
and:
http://en.wikipedia.org/wiki/Imperial_mammoth
From the second link:
" M. imperator ranged from Canada to New Mexico about 4.6 million - 17,000 years ago (Late Pleistocene)".
And the range of the two overlapped. Surely, even in an ice age, Mexico implies a fairly warm climate. So why could they not simply move north? The amswer? They became extinct about the same time as did the woolly mammoth. Did expanding forest (caused solely by warming climate remember) deal to them too?
Besides which pygmy mammoths had made it to islands off the California coast:
http://en.wikipedia.org/wiki/Pygmy_Mammoth
From the link:
"The late Pleistocene elephant may have lived on the islands until the arrival of the Chumash people during the early Holocene, between 10,800 and 11,300 years ago".
Coincidence, is it?
In Eurasia two mammoth species had survived until at least the late Pleistocene: the Songhua River mammoth in the east (Mongolia, Japan and North China) and the steppe mammoth in Central Asia.
http://en.wikipedia.org/wiki/Mammuthus_sungari
So why was this species not able to exploit the warming climate? No exact date is given for the extinction but I'm sure the date would tell us pretty much when the modern human population reached saturation point through the region.
http://en.wikipedia.org/wiki/Steppe_mammoth
Again, no accurate date for its extinction, but it certainly happened before the woolly mammoth's extinction. This, of course, is exactly what we would expect if, as humans moved progressively north, they had been responsible for the extinction. Even Neanderthals seem to have hunted mammoths in regions near the Caucasus Mountains. I've jotted down in my notes (from somewhere) that mammoth remains are common in Middle Paleolithic sites in the Northern Caucasus and Crimea (35,000 years ago) but such remains are not present in sites dated more recent than 30,000 years. Mammoths were extince in the region by then.
So were the mammoths hunted there steppe mammoth or woolly mammoth? Again my guess is that the steppe mammoth's extinction will date the Late Paleolithic progressive increase in the human population through Central Asia.
Post a Comment