It’s not arbitrary, it’s based on objective standards…
I wouldn’t say plenty. Certainly proportionally far fewer than in Africa.
There have been analyses done on this, and yeah, Africa fared far, far better than elsewhere in the world.
For example, Africa lost just 18% of its megafauna during the pleistocene prior to ~1000AD, compared with 36% for Eurasia and the astounding 88% in Australia, 83% for South America 72% in North America. (Barnosky (2004) “Assessing the Causes of Late Pleistocene Extinctions on the Continents” Science 306.) When we consider just the herbivores over one tonne in weight it’s even more stark, with the Americas, Europe and Australia losing 100% of their species, Asia losing >90% and Africa losing just 60%.
Those are some pretty stark differences in extinctions and highlight that Africa really is very different.
Let me get this straight. Your contention is that Africa supported, say, 1 megafuanal organism/ha, and North America only 1 per 5 ha? And that humans killed megafauna at a rate of 1 individual/ha, and as a result the animals in Africa survived and those in America were exterminated?
Is that your contention?
Well, yes, but as noted earlier, this totally fails to explain why the extinctions are spread over 40, 00 years and yet always coincide with human arrival.
What is this factor that is limiting capacity? Certainly it can’t be based upon primary productivity or utilisable feed density or soil nutrient levels or rainfall anything like that, because there is no such factor that would predict that the carrying capacity of the Pacific Northwest is *lower *than that of the Kalahari desert.
So since this is your theory, can you tell us what you think this mysterious limiting factor in the Pacific Northwest is? Can you then provide references that confirm its existence? And can you then explain how this factor limits densities of megafauna without also limiting human densities? As Colibri alluded to, Australia certainly has factors that will limit megafaunal densities, but those same factors also limited human densities. So how does your Factor X manage to limit megafaunal densities while allowing the support of high densities of humans?
From an ecological POV, none of this makes a great deal of sense.
It’s obvious that Africa is different, but there are obvious differences in the environment. Africa has the largest swath of equatorial land. It wasn’t as affected by the Ice Ages as the northern lands. All of the continents didn’t start out the same, and didn’t go through the same changes in conditions. So I don’t argue that Africa isn’t different, but that humans aren’t necessarily a major factor.
Then can you answer my questions in order to explain to me why you believe humans weren’t the major factor?
This is an issue that has been studied for many years by many notable ecologists. The consensus is that humans played a major role. What novel information do you have that leads yo to reject that?
Maybe so (I haven’t tried to tally it up) but it’s not by much. The Americas taken together have huge areas in the tropics, ranging over a wide range of habitats from desert to grassland to tropical rainforest. The difference isn’t enough to account for the huge difference in extinction rates.
Neither was South America or Australia, and their extinction rates were even greater than the northern continents.
Of course not. But the continents in which megafaunal extinctions were severe don’t differ in any consistent way from Africa, except in their history of human presence.
You haven’t made any substantive argument to support that supposition.
As a followup, I’ve done a considerable review of the scientific literature on the subject. While alternative explanations have been advanced for local megafaunal extinctions on particular continents, such as climate change, disease, an asteroid impact, and so forth, I am unaware of any analysis of the overall global patterns that can explain why the extinction was less in Africa based on any factor other than the differential impact of humans.
Just compare the lists of genera that became extinct in North America to the genera that became extinct in Asia and Africa.
The ecological diversity of large mammals in North America was astounding. I mean, really astounding. And note the interesting thing about the surviving North American megafauna–out of moose, elk, deer, bison, caribou, muskox, sheep, mountain goat and pronghorn, only the pronghorn wasn’t a relatively recent Asian immigrant.
You know, the descriptions of the gigantic herds of buffalo that stretched from horizon to horizon remind me of the Lystrosaur herds that dominated the globe after the Permian extinction. As one of the sole survivors of the mass extinction, bison populations exploded.
Actaully, not so much. In each areas, different species and amount of species went extinct, and over different timelines in each. It’s pretty obvious that man killed off the “megafauna” in NZ for example- and did it pretty damn fast. But that megafauna was flightless birds which had slid into Island gigantism. Island gigantism is fairly unstable to start with.
Now, let us take Australia. Not that many types were wiped out, basiclt just the diprotodontoids (you might call them “giant wombats”). There are several compting theories there:
*Climate change:
Australia has undergone a very long process of gradual aridification since it split off from Gondwanaland about 40 million years ago. From time to time the process reversed for a period, but overall the trend has been strongly toward lower rainfall. The recent ice ages produced no significant glaciation in mainland Australia but long periods of cold and very dry weather. This dry weather during the last ice age may have killed off all the large diprotodonts…
Human hunting: The “blitzkrieg theory” is that human hunters killed and ate the diprotodonts, making them extinct. The extinctions appear to have coincided with the arrival of humans on the continent, and in broad terms, Diprotodon was the largest and least well-defended species that died out. …But critics of this theory regard it as simplistic, arguing that (unlike New Zealand and America) there is little direct evidence of hunting, and that the dates on which the theory rests are too uncertain to be relied on.
Human land management
The third theory says that humans indirectly caused the extinction of diprotodonts, by destroying the ecosystem on which they depended. In particular, early Aborigines are thought to have been fire-stick farmers using fire regularly and persistently to drive game, open up dense thickets of vegetation, and create fresh green regrowth for both humans and game animals to eat…
Multiple causes
The above hypotheses are not necessarily mutually exclusive. Each of proposed mechanisms can potentially support the other two. For example, while burning an area of fairly thick forest and thus turning it into a more open, grassy environment might reduce the viability of a large browser (an animal that eats leaves and shoots rather than grasses), the reverse could also be true: removing the browsing animals (by eating them, or by any other means) within a few years produces a very thick undergrowth which, when a fire eventually starts through natural causes (as fires tend to do every few hundred years), burns with greater than usual ferocity.*
So, although the climate change in Australia was not “common” with that in NA, there was significant climate change- but of a different sort and over a different timeline. And, note that Australian megafaunal extinctions are also of a different sort over a different timeline.
We have debated the NA extinctions many times.
Note that Asia doesn’t seem to follow the “arrival of Man” pattern either. We don’t have a lot of data on South America.
So, of the continents, only NA and Australia seems to follow the “arrival of Man” pattern. In each case, there was a corresponding climate change, and in each case the pattern of extinctions was different.
No doubt, in each case, Man had a part. But did he pick off species that were going out due to climate change anyway?
On the other hand, mass extinctions have been occuring since the start of life on Earth, long before Man appeared.
Eocene-Oligocene extinction event- caused by climatic changes.
Middle Miocene extinction - caused by climate changes.
Aptian extinction - volcanic caused climate changes?
And then the “Big Five” which may have been caused by a catastrophic event or climate changes or other causes.
Cretaceous–Tertiary extinction (catastrophic event )
Triassic–Jurassic extinction
Permian–Triassic extinction
Late Devonian extinction
Ordovician–Silurian extinction
Regarding farming, one influence in Africa and India is(was) the presence of elephants: a herd of elephants can easily wipe out a farm, and before the invention of guns their presence was a limiting factor on how successful farming could be.
In fact, this touches on a pet theory of mine: that in addition to humans seizing the econiche of apex predator, when humans took up farming they replaced or competed with proboscideans for the role of what might be termed “apex herbivore”. That is, herbivores that as adults are nearly immune to predation and as part of their feeding process destroy woodlands.
No, not on a global scale. We’ve discussed this many times before, and I and Blake have tried to educate you on the issues. We seem to have failed. You always come back to rehash the same old arguments again and again. I’m not going to do it yet another time.
As I’ve stated many times previously in these threads, the general consensus at present is that the arrival of humans was the major trigger for the extinctions of megafauna on a global scale. Climate may have had an impact in some areas, but the megafaunal extinctions coincided with major climate change mainly in North America, and not in other areas.
Humans seem to have had no trouble exterminating proboscidians long before the invention of guns, based on the extinction of many species of mammoths and mastodonts in the Americas and some in Eurasia and Africa.
But there were no Global extinctions. The megafaunal extinctions missed both Asia and Africa.
We have just two continents- NA and Australia. Both had extinctions, both had climate changes that matched the extinctions- as well both had the arrival of man that matches.
Successful Mammal species seem to be rather restistant to extinction from hunting. Since 1800, not a single sucessful land mammal mega-fauna has been driven to extinction by hunting. It’s odd that a small handful of humans with flint spears could eradicate so many sucessful land mammal mega-faunal species, while tens of thousands of times more people, armed with repeating rifles- couldn’t do that same.
And, again, there is no "consensus’ on the subject. Every single unbiased scientific article I have read have agreed what there is is debate, not consensus.
True, but Africa and India probably had the highest coefficient of length of hominid presence/low climate stress in the world. So once those elephant populations survived human hunter/gatherers, they were poised to trample attempts to completely replace wild ecosystems with farmland. Elephants bear one calf at a time which takes years to mature, so they would probably be particularly slow adaptors.
You are confusing your admittedly expert opinion with the general consensus. I have provided cite after cite, source after source that say that the general scientific community agrees only that there is great debate on the subject.
In fact, it’s impossible to prove, which is why the various concept remain hypothesis, and do not even rise to a true scientific theory.
Sometimes, in science there are things which remain opinion and do not allow for black vs white, fact vs fallacy. In general, the causes of mass extinction are one of these. (The KT extinction is still hotly debated, even today)
You can’t “educate” me, as it’s a matter of opinion, not fact.
It’s true that generally humans are accepted as one of the significant causes, and climate change as another. Few claim either is THE single cause. I don’t claim that either- I agree that humans were part of the cause. You seem unable to admit that climate changes could have also been a cause.
All that the above demonstrates is a complete misunderstanding of what I have said in my posts, and a lack of familiarity with the bulk of the scientific literature.
Ok, my degree is 30 years old, and other than some volunteer work, I don’t do much work in the field. So, your opinion is better than mine.
So, let us take some other dudes opinions. http://www.sciencemag.org/cgi/content/abstract/306/5693/70
"Assessing the Causes of Late Pleistocene Extinctions on the Continents
Anthony D. Barnosky,1* Paul L. Koch,2 Robert S. Feranec,1 Scott L. Wing,3 Alan B. Shabel1
One of the great debates about extinction is whether humans or climatic change caused the demise of the Pleistocene megafauna. Evidence from paleontology, climatology, archaeology, and ecology now supports the idea that humans contributed to extinction on some continents, but human hunting was not solely responsible for the pattern of extinction everywhere. Instead, evidence suggests that the intersection of human impacts with pronounced climatic change drove the precise timing and geography of extinction in the Northern Hemisphere. The story from the Southern Hemisphere is still unfolding. New evidence from Australia supports the view that humans helped cause extinctions there, but the correlation with climate is weak or contested. Firmer chronologies, more realistic ecological models, and regional paleoecological insights still are needed to understand details of the worldwide extinction pattern and the population dynamics of the species involved. "
Do you agree those Professors are experts? Is this not a peer-reviewed cited and sourced scientific study? Do you agree that their article sez there is “great debate” (not “consensus”)? Do you agree that their study shows " evidence suggests that the intersection of human impacts with pronounced climatic change drove the precise timing and geography of extinction in the Northern Hemisphere"?
"Extinctions of megafauna species during the Late Quaternary dramatically reduced the global diversity of mammals. There is intense debate over the causes of these extinctions, especially regarding the extent to which humans were involved. Most previous analyses of this question have focused on chronologies of extinction and on the archaeological evidence for human–megafauna interaction. Here, I take an alternative approach: comparison of the biological traits of extinct species with those of survivors. I use this to demonstrate two general features of the selectivity of Late Quaternary mammal extinctions in Australia, Eurasia, the Americas and Madagascar. First, large size was not directly related to risk of extinction; rather, species with slow reproductive rates were at high risk regardless of their body size. This finding rejects the ‘blitzkrieg’ model of overkill, in which extinctions were completed during brief intervals of selective hunting of large–bodied prey. Second, species that survived despite having low reproductive rates typically occurred in closed habitats and many were arboreal or nocturnal. Such traits would have reduced their exposure to direct interaction with people. Therefore, although this analysis rejects blitzkrieg as a general scenario for the mammal megafauna extinctions, it is consistent with extinctions being due to interaction with human populations."
Now, see, I have found a article that agrees with you that “extinctions being due to interaction with human populations”. However, again note "There is intense debate over the causes of these extinctions, especially regarding the extent to which humans were involved. " It says "debate" not *“consensus”. *
The Introduction says clearly that there is great debate with both climatic changes and human predation being suggested hypothesis.
I have scoured jstor and google scholar and I can find no peer-reviewed scientific study that claims there is “consensus” on this subject. Each and every one- while taking both sides- agree only that there is great debate. I cheerfully concede that most articles come down upon the human caused side of the debate- but otoh most also agree climate changes were part (even tho a lesser part) of the equation.
If you come up with a peer-reviewed scientific cite that agrees there is “consensus” on this subject, I’d love to see it.
Let’s say that although there is a debate, the overwhelming weight of the evidence based on comprehensive review of the scientific literature is that humans, and not climate, were the primary cause on a global scale. Barnosky et al., which I originally cited to you years ago, and which you cite above but have obviously never actually read, is the most thorough review on the subject, along with a more recent review by Koch and Barnosky in the Annual Review of Ecology, Evolution, and Systematics. Their strong conclusion is that the main factor on a global scale was humans, with climate playing a role in some areas.
But I’ve said this to you several times before, and you never remember it.
But humans are the only cause all the events have in common. It seems to me to be special pleading to keep inserting “climate change” as a cause when it only applies to some cases. And there’s a conflict of interest here – it’s humans who seem to be arguing that “humans weren’t the only cause.” I have no doubt that a desire to somehow absolve humanity could color some peoples’ views – even scientists have their blind spots.