Post ice-age extinctions of large mammals linked to humans, not climate change

Jun 04, 2014 by Bob Yirka report
Restoration of a steppe mammoth. Credit: Kurzon/Wikipedia, CC BY-SA 3.0

(Phys.org) —A team of researchers with Aarhus University in Denmark has concluded that the die-out of large mammals after the last ice-age was due more too human activity than a changing environment. In their paper published in Proceedings of the Royal Society B: Biological Sciences, the team describes how they conducted a country by country survey of all known species extinctions from one thousand years ago to 132,000 years ago. In comparing what they found with known environmental changes during the same period they found a pattern emerging that fingered humans as the main cause of the majority of the extinctions.

As the ice melted at the end of the Pleistocene epoch about 12,000 years ago, large mammals (greater than 10 kilograms) such as the woolly mammoth, the giant sloth, cave dwelling lions, etc. began dying off, eventually disappearing altogether. The cause of the extinctions has, in many cases, been blamed on changing environmental conditions, despite a lack of evidence. In this new effort, the research team has found some evidence to suggest the die-offs were more likely caused by humans—either directly by hunting, or indirectly by burning vegetation needed for survival.

Suspecting that humans were the cause, the researchers conducted a survey of all known species of large mammals that went extinct during and after the Pleistocene epoch. To gain a new perspective they conducted the survey on a country by country basis, rather than by continent as past studies have done. The team then used the data they'd collected to perform a comparative analysis with known weather conditions in the areas where the animals went extinct. In so doing, the team found a pattern emerging—the shorter amount of time that the large mammals lived together with humans, the greater the number of species that went extinct. Put another way, the found that extinctions were few in Africa where large mammals and humans had existed since the time humans learned to hunt them. More extinctions occurred in Eurasia, but the greatest number by far occurred in the Americas and Australia, where humans arrived later, armed with much better hunting skills.

The giant sloth succumbed to the advance of humans.Credit: Wikimedia Commons

The researchers even went so far as to calculate the percentages of they believe can be blamed on humans—64 percent globally—while only 30 percent could be blamed on fast changing weather patterns (mostly in parts of Europe and Asia).

Explore further: India's ancient mammals survived multiple pressures

More information: Global late Quaternary megafauna extinctions linked to humans, not climate change, Proceedings of the Royal Society B, Published 4 June 2014 DOI: 10.1098/rspb.2013.3254

Abstract
The late Quaternary megafauna extinction was a severe global-scale event. Two factors, climate change and modern humans, have received broad support as the primary drivers, but their absolute and relative importance remains controversial. To date, focus has been on the extinction chronology of individual or small groups of species, specific geographical regions or macroscale studies at very coarse geographical and taxonomic resolution, limiting the possibility of adequately testing the proposed hypotheses. We present, to our knowledge, the first global analysis of this extinction based on comprehensive country-level data on the geographical distribution of all large mammal species (more than or equal to 10 kg) that have gone globally or continentally extinct between the beginning of the Last Interglacial at 132 000 years BP and the late Holocene 1000 years BP, testing the relative roles played by glacial–interglacial climate change and humans. We show that the severity of extinction is strongly tied to hominin palaeobiogeography, with at most a weak, Eurasia-specific link to climate change. This first species-level macroscale analysis at relatively high geographical resolution provides strong support for modern humans as the primary driver of the worldwide megafauna losses during the late Quaternary.

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Dug
3 / 5 (1) Jun 04, 2014
If you look at the human populations during these time periods - they were remarkably small and this is why their impacts have been minimized regarding mega fauna species. This study would be a lot stronger argument if there was at least some kind of quantifiable information regarding fossils that showed human hunting/trapping/consumption evidence compared to those that did not of the same species and comparisons to similar time period species not used by humans. Additionally, showing relationships between human population density and species extinction would be insightful - maybe that's what they mean by "hominin palaeobiogeography," but accurate population densities would be difficult to determine accurately. Having not read the paper, perhaps it only seems to be poorly supported based on the abstract that reflects zero quantification results, or not.
Captain Stumpy
5 / 5 (5) Jun 04, 2014
Having not read the paper
@dug
the paper is free... you can read the full paper here:
http://rspb.royal...254.full

on the same page, you can go to the heading "This Article" on the right of the title and author affiliations and find the link "Full text (PDF) Free"
select this and you can DL the PDF and read at your leisure.
Figure 1 specifically mentions palaeobiogeography as well as section "(b)The human palaeobiogeography hypothesis"
accurate population densities would be difficult to determine accurately
you might find more info in part 2 Material and methods and the section c
from the results
This analysis illustrates that the late Quaternary megafauna extinctions were strongly linked to hominin palaeobiogeography and only weakly to glacial–interglacial climate change


Rustybolts
5 / 5 (4) Jun 05, 2014
Humans would have love to hunt the big animals. Feed them longer and was easier to kill once they learned how.
Sinister1812
5 / 5 (1) Jun 05, 2014
Those massive animals would've been harder to hunt using simple tools and spears. Those animals were much more massive and dangerous compared to the ones around today. I can't imagine it would've been easy.
Torbjorn_Larsson_OM
5 / 5 (4) Jun 05, 2014
It is an old question, to be sure.

What this study has going for it is its scope. It is a longitudinal study vs land areas, and it teases out the increased efficiency in hunting. In comparison, using climate only has enough resolution but has poor prediction while humans only has sufficient prediction. But the combined model is better under measures to avoid over-fitting, I believe. (Have only skimmed the text for obvious problems. It is open access!)
Torbjorn_Larsson_OM
5 / 5 (3) Jun 05, 2014
@Dug: The hominin paleogeography hypothesis, that was in the model and establish that hunting is a factor, is that early hominins in Africa and Asia were less efficient and hence megafauna coevolved.

It is true that this is a coarse-grained model, albeit the first generic (they claim), so it is a causal study. (A basis of correlation, with testing for causality re climate and paleogeography evolution.) They do however address the question of sufficient mechanism by literature and by noting that the model conforms:

"Although strong scepticism continues about humans as the extinction driver, primarily based on an argued scarcity of archaeological evidence of megafauna kills [4,16], others have shown that that kill sites are not rarer than expected [58,59] and that prehistoric human populations had the potential to exterminate megafauna populations [7]. Our analysis further supports humans as the key driver ..."

[tbctd]
Torbjorn_Larsson_OM
5 / 5 (3) Jun 05, 2014
[ctd]

YMMV as always. This is maybe the first conclusive generic result and would certainly need a do over with more data at the very least. Certainly better human population studies would help, and will come too.

In fact, I think they may have unintentionally downgraded the test, as particle physicists nowadays make a preliminary method development on partial data and then open the "black box" to remaining data. That can be used to establish a necessary repeat. Now we have to wait for other groups doing it.

But I think that unless they botched the scope of understanding the mechanism they have uncovered (if this is the first study to have sufficient resolution), it is a tested theory, and they could reject the climate only contender.

E.g. humans are likely involved, whether at 100 % or their 60 % or less.
Torbjorn_Larsson_OM
5 / 5 (3) Jun 05, 2014
Speaking of botched, I did that with the description of particle physics methods.

They do a full method development, they are not supposed to change the result, but on anonymous data. E.g. an outside person has added an offset that is revealed later. (Here one could inject a trend, I would imagine, perhaps a strong one overpowering the potential paleogeography mechanism.)

Used on studies like these for "repeats", they would not be full repeats. But they would take out such systematic errors as subjective bias (trying to "fix" the data to fit the models by taking out outliers subjectively instead of by statistics, et cetera).
Torbjorn_Larsson_OM
5 / 5 (3) Jun 05, 2014
Oh, and maybe I should be clear, current human population data seem to give them sufficient resolution. So it is likely not a problem any longer, it's just that we should expect better data be forthcoming eventually (and make for a nice repeat/increased resolution).
Dug
not rated yet Jun 05, 2014
"The period of extinction in North America occurred approximately 11 500–10 000 years BP, well within our period of measured climate change, and broadly occurred when climate change was severe, but also consistent with the arrival of modern humans [3]." Evidence suggests that the earliest humans arrived in Americas 40KYA in successive waves and different routes. There population numbers were sparse and regional. Even 11KYA the question is whether their densities and associated hunting were sufficient enough to effect mega fauna populations. The extinction of these species was geographically complete by 11KYA - human populations were sparse especially in the Americas and not geographically uniform. This is where the papers modeling interpretations and interpolations falls apart. While hunting and ice age phenomena may have worked together, it isn't logical that human hunting and competition factors explain the extinction of both mega fauna food, non-food and predatory mega fauna.
Caliban
5 / 5 (3) Jun 05, 2014
All well and good, but it may be more complicated yet. Perhaps they were unaware of this
recent finding:

http://phys.org/n...bon.html ,

which certainly bears on the situation in North America, and possibly in the Global North, as well.

All things considered, it was probably a sliding-scale combination of climate entrained environmental change and human predation, with the relative magnitude of those forces, locally, being the key to the most powerful extinction driver in a given terrain.

An all-or-nothing, predation vs environment hyposthesis for this universal extinction just doen't seem to add up.

bradfordcutler
not rated yet Jun 05, 2014
I thought I would be dead and buried before the academic community, of which I was once a part of at one time, would come to this conclusion. We have all been starring at the evidence for the last 50 years but no one has been able to psychologically come to the realization and conclusion that humanity was to blame for such carnage of these beautiful creatures of God and the planet, but that is exactly what happened. All the solid evidence has been pointing to this. As a collector of Pleistocene stone figurine art, I was overtaken myself by the sheer numbers of mammoth figurines that I was finding both at home and on my ranch here in Texas. Almost all the stone figurines that I would collect, would have red ocher spotting at the end of the truck and on the body, clearly indicating a result of pulmonary wounds and general stab wounds about the torso. In addition there would always be a smooth area on the figurine from rub friction that no doubt was from a ceremony performed to release the spirit of the killed mammoth back into the spirit world to be recycled back to earth within a newly born earthbound calf. I'm the only one that I know that is currently working in this area and I am imparting this knowledge to the general public so that you can search yourself for the truth about the spiritual existence of early man that I have discovered. These figurines are extremely common in North America yet I have been the only one with the "vision" to discover them and correctly interpret their meaning. "Happy hunting".
ryggesogn2
1 / 5 (5) Jun 06, 2014
If true then aboriginal Americans were no better than the buffalo hunters.
Caliban
5 / 5 (4) Jun 07, 2014
If true then aboriginal Americans were no better than the buffalo hunters.


Ah, yeah, rygsuckn' --just can't prevent your idiot snout from emitting some trollblat, can you?

I'm sure that the Aboriginal Americans slaughtered whole herds numbering in the thousands, and left their flayed carcasses to the rot and the scavengers, simply to provide themselves with stylish new Wooly Mammoth Overcoats.

Moron.
Vietvet
4.2 / 5 (5) Jun 07, 2014
If true then aboriginal Americans were no better than the buffalo hunters.


Ah, yeah, rygsuckn' --just can't prevent your idiot snout from emitting some trollblat, can you?

I'm sure that the Aboriginal Americans slaughtered whole herds numbering in the thousands, and left their flayed carcasses to the rot and the scavengers, simply to provide themselves with stylish new Wooly Mammoth Overcoats.

Moron.


Rggy gets dumber with every post.
bradfordcutler
not rated yet Jun 08, 2014
For the record, it was the white settlers that hunted the passenger pigeon to extinction through deliberate over-hunting and they came within about 500 buffalo of outright elimination of that species as well,   It was wanton slaughter of buffalo sometimes shot from moving trains as they moved West with no intention of respecting the death and/or use of the fallen animals.  Simply put, it was an act of cowardly immorality and certainly not one of humanities finest moments. On the other hand, early man both here and in Eurasia had a deep spiritual reverence for the animals they harvested for food, clothing and other resources as well.  The art work I have collected speaks to that loudly and consistently.  Most of the mammoth (for example) stone figurines I have collected over the years primarily in Texas but elsewhere as well have exhibited extreme gratitude to the spirit world for this animal resource that they so dearly depended on just by examining the sheer numbers and the amount of ceremonial rubbing areas on these rocks. It was done often to the point where some areas on the rocks were as smooth as highly polished glass.  It took a tremendous amount of time to get this result by hand polishing.  They of course lacked the knowledge but not the concern of conservation, and as a result, over-hunted the species to the point of extinction, but at no time do I think they were aware of doing so as their response was to beckon the spirit world for a bountiful replacement in order to assure their survival.  Take the time to go outside today and collect some rocks on the ground.  Look for what I have described here and from my earlier postings,…..you will be surprised at what you find and you will ask yourself, how come no one has ever told me about this and I cannot answer that other that there are trillions of them littered about the ground in North America for all of you to enjoy and discover the spiritual secrets of early man here and in Eurasia. Happy Hunting!
ryggesogn2
1.5 / 5 (4) Jun 08, 2014
but at no time do I think they were aware of doing so

That excuses them?
barakn
4.2 / 5 (5) Jun 08, 2014
but at no time do I think they were aware of doing so

That excuses them? -soggyring2

Good point. Your do-nothing attitude about the climate is going to lead the extinction of thousands of species, but I'm sure you'd be incensed if you were to be held to account for it, perhaps by being strung up by your thumbs and having your nipples cut off. Perhaps people should be excused for being ignorant.