Posted on 08/24/2010 6:46:14 AM PDT by decimon
The cave bear started to become extinct in Europe 24,000 years ago, but until now the cause was unknown. An international team of scientists has analysed mitochondrial DNA sequences from 17 new fossil samples, and compared these with the modern brown bear. The results show that the decline of the cave bear started 50,000 years ago, and was caused more by human expansion than by climate change.
"The decline in the genetic diversity of the cave bear (Ursus spelaeus) began around 50,000 years ago, much earlier than previously suggested, at a time when no major climate change was taking place, but which does coincide with the start of human expansion", Aurora Grandal-D'Anglade, co-author of the study and a researcher at the University Institute of Geology of the University of Coruña, tells SINC.
According to the research study, published in the journal Molecular Biology and Evolution, radiocarbon dating of the fossil remains shows that the cave bear ceased to be abundant in Central Europe around 35,000 years ago.
"This can be attributed to increasing human expansion and the resulting competition between humans and bears for land and shelter", explains the scientist, who links this with the scarce fossil representation of the bear's prey in the abundant fossil record of this species.
In order to reach their conclusions, the team of scientists, led by the Max Planck Institute for Evolutionary Anthropology (Germany) studied mitochondrial DNA sequences from bear fossils in European deposits (Siberia, Ukraine, Central Europe and the Iberian Peninsula, specifically Galicia), and carried out a Bayesian analysis (of statistical probability).
The scientists also made comparisons with the modern brown bear (Ursus arctos) and with fossil samples of this species of bear, and managed to show why one became extinct and the other did not. In order to demonstrate this, the study analysed 59 cave bear DNA sequences and 40 from the brown bear, from between 60,000 and 24,000 years ago for the cave bear and from 80,000 years ago up to the present day for the brown bear.
Decline of the caves, extinction of the bears
The impoverishment of ecosystems during the last glacial maximum was "the 'coup de grace' for this species, which was already in rapid decline", the author explains.
The present day brown bear did not suffer the same fate and has survived until today for one simple reason – brown bears did not depend so heavily on the cave habitat, which was becoming degraded, and this is why they did not follow the same pattern as the cave bears.
"Brown bears rely on less specific shelters for hibernation. In fact, their fossil remains are not very numerous in cave deposits", the Galician researcher says.
The definitive extinction of the cave bear "broadly" coincides with the last cooling of the climate during the Pleistocene (between 25,000 and 18,000 years ago), which may have led to a reduction in shelter and the vegetation that the animals fed on.
The cave bear inhabited Europe during the Late Pleistocene and became definitively extinct around 24,000 years ago, although it held out for a few thousand years longer in some areas, such as the north west of the Iberian Peninsula, than in other places. This ursid was a large animal, weighing 500 kg on average, and was largely a herbivore. The bear hibernated in the depths of limestone caves, where the remains of individuals that died during hibernation slowly accumulated over time.
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References:
Stiller, Mathias; Baryshnikov, Gennady; Bocherens, Herve; Grandal D'Anglade, Aurora; Hilpert, Brigitte; Muenzel, Susanne C.; Pinhasi, Ron; Rabeder, Gernot; Rosendahl, Wilfried; Trinkaus, Erik; Hofreiter, Michael; Knapp, Michael. "Withering Away-25,000 Years of Genetic Decline Preceded Cave Bear Extinction" Molecular Biology and Evolution 27(5): 975-978, mayo de 2010. doi:10.1093/molbev/msq083
I suspect the humans ate the game up in winter and the bears starved to death in the Spring.
The coming Ice Age will prove the value of the greasy, tender, overweight Leftwingtards ~ and don’t you forget that.
The reporter indicates that as there were fewer bears there were fewer different sorts of mtDNA ~ yet, the thesis here is that human presence was depriving the Cavebears of food ~ that is, range.
Think about that a moment. We have human beings, and as they spread out into more and more isolated groups way-back-when there's less breeding with the ol'gals "down home" and those local mtDNA strands can go ahead and be mutated (randomly) and show up in all the locals in just a few generations.
We use this information to track and trace human expansion ~ but it takes "isolation" from all the other humans for this trick to work.
With these Cavebears the guy is telling us that they got isolated by humans as their numbers dwindled but the researchers found FEWER different mtDNA strands.
That information is contradictory. In fact, it indicates that one sort of Cavebear came to dominate the whole species, which would mean little, if any, isolation of one group of Cavebears from the other Cavebears.
In that case I would suspect that the Cavebears all died off fairly rapidly from DISEASE ~ maybe something like West Nile Virus.
We saw that happen with the crows in the Eastern United States. That one virus wiped out the vast flocks that used to fly around. Now we have crows coming back who are immune to the virus, but there still aren't many, and I just bet there are many fewer mtDNA lines among the crows in North America these days than there were before that plague.
Thanks for your post. When I saw the time frames, I suspected the last glacial cycle had a hand in doing them in.
The human population 50K ya had begun to recover from the great Toba Megavolcano around 74K years ago. I imagine the cave bear population was also reduced by Toba, but humans resurged more so than the cave bears not being limited to cave habitat.
If I recall correctly, the comet was around 13,000 years ago, the younger Dryas around 11,000 ya. Actually, the comet may have caused a surge of fresh water thus changing the North Atlantic Deep Water circulation and bringing on the cold. Actually concentrated salt when ice freezes in the north is what keeps it going. In fact, a big danger if the Arctic ice melts in the summer is that fresh water will be increased in the North Atlantic, slowing NADW and causing severe winters in Britain and Europe.
Lots of cold, regrowth of glaciers, etc in Europe.
The last big glaciation ended with the Bolling Interstadial, which is a period of warm weather starting about 14000 years ago, and ending about 12,800 years ago.
My preference is to use the major sea-level rises as the touchstone for estimating aggregate global climate however.
If you think of the Bolling Interstadial as being the beginning of the current Interglacial, and with interglacials being typically about 10,000 years long, we are already 4000 years into the next glacial period BUT where's the ice?
If you think of the Bolling Interstadial as a brief interruption of the last period of glaciation, and not as the beginning of the current warm period, then we are about 700 years away from the beginning of the next major glaciation.
If the comet interrupted the current warm period, we are overdue. if the comet simply returned things to normal by interrupting an anamolous warm spell, we have time to waste.
A third view is it doesn't matter because we have gained control of the heating and cooling of the Earth by generating our own clouds, carbon dioxide load and we have nukes if need be.
Given the choice between returning to the world climate of 12 million years ago or letting a couple of miles of ice grind over the United States and Europe, I'll take the warmth any time.
So, tens of thousands of years of a flood to create this process?
I doubt it.
Besides, wasn’t it 40 days/nights?
We conclude that neither the effects of climate change nor human hunting alone can be responsible for the decline of the cave bear and suggest that a complex of factors including human competition for cave sites lead (sic) to the cave bear's extinction.If scientists just blindly collect data and never make a guess at its meaning, then they aren't scientists. How does one generate hypotheses without speculation?
It's often the laymen--including the lesser science reporters--who misuse the possibilities they suggest in the scientific literature.
Generally, they are thought to have been herbivores--based on teeth, mandible, and skull morphology, as well as isotope work (generally low 15N)--although some researchers think that some populations (Romania?) might have become omnivorous when stressed. That is still debated, however.
I have to doubt some of your claims, muawiyah. Meltwater Pulse 1A was a couple of inches per year. It looks dramatic on graphs covering many centuries, but it’s not like that all occurred at once. We don’t see Storegga-like evidence of what you describe. Obviously, there were GLOF events, but they are localized.
Note also that the hypothetical comet was about 13 ka, not 11 ka.
Isolation, even without mutation, will do it.
“Decline of the caves, extinction of the bears.”
The present day brown bear did not suffer the same fate and has survived until today for one simple reason – brown bears did not depend so heavily on the cave habitat, which was becoming degraded, and this is why they did not follow the same pattern as the cave bears.
I’m not sure how caves ‘decline’ but the implication is that there were fewer caves.
So does the argument go that we ran them out of their caves or they ran out of habitable caves because of changes in the ecosystem?
Perhaps we were filling up the entrances with rocks so they couldn’t get in? Or quietly killing them in their sleep while they were in hibernation.?
Them was some badass red-haired neanderthals.
The CoCC authors also refer to a couple of earlier waves of high-velocity debris from the same source.
Figures he’d be involved. ;’)
Try my post at #47 for a more exacting coverage of when things happened ~ 15 was a quick off the cuff answer to a general issue ~ wasn’t meant to be definitive.
Great, informative posts. Thanks.
Now about Storegga-like events ~ those involve physical displacement, by a landslide, earth-fault movement, etc.. What I'm concerned with is quite a bit different. That is the sudden break of an ice dam that releases huge amounts of water.
Glacial Lake Agassiz has been studied extensively. Now, scale that up to something the size of Antarctica. Let an ice wall form at the boundary of the once far larger ice sheet as it melts at the end of the period of maximum glaciation.
The circum polar cyclone will take care of keeping the water draining to the lowlands at the boundary between sea ice and land COLD ENOUGH TO REFREEZE to form that wall.
Let the wall build up to some unsustainable height and there ought to be a sudden break, just like with Glacial Lake Agassiz' ice dam.
Pour out a couple of miles of melted ice sheet, with vast quantities of ice into the ocean surrounding Antarctica and you would have the largest tsunami possible on the planet.
There'd be no more rock debris from this sort of event than you'd get from any flow of just water.
That would be quite enough to destroy virtually all of the cheetahs but a mother with cubs hidden in a cave up a mountain side somewhere in the Kalahari! Their adaptation to exceedingly flat alluvial plains would have killed all but that cat! Something similar would happen on all of the coastlines of every South-facing piece of continental landmass.
I'd like to note here that due to the fact ocean levels were quite a bit lower at that time the worst damage would be in areas well offshore.
Okay, because even in a dry-->wet base situation with floatation, you wouldn't get enough to create what you were suggesting!
Glacial Lake Agassiz has been studied extensively. Now, scale that up to something the size of Antarctica. Let an ice wall form at the boundary of the once far larger ice sheet as it melts at the end of the period of maximum glaciation.
I don't see your GLOF mechanism. Are you suggesting a MLD or Jökulhlaup?
Agassiz was cratonic. Antarctica is an entirely different story.
Also, if you have excess melting, how would you get the thickness required on such a small continent?
So, think about what's happened since the Glacial Maximum ~ MILES of Ice have melted (one way or the other) and as that has happened the two islands have rebounded.
Prior to that, there was so much ice that Antarctica was actually a very large divot or "crater" compared to the normal curve of the Earth.
The melt simply took place faster than the rebound!
Given the scale I'm not sure you want to compare this to a Jökulhlaup where you have a given amount of meltwater at the base of a glacier, an icedam breaks, and then the covering ice ~ far more massive than the meltwater ~ simply presses the water out through the hole.
This is simply more like a very large ice dam on the order of thousands of feet in height that has a wide area collapse. The water behind the dam simply pours out as fast as gravity can sustain the project. Kind of like a Johnstown Flood on steroids.
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