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But aren't these possibilities due to over-population rather than climate change?

Our total ecological footprint is less due to population and more to the way we fill up all and then some. Most of the worlds population is living on a sustainable level even at our current population, but white people are as a group way over the limit.

"Over-population" is a term that when uttered in relation to over current situation in my ears sounds like prioritizing the western lifestyle over poor people's lives. Not that I think you meant it that way.

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by A swedish kind of death on Tue May 10th, 2011 at 04:14:12 PM EST
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Very good point. I think it's interesting to consider why the western lifestyle is so voracious and also whether or not there is anything fundamentally unique about it. For the latter I tend to think not.
by Jace on Wed May 11th, 2011 at 10:06:01 AM EST
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One can point to Chaco Canyon, Easter Island, Mayan city states to show the western lifestyle isn't unique.  

Not even unique to hominids.  The Saber-toothed cat lasted for 42 million years.  Our earliest ancestor showed up ~14 million years ago.  On the record being a Saber-toothed tiger is a MUCH better way to make a living.  

Species finds a way to make a living, population increases under the system that way creates, eventually the system goes sour, population crashes.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre

by ATinNM on Wed May 11th, 2011 at 01:59:43 PM EST
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... is an excellent cautionary tale of the dangers of specialization on a lifestyle that is excessively dependent where the climate is with respect to the ice age cycle.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Fri May 13th, 2011 at 12:02:57 PM EST
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Saber-toothed tigers are also an excellent example of the consequences of human over-hunting. From the current issue of Conservation magazine:

More than 25,000 years ago, one megafaunal species--we humans--began to spread rapidly around the globe and in the process helped to wipe out about half of all land mammals weighing more than 44 kilograms (97 pounds). "More than 101 genera perished," Anthony Barnosky, an ecologist at University of California, Berkeley, reported in a 2008 study in Proceedings of the National Academy of Sciences (PNAS). Among the victims were whole groups of mammoths, mastodons, saber-toothed tigers, giant ground sloths, and big beavers. Many vanished in just a 4,000-year span that ended about 11,000 years ago. By then, Australia had lost roughly 88 percent of its big mammal groups, South America 83 percent, and North America 72 percent. Africa did better during what is now called the Quaternary Megafauna Extinction (QME), losing about one-fifth of its big species, while Eurasia lost one-third.

Exactly what caused the QME has been the subject of long and fierce debate, but most explanations finger some combination of two ingredients: human hunters and rapid climate change. It doesn't take a PhD to realize that big mammals roaming across vast territories were obvious, attractive targets for hungry hunters seeking the biggest bang for their buck. It takes a little math, however, to see just how quickly unconstrained "overkill" can eliminate a species, such as the elephant, that reproduces slowly (as big mammals tend to). Sometimes, it can take just a few human generations. Toss hunting pressure into an environment already changing rapidly due to events such as human-set fires and yo-yo climate shifts, and it's no surprise that the stress "robbed global ecosystems of the biggest animals on Earth," Barnosky told a packed lecture hall a few years ago.

By his count, just 183 large-mammal species survived the catastrophe, often in dramatically reduced numbers. And their days are numbered unless we learn from the past, he argues in his provocative and eye-opening PNAS paper. The fundamental problem, he says, is that we're literally taking the lion's share of Earth's resources--and the shares needed by all other megafauna, too--for ourselves. The QME represented "a dramatic change in the way energy flowed through the global ecosystem," he writes. Before the extinction, there was easily enough "biomass"--the fundamental source of energy created when plants convert the sun's rays to edible tissue--to support some 350 big-mammal species. As hungry Homo sapiens spread, however, "energy began to flow toward a single megafauna species: humans." In addition to simply eating other big animals, we grabbed vast swaths of their habitat to grow crops and raise cows, goats, and sheep. In essence, Barnosky says, "we replaced the extinct megafauna with us and in the process lost a bunch of species that are never coming back because we now have grabbed their biomass."

This article also adds an interesting twist to the discussion of fossil fuels (and human population growth and...):
One puzzle, however, remains: Why have just a handful of big mammals actually gone extinct in the past few thousand years, even as human and livestock populations skyrocketed? One answer is that some, such as the American bison, are actually "dead species walking"--reduced to small, unsustainable population sizes or marginal habitat fragments and unable to survive without human help. Another answer, believes Barnosky, is that we temporarily took pressure off wild ecosystems when we discovered fossil fuels and then used that energy to supercharge our ability to feed and shelter ourselves. But that era appears to be closing, he notes, as humans press in on the few remaining habitats still dominated by nonhuman megafauna. It's no coincidence, he says, that human impacts now threaten some 90 species of large mammals, including 40 percent of those in Africa, a continent that made it through the QME largely unscathed. And with a rapidly warming climate taking hold, he says, the present is beginning to look eerily like the past: "Growing human populations and climate change? Beginning to sound familiar?"
by Jace on Sat May 14th, 2011 at 10:47:40 AM EST
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Since Smilodon Populator went extinct in South America before humans seem to have made it down to South America, its normally put down to the start of the interglacial and the greater dependence of the saber tooth cats than other large cat species on large prey.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Sat May 14th, 2011 at 09:40:57 PM EST
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The arrival date of humans in South America is still unclear but it appears that there may very well have been some overlap between Smilodon populator (extinct circa 10,000 years BP) and humans. From Wiki:
The 14,000 BP immigration date maximum, however, has been challenged. Claims have been made for human presence in the 20,000-30,000 BP timeframe at Pennsylvania's Meadowcroft Rock Shelter and in California's Yuha Desert as well as sites in South America [re: Chile], Central America, and Mesoamerica.

Like many other sites, there are Mastodon bones present at Monte Verde. Smilodon may very well have been over-specialized and preyed only on big animials but then so do (did) we. Loss of habitat and loss of food also lead to extinction.

by Jace on Sun May 15th, 2011 at 11:44:32 AM EST
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And in any event, whether the Smilodon lost its prey directly to climate change or to the lazy fire-hunting of big game by early man, in either event at those population densities, the American cats that were able to survive on smaller game had no trouble surviving all the way up to the present human-induced mass extinction.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
by BruceMcF (agila61 at netscape dot net) on Mon May 16th, 2011 at 07:00:15 PM EST
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