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Sixth great extinction? Or scaring the folks?


At ScienceDaily (Mar. 5, 2011), we are invited to contemplate, “Has Earth’s Sixth Mass Extinction Already Arrived?”,

With the steep decline in populations of many animal species, from frogs and fish to tigers, some scientists have warned that Earth is on the brink of a mass extinction like those that occurred only five times before during the past 540 million years.Each of these ‘Big Five’ saw three-quarters or more of all animal species go extinct.

Is a three-quarters disappeance – as hinted by the University of California, Berkeley, paleobiologists who published a study in Nature, March3, – at all likely to happen, short of a worldwide nuclear holocaust or giant asteroid hit?

Tigers are featured in the article but – and here is one difficulty – tigers are top predators. Surely their possible disappearance in the wild would lead to an increase in the numbers of their prey?

As it happens, further into the column inches, we encounter more hope:

“So far, only 1 to 2 percent of all species have gone extinct in the groups we can look at clearly, so by those numbers, it looks like we are not far down the road to extinction. We still have a lot of Earth’s biota to save,” Barnosky said. “It’s very important to devote resources and legislation toward species conservation if we don’t want to be the species whose activity caused a mass extinction.”Coauthor Charles Marshall, UC Berkeley professor of integrative biology and director of the campus’s Museum of Paleontology, emphasized that the small number of recorded extinctions to date does not mean we are not in a crisis.

“Just because the magnitude is low compared to the biggest mass extinctions we’ve seen in a half a billion years doesn’t mean to say that they aren’t significant,” he said. “Even though the magnitude is fairly low, present rates are higher than during most past mass extinctions.”

Okay, but how are the rates calculated? I suspect it is easier to know how many species are going extinct today than it would be to know how many went extinct in the Cretaceous.

Even the Berkeley paleobiologists seem to recognize that they are conducting a fire drill, at least in countries where major projects are already stopped or rerouted because of damage to wildlife habitats. And about the others, it is striking how little attention gets directed to opinion leaders there. It’s always directed to people like me, who recycle our cartridges and sort our garbage.

Hi Denyse, Willis Eschenbach wrote an excellent expose of the claims that Earth's sixth great extinction has begun in an article entitled, Where are the Corpses? Eschenbach's research totally discredits the oft-heard claim that habitat reduction is causing, or will cause, the extinction of a large percentage of the Earth's species - and in particular, birds and mammals. Eschenbach tested this claim by applying it to the historical record. He decided to investigate the timing and number of mammal and bird extinctions in modern times (the last 500 years) which are due to habitat reduction. The species-area relationship (which ecologists use) predicts that there should have been a very large number of recorded bird and mammal extinctions from habitat reduction over the last 500 years. Eschenbach found that the historical extinction rate has never been greater than 1.8 species per year. What's more, the vast majority of these species extinctions were the result of imported alien species being introduced to Australia and to various islands around the world, and were not caused by habitat reduction. If we look at continental species of birds and mammals that have gone extinct over the last 500 years, we find that there are less than a dozen - and most of these were made extinct by hunting, rather than habitat reduction. Finally, if we look at forest species of birds and mammals on the world's continents, we find that there are no recorded continental forest bird or mammal extinctions from any cause. Summarizing his findings for the past 500 years, Eschenbach wrote:
1) When European species met isolated local species, a number of the local species died. The Australian and island species were extremely vulnerable to pressure from imported humans, mammals, birds, plants, and diseases. 95% of all recorded bird and mammal extinctions are island or Australian species. 2) When the European species arrived, Australia and most islands had been separated from the continents for forty million years or so. The initial introduction of European species into island habitats was a one-time event. While alien species will always a problem for islands, this massive onslaught of the first coming of the European species will never be repeated — there are no places left with forty million years of isolation. 3) Total habitat destruction drove one bird to extinction. 4) While habitat reduction has been claimed as contributing (in an unknown degree) to three continental bird extinctions, to date no continental mammal or bird has been seen to go extinct due to habitat reduction alone. Three continental mammals have gone extinct — one antelope hunted to extinction, and a rare rabbit and a rarer antelope gone from unknown causes. Six continental birds have gone extinct — 3 prolific terrestrial bird species hunted to extinction, and 3 single-habitat freshwater bird species hunted, drained dry, eaten by fish, and polluted to extinction. (Emphases mine - VJT.)
Eschenbach contrasts his findings with the dire claims made by biologist E. O. Wilson:
In 1988, Wilson said that a 40% reduction in forest habitats had already occurred (Wilson 1988). Using Wilson’s "maximally optimistic" z value of .15 and his 1% annual forest loss, with 40% habitat reduction in 1988, the total species loss to up to 1998 should be 1,088 continental bird and mammal extinctions. Over a thousand continental bird and mammal extinctions predicted, and not one of them shows up in the record. ... Professor Wilson's ... explanation for the lack of predicted extinctions is that they do not happen at once. He says that the "species in a reduced habitat may take from 25 to 100 years to go extinct", and that research has shown that the rate of these delayed extinctions drops off exponentially with time (Wilson 2001). While this seems plausible, even if it were true it wouldn't keep us from seeing the predicted extinctions. We can see why by applying the exponential die-off to the 1,088 bird and mammal extinctions said to have occurred by 1998. Let's assume all 1,088 of them fatally lost habitat at some point since 1948, but they won't die out for 100 years. 1,088 species lost in 50 years (1948-1998), that works out to 21.76 per year, about 22 species "doomed to extinction" each year since 1948. With exponential decay, to still have one species of 100 left alive after 100 years, the exponent needs to be 1 – (1/100)^(1/100), or .045. This means that 4.5% of the remaining doomed species should go extinct each year. But if we had doomed 22 bird and mammal species to extinction every year since 1948, and only 4.5% of the doomed species went extinct each year, then by 1960, of the 261 predicted eventual bird and mammal extinctions, we should have seen 65 extinctions. By 1980, of 696 predicted eventual extinctions, we should have seen 340. And by the year 1998, of the 1,088 extinctions predicted by species-area calculations, we should have seen 672 actual extinctions of continental birds and mammals. We have seen none. (Emphases mine - VJT.)
Eschenbach goes on to say that even if the extinction of a typical species took place over 1,000 years, rather than the shorter times of 50 to 100 years stated by Wilson, we still should have already seen 118 bird and mammal extinctions from the 1088 continental bird and mammal species that are supposed to be "doomed", and even if the extinction occurred over a period of 5,000 years, we still would have seen 25 extinctions from habitat reduction. In fact, we have seen none. Eschenbach is greatly concerned that his findings will be mis-used to justify deforestation, and he emphatically states that he intends no such thing:
None of this implies that habitat destruction, forest fragmentation, or loss of species diversity are incidental or unimportant issues... None of this implies that extinctions will either rise or fall in the future... And finally, none of this implies that habitat destruction has no effect on the risk of extinction.
Nevertheless, he is compelled to state:
Extinction records do show that on all the continents of the world, there are no recorded cases of a forest bird or mammal that has gone extinct from any cause. This is despite the fact that humans have been reducing and fragmenting all natural habitats, including first the continental temperate forests and lately the continental tropical forests, for the 500 years covered by our extinction record.
It certainly sounds as if claims about a "sixth great extinction" are being orchestrated for political purposes by scientists who should know better. vjtorley
G. G. Kochemasov, "On the Uniqueness of Earth as a Harbor of Steady Life: A Comparative Planetology Approach," Astrobiology 7 (June, 2007): 518. Bantay
Very interesting. Multiple extinctions are consistent with the Old Earth Creation view, per Dr. Hugh Ross's testable creation model, purporting that God intervened in earth's developmental history, wiping out entire types and later species, then replenishing earth later with new species better suited for new conditions on earth, without clear, transitional markers. "These targeted extinctions require events that selectively, and with precise timing, remove the outdated species and their ecological support system. New data shows that asteroid and comet collisions ideally provide for such extinctions.2 Earth happens to be optimally located within the solar system's layout to receive the just-right number and kind of extinction-causing impacts. If Earth were much nearer to Mars' orbit, asteroid and comet collisions would be too frequent and too extreme. If Earth were much nearer to Venus' orbit, collisions would occur too seldom and be too weak to bring about the necessary extinctions." http://www.reasons.org/evolution/speciation-events/biology%E2%80%99s-big-bangs Bantay

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