Species Loss: It is statistics but not a game

Most biologists will tell you that the Earth is losing species faster than it is replacing them. One prominent biologist, Simon Stuart, chair of the Species Survival Commission for the International Union for the Conservation of Nature (IUCN), has said about two new reports coming out in March (2010):

“Measuring the rate at which new species evolve is difficult, but there’s no question that the current extinction rates are faster than [replacement]; I think it’s inevitable.”

The IUCN created shock waves with its major assessment of the world’s biodiversity in 2004, which calculated that the rate of extinction had reached 100-1,000 times that suggested by the fossil records before humans.

No formal calculations have been published since, but conservationists agree the rate of loss has increased since then, and Stuart said it was possible that the dramatic predictions of experts like the renowned Harvard biologist E O Wilson, that the rate of loss could reach 10,000 times the background rate in two decades, could be correct.

“All the evidence is he’s right,” said Stuart. “Some people claim it already is that … things can only have deteriorated because of the drivers of the losses, such as habitat loss and climate change, all getting worse. But we haven’t measured extinction rates again since 2004 and because our current estimates contain a tenfold range there has to be a very big deterioration or improvement to pick up a change.”

[Source: The Guardian]

What may be meant by “measuring the rate at which new species evolve is difficult” is that we don’t know how many species there are. Current knowledge puts the number at about 2 million species, but most biologists believe it to be more like 5 – 30 million species. Based on the fossil record, which is incomplete, only about 2-4% of species that have ever lived are now alive; extinction is part of the natural process. Also based on the fossil record, it is estimated that historic rate is 1 species lost per 1,000,000 species, per year.

Since 1500 (AD) only 869 extinctions have been formally described. However, of the roughly 2 million known species, about 3% have a known conservation state (e.g. species census). Only this base figure is used to extrapolate the rate of loss of species at approximately 100 to 1,000 per million species per year. This rate of loss is comparable to five previously known “mass extinctions.”

A quick analysis of almost all the numbers reveals they are very rough estimates based on incomplete information. Not good statistics. This is where critics jump in first. Pointing out the lack of accuracy is usually taken a further step to ‘untrustworthy figures.’ Since the species loss estimates are often cited as evidence for global warming – and indeed most biologists point to human activity, including man-made climate change as a key reason for species loss – the lack of trustworthy estimates is considered (another) sign of the weakness of global warming theories, and the lack of a pressing need to do anything about it.

The counter argument is fairly simple: Rough or not (“precision” is not a word used around this kind of biology), the magnitude of the numbers estimated for species loss is far greater than the magnitude of possible error. In short, to ignore the existence of an ongoing “mass extinction” is to pin too much weight on a false sense of statistical accuracy. This argument is extended (by a Swedish study) that warned about any species loss over 10 times the background rate (10 species per million per year) as bad for human beings. Most biologists think the current rate is much higher than that. It’s that “much higher” expression that forms the margin (or cushion) to say that whatever the inaccuracy of estimates, the rate of loss is still too high – and it is indicative of something unusual, a mass extinction period.

Three comments: The scale of time and numbers – and ignorance – in the species loss statistics is so great, all parties generally feel free to throw around numbers without much reference to supporting evidence.

Much of the supporting evidence is not in the aggregate numbers, but in the painstaking individual studies of ecosystems, the fossil record at specific locations (and times), and the tracking of specific species (like hunting and fishing records for species). Biologists will point to ‘large numbers’ of such studies all pointing in the direction of increasing species loss in the last two hundred years.

In addition to the statistics, such as they are, there is an appeal to ‘common sense:’ It’s obvious that human beings are using and changing more of the world’s surface than ever before. This inevitably will impact other living things that use this same area. That impact will usually be negative; in fact, it will usually lead to extinction for some (or many) species.

In short, we’ll be arguing the magnitude of species loss for a long time to come, but that argument won’t change the fact that we are losing species faster than they are evolving.

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One Comment

  1. Jeff
    Posted December 23, 2010 at 12:52 am | Permalink

    Do you have any idea how long it takes for a species to evolve? millions of years!!!! Of course were not replacing the species were losing. God this world is stupid.

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