Biólogos evolucionistas erraram feio em matemática: cálculo das taxas de extinção exageradas

sexta-feira, maio 20, 2011

Species Extinction Rates Have Been Overreported, New Study Claims -- But Global Extinction Crisis Remains Very Serious

ScienceDaily (May 18, 2011) — The most widely used methods for calculating species extinction rates are "fundamentally flawed" and overestimate extinction rates by as much as 160 percent, life scientists report May 19 in the journal Nature.

While methods currently used to estimate extinction rates may be erroneous, Earth is losing habitat faster than at any time over the last 65 million years, experts say. (Credit: © kikkerdirk / Fotolia)

However, while the problem of species extinction caused by habitat loss is not as dire as many conservationists and scientists had believed, the global extinction crisis is real, says Stephen Hubbell, a distinguished professor of ecology and evolutionary biology at UCLA and co-author of the Nature paper.

"The methods currently in use to estimate extinction rates are erroneous, but we are losing habitat faster than at any time over the last 65 million years," said Hubbell, a tropical forest ecologist and a senior staff scientist at the Smithsonian Tropical Research Institute. "The good news is that we are not in quite as serious trouble right now as people had thought, but that is no reason for complacency. I don't want this research to be misconstrued as saying we don't have anything to worry about when nothing is further from the truth."

Because there are very few ways of directly estimating extinction rates, scientists and conservationists have used an indirect method called a "species-area relationship." This method starts with the number of species found in a given area and then estimates how the number of species grows as the area expands. Using that information, scientists and conservationists have reversed the calculations and attempted to estimate how many fewer species will remain when the amount of land decreases due to habitat loss.

"There is a forward version when we add species and a backward version when we lose species," Hubbell said. "In the Nature paper, we show that this surrogate measure is fundamentally flawed. The species-area curve has been around for more than a century, but you can't just turn it around to calculate how many species should be left when the area is reduced; the area you need to sample to first locate a species is always less than the area you have to sample to eliminate the last member of the species.

"The overestimates can be very substantial. The way people have defined 'extinction debt' (species that face certain extinction) by running the species-area curve backwards is incorrect, but we are not saying an extinction debt does not exist."

How confident is Hubbell in the findings, which he made with ecologist and lead author Fangliang He, a professor at China's Sun Yat-sen University in Guangzhou and at Canada's University of Alberta?

"100 percent," he said. "The mathematical proof is in ouu paper."

Read more here/Leia mais aqui: Science Daily


Species–area relationships always overestimate extinction rates from habitat loss

Fangliang He & Stephen P. Hubbell

Corresponding authors

Nature 473, 368–371 (19 May 2011) doi:10.1038/nature09985Received 21 December 2010 Accepted 08 March 2011 Published online 18 May 2011

Extinction from habitat loss is the signature conservation problem of the twenty-first century1. Despite its importance, estimating extinction rates is still highly uncertain because no proven direct methods or reliable data exist for verifying extinctions. The most widely used indirect method is to estimate extinction rates by reversing the species–area accumulation curve, extrapolating backwards to smaller areas to calculate expected species loss. Estimates of extinction rates based on this method are almost always much higher than those actually observed2, 3, 4, 5. This discrepancy gave rise to the concept of an ‘extinction debt’, referring to species ‘committed to extinction’ owing to habitat loss and reduced population size but not yet extinct during a non-equilibrium period6, 7. Here we show that the extinction debt as currently defined is largely a sampling artefact due to an unrecognized difference between the underlying sampling problems when constructing a species–area relationship (SAR) and when extrapolating species extinction from habitat loss. The key mathematical result is that the area required to remove the last individual of a species (extinction) is larger, almost always much larger, than the sample area needed to encounter the first individual of a species, irrespective of species distribution and spatial scale. We illustrate these results with data from a global network of large, mapped forest plots and ranges of passerine bird species in the continental USA; and we show that overestimation can be greater than 160%. Although we conclude that extinctions caused by habitat loss require greater loss of habitat than previously thought, our results must not lead to complacency about extinction due to habitat loss, which is a real and growing threat.

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Eu queria ver a cara da Galera dos meninos e meninas de Darwin, oops, desta galera não, mas da turma dos ecochatos que ficam assustando a humanidade como verdadeiros Zés do Apocalipse falando da iminência de um desastre ecológico de escala mundial.

Qual a lição que se aprende deste artigo? Que além de Biologia, é preciso fazer o dever de matemática. 160% de erro é erro pra dedéu, mano!!!