A paper casting doubt on a widely used method of calculating extinction rates has fuelled furious debate in scientific circles, with some arguing it ignores important evidence and others saying it has been misinterpreted and sensationalised.
The paper, titled ‘Species–area relationships always overestimate extinction rates from habitat loss’ written by Fangliang He from the University of Alberta in Canada and Sun Yat-sen University in China, and Stephen Hubbell from the University of California in the U.S., examined the practice of using a species–area relationship curve to estimate extinction rates.
That means looking at how many species are found in habitats of increasing area, and then working backwards to calculate how many would disappear if particular proportions of the habitats were destroyed.
The researchers conducted new modelling and concluded that guessing the extinction rate using a SAR curve led to wildly overblown results, with some overestimations higher than 160%.
The authors were careful to stress that this did not mean that biodiversity loss was a non-issue.
“There is likely to be concern that these results could jeopardize conservation efforts and be falsely construed in some quarters to imply that habitat loss is not a problem. Nothing could be further from the truth,” they wrote.
“There is no doubt whatsoever that the Millennium Ecosystem Assessment has correctly identified habitat loss as the primary threat to conserving the Earth’s biodiversity, and the sixth mass extinction might already be upon us or imminent. Our results do indicate, however, that the backward SAR is not the correct way to estimate the magnitude of the current extinction event.”
The paper drew an angry response from Stuart Pimm, professor of Conservation Ecology at Duke University, who told widely read conservation website mongabay.com that the article was “inaccurate”.
“It considers only a very small part of the problem,” Professor Pimm told mongabay.com.
“The claims in the title are simply false and constitute nothing more than arrogant posturing on part of authors who would not have got their paper published had they not seen fit to ignore and misquote an extensive body of literature published in prestigious international journals.”
Others have sprung to the defence of the paper’s authors, saying critics have misinterpreted the article’s findings.
“The ultra-conservatives have grabbed this as a weakness in the ranks, fuelled by some knee-jerk responses by some sections of the scientific community,” said Professor Corey Bradshaw, the director of Ecological Modelling at the University of Adelaide.
“The rate of loss isn’t necessarily the same as the rate of discovery. That’s the point – and I stress, the ONLY point – of the He and Hubbell paper,” he told The Conversation.
“This isn’t a universal damnation of extinction rates, not by any stretch. All it says is in situations where the rates of extinction are based on accumulation curves only and where the species within are distributed patchily (as most species are at least at some spatial scale of measurement), in those cases you will overestimate the extinction rate. That’s all it says.”
Professor Bradshaw, who blogged about the paper on his website Conservation Bytes, said the paper’s conclusions had been blown out of proportion.
“The title is a bit unfortunate because, although strictly correct, you can read it uncritically and assume that all extinctions estimates are overestimates,” he said.
“It’s only one small dimension of the picture because you have various components pulling the extinction rates in different ways – partial information on distribution, partial information on loss rates and lag times.”