The most widely-used method for calculating species extinction is apparently “fundamentally flawed” and can overestimate extinction rates by as much as 160 percent. However, the authors of the study add that habitat loss is still the main threat to biodiversity.
As there are few ways of directly predicting extinctions, scientists use a mathematical model called the ‘species-area curve’. This starts with the number of species in an area and estimates how many species there will be as the area is increased. The calculations can then be reversed to estimate how many fewer species there will be when the amount of land decreases due to habitat loss.
However, the authors of this new study say that this method is too simplistic and fails to take into account the full complexity of what influences species numbers.
Co-authors Professor Stephen Hubbell, from the University of California, Los Angeles, and Professor Fangliang He, from Sun Yat-sen University, China, said “estimates based on this method are almost always much higher than actually observed.”
This may go some way to explain why past predictions of extinction rates – such as the 1980 US National Research Council report which predicted losses of millions of species by the year 2000 – have not been realised.
- Situation not as dire as believed
While the results of this study show that the problem of species extinction caused by habitat loss is not as dire as many conservationists and scientists had believed, some are concerned about the way the results could be interpreted.
Jean Christophe Vie, the IUCN’s Species Programme deputy director, said that it was good that it was a clear effort to “get the science right”, but that he is “worried about how this report could be used by people who are reluctant to take environmental issues seriously.”
“What is the actual concern is the rate of decline in populations,” he went on to say. “You do not see that many extinctions, but you do see many more species that are ending up with very small populations. So, focusing purely on extinctions is – to me – a problem.”
In their paper, Professors He and Hubbell warned that their study must not “lead to complacency about extinction [as a result of] habitat loss”, which was a “real and growing concern”.
“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”, said Hubbell.
“We have bought a little more time with this discovery, but not a lot.”
Read more about this at Nature – ‘Hidden assumption hypes species-loss predictions’.
Alex Royan, ARKive Species Text Author