In “Calculations may have overestimated extinction rates” (New Scientist, 18 May 2011), Debora MacKenzie advises that a mathematical error undetected for decades may affect estimates of extinction rates (the “sixth great extinction,” said to be due to human dominance):
It is impossible to accurately measure extinction rates. Dozens of new species are identified each year, and counting those that disappear is hard because many are small and live in poorly studied, mainly tropical environments.
In fact, one third of species believed extinct have turned up again.
This could be due, in part, to the fact that the species most likely to be extinguished by human dominance may include species that are likely to avoid humans in any event. Their demise was prematurely announced on the basis that no one saw any of them for decades. But then one day …
MacKenzie explains that extinction rates
are often predicted from a mathematical model based on habitat loss, which is more easily measured. The larger the area you survey, the more species you encounter. Ecologists calculate a curve called the species area relationship (SAR) for an ecosystem by measuring the area they must survey to encounter the first individual of each successive species. To establish the number of extinctions caused by habitat destruction, they run the SAR calculation in reverse.
They had a sense that something was wrong with this approach, mathematically. Their mathematical model of data captured from forest plots worldwide always featured more species than expected. Then the penny dropped:
Using the reverse SAR method, biologists have assumed that a species is lost with the destruction of an area of habitat equivalent to the area needed to first encounter it. But in reality, the species is lost only with destruction of the habitat area that includes every individual of the species, which is always larger. Consequently, the SAR method loses species too fast.
Correcting for the species’ entire area showed that SAR gave losses at 83 and 165 per cent higher than the corrected method.
Actual extinction risks is a critical subject now because the economic downturn affects conservation budgets. The last thing conservation biologists need is bad data that results in blowing the budget on a phantom problem. In the worst case scenario, legislation or court decisions demand that the budget be spent solving a problem that doesn’t exist.