Exaggerating Species Extinction

A new paper in Nature has sparked a firestorm of debate over species extinction rates. The paper, by two ecologists, shows how the use of the species-area curve produces inflated projections of species extinction rates. As an accompanying article in Nature explains:

The most common method of predicting extinction rates relies on the species–area curve, the mathematical relationship showing that larger areas tend to contain greater numbers of species.

Researchers typically extrapolate backwards from this curve to calculate how many extinctions can be expected from a given amount of habitat loss. But that is inaccurate, say the study authors, because the area that must be removed to cause extinction is always larger than the area needed to encounter a species for the first time.

“Extrapolating backwards makes a hidden assumption that any loss of population, regardless of how small, commits a species to extinction — which is not reasonable,” says Stephen Hubbell, a theoretical ecologist at the University of California, Los Angeles, and co-author of the paper.

As you might expect, the paper has sparked substantial criticism and debate, as noted in Greenwire and on Dot Earth, even though there have been concerns about the reliability of the species-area curve for some time. One reason for the intense debate is the well-intentioned fear that research of this sort will dampen concerns about biodiversity loss. If, as the study suggests, expected extinction rates are far lower than conventional estimates, will this lessen the urgency of biodiversity conservation? Perhaps, but that would not justify relying upon erroneous extinction estimates. Moreover, even if projected species extinction is only half of conventional estimates, it is still a serious concern.