Conservation targets too small to fight extinction, study argues

A new study issues a stern warning: Conservation biologists are setting their minimum population size too low to prevent extinction.

This study has already received substantial press. At CM, we typically avoid studies already in the spotlight in favor of research that would otherwise pass under the radar screen. However, we felt that the findings in this study are particularly pertinent and deserve wide consideration. Plus, our friend Corey at ConservationBytes is a co-author.

The researchers conducted a review of minimum population size requirements for species based on empirical and theoretical estimates made over the past few decades. They found that the scientific literature overwhelmingly shows that thousands of individuals are required for a population to have a likely chance of surviving environmental fluctuation and catastrophic events.

This figure contrasts with population targets in the hundreds often set by scientists and policy makers. Lead author, Lochran Traill from the University of Adelaide, states:

"Conservation biologists routinely underestimate or ignore the number of animals or plants required to prevent extinction. Often, they aim to maintain tens or hundreds of individuals, when thousands are actually needed. Our review found that populations smaller than about 5000 had unacceptably high extinction rates. This suggests that many targets for conservation recovery are simply too small to do much good in the long run."

The researchers reject the popular notion of the '50/500' rule in species conservation programs. The idea behind this rule is that an absolute minimum number of individuals (i.e. 50) is needed to avoid the damaging effects of inbreeding and a larger number (i.e. 500) is preferable in order to avoid extinction due to the inability to adapt to otherwise harmful environmental changes. According to Traill:

Our research suggests that the 50/500 rule is at least an order of magnitude too small to effectively stave off extinction. This does not necessarily imply that populations smaller than 5000 are doomed. But it does highlight the challenge that small populations face in adapting to a rapidly changing world.

The study calls for a raising of the bar among scientists and policy makers. Otherwise we're just managing for extinction.

--Reviewed by Rob Goldstein

Source:	Biological Conservation
Title:	Pragmatic population viability targets in a rapidly changing world
Authors:	a) Lochran Traill, a) Barry Brook, b) Richard Frankham and a) Corey J.A. Bradshaw
	a) University of Adelaide, Australia b) Macquarie University, Australia