Managing for extinction

9 10 2009

ladderAh, it doesn’t go away, does it? Or at least, we won’t let it.

That concept of ‘how many is enough?’ in conservation biology, the so-called ‘minimum viable population size‘, is enough to drive some conservation practitioners batty.

How many times have we heard the (para-) phrase: “It’s simply impractical to bring populations of critically endangered species up into the thousands”?

Well, my friends, if you’re not talking thousands, you’re wasting everyone’s time and money. You are essentially managing for extinction.

Our new paper out online in Biological Conservation entitled Pragmatic population viability targets in a rapidly changing world (Traill et al.) shows that populations of endangered species are unlikely to persist in the face of global climate change and habitat loss unless they number around 5000 mature individuals or more.

After several meta-analytic, time series-based and genetic estimates of the magic minimum number all agreeing, we can be fairly certain now that if a population is much less than several thousands (median = 5000), its likelihood of persisting in the long run in the face of normal random variation is pretty small.

We conclude essentially that many conservation biologists routinely underestimate or ignore the number of animals or plants required to prevent extinction. In fact, aims to maintain tens or hundreds of individuals, when thousands are actually needed, are simply wasting precious and finite conservation resources. Thus, if it is deemed unrealistic to attain such numbers, we essentially advise that in most cases conservation triage should be invoked and the species in question be abandoned for better prospects

A long-standing idea in species restoration programs is the so-called ‘50/500’ rule; this states that at least 50 adults are required to avoid the damaging effects of inbreeding, and 500 to avoid extinctions due to the inability to evolve to cope with environmental change. Our research suggests that the 50/500 rule is at least an order of magnitude too small to 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.

We are battling to prevent a mass extinction event in the face of a growing human population and its associated impact on the planet, but the bar needs to be a lot higher. However, we shouldn’t necessarily give up on critically endangered species numbering a few hundred of individuals in the wild. Acceptance that more needs to be done if we are to stop ‘managing for extinction’ should force decision makers to be more explicit about what they are aiming for, and what they are willing to trade off, when allocating conservation funds.

CJA Bradshaw

(with thanks to Lochran Traill, Barry Brook and Dick Frankham)

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This post was chosen as an Editor's Selection for ResearchBlogging.orgResearchBlogging.org

Traill, L.W., Brook, B.W., Frankham, R.R., & Bradshaw, C.J.A. (2009). Pragmatic population viability targets in a rapidly changing world Biological Conservation DOI: 10.1016/j.biocon.2009.09.001


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18 10 2011
Not magic, but necessary « ConservationBytes.com

[...] a rather detailed, 10-page article in Trends in Ecology and Evolution that attacked our concept of generalizing minimum viable population (MVP) size estimates among species. Steve Beissinger of the University of California at Berkeley, one of the [...]

8 01 2011
S.A.F.E. = Species Ability to Forestall Extinction « ConservationBytes.com

[...] unrelated, Minimum viable population size: a meta-analysis of 30 years of published estimates and Pragmatic population viability targets in a rapidly changing world) have shown that there is in fact little variation in this number among the best-studied species; [...]

15 12 2009
A magic conservation number « ConservationBytes.com

[...] magic conservation number 15 12 2009 Although I’ve already blogged about our recent paper in Biological Conservation on minimum viable population sizes, American Scientist just did a great [...]

12 11 2009
Raise targets to prevent extinction « ConservationBytes.com

[...] targets to prevent extinction 12 11 2009 I know I’ve blogged recently about this, but The Adelaidean did a nice little article that I thought I’d reproduce here. The source [...]

21 10 2009
CJAB

The paper was covered in Time Magazine, New Scientist, Conservation Magazine and a heap of other media outlets worldwide. Check out http://conservationbytes.com/corey-j-a-bradshaw/recent-media/ for links.

16 10 2009
ResearchBlogging.org News » Blog Archive » Editor’s Selections: Ants, Extinctions, and Monogamy

[...] How many individuals of a species are required to stave off extinction from man-made causes? Sadly, more than we thought. [...]

10 10 2009
Twitter Trackbacks for Managing for extinction « ConservationBytes.com [conservationbytes.com] on Topsy.com

[...] Managing for extinction « ConservationBytes.com conservationbytes.com/2009/10/09/managing-for-extinction – view page – cached That concept of ‘how many is enough?’ in conservation biology, the so-called ‘minimum viable population size‘, is enough to drive some conservation practitioners batty. — From the page [...]

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