18 October 2009

More than at risk

A new paper from the University of Adelaide and the Macquarie University, Australia, suggests that conservation biologists are making a big mistake.

They are setting too low the minimum number of individuals considered needed for a species to survive in the long term. This would underestimates the risk of extinction by not fully allowing for the dangers posed by the loss of genetic diversity.

The authors point out that, often, conservation biologists "aim to maintain tens or hundreds of individuals, when thousands are actually needed".

The article found that "populations smaller than about 5000 had unacceptably high extinction rates". According to the authors, this suggests that many targets for conservation recovery are simply too small to do much good in the long run.


Image from: http://susty.com/iucn-red-list-threatened-endangered-species/

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

Abstract: To ensure both long-term persistence and evolutionary potential, the required number of individuals in a population often greatly exceeds the targets proposed by conservation management. We critically review minimum population size requirements for species based on empirical and theoretical estimates made over the past few decades. This literature collectively shows that thousands (not hundreds) of individuals are required for a population to have an acceptable probability of riding-out environmental fluctuation and catastrophic events, and ensuring the continuation of evolutionary processes. The evidence is clear, yet conservation policy does not appear to reflect these findings, with pragmatic concerns on feasibility over-riding biological risk assessment. As such, we argue that conservation biology faces a dilemma akin to those working on the physical basis of climate change, where scientific recommendations on carbon emission reductions are compromised by policy makers. There is no obvious resolution other than a more explicit acceptance of the trade-offs implied when population viability requirements are ignored. We recommend that conservation planners include demographic and genetic thresholds in their assessments, and recognise implicit triage where these are not met.

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