Small thinking in conservation could help drive many of the world’s plants and animals to extinction, according to Australian researchers.

Populations of endangered species aren’t likely to survive global climate change or habitat loss unless they number around 5,000 mature individuals or more, warn the scientists from the University of Adelaide and Macquarie University. Their findings were published this week in the journal Biological Conservation.

“Conservation biologists routinely underestimate or ignore the number of animals or plants required to prevent extinction,” said lead author Lochran Traill from the University of Adelaide’s Environment Institute. “Often, they aim to maintain tens or hundreds of individuals, when thousands are actually needed. Our review found that populations smaller than about 5,000 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.”

A longstanding idea in species restoration programmes 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 are needed 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 effectively stave off extinction,” Traill said. “This does not necessarily imply that populations smaller than 5,000 are doomed. But it does highlight the challenge that small populations face in adapting to a rapidly changing world.”

“Genetic diversity within populations allows them to evolve to cope with environmental change, and genetic loss equates to fragility in the face of such changes,” said Richard Frankham from Macquarie University’s Department of Biological Sciences.

Conservation biologists worldwide are battling to prevent a mass extinction event in the face of a growing human population and its associated impact on the planet.

“The conservation management bar needs to be a lot higher,” Traill said. “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.”

Other co-authors of the study include Corey Bradshaw and Barry Brook, both from the University of Adelaide’s Environment Institute.

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