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November 2009 Issue
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Raise targets to prevent extinction


Conservation biologists are setting their minimum population size targets too low to prevent extinction, according to a new study led by University of Adelaide researchers.

The study, published online recently in the journal Biological Conservation, showed 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.

"Conservation biologists routinely underestimate or ignore the number of animals or plants required to prevent extinction," said researcher Dr 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 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."

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 effectively stave off extinction," said Dr Traill. "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."

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," says Dr Traill. "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 researchers in the study were Associate Professor Corey Bradshaw and Professor Barry Brook, both from the University of Adelaide's Environment Institute, and Professor Richard Frankham, from Macquarie University's Department of Biological Sciences.

Meanwhile, Associate Professor Bradshaw was awarded this year's Royal Society of SA's prestigious Andrewartha Medal for his outstanding research as an early career scientist.

Society president Dr John Jennings said conservation ecologist Corey Bradshaw already had an impressive and rapidly building record of publications, including many in prestigious journals such as Nature.

"Associate Professor Bradshaw is addressing the modern concern with sustainability and what happens when ecosystems begin to unravel due to the effects of human activity," said Dr Jennings.

"He is also a highly successful facilitator being actively involved in building collaborative links between researchers throughout Australia and overseas."

Associate Professor Bradshaw is jointly appointed with SARDI's Marine Innovation SA and has particular strengths in conservation ecology and extinction dynamics, population dynamics, sustainable harvest and invasive species management. More recently, he directed his focus on shark conservation and ecology.

Story by Robyn Mills

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Illegal harvest and habitat loss have reduced the population of Black Rhino (Diceros bicornis) to a worldwide total of less than 2500.
Photo courtesy of Simon Morgan

Illegal harvest and habitat loss have reduced the population of Black Rhino (Diceros bicornis) to a worldwide total of less than 2500.
Photo courtesy of Simon Morgan

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