Conservation biologists are setting their minimum population size
targets too low to prevent extinction.
That’s according to a new study by University of Adelaide and
Macquarie University scientists which has shown 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.
The findings have been published online in the journal Biological
"Conservation biologists routinely underestimate or ignore the number
of animals or plants required to prevent extinction," says lead author
Dr Lochran Traill, from the University of Adelaide’s Environment
"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," says 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."
Team member Professor Richard Frankham, from Macquarie University’s
Department of Biological Sciences, says: "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."
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."
Source : University of Adelaide