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WILDLIFE corridors that link larger pieces of unspoilt habitat can help some
species to survive, according to researchers who have been studying voles in the
forests of Washington state. The researchers have shown for the first time that
the genetic variation between different populations of the voles proves that
they have been using wooded corridors connecting stretches of the unlogged
habitat.

The voles travel along the corridors and often find a mate from a different
patch of forest. “This is the first clear demonstration of corridor use using
genetic techniques,” says Stephen Mech, now at the University of Memphis in
Tennessee. “We were able to show that corridors do improve movement and gene
flow across a fragmented landscape.”

Previous attempts to show that animals use wildlife corridors have involved
attaching radio transmitters to creatures and tracking them, or by tagging
animals and recapturing them later. But these techniques are very
labour-intensive, say the researchers, and they only show that animals have been
moving along a corridor. They do not prove that separate populations of animals
that are only connected by a corridor are interbreeding.

Mech and his colleagues at Washington State University in Pullman studied
different populations of red-backed vole (Clethrionomys gapperi) in a
forest in the Pend Oreille River basin. The forest had been partially logged 15
years ago. The voles only live under the protection of the mature closed-canopy
forest and they will not cross areas that have been logged.

The researchers looked at microsatellites—highly variable pieces of
DNA—to determine exactly how closely related the voles were. They studied
populations from three different habitats: voles living in zones with continuous
forest; those that had been separated by a logged area; and those that were
still linked by a corridor that the loggers had left.

Their findings are in line with the theoretical predictions of the value of
wildlife corridors. Populations of voles living in the same unbroken forest
tract were the most closely related. But those populations that were connected
by a corridor were significantly more closely related than voles that had been
isolated.

The team also compared the genetic variation of populations of deer mouse
(Peromyscus maniculatus), a species that is happy to cross logged areas
of forest. Here the populations in the different habitats showed no genetic
variation.

Nicholas Haddad, an ecologist at North Carolina State University in Raleigh,
says this comparison shows that the corridors will only benefit some animals.
“It helps shift the debate away from the expectation that every species should
use corridors, which has been a fault of past studies,” he says.

Mech hopes that microsatellite DNA analysis will be used to determine the
interactions of other populations of animals. “You can use these techniques at
much larger spatial scales, and for other animals that are harder to study by
mark-and-recapture,” he says.