When forests are divided by housing developments or logging, strips are sometimes left to allow animals to travel between remaining patches of habitat. But do such green corridors really work? Yes, researchers argue in the April issue of Conservation Biology. It's the first time genetic tools have been used to study the use of corridors.
A species faces new dangers when its population is fragmented. The smaller groups stand a greater chance of being wiped out by food shortages or other vagaries of nature. In addition, small populations can lose the genetic diversity that provides resilience to environmental change. To diffuse these threats, conservation biologists suggest creating or leaving corridors of the natural landscape to let animals move between the habitat patches. However, there are only scant data on whether animals do indeed travel along such strips, let alone whether they mate with inhabitants of other patches.
Now there's an answer. Researchers at Washington State University, Pullman, looked at populations of red-backed voles (Clethrionomys gapperi) in northeastern Washington. The voles prefer forests with closed canopies and can make do living in such sites in managed forests. Populations connected by corridors are more genetically similar than those separated by clear-cuts, the researchers found. That means the animals move through the corridors and breed with other populations, says study author Stephen Mech, now a conservation biologist at the University of Memphis in Tennessee. "Corridors are effective and can reduce, to some extent, the negative effects of fragmentation," Mech says. In managed forests, maintaining corridors is also "relatively cheap and easy," he adds.
"It's a solid study," says Nick Haddad, an ecologist at North Carolina State University in Raleigh, "and it's unique in that nobody's looked at the effects of corridors on gene flow."
The study also suggests that leaving forests untouched is an even better way to maintain gene flow. Populations linked only by corridors were not as closely related as those that could roam throughout continuous closed-canopy forests.