Perspectives OnLine - Summer 2001: Feature Article / "Corridors to Conservation"
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NC State University

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Corridors to Conservation
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Photo by Herman Lankford

f you were a nation and an outside super-power balkanized you into several no-longer-contiguous land masses, would your people survive? That’s not exactly the crux of current wildlife conservation research by N.C. State University’s Dr. Nick Haddad, but it’s close.

“Conservation biologists basically know species loss is caused by habitat loss and fragmentation. What we don’t know is the best way to save species, but we know that if we save habitat we can maintain species,” says Haddad, an assistant zoology professor who recently received the Achievement Award for New Scholars from the Conference of Southern Graduate Schools.

“The problem is that our case for saving habitat has been built more from intuition than from real hard-core evidence, and our work aims to correct that,” he says.

To discover the best ways to preserve biodiversity, Haddad and his research team examine small wildlife-containing areas — patches — and corridors, thin habitat strips such as power line easements and forested buffers along riverbanks that connect such patches.

“We study corridors because they connect otherwise isolated habitat areas, helping prevent population loss from isolated habitats,” Haddad says.

Haddad’s studies are set up on specially prepared experimental landscapes of U.S. Forest Service-controlled pine forest near the Savannah River Site, a nuclear power plant complex near Augusta, Ga.

Using open, non-forested corridors to connect isolated patches of same-size and same-shape habitat, he studies how these corridors affect plant and animal dispersal. To create valid comparisons, Haddad also studies some unconnected patches.

Ideally, Haddad says, corridors should encourage animals and plants to move among the patches. And such movement should lead to increased genetic diversity and allow plants and animals to colonize patches where their populations may have become extinct.

Photo by Herman Lankford

To test his theories, Haddad has concentrated for the past seven years on how corridors affect butterfly movement, although his group also studies corridor effects on small mammals and plants.

By releasing, then recapturing, hand-marked butterflies and noting their movements, he has shown that individual butterflies move in ways that allow him to observe and measure corridors’ effects.

Here are a few of those observations:

• Corridors increase patch-to-patch movements of some species usually confined to specific habitats such as fields and meadows: certain butterflies, other insect pollinators and some plants with seed dispersal restricted to specific habitats.


• Butterflies that usually don’t cross habitat boundaries — bouncing instead off boundaries and back into their own patches — use corridors to promote their dispersal.


• There has been an increase in butterfly populations already using natural corridors for movement, but no increase in those that can survive in a variety of habitats. To discover why, Haddad’s team is examining several hypotheses, including the possibility that higher population sizes are caused by increased movement between connected patches or by other changes in patch size and shape caused by corridors.


• There is no apparent effect on some butterflies — habitat generalist species that already move freely from patch to patch — nor on small mammals when their patches are connected to other patches via corridors.

“Corridors seem to be most effective when they contrast with surrounding unsuitable landscapes,” Haddad says. “They are the most important when the distance between corridors is large. Even low-quality corridors may be effective.

“And because habitat-restricted species are most often threatened by habitat fragmentation, corridors should provide an effective conservation tool for them,” he says.

Since corridors might not always affect every species positively, Haddad’s team now is studying how corridors influence mice responses to predators. The team also is studying plant diversity and gene flow in holly and wild chilies, as well as the role of seed dispersal and pollination in gene flow.

Haddad hopes to learn which species potentially would use corridors and to provide guidelines so wildlife conservationists, planners and land managers can advocate corridors to promote less-restricted wildlife movement, thus reducing population isolation and maintaining biodiversity in fragmented landscapes.

“The use of corridors for species and population conservation should be relatively easy politically because the corridors involve relatively small habitat areas and often follow areas that would be conserved anyway,” Haddad adds.

In new experiments, Haddad’s group is separating the effects of patch size and shape from corridor effects and testing how well their team’s small-scale experimental results can predict plant and animal distributions and population sizes on a much larger scale, for instance, in a managed pine forest.

Haddad’s Web page is at http://www4.ncsu.edu/~haddad/


 


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