Roadsides may provide butterfly corridors

Iowa has among the highest road density nationwide and, in a conservation twist, this may actually benefit some kinds of wildlife. The state has lost more than 99% of its tallgrass prairie, and restoring prairie along roadsides may help butterflies, according to new research in the April issue of Conservation Biology.

This is the first study showing that restoring native habitat along roadsides can benefit wildlife.

"Our data offer some preliminary evidence that restored roadsides may be able to link habitat," say Leslie Ries, who did this work while at Iowa State University in Ames and is now at Northern Arizona University in Flagstaff, and her two co-authors.

Conservationists have suggested that restoring native plants along roadsides could both connect habitat fragments and increase the overall amount of habitat. Roadsides comprise about 20 million acres of land in the U.S. and many kinds of animals -- including insects, amphibians, birds and small mammals -- use roadside vegetation as habitat.

While Iowa's roadsides have traditionally been monocultures of non-native grasses, some counties in the state have begun reintroducing native prairie plants. Many of these plants provide nectar for adult butterflies and food for caterpillars. Nearly half of Iowa's 44 at-risk butterflies depend on prairies.

To determine how restoring prairie along roads affects butterflies, Ries and her colleagues compared the abundance and diversity of butterflies in 12 prairie roadside areas (4 native and 8 restored) and 12 nearby roadsides that were dominated by weeds or non-native grasses. All the roadsides were bordered by row crops. The butterflies were

The researchers found that prairie roadsides benefitted the regal fritillary and other butterflies that were more sensitive to habitat disturbance such as row-cropping and urban development. These "habitat-sensitive" butterflies were both more diverse and more abundant along prairie roadsides. For instance, compared to grassy roadsides, prairie roadsides had twice as many species of habitat-sensitive butterflies and five times as many of them overall.

Moreover, butterflies in prairie roadsides were less likely to cross the road: the number of butterflies that turned at the edge of road and went back into the roadside was 77% in prairie roadsides compared with roughly 50% in grassy or weedy roadsides. The fact that butterflies were more likely to stay in prairie roadsides has two implications: first, their risk of death may be lower and second, they might use this habitat as corridors or stepping stones between prairie fragments, say Ries and her colleagues.

However, living along roads has several drawbacks, including being hit by cars and being contaminated by the heavy metals in exhaust. So the big question about restoring roadsides is: Do the benefits of this additional habitat outweigh the risks? "We don't know the answer to this for any species," says Ries. The answer may vary with the species, which means managers may have to attract some species while repelling others.

In addition to helping butterflies, roadsides could help insect pollinators, which are imperiled nationwide. Ries proposes to study this in Arizona, where roadsides collect twice as much water as the bordering desert habitat, suggesting that even unrestored roadsides could provide valuable habitat for pollinators.

Ries' co-authors are: Diane Debinski and Michelle Wieland, both of Iowa State University in Ames.

For faxes of papers, contact Robin Meadows [email protected]

More information about the Society for Conservation Biology can be found at http://conbio.net/scb/