In addition, says Dr. Nick Haddad, associate professor of zoology at NC State and a co-author of the paper describing the research, the study shows that easy-to-measure animal behaviors can serve as predictors for whether landscape corridors will be effective dispersal mechanisms for those specific animals and the plants they eat.
The research is published in the July 1 edition of Science.
Haddad and other scientists have published a number of studies on the efficacy of landscape corridors in promoting dispersal of animals. Haddad says corridors essentially reconnect habitats that were once connected before fragmentation – brought on by urban or farm development, for example – threatened native animals and plants. Lack of dispersal means animals and plants become vulnerable to being lost or developing negative genetic effects found in small populations, like those acquired through inbreeding, Haddad says.
The researchers tested their corridors at the Savannah River Site National Environmental Research Park, a federally protected area on the South Carolina-Georgia border that is mostly dominated by pine tree forests. At the researchers' request, the U.S. Forest Service arranged eight similar sites; each site included five areas cleared of trees. The central patch was connected to one other patch by a 150-meter-long, 25-meter-wide corridor, while three other patches were isolated from the central patch – and themselves – by forest.
In the study, the researchers found that Eastern Bluebirds, one of the major seed dispersers in South Carolina, were 31 percent more likely to be found in the center of connected patches than the center of unconnected patches. The study also showed that seeds from wax myrtle plants – found in the fecal matter of the birds – were 37 percent more likely to be found in traps in the center of connected patches than in traps in the center of unconnected patches.
These results – showing increased movement of animals and plants in habitats connected by corridors – mimicked other previously published studies done by these and other researchers, Haddad says.
But this study has an even more important and broad impact, according to Haddad.
The researchers observed behaviors of bluebirds during the course of the study and found that the birds were not necessarily using the landscape corridors, but were instead often traveling along the edges of the corridors.
Using these behaviors in a predictive model, the researchers arrived at estimates of the numbers of birds distributing seeds to both the connected and unconnected patches.
The study shows a "tight fit" between predictions and actual seed movement.
"From behavioral studies, we can predict how animals will move in large-scale landscapes," Haddad says. "This study is specifically designed to understand how species might move through corridors. But understanding behavioral approaches is important in any context where you're worried about the spread of organisms through a landscape, like the spread of non-native invasive species or birds that carry diseases."
The study was funded by the National Science Foundation and by the Department of Energy-Savannah River Operations Office through the U.S. Forest Service Savannah River Institute.
Note to editors: An abstract of the paper follows.
"Effects of Landscape Corridors on Seed Dispersal by Birds"
Authors: Douglas J. Levey, Benjamin M. Bolker, Joshua J. Tewksbury, University of Florida; Sarah Sargent, Allegheny College; Nick M. Haddad, North Carolina State University
Published: July 1, 2005, in Science
Abstract: Habitat fragmentation threatens biodiversity by disrupting dispersal. The mechanisms and consequences of this disruption are controversial, primarily because most organisms are difficult to track. We examined the effect of habitat corridors on long-distance dispersal of seeds by birds, and tested whether small-scale (<20 meters) movements of birds could be scaled up to predict dispersal of seeds across hundreds of meters in eight experimentally fragmented landscapes. A simulation model accurately predicted the observed pattern of seed rain and revealed that corridors functioned through edge-following behavior of birds. Our study shows how models based on easily observed behaviors can be scaled up to predict landscape-level processes.
Journal
Science