Dr. Nick Haddad,
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Show Wildlife Corridors Promote Animal, Plant Dispersal
of a landscape corridor connecting two patches
of habitat at the Savannah River Site National
Environmental Research Park.
by a North Carolina State University zoologist and
colleagues from the University of Florida and Allegheny
College says that landscape corridors – strips
of land connecting separated areas of similar habitat – are
effective in promoting animal and plant seed movement
to help sustain diversity and dispersal of native animals
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
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.
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
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
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.
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
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
Note to editors: An abstract of the paper follows.
of Landscape Corridors on Seed Dispersal by Birds”
J. Levey, Benjamin M. Bolker, Joshua J. Tewksbury,
University of Florida; Sarah Sargent,
Allegheny College; Nick M. Haddad, North Carolina
Published: July 1, 2005, in Science
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
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.