Using diffusion models to simulate the effects of land use on grizzly bear dispersal in the Rocky Mountains
Authored by Randall B Boone, ML Hunter
Date Published: 1996
DOI: 10.1007/bf02087113
Sponsors:
United States Department of Agriculture (USDA)
Platforms:
Microsoft Visual Basic
Model Documentation:
Other Narrative
Model Code URLs:
Model code not found
Abstract
Timber harvests proposed for Trail Creek Watershed, in southwestern
Montana, U.S.A., have been opposed because grizzly bear (Ursus arctos
horribilis) dispersal from northern Montana wildernesses into the
Greater Yellowstone Ecosystem may be less likely. We used an
individual-based model to simulate grizzly bear responses to: 1)
region-level management practices represented by ownership patterns, and
2) watershed-level changes in habitat availability due to proposed
harvests and road building. We assigned permeabilities (i.e., values
that represent how easily a bear can move through a patch) to ownership
blocks (region-level) and habitat patches (watershed-level) based upon a
literature review, and used a correlated random-walk diffusion model to
simulate movements. Simulated bears were placed into rasterized
landscapes in a stratified random manner. At the regional level, bears
moved less than or equal to 1500 times (i.e., approximate to 1530 km), and their destinations were tallied. At the watershed level, the number
of moves required for bears to leave the watershed were tallied.
Sensitivity analyses were used to determine the variability of the
results with respect to changes in some parameters of interest (i.e,, permeabilities of private lands, harvest permeabilities, and disturbance
indices).
With the permeability of private land set at 50 (range: 0 to 99), simulated grizzlies did not disperse from the Scapegoat and Bob Marshall
Wildernesses into Yellowstone National Park (0 of 10000 simulated
individuals), Under the assumptions of this model, a linkage between the
wildernesses in northern Montana and Yellowstone does not appear to
exist. However, a significant number of simulated grizzlies (41\%)
dispersed from Anaconda Pintler Wilderness, which is near Trail Creek
Watershed, into the wilderness ES in eastern Idaho. A linkage may exist
between these sites.
At the watershed-level, removal of forest habitat under proposed Harvest
I (1.77\% of the watershed cut) led to simulated grizzlies using
slightly more moves (i.e., less than or equal to 5.6\%, P = 0.042) to
exit the watershed than under existing conditions. Harvests of 3.5\% of
the watershed (planned Harvest Il) did not alter the number of moves
required to exit the watershed (P = 0.068). When disturbances associated
with roads and harvests were also examined, large increases in number of
movements required to exit the watershed occurred (less than or equal to
151\%, P = 0.002). These analyses suggest that grizzly bears would be
disturbed while timber harvests were ongoing, but that long-term changes
in movement would not occur if roads were closed following harvests. The
analyses demonstrate the utility of applying individual-based diffusion
models to landscape-level movements of animals, and identifies the need
for telemetry studies to determine movement rates through specific
habitats.
Tags
movements
Conservation
Food-habits
Resource-extraction industries