Geoscience Reference
In-Depth Information
Table A1.
(continued)
Node
Name
Node Title
Node Description
States
Expressing this value as a change from the current time allows the model to show that
conditions improve in a hind cast back to the period of 1985-1995.
This measurement is available only from the polar basin ecoregions because all other
management units occur in areas that are essentially all shelf. hence, the measurement
of distance to shelf means nothing.
M
Ecoregion
Geographic region used for combining populations of polar bears.
Polar_Basin_
Divergence
Polar_Basin_
Convergence
Archipelago
Seasonal_Ice
Output Nodes
a
D1
Overall
Population
Outcome
Composite influence of numerical response and distribution response.
larger
same_as_now
smaller
rare
extinct
C4
Numerical
Response
This node represents the anticipated numerical response of polar bears based upon the
sum total of the identified factors which are likely to have affected numbers of polar
bears in any particular area.
increased_density
same_as_now
reduced_density
rare
absent
C3
Distribution
Response
This is the sum total of ecological and human factors that predict the future distribu-
tion of polar bears.
Reduced but Resident: habitat has changed in a way that would likely lead to a reduced
spatial distribution (e.g., because of avoidance of a human development or because sea
ice is still present in the area but in more limited quantity). Bears would still occur in
the area, but their distribution would be more limited. Transient = habitat is seasonally
limited or human activities have resulted in a situation where available ice is precluded
from use on a seasonal basis.
same_as_now
reduced_but_resident
transient_visitors
extirpated
Summary Nodes
C2
Pollution
This is the sum of pollution effects from hydrocarbon discharges directly into arctic
waters and from other pollutants brought to the Arctic from other parts of the world.
The FWS listing proposal included pollution as one of the “other factors” along with
direct human bear interactions that may displace bears or otherwise make habitats less
reduced
same_as_now
elevated
greatly_elevated
satisfactory. I viewed the main effect of pollution as a potential effect on population
dynamics. Clearly, severe pollution as in an oil spill, for example, could make habitats
unsatisfactory and result in direct displacement. The main effect, however, is likely
to be how pollution affects immune systems, reproductive performance, and survival.
hence, I have included input from this node as well as from the human disturbance
node into both the habitat and the abundance side of the network by including input
from factor E into both population effects and habitat effects.
C1
human
Disturbance
This node expresses the combination of the changes in “other” direct human dis-
turbances to polar bears. This does not include changes in sea ice habitat. Nor does
it include the contamination possibilities from hydrocarbon exploration. Those are
covered elsewhere. It does cover the direct bear-human interactions that can occur in
association with industrial development.
reduced
same_as_now
elevated
greatly_elevated
h
Crowding
Tolerance
The degree to which polar bears may tolerate increased densities that may result from
migration of bears from presently occupied regions that become unsuitable to other
regions already occupied by polar bears.
none
moderate
high
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