Geoscience Reference
In-Depth Information
ble measures of the interiors of home ranges or uses unstable measures of the
periphery.
Gautestad and Mysterud (1993, 1995) appear to have run their simula-
tions using simulated utility distributions so large that their simulated animals
could not use their whole “home ranges” within biological meaningful time
periods. When this is the case, estimates of home ranges should increase in size
as more and more simulated data points are used for the estimates. Indeed,
after thousands of data points were used, the estimated home range areas do
reach asymptotes at the areas of the utility distributions (Gautestad and Mys-
terud, personal communication), but note that this implies that equation 3.1
is not accurate for large
n
.
Some real animals may not use within a single year (or within some other
biologically meaningful period) all the areas with which they are familiar. This
raises the question of whether areas not used by an animal during a biologically
meaningful period of time should be included in the estimate of its home
range. Perhaps Gautestad and Mysterud's simulated utility distributions actu-
ally represent animals' cognitive maps. Is an animal's cognitive map its home
range? Or is its home range only the areas with which it is familiar
and
that it
uses? No definitive answers exist for these questions. Equation 3.1 may be true
for some animals. It is most likely to be true for animals that are familiar with
areas far larger than they can use in a biologically meaningful period of time.
And if equation 3.1 is true, then the time periods over which we estimate
home ranges may be as important as the numbers of locations. The time peri-
ods must be biological meaningful periods. To obtain accurate estimates of
animals' home ranges, we may need to collect as many data as possible, organ-
ized into biologically meaningful time periods.
Another solution exists to the contradiction (not necessarily an independent
solution). Gautestad and Mysterud estimated home range areas using 100 per-
cent minimum convex polygons (but using the fudge factor
Q
(
n
)), which use
only extreme, unstable data and must increase whenever an animal reaches a
new extreme location. They purposefully incorporated occasional sallies into
their model but did not exclude them from their home range calculations.
Small changes in sampling points at the extremes of animals' home ranges can
lead to huge differences in calculated home range areas although the animals
may not have changed use of the interiors of their home ranges. I calculated
home ranges areas for black bears using a kernel estimator, which emphasizes
central tendencies, which are stable; home range estimates from kernel estima-
tors do not change each time an animal explores a new extreme location.
Finally, Gautestad and Mysterud's model may be unrealistic. Any model of
