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We choose to separate the effects of hunting from those of the disease. The results
are shown in Figure 15.9. Note that the fox population declines to an average steady
cycle with a mean of about 22,000 foxes, this is a 72 percent reduction from initial
population levels. From this model run, our estimate of the effect of rabies is that
the population will suffer a severe setback (a reduction to one-quarter of the healthy
mean) but the fox does not disappear from the landscape. To ecologists, this is the
good news: the fox is not eliminated by the disease. To public health officials, the
news is not so good: diseased foxes remain in the state, albeit at much reduced lev-
els; therefore, some threat of spread of the disease into the pet population remains.
15.2.15 Hunting Pressure
We then introduced the full effect of the estimated current level of hunting. The
results indicate that the healthy fox population disappears over a 25-year period at
current rates. Our hunting rates are constant from year to year however, an assump-
tion which cannot be totally accurate. Some of the fox hunting is for pelts, and that
portion (unknown) of the hunting pressure would fluctuate with the price of pelts
and the availability of foxes.
The Illinois fox population, subjected to current hunting pressures, declines to
essentially zero over the ensuing 25 years with the concurrent introduction of the
disease. We made several more runs with the hunting pressure reduced to one-half
and then one-quarter of the full-scale current hunting pressure. As one reduces the
hunting pressure, the fox population approaches the no-hunting, cyclic result dis-
cussed earlier, , with most of the recovery made when the hunting pressure was
halved. It was possible to show that a small amount of hunting will reduce the num-
ber of rabid foxes in the endemic stage of the disease.
15.2.16 Controlling the Disease
Control of wildlife disease is often expensive. Evaluation of control measures in dy-
namic modeling facilitates decision making and gives policy makers additional in-
formation and insight into the effects of the control measures tested. Use of dynamic
models in the study of wildlife diseases also identifies areas where information is
lacking.
Control attempts without clear knowledge of the spatial qualities of the studied
population or disease can produce less than optimal results
47
.Bogel et al. suggested
that methods used in advance of a rabies epizootic would not be effective in con-
trolling the spread of the disease once the epizootic has begun
48
. Additional work
47
Cowan, I.M. 1949. Journal of Mammalogy 30 396-398.
48
B ogel, K., H. Moegle, W. Krocza, and L. Andral. 1981. Bulletin of the World Health Organiza-
tion 59 269-279.
