Database Reference
In-Depth Information
1: ACORN MAST INDEX
2: ACORNS AVAILABLE
200.00
100.00
2
2
2
1
2
1
1
1
0.00
0.00
208.00
416.00
624.00
832.00
Fig. 7.7
Because DEER PERCENT HABITAT USE is a function of the presence of
acorns in the forest, we modeled acorn fall by using a sine function (Figure 7.6).
As soon as the acorn production is randomly selected in the oak-acorn sector (dur-
ing the last week of summer) and the acorn mast index is generated, a sine wave
of acorn availability develops, peaks during late September into October, and then
declines. Since we roughly correlated the percent habitat use with the acorn mast
index, we have assumed that acorn availability is proportional to the acorn mast
index.
Based on the appearance and disappearance of acorns, the deer increase and then
decrease their numbers in our model forest during the fall. Additionally, the max-
imum deer number is based on acorn production. In large mast years, more deer
should come into our model. Figure 7.7 displays the acorn mast index in the late
summer, and the subsequent autumnal acorn availability. Figure 7.8 shows the rela-
tionship between acorn mast index and deer wondering through our model.
Tick burdens on mice and deer are important, for we assumed that they represent
the carrying capacity for our tick stage populations. Tick burdens on mice were
assumed to be related to the number of tick larvae and nymphs found on mice during
the spring and summer seasons. We used data collected from the 1990 and 1992-
1997 seasons in Castle Rock State Park, Illinois. The data provided a mean number
of larvae and nymphs on mice for a particular sampling day during a particular
month. In order to ascertain what the tick burden would be for a particular week, we
considered the biology of tick feeding. For example, larvae require about 4 days to
successfully feed, whereas nymphs require about 4.5 days. In order to acquire the
weekly larval tick burden for this part of the model (Figure 7.9) we specified the
following relationship:
