Database Reference
In-Depth Information
CARRY R2
CARRY R1
DUMP2
DUMP1
R COUNT1
R COUNT2
K2
K1
Fig. 15.1
where MOD is the built-in function that computes the remainder (modulo) of a
division—in our case the division of TIME by 52 (Figure 15.1). We make use of
the MOD function here to set up a recurring counter. Note that with some DT val-
ues, whose fractional representation does not have
n
2
in the denominator, STELLA
rounds the remainder in the MOD function; so the re-starting values of R COUNT1
and R COUNT2 for each new year are not exactly zero.
When overcrowding develops, healthy adult insects leave their home field and
join the other population. Furthermore, it is assumed that 10% of healthy adults
migrate under all circumstances. Changes in population sizes are no longer only
dependent on births and on deaths but additionally on migration.
The model is composed of the following additional modules. The first captures
the population dynamics of healthy insects in the first field (Figure 15.2).
The second module is set up to calculate the change in nymph and adult popula-
tion in field 1 that are affected by the disease (Figure 15.3).
A virtually identical second set of these modules captures the dynamics of the
populations in field 2. Parameters relevant to both healthy and diseased insects in
both fields are calculated in the following modules. They include
•
a calculation of the total number of adults in each fields, ALL ADULTS 1 and
ALL ADULTS 2;
•
the ratio of the total number of adults in each region to the carrying capacity of
the respective region, FRXNL CAP1 and FRXNL CAP2;
•
experimental maturation rates for healthy and diseased insects, F1 H, F1 D;
•
model maturation rates U1 H, U1 D;
•
experimental laying rates A2 H, A2 D;
•
experimental daily adult survival fractions per stage, S2 H , S2 D; and
•
adult mortality rates B1 H, B1 D, B2 H, B2 D.
The latter are calculated in the module of Figure 15.4, using the following exponen-
tial functions:
B1 H
=(
1
−
EXP
(
LOGN
(
S1 H
)
∗
F1 H
∗
DT
))
/
DT
(15.5)
B1 D
=(
1
−
EXP
(
LOGN
(
S1 D
)
∗
F1 D
∗
DT
))
/
DT
(15.6)
