Database Reference
In-Depth Information
Chapter 15
Spatial Pestilence Dynamics
15.1 Diseased and Healthy Immigrating Insects
This chapter expands and refines some earlier models, which included life stages
of insects, by specifically distinguishing two cohorts of a population infected with
a disease. The two populations modeled here are insects that suffer from a disease
that increases mortality for the infected nymphs and adults and also decreases their
egg-laying rate. Unlike the previous chapters, we assume two populations of insects
living in two fields. One of the fields has generally better living conditions than the
other, although a current year's carrying capacities are randomly generated and there
is some overlap in the ranges within which carrying capacities fluctuate.
The carrying capacities of the two fields have a direct effect on birth rates. The
carrying capacities of the two fields are defined as
K1
=
IFCARRY R1
666 THEN2
ELSE IF CARRY R1
>.
<.
333 THEN
.
5
(15.1)
ELSE1
and
K2
=
IF CARRY R2
666 THEN 4
ELSE IF CARRY R2
>.
<.
333 THEN 1
(15.2)
ELSE 2
respectively, with CARRY R1 and CARRY R2 as random numbers between 0 and 1.
These random numbers are calculated in the following module with
R COUNT1
=
IF MOD
(
TIME
,
52
)=
0 THEN RANDOM
(
0
,
1
)
/
DT ELSE 0
(15.3)
and
R COUNT2
=
IF MOD
(
TIME
,
52
)=
0 THEN RANDOM
(
0
,
1
)
/
DT ELSE 0
.
(15.4)
