POP DENSITY ¼ POPULATION= VA effect à 1 þ :0001 þ FIXED AREA à 0
ð
Þ
ð22:1Þ
We can make use of either a fixed area or a variable area in our calculation of the
population density simply by multiplying one of them by one and the other by zero.
With this setup, the model can easily be run under alternative assumptions without
having to re-do parts of the diagram.
Figure 22.2 shows that part of the model that traces the birth rate history and the
extent to which that history is remembered. The resulting population and the
desired population then define a gap that is used to set the new birth rate, given
some sensitivity with which the population is able to react to the size of this gap
(Fig. 22.3). The gap itself is defined as the difference between the desired population size and the size of the population two time periods earlier, using the DELAY
built in function:
GAP ¼ DESIRED POP À DELAY POPULATION; 2
ð
Þ
ð 22:2Þ
In essence, we assume here that it takes two periods of time to obtain a
population census.
The GAP is then normalized (Fig. 22.3) by the current population level and multiplied by a reaction sensitivity to get the fractional birth rate (FRACTIONAL BR).
Fig. 22.1
Fig. 22.2
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22 Adaptive Population Control
ð
Þ
ð22:1Þ
We can make use of either a fixed area or a variable area in our calculation of the
population density simply by multiplying one of them by one and the other by zero.
With this setup, the model can easily be run under alternative assumptions without
having to re-do parts of the diagram.
Figure 22.2 shows that part of the model that traces the birth rate history and the
extent to which that history is remembered. The resulting population and the
desired population then define a gap that is used to set the new birth rate, given
some sensitivity with which the population is able to react to the size of this gap
(Fig. 22.3). The gap itself is defined as the difference between the desired population size and the size of the population two time periods earlier, using the DELAY
built in function:
GAP ¼ DESIRED POP À DELAY POPULATION; 2
ð
Þ
ð 22:2Þ
In essence, we assume here that it takes two periods of time to obtain a
population census.
The GAP is then normalized (Fig. 22.3) by the current population level and multiplied by a reaction sensitivity to get the fractional birth rate (FRACTIONAL BR).
Fig. 22.1
Fig. 22.2
184
22 Adaptive Population Control