(here 4 %) as the mean of this distribution. The STELLA diagram is shown in
Fig. 3.1. It contains a module that calculates the average population size AVG POP
over time by summing the population over time and dividing by time.
The results of this model are shown in Fig. 3.2.
The remarkable result is that the population reaches a somewhat steady
condition—it is not expanding off to infinity at a net 3 % growth rate as implied
by the net birth rate of 7 %. At first the population grows exponentially but it then
Fig. 3.1
Fig. 3.2
3.1 Risky Population Model
43
Fig. 3.1. It contains a module that calculates the average population size AVG POP
over time by summing the population over time and dividing by time.
The results of this model are shown in Fig. 3.2.
The remarkable result is that the population reaches a somewhat steady
condition—it is not expanding off to infinity at a net 3 % growth rate as implied
by the net birth rate of 7 %. At first the population grows exponentially but it then
Fig. 3.1
Fig. 3.2
3.1 Risky Population Model
43