Testing the 1st Model

Figure 3 shows the simulated growth in the moth populations if the model is initialized with 2 black preadults, 2 white preadults and zero adults. The time graph shows the populations growing to a dynamic equilibrium of around 100 black adults and 100 white adults. With a total of around 200 adults, the moths are exposed to 60% losses in the preadult stage. This density dependent loss fraction is responsible for controlling the eventual size of the two populations.

Figure 3. Results from the introductory model.

The 200 adults could occupy a small area, so the population in a study region might be measured in the thousands. The magnitudes aren't of interest here. It's the ratio of the two populations that we want to study. Figure 3 shows that the two populations would maintain a 1:1 ratio over time. The 1:1 ratio makes sense because the two populations start out with the same number of individuals in the preadult stage; they are exposed to the same losses in both stages of their life cycle; and the females have the same brood sizes.

The 1:1 ratio makes sense for this model, but it does not match ratios observed in nature. Let's now consider whether genetic differences could lead to differences in the population sizes.