6 Predicting How Populations Will Evolve
Before working on this section, click the Reset link at the upper-right corner of your Ducks & Gators window.
By now you are familiar with the biology of our virtual ducks. Genotype determines color. Color influences the risk of being eaten in any given close encounter with a gator. The density of gators influences the overall chance of surviving long enough to breed.
Choose a genetic model—a set colors for the three genotypes—that strikes you as interesting. Now click on the Monitor Evolution tab. You now have a population of ducks in which the frequency of allele A1 is 0.5—as is the frequency of allele A2:
Note that individual ducks of all three genotypes are present. For now, set the Number of gators to 6 and the Population Size to 200. Click the New ducks button.
- Predict how your population will evolve over several generations. That is—predict which color(s), and thus genotypes, will become common and which will become rare. Record your prediction, along with a brief explanation of your reasoning.
Click the Start button. Your ducks will swim around for 360 timesteps. Then the survivors will mate at random, lay eggs, and die. After a brief incubation period, the eggs will hatch into a new generation of ducks. The model will run for 15 generations.
- Was your prediction correct? Briefly explain.
Try a different genetic model—that is, a different set of colors for three genotypes. Try to set up a model that will result in your population evolving differently than it did before. If the frequency of A1 rose quickly in your previous model, try to set up a model in which the frequency of A1 rises slowly. Or a model in which the frequency of A1 falls. Or in which the frequency of A1 remains at an intermediate value.
Predict how your population will evolve over several generations. Record your prediction, along with a brief explanation of your reasoning.
Was your prediction correct? Briefly explain.
Experiment with different genetic models until you are confident that you can predict, at minimum, whether allele A1 will rise or fall in frequency. In the next section we will consider how you can predict how quickly it will do so.