Questions for Week 9 Evolutionary Computation III

This week’s lab introduces a new modelling program, NetLogo. 

• Read the Introduction to what NetLogo does on p. 1 of the NetLogo User Manual
• Work through Tutorial #1 (pp. 17-24)  of the User Manual to learn about the Wolf Sheep Predation Model
• Read the background to the model from the Information Tab in the model window.
• Answer the questions below (these are the only ones you need to hand in).

1. a. Using the default parameters (including grass off), run the model 8 times. For each trial record whether the both sheep and wolves go extinct, or only wolves go extinct, or neither go extinct within 1000 generations.

b. Can you find a set of parameters (without setting the grass on) in which the sheep and wolf populations reliably do not go extinct. Explain your result.

2. a. Reset the model to the default parameters (reload the model if necessary). Turn on the grass and set the initial number of wolves to zero. Run the model several times (up to 500 generations). Do either sheep or grass go extinct in any trials? Compare your results to those of question 1 and explain the reasons for any differences.

b. Run one trial for 1000 generations and export the plot to an excel spreadsheet. Calculate the average number of sheep for the last 500 generations.

c. Look up the description of the model and describe what variables are represented by the sliders for grass-delay, init-sheep, sheep metabolism and sheep-reproduce. Run the model several times and see if it is stable for different parameter values.

d. Change each of the parameters in 2c in turn, keeping all other parameters the same as in 2b. For each modification, run one trial for 1000 generations, export the plot to an excel spreadsheet, and calculate the average number of sheep for the last 500 generations.

e. Collate your results from 2b. and 2d into a table. Explain the similarities and differences in the simulations for different parameters.

3. Reset the model to the default parameters. Turn the grass on.
a. Describe the behaviour of the model with the three organisms.
b. Test a variety of parameters and describe what sets of parameter settings would give
(i) fluctuating populations
(ii) stable non-fluctuating populations (non-extinct)
(iii) populations in which either or both sheep and wolves go extinct.

4. Try out other models from the models library, and describe one of the better ones. Explain briefly what it is designed to show and what results are given in the model.