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Modelling predator-prey interactions

1. Modelling the dynamics of a single population

Step 1
Add two  compartments to the desktop, and rename them rabbits and foxes
Step 2
Draw a  flow into the rabbits compartment, and rename it rabbit repro
Step 3
Draw a  flow out of the rabbits compartment, and rename it predation
Step 4
Draw an influence arrow from:
  • the rabbits compartment to the rabbit repro flow;
  • the rabbits compartment to the predation flow;
  • the foxes compartment to the predation flow;

Your model diagram should now look like this:

Step 5
Enter the following expression for the rabbit repro flow: 0.5*rabbits
Step 6
Enter the following expression for the predation flow: 0.01*rabbits*foxes
Step 7
Set the initial value for the rabbits compartment to 5000
Step 8
Set the initial value for the foxes compartment to 45
Step 9
“Build” the model.
Step 10
Change the Run Control settings:
  • Set Execute for to 50
  • Set Time step #1 to 0.1
Step 11
Set up a plotter display for the rabbits compartment.
Step 12
Run the model

Note that the population grows exponentially — there is nothing to hold it in check.


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