Wolf Sheep Predation

NetLogo Web & Network Notebook

Wolf Sheep Predation Model

NetLogo Web

This model explores the stability of predator-prey ecosystems. Such a system is called unstable if it tends to result in extinction for one or more species involved. In contrast, a system is stable if it tends to maintain itself over time, despite fluctuations in population sizes

one unit of energy is deducted for every step a wolf takes - when running the sheep-wolves-grass model version, one unit of energy is deducted for every step a sheep takes

There are three monitors to show the populations of the wolves, sheep and grass and a populations plot to display the population values over time.

If there are no wolves left and too many sheep, the model run stops.

When running the sheep-wolves model variation, watch as the sheep and wolf populations fluctuate. Notice that increases and decreases in the sizes of each population are related. In what way are they related? What eventually happens?

In the sheep-wolves-grass model variation, notice the green line added to the population plot representing fluctuations in the amount of grass. How do the sizes of the three populations appear to relate now? What is the explanation for this?

Why do you suppose that some variations of the model might be stable while others are not?

Try adjusting the parameters under various settings. How sensitive is the stability of the model to the particular parameters?

Can you find any parameters that generate a stable ecosystem in the sheep-wolves model variation?

Try running the sheep-wolves-grass model variation, but setting INITIAL-NUMBER-WOLVES to 0. This gives a stable ecosystem with only sheep and grass. Why might this be stable while the variation with only sheep and wolves is not?

Notice that under stable settings, the populations tend to fluctuate at a predictable pace. Can you find any parameters that will speed this up or slow it down?

https://ccl.northwestern.edu/netlogo/models/WolfSheepPredation