Predator Prey Grass

This model is derived from Wilensky, U. (1997). NetLogo Wolf Sheep Predation model. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL. The following description is based on their description of their model.

In the original version (predprey.nva) wolves and sheep wander randomly around the landscape, while the wolves look for sheep to prey on. Each step costs the wolves energy, and they must eat sheep in order to replenish their energy – when they run out of energy they die. To allow the population to continue, each wolf or sheep has a fixed probability of reproducing at each time step. This produces interesting population dynamics, but is ultimately unstable.

This version includes grass (green) in addition to wolves and sheep. The behavior of the wolves is identical to the first variation, however this time the sheep must eat grass in order to maintain their energy – when they run out of energy they die. Once grass is eaten it will only regrow after a fixed amount of time. This variation is more complex than the first, but it is generally stable.

Nova Online: Predator Prey Grass (opens in new tab)

Running this model:
1. Click on the “Capture” button in the tool bar.
2. Click “Load” next to “Capture.”
3. Click “Exec” to run the model through multiple iterations. Click “Stop” to stop the graph.
4. To run the model step by step, click “Capture,” “Load,” “Init,” then “Step.”