Exploring Netlogo Models

Wolf Sheep Predation: We discovered that when there is infinite grass, the population is unstable.  Either the wolves die out, or, usually, the sheep have a population explosion, then the wolves have a population explosion, then the sheep die out, then the wolves die out.  Regardless of how we changed the variables, we couldn’t make it sustainable.  When there was finite grass, as long as the variables weren’t too extreme, everything would be stable and periodic.

Frogger: We explored getting the frog to the lily pads. It was hard at the very end. We also didn’t realize that when you got a frog to a lily pad, another one would spawn at the bottom. It took us a while to realize that to win the level you had to get 5 frogs to the lily pads, and each to a different lily pad. Luckily, the timer restarted with each new frog spawn, but we still couldn’t finish the level.

For Rebellion, we tried dropping the legitimacy immediately versus over time. Dropping it immediately by a small amount causes a bigger rebellion because fewer people are in jail. We also removed movement, but we didn’t see the effects described. We found overall that the rebellions were fairly regular and periodic, unless there were very few cops, in which case the rebellions would be constant. We also found that cop density of 5% seemed to be the magic point between wide scale rebellion and no rebellion (kind of like the tree simulation where 60% tree density suddenly let the fire spread a lot). Anything above 5% cop density led to only a couple isolated individuals rebelling, who were quickly jailed.

Climate Change: We decided to extend the global warming simulation. In the original simulation, sunlight waves come in from the atmosphere (the yellow shapes), and either are reflected back to the atmosphere or become trapped in the ground as the red heat dots. The heat bounces around in the Earth for a while, raising the temperature. Heat can leave from the Earth’s surface as IR waves on the right side of the screen, and if it does, it lowers the Earth’s temperature. The simulation lets you add clouds, which reflect incoming sunlight waves, and CO2, which reflect outgoing IR waves.

Before:

We decided to add trees to the Earth’s surface that would absorb any CO2 that got close to it. We made a new breed of turtles called trees (surprise!), added a tree density slider, and added code so the green triangles that appear in the green band of the surface are dependent on the density entered. In the extended model, when any of the CO2 molecules that are randomly floating around the atmosphere gets too close to the green triangle trees, it is “eaten” by the trees.

After: