A Three Trophic-Level Ecosystem Simulator
[In Java, running on your browser...]
Author: William Harms e-mail

Capture01.BMP (361062 bytes)Predator-Prey cycles have a tendency to amplify, leading to the crash of one or both. There are a number of mechanisms which may damp these destructive oscillations. This simulator is a tool   (sort of a toy system) to explore some of them.

Prey are Blue, Predators are Yellow, and Resource is Green. Resource level in each patch is indicated by the level of green. Predators and prey both move between patches with the same probability at each cycle (the "Movement Rate"). Prey consume the renewable resource. Both prey and predators have metabolisms of 1 resource unit per cycle. If they reach their reproductive level they reproduce. Both parent and offspring are left with  half of what remains of the reproductive level resource after reproductive costs are assessed.

Individuals randomly bump into others in the patches. If predator bumps into prey, then the prey gets consumed according to the Predator Efficiency. Predators get the prey's resource times the Assimilation Efficiency.

Movement rate (which affects the encounter rate) is probably the most critical variable. Barriers and edges help a lot. Barriers come in random and grid. (Or you can click on patches to create your own.) Different topologies have different amounts of edges. Edges can be turned into cliffs with "Edge Kill". Bigger grids can help, but not always.

Just click on the image of the simulator to start it in your browser. It will start in a new window. Note that Java applets have no access to your files. They run on a "virtual machine" inside your browser. This simulator is not recommended for older Macintosh's. Seems Java's approach to multi-tasking ("threads") ran into trouble with memory protection. I have heard that this problem has been corrected with newer browsers and operating systems. In general, the faster your machine the better, but I wrote this on my old Pentium 166. The download files are less than 25k (about the size of the .gif to the right.)  Java needs to be enabled on your browser, of course.


Capture01.gif (21308 bytes)Notes on the controls :

Controllable Variables: Use the list box to see the value of the variable. To change it, just type the new value and hit the button. Variables marked by the * won't change until the simulator is reset and the grid rebuilt.