At the St. Louis Zoo they have an exhibit building called the Living World that contains only a few live animals but is more of a ecology teaching exhibit. Inside they have a large long fish tank that represents a small river ecosystem. Next to it is a computer touch screen with a simulation of a pond environment with several species. Each species is represented by a population bar at the side of the screen. If I remember right the species were bluegill, bass, turtles, crayfish, and algae. The sim started with all the populations at a 50% level on the bar which represented a perfect balance in the pond. By touching the bar graph for any species you could increase or decrease the population of that species and put the pond out of balance. It then would show how the other species populations would rise and fall in response over time. You could also eliminate one (ex. bass) and watch the other populations explode then crash until the only thing remaining was algae. I don't know how accurate it was but it was fun to play with.

Does the name Pavlov ring a bell?