This ecosystem model has no pretension to be realistic, but it allowed me, and hopefully you, to become familiar with the concept of balance, essential in an ecosystem. The evolution of this ecosystem depends on a few variables that you can modify to observe the impact they may have. This ecosystem contains two types of virtual entities: prey and predators, likely to eat the latter. Our ecosystem is a discrete world (a torus, which we will display as a rectangle) containing a certain number of boxes, identified by their (full) x and y coordinates. Each prey (and each predator) is in a casedata and can move. At a given moment, a box can contain several prey and several predators.