This is a classic boom-bust simulation involving predators and prey. And, in this case, plants. Run it a couple of times, and if it doesn't crash your browser, you will discover that the plants always win.
This version is tuned to create a long lasting (if somewhat hardware intensive) simulation as the predators (red) hunt the prey (blue), which are themselves surviving off the grass (green).
Plants are slow but persistent in their spread.
Prey (sheep?) are swift but usually aimless, except for their occasional cross-terrain linear trecks. They have no fear of predators, and are generally content to sit and munch if they can.
Predators are in constant, desperate need of food to stave off starvation and hopefully meet a mate. Over time, they begin to hunt in packs.