WaTor (Water Torus)

WaTor is Water Torus. Water represents here the sea and torus is a closed area like a bike tube for instance.
In the sea WaTor are living fish and sharks. The fish are multiplying on certain rules, the sharks eating fish for living and multiplying.
Low shark population leads to increasing fish population strongly. Sharks will multiply itself and destroying their live base, the fish population.
The low population of fish leads to hungry and dying sharks. And so on.
WaTor shows you very nice the development of a predator-prey-relation. Also known as the Lotka-Volterra-equations.

For more information see the recommended Wikipedia article.