Lotka Volterra prey-predator model
Grazing rabbits are hunted by lynx which depend on them for their survival.
You can modify the birth rate, the impact on the environment (supposed to be detrimental when >0) and the initial (bright blue) points. The same equation governs not only the prey-predator relationship but as well a symbiotic or a competitive relationship when the ecological impacts of one specie over the other is tweaked.