This form of modeling dynamic systems is based on "stocks" (amounts) and "flows" (rates of change). For the predator-prey model we ask what factors impact the flows (the thick arrows) into and out of the populations of sheep and wolves (the stocks)? The dotted arrows can be used to connect and describe the relationships within the model. Additional variables, e.g, sheep fertility, can be added to the model to make relations clearer.

Overall, the dynamics for this kind of modeling centers on the factors that impact the flows. Click on any of the flow-arrows to see how the factors connect by the dotted arrows are used to determine the flows in or out of the stocks (the populations).