This section presents a model of predator and prey where association includes only natural growth or decay and the preadator-prey interaction itself. All other relationships are considered to be negligible. We will assume that the prey population grows exponentially in the absense of predation, while the predator population declines exponentially if the prey population is extinct. The predator-prey interaction is modeled by mass action terms proportional to the product of the two populations. The model is named the Lotka-Volterra system.