  If population sizes are large, they can be studied using deterministic models, that is, fluctuations in populations sizes due to chance factors (such as accidental births and deaths) can be ignored. Usually a model considers members of a single or a very few interacting species, for instance, a few predator and a prey  species.[13]  A typical result, based on the Lotka-Volterra (coupled differential equations) model, is that predator-prey interactions lead to population cycles, with the predator population cycle temporally tracking the prey population cycle. The explanation of this phenomenon is straightforward: as prey populations increase, the increased availability of resources allows a rise in predator populations a little later in time. But the increase of predators leads to an increase of prey consumption and, consequently, a decrease in prey populations. But, now, the lack of resources leads to a decline of predator populations. As predator populations decline, prey populations increase initiating the cycle once again. See Figure 1: