The model developed by the researchers is a set of four equations designed to describe the dynamics of the system. They tested the model by running experiments using a water-containing apparatus, in which they placed the predator rotifers Brachionus calyciflorus and the prey algae Chlorella vulgaris.
During 18 experimental trials, they varied the concentration of nitrogen pumped into the system and the dilution rate of the water in the system. The nitrogen concentration determined the birth rate of the algae, which, in turn, determined the rotifers' birth rate.
Those trials yielded results expected by the model, varying according to the nitrogen concentration input and the rate at which the water was diluted. At low nitrogen levels, the two species coexisted at an equilibrium or in cycles. At intermediate dilution rates, the populations oscillated, while they remained at equilibrium at high and low dilution levels.
Shertzer, the NC State biomathematics doctoral candidate, said the research indicates that internal population limitations such as predator-prey interactions can drive population cycles without any forcing from external limitations such as environmental conditions. And, he explains, the research team has demonstrated that researchers don't need to know everything about an environmental system to predict its population dynamics.
"It is a really simple model that's able to catch the important mechanisms of the system necessary to describe the system," he said. "This shows that you don't necessarily need to track every detail to make accurate predictions." Shertzer continues to work with Dr. Stephen Ellner to refine the model.