An integer-valued mathematical model of lake communities: chaotic and long-period oscillations in the fish population size

We present the results of a mathematical model for the aquatic communities which include zoo-plankton, planktivorous fish and predator fish. The aquatic populations are considered to be body mass- and age-structured, while the trophic relations between the populations to be correspondingly status-specific. The model reproduces diverse dynamic regimes as such steady states and oscillations in the population size. Oscillations in the fish population size are shown to be both regular and irregular. We show that the period of the regular oscillations can be up to decades. The irregular oscillations are shown to be both chaotic and non-chaotic. Analyzing the dynamics in the model parameter space has enabled us to conclude that predictability of fish population dynamics can face difficulties both due to dynamical chaos and to the competition between various dynamical regimes caused by variations in the model parameters, specifically in the zooplankton growth rate.