Simple predator-prey interactions control dynamics in a plankton food web model

A plankton food web model is analysed using interaction parameter values appropriate to the upper mixed layer of the high latitude oceans. The dynamics of this four-variable system are analysed in terms of the dynamics of much simpler two-variable predator-prey subsystems. Thus, the food web's robust, periodic, four-dimensional dynamics are explained by means of two-dimensional spirals and limit cycles. These dynamical subsystems are coupled by means of an omnivore that transfers control of the dynamics between the two predator-prey subsystems. The food web may substantially decouple the predator-prey subsystems so that the oscillating phytoplankton/zooplankton blooms exhibit population collapses when bacterial 'breathers' briefly dominate after growing dramatically from low background levels. This regular bloom/breather behaviour becomes benignly chaotic when the system is mildly forced by the annual cycle of the sun's irradiance. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.