Vertical Migration of Zooplankton: A Game Between Predator and Prey

Abstract

Many zooplankters in lakes and oceans assemble in the upper waters at night and sink to the lower layers in the day. Planktivores also migrate following zooplankters. This diel migration is studied by analyzing a habitat selection game between predators and prey, based on the predation hypothesis, i.e., in the daytime zooplankton avoid predators (fish) that hunt by sight at the cost of reduced grazing on phytoplankton. The equilibrium distribution of the game is as follows. When the efficiency of predation by sight is low, both predator and prey concentrate in the upper layer (night phase), and, when it is high, most zooplankton stay in the lower layer and the fish population is distributed between both layers (day phase). The equilibrium distribution of zooplankton discontinuously changes with the predation efficiency at a threshold value. Since the predation efficiency varies with light intensity, diel migration pattern is expected, and the following results are shown. 1. The change in zooplankton distr...