Encounter Probabilities and Community Structure in Zooplankton: a Mathematical Model

Abstract

Predator-prey interactions between swimming animals of the zooplankton are studied in a mathematical model. The assumptions are: the animals are points in a 1 m3 homogeneous space; the animals move at random and are randomly distributed; and the predator animal has an encounter radius given by its sensory system. The mathematics of encounter probabilities are developed for a 3-dimensional space. The results show 2 optimal strategies: cruising predators which prey upon slow moving animals (herbivores), and ambush (nonmoving) predators which prey upon fast cruising prey. Of the variables used (population densities, speeds of the 2 animal species and encounter radius) the encounter radius has the greatest influence on the encounter probabilities. The results suggest a simple community structure and point to the importance of studies on liver zooplankton.