Incorporating complex foraging of zooplankton in models: Role of micro- and mesoscale processes in macroscale patterns

Abstract

There is a growing understanding that population models describing trophic interactions should benefit from the increasing knowledge of the complex foraging behavior of individuals constituting those populations. A notable example is the modelling of planktonic food chains where the foraging behavior of herbivorous zooplankton is often complicated and involves active vertical displacement (migration) in the water column with the aim of optimizing the fitness under constantly varying environmental conditions such as distribution of predators, location of food, temperature gradient, oxygen concentration, etc. Vertical migration of zooplankton takes place on different time and space scales ranging from seconds and centimeters to months and the size of the whole euphotic zone. Taking into account active foraging behavior of zooplankton would alter theoretical predictions obtained with earlier plankton models where such behavior has often been ignored - especially in the mean-field models which operate with integrated species biomasses/densities. In this paper, I revisit two important aspects of incorporating patterns of active zooplankton feeding in models, based on recent progress in field observations and experiments. Firstly, I investigate how complex foraging movement of herbivores in the column can alter the shape of the zooplankton functional response on different spatial and temporal scales - in particular, I scale up the local functional response to macroscales (the whole euphotic zone) and show the emergence of a sigmoid functional response (Holling type III) on the macroscale based on a non-sigmoid local response on microscales. Secondly, I theoretically investigate the role of intra-population variability of the feeding behavior of grazers (implying physiological and behavioral structuring of a population) in the persistence of the whole population under predation pressure. I show that structuring of the population according to feeding behavior would enhance the population persistence in a eutrophic environment thus preventing species extinction. © 2013 Springer-Verlag Berlin Heidelberg.