Population growth and vertical distribution of light-limited phytoplankton under non-homogenous grazing pressure
Department of Evolution, Ecology, and Organismal Biology, The Ohio State University
(March 1, 2012 10:30 AM - 11:30 AM)
Most phytoplankton movement is passive and occurs through either sinking/ floating (depending on their density relative to water) or through turbulent diffusion. As they move vertically in the water column, phytoplankton experience gradients in critical environmental factors, such as light intensity and nutrient concentrations. The rate at which phytoplankton move across these gradients can be critical to their persistence and vertical distribution. Grazing can also play a critical role in dictating where in the water column phytoplankton are found. However, theoretical models of critical sinking and diffusion rates either do not explicitly consider grazing loss or treat it as vertically homogenous, thus making it independent of movement. In nature, however, grazing intensity is often vertically heterogeneous. Despite its common occurrence, how such grazing heterogeneity influences critical rates of phytoplankton movement is not well understood. Here we put forth some basic predictions regarding phytoplankton persistence and spatial heterogeneity of grazing, using a reaction-diffusion-advection model. We introduce some new ideas to investigate the combined effects of advection, diffusion, and heterogeneous grazing pressure on the persistence of phytoplankton and to determine the unique number of critical sinking/buoyant rates that are specified by the inclusion of depth dependent mortality that is a result of heterogeneous predation.