The Dynamics of Location: Influence of Predation by Chaoborus Larvae on Rotifer Diel Vertical Migration Patterns

The locations of freshwater organisms in lakes are determined by the convergence of many competing factors. While predation pressure is one of these, also important are areas of food concentration and the physical and chemical constraints of a system. Diel vertical migration is a behavior exhibited by freshwater organisms in many taxa that is the result of balancing these factors. Diel vertical migration consists of movement by these organisms throughout the water column in accordance with a 24 hour cycle. This oscillation is generally driven by the competing factors of predation pressure and food acquisition, and is modified by physical and chemical requirements.In the Low Lake system during the summer of 2012, two groups of organisms were engaged in diel vertical migration: rotifers and Chaoborus. While some instars of Chaoborus were exhibiting a typical diel vertical migration pattern, the migration pattern of the rotifers was the opposite. While the migration pattern of the Chaoborus was likely driven by fish predation, that of the rotifers was driven by Chaoborus predation pressure resulting from their diel vertical migration. The migration patterns in both of these groups of organisms were also driven by differential locations of food resources. The migration patterns of rotifers and Chaoborus in Low Lake are an excellent example of how the changing locations of organisms in a lake are the result of balancing many factors that influence the fitness of these organisms.