Shape and dynamical consequences of the functional response of Daphnia magna

Abstract: The zooplankter genus Daphnia have been one of the most popular model organism for studies on population dynamics for a long time. Most models constructed as a part of these studies use a Type II Hollings functional response and whether the Type III response typeoccurs in Daphnia sp. or not has been the subject of debate. Recent studies, however, reveal evidence of a Type III response and challenge this opinion. This study explains and illustrates the theoretical instability of a system modelled with the type II response and the more stable nature of a type III system through the use of both simulations and graphs.Furthermore, both a short term experiment in which Daphnia magna were fed Monoraphidium minutum so that the functional response could be studied and a long term experiment with the purpose of constructing a model that describes the population dynamics were performed. The functional response experiment indicated the possibility of a type III functional response, but due to large variation within low food density treatments it cannot be clearly distinguished from a type II response. The general trend, however, seems to indicate that if there is a type III response, it is not stabilizing. Unfortunately, the long termdynamics experiment suffered from too much unexplainable D. magna mortality to conclude anything besides the fact that enrichment seems to increase the maximum number Daphniaof individuals the system may sustain. Future studies should consider the improvements suggested of the experimental design to help prevent similar problems.