| Diel vertical migration (DVM), a zooplankton behavior in which they spend their days at the surface and nights deeper in the water column, is a phenomena found in many taxa of zooplankton. Most scientists believe it functions to balance the need for food and the need to avoid predation. Although it is widespread, this behavior varies tremendously by species, size, location, sex, and stage. This thesis investigates the variability of DVM in the common marine copepod Calanus finmarchicus using three models: (1) optimization, (2) periodic dynamical systems, and (3) stochastic models.; The optimization models are dynamic programs with various fitness functions that determine the optimal habitat choice, based on weight and time in the season. These models identify factors important in the reproductive success of an individual zooplankton in a constant environment. Critical issues vary by fitness function but include food variability and variation, predation risk, and the difference between the gain from feeding and the cost of reproduction. Periodic dynamical systems account explicitly for competition between two zooplankton species with different migration patterns, using a single phytoplankton resource. In this model, migration patterns have the same period (corresponding to one day) but differ in initiation time, mean depth, and amplitude. The greatest differences in competitive outcome are found in varying migration times, which have one of several evolutionary outcomes depending on the parameters. The third model, a continuous time Markov Chain, also examines a one phytoplankton-two zooplankton system. Stochasticity is added to the birth and death rates of each species. The analysis compares the probability of extinction and time to extinction of a deterministic system and a system with a quasistationary distribution and finds conditions for the two approximations to be close. |
