A Model Of Venturous Revenue On The Diel Vertical Migration Of Planktonic Copepod

A model is developed to analyze the tradeoff between benefits and costs involved in the strategies for the normal DVM of copepod. The venturous revenue is used as the criterion for this optimal tradeoff. It is a function of the environmental factors and the age of copepod. During vertical migration, the copepod is assumed to instantaneously check the variations of the environmental parameters and can thereby make the optimal behavioral strategy to maximize the value of venturous revenue, i.e., taking up as much food as possible at as less cost of mortality as possible. The model is run in the simplified and typical cases of spring, the fall and the summer stratified water column in the temperate regions. The main results go as follows:1. The DVM behavior of the copepod is controlled by multi-factors. The diversified migrating patterns show that copepod is the active decision-maker, which can achieve the optimal food intake during its avoiding predation by performing the normal DVM;2. Age as one of the internal factors can affect the value of venturous revenue through acting on the checking results of the external factors (e.g., predation pressure), and thereby affect the optimal migrating strategies. Therefore, the patterns for DVM vary with the change of the animal's age. In general, the older the copepod is, the earlier and stronger the DVM is performed.3. Food, temperature and predation pressure directly act on the value of venturous revenue and are major environmental factors affecting DVM of the copepod. In the summer stratified water column, the deeper the maximum depth of food distribution is, the stronger the DVM is performed; The increase of the gradient of temperature in the thermocline layer can decrease the magnitude of the DVM and form the thermal barricade to the copepod; The effects of the predation pressureon DVM is complex. On the one hand, the variations in the distribution depth of the predation pressure vs. the thermocline layer or the depth of the maximum foodcan modify the DVM patterns of the copepod. On the other hand, different predation pressure induces different DVM patterns. The stronger the predation pressure is, the stronger the DVM is performed. When the predation pressure increases to enough extent, the copepod will stop ascending to the upper water column and stay long in the lower water layers to likely enter a state of predation-induced diapause.