The consumers sector estimates the total amount of herbivorous consumer biomass within the system. An indepth analysis of the development of the consumers submodel is provided in Behm and Boumans (2001). Consumers are grouped based on estimated time it takes to travel from one cell to another. There are 3 consumer groups currently incorporated into the consumers sector: fast-moving, slow-moving, and sedentary. Biomass for each group increases through ingestion and decreases through egestion, respiration, and mortality.
Spatial Movement
Consumer movement is determined by the following set of rules: if there are more consumers in the current cell than in the north cell and if there is more food in the north cell, then consumers will move into the north cell. The same guidelines are used for movement to the east, south, and west cells. Note that this model does not allow for diagonal movement or competition among the 3 groups. How fast the consumer moves into the next cell is determined by the travel time.
Ingestion
Ingestion is determined by the ingestion rate, metabolic activity, and preference for food types. Only shoots and wrack are portrayed in the image below for simplicity, but phytoplankton, seaweed, roots and rhizomes, and epiphytes are also considered as food sources. The ratio of preference for one food source to the sum of all preferences is the main influence on food-specific ingestion rate. Preference for a particular food source is also dependent on the amount of food available. For example, if a consumer has a preference for both epiphytes and phytoplankton, but there are hardly any epiphytes available, preference for phytoplankton will increase and preference for epiphytes will decrease.
