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Models
The Model used to create a Virtual Ecosystem
The model comprises a set of primitive equations. They define the functions of the basic elements of the virtual ecosystem.
Metamodel
To achieve the high level of automation of the VEW, the model is constrained by LEI-IBM metamodel. In computer terminology it permits agent-based modelling. VEW4 is further constrained to simulate a one-dimensional ecosystem. The plankton can move up and down but not sideways. The environment changes because of vertical flux divergences. Horizontal flux divergences are all zero. Finally, the biology is limited to plankton, which by definition cannot change their ambient environ ment by swimming horizontally. The VEW's kernal (called Planktonica) ensures that all model equations obey the metamodel.
The model
The LEI-IBM metamodel permits great flexibility in the choice of model equations. You add new equations to choice. The VEW Archive provides a set of default equations. And it stores the specification of all previous models, species and biological primitive equations. They appear in picklists to serve as components of the specification for a new virtual ecosystem.
Physics
(1) An optical sub-model to compute the solar irradiance profile in 24 wavebands.
The VEW offers three versions:
(a) Empirical (after Morel), (b) Monte Carlo and (c) RadiativeTransfer Equation.
(2) A mixed layer sub-model to compute the turbulent kinetic energy profile.
Chemistry
Each chemical element in the virtual ecosystem can exist in solution (in various compounds) and in the living plankton, and in the corpses of dead plankton and in facal pellets. The chemicals can be nutrients, pigments, isotopes, passive tracers, and contaminants.
Biology
The biological equations h-ave the following hierarchy:
| (1) Function | Biological primitive equations (e.g. for photosynthesis or foraging). |
| (2) Functional group | Each group shares the same set of biological equations (There are two groups in the WB model: diatoms & calanoid copepods). |
| (3) Species | The species in a functional group have the same biological equations, but different values of the parameters in those equations. A species might be defined by twenty parameters. |
| (4) Allometric set of species | For some investigations it is convenient to defi ne an allometric set of species. In which case, the value of each parameter is related to the plankter.s size. |
| (5) Variety | Alleles of a species differing in the value of one parameter. |
| (6) Community | A set of functional groups each with its set of species. |
