The role of migrations in ecosystem simulation
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The role of migrations in ecosystem simulation

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The  role of migrations in ecosystem simulation
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    The Dynamical Numerical Marine Ecosystem Simulation (DYNUMES) model is unique in its ability to simulate, in addition to growth, apex predation, inter-species predation and fishery, spatial and temporal biomass distribution fluctuations caused by fish migrations. Two types of fish migration simulations are discussed: seasonal migrations for spawning and foraging and migrations to regions of optimum environmental conditions (optimum temperature). The general formulation of migration simulation is a three-step process. First, migration velocities are calculated for each migrating species. Secondly, the migrating fraction of the biomass is separated from the non-migrating fraction. Finally, gradients in migrating biomass are calculated and the migrated biomass is computed using a finite difference advection equation. Migrations are simulated over a short time period for stability; several migration calculations are performed during each monthly model time step. At the end of each model month, conservation of biomass is enforced and random diffusion is simulated. The specifics of the calculations as they apply to both seasonal and temperature induced migrations are presented and the results are discussed. Migration simulation enhances the realism of ecosystem simulation models. In addition, it provides a means of studying spatial and temporal changes in predation mortality caused by changes in predator-prey overlap, fluctuations in biomass distributions caused by anomalous environmental conditions, and other space and time dependent factors in the ecosystem.
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