Changes between Version 5 and Version 6 of EwEugDealingWithOpenSystemProblems


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Timestamp:
2010-01-28 14:26:41 (9 years ago)
Author:
varunr
Comment:

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  • EwEugDealingWithOpenSystemProblems

    v5 v6  
    55For almost every defined Ecopath study area, there will be some species that have life cycles that take them outside the defined area for at least part of each year.  Movements (exchange) of biomass across the area boundary can be of two types: dispersal, involving unidirectional movement of organisms to and from sink and source populations outside the study area; and migration, involving regular, repeated movements into and out of the area by the same individuals.  These are fundamentally different processes, with very different policy consequences.  Dispersal acts as an extra mortality-agent and recruitment-source independent of fisheries and other impacts in the study area, while migration exposes organisms from the study area to particular risks and opportunities for part of the time, without acting as a ‘permanent’ drain or source of those organisms. 
    66 
    7 Dispersal can be represented in both Ecopath and Ecosim by setting immigration and emigration rates in the [wiki:OtherProduction Other Production] form in Ecopath. These rates are used in the Ecopath mass balance and are treated in Ecosim as unidirectional (non-migratory) dispersal rates.  True migration is more complex to deal with, and Ecosim will give misleading answers if migration is represented only by immigration/emigration rates from Ecopath. 
     7Dispersal can be represented in both Ecopath and Ecosim by setting immigration and emigration rates in the [wiki:EwEugOtherProduction Other Production] form in Ecopath. These rates are used in the Ecopath mass balance and are treated in Ecosim as unidirectional (non-migratory) dispersal rates.  True migration is more complex to deal with, and Ecosim will give misleading answers if migration is represented only by immigration/emigration rates from Ecopath. 
    88 
    99There are two broad options for dealing with directed migration to and from the Ecopath study area so as to avoid misleading predictions in Ecosim: