Changes between Version 2 and Version 3 of EwEugRepresentationOfMultiStanzaLifeHistoriesInEcopathEcoSimAndEcospace


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Timestamp:
2010-01-28 15:10:06 (9 years ago)
Author:
varunr
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  • EwEugRepresentationOfMultiStanzaLifeHistoriesInEcopathEcoSimAndEcospace

    v2 v3  
    11== 2.9 Representation of multi-stanza life histories in Ecopath, Ecosim and Ecospace == 
    22 
    3 See[wiki:EwEugEditGroups Edit Groups] for instructions on defining multi-stanza groups in EwE6. See [wiki:EwEugEditMultiStanzaGroups Edit Multi-stanza Groups] for instructions on setting parameters for multi-stanza groups. 
     3See [wiki:EwEugEditGroups Edit Groups] for instructions on defining multi-stanza groups in EwE6. See [wiki:EwEugEditMultiStanzaGroups Edit Multi-stanza Groups] for instructions on setting parameters for multi-stanza groups. 
    44 
    55EwE users can create a set of biomass groups representing life history stages or stanzas for species that have complex trophic ontogeny.  Mortality rates (''M0'', predation, fishing) and diet composition are assumed to be similar for individuals within each stanza (e.g. larvae having high mortality and feed on zooplankton, juveniles having lower mortality and feed on benthic insects, adults having still lower mortality and feed on fish).  Users of this feature must enter baseline estimates of total mortality rate ''Z'' and diet composition for each stanza, then biomass, ''Q/B'', and ''BA'' for one “leading” stanza only. 
     
    1313Under the stable age distribution assumption, the relative number of age “''a''” animals is given by'' l,,a,,/''''S''''l,,a,,'' where the sum is over all ages, and ''l,,a,,'' is the population growth rate-corrected survivorship, 
    1414 
    15 ../Resources/Images/0800001D.png 
     15[[Image(wiki:EwEugImages:0800001D.png]] 
    1616 
    1717where the sum of ''Z''’s is over all ages up to “''a''” and the BA/B term represents effect on the numbers at age of the population growth rate (e.g. the cohort born one year ago should be smaller by the factor ../Resources/Images/0800001E.png than the cohort born “a” years ago, if the relative population growth rate has been BA/B) for at least “a” years).  Further, the relative biomass, b, of animals in stanza s should be 
    1818 
    19 ../Resources/Images/0800001F.png 
     19[[Image(wiki:EwEugImages:0800001F.png]] 
    2020 
    21 where ../Resources/Images/08000020.png is the von Bertalanffy (1938) prediction of relative body weight at age a. 
     21where [[Image(wiki:EwEugImages:08000020.png]] is the von Bertalanffy (1938) prediction of relative body weight at age a. 
    2222 
    2323Knowing the biomass, ''B'', for one leading stanza, and the ''b,,s,,'' for each stanza ''s'', the biomasses for the other stanzas can be calculated by first calculating population biomass 
    2424 
    25 ../Resources/Images/08000021.png, 
     25[[Image(wiki:EwEugImages:08000021.png]], 
    2626 
    2727then setting ''B,,s,,'' = ''b,,s,,B'' for the other stanzas. ''Q/B'' estimates for non-leading stanzas are calculated with a similar approach, assuming that feeding rates vary with age as the 2/3 power of body weight (a “hidden” assumption in the von Bertalanffy growth model). This method for ‘extending’ biomass and ''Q/B'' estimates over stanzas avoids a problem encountered in earlier ‘split-group’ EwE representations, where users could enter juvenile biomasses and feeding rates quite inconsistent with the adult biomasses and feeding rates that they had entered. The internal calculations of survivorship and biomass are actually done in monthly age steps, so as to allow finer resolution than one year in the stanza biomass and mortality structure (e.g., larval and juvenile stanzas that last only one or a few months). 
     
    3939Representation of stanzas that occur outside the modelled system? It is common, especially in models for coastal ecosystems, to have species that spend only part (or none) of their time in the system.  For example, juvenile rearing may be in the modelled ecosystem, but adult foraging and harvest impacts may occur in outside areas.  The preferred way to handle trophic/fishery impacts for such species in EwE is to treat part (or all) of the diet for outside-migrant stanzas as imported, rather than to model the movement into and out of the system as immigration/emigration rates.  With the diet import convention, EwE will still handle overall fishery impacts at the population scale whether or not these impacts occur within the modelled system; all that will be “lost’ is dynamic change in food availability (and feeding rates) and predation mortality of organisms during times when they are outside the modelled system (outside world treated as having constant trophic conditions).  Most often, the stanzas that reside outside the modelled system are older fish, for which the assumption of constant resource availability and natural mortality risk may be quite reasonable.  When it appears that using the diet-import convention is inappropriate due to changing trophic conditions outside the modelled system, then the modelled system should be extended to include the ‘outside’ trophic interactions of concern. 
    4040 
    41 The multi-stanza representation is quite flexible, and users may find other ways to use it for effectively representing ‘problem processes’ in ecological systems.  Such findings can be reported to [[http://www.ecopath.org/|www.ecopath.org]] for use by others. 
     41The multi-stanza representation is quite flexible, and users may find other ways to use it for effectively representing ‘problem processes’ in ecological systems.  Such findings can be reported to [http://www.ecopath.org/ !EcoPath] for use by others.