Changes between Version 3 and Version 4 of EwEugRepresentationOfMultiStanzaLifeHistoriesInEcopathEcoSimAndEcospace


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Timestamp:
2010-01-28 15:10:40 (10 years ago)
Author:
varunr
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  • EwEugRepresentationOfMultiStanzaLifeHistoriesInEcopathEcoSimAndEcospace

    v3 v4  
    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 [[Image(wiki:EwEugImages: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 [[Image(wiki:EwEugImages:0800001F.png]] 
     19[[Image(wiki:EwEugImages:0800001F.png)]] 
    2020 
    2121where [[Image(wiki:EwEugImages:08000020.png]] is the von Bertalanffy (1938) prediction of relative body weight at age a. 
     
    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 [[Image(wiki:EwEugImages: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).