Changes between Version 1 and Version 2 of EwEugPrimaryProductionRequired


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Timestamp:
2010-11-23 01:45:26 (9 years ago)
Author:
shermanl
Comment:

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  • EwEugPrimaryProductionRequired

    v1 v2  
    11== 7.20 Primary production required == 
    22 
    3 For terrestrial systems, it has been shown by Vitousek et al. (1986), based on a detailed analysis of agriculture, industry and other activities, that nearly 40% of potential net primary production is used directly or indirectly by these activities. Comparable estimates for aquatic systems were not available until recently, though a rough estimate, of 2% was presented in the same publication. This figure, much lower than that for terrestrial systems, was based on the assumptions that an ‘average fish’ feeds two trophic levels above the primary producers, and has been since revised upward (Pauly and Christensen, 1995). 
     3For terrestrial systems, it has been shown by Vitousek et al. (1986), based on a detailed analysis of agriculture, industry and other activities, that nearly 40% of potential net primary production is used directly or indirectly by these activities. Comparable estimates for aquatic systems were not available until recently, though a rough estimate, of 2% was presented in the same publication. This figure, much lower than that for terrestrial systems, was based on the assumptions that an 'average fish' feeds two trophic levels above the primary producers, and has been since revised upward (Pauly and Christensen, 1995). 
    44 
    5 The crudeness of Vitousek et al.s approach for the aquatic systems was due mainly to lack of information on marine food webs, especially on the trophic positions of the various organisms harvested by humans. Models of trophic interactions may however help overcome this situation, and an alternative approach, based on network analysis, may be suggested for quantification of the primary productivity required to sustain harvest by humans (or by analogy by any other group that extracts production from an ecosystem). 
     5The crudeness of Vitousek et al.'s approach for the aquatic systems was due mainly to lack of information on marine food webs, especially on the trophic positions of the various organisms harvested by humans. Models of trophic interactions may however help overcome this situation, and an alternative approach, based on network analysis, may be suggested for quantification of the primary productivity required to sustain harvest by humans (or by analogy by any other group that extracts production from an ecosystem). 
    66 
    77To estimate the primary production required (PPR, Christensen and Pauly, 1993a) to sustain the catches and the consumption by the trophic groups in an ecosystem, the following procedure has been implemented in Ecopath: First, all cycles are removed from the diet compositions, and all paths in the flow network are identified using the method suggested by Ulanowicz (1995). For each path, the flows are then raised to primary production equivalents using the product of the catch, the consumption/production ratio of each path element times the proportion the next element of the path contributes to the diet of the given path element. For a simple path from trophic level (TL) I (primary producers and detritus), over TL II and III, and on to the fishery, 
     
    1313[[Image(wiki:EwEugImages:08000080.png)]] 
    1414 
    15 For the general (and more realistic) case where the pathways includes branching the PPR corresponding to a catch Y of a given group can be quantified by summing over all pathways leading to the given group the PPRs 
     15For the general (and more realistic) case where the pathways includes branching the PPR corresponding to a catch Y of a given group can be quantified by summing over all pathways leading to the given group the PPR's 
    1616 
    1717[[Image(wiki:EwEugImages:08000081.png)]] '''Eq. 44''' 
    1818 
    19 where ''P'' is production, ''Q'' consumption, and ''DC'' is the diet composition for each predator/prey constellation in each path (with cycles removed from the diet compositions). 
     19where ''P'' is production, ''Q'' consumption, and ''DC' '' is the diet composition for each predator/prey constellation in each path (with cycles removed from the diet compositions). 
    2020 
    2121The ''PPR'' required to sustain the catch is presented as a page on the ''PPR'' form. 
     
    2323Further, the ''PPR'' for sustaining the consumption of each trophic group in a system can be estimated from the same equation as above by substituting the catch, ''Y'', with the production term, ''P'', calculated as the production/biomass ration, ''P/B'', times the biomass, ''B''. This is presented on a separate page on the ''PPR'' form. 
    2424 
    25 ''PPR'' should actually be interpreted as flow from Trophic Level I as it includes primary production as well as detritus uptake. The denominator, ''PP'', thus actually includes all ‘new’ flow to the detritus groups, i.e. flow from primary producers and import of detritus. 
     25''PPR'' should actually be interpreted as flow from Trophic Level I as it includes primary production as well as detritus uptake. The denominator, ''PP'', thus actually includes all 'new' flow to the detritus groups, i.e. flow from primary producers and import of detritus. 
    2626 
    2727The ''PPR'' is closely related to the emergy concept of H. T. Odum (1988), and is proportional to the ecological footprint of Wackernagel and Rees (1996).