Changes between Version 10 and Version 11 of EwEugVulnerabilitiesInEcosim


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Timestamp:
2014-02-06 06:50:48 (4 years ago)
Author:
jeroens
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  • EwEugVulnerabilitiesInEcosim

    v10 v11  
    2828'''Figure 3.3''' Simulation of flow between available (''V,,i,,'') and unavailable (''B,,i,, - V,,i,,'') prey biomass in Ecosim. ''a,,ij,,'' is the predator search rate for prey ''i'', ''v'' is the exchange rate between the vulnerable and not-vulnerable state. Fast equilibrium between the two prey states implies ''V,,i,,'' = ''vB,,i,,'' / (''2v'' + ''aB,,j,,''). Based on Walters et al. (1997). 
    2929 
    30 == '''Note from about vulnerabilities and the EwE user interface''' == 
     30== Note about vulnerabilities and the EwE user interface == 
    3131'''Carl Walters, 5 February 2014''' 
    3232 
     
    3737We use the kij interface option rather than allowing users to directly enter ''vij''s for two reasons: (1) in order for the initial ecopath biomasses to be near equilibrium, ''vij'' must be set to at least ''Mij'' (otherwise the model predicts initial consumption flows ''Qij'' below the ecopath base values), and (2) it is much easier for most users to think predation rate limits by thinking about how much larger ''Mij'' might ever be than its initial ecopath base value. So if we didn't use the multiplier parameterization, users would have to go through messy independent analyses in order to provide reasonable direct settings for the ''vij''. 
    3838 
    39 It is always difficult to specify reasonable ''kij'' values for ecological linkages involving non-exploited species; typically we must resort to thinking about the fine-scale spatial structure of the trophic interaction, in particular whether only a small proportion of the prey are exposed to predation at any moment e.g. as occurs with fish feeding on benthic invertebrates that are mostly hidden from sight at any moment. For exploited species, we can often obtain better ''kij'' estimates by noting that ''kij'' represents not only the upper limit on how much food these species can get, but also how much higher their percapita consumption rates can get when they are less abundant, i.e. how strong their compensatory response is to reduction by fishing; very low ''kij'' values imply very strong compensatory responses, i.e. big increases in ''Qij/Bj=aijvijBi/(2vij+aijBj)'' as Bj decreases.  Note that ecosim allows users to specify in low ''kij'' cases whether the predator just realizes higher per-capita consumption rates ''!Qij/Bj'' as ''Bj'' decreases, or instead translates the potential increase in food intake rate into reduced foraging time and hence reduced vulnerability to its predators (actually a more common response, especially in juvenile fish, than increased growth rate). 
     39It is always difficult to specify reasonable ''kij'' values for ecological linkages involving non-exploited species; typically we must resort to thinking about the fine-scale spatial structure of the trophic interaction, in particular whether only a small proportion of the prey are exposed to predation at any moment e.g. as occurs with fish feeding on benthic invertebrates that are mostly hidden from sight at any moment. For exploited species, we can often obtain better ''kij'' estimates by noting that ''kij'' represents not only the upper limit on how much food these species can get, but also how much higher their percapita consumption rates can get when they are less abundant, i.e. how strong their compensatory response is to reduction by fishing; very low ''kij'' values imply very strong compensatory responses, i.e. big increases in ''!Qij/Bj=aijvijBi/(2vij+aijBj)'' as Bj decreases.  Note that ecosim allows users to specify in low ''kij'' cases whether the predator just realizes higher per-capita consumption rates ''!Qij/Bj'' as ''Bj'' decreases, or instead translates the potential increase in food intake rate into reduced foraging time and hence reduced vulnerability to its predators (actually a more common response, especially in juvenile fish, than increased growth rate). 
    4040 
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