Changes between Version 4 and Version 5 of EwEugVulnerabilitiesInEcosim


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Timestamp:
2010-11-21 22:43:19 (9 years ago)
Author:
shermanl
Comment:

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  • EwEugVulnerabilitiesInEcosim

    v4 v5  
    99The converse (bottom-up control) is the situation that occurs when a prey is protected most of the time, (e.g., by hiding in crevices) and becomes available to predators only when it leaves the feature that protects it. Here being caught is a function of the prey's behaviour.  Bottom-up control usually leads to unrealistically little biomass changes in the prey and predator(s) concerned, but which usually do not propagate through the other elements of a food web. 
    1010 
    11 To model this aspect of predator-prey interactions, the group biomasses (B) on the underlying Ecopath model were reconceived in Ecosim as consisting of two components, one vulnerable, the other invulnerable to predation (B' and V, respectively in Figure 3.3). Further, it is assumed that there is a flow (''''v,,ij,,'''') of organisms from the invulnerable to the vulnerable stage, and conversely (''v,,ji,,''), with the assumption v = ''''v,,ij,,'''' = ''v,,ji,,''. 
     11To model this aspect of predator-prey interactions, the group biomasses (B) on the underlying Ecopath model were reconceived in Ecosim as consisting of two components, one vulnerable, the other invulnerable to predation (B' and V, respectively in Figure 3.3). Further, it is assumed that there is a flow (''v,,ij,,'') of organisms from the invulnerable to the vulnerable stage, and conversely (''v,,ji,,''), with the assumption v = ''v,,ij,,'' = ''v,,ji,,''. 
    1212 
    1313As might be seen in Figure 3.3, when v is high, the rapid replenishment of vulnerable biomass depleted by predator will rapidly drain the invulnerable part of the biomass.  Thus, with v set high, predation control will be top down. Conversely, if v is low, replacement of depleted biomass from the invulnerable to the vulnerable part of the population will be slow, and the amount that the predators consume will be largely determined by the low value of v, rather than by their own biomass.  Thus, when v is low, control is bottom up. 
    1414 
    15 The vulnerability parameters are among the most important parameters that users change to improve the agreement of the model's predictions with historical data (see [[Time series fitting in Ecosim.htm|Time series fitting in Ecosim]], [[Hints for fitting models to.htm|Hints for fitting models to time series reference data]] and [[Effect of P B Z and vulnerability.htm|Effect of P/B (Z) and vulnerability for time series fitting]]). See [[Vulnerabilities flow control.htm#_Vulnerabilities|Vulnerabilities]] for help on setting vulnerabilities in Ecosim. See [[Fit to time series.htm|Fit to time series]] for help with Ecosim's parameter search interface. 
     15The vulnerability parameters are among the most important parameters that users change to improve the agreement of the model's predictions with historical data (see [EwEugTimeSeriesFittingInEcosimEvaluatingFisheriesAndEnvironmentalEffects Time series fitting in Ecosim], [EwEugHintsForFittingModelsToTimeSeriesReferenceData Hints for fitting models to time series reference data] and [EwEugEffectsOfPbZandVulnerabilityForTimeSeriesFitting Effect of P/B (Z) and vulnerability for time series fitting]). See [EwEugVulnerabilitiesFlowControl Vulnerabilities] for help on setting vulnerabilities in Ecosim. See [EwEugFitToTimeSeries Fit to time series] for help with Ecosim's parameter search interface. 
    1616 
    1717Further reading: Walters and Juanes (1993), Walters et al. (1997), Walters and Korman 1999, and Walters and Martell (2004).