Changes between Version 1 and Version 2 of EwEugNotesOnParameterizingAnEcopathModel


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Timestamp:
2010-11-23 01:14:56 (9 years ago)
Author:
shermanl
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  • EwEugNotesOnParameterizingAnEcopathModel

    v1 v2  
    3232The sections below may help you evaluate the results of a run. 
    3333 
    34 '''Are the EEs between 0 and 1?''' 
     34'''Are the EE's between 0 and 1?''' 
    3535 
    3636When examining the output of a run, the first and perhaps most important items to consider are the ecotrophic efficiencies (which are usually calculated). The values should be between 0 and 1 (inclusive). Here, a value of zero indicates that any other group does not consume the group in the system, and neither is it exported. Conversely, a value near or equal to 1 indicates that the group is being heavily preyed upon or grazed and/or that fishing pressure is high, leaving no individuals to die of old age. The whole range of ecotrophic efficiencies can be found in nature. However, a generalization has emerged from previous modelling: for most groups, the ''EE'' should be close to one, the exceptions being top predators and primary producers. 
     
    3838If, in a first run, any of the'' EE'' values are larger than 1, something is wrong: it is not possible for more of something to be eaten and/or caught than is produced. The problem can of course be due to the equilibrium assumption not being met, e.g., when the model includes a new fishery on a previously unexploited stock. Unless this is known to be the case, you should have a closer look at the input parameters. 
    3939 
    40 It may be worthwhile to check the food consumption of the predators, and the production estimates of the group. Compare the food intake of the predators with the production of their prey. Most often, the diet compositions will have to be changed - often the diets are more ‘pointers’ to, than reliable estimates of the real values. 
     40It may be worthwhile to check the food consumption of the predators, and the production estimates of the group. Compare the food intake of the predators with the production of their prey. Most often, the diet compositions will have to be changed - often the diets are more 'pointers' to, than reliable estimates of the real values. 
    4141 
    42 Often ‘cannibalism’ in the sense of within-group predation causes problems. If a group contributes 10% or more to its own diet, this alone may result in consumption being higher than the production of the group. The solution to this is to split the group into juveniles and adults, with the adults acting as predator on the juveniles. The juveniles must then have a higher production rate than the adults, as production is almost always inversely related to size. Splitting groups into juveniles and adults is also useful for the Ecosim discussed later. 
     42Often 'cannibalism' in the sense of within-group predation causes problems. If a group contributes 10% or more to its own diet, this alone may result in consumption being higher than the production of the group. The solution to this is to split the group into juveniles and adults, with the adults acting as predator on the juveniles. The juveniles must then have a higher production rate than the adults, as production is almost always inversely related to size. Splitting groups into juveniles and adults is also useful for the Ecosim discussed later. 
    4343 
    44 It is advisable to make one change at the time when editing input parameters. Make that one change, rerun the [[Basic estimates.htm|Basic estimates]] routine, re-examine the run, and if necessary re-edit the data, etc. Continue with one change at a time until you get a run you consider acceptable. Make sure, through the entry of remarks in the [wiki:EwEugGeneralFeaturesOfTheGraphic Remarks window], to record en route what you do and why. 
     44It is advisable to make one change at the time when editing input parameters. Make that one change, rerun the [EwEugBasicEstimates Basic estimates] routine, re-examine the run, and if necessary re-edit the data, etc. Continue with one change at a time until you get a run you consider acceptable. Make sure, through the entry of remarks in the [EwEugGeneralFeaturesOfGui Remarks window], to record en route what you do and why. 
    4545 
    4646'''Ecotrophic efficiency of detritus''' 
     
    4848The ecotrophic efficiency, ''EE'', of a detritus group is defined as the ratio between what flows out of that group and what flows into it. Under steady-state assumption, this ratio should be equal to 1. 
    4949 
    50 The fate of the detritus (DF) can be entered ([[Detritus fate.htm|Detritus fate form]]). If all detritus from a detritus group is directed to other detritus boxes the EE of the group will be 1. 
     50The fate of the detritus (DF) can be entered ([EwEugDetritusFate Detritus fate form]). If all detritus from a detritus group is directed to other detritus boxes the EE of the group will be 1. 
    5151 
    5252Estimates of ''EE'' of less than 1 indicate that more is entering a detritus group than is leaving it. 
     
    5656Of importance for the flow to detritus is the parameter for non-assimilated food. The default value of 0.2 often underestimates egestion, especially for herbivores and detritivores. For instance that a value of 0.4 for zooplankton often leads to more reasonable respiration/biomass ratios than 0.2. Higher parameter values means that a greater flow is directed to detritus and less to respiration for a given group. 
    5757 
    58 '''Are the ‘efficiencies’ possible?''' 
     58'''Are the 'efficiencies' possible?''' 
    5959 
    6060Recall that the gross food conversion efficiency, ''GE'', is defined as the ratio between production and consumption. In most cases, production/consumption ratios will range from 0.1 to 0.3, but exceptions may occur, (e.g., bacteria, nauplii, fish larvae and other small, fast-growing organisms). If the ''GE'' values are unrealistic, check the input parameters, especially for groups whose production has been estimated. In such cases, carefully editing the diet composition of the predators of the problem groups will generally help.