Changes between Version 1 and Version 2 of EwEugElectivity


Ignore:
Timestamp:
2010-11-23 01:34:27 (7 years ago)
Author:
shermanl
Comment:

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  • EwEugElectivity

    v1 v2  
    11== 7.11 Electivity == 
    2 The electivity (selection index) describe a predator’s preference for prey. It scales from -1 to 1; where -1 indicates total avoidance of a prey; 0 indicates that a prey is taken in proportion to its abundance in the ecosystem; and 1 indicates total preference for a prey. The electivity values are highlighted using a colour scale for the background, scaling from –1 (white) to 1 (red) using shades of red for intermediate values. The electivity index displayed is the standardized forage ration of Chesson (1983), see below. 
     2The electivity (selection index) describe a predator's preference for prey. It scales from -1 to 1; where -1 indicates total avoidance of a prey; 0 indicates that a prey is taken in proportion to its abundance in the ecosystem; and 1 indicates total preference for a prey. The electivity values are highlighted using a colour scale for the background, scaling from -1 (white) to 1 (red) using shades of red for intermediate values. The electivity index displayed is the standardized forage ration of Chesson (1983), see below. 
    33 
    44One of the most widely used indices for selection is the Ivlev electivity index, ''E,,i,,'' (Ivlev 1961) defined for a group (''i'') as: 
    55 
    6 ''E,,i,, = (r,,i,, P,,i,,) / (r,,i,, +P,,i,,)'' 
     6''E,,i,, = (r,,i,, - P,,i,,) / (r,,i,, +P,,i,,)'' 
    77 
    88where ''r,,i,,'' is the relative abundance of a prey in a predator's diet and ''P,,i,,'' is the prey's relative abundance in the ecosystem. E''i'' is scaled so that ''E,,i,,'' = -1 corresponds to total avoidance of, ''E,,i,,'' = 0 represents non-selective feeding on, and ''E,,i,,'' = 1 shows exclusive feeding on a given prey'' i''. Note that within Ecopath, ''r,,i,,'' and ''P,,i,,'' refer to biomass, not numbers.