Pielou J (All samples) |
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This measure of Equitability compares the observed Shannon-Wiener index against the distribution of individuals between the observed species which would maximise diversity.
If H is the observed Shannon-Wiener index, the maximum value this could take is log(S), where S is the total number of species in the habitat. Therefore the index is:
J = H/log(S).
There is a big problem with this index. You do not know S! The program assumes that the total number of species observed over all the samples equals S. Therefore you should consider two points before using this index:
1. Have all the chosen samples come from the same habitat? The heterogeneity test button (see Testing for Heterogeneity) might be useful to help you to decide. 2. Has the sampling been sufficient to sample all species? Examination of the species accumulation curve may help you decide this. |