0.932
1.6094
0.1094
0.932
1.6094
0.1094
Pielou's Evenness Calculator computes the evenness component of biodiversity from the Shannon diversity index and species richness. Evenness (J) measures how equally individuals are distributed among species, independent of how many species are present. A community where all species are equally abundant has J = 1, while one dominated by a single species has J approaching 0.
Enter the Shannon diversity index (H') and the number of species (S) to calculate Pielou's evenness. This measure helps disentangle the two components of diversity: richness (how many species) and evenness (how equal their abundances).
Pielou's evenness (J) is the ratio of observed Shannon diversity to the maximum possible Shannon diversity:
J = H' / H'max = H' / ln(S)
Where H' is the observed Shannon index (using natural logarithm) and S is the number of species. H'max = ln(S) would occur if all S species had identical abundances (perfect evenness).
The H' deficit (H'max - H') indicates how much diversity is lost due to uneven abundances. J ranges from 0 to 1, where 1 means perfect evenness and values near 0 indicate extreme dominance by one or few species.
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Results
With H' = 1.5 and 5 species, J = 0.93. This is very close to 1, indicating that species are nearly equally abundant.
Inputs
Results
With H' = 1.0 and 10 species, J = 0.43. Despite having many species, the community is quite uneven, with most individuals concentrated in a few species.
Pielou's evenness separates the evenness component from the richness component of diversity. Two communities can have the same Shannon index but very different evenness: one might have few species that are all equally common, while the other has many species with one dominating. Evenness helps identify whether low diversity is due to few species (low richness) or unequal abundances (low evenness).
J is dependent on species richness (S), and its value tends to increase with S even when the underlying evenness pattern is the same. This makes J difficult to compare between communities with very different numbers of species. Also, J is bounded by the observed S, which itself depends on sampling effort. Some ecologists prefer other evenness measures that are less sensitive to richness.
Alternatives include the Simpson-based evenness (E1/D = (1/D)/S), the Bulla evenness index (based on overlap), and the Smith-Wilson evenness index (based on variance of abundances). Evar, proposed by Smith and Wilson, is less correlated with species richness than Pielou's J. The choice of evenness measure can affect ecological conclusions.
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