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The Shannon Diversity Index Calculator computes the Shannon-Wiener diversity index (H') from species abundance data. This is one of the most widely used measures of ecological diversity, accounting for both species richness (number of species) and evenness (how equally individuals are distributed among species).
Enter the abundance (number of individuals) for up to three species. The calculator returns H' (using natural logarithm), the total number of individuals, species richness, and Pielou's evenness (J). Higher H' values indicate greater diversity. For communities with more than three species, this simplified calculator can be applied iteratively or used as a learning tool.
The Shannon index is calculated as:
H' = -SUM(pi x ln(pi))
Where pi is the proportion of individuals belonging to species i (pi = ni / N), and the sum is over all species present. The natural logarithm (ln) is used by convention in most ecological applications.
Pielou's evenness is: J = H' / H'max = H' / ln(S)
Where S is the number of species. J ranges from 0 (completely uneven) to 1 (perfectly even). A community with more species and more even abundances has a higher H'. Typical values range from 1.5 to 3.5 for most ecological communities.
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Three species with abundances 50, 30, and 20 give H' = 1.03. With maximum H' = ln(3) = 1.099, the evenness J = 0.94, indicating fairly even distribution.
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When one species dominates (95%), H' drops to 0.21 and evenness is only 0.19, indicating very low diversity despite three species being present.
The Shannon index (H') quantifies the uncertainty in predicting the species identity of a randomly chosen individual. Higher H' means greater uncertainty, which corresponds to higher diversity. It combines two components: species richness (more species increases H') and evenness (more equal abundances increase H'). It is analogous to the entropy concept in information theory.
For most ecological communities, H' typically ranges from 1.5 to 3.5. Values below 1 indicate low diversity (few species or highly uneven abundances). Values above 3 indicate high diversity. However, the maximum possible H' increases with species richness (H'max = ln(S)), so comparisons should be made between communities with similar richness or by using the evenness measure J.
The Shannon index can be calculated with any logarithm base. Natural logarithm (ln) is most common in ecology, giving H' in units of "nats." Log base 2 gives H' in "bits" (used in information theory). Log base 10 gives "bans" or "hartleys." The choice of base affects the numerical value but not the relative ordering of communities. Always state which base is used when reporting H' values.
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