Species Diversity Index Calculator
The Shannon and Simpson diversity indices from a list of species counts — with evenness, the effective number of species, and which species dominates.
Richness is how many species; diversity also asks how evenly individuals are spread among them.
How the species diversity index calculator works
Richness is how many species; diversity also asks how evenly individuals are spread among them. Shannon's index weights every species by its share; Simpson's asks how likely two random individuals are to be the same species and emphasises the common ones.
The effective number of species — e raised to Shannon — is the most readable: it is the number of equally common species that would give the same diversity. Ten species where one holds 90% of individuals is effectively about two.
Formula: H = −Σ pᵢ ln pᵢ; D = 1 − Σ pᵢ²; effective species = e^H
Worked examples
| Inputs | Shannon index H | Note |
|---|---|---|
| Ten species, uneven | 1.5807 | effectively about five |
| Perfectly even | 1.6094 | H = ln 5, evenness 1 |
| One dominant | 0.235 | effectively barely more than one |
FAQFrequently asked questions
What is the Shannon index?
A measure of diversity that weights each species by its share of individuals. Higher is more diverse; it rises with both richness and evenness.
What is the effective number of species?
e raised to the Shannon index — the number of equally common species with the same diversity. It is the figure to quote, because H itself has no intuitive units.
What is the difference from Simpson?
Simpson's index is the chance two random individuals differ in species. It weights common species more heavily and is less sensitive to rare ones.
What is evenness?
Shannon divided by its maximum, ln S. One means every species is equally common; near zero means one species dominates.
Why does richness alone mislead?
Because ten species with one at 90% is not a diverse community. Diversity indices exist precisely to say how much the count overstates.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- Wellcome Sanger Institute — a leading UK genomics institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.