Calculates the Shannon diversity index, a standard ecology measure combining how many species are present and how evenly their populations are distributed.
How it works
Each species’ proportion of the total population is multiplied by the natural log of that same proportion, summed across all species, and negated.
What this does not include
This does not include other diversity indices like Simpson’s index, which weight rare and common species differently — this calculator specifically computes the Shannon-Wiener index.
How to use this calculator
- Enter the individual count for each species observed (up to five).
A worked example
Three species with equal counts of 10 each: Shannon diversity index = 1.0986 — maximum diversity for 3 species, since evenness is perfect.
Three species with uneven counts (50, 25, 25): Shannon index = 1.0397 — lower than the perfectly even case, despite the same total population and species count.
A single species present: Shannon index = 0 — no diversity at all.
What the variables mean
| Variable | Meaning |
|---|---|
| Species counts | Population count for each species present |
Edge cases worth knowing
More even distribution across species increases diversity, even with the same species count. The two 3-species examples above show this directly — equal counts score higher than uneven ones.
A single species always scores zero diversity — there’s no variety to measure when everything belongs to one group, regardless of population size.
Frequently asked questions
Why does an even distribution score higher than an uneven one?
Because the Shannon index rewards balance as well as richness — a community dominated by one species is considered less diverse than one where species are more evenly represented, even with the same total species count.
What does a Shannon index of 0 mean?
Exactly one species was found — with no other species present, there’s no diversity to measure.
Is a higher Shannon index always better for an ecosystem?
Generally higher diversity is considered a sign of ecosystem health and resilience, though interpretation always depends on the specific ecosystem and what’s being compared.
