Species Diversity Index Calculator
Two Ecosystems Can Have the Same Species Count and Very Different Diversity
Count four species in a plot and you might assume the ecosystem is equally diverse whether those four species are represented evenly or dominated by one. They're not the same at all — a community where one species makes up 91% of individuals is functionally far less diverse than one split evenly four ways. Diversity indices exist specifically to capture that difference in evenness, not just species richness.
The Formulas
Simpson's Diversity Index: D = 1 − Σ(pi2)
In both formulas, pi is the proportion of individuals belonging to species i out of the total counted. Shannon's index weighs rare species more heavily through the logarithm; Simpson's index is more sensitive to dominant species through the squared term.
Where This Calculation Matters
- Ecological monitoring — tracking diversity index changes over time reveals whether an ecosystem is recovering, degrading, or stable.
- Conservation prioritization — comparing diversity indices across sites helps identify which habitats warrant protection.
- Environmental impact assessment — pre- and post-development diversity comparisons quantify ecological disturbance.
- Microbiome studies — the same indices are applied to bacterial community composition in gut, soil, and water microbiome research.
How Evenness Changes the Index (4 Species, N = 100)
| Species Counts | Shannon (H') | Simpson's (D) |
|---|---|---|
| 25, 25, 25, 25 (perfectly even) | 1.3863 | 0.7500 |
| 70, 10, 10, 10 | 0.9404 | 0.4800 |
| 91, 3, 3, 3 (one dominant) | 0.4014 | 0.1692 |
Both indices peak at perfect evenness and fall as one species comes to dominate — but note the counts and totals never change here, only the distribution among species.
How to Use This Calculator
- Choose the index to compute: Shannon or Simpson's.
- Enter Species counts as a comma-separated list (e.g. 12,7,25,3), with at least two species.
- Select Calculate to get the diversity index for that community.
Related Calculations
Tracking how a population within one of these species changes over time? See the Population Growth Calculator. For cell-level division counts within an individual organism, use the Cell Division Time Calculator.