Ecology & Environment
Biodiversity Index Calculator
Calculate total observations, Simpson diversity, Shannon entropy, and the Shannon effective number of species from four abundance counts. The species-wheel visual makes dominance and evenness visible before the indices are interpreted.
Total observations-
Simpson diversity index-
Shannon diversity index-
Effective species count-
Decision view
Species abundance and diversity structure
Species abundance and diversity structureFour abundance shares reveal dominance and evenness before Simpson, Shannon, and effective-species values are interpreted.
Exact scenario comparisonSpecies 1 count changes while all other entered assumptions remain constant.
| Species 1 count | Total observations | Simpson diversity index | Shannon diversity index | Effective species count |
|---|
How to use Biodiversity Index Calculator
- Enter counts collected with the same sampling method, area, effort, and taxonomic resolution.
- Check the abundance wheel for dominance or near-even composition.
- Compare indices only across samples with defensible detection and effort consistency.
Calculator guide
Understanding Biodiversity Index Calculator
Diversity reflects both richness and evenness. Four sites can contain the same number of species yet produce different Simpson and Shannon values when abundance is concentrated differently.
Calculation method
How the calculation works
Calculate Simpson and Shannon diversity from four entered abundance counts and convert Shannon entropy to an effective species count. Sum all counts, calculate Simpson diversity from pairwise abundance proportions, calculate Shannon entropy from each positive share, and exponentiate Shannon entropy for the effective species count.
Interpretation
Read indices with the abundance pattern
A single number can hide which species dominates or disappears.
Worked situations
Practical examples
- Counts 40, 30, 20, and 10 total 100 observations.
- The Simpson diversity index is about 0.707.
- Shannon entropy is about 1.280, corresponding to roughly 3.596 equally common species.
Better inputs
Useful tips
- Retain raw counts with every reported index.
- Use rarefaction or occupancy methods when sampling effort or detectability differs.
- Report richness, evenness, and index definition because several Simpson conventions exist.
Before relying on the result
Limitations and common mistakes
- Exactly four entered abundance groups are modeled.
- Unobserved species, detectability, unequal effort, spatial dependence, and identification error are excluded.
- The indices do not directly measure ecosystem health, rarity value, or functional diversity.
Reference
Key terms
- Richness
- Number of species or groups represented.
- Evenness
- How similarly observations are distributed among species.
- Shannon entropy
- Abundance-weighted uncertainty measure using natural logarithms.
- Effective species
- Number of equally common species producing the observed Shannon entropy.
Important note
Calculated from the entered environmental values using the displayed model. Measurement quality, local conditions, system boundaries, and source data affect interpretation.
Frequently asked questions
Is a higher index always better?
It indicates greater diversity under that formula, not automatically better ecosystem condition.
Why calculate effective species?
It expresses Shannon entropy on an intuitive species-count scale.
Can zero counts be entered?
Yes, but they contribute neither abundance nor entropy and do not represent observed richness.
Can I compare samples with different totals?
Proportion-based indices allow arithmetic comparison, but sampling effort and detectability must still be comparable.