Evenness Index Calculator
Free Evenness index Calculator for biodiversity ecosystem. Enter variables to compute results with formulas and detailed steps.
Formula
Pielou J = H / Hmax = H / ln(S)
Pielou evenness divides observed Shannon index by maximum possible Shannon index for the species count. Values near 1 indicate equal abundances, near 0 indicate strong dominance.
Worked Examples
Example 1: Bird Community
Problem: 15 bird species, Shannon H = 2.2, Simpson D = 0.88, dominant species 18% of individuals, 400 total.
Solution: Hmax = ln(15) = 2.708\nPielou J = 2.2 / 2.708 = 0.8124\nSimpson E = 0.88 / (1 - 1/15) = 0.9429\nBerger-Parker = 0.18\nRating: Moderately Even
Result: Pielou J: 0.812 | Simpson E: 0.943 | Rating: Moderately Even
Example 2: Degraded Grassland
Problem: 8 plant species, Shannon H = 0.9, Simpson D = 0.55, dominant species 45%, 200 total.
Solution: Hmax = ln(8) = 2.079\nPielou J = 0.9 / 2.079 = 0.4329\nSimpson E = 0.55 / (1 - 1/8) = 0.6286\nBerger-Parker = 0.45\nRating: Slightly Uneven
Result: Pielou J: 0.433 | Simpson E: 0.629 | Rating: Slightly Uneven
Frequently Asked Questions
What is species evenness?
Species evenness measures how equally individuals are distributed among species in a community. A community with 100 individuals split as 10 per species across 10 species has perfect evenness, while one with 91 individuals of one species and 1 each of 9 others is highly uneven. Evenness ranges from 0 (completely dominated by one species) to 1 (all species equally abundant). It is a key component of biodiversity alongside species richness.
How is Pielou J evenness calculated?
Pielou J evenness (also called Pielou equitability index) is calculated as J = H / Hmax, where H is the observed Shannon diversity index and Hmax is the maximum possible Shannon index for the given number of species. Hmax equals the natural logarithm of species count, ln(S). A J value of 1.0 means all species are equally abundant, while values approaching 0 indicate extreme dominance by one or few species. It is the most widely used evenness measure in ecology.
What is the Shannon diversity index?
The Shannon diversity index (H) quantifies the uncertainty in predicting the species identity of a randomly chosen individual from the community. It is calculated as H = -sum(pi x ln(pi)), where pi is the proportion of individuals belonging to species i. Higher values indicate greater diversity. H increases with both species richness and evenness. For a given number of species, H is maximized when all species are equally abundant, giving H = ln(S).
How does Simpson evenness differ from Pielou evenness?
Simpson evenness divides the Simpson diversity index (D) by its maximum value for S species: E = D / (1 - 1/S). While Pielou J is based on Shannon diversity and is sensitive to rare species, Simpson evenness is weighted toward dominant species and is less affected by rare species with very few individuals. The two indices can give different assessments of the same community, so reporting both provides a more complete picture of community structure.
What is the Berger-Parker dominance index?
The Berger-Parker dominance index (d) is the simplest dominance measure, calculated as the proportion of the most abundant species: d = Nmax / N, where Nmax is the number of individuals of the dominant species and N is total individuals. It ranges from 1/S (perfect evenness) to 1 (complete dominance). The complement (1 - d) serves as an evenness measure. Despite its simplicity, it is widely used because the dominant species often has the largest ecological impact.
Why does evenness matter for ecosystem function?
Evenness affects ecosystem function because communities dominated by one species are more vulnerable to disruption. If the dominant species is lost to disease or environmental change, a highly uneven community loses most of its biomass and function. Even communities maintain function better because multiple species contribute substantially, providing insurance against the loss of any single species. Research shows that evenness promotes ecosystem stability, productivity, and resistance to invasion.