Shannon Diversity Index Calculator
Calculates the Shannon Diversity Index (H') for a community with up to three species, quantifying both species richness and evenness. Used by ecologists and conservationists to compare biodiversity across different habitats or time points.
About this calculator
The Shannon Diversity Index (H') is a widely used metric that accounts for both the number of species present (richness) and the relative abundance of each species (evenness). The formula is: H' = −Σ(pᵢ × ln(pᵢ)), where pᵢ is the proportion of individuals belonging to species i (pᵢ = nᵢ / N, with N = total individuals), and the sum is taken over all species present. A community with a single species has H' = 0, indicating no diversity. Higher H' values indicate greater diversity; typical values range from 1.5 to 3.5 for most ecological communities. The natural logarithm (ln) is standard, though log₂ and log₁₀ are sometimes used in other disciplines. The index is sensitive to both rare and dominant species, making it more informative than a simple species count.
How to use
Suppose you survey three species: Species 1 = 50 individuals, Species 2 = 30 individuals, Species 3 = 20 individuals. Total N = 100. Proportions: p1 = 0.5, p2 = 0.3, p3 = 0.2. Apply the formula: H' = −[(0.5 × ln(0.5)) + (0.3 × ln(0.3)) + (0.2 × ln(0.2))] = −[(0.5 × −0.6931) + (0.3 × −1.2040) + (0.2 × −1.6094)] = −[−0.3466 − 0.3612 − 0.3219] = −(−1.0296) ≈ 1.03. Enter your species counts to compute H' for your community.
Frequently asked questions
What is a high versus low Shannon Diversity Index value in ecology?
Shannon Diversity Index values generally range from 0 to around 4–5 in most natural communities. A value of 0 means only one species is present, with no diversity at all. Values between 1.5 and 2.5 are considered moderate diversity, typical of disturbed or simplified ecosystems. Values above 3 are associated with highly diverse, relatively undisturbed communities such as tropical rainforests or coral reefs. Context matters greatly — a value considered high in a temperate grassland may be low for a tropical community — so H' is most useful when comparing similar ecosystem types or tracking changes in the same system over time.
How is the Shannon Diversity Index different from species richness?
Species richness is simply the count of distinct species in a community, with no regard to how abundant each species is. The Shannon Index combines both richness and evenness: two communities can have the same number of species but very different H' values if one is dominated by a single species while the other has roughly equal abundances. For example, a community of 100 individuals split 98-1-1 across three species has far lower H' than one split 34-33-33, even though both have three species. This makes H' more ecologically meaningful than raw species count for assessing true biodiversity.
Why does the Shannon formula use a negative sign in front of the sum?
Each term in the sum, pᵢ × ln(pᵢ), is inherently negative or zero because pᵢ is a proportion between 0 and 1, and the natural log of any number between 0 and 1 is negative. Summing these negative terms produces a negative total. The negative sign in front of the summation (−Σ) flips the result to a positive value, which is easier to interpret as an index of diversity. This sign convention is purely mathematical and ensures that H' is always ≥ 0, with higher positive values representing greater diversity.