Simpson's Diversity Index Calculator
Understanding Simpson's Diversity Indices
Simpson's Diversity Index is a measure of diversity that takes into account both species richness (the number of species present) and species evenness (the abundance of each species). There are several common forms of the index:
1. Simpson's Index (D):
D = Σ [ nᵢ * (nᵢ - 1) ] / [ N * (N - 1) ]
Σrepresents the sum across all species.nᵢis the number of individuals in species i.Nis the total number of individuals of all species.- This index (D) measures the probability that two individuals randomly selected from a sample will belong to the same species.
- Values range from 0 to 1. A value of 0 represents infinite diversity, and a value of 1 represents no diversity (only one species present). This inverse relationship with diversity can be counterintuitive.
2. Gini-Simpson Index (1 - D):
1 - D = 1 - { Σ [ nᵢ * (nᵢ - 1) ] / [ N * (N - 1) ] }
- This index measures the probability that two individuals randomly selected from a sample will belong to different species.
- Values range from 0 to 1. A value of 0 represents no diversity, and a value closer to 1 represents higher diversity. This is often preferred due to its more intuitive interpretation.
3. Inverse Simpson Index (1 / D):
1 / D = [ N * (N - 1) ] / Σ [ nᵢ * (nᵢ - 1) ]
- This index represents the effective number of species if all species were equally abundant.
- The value starts at 1 (for a single-species community) and increases with diversity. The maximum value is S (species richness).
Species Richness (S): The total number of different species in the community.
Important Note: The calculation of D requires N > 1. If N ≤ 1, D is typically considered undefined or 1 (no diversity possible with 0 or 1 individual for pairwise comparison).
How to Use:
- Enter the number of individuals for each species found in your sample. Use the "Add Species" button to add more input rows if needed.
- Click "Calculate Diversity Indices" to see the results.