Expert in biodiversity metrics and ecological statistics.
Use our Simpson’s Diversity Index Calculator to measure the biological diversity of an ecosystem. This tool quantifies species richness and evenness, helping ecologists and students analyze population health with precision.
Simpson’s Diversity Index Calculator
Enter the number of individuals for each species below:
Simpson’s Diversity Index Formula
$$D = \frac{\sum n(n-1)}{N(N-1)}$$
Source: Britannica – Diversity Index | Wikipedia
Variables:
- $n$: The total number of organisms of a particular species.
- $N$: The total number of organisms of all species.
- $D$: Simpson’s Index (Value ranges from 0 to 1).
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What is Simpson’s Diversity Index Calculator?
The Simpson’s Diversity Index is a mathematical measure used to characterize the species diversity in a community. Unlike simple species richness, which only counts the number of different species, this index takes into account the proportion of each species within the sample.
In ecology, a lower value of $D$ suggests higher diversity, whereas a value closer to 1 indicates a dominance by a single species. To make interpretation more intuitive, researchers often use $1 – D$ (The Simpson’s Index of Diversity), where higher values represent greater biodiversity.
How to Calculate Simpson’s Diversity Index (Example)
- Count your species: Suppose you find 10 Maples, 5 Oaks, and 2 Pines.
- Determine $N$: Total population $N = 10 + 5 + 2 = 17$.
- Calculate $n(n-1)$ for each:
- Maple: $10 \times 9 = 90$
- Oak: $5 \times 4 = 20$
- Pine: $2 \times 1 = 2$
- Sum the results: $\sum n(n-1) = 90 + 20 + 2 = 112$.
- Apply the formula: $D = 112 / (17 \times 16) = 112 / 272 \approx 0.411$.
Frequently Asked Questions (FAQ)
What is a “good” Simpson’s Index value?
There is no single “good” value as it depends on the ecosystem. However, for $1-D$, a value closer to 1 represents an extremely diverse community.
What is the difference between $D$ and $1-D$?
$D$ measures dominance (probability that two individuals belong to the same species). $1-D$ measures diversity (probability they belong to different species).
Can I use this for non-biological data?
Yes, it can be used in economics to measure market concentration (known as the Herfindahl-Hirschman Index) or in social sciences.
Why is $N(N-1)$ used instead of $N^2$?
The $N(N-1)$ correction is used for finite sampling without replacement, which is standard in field ecology.