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Index of Diversity (AQA) Calculator

AQA-specific measure of biodiversity relating species and individual counts.

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Index of Diversity

Formula first

Overview

The Index of Diversity quantifies the biodiversity of a habitat by relating the number of different species present to the total number of individual organisms. Unlike simple species counting, this formula accounts for the relative abundance of each species, preventing a single dominant species from over-representing the ecosystem's health.

Symbols

Variables

N = Total Organisms, n(n-1) = Sum of n(n-1), d = Index of Diversity

Total Organisms
Variable
Sum of n(n-1)
Variable
Index of Diversity
Variable

Apply it well

When To Use

When to use: Use this formula when comparing the biodiversity of two different areas or monitoring changes in a single habitat over time due to succession or human impact. It is most effective when you have quantitative data for all species in a community, typically collected via random sampling.

Why it matters: A high index value indicates a stable, diverse ecosystem with many niches, meaning it is more likely to withstand environmental shifts or disease. Conversely, a low index suggests a stressed environment or one dominated by a few species, which is often a priority for conservation efforts.

Avoid these traps

Common Mistakes

  • Using N-1 incorrectly or confusing with Simpson's Index.
  • Convert units and scales before substituting, especially percentages, time units, or powers of ten.
  • Interpret the answer with its unit and context; a percentage, rate, ratio, and physical quantity do not mean the same thing.

One free problem

Practice Problem

A student samples a pond and finds three species of water insects. Species A has 10 individuals, Species B has 5, and Species C has 2. Calculate the index of diversity (d) for this pond, rounding to two decimal places.

Total Organisms17
Sum of n(n-1)112

Solve for:

Hint: Calculate N(N-1) first, then divide by the sum of n(n-1).

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. AQA Biology A Level Year 1 & 2 by Glenn and Susan Toole
  2. Wikipedia: Diversity index
  3. AQA Biology A Level Year 1 & 2 Student Book by Jo Locke, Helen Harden, Mark Smith, Pauline Lowrie, Mike Boyle, Diane Nuttall, and John
  4. Toole, Glenn, and Susan Toole. AQA Biology A-level Year 1 & 2. Oxford University Press, 2015.
  5. Magurran, Anne E. Ecological Diversity and Its Measurement. Princeton University Press, 2004.
  6. Wikipedia: Simpson index
  7. AQA A-Level Biology — Populations in Ecosystems