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Species counts · richness and evenness
Biodiversity index calculations
Calculate biodiversity indices from original species-count data, using the stated AQA or OCR formula. Compare values calculated with the same formula.
Method and worked examples ↓Learn the method
How to approach these questions
- N is the total number of organisms. Each n is the count for one species.
- For d, calculate n(n − 1) separately for each species before adding the terms.
- For D, square each species proportion separately, add the squares, then subtract the sum from 1.
- Higher values indicate higher diversity for each of these forms, but their numerical scales differ. Compare sites using the same formula and comparable sampling.
Worked examples
Two species each have 10 individuals. Calculate the AQA subject-content index d.
N = 20. Σn(n − 1) = 10 × 9 + 10 × 9 = 180. d = 20 × 19 ÷ 180 = 2.11 to 3 significant figures.
Use D = 1 − Σ(n/N)² for the same counts of 10 and 10.
The proportions are 0.5 and 0.5. D = 1 − (0.5² + 0.5²) = 0.50. This is not the same numerical scale as d = 2.11.
Keep practising
Topic map and study list · Practical data guides · Active recall decks
Course resources
AQA A-level Biology · OCR A A-level Biology · Textbook answers
Skill coverage follows the common A-level science subject content. Check your board’s current requirements: AQA 7402 and OCR A H420.