Overview
This lecture explains biodiversity and demonstrates how to calculate it in an area using Simpson's Index of Diversity, including examples and interpretations.
What is Biodiversity?
- Biodiversity measures the variety and abundance of different species in an area.
- High biodiversity means many different species and many individuals of each species.
- Low biodiversity means few species or dominance by one species.
Simpson's Index of Diversity
- Simpson's Index quantifies biodiversity using species counts in a sample area (quadrat).
- The index value ranges from 0 (no diversity) to 1 (high diversity).
- A higher value indicates greater diversity.
Key Variables in the Formula
- “N” (capital N) stands for the total number of individuals in a sample.
- “n” (lowercase n) is the number of individuals of each specific species.
Formula and Calculation Steps
- The preferred formula for Simpson's Index of Diversity is:
D = 1 - [ÎŁn(n-1)] / [N(N-1)].
- Subtracting one in n(n-1) and N(N-1) accounts for pairs of individuals, not just totals.
- If a species has only one individual, its contribution is nullified by the n-1 part.
Example Calculations
- A sample dominated by one species (e.g., 36 of one type) gives a low D value (~0.15), indicating low diversity.
- Even distribution among species (e.g., 6 each of three types) gives a higher D value (~0.71), indicating high diversity.
- More species with varied but larger counts give the highest D value (~0.82), indicating the most diversity.
Interpreting Results
- A value close to 0 means low diversity (likely dominated by one species).
- A value close to 1 means high diversity (many species are well represented).
- The index can help compare sites or track changes in biodiversity, e.g., along a transect away from human habitats.
Key Terms & Definitions
- Biodiversity — the range and abundance of different species in an area.
- Simpson's Index of Diversity (D) — a calculated value representing the probability that two individuals randomly selected from a sample will be of different species.
- Quadrat — a square sample plot used for ecological study.
- N — total number of individuals in the sample.
- n — number of individuals of a particular species.
Action Items / Next Steps
- Practice calculating Simpson’s Index for different sample data sets.
- Consider setting up a transect and collecting quadrat data to observe biodiversity changes.
- Review the difference between Simpson’s reciprocal and diversity indices.