4.18—Comparing biodiversity with index of diversity

The index of diversity compares communities using both the total number of organisms and how evenly individuals are distributed among species: D = N(N−1) / Σn(n−1). N is the total count and n is the count for one species.

Add all individuals to find N, calculate N(N−1), calculate n(n−1) for every species and sum those terms, then divide. A larger D indicates greater diversity under this formula.

For N = 202 and Σn(n−1) = 6884, D = 202×201 ÷ 6884 ≈ 5.90. Two habitats with the same richness can still have different D values if one is dominated by one species.

Use the exact formula and counts supplied; do not confuse D with species richness or with the heterozygosity index. Comparing habitats also requires comparable sampling effort.