Two insect communities have identical species richness but different evenness. Which index would best capture this difference?

Correct answer: (a) Shannon diversity index

Explanation

Species richness counts only the number of species. Evenness describes how equally the individuals are spread among those species. Two communities with the same number of species can differ greatly in evenness.

The Shannon diversity index (H′) takes into account both richness and the relative abundance of each species, so it changes when evenness changes. It is the best of these for detecting the difference.

• Simpson's dominance index mainly reflects how much the commonest species dominate.
• Margalef's index adjusts richness for the number of individuals, but ignores how they are spread.