A consumer's guide to evenness indices

Many indices have been proposed for measuring species evenness in ecological communities, but there is no consensus on which are best. We assemble criteria for an appropriate index for the evenness of a biological sample. The most important criterion is that evenness should be independent of species richness. Twelve previously proposed indices and variants are considered, and two apparently new indices. Four indices are recommended as joint best buys: A) If symmetry between minor and abundant species is not important, or if it is required that the index be less affected by minor species: 1) If it is essential that the index be able to reach a minimum of zero with any particular number of species, or if the shape of the index response to an evenness gradient is important: E(1 D) (based on a common form of Simpson's index). 2) If good mid-range behaviour is desired: E' (proposed by Camargo). B) If equal sensitivity to minor and abundant species is required: 1) If the shape of the index response to an evenness gradient is not important, the clear winner is: E(Q) (a new index). 2) If the shape is important: E(van) (another new index). The overall recommendation for general use is E(van).