A functional evenness index for microbial ecology.

Microbial ecologists attempting to describe community structures through the use of synthetic parameters face enormous difficulties. These stem in part from the necessity of using standard taxonomic reference levels in a field where the species level is poorly defined. This paper presents an attempt to obviate this problem. A "functional evenness" index (E) is defined using information measures; it is based directly on the characteristics of the bacteria, as determined, for example, with the API 20B method. Comparisons of this index with classic structure indices, such as taxonomic evenness (Pielou) or systematic dominance (Hulburt), show that it behaves like an evenness index, while bypassing the taxonomic study required before computation of the classic indices. Its use is illustrated with samples of aerobic heterotrophic bacteria obtained from brackish lagoon sediments.