The logseries distribution and Mountford's similarity index as a basis for the study of stream benthic community structure

SUMMARY. 1. Of the various approaches to studying species-abundance patterns in aquatic ecosystems (particularly streams) the logseries distribution is the most appropriate. The distribution parameter, α, is readily estimated and goodness-of-fit of the model to the data can be estimated.
2. A method exists which uses a to calculate an index of similarity from which cluster dendrograms can be constructed and the clusters tested for significant differences. Assumptions and calculations are presented.
3. Procedures are illustrated, with examples from Idaho streams, and approaches to interpreting the results are included.
4. Studies of stream macro invertebrates can fulfill the assumptions of the logseries distribution but cannot meet those of commonly used diversity indices.