Diversity, biotic and similarity indices: A review with special relevance to aquatic ecosystems

Abstract

Diversity Indices, Biotic Indices and Similarity Indices are reviewed considering their ecological application, both theoretical and practical. Eighteen diversity indices in eight groups, nineteen biotic indices in ten groups and five similarity indices are examined for their applicability to biological systems, particularly aquatic ecosystems. All the diversity indices were found unsuitable except for Simpsons D, Hurlberts PIE, indices based on the theory of Runs (SCI and TU) and possibly McIntosh's M. Indices based on information theory, such as H′ and H, although the most commonly used diversity indices were unsatisfactory due to the lack of exploration of their biological relevance. The use of H′ in aquatic ecosystems is only justified until the more satisfactory indices are adequately field tested.Biotic indices are highly specialised for a particular type of water pollution, usually organic pollution. Chutter's and Chandler's biotic index appear to be most favoured. In their present form, however, such indices are necessarily limited to the geographical area in which the tolerance lists were compiled. Although many comparisons have been made between diversity indices and biotic indices, these were found to be spurious as one index reflects community structure the other the physiological response of indicator species to one type of pollution. Such comparisons have usually been justified by claiming that one index performs better when compared to the term “water quality”, which is usually left undefined.The five similarity indices examined have been used in aquatic systems. It is not clear which of these indices is best to use. The percentage similarity index (PSC) and Pinkham and Pearson's index (B) appear to be most favoured for aquatic systems, though there is a need for further research and field testing of similarity indices for water pollution.The relationship and definitions of diversity and stability are examined. Though discussion is by no means concluded on this topic it is clear that diversity does not automatically lead to either stability or instability but may be found with both. Disturbance to an ecosystem may often increase diversity provided it is of intermediate frequency, yet an ecosystem may also become more diverse without becoming less stable.The numbers of these three types of indices have become legion, as has their use. It is time that only those indices with biological relevance were used. It is hoped that work will now concentrate on the promising members of the two indices of community structure (diversity and similarity) as these are of broad applicability while biotic indices are limited to one or a few pollutants and one geographical area.