Average functional distinctness as a measure of the composition of assemblages

Abstract

AbstractSomerfield, P. J., Clarke, K. R., Warwick, R. M., and Dulvy, N. K. 2008. Average functional distinctness as a measure of the composition of assemblages. – ICES Journal of Marine Science, 65: 1462–1468. Indices are used to quantify change in the environment by reducing aspects of environmental complexity to numbers. Biodiversity indices are typically calculated using the numbers of species and their relative abundances. A recent advance has been the development of additional measures of diversity, such as phylogenetic diversity, based on relationships between organisms. The emerging paradigms of the importance of biodiversity to ecosystem services and the ecosystem approach to fishery management could be well served by the development of indicators of ecosystem functioning. We discuss how relatedness measures may be adapted to quantify aspects of community structure of relevance to ecosystem functioning, by combining information on species’ occurrence, life history, and ecological traits. We present an index that reflects average functional distinctness within assemblages. We illustrate the approach using North Sea fish. Results reveal that average functional distinctness is not independent of taxonomic distinctness. This is expected, but the weakness of the relationship suggests that both indices may prove useful, because they are not constrained to convey the same information about samples. Both indices are shown to be weakly related to species richness, which was not expected. This is a consequence of differences in the frequencies of occurrence among species.