MEPS 215:69-77 (2001)  -  doi:10.3354/meps215069

ABSTRACT: We present a new similarity index, taxonomic similarity (Δ_S), which can be used to measure β-diversity. Δ_S utilises species presence/absence data, and incorporates both higher taxon richness and evenness concepts. It is derived from the average taxonomic distance (relatedness) of any 2 species from different sites. Therefore Δ_S is analogous to taxonomic distinctness recently developed for biodiversity assessment at α- and γ - (landscape or seascape) scales. Δ_S is a new index, although its derivation uses a concept similar to the Œoptimal taxonomic mapping statistic¹ developed independently for quantifying structural redundancy in marine macrobenthos. Using echinoderm data, we show that Δ_S exhibits smoother behaviour and is less influenced by species richness, and hence sampling effort, than the widely used Jaccard coefficient of species similarity. We also believe Δ_S to be a more intuitive and comprehensive measure of similarity than Jaccard and other conventional indices based solely on species held in common. Taxonomic similarity between sites is computed for echinoderms examined over 3 different spatial scales: local/small-scale (<10 km), intermediate-scale (10 to 100s km) and province/oceanic-scale (100s to 1000s km). Taxonomic similarity between sites increases progressively with spatial scale, with significantly lower values and higher β-diversity at small spatial scales. The same pattern is evident for species similarity, using the Jaccard coefficient. Possible explanations for this pattern centre on: (1) the large-scale oceanic area examined (Indo-West Pacific), representing a metapopulation of echinoderms for the 2 other, smaller areas examined within (Pula Wé, Sumatra and Lakshadweeps); (2) greater biophysical instability and unpredictability at small spatial scales. Compared with larger spatial scales, these may be characterised by greater likelihood and influence of species migrations and extinctions on a site¹s total species composition. Hence, species composition may be highly changeable at small scales, leading to high β-diversity. These findings are based on 1 set of comparative data for 1 faunal group. Any wider conclusions drawn would be premature, although corals may also show greater β-diversity at small spatial scales. The extent to which patterns observed are evident for other marine species groups is not well known.

KEY WORDS: Biodiversity · β-diversity · Taxonomic similarity · Echinoderms · Indo-West Pacific