Kazuhiro KATOH （the University of Tokyo）
Replicated samples from a single ecological community are not identical with each other in species composition. It is because of statistical variability caused by random sampling and also because of spatial heterogeneity within habitat. Based on the analysis of replicated field samples and bootstrap simulation samples, I found that Bray-Curtis index, the most popular quantitative similarity index, tended to be more influenced by spatial heterogeneity than Jaccard's coefficient that is the most popular qualitative similarity measure. Qualitative variation in species composition among replicated field samples was largely interpreted by statistical variability while quantitative one was not. It was also indicated that environmental stress could reduce variation in quantitative species composition among replicated field samples, presumably because of restricted spatial heterogeneity. The statistical characteristics of Jaccard's coefficient were different from those of qualitative similarity measures: the number of relatively abundant species is a possible factor that determines statistical variability of Jaccard's coefficient.
Bray-Curtis index, species diversity, Diatom assemblages, Jaccard's coefficient, similarity