Phylogenetic Approaches for Describing and Comparing the Diversity of Microbial Communities

Diversity is the hard currency of ecologists. Various statistics have been developed for summarizing the diversity of an eco-logical community. A commonly adopted summary statistic is the Shannon-Weiner index: H #!pilnpi, where pi is the frequency of the ith species. In addition, species richness (the number of different species) often is reported, and recent work emphasizes the importance of accurate estimates of species richness when ecological communities and processes that affect the composition of communities and the function of ecosys-tems are described (5). The significance of diversity is often inferred by comparing communities characterized from differ-ent environments. Typically, such comparisons rely on stan-dard measures of overlap, including the percentage of species shared by two communities or similarity indices. One of the indices used is Sorensen’s index: S S12/0.5(S1! S2), where