Simulated communities with distinct relative abundance profiles. (a) Relative abundances of 15 genera in three simulated communities and the simulated reference database. Pop1 is not strongly dominated by any taxon, but it is has unique taxa (Ruminococcus). Pop2 is dominated by Prevotella, which occurs at much lower levels in the other communities, and lacks Akkermansia. Pop3 is dominated by Bacteroides and Faecalibacterium, which occur at lower levels in the other communities, and lacks Prevotella. (b) Correspondence analysis of a matrix giving the number of sequences belonging to each genus in the three simulated communities and reference database (with genera as rows and communities as columns). Each panel shows two of the first three components plotted against each other; these components capture a significant part of the variation among the communities and reference database.