Comparison of OTU sets to true species clusters. The innermost rings represents the 20 most abundant species in the sample. Each species shown has ≥ 40 sequences in the dataset (total observations shown next to name of each species). The middle ring displays OTUs of the methodology using the parameters that resulted in the closest approximation of the species structure. The outer ring is an OTU set generated from methodologies used to study microbial communities of (a) soil  and (b) termite hindguts . Previously published methodologies partition most species into several OTUs, resulting in an over-fragmentation of the species-level structure of the environment.