Rarefaction curves, principles underlying unstable complete linkage (CL) clustering, and PCoA based on the Bray-Curtis distance. (a) Rarefaction curves generated with CL clustering at five different depths. Point A is the number of OTUs at 30,000 sequences from the 100% dataset, and point B is the number of OTUs at 30,000 sequences from the 60% dataset. (b) Principles underlying unstable CL clustering at two sampling depths. White circles indicate individual sequences that were included in both the small and the large subsamples, and dark circles indicate sequences that were added only in the large subsample. Lines indicate pairs of sequences with distances equal to or smaller than the threshold, which could therefore be linked into a single OTU. Large circles in red or blue indicate OTUs in the small and the large subsamples, respectively. (c) PCoA based on the Bray-Curtis distance, comparing 60% subsamples with the full datasets using CL. All of the subsamples were rarefied to 30,000 sequences per sample to be included in this analysis.