Principles underlying unstable distance-based greedy clustering (DGC) and abundance-based greedy clustering (AGC), rarefaction curves, and PCoA based on the Bray-Curtis distance. (a, b) Principles underlying unstable DGC (a) and AGC (b) 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. Yellow dots indicate OTU centroids. 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, d) Rarefaction curves generated with DGC (c) and AGC (d) at five different depths. (e, f) PCoA based on the Bray-Curtis distance, comparing 60% subsamples with the full datasets using AGC (e) and DGC (f). All of the subsamples were rarefied to 30,000 sequences per sample to be included in this analysis.