Figure 2. Four core methods identify different sets of core taxa from abundance data in a study of human microbiomes (a), HMP, (Consortium, 2012); and b) Arabidopsis thaliana , (Lundberg et al., 2012). Additionally, the sets of core and non-core taxa do not exhibit categorically distinguishable abundances. The outlined bins denote whether taxa in the bin were included within the core. Fill color corresponds to taxa counts. The hard cutoff and proportion of reads methods categorize taxa on the basis of an abundance threshold (horizontal axis) without accounting for variance (vertical axis), whereas methods based on the proportion of replicates incorporates both abundance and variance criteria.