Relationship between the relative abundance of species as observed via amplicon sequencing and their absolute abundances. The upper panel shows the relative abundance of two species A (shades of blue) and B (shades of pink) at two time points in a theoretical experiment. From t1 to t2, a decrease in relative abundance of species B is observed, coupled to an increase in relative abundance of species A.  The relative abundance pattern observed at t2 could have been caused by five changes in the biomass and absolute abundance of the microbial community as shown in the lower panel. Time point t1 is shown for comparison.