Density profile for a single non-responder OTU. The $^{13}$C-cellulose
treatment is in blue and the control treatment is in orange. The vertical line
shows where high density fractions begin as defined in our analysis. The right
panel shows relative abundance values in the high density fractions for each
gradient (The boxplot line is the median value. The box spans one
interquartile range (IR) about the median, whiskers extend 1.5 times the IR.  

