Hypothetical size-biased indicator system (IHs) where macroinvertebrate size and indicator value are linearly correlated, resulting in a non-linear increase in organism densities with respect to size.

Size differences were converted to differences in relative abundance by assuming an allometric size (S) density (d) relationship (S = d-0.75; [45]) and taking organism size as the diameter of a circle (which was mapped in two-dimensions). The seven classification groups of macroinvertebrate size described by Tachet et al. (2000) [46] are provided for comparison.