Diversity patterns between river sections.

Diversity of benthic macroinvertebrates collected from 168 low-mountain streams and rivers in the German state of Hessen, sampled between 2005 and 2008. (a) Local taxonomic richness, (b) rarefied richness (corrected for 100 organisms), (c) Simpson’s diversity, and (d) beta diversity (beta dispersion, distance to group centroid), between headwaters (light; N = 48), mid-sized streams (medium; N = 69), and large rivers (dark; N = 51). Boxes represent the interquartile range (IQR), and whiskers are the furthest point within 1.5 x IQR above or below the IQR. Values beyond this range are plotted as individual points. Central line represents the median. Local taxonomic richness (P < 0.01), rarefied richness (P < 0.01), and Simpson’s diversity (P < 0.05), but not beta dispersion (P > 0.05) differed significantly between the three sections. See text for full results. Different letters on the plot indicate significant differences between stream sections according to Tukey’s HSD test.