Graphs represent the variation in the proportion of (A) total taxa richness and (B) EPT richness between the first Surber sample and the cumulative sample in relationship to the substrate index and water depth and velocity. Samples with identical values of the variables (i.e. the same proportion of taxa at the same depth) overlap in the graph. Boxplots (C) represent the proportion of EPT individuals in relationship to the water velocity: the vertical black line indicates the median, while the lower and upper edges of the boxes represent the first and the third quartiles respectively.