Figure 4: Level of invasion in 24 riparian wetlands illustrated by (a) relative richness, cover and dominance of all alien species, and (b) relative richness and cover of two functional groups – amphibious and terrestrial alien species. (a) Size of the circles indicates Simpson's dominance index calculated using alien species only (range: 0.10–0.54; larger circles indicate wetlands where alien species cover is dominated by fewer species); black line is the line of best fit. (From Catford et al. 2012)