Fig. 3. Relationship between anuran relative abundance, species richness, and distance to Highway 401 (residuals after controlling for significant local predictors; Table 3) in 2006 (n = 34). The lowess smoothing line is shown. For species fitted with a piecewise regression model, the breakpoint of the best fitting model is shown by heavy solid vertical line; the second best-fitting breakpoint for the American toad, chorus frog, and species richness is shown by the second, but thinner, solid vertical line. One SD below the smallest breakpoint and 1 SD above the largest breakpoint are shown (dashed vertical lines). For the leopard frog and green frog, relative abundance was defined as the maximum number of adults seen during visual surveys. For all other species, relative abundance was defined as the chorus counts summed over all surveys.