Fig. 4. Relationship between anuran relative abundance/species richness and distance to Highway 401 (residuals after controlling for significant local predictors; Table 3) in 2007 (n = 22). The lowess smoothing line is also 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 wood frog and the second and third best-fitting breakpoints for the gray treefrog are shown by thin solid vertical lines. One standard deviation below the smallest breakpoint and one 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.