Table 1. Summary of statistical models (2006 data) of the relationships between anuran relative abundance and anuran species richness and distance to Highway 401 as measured by linear, log-linear, and piecewise regressions. In cases in which more than one breakpoint was estimated (*), only the estimate from the best-fitting model is shown. Statistical significance of the coefficients is indicated as follows: * P < 0.05; ** P < 0.01; *** P < 0.001. N/A indicates that no piecewise regression was attempted as no threshold was apparent from visual examination of the data. We used a Gaussian link function for species richness and a Poisson link function for the American toad; all other analyses use the negative binomial link function. Response Simple Linear Model Log Linear Model Piecewise Regression Model AICc Slope: Distance to Highway AICc Slope: log(Distance to Highway) AICc Breakpoint (m) Slope before breakpoint Difference in Slope Parameter Species Richness 124.7 0.0012 ±0.0003*** 114.5 1.160 ±0.2017*** 119.8 640.9 ±183.1* 0.0049 ±0.0015*** -0.0045 ±0.0016** Wood Frog Summed Calling 94.2 0.0012 ±0.0003*** 86.8 1.291 ±0.3152*** 94.1 827.8 ±204.7 0.0038 ±0.0016*** -0.0034 ±0.0016* Western Chorus Frog Summed Calling 78.7 0.0009 ±0.0004 76.2 0.8939 ±0.3886* 74.2 1470.0 ±290.7 0.0018 ±0.0007 -0.0063 ±0.0019* Spring Peeper Summed Calling 200.7 0.0003 ±0.0002 193.5 0.4310 ±0.1126*** 189.6 273.8 ±55.77 0.0094 ±0.0047* -0.0094 ±0.0047*** Leopard Frog Maximum Adults 154.6 0.0007 ±0.0002** 153.1 0.6209 ±0.1830*** 156.7 935.9 ±412.0* 0.0019 ±0.0009** -0.0016 ±0.0010 American Toad Summed Calling 112.6 0.0002 ±0.0001 110.8 0.2631 ±0.1294* 109.0 246.4 ±56.35* 0.0107 ±0.0041 -0.0106 ±0.0041* Gray Treefrog Summed Calling 129.2 0.0004 ±0.0002 125.8 0.5268 ±0.1988** 127.2 245.9 ±54.1 0.0163 ±0.0101 -0.0162 ±0.0101** Green Frog Maximum Adults 246.0 0.0003 ±0.0001* 245.8 0.2827 ±0.1368* N/A N/A N/A N/A