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