Table 4. Comparison of the threshold distance ( 1 SD) from 2006 and 2007 that the road effect zone of Highway 401 extended into the landscape for anuran relative abundance and species richness, as estimated from the breakpoints of piecewise regressions. For cases in which more than one breakpoint was estimated (*) (e.g., American toad in 2006; Figs. 3 and 4), only the estimate from the best-fitting model is shown. N/A indicates that no statistically significant (P < 0.05) "difference in slope parameter" was present, or that no piecewise regression was attempted because a threshold was not apparent from visual examination of the data. A piecewise regression was not attempted for the chorus frog in 2007 because of the low number of presences (7) of this species in that year.


Response Breakpoint (m) (2006) Breakpoint (m) (2007)
Species Richness 640.9 ± 183.1* 675.4 ± 245.2
Wood Frog Summed Calling 827.8 ± 204.7 529.94 ± 94.6*
Western Chorus Frog Summed Calling 1417.0 ± 290.7* N/A
Spring Peeper Summed Calling 273.8 ± 55.8 211.8 ± 26.6
Leopard Frog Maximum Adults N/A N/A
American Toad Summed Calling 246.4 ± 56.4* 149.8 ± 27.1
Gray Treefrog Summed Calling 245.9 ± 54.1 316.2 ± 98.0*
Green Frog Maximum Adults N/A N/A