The relative effects of road traffic and forest cover on anuran populations

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Description/Abstract

Road traffic and the loss of forests are both known to have negative effects on anurans. However, the relative importance of these two predictors is poorly understood because for est cover in the landscape is usually negatively correlated with the density of roads and traffic. To evaluate the independent effects of traffic and forest cover, we selected 36 ponds near Ottawa, Canada, at the center of four landscape types: low forest/low traffic; low for est/high traffic; high forest/low traffic; and high forest/high traffic, where traffic and forest cover were measured within 100 - 2000 in of the edge of each pond. We surveyed all ponds in 2005 and re-surveyed a 23-pond subset in 2006. The negative association between species richness and traffic density was stronger (partial R-2=0.34; P <.001) than the positive asso ciation of species richness with forest cover (partial R-2=0.10; P >.05) in the landscape. Three of six common species showed stronger associations with traffic density than with forest cover - Bufo americanus, Rana pipiens, and Hyla versicolor; two species - Pseudacris cru cifer and Rana syluatica - showed stronger associations with forest cover than with traffic; while Raria clamitans showed similar associations with traffic and forest cover. Our results show that the overall negative effect of traffic on anuran populations in northeastern North America is at least as great as the negative effect of deforestation, and also that the relative effects of these two predictors on anuran abundance vary between species