The effects of species behavioural responses to roads and life history traits on their population level responses to roads

There is now a growing body of evidence that roads and traffic reduce populations of a wide variety of species (Fahrig and Rytwinski, 2009; Benitez-Lopez et al., 2010), and efforts to mitigate road effects are now common in new highway construction projects (Beckmann and Hilty, 2010). To ensure mitigation will be effective at reducing/eliminating road related impacts on wildlife, it is important to have some validated theory that allows us to predict which species or species groups are most vulnerable to road effects at the population level, and the likely causes of those impacts, so that mitigation efforts can be tailored to those species. The overarching goal of my dissertation is to advance our understanding of the circumstances in which roads affect population persistence. In Chapter 1, I conducted extensive field surveys to quantify the relationships between road density and abundance for a wide range of mammal species in eastern Ontario. My results show that mammal species with lower reproductive rates, greater mobilities, and larger body sizes are more susceptible to negative road/traffic effects at the population level. In Chapter 2, I broadened the scope of the investigation by using a meta-analysis to combine empirical results of population level effects of roads from studies across the globe and on multiple taxa, to identify the species or species groups whose populations are most likely to be reduced by roads. These results confirm that wide-ranging large mammals with low reproductive rates are more susceptible to negative road effects at the population level. In addition, they indicate that birds with larger territories, all amphibians and reptiles, and species that do not avoid roads or are disturbed by traffic are susceptible to negative road effects. In Chapter 3, I used a simulation model to develop general hypotheses and predictions specifically of the circumstances leading to neutral and positive effects of roads on population abundance. My results suggest that there are many species and situations for which road mitigation is not necessary. Taken together, my results demonstrate that priority for mitigation should be directed towards wide-ranging large mammals with low reproductive rates, birds with larger territories, and all amphibians and reptiles. More generally, mitigation should focus on species that do not avoid roads or are disturbed by traffic, and on all large species types.