There is growing evidence that roads and traffic reduce populations of many species and efforts to mitigate road effects are now common. To maximise understanding of road impacts and for conservation of particular species, we need to know how roads affect the viability of a group of individuals of the species rather than a single individual. Roads and traffic affect wildlife populations in three major ways, by (i) increasing mortality, (ii) decreasing habitat amount and quality and (iii) fragmenting populations into smaller sub-populations which are more vulnerable to local extinction. To ensure mitigation is effective, we need to identify the species most affected, and the cause(s) of the effects, so that appropriate mitigation can be tailored to those species. 1 Mammals: Larger, more mobile species with lower reproductive rates are more susceptible to road mortality, and species that avoid roads from a distance due to traffic-related disturbance are susceptible to habitat fragmentation, loss and degradation. 2 Birds: Species that have large territories and possibly species that are low flying, ground dwelling and/or heavy relative to their wing size are more susceptible to road mortality. 3 Amphibians and reptiles: All species, regardless of life history traits, are prone to negative road effects as they are particularly susceptible to road mortality and habitat fragmentation by roads. 4 A species response to roads and traffic will vary depending on its conservation status, geographical location, habitat preferences, road type and/or traffic volume. 5 There are still many species for which we do not know the population-level effects of roads. To ensure mitigation will be effective for as many species as possible, research is needed on the effects of roads on a broader range of species. This chapter provides a high-level overview of the population-level effects of roads on animals using the available data from 75 studies. For more detailed information on specific species groups, please refer to Chapters .

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Keywords Attraction to roads, Habitat connectivity, Habitat fragmentation, Population abundance, Road impacts, Road mortality, Road surface avoidance, Species traits, Traffic disturbance avoidance, Vehicle avoidance
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Rytwinski, T. (Trina), & Fahrig, L. (2015). The Impacts of Roads and Traffic on Terrestrial Animal Populations. doi:10.1002/9781118568170.ch28