Abstract
ContextTransportation and wildlife agencies may consider the need for barrier structures and safe wildlife road-crossings to maintain the long-term viability of wildlife populations. In order to prioritize these efforts, it is important to identify species that are most at risk of extirpation from road-related impacts.PurposeOur goal was to identify reptiles and amphibians in California most susceptible to road mortality and fragmentation. With over 160 species and a lack of species-specific research data, we developed an objective risk assessment method based upon road ecology science.MethodsRisk scoring was based upon a suite of life history and space-use characteristics associated with negative road effects applied in a hierarchical manner from individuals to species. We evaluated risk to both aquatic and terrestrial connectivity and calculated buffer distances to encompass 95% of population-level movements. We ranked species into five relative categories of road-related risk (very-high to very-low) based upon 20% increments of all species scores.ResultsAll chelonids, 72% of snakes, 50% of anurans, 18% of lizards and 17% of salamander species in California were ranked at high or very-high risk from negative road impacts. Results were largely consistent with local and global scientific literature in identifying high risk species and groups.ConclusionsThis comparative risk assessment method provides a science-based framework to identify species most susceptible to negative road impacts. The results can inform regional-scale road mitigation planning and prioritization efforts and threat assessments for special-status species. We believe this approach is applicable to numerous landscapes and taxonomic groups.
Highlights
There have been many attempts to better characterize and quantify threat criteria in order to classify species at higher risk of extinction at state, national, and global levels (Congress 1973 (U.S Endangered Species Act); Mace et al 2008; Hobday et al 2011; Thomson et al 2016; IUCN 2017)
Roads are a significant threat to wildlife populations (e.g., Forman et al 2003; Andrews et al 2015a; van der Ree et al 2015), causing both barrier and depletion effects
For all Maximum Population Movement Distance (MPMD), we report a relative confidence level based upon the number and quality of studies, sample sizes, and locations in or adjacent to California
Summary
There have been many attempts to better characterize and quantify threat criteria in order to classify species at higher risk of extinction at state, national, and global levels (Congress 1973 (U.S Endangered Species Act); Mace et al 2008; Hobday et al 2011; Thomson et al 2016; IUCN 2017). Roads are a significant threat to wildlife populations (e.g., Forman et al 2003; Andrews et al 2015a; van der Ree et al 2015), causing both barrier (habitat fragmentation) and depletion (road mortality) effects. Depletion effects include all of the risks from barrier effects as well as reduced survivorship, making high road mortality an even greater concern (Jackson and Fahrig 2011). Among other stressors, such as habitat loss and fragmentation, invasive species, pesticide use, changing climate, and disease, the negative impacts from roads may independently or cumulatively threaten the persistence of populations and even species
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