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Mammals with large home ranges, low reproductive rates, and small body sizes are most vulnerable to roads: A meta-analysis

Patterson, Sean1; Fahrig, Lenore1; Jaeger, Jochen2; Meek-Sauriol, Oriana2; Teixeira, Fernanda3; Torres, Aurora4; Rytwinski, Trina1

Published Oct 03, 2025 on Dryad. https://doi.org/10.5061/dryad.1g1jwsv9v

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Abstract

In a previous meta-analysis, mammals with large home ranges, low reproductive rates, and large body sizes were found to respond most negatively to roads. However, due to correlations among these traits, it is not known whether these responses were due to a subset or all three traits. We conducted a multiple meta-regression of the effects of species traits on mammal responses to roads, using data from 92 studies, to determine whether an analysis with a larger sample size and controlling for correlations among traits will support the previous findings. The results reinforce the findings that mammals with larger home ranges and lower reproductive rates respond more negatively to roads. Surprisingly, we found that when controlling for the effects of home range size and reproductive rate, larger mammals respond less negatively to roads than smaller mammals. We speculate that the positive effect of body size is due to driver avoidance of collisions with larger mammals and/or differences in road attraction and car avoidance behaviors of larger vs. smaller species that allow larger mammals to extract benefits of roads while avoiding oncoming vehicles. We also found high variability of individual responses to roads, above what could be explained by the species traits model, most likely due to site and/or species-specific characteristics. Synthesis and applications: Road mitigation for mammals should ideally be informed by site level knowledge and generally involve prioritizing species with the combination of larger home ranges, lower reproductive rates, and smaller body sizes. To protect these vulnerable mammals from roads, we should maintain low road densities and install small-mesh mitigation fencing along roads. This differs from current road mitigation efforts which are typically targeted towards large mammals (e.g., large-mesh fencing along roads) and are often ineffective for smaller mammals.