What's stopping you? Variability of interstate highways as barriers for four species of terrestrial rodents

Abstract

Landscape features that form a barrier for one species may not be a barrier for others, depending on how each species perceives the feature. Barriers may not be equivalent, due to unique characteristics at different locations, which may ameliorate barrier effects. In this study, we employed population genetics techniques to investigate how four Rodentia species with differing life history characteristics (fox squirrels [Sciurus niger], eastern gray squirrels [Sciurus carolinensis], eastern chipmunks [Tamias striatus], and white‐footed mice [Peromyscus leucopus]) responded to interstate highways as barriers to movement at seven locations with differing site‐specific landscape features. For comparative purposes, we included control sites that lacked heavily trafficked roads. We detected genetic differentiation relative to interstate highways among the gray squirrels, chipmunks, and white‐footed mice, but signals for differentiation among those three species varied by site, suggesting that site‐specific features are important considerations for species responses to high‐traffic roads. Chipmunk and gray squirrel populations, two forest specialist species that avoid open areas, exhibited more genetic structure corresponding with highways than either white‐footed mice (a nocturnal generalist) or fox squirrels (a larger‐bodied specialist that traverses open areas more readily than the other species in this study). Fox squirrels did not exhibit genetic differentiation at any site, whereas gray squirrel study populations evinced no population differentiation at sites with bridges spanning the interstate highway. Chipmunks also exhibited population differentiation at two of the control sites, indicating that less obvious barriers in the landscape may be as important as roads for sensitive species. We interpreted variation in genetic differentiation of species across sites in the context of how interstate highway features (i.e., the presence and condition of drainage culverts and bridges near study sites), combined with species‐specific life history characteristics, influence the barrier potential of highways. Culvert presence generally corresponded with a low or nonexistent barrier effect; however, an open, large culvert (>8 m in height) may create a semi‐permeable barrier for species that avoid open areas. Bridge presence appeared to facilitate gray squirrel and chipmunk dispersal across highways.

Anthropogenic and natural barriers affect genetic connectivity in an Alpine butterfly

“…Patterns seem to depend on the size of the barrier, the species under consideration, and the statistical power to resolve such relationships (Ćosić et al., 2013; Hayes & Sewlal, 2004). Anthropogenic barriers can include human settlements, agriculture, roads, and highways (Fraser et al., 2019; Goldberg & Waits, 2010; Hennessy et al., 2018; Marquardt & Marcus, 2018; Miles et al., 2019; Nilsson et al., 2013; Yang et al., 2011). Within a conservation context, roads represent a particularly important barrier because they are a common source of habitat fragmentation and may cause high mortality (Beebee, 2013; Muñoz et al., 2015).…”

“…Within a conservation context, roads represent a particularly important barrier because they are a common source of habitat fragmentation and may cause high mortality (Beebee, 2013; Muñoz et al., 2015). Roads have been repeatedly shown to cause genetic differentiation in diverse terrestrial taxa including mammalian carnivores, rodents, amphibians, and insects (Hennessy et al., 2018; Johansson et al., 2005; Muñoz et al., 2015; Riley et al., 2006). One possible cause is road kill; especially for small insects that are overrepresented in road kill (Muñoz et al., 2015; Skórka et al., 2013; Soluk et al., 2011).…”

College squirrels gone wild? Using Sciurus carolinensis behavior to assess the ecosystem value of urban green spaces

“…Much evidence suggests that vehicle tra c generally negatively impacts wildlife, but the extent to which urban road use impacts animal foraging costs is not well documented. In general, roads are much more likely to have negative effects on animal abundances and behavior than positive effects (Speziale et al 2008;Fahrig and Rytwinski 2009;Baxter-Gilbert et al 2015), and limited evidence suggests that at least major roadways limit movement of eastern gray squirrels (Hennessy et al 2018, although see Fey et al 2018 for a contrasting result for urban red squirrels). Our results showing higher GUDs closer to urban roads suggest that road proximity and tra c affect gray squirrels' perception of risk.…”

Temporal clustering of prey in wildlife passages provides no evidence of a prey-trap

“…By reducing the functional connectivity of landscapes, roads can restrict dispersal and gene flow to subdivide populations, ultimately reducing genetic diversity 2 , 3 . Barrier effects may be especially prevalent for small animals with limited mobility 6 , 7 and high sensitivity to road surfaces and traffic 8 , 9 .…”