Disentangle the Causes of the Road Barrier Effect in Small Mammals through Genetic Patterns

Abstract

Road barrier effect is among the foremost negative impacts of roads on wildlife. Knowledge of the factors responsible for the road barrier effect is crucial to understand and predict species’ responses to roads, and to improve mitigation measures in the context of management and conservation. We built a set of hypothesis aiming to infer the most probable cause of road barrier effect (traffic effect or road surface avoidance), while controlling for the potentially confounding effects road width, traffic volume and road age. The wood mouse Apodemus sylvaticus was used as a model species of small and forest-dwelling mammals, which are more likely to be affected by gaps in cover such as those resulting from road construction. We confront genetic patterns from opposite and same roadsides from samples of three highways and used computer simulations to infer migration rates between opposite roadsides. Genetic patterns from 302 samples (ca. 100 per highway) suggest that the highway barrier effect for wood mouse is due to road surface avoidance. However, from the simulations we estimated a migration rate of about 5% between opposite roadsides, indicating that some limited gene flow across highways does occur. To reduce highway impact on population genetic diversity and structure, possible mitigation measures could include retrofitting of culverts and underpasses to increase their attractiveness and facilitate their use by wood mice and other species, and setting aside roadside strips without vegetation removal to facilitate establishment and dispersal of small mammals.

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

“…This corresponds with results from Ascensão et al. () that found lower F st exhibited by wood mice ( Apodemus sylvaticus ) at a highway site with a higher proportion of culverts than similar sites with higher F st and fewer culverts. On the other hand (and rather surprisingly), one very large culvert at site HC may have contributed to the population differentiation that we observed in the gray squirrel, chipmunk, and white‐footed mouse populations.…”

“…) and on one or two species (e.g., Ascensão et al. ). If site‐specific characteristics interact with the life history characteristics of species, thereby leading to variance in the permeability of highway systems, single‐site studies would be unlikely to elucidate such differences (Peter et al.…”

Edge effects on small mammals: Differences between arboreal and ground‐dwelling species living near roads in Brazilian fragmented landscapes

“…However, even in temperate zones the responses of specialized arboreal species to the different effects of fragmentation are more varied than the responses of generalist ground-dwelling species (Michal & Rafal 2014). Small mammals in temperate zones show differing responses to the road barrier effect: some experience deleterious effects to the genetic structure of their populations (Ascensão et al 2016), whereas effects are more neutral for species able to move through the landscape and maintain interconnected population (Grilo et al 2016). These different patterns exemplify species-specific relationships to roads and the landscape in general, and show the importance of considering small mammal species individually according to their habits and behaviours.…”

“…prioritize expansion of the road network in areas that are already cleared and which have unexplored economic potential) (Laurance et al 2014); and implement mitigation strategies (e.g. improve the environment of wildlife passages with habitat surrogates such as rocks and wood, or shelves and ramps that separate species) that consider the behavioural response of the target species to different disturbances (Ascensão et al 2015(Ascensão et al , 2016D'Amico et al 2015).…”

Latitudinal biodiversity gradients at three levels: Linking species richness, population richness and genetic diversity

“…tens to hundreds of years instead of thousands or millions) due to stochastic processes as well as increasing anthropogenic impacts (Goossens et al, ; Riley et al, ; Weider, Lampert, Wessels, Colbourne, & Limburg, ). Human impacts can cause species range barriers more quickly than otherwise expected, greatly reducing connectivity and thus increasing the likelihood of population differentiation (Ascensão et al, ; Cheptou, Hargreaves, Bonte, & Jacquemyn, ; Meyer, Kalko, & Kerth, ; Riley et al, ). Alternatively, human influences can homogenize populations by the movement of individuals through introductions, translocations, stocking and supplementation (Johnson et al, ; Tringali & Bert, ).…”