Roads have become integrated into our world and are a central function to human society. When barriers are placed around roads, this in turn affect wildlife’s ability to move as well as the trajectory and evolution of wildlife populations; this is known as the barrier effect as wildlife learn to avoid roads with barriers around them. However, how exactly do barriers impact our wildlife and cause them to avoid roads?
The Barrier Effect
Roads can impose a barrier effect to occur in wildlife populations, causing wildlife to decrease their dispersal rates and limit the amount of demographic rescue and gene flow within a population; this in turn increases the species potential of going extinct. The barrier effect is related to the impacts of roads and affects several wildlife populations; it’s usually caused by behavioral responses to roads (i.e., road avoidance), emissions associated with the road (i.e., traffic-emissions avoidance), and/or the circular activity of vehicles on a road (i.e., vehicle avoidance).
Road avoidance by wildlife is usually dependent on the surface material of the road itself or the clearance of vegetation near the road. Traffic-emission avoidance is dependent upon the long-ranging disturbances coming from roads, such as dust, light, vibrations, and/or noise. Vehicle avoidance is dependent upon the behavioral response of a species of wildlife that has the movement and cognitive capacity to avoid vehicles on a road. All of these types of avoidances are drivers of the barrier effect and cause wildlife to avoid roads.
An example of the barrier effect can be seen with the federal plans to complete a continuous wall along the U.S.-Mexico boundary. Implementing this wall would threaten the existence of multiple plant and animal species, as many species migrate terrestrially between the U.S. and Mexico. Though this example is not of a road itself, it emphasizes why wildlife populations have road avoidance due to barrier effects.
Barriers, whether along a road or between countries, present physical limitations to wildlife, preventing and/or discouraging wildlife from accessing vital resources such as food, water, mates, or disrupt annual or seasonal migration and dispersal routes. These barriers, whether border walls or for transportation infrastructures, not only affect wildlife, but also cause habitat fragmentation, soil erosion, changes in fire regimes, and altering of hydrological processes through causing floods. From this, it seems that each species of wildlife has a how and why to the reasons for road avoidance, however, this is an issue that needs future considerations and research needs.
Future Considerations & Research Needs
Behaviors vary across all species of wildlife, however, with the use of basic ecology, predictions can be made for the primary response wildlife populations will have to roads and therefore provide increased predictive ability about how barrier effects of roads are perceived as a risk to wildlife. This is a solution for researchers concerned about this issue, as they can conduct studies on specific species of wildlife or a specific road to understand why the animals in that area are avoiding it.
Other solutions can include the need to identify species surrounding the road area, the habitats and ecological resources at risk from the barrier being constructed, designing barriers to have maximum wildlife permeability wherever possible, and/or restoring habitats when the harm to the environment is inevitable. Though we may be a long ways away from finding a solution to wildlife displaying barrier effects from road avoidance, researchers can still assess the primary responses of wildlife species to better understand what the causes of road avoidance may truly be, and help to construct better roadway systems for both wildlife and the environment in the future.
The barrier effect is a very real and pervasive threat to wildlife, as it may cause them to avoid certain areas of vital habitat key to their survival all because of our major transportation infrastructures deterring them away. Collaboration from researchers based in wildlife biology, ecology, and even road ecology could all work together to implement the solutions listed above so our roads no longer deter our wildlife from their native land.
