Roads dominate landscapes around the globe and have tremendous impacts on the natural world.
According to Dr. Jochen Jaeger, an expert road ecologist at Concordia University, and colleagues, the four main threats of roads to wildlife are:
- Habitat loss
- Direct mortality
- Inaccessibility to resources
- Population subdivision
Together, these four threats reduce population size of many plant and animal species. Species at risk are especially susceptible to the threats of roads since small populations are more vulnerable to extinction than are large populations.
Within the province of Ontario, Southern Ontario has the greatest density of people and roads. It is also home to the highest number of Species at Risk in the province. The vast road network, high traffic volume and abundance of biodiversity in the region increase the probability of a wildlife/vehicle collision.
The Ministry of Transportation of Ontario reports approximately 14,000 wildlife/vehicle collisions annually and acknowledges that many more go unreported, especially those involving small wildlife, including species at risk reptiles, amphibians and birds.
Aside from the physical loss of habitat from road construction and the land around that is often developed, roads lead to a decrease in habitat quality. Pollution in the form of litter, light, noise, chemical, heat and vibrations all lower habitat quality for local wildlife. For example, a population of frogs living beside a highway must expend more energy to call louder and more often to attract a mate over the ambient noise of traffic.
Roads also facilitate the spread of invasive species. As traffic rushes by, the generated wind carries seeds of salt-resistant and pollution-tolerant plants along the length of the route. For example, the common reed, Phragmites australis, can be seen lining highway corridors for long stretches. This plant can then spread into neighbouring wildlife habitats where it may outcompete local biodiversity.
Direct mortality caused by wildlife/vehicle collisions can drastically impact local animal populations. In addition, wildlife on the road is a hazard to humans. A collision with a large animal may be fatal for motorists, as can swerving to avoid small wildlife. Many species at risk whose populations are affected by roads are slow-moving animals, such as reptiles and amphibians that do not readily avoid roads or vehicles. These species can experience extremely high mortality rates due to roads. Economically, such incidents can represent hundreds of millions of dollars annually in Canada (taking into consideration insurance, road clean up and time lost in the transport of goods and services).
Inaccessibility to Resources
Roads fragment the landscape and may prohibit animals from accessing critical resources such as food, shelter and mates. Populations will decline over time when they cannot access all of the resources that they need.
When populations are sub-divided and gene flow is reduced or ceases, populations become more vulnerable to succumbing to extreme environmental events (e.g. flooding, drought, disease, etc.).