Roads & Habitat Fragmentation

Habitat fragmentation occurs when human-made barriers such as roads, railroads, canals, electric power lines, and pipelines penetrate and divide wildlife habitat. Of these, roads have the most widespread and detrimental impacts.   For many years ecologists and conservationists have documented the adverse relationship between roads and wildlife. They have identified four ways that roads and traffic detrimentally impact wildlife populations:

1. they decrease habitat amount and quality
2. they increase mortality due to wildlife-vehicle collisions (road kill)
3. they prevent access to resources on the other side of the road; and
4. they subdivide wildlife populations into smaller and more vulnerable sub-populations (fragmentation). Habitat fragmentation can lead to extinction or extirpation if a population’s gene pool is restricted enough.

The first three impacts (loss of habitat, road kill, and isolation from resources) exert pressure on various animal populations by reducing available resources and directly killing individuals in a population.  For instance, road kills do not pose a significant threat to healthy populations but can be devastating to small, shrinking, or threatened populations.   In addition, habitat loss can be direct, if habitat is destroyed to make room for a road, or indirect, if habitat quality close to roads is compromised due to emissions from the roads (e.g. noise, light, runoff, pollution, etc.).

Finally, species that are unable to migrate across roads to reach resources such as food, shelter and mates will experience reduced reproductive and survival rates, which can compromise population viability.

In addition to the first three factors, numerous studies have shown that the construction and use of roads is a direct source of habitat fragmentation.  As mentioned above, populations surrounded by roads are less likely to receive immigrants from other habitats and as a result, they suffer from a lack of genetic diversity.  The relationship between roads and habitat fragmentation is well documented.

After years of research, biologists agree that roads and traffic lead to habitat fragmentation, isolation and road kill, all of which combine to significantly compromise the viability of wildlife populations throughout the world.