There are many hallmarks of human influence in a given ecosystem or habitat. It seems, though, that our habit of leaving roads in our wake pretty much everywhere may be the best predictor of our effect on the world around us.

“Biodiversity loss may occur directly via road-kill events, disturbance or pollution, or indirectly by stimulating and facilitating loss of habitat, and forming barriers to dispersal and gene flow,” wrote study authors in Proceedings of the Royal Society B. “Roads also affect biodiversity through reduction in habitat quality, facilitating human access to frontier landscapes, increasing opportunities for selective logging and bushmeat hunting, increased risk of forest fires and the creation of edge effects at road-habitat boundaries.”

In spite of that litany of negative effects, the authors note that there has not been an abundance of research done actually quantifying some of the problems. How precisely do road networks affect animals, in this case birds? In particular, they focused on how roads affect birds in the Brazilian Amazon, a place where road networks grew by almost 17,000 kilometers (about 10,500 miles) each year between 2004 and 2007.

They found a significant positive correlation between a metric called “roadless volume” (essentially a measure of road density) and species richness of birds; in other words, fewer roads meant more birds. The roads seemed to have more of an effect on species richness than even forest cover (though that was also significantly related to species). Roadless volume also had an effect on species composition; the number of unique species of bird present in a given area increased with fewer roads.

This is an important finding mostly because of the independent effect. Roads are not just a symptom of habitat loss in general, they seem to play a specific role, on their own, in reducing biodiversity. The authors suggest three mechanisms in particular for the effect of the roads: fragmentation and creation of barriers for species movement; the precipitation of environmental changes such as an altered microclimate, and differing light and foliage levels; and finally, roads may serve as a proxy for damaging practices such as logging.

“Our results indicate that roadless volume may act as an ‘early warning metric’ of species loss, picking up regions that have not yet been deforested, but that are subject to other disturbance events,” the authors wrote. Adding this sort of check seems like a no-brainer, given its ease and apparent utility. Simply looking for the presence of a road, rather than trying to assess forest cover and habitat degradation via satellite image, may help us better assess where conservation efforts should focus. – Dave Levitan | October 7 2014

Source: Ahmed SE, Lees AC, Moura NG, et al (2014). Road networks predict human influence on Amazonian bird communities, Proceedings of the Royal Society B, 281;20141742. DOI: 10.1098/rspb.2014.1742

Image: shutterstock.com, Jozef Sowa