Roads represent one of the biggest disruptions to landscape connectivity. An expanding human population and the global popularity of cars mean that more traffic is on the way. In light of this inevitability, what is the best strategy to mitigate fragmentation: maintain fewer roads with greater volume of traffic, or minimize traffic in any given spot with a greater density of smaller roads? Rhodes et al. compare these two strategies by modeling koala mortality in eastern Australia based on increased traffic versus greater road density.
Their results provide unique insight for road network planning: in most cases, allowing higher volume on fewer roads had less impact than increasing road density. The opposite was true only when traffic was very high and road density was very low. Male koalas were more susceptible to collision than females, suggesting that they (and more mobile species in general) would benefit most from upgrading existing roads rather than building new ones. The overall message is that road planners are almost always better off increasing the capacity of existing roads instead of expanding the network. This allows for greater overall habitat connectivity and an overall better strategy to minimize human disturbance. The next step is to integrate these results with strategies such as wildlife crossings or culverts to map out the best wildlife management plans.
Rhodes, J. R., D. Lunney, J. Callaghan, and C. A. McAlpine. 2014. A few large roads or many small ones? How to accommodate growth in vehicle numbers to minimise impacts on wildlife. PLoS ONE DOI: 10.1371/journal.pone.0091093.