The effects of an arid-zone road on vertebrates: what are the priorities for management?

Abstract

The strategic management of the impacts of roads on vertebrates is hampered by a lack of information on 1) the scale of such impacts in different ecosystems, 2) the responses of populations and communities, and 3) the relative vulnerabilities of various vertebrate groups. We therefore examined the effects of a typical road in an arid ecosystem on kangaroo populations and communities, threatened small mammal species (Sminthopsis macroura and Leggadina forresti), and small mammal and lizard communities over two years. We determined which vertebrate populations and communities were negatively affected by the road, thereby informing management priorities for mitigating road effects. The study was conducted along the Silver City Highway on the UNSW Arid Zone Research Station, Fowlers Gap, in north-western New South Wales. We found that the road influenced the spatial distribution of kangaroos relative to the road, particularly those of Macropus rufus, and was associated with increased kangaroo mortality. Further, the road altered the composition of small mammal and lizard communities and reduced the abundance of S. macroura. However, roadkill of kangaroos did not significantly affect the population demographics or community composition of kangaroos. There were no changes in sex ratios (female dominance) which would threaten the sustainability of S. macroura and L. forresti populations near the road. Further, changes in the species composition of small mammal and lizard communities were likely to be localised near the road, rather than altered at larger scales, because the differences in resource availability driving community differences were restricted to a narrow band immediately adjacent to the road. Thus, none of the vertebrate taxa studied were significantly threatened by the presence of the road and its associated vehicle traffic. Even so, we recommend that management efforts focus on reducing the frequency of kangaroo roadkill (the most serious animal and human welfare issue) through encouraging the growth of shrubs and low vegetation unpalatable to kangaroos adjacent to arid-zone roads. Such a management strategy could also have positive flow-on effects for other vertebrate taxa, and could restore the natural integrity of arid landscapes near roads.