Linking habitat suitability and road mortalities across geographic ranges

Abstract

Protected areas are established to conserve biodiversity and facilitate resilience to threatening processes. Yet protected areas are not isolated environmental compounds. Many threats breach their borders, including transportation infrastructure. Despite an abundance of roads in many protected areas, the impact of roads on biota within these protected areas is usually unaccounted for in threat mitigation efforts. As landscapes become further developed and the importance of protected areas increases, knowledge of how roads impact on the persistence of species at large scales and whether protected areas provide relief from this process is vital. We took a two-staged approach to analysing landscape-scale habitat use and road-kill impacts of the common wombat (Vombatus ursinus), a large, widely distributed herbivore, within New South Wales (NSW), Australia. Firstly, we modelled their state-wide distribution from atlas records and evaluated the relationship between habitat suitability and wombat road fatalities at that scale. Secondly, we used local-scale fatality data to derive an annual estimate of wombats killed within an optimal habitat area. We then combined these two approaches to derive a measure of total wombats killed on roads within the protected area network. Our results showed that common wombats have a broad distribution (290,981 km2), one quarter (24.9 %) of their distribution lies within protected areas, and the percentage of optimal habitat contained within protected areas is 35.6 %, far greater than the COP10 guidelines of 17 %. Problematically, optimal habitat within protected areas was not a barrier to the effects of road-kill, as we estimated that the total annual count of wombat road-kill in optimal habitat within protected areas could be as high as 13.6 % of the total NSW population. These findings suggest that although protected areas are important spatial refuges for biodiversity, greater effort should be made to evaluate how reserves confer resilience from the impacts of roads across geographic ranges.