The relative influence of adjacent road characteristics and habitat on lizard populations in arid shrublands

Reptile populations are declining worldwide, and anthropogenic habitat loss and fragmentation are frequently cited causes. As road networks continue to expand globally, indirect impacts to adjacent wildlife populations remain largely unknown. In addition, quantifying direct effects, such as road mortality, can be difficult because scavengers can rapidly remove carcasses from the road and cause underestimation of mortality counts. Therefore, we had two objectives for this project: 1) to evaluate the relative influence of three different road characteristics (surface treatment, width and traffic volume) and habitat features on populations of northern sagebrush lizards ( Sceloporus graciosus graciosus), plateau fence lizards ( S. tristichus) and greater short-horned lizards (Phrynosoma hernandesi) in mixed arid shrubland habitats in southwest Wyoming, and 2) to determine the effect that scavengers might have had on our ability to accurately detect reptile road mortality during extensive driving surveys in 2009 using unique simulated snake carcasses made out of Burbot ( Lota lota), a locally invasive fish species. With regards to the first objective, we found that neither lizard presence, nor relative abundance was significantly related to any of the assessed road characteristics, although there was a trend for higher Sceloporus spp. abundance adjacent to paved roads. Sceloporus spp. relative abundance did not vary systematically with distance to the nearest road. Rather, both Sceloporus spp. and greater short-horned lizards were strongly associated with particular habitat characteristics adjacent to roads. These results suggest that characteristics of roads do not significantly influence adjacent lizard populations, at least in our system. With regards to the second objective, we found that removal of simulated carcasses was higher than expected on paved roads in all study areas, with an average of 74% of the carcasses missing within 60 h. Carcass removal was lower than expected on dirt and two-track roads in all study areas, with an average of 33% and 31% missing on dirt and two-track roads, respectively, after 60 h. Carcass size was not a significant predictor of time of removal. Scavengers may therefore negatively impact the ability of researchers to accurately detect herpetofaunal road mortality, especially on paved roads where road mortality is likely the most prevalent.