Road density and wetland context alter population structure of a freshwater turtle

Abstract

AbstractRoads are detrimental to wildlife populations that require contiguous networks of terrestrial and aquatic habitats. Many species of freshwater turtles are sensitive to habitat fragmentation caused by roads, and are susceptible to road mortality during overland migrations. The common long‐necked turtle (Chelodina longicollis) is anAustralian freshwater turtle that frequently moves between wetlands, and so populations may incur negative impacts from road effects. Here, we assessed the relationship betweenC. longicollisand road density and landscape variables within populations inhabiting 20 wetlands distributed throughout greaterMelbourne,Australia. The size frequency distribution ofC. longicollisat sites surrounded by high road densities was skewed towards larger individuals, but there was no difference in the frequency of juveniles between high and low road density sites. Regression modelling revealed a clear positive relationship between road density and carapace length (CL) ofC. longicollis; the meanCLat a site with the highest road density was predicted to be 23% greater than meanCLat a site surrounded by no roads. FemaleCLwas also positively related to road density. There was a clear positive relationship between wetland age andCL, although this relationship was not as strong. While there was no relationship evident between road density and the proportion of femaleC. longicollisat a site, more females were captured at smaller ephemeral sites surrounded by a high proportion of green open space and located near drainage lines. We did not find evidence of sex‐related differences in road effects. These results suggest that roads may be affectingC. longicollisin the study area, but the direct cause of any effects is difficult to identify.