The effect of traffic intensity on ground beetle (Coleoptera: Carabidae) assemblages in central Sweden

Ground beetle assemblages were studied by pitfall trapping during summer 2006 in the municipality of Leksand (Sweden) along a gradient in traffic intensity (10 replicates in high and low traffic and five in no traffic) and at progressive distances from the roadside (5, 15, 40 and 80 m). The ground beetles’ activity density was larger in high- with respect to low-traffic areas. Rarefaction analysis showed that richness did not differ between high and low traffic, whereas it was higher in high and low compared to no-traffic areas. Rarefaction analysis performed in high- and low-traffic areas separately showed that species richness was higher at shorter distance from the road in both treatments. Gradient analysis showed that traffic intensity influenced carabid species composition, although the proportion of explained variation was rather low. Mean body length differed between the three treatments, where ground beetles were larger in no-traffic areas. The proportion of macropterous and diet-generalist beetles did not differ amongst the three treatments. However, there was a difference in the proportion of macropterous beetles in low-traffic areas amongst sampling distances, and in the proportion of diet-generalist beetles amongst sampling distances at both high- and low-traffic areas. The proportion of diet-generalist beetles decreased with increasing distance from the road in both treatments. Our study suggests that major roads have a significant effect on ground beetles assemblages. However, many changes in assemblages and morpho-ecological adaptations followed the gradient in traffic intensity, suggesting that also minor roads affect ground beetle composition. Therefore, efforts to improve habitat connectivity should also consider low-traffic roads.