Ground beetle assemblages respond to motorway proximity through changes in functional rather than taxonomic diversity in a grassland ecosystem

Abstract

Despite being among the best-studied insect groups in road ecology, assemblage-level effects of major roads on ground beetles have rarely been investigated from the functional perspective. In this study we adopted both species-based and trait-based approaches to investigate spatial dynamics of ground beetle assemblages with respect to motorway proximity and identify main environmental drivers of the observed changes. In 2018, ground beetles were sampled by pitfall traps within homogeneous portions of a grassland habitat in Lika region, Croatia, in eight locations at five distances from a motorway: 10, 25, 50, 100 and 500 m. While no significant spatial patterns were found in taxonomic assemblage metrics, confirming that road-related effects are less prominent in open compared to closed habitat types, functional diversity of ground beetles increased with motorway proximity, possibly owing to an edge effect. Our findings show that, in grassland ecosystems, motorways are likely to affect ground beetle assemblages primarily through changes in vegetation height, with highly vegetated roadsides potentially acting as habitat corridors or supplementary habitats for generalist and mesophilous species.