Motorway proximity affects spatial dynamics of orthopteran assemblages in a grassland ecosystem

Abstract Major roads have become significant components of environmental change but their impacts on invertebrate assemblages are insufficiently understood, and therefore rarely considered in road‐planning and management. In the current study, we test (i) whether and how orthopteran assemblages change with distance from a motorway, and (ii) how road‐induced changes in noise level, vegetation height and microclimate affect assemblage metrics and spatial distribution of orthopteran species. In 2018, we sampled orthopterans at five distances from a motorway: 10, 25, 50, 100 and 500 m, in eight locations within homogeneous portions of a grassland habitat in Lika region, Croatia, using two sampling methods: pitfall trapping and sweep‐netting. Orthopteran abundance, species richness, true diversity and conservation value decreased at the sites closest to the motorway in the pitfall dataset, primarily due to negative responses of species with low‐frequency acoustic signals. Road‐influenced vegetation height had a stronger overall impact on orthopteran assemblages than traffic noise and/or microclimate; increased diversity and conservation value at 25 m from the motorway suggest an effect similar to early stages of vegetation succession. This study shows, for the first time, that a major road can induce changes in adjacent orthopteran assemblages, but negative impacts are confined to a narrow zone. Our results indicate that road‐induced changes in orthopteran assemblages could be more efficiently assessed using pitfall trapping than sweep‐netting. Increasing heterogeneity of roadside habitats by appropriate vegetation management could help mitigating negative road impacts on Orthoptera in the study area, while contributing to higher diversity of their assemblages.