engleski

Orthopteran assemblages in a roadside habitat: adverse effects of traffic noise and vegetation height

As integral elements of the 21st century landscape, major roads have a profound environmental impact, inducing changes in roadside habitats both directly through pollution and soundscape alteration, and indirectly through changes in vegetation structure and microclimate. Despite their importance in terrestrial ecosystems, ecological effects of roads on insects are still rarely considered in road-planning and management due to the scarcity of data, particularly at the assemblage level. In a five-month study conducted along the largest Croatian motorway in 2018, we sampled orthopteran (Insecta: Orthoptera) assemblages at five distances from the road: 10, 25, 50, 100 and 500 m, in eight locations within a homogeneous grassland habitat. We used two sampling methods: pitfall trapping and sweep netting. Generalized linear mixed models were constructed to test for spatial differences in assemblage metrics and to assess the relationships between orthopteran assemblages and road-influenced environmental factors: traffic noise, vegetation height and soil moisture. Variation partitioning and redundancy analysis were performed to evaluate the influence of these factors on spatial distribution of orthopteran species in the study area. Orthopteran assemblage metrics exhibited significant spatial variation with distance from the motorway in the pitfall dataset. Decrease in abundance, species richness, diversity and conservation value within the first 10 m from the road was likely associated with negative responses of geobiont and geo-chortobiont species with low-frequency signals to traffic noise and, potentially, low soil moisture. At larger distances, however, these species may benefit from noise reduction by overlaying vegetation ; traffic noise had a stronger overall impact on chortobiont species sampled by sweep-net. Nevertheless, orthopteran assemblages were primarily affected by road-induced changes in vegetation height ; an increase in habitat heterogeneity compared to more distant sites may have prompted an increase in assemblage metrics at 25 m from the road. In contrast to previous findings, pitfall trapping proved to be a useful method for road impact assessment and monitoring of roadside Orthoptera. This study shows, for the first time, that major roads affect orthopterans at the assemblage level, but different subsets of orthopteran assemblages are affected in different ways. Our findings have profound implications for roadside vegetation management strategies aiming to mitigate negative impacts of transport infrastructure, and anthropogenic change in general, on terrestrial invertebrates.

road proximity ; assemblage metrics ; environmental factors ; sampling method ; Croatia

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