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

Abstract

1. 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.2. 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.3. 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.4. 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.5. 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.6. 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.7. Our results indicate that road-induced changes in orthopteran assemblages could be more efficiently assessed using pitfall trapping than sweep-netting.8. 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.

Vegetation Height as the Primary Driver of Functional Changes in Orthopteran Assemblages in a Roadside Habitat

“…Comparing the results presented here with the results obtained from the same assemblages using taxonomic assemblage metrics, it is evident that orthopterans sampled by sweep-net respond to road proximity mainly in functional terms, and orthopterans sampled by pitfall traps in taxonomic terms (assemblage metrics exhibited a significant decrease at roadside sites; see Rebrina et al [32]). It seems to suggest the higher functional resistance rather than taxonomic resistance of the ground-dwelling assemblage component, which retains a similar functional structure, despite the changes in taxonomic composition [70].…”

“…The latter seems to induce functional changes in orthopteran assemblages primarily through modifications in vegetation cover, causing shifts in functional traits related to mobility, feeding habits and lifestyle. Finally, contrasting spatial patterns of both functional and taxonomic assemblage metrics (see [32]) between sweep-net and pitfall datasets suggest that the full extent of road-induced changes in orthopteran assemblages can only be assessed using a combination of sampling methods. selection and delineation of the study area, and for the identification of vegetation types.…”

“…Likewise, functional responses of orthopteran assemblages to road proximity could provide a good indication of the extent to which such disturbances affect ecosystem processes and their potential for recovery or further degradation [ 29 ]. Road ecology research to date, however, has focused mainly on individual orthopteran species used as models in the studies on acoustic interference with traffic noise [ 30 , 31 ], with only a few papers addressing assemblage-level road effects [ 32 ].…”

“…Previous studies have reported a decrease in Orthoptera biomass with road proximity [ 7 ], but also observed that the type of roadside vegetation has a strong influence on orthopteran abundance in urban environments [ 33 ]. In a recent study conducted within a grassland ecosystem in the Lika region, Croatia, Rebrina et al [ 32 ] found that a major road can induce changes in the composition and structure of adjacent orthopteran assemblages. Assemblage responses differed depending on both the distance from the road and the assemblage component, i.e., plant-dwelling vs. ground-dwelling; only the latter exhibited significant spatial patterns.…”

“…Therefore, expanding on the taxonomically-based approach adopted by Rebrina et al [ 32 ] to study road-associated changes in grassland Orthoptera assemblages sampled by sweep-net and pitfall traps, respectively, we defined two major aims of the current study. Firstly, we aim (1) to investigate the spatial dynamics of functional diversity (evaluated by two distinct diversity measures) and six functional traits (body size, hind femur length to body size ratio, flight capacity, feeding guild, lifestyle and moisture preference) within the same orthopteran assemblages in relation to motorway proximity.…”