Landscape diversity can promote functional diversity of spider assemblages while habitat characteristics filter for specific traits

Abstract Agricultural landscape simplification due to the loss of semi‐natural habitats can act as an environmental filter for species and their functional traits. Both local‐ and landscape‐level factors can shape community structure; although through different mechanisms. In this study, we investigated the role of spontaneous grass field margins in enhancing the taxonomic and functional diversity of ground‐active spider assemblages in wheat fields along a landscape diversity gradient. Using pitfall traps, we sampled spiders from 16 wheat fields and three habitat types: the inner field, the field edge and the adjacent grass margin. We collected 2119 spiders (1887 adults) from 72 species and 16 families. Linyphiidae and Lycosidae were the dominant families, comprising 50% and 31% of all sampled individuals, respectively. Landscape diversity had a marginally significant positive effect on functional dispersion, a metric of functional diversity, but did not significantly affect spider activity density or richness. Habitat type had a significant effect on functional diversity but had no effect on activity density and species richness. The spider assemblage in the inner field habitat was less functionally diverse than the assemblages in both the field edge and grass margin habitats. Moreover, grass margins hosted a distinct spider assemblage characterised by larger, free‐hunting and less ballooning species compared to the inner field and field edge habitats. Our results suggest that habitat type, and to a lesser extent also landscape diversity, can support more functionally diverse spider assemblages and contribute to shaping the functional structure of ground‐active spider assemblages. Particularly, spontaneous grass margins can support large, free‐hunting spider species that are absent in wheat fields, potentially enhancing biological control in agricultural landscapes. These results are important for designing agricultural landscapes that promote pest control and for understanding how spider functional traits respond to both local‐ and landscape‐scale factors. Read the free Plain Language Summary for this article on the Journal blog.