Limited functional response to agroecological practices in spider communities in arable crops

Spiders are versatile and abundant predators in agroecosystems, and hence crucial biological pest control agents. This study compares the effects of agroecological (e.g. pesticide-free, wildflower strips, mechanical weeding) to conventional management on spider functional communities in paired wheat, barley, and oilseed rape fields in Switzerland. Using partial RLQ and fourth-corner analyses, we assess the response of spider traits to management aspects, vegetation architecture and landscape heterogeneity. We recorded 7151 adult spiders representing 84 species across three crops, with community composition differing significantly among crop types but not between management systems. Trait–environment relationships were generally weak, arguably due to a strongly pre-selected disturbance-tolerant species pool. Pairwise analyses revealed that crop height, bare soil, and pesticide use influenced specific guilds – such as negative associations of ambush predators with bare soil, of ruderal-habitat species with tall crops, and positive links of orb weavers with all crops and sheet weavers with high landscape diversity. Overall, within the spatial and temporal scope of this study, we found limited evidence that the agroecological measures implemented were associated with consistent shifts in spider functional composition, suggesting that crop type and local context outweighed management-related effects under the conditions studied.