Distance effects of cropland boundaries on spider and carabid beetle assemblages in Beijing.

Agricultural environmental management practices, such as establishing wildflower strips, can mitigate the loss of natural enemy diversity caused by habitat fragmentation and agricultural intensification. However, carabid beetles and spiders of different functional groups may exhibit divergent responses to these strips and heterogeneous distance effects due to their distinct ecological traits. Here, we used pitfall trapping to compare the diversity of carabid beetles and spiders in 2 boundary habitats (artificial flower strips vs. natural grass strips) in 7 fields in Beijing and at different distances from farmland boundary. The responses of spider and carabid beetle abundance, richness, and assemblage structure to boundary management varied by functional group. Natural grass strips supported a higher total spider abundance, overall richness, and richness of large spiders during the early crop stage, while artificial flower strips enhanced the abundance and richness of web-building spiders, small beetles and herbivorous beetles in the late crop stage. A distance effect was observed only in the abundance of small spiders in natural grass strips and in the abundance of herbivorous beetles in artificial flower strips across the distance gradient. Additionally, the assemblage structure of carabid beetles exhibited significant differentiation between farmlands with artificial flower strips and those with natural grass strips. Our study emphasizes the complementary roles of artificial flower strips and natural grass strips in maintaining spider and carabid diversity and suggests that boundary management should be tailored to target functional groups to mitigate the impact of agricultural intensification on the diversity of carabid beetles and spiders.