Landscape composition influences the activity density of Carabidae and Arachnida in soybean fields

Abstract

The distribution and abundance of semi-natural and crop habitats within agricultural landscapes is likely to greatly influence population dynamics of ground-dwelling arthropods. We investigated the influence of landscape heterogeneity and composition on the pitfall trap catch of Carabidae, Araneae, and Opiliones in soybean fields. Although we hypothesized that each predator group would increase with landscape heterogeneity and the amount of semi-natural habitat; we found variation in the response of the study organisms. The activity density of Araneae supported our hypothesis, increasing in soybean fields in landscapes with an abundance of forests and grasslands. The diversity of Carabidae in soybean fields increased in landscapes with an abundance of grassland habitat but the activity density of Carabidae declined. This decline was driven extensively by the species Poecilus chalcites which was less abundant in fields located within grassland-rich landscapes. Opiliones declined with increasing landscape heterogeneity but increased within forested landscapes. The spatial scale at which taxa responded to landscape composition also varied. Our hypothesis was that dispersal capacity would influence the spatial scale at which ground-dwelling arthropods responded to landscape structure. We found that Carabidae, which generally disperse by walking, responded to smaller spatial scales than linyphiid spiders, which frequently balloon. However, Lycosidae and Opiliones which also disperse mainly by walking as adults responded at larger spatial scales. These data suggest that understanding taxon-specific relationships to landscape variables should be considered in analyses of arthropod response to landscape structure.