Effects of hedgerows and riparian margins on aerial web-building spiders in cereal fields

Abstract

Spiders (Araneae) are dominant predators in agro-ecosystems. Terrestrial seminatural habitats, such as hedgerows and grassy field margins, can enhance the abundance and diversity of spiders in adjoining fields, whereas the potential of riparian margins has rarely been studied. We compared the effects of hedgerows and riparian margins on aerial web-building spiders in adjacent cereal fields. While species richness and overall abundance did not significantly respond to distance from or type of field margin, each of the four dominant species responded differently. The abundance of Tetragnatha cf. montana Simon 1874 increased towards both hedgerows and riparian margins. Tetragnatha extensa (Linnaeus 1758) differentiated between field margin types and abundances increased only towards riparian margins. By contrast, Phylloneta impressa (L. Koch 1881) abundances decreased from field centers towards the field margins irrespective of the type. Type of field margin and distance showed an interactive effect on Mangora acalypha (Walckenaer 1802) abundances, which decreased from field centers towards hedgerows but changed only little towards riparian margins. Increasing spider densities towards field margins can be explained by the preference of spiders for adjoining seminatural habitats (overwintering, food availability, microclimate, vegetation structure), whereas increases towards field centers might be caused by interspecific competition and enhanced predation pressure near seminatural habitats and high prey numbers in crop fields. Overall, our study demonstrates that aerial web-building spider species respond differently to hedgerows and riparian margins.