Landscape effects on recolonisation patterns of spiders in arable fields

The influence of the availability of surrounding boundaries and grasslands on the recolonisation of lycosid and linyphiid spiders was studied in early spring in 12 winter barley fields situated in differently structured landscapes. It was found that the more cursorial lycosid spiders foremost showed a dependence on time when recolonising arable fields, and increased in numbers during the critical time of pest establishment, although lycosid species richness also was related to the surrounding landscape. Linyphiid spiders, which are more likely to disperse by air than lycosids, did not show an increase in numbers over time, but were more affected by the surrounding landscape. However, these spiders also showed a dependence on time, because the positive effect of surrounding boundaries was significant in the beginning but not at the end of the study period. Thus, most spiders showed a difference in migration patterns over time and both spider families were positively influenced by the surrounding boundaries and grasslands during recolonisation of crop fields after winter. In order to enhance pest suppression by spiders, overwintering structures should be provided in crop-dominated landscapes to facilitate spider migration into crop fields during early spring.