Epsilon Open Archive

Abstract

Spiders in agroecosystems play a role in natural pest suppression and contribute to biodiversity. In this thesis I have investigated if and when spiders recolonise cereal fields in spring when they have the potential to suppress establishing pest aphid populations. Furthermore, the influence of different environmental factors on spiders has been investigated to understand how it might be possible to provide suitable conditions for enhancement of their populations. Linyphiid spiders recolonised fields after being negatively affected by sowing in spring, while lycosid spiders were unaffected. Conversely, lycosids showed a recolonisation in winter cereals after overwintering, but not linyphiids. But linyphiid migratory patterns also differed over time, because they were positively influenced by landscape heterogeneity in the beginning of spring but not at the end. Diversity of lycosid and linyphiid spiders was positively influenced by perennial crops and forest in the surrounding landscape. Field margins were found to be a key habitat for the diversity of both spider families. Lycosid abundance was affected on the habitat scale and linyphiid abundance on the larger landscape scale, which can be explained by the families' different modes of dispersal. Farming systems, conventional or organic, contained different compositions of lycosid and linyphiid species. The dominant lycosid and linyphiid species were more abundant at organic sites. Body condition of Pardosa (Lycosidae) turned out to be superior in landscapes dominated by large fields with annual crops, irrespective of farming system, perhaps because of less competition for available resources. This thesis provides evidence that spiders are present in crop fields early in spring when they have the opportunity to suppress establishing aphid pests. Different spider species were associated with different farming systems, but the abundances of the most common species were enhanced by organic management. A diverse landscape with easy access to perennial crops and field margins will augment both number of species and individuals of spiders.