title: Food web structure and biocontrol in a four-trophic level system across a landscape complexity gradient.
abstract: Decline in landscape complexity owing to agricultural intensification may affect biodiversity, food web complexity and associated ecological processes such as biological control, but such relationships are poorly understood. Here, we analysed food webs of cereal aphids, their primary parasitoids and hyperparasitoids in 18 agricultural landscapes differing in structural complexity (42-93% arable land). Despite little variation in the richness of each trophic group, we found considerable changes in trophic link properties across the landscape complexity gradient. Unexpectedly, aphid-parasitoid food webs exhibited a lower complexity (lower linkage density, interaction diversity and generality) in structurally complex landscapes, which was related to the dominance of one aphid species in complex landscapes. Nevertheless, primary parasitism, as well as hyperparasitism, was higher in complex landscapes, with primary parasitism reaching levels for potentially successful biological control. In conclusion, landscape complexity appeared to foster higher parasitism rates, but simpler food webs, thereby casting doubt on the general importance of food web complexity for ecosystem functioning.
authors.affiliation: Department of Crop Science, Agroecology, Georg-August-University, Grisebachstrasse 6, 37077 Göttingen, Germany. vgagic@gwdg.de
authors.forename: Vesna
authors.initials: V
authors.lastname: Gagic
authors.forename: Teja
authors.initials: T
authors.lastname: Tscharntke
authors.forename: Carsten F
authors.initials: CF
authors.lastname: Dormann
authors.forename: Bernd
authors.initials: B
authors.lastname: Gruber
authors.forename: Anne
authors.initials: A
authors.lastname: Wilstermann
authors.forename: Carsten
authors.initials: C
authors.lastname: Thies
mesh_terms: D000383:Agriculture; D000818:Animals; D001042:Aphids / Q000502:physiology*; D020387:Food Chain; D006790:Host-Parasite Interactions; D006927:Hymenoptera / Q000502:physiology*; D010572:Pest Control, Biological / Q000379:methods*; D013045:Species Specificity