Food webs in barley fields: implications for biological control


Abstract: The feeding patterns of generalist predators have important implications for biological control, but in the past it has been difficult to get a comprehensive picture of predator food webs due to difficulties in quantifying feeding links. However, recent developments in molecular methodology provide opportunities to parameterize predator-prey food webs with a high level of spatio-temporal resolution. We have constructed food webs of generalist carabid beetles and spiders and their prey in Swedish spring-sown barley fields using multiplex molecular gut content analysis, and explored implications for cereal aphid biological control. We investigated the presence of DNA of 13 different intraguild and extraguild prey types in the guts of > 3500 generalist predators in 10 barley fields during the aphid colonization and population growth phase. We found that although carabid beetles and spiders frequently fed on a range of different prey types, they maintained high levels of aphid pest predation during both phases of aphid population dynamics. Neither feeding on intraguild prey or alternative extraguild prey diverted the predators from aphid feeding. Overall we found strikingly low levels of specialization in the food webs, suggesting a high level of functional redundancy in the predator communities. However, we still detected certain changes in prey choice over time with small carabids and spiders preferring to feed on aphids early in the season, while larger carabids preferred to feed on aphids later on. In a newly started project we will explore whether the high redundancy observed in these generalist predator communities can provide resilience against climate change and environmental variability.

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