Natural enemy diversity generally strengthens biological control, but individual studies have found anything from positive to negative effects. However, most studies investigating the impacts of natural enemy diversity on pest suppression have focused on short term effects, while ignoring the stability in pest suppression across time and space. Theory predicts that a high diversity of redundant species (i.e., species currently doing the same job) should stabilize ecosystem functioning, since different species are likely to be important during different environmental conditions. This implies that a high natural enemy diversity should provide an insurance against global environmental change. We will here present how generalist predators contribute to stability of aphid biological control in Swedish barley fields under varying landscape complexity and climate change. We have found that ground dwelling predators such as spiders and carabids can reduce aphid pest damage with 50% in such fields, and that the level of aphid biological control is higher in more complex landscapes (Rusch et al. 2013). In recent work, exploring feeding preferences of the most common carabid and spider species on over ten prey types with molecular gut content analysis we have confirmed that these species are highly generalistic and that a high diversity of predators contribute to aphid biological control (Roubinet et al. 2017). Our preliminary analyses suggest that the level of redundancy in aphid predation increases with landscape complexity, suggesting that barley fields in complex landscapes not only currently has more effective aphid biological control but that the stability of aphid control is likely to be higher in such landscapes. We are currently investigating the climate niches of different predators in relation to temperature and rainfall. These niches will be combined into climate niches for predator communities in different types of landscapes and we will test if the level of climate resilience (Kühsel and Blüthgen 2015) in predator communities is higher in complex landscapes. Finally, we will conduct mesocosm experiments under different climate scenarios to test if predator communities with different levels of redundancy and climate resilience really contribute to more stable biological control of aphids.
(1) Rusch, A., Bommarco, R., Jonsson, M., Smith, H.G. & Ekbom, B. 2013. Flow and stability of natural pest control services depend on landscape complexity and crop rotation in the landscape. J Appl Ecol 50, 345-354.
(2) Roubinet, E., Birkhofer, K., Malsher, G., Staudacher, K., Ekbom, B., Traugott, M. & Jonsson, M. 2017. Diet of generalist predators reflects effects of cropping period and farming system on extra- and intraguild prey. Ecol Appl 27, 1167-1177.
(3) Kühsel, S. & Blüthgen N. 2015 High diversity stabilizes the thermal resilience of pollinator communities in intensively managed grasslands. Nature Comm 2015. 6: p. 7989.