Arthropod Mediated Ecosystem Services (Woltz)
Ecosystem services are ecological functions that support human existence. Insects provide ecosystem services including decomposition, pollination, and biological control of crop pests by predator and parasitoid natural enemies. Landscape structure affects insect abundance and community composition, which, in turn, affects ecosystem services provided by insects. In particular, diverse landscapes with greater proportions of non-crop habitat have been shown to have higher biocontrol rates and less crop damage than more simplified landscapes.
Vegetation structure also affects insect communities and biocontrol services on a local scale. Non-crop habitat adjacent to crop fields provides resources to natural enemies contributing to greater pest control. Additionally, local habitat can be manipulated to provide natural enemies with resources like alternative prey and refuge habitat to optimize their performance, a practice known as habitat management. However, the ability of habitat management to increase biocontrol services likely depends on a landscape context. Highly diverse landscapes may already supply natural enemies with necessary resources, while extremely simplified landscapes may not support sufficient natural enemy populations to measure significant effects of habitat management. We predicted that the ability of habitat management to improve biocontrol services in crop fields would be maximized at some intermediate level of landscape diversity.
Soybean aphid, Aphis glycines, and its coccinellid predators were used as a model system to elucidate the effects of habitat management and landscape on biocontrol services in soybean fields. We manipulated floral resources by planting strips of buckwheat adjacent to soybean fields situated in landscapes of varying complexity and composition and measured resultant changes in levels of biocontrol services. Coccinellid abundance was always higher in buckwheat strips compared to control field edges. However, coccinellid abundance was not higher in soybean fields adjacent to buckwheat strips compared to control soybean fields. Instead, coccinellid abundance in soybean fields was influenced by the surrounding landscape, and increased with the abundance of semi-natural habitat in the landscape. Broadly, this project informs us about the relative influences of landscape and local scale resources on predators in agroecosystems, and suggests that management to increase biocontrol services in field crops will need to take place at the landscape level.