The impact of surrounding agricultural land use on syrphid fly communities in semi-natural grasslands

Abstract

Agricultural intensification is seen as a major threat to global biodiversity. Semi-natural grasslands play an important role in maintaining biodiversity in agricultural landscapes. Biodiversity and community structure in semi-natural grasslands depends not only on local management but also on the surrounding land-use. Further knowledge on landscape-scale effects would help improving the management of agricultural system.

In this study, I evaluated the impact of surrounding landscape compositions on the abundance and diversity of syrphid flies, a group of dipteran insects providing important ecosystem services like pollination and pest control. The positive effect of semi-natural habitats well investigated for syrphid communities in crops, but how it transfers to communities found in semi-natural habitats is poorly known. 72 transects within 18 semi-natural grassland sites around Lund were sampled in July and August, 2021. 568 individuals in 24 species are eventually collected and identified.

Results of Linear Mixed Models (LMM) show a weak positive correlation between grassland ley cover and syrphid abundance/diversity (possibly caused by higher flower density), along with a weak negative correlation between arable crop cover and diversity of syrphid subfamily Eristalinae (possibly caused by lower larval fitness). The results suggest that further investigations into the mechanism by which grassland leys lead to higher syrphid abundance and diversity in semi-natural grasslands are warranted. The negative effect of arable crop cover on Eristalinae stresses the importance of conserving and restoring less-disturbed habitats suitable for the different life-stages of these species.

Popular Abstract

Surrounding land-use may affect the diversity of hoverflies in semi-natural grasslands.

Modern agricultural systems have led to the expansion of arable crops to increases crop production and profitability of farming more profitable, often at the cost of loss of natural and semi-natural habitats. The remaining fragments of such habitats are considered important for maintaining local biodiversity, and their conservation has received attention from both the government and the public. Organisms living in natural or semi-natural habitats are able to make use of resources in surrounding land-uses, but the extent to which surrounding land-uses can affect biodiversity in natural and semi-natural habitats is still not fully studied. Hoverflies (Family Syrphidae) provide dual ecosystem services in pest control (larvae) and pollination (adults) of both wild plants and crops. Unlike bees, they are not bond to nests and thus have higher dispersal ability. Studies focusing on the relationship between landscape and syrphid diversity are relatively rare and sometimes contradictory.

To better understand how surrounding land-use affects hoverflies I studied 18 semi-natural grassland sites across Scania in southern Sweden. Sites were selected to cover a gradient of arable crop cover in the surrounding. The other surrounding land-uses were grassland leys, permanent grasslands or forests, some open water and urban areas. I caught hoverflies from flowers with a sweep-net and identified them in the lab, before analyzing the assessing between the hoverflies and the landscape-scale land-use. At the same time, I assessed the links between hoverflies and plants.

According to my results, grassland leys have a potential to enhance hoverfly diversity and abundance. Flowers in grassland leys are likely to attract hoverflies, and these grasslands are potentially appropriate habitats for predatory larvae. The cover of arable crops may reduce the diversity of Eristalinae, a group of hoverfly species whose larvae mostly feed on decaying matter, a resource that is scarce in arable crops. However, the exact mechanism of these relationships needs to be addressed in further studies. This study illustrates that organisms with different traits react differently to the environment. If we want to conserve species with rare traits, approaches designed for common ones are not enough.

Master’s Degree Project in Biology, 30 credits.
Department of Biology, Lund University

Advisor: Yann Clough and Rune Bygebjerg
Centre for Environmental and Climate Science

• author: Liu, Haowen
• supervisor: Yann Clough; Rune Bygebjerg
• organization: Degree Projects in Biology
• course: BIOM02 20202
• year: 2021
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9061276
• date added to LUP: 2021-07-08 07:45:13
• date last changed: 2021-07-08 07:45:13