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Contributed Talk

Session: : Agriculture 1

COS 1-4 - CANCELLED - Complex temporal trends in biomass and abundance of Diptera driven by the impact of agricultural intensification on community-level turnover

Monday, August 7, 2023
2:15 PM – 2:30 PM PDT
Location: B110
Abstract: Insect declines have been reported widely and are likely to be important for transforming ecosystems. Land use change is recognised as a major cause of change in insect biodiversity and abundance. However, a lack of long-term data on land use change means few studies have linked long-term trends in insect abundance to temporal change in land use, and often assume a simple space-for-time substitution. We used 11 years (2006-2016) of monitoring data for Diptera sampled in the summer season on 40 farms distributed over ~10,000 km2 in southern Québec, Canada, to quantify the impact of agricultural intensification on temporal trends in abundance and biomass of Diptera (true flies). Although we found no overall change in either biomass or abundance between 2006 and 2016, there was a large difference in temporal trends between sites, which we found to be driven by land use change. Contrary to expectation, increases in abundance over time were greater in areas with higher agricultural intensification, especially with an increase in cereal crop density. In contrast, declines in dipteran biomass were steeper in areas of increasing agricultural intensification with a shift toward maize and soy production. Both abundance and biomass of Diptera remained most stable over time in areas of higher forest cover. We found steeper declines in biomass per total number of Diptera with increasing agricultural intensification, suggesting a shift toward a community of smaller-bodied flies with lower individual biomass is occurring. Our results reveal further complexities in insect trends driven by changes in land use and show the importance of long-term monitoring and the use of multiple indicators for understanding biodiversity change.