Syrphid fly response to urban heat islands varies with functional traits

Syrphid flies (Diptera, Syrphidae) play important ecological roles as pollinators, pest control agents, and decomposers. Communities are influenced by environmental variables such as land use. However, these interactions are poorly studied in urban landscapes. We used pan traps in community gardens, cemeteries, and parks in Montreal, Canada, to investigate syrphid fly communities in an urban landscape and describe how site surface area and heat island cover shape these communities. We estimated the species richness of communities and the occupancy patterns of three syrphid functional groups (insectivores, terrestrial saprophagous, and aquatic saprophagous). We captured 1,791 specimens from 48 species. Species richness increased with site surface area but did not vary with the level of urbanisation. The occupancy of the three groups did not change with site surface area. Syrphid flies of the terrestrial saprophagous group were less likely to occur on sites with high urbanisation, but the occupancy of insectivore and aquatic saprophagous groups did not vary with the variable. Implications for insect conservation Our results highlight that cities can harbour diversified syrphid fly communities and that certain functional groups are tolerant to urbanisation pressures. Our study suggests that conservation measures targeting syrphid flies in cities must be adapted to functional traits and larval requirements.