Trophic structure in an Arctic terrestrial Diptera assemblage

Background/Question/Methods

The impact of climate change on the Arctic is likely to be significant with recent documented changes in sea ice, and phenological shifts in plants and vertebrates. Insects are the dominant animals in northern ecosystems, and climate change could affect insect community structure through trophic cascades caused by changes in primary production. Flies (Diptera) are the most diverse and abundant insect order in the Arctic. They are integral to every terrestrial food web in the north, occupying diverse ecological roles. As such, community and trophic structure in Arctic Diptera may respond quickly to climate mediated changes. Yet, little information exists on terrestrial arctic arthropod food webs. Our objective was to document the trophic and community structure of Diptera at a low Arctic site in Canada. We assessed whether the terrestrial Diptera assemblage maintained the same trophic structure throughout the season. Diptera were collected in mesic and wet sites at Kugluktuk, Nunavut, using Malaise and pan traps through the active summer season (late June to mid-August). Higher Diptera were identified to genus or species. Weekly diversity patterns were assessed for functional groups (trophic guilds), and compared to patterns from a temperate dataset in southeastern Canada with a longer active season.

Results/Conclusions

Analyses of the Arctic assemblage were based on 5833 specimens representing 202 taxa. Species-rich families included Muscidae (39 species), Empididae (31), Scathophagidae (24) and Syrphidae (16). Empididae was by far the most abundant family (2864 specimens). Overall abundance was unimodal with a sharp peak in early July, whereas species richness was more uniform (13.5-18% of the total number were collected in each of the weeks: 03 July – 10 August). Patterns in predaceous, phytophagous and saprophagous trophic groups were comparable to patterns in the overall arctic assemblage, although the early peak in abundance was largely driven by predators (especially Empididae). The NMDS of predators suggested that weekly turnover of predaceous species was high, despite relatively uniform overall species richness throughout the sampling period. Nonetheless, trophic structure overall remained stable, with predators always dominating (75-90% of total per week), followed by saprophages, phytophages and parasites, respectively. In our temperate dataset, saprophagous Diptera were both numerically dominant and species rich. Based on our results, it appears that the lack of a significant accumulation of litter and available decaying organic matter in many tundra sites reduces the dominance of detritus-based assemblages, at least in Diptera.