Phenology and temporal species turnover in an Arctic Diptera assemblage

Background/Question/Methods

Documenting climate change impacts in northern ecosystems is a current priority in ecology and conservation. Recent research has documented phenological shifts in plants and vertebrates; however, we still lack baseline data to measure the extent of change in many other taxa. Flies (Diptera) are the dominant arthropods in the Arctic and occupy diverse ecological roles. As such, climate-mediated changes in community structure and phenology may be clearly reflected in Arctic Diptera. Despite this, there has been little research on diversity and phenology of northern flies. Our objective was to document patterns of Diptera diversity and seasonal activity at a low Arctic site in Canada. We assessed whether the Diptera assemblage showed successive peaks of activity by different species throughout the season or whether most species were active throughout the summer. Diptera were collected at Kugluktuk, Nunavut, using Malaise traps at mesic and wet sites through most of the active summer season (late June to mid-August). Higher Diptera were identified to genus or species level. Weekly diversity patterns were assessed for taxonomic groups (species and/or genera) and 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 4608 specimens representing 123 Diptera taxa. Overall abundance was unimodal with a sharp peak (53% of all specimens) in early July. Overall species richness was almost uniform in weeks 2-7 (03 July – 10 August), with 14-16% of the total number of species collected in each week. NMDS ordination of overall diversity indicated that weekly species turnover was high, despite the uniform overall richness. Distribution of predaceous, phytophagous and saprophagous trophic groups was comparable to overall taxonomic patterns, although the early peak in abundance was largely driven by predators. In contrast, the distribution of overall abundance in the temperate peatland data set (146 species) was more evenly distributed, but unimodal, and there was a more pronounced peak in species richness in mid-season. Our results suggest that, in a truncated arctic flight season, successive activity periods by different species are maintained, although on shorter time scales than in temperate systems, despite uniform overall species richness through the season.