Spatial distribution of acalyptrate fly (Diptera) assemblages in Northern Canada

Flies (Diptera) are the dominant animal in the North yet are underrepresented in ecological studies. Our study aimed to examine the diversity patterns of the poorly documented acalyptrate flies across the Canadian North. Our main objective was to determine large- and small-scale drivers of species richness, abundance and community composition of acalyptrate fly assemblages. We collected flies at 12 Canadian sites in three ecoclimatic zones (Northern Boreal, Sub-Arctic and High Arctic), from two habitats (wet and mesic). We tested the effect of climatic variables and habitat on species richness and abundance using a generalized linear mixed-effects model, and on community composition using permutational multivariate analysis of variance. Species turnover between sites and ecoclimatic zones was examined by testing for multivariate homogeneity of group dispersions and visualised using non-metric multidimensional scaling. We identified 3631 acalyptrate flies, belonging to 333 species. Diversity measures and community composition were associated with seasonal and limiting temperature variables, consistent with the latitudinal diversity gradient seen in other animal groups. However, habitat only explained a small portion of the variation in our data, and only for observed species richness and species composition. Turnover patterns showed slight, statistically non-significant variation across zones. The High Arctic ecoclimatic zone was as spatially heterogenous in composition as the Northern Boreal and Sub-Arctic ecoclimatic zones but hinted at complex interplays between geographical and glacial legacies. Our results contradict the historical view of Arctic arthropod diversity as simple and uniform, and may serve as a baseline for future biodiversity monitoring.