PS 3-33
Rethinking northern food webs: impact of high taxonomic and trophic diversity in arctic terrestrial arthropods
Terrestrial arthropods are depicted as minor players in most arctic food web diagrams, where they are generally treated as food for vertebrates, detritivores, and occasionally herbivores. Links between arthropod groups are generally not considered. This perception may arise from the assumption that arctic arthropods have low species richness and limited trophic diversity. Until very recently, most literature on arctic arthropods suggested that species richness above tree line is low (e.g., 2000 species in North America), phylogenetic diversity was low, and detritivores were the dominant trophic group. Flies (Diptera) are the dominant terrestrial insect taxon in the north, especially above treeline. Diptera diversity does not decline as dramatically with increasing latitude as in other insect orders, and some families are more species rich above treeline than in other biomes. Diptera are also the most trophically diverse terrestrial arthropod taxon in the arctic. We have studied Diptera diversity since 2010 in 12 sites across the north boreal, subarctic and high arctic in Canada. Our objectives are to document the taxonomic and ecological diversity of northern Diptera; to assess community structure at a continental-level spatial scale; and to assemble baseline data on the roles of Diptera in northern terrestrial food webs.
Results/Conclusions
We documented unexpectedly high species richness in several target families of Diptera. Several hundred species of higher Diptera have been identified from each of multiple sites in Nunavut, Yukon and Manitoba for which we have more comprehensive sampling. This has increased, sometimes by an order of magnitude, the number of species known above treeline. The family Chloropidae, for example, was previously considered to include two species, both herbivores, above tree line in North America. We have recorded more than 60 chloropid species, representing herbivorous guilds (stem-borers, seed-feeders), saprophagous species, and multiple guilds of specialist predators. The pattern is similar in other families (e.g. Scathophagidae, Empididae, Piophilidae), in which more species than expected, occupying more trophic roles than predicted by the literature, must now be accommodated in food webs, as well as in assessments of arthropod community structure in apparently simple northern ecosystems. This increasing species richness has implications for our understanding of the phenology and species co-occurrence of arctic flies. Temporal species turnover is high, and previous models that predicted a single early-season peak of activity in arctic Diptera are not supported by our results, which document high species richness, abundance and turnover throughout the brief arctic summer.