Adverse effects of Diptera flies on northern ungulates: Rangifer, Alces, and Bison

Flies (Diptera) damage ungulates far beyond the injury of their bite wounds: they are vectors of diseases and cause ungulates to lose foraging opportunities due to avoidance behaviour. We can use the behavioural and physiological responses of bison Bison spp. (Artiodactyla: Bovidae), caribou/reindeer Rangifer tarandus (Artiodactyla: Cervidae), and moose/elk Alces alces (Artiodactyla: Cervidae) to assess the impacts of flies on these ungulates. Ungulates rely on morphological and physiological resistance to flies at low intensities of exposure. However, as fly exposure increases, ungulates begin to react with behavioural avoidance in addition to increasing their physiological response. Rangifer tarandus are highly sensitive to flies and respond quickly to their presence by avoidance behaviours that incur fitness costs through reduced body mass. Alces alces are less reactive to fly exposure, enduring the presence of flies and maintaining a low loss of fitness, sometimes dying from the cumulative effects of exposure. Bison spp. may use a facultative strategy that depends upon the prevalence of flies and associated diseases in their environment. Among these strategies, variables such as the type of fly bite, presence and degree of infection, and heritability of resistance affect individual host survival. Relationships between flies and ungulates can integrate multiple scales of organisation in the ecosystem to reflect system stability. Climate change is predicted to alter the species composition and seasonal phenology of flies and the associated effects of wounding and vector-borne disease on ungulate populations that are central to the functions of Arctic and temperate ecosystems in the Northern Hemisphere.