Aquatic insects are a common and important subsidy to terrestrial systems yet little is known about how these inputs affect terrestrial food webs, especially around lakes. Mývatn, a lake in northern Iceland, has extraordinary midge (Chironomidae) emergences that result in large inputs of biomass and nutrients to terrestrial arthropod communities. We simulated this lake-to-land resource pulse by collecting midges from Mývatn and spreading their dried carcasses on 1-m2 plots at a nearby site that receives very little midge deposition. We hypothesized a positive bottom-up response of detritivores that would be transmitted to their predators and would persist into the following year. We sampled the arthropod community once per month for 3 consecutive summers; measuring arthropod density and natural stable isotope ratios (δ13C and δ15N).
Results/Conclusions
Midge addition resulted in significantly different arthropod communities and increased densities of some taxa. Detritivores, specifically Diptera larvae, Collembola and Acari increased in midge-addition plots, and so did some predators and parasitoids. Arthropod densities remained elevated in years following midge addition and multiple years of midge addition further increased the density of higher-order consumers (e.g., Coleoptera and Hymenoptera). Both detritivores and predators were isotopically enriched in midge-addition plots, with detritivorous Collembola showing the most dramatic shift. Resources cross ecosystem boundaries and are assimilated over time because of life-history strategies that connect aquatic and terrestrial food webs and these systems cannot be fully understood in isolation from each other.