Island biogeographical patterns of arthropod communities at Mývatn in northeast Iceland

Mývatn is a shallow, hyper-eutrophic lake in northeast Iceland with widely fluctuating and often hugely abundant midge (Chironomidae) emergences. The midge emergence and subsequent deposition on the surrounding landscape creates a subsidy of aquatic nutrients to the terrestrial food web. Previous work has shown that the abundance of arthropods increases with proximity to the shore. The present study investigates the patterns of arthropod abundance on islands in the lake. Islands range in area from 1 to 36.4 x 104 m2, representing a large variety in resource bases for the arthropod communities on respective islands. However, high midge deposition on the islands may counteract the otherwise limited nature of resources there. I measured the presence and abundance of arthropod species and midge deposition on islands. In addition, midge infall and arthropod abundance were measured close and far from the shore on the mainland. Midge infall decreases exponentially with distance from shore. Sampling consisted of pitfall traps for terrestrial arthropods and passive infall traps for midges between late May and early August, 2010. Arthropods of interest were identified to species in order to make inferences regarding trophic roles and life histories. Subsidies of aquatic nutrients to islands with otherwise fixed terrestrial resource bases may prove an important determinant in the island biogeography of arthropod communities.