The movement of organisms and material across ecosystem boundaries is fundamental to many ecological processes. Bodies of water regularly produce large numbers of aquatic insects that swarm on their shorelines. On the shorelines of lakes numerous aquatic insects may influence terrestrial arthropods by feeding detritivores and predators alike. Because midges are so abundant at Lake Mývatn, Iceland it is an ideal place to examine how aquatic insects influence bottom-up and top-down forces on land. First, to determine the amount and spatial distribution of midge deposition on land I measured the density of midges that emerged from Lake Mývatn and their abundance around the lake. From these data I created a model to estimate midge deposition on the land adjacent to the lake that suggests midges provide substantial quantities of nutrients to the shoreline. Second, to examine longer term impacts of midges on I sampled terrestrial arthropod assemblages across a midge input gradient at Mývatn and three other lakes in northeast Iceland. The results show that detritivorous, herbivorous, and predatory arthropods are all positively related to terrestrial midge inputs, across space and time. Third, to understand the influence of midges on short term food web interactions the indirect effect of live midges on terrestrial arthropods through shared predators was examined. Midges are positively associated with predatory wolf spider reproduction, and weakly linked to wolf spider density. However, experiments in the lab and field demonstrated a reduction of spider predation in the presence of live midges. Specifically, when midges are absent wolf spider density is positively related to predation rates, but in the presence of live midges this effect disappears. Reductions in predation by wolf spiders at low midge density suggest that the positive indirect effect of midges persists even at high predator density. As a whole this work has presents a new method of measuring the movement of aquatic insects to land and insights about possible aquatic insect fertilization of riparian areas, responses of terrestrial arthropods in multiple trophic levels to aquatic inputs, and an apparent mutualism between insects from a lake and those on land.
|School||THE UNIVERSITY OF WISCONSIN - MADISON|
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