Ecosystem Consequences of Trophic Exchange From A River to Its Watershed

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9645175 Power These investigators will study the effects of river subsidized insect production on a range of watershed consumers that differ in their abilities to track and translocate this resource. In order of increasing mobility, these consumers are filmy dome spiders, tetragnathid spiders, cursorial wolf spiders, western fence and sagebrush lizards, and three common species of bats. This research will test the prediction that ecosystem-level effects of aquatic insect subsidies on these consumers will depend on the scale of their activities. For example, bats may be the most important guild in translocating nutrients from the river to upland portions of the watershed, while lizards may have locally intensified impacts on their terrestrial prey, due to the river subsidies. Emergence traps, sticky traps, and quantitative exuviae collections will be used to monitor spatial and temporal variation in insect emergence and subsequent dispersal. Coordinated monitoring of consumer densities and activities will be used to assess their resource tracking in space and time. Insect emergence and subsidies will also be manipulated experimentally on spatial scales relevant to spiders and lizards, respectively. In these experiments, we will test the ability of particular consumers to track variation in their resources, and test an anticipated tradeoff between tracking ability and the impact of local resource variation on per capita performance of consumers. During the three years of this study, the investigators anticipate that year-to-year variation in hydrologic regimes will strongly affect the timing and magnitude of insect production, as it has over the ten previous years that we have studied this river food web. Studying this variation and its effects on watershed insectivores will help to forecast how river hydrologic regimes, including those altered by land use or climate change, will influence adjacent terrestrial communities.