Microparasites have recently caused the collapse of populations of a dominant insect competitor in coldwater streams in Michigan. This has provided a unique natural experiment to examine the organization of entire stream communities. The major objectives of this research are:1) to utilize this natural experiment as well as manipulative experiments, to assess mechanisms by which this dominant species affects the structure of trout stream food webs, 2) to determine the extent to which communities dominated by this species represent stable community configurations; and 3) to study the important processes regulating the abundances of this dominant consumer. The PIs will monitor responses (composition and abundances, biomass, and growth rates) of all trophic levels to the treatments created by the natural experiment. A powerful feature of the natural experiment is that essentially identical food web perturbations have been experienced at a series of diverse sites, with a variety of environmental characteristics (e.g., stream size, trophic structure, physical/chemical attributes). Thus, the results should have considerable general applicability. Manipulative experiments will be performed to:1) determine the pathways and strengths by which interactions stemming from the dominant consumer affect the remainder of the community; and 2) identify the processes regulating the abundances of the dominant consumer. By utilizing this combination of approaches, this project will provide a comprehensive understanding of the mechanisms structuring coldwater stream communities and the stability of stream communities. This study will be one of the first to document the role of parasites in the population dynamics of lotic invertebrates.
