0089736<br/>Kohler<br/>Long-term experiments performed at large spatial scales are costly, logistically difficult, and, as a consequence, seldom well replicated. But because smaller-scale experiments may not readily scale up to larger contexts, large-scale experiments may be critically important in understanding the processes influencing ecological communities in natural ecosystems. This LTREB project will continue the study of a naturally replicated, whole-ecosystem perturbation brought about by disease-induced reductions in populations of a dominant herbivore, the caddisfly, in cold water streams in Michigan and Maine. Maintenance of caddisfly populations at low levels by repeated outbreaks of a host-specific pathogen was first observed in the late 1980's in several hydrologically stable streams in Michigan's Lower Peninsula that were already the subject of long-term monitoring. Results to date from these systems indicate that biotic processes play a major role in organizing their communities. In the mid-1990's, a foundation was laid to assess the generality of these findings through the addition of study streams in two regions (western Upper Peninsula, Michigan, western Maine) having similar communities as the Michigan Lower Peninsula sites, but where hydrologically-derived disturbances should be more pronounced and frequent. This study will continue monitoring of biotic communities in streams in all three regions that have had, or are likely to have, substantial pathogen-induced variation in their caddisfly populations over time. These data series will allow the investigators to (1) discriminate among mechanistic models of trout stream community dynamics, (2) determine whether the long-term interactions between caddisfly and its pathogen is cyclic or stable, and (3) assess whether the relative importance of biotic and abiotic processes in affecting trout stream communities varies over a gradient of hydrologic stability.
LTREB: Collaborative Research: Structure and Resilience of Trout Stream Food Webs