Several studies have reported a positive relationship between species richness and ecosystem functioning. However, if much of a particular ecosystem function is performed by one species (i.e. a functionally dominant species) and this species is also a competitive dominant that excludes other taxa from a habitat, then it is possible to obtain a negative relationship between richness and ecosystem functioning. Results of a leaf pack breakdown experiment in a small stream suggested that the caddisfly Pycnopsyche gentilis, a common detritivorous insect in North American headwater streams, was both a functional and competitive dominant. In a second experiment we compared the effect of Pycnopsyche on leaf breakdown to that of other detritivore taxa by enclosing them with leaf packs in a section of headwater stream in which they were uncommon (Pycnopsyche transplant experiment). Final leaf pack mass was significantly lower in the Pycnopsyche enclosure treatment; leaves exposed to a greater diversity of detritivores displayed little reduction in leaf mass. These results demonstrated that Pycnopsyche was a functionally dominant detritivore. In a third experiment (Pycnopsyche density experiment) we found that Pycnopsyche was also a competitively dominant species. Leaf packs and large Pycnopsyche were placed in enclosures that were permeable to the majority of other detritivores but not Pycnopsyche. Leaf mass lost increased with increasing Pycnopsyche density. Leaf packs exposed to Pycnopsyche, however, contained fewer detritivore taxa which suggested that Pycnopsyche was also a competitive dominant. There was a negative relationship between three measures of diversity and leaf litter breakdown in the Pycnopsyche density experiment. Experiments conducted in natural communities that incorporate important species interactions may produce diversity‐ecosystem function relationships other than the positive ones that are commonly reported.

Brown Trout Salmo trutta are a popular sport fish, and numerous populations that are unable to successfully reproduce are maintained with supplemental stockings in waters with habitat that can support individual survival (e.g., appropriate thermal refuge). Long-term management of these populations requires understanding of their population dynamics to determine harvest restrictions and stocking rates. The objective of this research was to describe population dynamics of a tailrace Brown Trout fishery using an integrated population model (IPM) that incorporates monitoring data and low-cost batch mark-recapture data. Further, we evaluated the relationship between water temperature and survival. We hypothesized that annual survival would be lower at high water temperature. Additionally, we used the IPM to project the Brown Trout population based on two different management scenarios (no minimum length limit with seven-fish bag limit and 356-mm-TL minimum length limit with two-fish bag limit). Management outcomes explored include total population size, age frequencies, and length indices. The results of this study suggested that recreational harvest and water temperature were the two main factors influencing the Brown Trout population. Water temperature was found to be a major factor in determining survival of Brown Trout. Simulations under various minimum length limits indicated the minimum length limit of 356 mm TL and a two-fish bag limit will substantially increase the population size but with a reduction in length indices. Integrated population models have been applied historically to large systems with significant amounts of data. Estimates of survival and detection are important components of an IPM; to our knowledge, the IPM used here is the first to integrate batch mark-recapture data to estimate these key parameters. The data and modeling approach used here demonstrate the value of using novel statistical methods to make the most efficient use of low-cost survey data.Having been introduced outside of their native range, Brown Trout Salmo trutta are a popular sport fish throughout the world. They are not native to the Appalachian Mountains, but numerous fishable populations are sustained via supplemental stockings in streams that provide appropriate habitat. The coolwater and coldwater discharges from dams provide the unique habitat Brown Trout require to survive and, in some cases, successfully reproduce. The importance of these fisheries to the public has been evaluated by several states, and it was determined that southeastern trout anglers target these resources frequently and generate significant economic