Competition, Food Consumption, and Production of Sculpins and Trout in Laboratory Stream Communities

Intraspecific and interspecific competition for food were studied in simple communities in laboratory streams stocked with reticulate sculpins (Cottus perplexus), cutthroat trout (Salmo clarki), and carnivorous stoneflies of the genus Acroneuria. Herbivorous midge larvae were the principal prey organisms. Different combinations and densities of the carnivorous species were used in different streams and experiments. The rates of food consumption, respiration, and growth of sculpins and trout in the laboratory stream communities were found to be functions of prey density. Measurements of prey density thus may be useful measures of food availability for certain predators in some aquatic systems. Prey density in the streams was a function of predator density. These findings together suggest possible ways of modeling the production of a predator by using functions of the densities of the predator, its competitors, and its prey. Such models may make it possible to identify the seasonal or ecosystem changes that alter the relationships between the biomass and production of a predator and may be useful for predicting the biomass of a predator that would maximize its production.