THE ROLES OF PREDATION, COMPETITION, AND EXPLOITATION IN THE TROPHIC DYNAMICS OF A WARMWATER STREAM - A MODEL SYNTHESIS, ANALYSIS, AND APPLICATION

We developed a trophic dynamic model of key populations and processes in the New River, West Virginia, to identify the mechanisms most respo nsible for maintaining food web structure. Key populations were repres ented by thirteen model components and were aquatic insects; age-1 and age-2 crayfish (three species); age-1 and age-2 hellgrammites (Coryda lus cornutus larvae); non-game fishes; age-0, age-1, and adult smallmo uth bass (Micropterus dolomieu); age-0, age-1, and adult rock bass (Am bloplites rupestris); and age-0, age-1 to age-3, and adult flathead ca tfish (Pylodictis olivaris). In this system, crayfish and hellgrammite s are harvested to provide bait for the recreational fishery that exte nsively exploits the three predatory fish species. Predation and intra specific regulation were represented with nonlinear algorithms, and li near terms represented fishery harvests. Interspecific competition amo ng components occurred through predation on shared prey. Error analysi s of the model suggested that predation was the most important mechani sm in maintaining system structure (the disposition of biomass among s ystem components). Further, the trophic relation between each componen t and its prey accounted for 34-64% of the variability in food web str ucture, whereas predation on each component explained 1-24% of food we b structure variability. Therefore, so-called 'bottom-up' effects were more influential than 'top-down' effects. Interspecific competition a nd intraspecific regulation had secondary roles in maintaining New Riv er food web structure, although intraspecific regulation was most impo rtant to aquatic insects, which were not predatory in our model. Both forms of competition are probably tempered by extensive predation and exploitation in the New River system. Exploitation was a secondary str ucturing agent to adult smallmouth bass, which experience a high rate of harvest in the New River.