CS35 Trophic Dynamics
Date: Friday, June 14, 2002
Time: 10:45:00 AM
Location: Carson A
AnsonJM, University of Washington, Seattle, USA, janson@u.washington.edu
Schindler, D, E, University of Washington, Seattle, USA, 
Scheuerell, M, D, University of Washington, Seattle, USA, 
Fresh, K, L, Washington State Department of Fish and Wildlife, Olympia, USA, 
Litt, A, H, University of Washington, Seattle, USA, 
Shepherd, J, H, University of Washington, Seattle, USA, 
Sibley, T, H, University of Washington, Seattle, USA, 
Planktivore diet switching and zooplankton community dynamics
Selective foraging by planktivorous fishes often causes shifts in zooplankton community composition. Shifts in the zooplankton community composition, in turn, have important implications for phytoplankton grazing rates and nutrient recycling. Furthermore, species-specific predation by planktivores may release undesirable zooplankton from a competitive disadvantage and help to stabilize their populations. We estimated species-specific feeding selectivity by juvenile sockeye salmon on the dominant zooplankton of Lake Washington (WA, USA) on 12 occasions throughout 5 years. We found that the abundance of Daphnia (the preferred prey in the system) drives selectivity on all other important zooplankton species. Once adult Daphnia densities reach 0.8 org/L, predation on both cyclopoid and calanoid copepods approaches zero, and the fish feed almost exclusively on Daphnia. This predation response by the juvenile sockeye has important implications for the zooplankton community structure because Daphnia have the highest intrinsic rate of increase among the zooplankton prey. Finally, we use a simulation model to demonstrate how a prey switching response by juvenile sockeye increases the densities of competitively inferior zooplankton taxa.