PARENT SESSION
Poster Session #23: Fish, Lakes, Streams, and Wetlands.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Effects of predator switching behavior on the stability of zooplankton communities.

Anson, Jennifer¹, Schindler, Daniel¹, Scheuerell, Mark¹, Fresh, Kurt², Litt, Arni¹, Sibley, Thomas¹, ^{1 2}

ABSTRACT- Planktivores do not forage equally on all prey species and this selectivity causes shifts in community composition. Shifts in community composition, in turn, have important implications for grazing on phytoplankton and for nutrient recycling. Furthermore, this species-specific predation by planktivores may also release other zooplankton from a competitive disadvantage and help to stabilize their populations. We studied juvenile sockeye salmon diets, coordinated with zooplankton sampling, to estimate species-specific feeding selectivity of sockeye on the dominant zooplankton of Lake Washington (WA, USA). We show that the abundance of Daphnia (the preferred prey in the system) drives selectivity on all other important zooplankton species. Once 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 planktivore has important implications for community structure because the preferred prey have the highest intrinsic rate of increase among the zooplankton prey. We use a simulation model to explore the effect of this non-linear switching response of the predator on zooplankton community dynamics. The model results show that a switching response in the foraging behavior of planktivores results in a more diverse zooplankton community than persists in systems with relatively inflexible predators.

KEY WORDS: predation, zooplankton, lake, community