Elizabeth C. Clark

EFFECT OF PREDATOR DIVERSITY ON TROPHIC CASCADE STRENGTH: DOES PREY DIVERSITY MATTER? Elizabeth C. Clark¹, Jonathan M. Chase¹, Biology Department, Washington University, St. Louis, MO¹.

The effects of predator diversity on trophic cascades are important in ecosystem management. In this pond mesocosm experiment, we examined how different levels of predator diversity affect trophic cascade strength in food webs of varying prey diversity. We manipulated diversity in a 2x2 factorial design, with high and low diversity of benthic and pelagic predators and prey. Of the three measures of primary productivity (phytoplankton density, periphytic algae biomass, and filamentous surface algae biomass), only periphytic and surface algae exhibited significant differences between treatments. Surface algae biomass was highest in high prey and high predator diversity treatments, indicating that the strongest prey suppression may occur when niche partitioning allows for a reduction in intraguild predation. Periphytic algae biomass at high predator and high prey diversities was lower than but not significantly different from biomass at low predator and low prey diversities. Because these periphytic algae in high predator and high prey diversity treatments would have received more shade from filamentous surface algae than in other treatments, it is possible that this competitive exclusion prevented the periphytic algae from showing the same response as surface algae to high predator and high prey diversity. In a benthic pond system, increasing predator diversity may strengthen or dampen trophic cascades depending on the diversity of prey species.