PARENT SESSION
Poster Session 29: Predator / Prey Ecology
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Non-lethal effects of the invasive invertebrate predator, Bythotrephes, on Lake Michigan zooplankton.

Pangle, Kevin^{*,1, 2}, Peacor, Scott^{1, 2}, ¹ Michigan State University, East Lansing, MI, USA² National Oceanic and Atmospheric Administration, Ann Arbor, MI, USA

ABSTRACT- Non-lethal effects may play a critical role in the net effect predators have on a food web, but little is known regarding their magnitude. In this study, we evaluated the influence of non-lethal effects of an invasive invertebrate predator, Bythotrephes longimanus, on Lake Michigan zooplankton. We first conducted laboratory experiments that examined the behavioral response of Daphnia mendotae to the presence of Bythotrephes. Over the duration of a 4-day column experiment, we found that Daphnia responded to Bythotrephes kairomones by exhibiting diel vertical migration. This antipredator behavior led to a 38% reduction in the individual growth rate of the experimental organisms, shedding insight into degree of growth rate loss Daphnia will incur to avoid predation risk. Laboratory experiments also found that Daphnia respond differentially to lake water collected from areas that contained different densities of Bythotrephes. A similar pattern was observed in Lake Michigan field survey data, which showed that changes in the vertical distribution of multiple zooplankton prey species coincided with fluctuations in Bythotrephes density. Analysis of the survey results indicate that non-lethal (trait-mediated) and lethal (density-mediated) effects of Bythotrephes on zooplankton population growth rate were on the same order of magnitude. We discuss the potential community level consequences of the Bythotrephes-induced behavioral changes in zooplankton prey. This study also indicates that research on the effects of invasive species should include examination of non-lethal effects, even given the short evolutionary coexistence.

Key words: non-lethal, antipredator behavior, zooplankton, trait-mediated