PARENT SESSION
Poster Session 33: Trohpic Structure
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Determining the relative influence of resource composition and predation on zooplankton populations over a growing season: an investigation using time series analysis.
Tillmanns, Angeline*,1, Ladouceur, Margo1, Pick, Frances1, 1 University of Ottawa, Ottawa
ABSTRACT- Seasonal changes in zooplankton community composition have been linked to resource composition and predation but the relative importance of each remains uncertain. Understanding the tritrophic relationship between phytoplankton, zooplankton and planktivorous fish is especially pertinent when manipulating a lake to control for ecosystem properties such as water clarity. Using a high temporal resolution (sampling interval of 3 days) we employed time series analysis to determine the relative influence of resource composition and predation on zooplankton population dynamics over a growing season. During the open water season of 2003, zooplankton and phytoplankton samples were collected from Constance Lake, a mesotrophic, shallow lake located in west Ottawa, Ontario. The lake rarely stratifies and the phytoplankton community fluctuates between diatom and cyanobacteria dominance over much of the summer. Cladocerans and rotifers were counted to genus level and copepods were counted to order. The number of eggs was also recorded for cladocerans so both instantaneous and realized growth rates could be estimated. The death rate was taken as the difference between the two and was assumed to be the result of predation by planktivorous fish. Phytoplankton community was estimated by chlorophyll composition and size fraction and was checked against bi-monthly phytoplankton counts. Preliminary results reveal a strong top-down influence on zooplankton community composition even though edible phytoplankton were available to grazers late in the season.
Key words: Trophic cascade, Zooplankton, Shallow lake, Time series analysis