From ceginfo@u.washington.edu Mon Sep 10 11:10:27 2001 Received: from jason02.u.washington.edu (jason02.u.washington.edu [140.142.8.52]) by lists.u.washington.edu (8.11.2+UW01.01/8.11.2+UW01.04) with ESMTP id f8AIAD0125842 for ; Mon, 10 Sep 2001 11:10:13 -0700 Received: from homer05.u.washington.edu (ceginfo@homer05.u.washington.edu [140.142.15.39]) by jason02.u.washington.edu (8.11.2+UW01.01/8.11.2+UW01.04) with ESMTP id f8AIAC061896; Mon, 10 Sep 2001 11:10:12 -0700 Received: from localhost (ceginfo@localhost) by homer05.u.washington.edu (8.11.2+UW01.01/8.11.2+UW01.04) with ESMTP id f8AIABP175916; Mon, 10 Sep 2001 11:10:12 -0700 Date: Mon, 10 Sep 2001 11:10:11 -0700 (PDT) From: Civil and Environmental Engineering To: , Subject: MSE Defense for Marta Danielsdottir - Sept. 21 (fwd) Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII The final examination for Marta Danielsdottir for the MSE degree will be held on Friday September 21, 2001 at 10:30 in More 221. Bottom-up Control of Top-down Processes in Planktonic Food Webs Abstract Many studies have attempted to untangle the natural processes and anthropogenic factors that regulate algal biomass and fisheries production. The results of those studies have often been contradictory and intensely debated. A strong correlation between certain biochemical characteristics of algae and zooplankton growth has been found in recent studies, suggesting that algal food quality may have great impacts on pelagic food-web interactions. In order to investigate the theoretical role that algal food quality might play in regulating pelagic food web interactions, I built a mathematical model of food web interactions and dynamics. The model consisted of three interactive dynamic sub-models; one for dissolved phosphorus, one for phytoplankton and one for zooplankton. Phytoplankton food quality was incorporated into the model through zooplankton growth efficiency (GE). The model was run for a gradient of both algal food quality and total phosphorus (TP) in the system. The following response variables were calculated: phytoplankton biomass, zooplankton biomass, the ratio of phytoplankton production and biomass, and the ratio of zooplankton and phytoplankton biomass. In order to compare the importance of various coefficients used in the model (including TP and GE) in regulating the response variables, I performed a two pronged Monte Carlo sensitivity analysis using the observed uncertainty in published coefficient values. My results showed that compared to TP, phytoplankton food quality was very important in regulating phytoplankton biomass, the phytoplankton production to biomass ratio, and the ratio of zooplankton and phytoplankton biomass. TP was very important in regulating zooplankton biomass, while phytoplankton food quality was of negligible importance for that response variable. When varying phytoplankton food quality for herbivorous zooplankton, my model exhibited a wide range of responses which encompassed most previous (and often times seemingly contradictory) model predictions and empirical observations. Herbivore control of plant biomass was very strong when phytoplankton food quality was high, and virtually non-existent when phytoplankton food quality was low. This suggests that phytoplankton food quality may help explain the contradictory predictions of different models and theories on trophic interactions. The sensitivity analyses showed that both TP and GE were amongst the most important coefficients overall. Phytoplankton maximum growth rate, the half saturation constant for phytoplankton growth, and zooplankton starvation were also very important coefficients. My results indicate that in order to understand the response of pelagic food webs to perturbations, algal food quality for herbivorous zooplankton should always be considered. Professor Michael T. Brett, Chair Room Reservation #25376 Marcia Buck, Graduate Advising Dept. of Civil & Environmental Engineering, Box 352700 University of Washington Seattle, WA 98195-2700 (206) 543-2574, Fax: (206) 685-9185 .