1. POSTER TEMPLATE BY: www.PosterPresentations.com The microcosm replicates were heat-sterilized 150mL Nalgene bottles, containing liquid medium and nutrients. The food webs consisted of mixed bacteria resources, the bactivorous protist prey species, Chilomonas sp., and the generalist omnivore, Blepharisma americanum. There were two dispersal treatments, high and low, crossed with three productivity treatments. Dispersal rates were manipulated by introducing new individuals into replicates three times a week following published intervals (Holyoak 2000). Productivity differences were established by providing three levels of bacteria resources (0.1 pellet/L, 1.0 pellet /L and 3.0 pellet/L). We ran the experiment for 40 days – roughly 50 protist generations and the normative time for simple bottle communities to reach dynamical equilibrium. We collected fine-scale time series data of protist densities and cell volumes (sampling every other day) from each bottle using published methods (Fox 2007). In brief, protists are counted under a microscope in aliquots from a small (0.1mL) subsample taken from each homogenized bottle. EFFECTS OF PRIMARY PRODUCTIVITY ON THE DYNAMICS OF SPATIALLY ASSEMBLED COMMUNITIES WITH OMNIVORY Heather David, Co-P.I. Ashkaan Fahimipour, P.I.: Dr. Kurt E. Anderson Department of Biology, UC Riverside ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION CITATIONS ACKNOWLEDGEMENTS The structure of ecological systems is heavily influenced by spatial flows of colonists (i.e., colonization) from outside systems. Whether variation in a community’s primary productivity alters the effects of colonization remain unclear. Studies of specialized consumers in three level food webs show marked biomass increase with increased nutrient enrichment. However, in systems with omnivory, predators may interrupt the food chain by directly consuming basal resources. Thus, the interaction between productivity and colonization rate remains unknown for systems characterized by omnivory. Here, we use an array of laboratory microcosms to test the hypothesis that the effects of colonization on the structure and dynamics of communities characterized by omnivory are influenced by productivity manipulation. Replicate microcosms containing protists; Blepharisma sp. (omnivore), Chilomonas sp.(intermediate consumer), and mixed bacteria; Serratia marscecens, Bacillus cereus and Bacillus subtilis ; were established in 150 mL bottles (“mainlands”), which supply small 30 mL “islands” of varying productivity levels with colonists. Productivity (bacteria) is manipulated by altering nutrient concentrations in the “islands” which affects enrichment and maximum density. Fresh individuals are dispersed to the “islands” three times a week in amounts which simulate proximate and isolated spatial locations. We expect a clear indication of how primary productivity influences the community either by facilitating or inhibiting protist population growth. This study will inform ecological theory by demonstrating interactions between broad scale spatial processes, and local resource conditions. Mixed Bacteria: Taken with a Leica microscope camera at 400x. Ecosystems in nature are spatially subdivided and are connected by dispersal of individuals (Levin 1992). How dispersal affects these ecosystems is our area of focused interest. Within ecosystems, system dynamics with predator-prey and competition interactions have been well documented (DeAngelis 1992). However, systems with omnivory have features differing from systems previously studied (Diehl and Feissel 2000, Pimm and Lawton 1978; Matsuda et al. 1986; Law and Blackford 1992; Thingstad et al. 1996; Holt and Polis 1997). Statistical analyses of empirical data and studies of analytical models have hinted that other factors in a food web with omnivory and variation in colonization rate (i.e., the rate at which new individuals enter a community) among habitats cause the disaccord between trophic cascade theory and data, but studies that directly test these hypotheses are scant (Polis et al. 1997; Polis et al. 2000; Bruno & O’Connor 2005; Borer et al. 2005; Fox 2007; Holt et al. 2010). Above is the omnivore Blepharisma sp. in its carnivorous morphological state. Taken with a Leica microscope camera. 100x. The author thanks NSF and the UC Riverside CAMP program for funding, as well as the University of California, Riverside HSI-STEM program, as well as the entire Anderson Lab for their support. "Seneca River in Jordan NY" by MTBradley - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Seneca_River_in_Jo rdan_NY.jpg#mediaviewer/File:Seneca_River_in_Jordan_N Y.jpg The protist Tetrahymena hunts E. coli in this photo illustration, which features a microscope image of Tetrahymena (left). Credit: University at Buffalo Read more at: http://phys.org/news/2013-06-dangerous-strains-coli-linger- longer.html#jCp Spatially subdivided ecosystems were established in laboratory microcosms. Five mainlands were each connected to three proximate islands and three isolated islands (pictured right). The data for Blepharisma are highly non-linear, and will require alternative analyses that account for these non-linearities. It is clear that the relationship between productivity and Blepharisma densities in high colonization rate bottles is hump-shaped. To formally analyze such data, we need to employ likelihood based non-linear model fitting. This will be a goal for future analyses. It's clear from these preliminary results that productivity and colonization rate have complex and non-intuitive consequences for population dynamics in this system. Determining what these effects are will require sophisticated time-series analyses of population dynamics. These include likelihood-based model fitting and information-theoretic techniques. However, the general result – that productivity and colonization rate interact to influence population dynamics in food webs – is one that is of great interest to the broader ecological community, given the ubiquity of both of these processes in nature. Fig. 1. Mean long-term species density as a function of colonization rate and productivity. Results of linear mixed effects models (LME): Chilomonas densities are higher in low colonization rate ponds than in high colonization rate ponds (negative effect of colonization rate on Chilomonas density; F 1,20 = 5.389, P = 0.0309). Productivity has no effect on Chilomonas densities when colonization rate is low, but Chilomonas densities decrease with productivity when colonization rate is high (colonization rate x productivity interaction; F 2,20 = 2.852, P = 0.0413). Fig. 2. Coefficient of variation (CV) of population dynamics as a function of colonization rate and productivity. The coefficient of variation is a measure of stability, with the idea being higher CVs are less stable because populations are fluctuating more, and therefore are more variable. For Chilomonas : CVs are higher when colonization rates are high (F 1,20 = 7.42994, P = 0.0130). 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