Population Dynamics of Daphina magna in relation to Carrying Capacity in Closed Ecological Systems Reported by Yuichi “Eugene” Saito and David Barbee Faculty Mentor: Frieda Taub School of Aquatic and Fisheries Sciences, the University of Washington, Seattle WA Methods Introduction Nutrients recycle through organisms and constitute food chains and food webs. On Earth, the process of nutrient cycling takes place on a scale that is difficult to study. Closed Ecological Systems (CES) are miniature models of our planet; they function with little substance exchange. Solar energy is the only substantial input. CES are a way to study how resources are recycled on earth without the difficulty of a large scale. The peak number of Daphnia increased as the container size increased, but the peak density of Daphnia magna (/ml) might be inversely related to size of bottles: the smaller the container is, the greater the density is. The carrying capacity of Daphnia magna to date seemed to be correlated to not only bottle sizes but also availability of gas exchanges. Rapid increase of algae results in rapid increases of Daphnia population, which was remarkably observed in the open system. Closure restricts gas exchange, especially of CO 2 which is required for photosynthesis and of O 2, a waste product of photosynthesis, but a requirement of Daphnia. Greater Daphnia populations in the open systems suggests that CO 2 may have been limiting. The “Kent water” is the source of bicarbonate, the only significant CO 2 source, other than Daphnia respiration. Conclusion Figure 3. A comparison of the mean Daphnia densities over 36 days between closed and open systems: Daphnia populations reached the highest peak densities (highest birthrates), but then crashed (highest death rates) in the smallest open systems. Systems with lower Daphnia peaks had greatest persistence of Daphnia populations. Goal: Does container size affect Daphnia populations in Open and Closed Ecological Systems? A total of 36 ecological systems (ES) were setup in 6 closed bottles of 3 sizes with matching open bottles for comparison, so 18 Closed Ecological Systems (CES) and 18 Open Ecological Systems (OES). Data were gathered biweekly by counting the population of Daphnia magna. We explored the concept how size and volume effect the self-sustaining closed ecological systems. We set up three sizes of CES in closed bottles consisting of inorganic medium, two species of algae, and the grazer Daphnia magna. We also set up the same sized systems in open bottles for comparison. *Daphnia can be reproductively mature six days after birth. Figure 2. Open system: The peak mean densities increased as container size decreased Closed system: Low mean peak density in largest (755ml) containers, but high densities in smaller (73ml, 272ml) containers Figure1. The peak mean populations increased as container size increased in both closed and open systems. Results Of the 36 ES, 29 had Daphnia populations persisted to day 36. In these 29 ES, the population peak occurred between days 11 and OES and 2 CES lost the Daphnia populations by day 36. A comparison of mean peak Daphnia populations resulted in greater the number of Daphnia as bottle size increases (Fig.1); however, the mean peak density (animals/ml) was reversed; greater density in smaller bottles (Fig.2). Tests of mean peak density (animals/ml) differences: 1.Bottle size effect: The larger the bottle, the more Daphnia per system, but the lower the density (Daphnia /ml), p = at  = Open vs. closed treatment effect: Closed systems had lower densities (Daphnia/ml) than open systems, p = at  = Interaction effect: Significant as well, p = at  = A photographic process was developed to count large populations of Daphnia The image processing increased the contrast of Daphnia magna with the surrounding medium, and allowed living individuals to be counted by eye. Diagram of experimental setup, using a Nikon Coolpix 995 digital camera Before and after the image analysis process: Daphnia contrast with the surrounding medium is enhanced. Daphnia density (/ml) Day Data analysis: We compared mean peak density of Daphnia among three different sizes of open and closed systems by using the two-way ANOVA statistical test to determine significance. 1. Bottle size effect if there is any difference between small, medium, and large bottles. 2. Open vs. closed treatment effect if there is any difference between open and closed systems. 3. Interaction effect between “open effect at small, medium, and large sizes” and “closed effect at small, medium, and large sizes.”