The Effects of Population Density on the Reproduction and Survival of Daphnia Magna

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Abstract The population dynamics of Daphnia magna are observed under three different conditions; low, medium, and high density. The effects of different population densities on the survivorship and reproduction of Daphnia are observed over a two-week period within a lab environment. Over the two week period, the numbers of parent Daphnia alive and dead are recorded daily, along with the amount of offspring produced each day. From the main parameter investigated, the net reproductive rate, the results of the experiment support that higher densities result in less successful reproduction and decreased fecundity. Values for the instantaneous growth rate of the populations also suggests that low and medium density populations allow for…show more content…
This can explain why growth and survivorship seem to remain constant within a population regardless of resource availability. Ban et al. (2009) also found that Daphnia pulex grown under crowded conditions grew much more slowly than those that were grown alone, even when the food supply was sufficient. The individuals grown in a high density population were also observed to have a smaller net reproductive rate, due to the essential need for them to conserve resources necessary for their own survival. These sources, as well as the results obtained from our experiment, support the claim that higher population densities result in reduced rates of reproduction and decreased chances of survival. Methods The experiment took place in a laboratory setting, and the first step was obtaining sixty individual Daphnia magna (that were neither adults nor tiny offspring) from a large tank in the lab. These individuals were equally divided into three groups; low density, medium density, and high density. The twenty Daphnia assigned to the low density group were split into four groups of five and pipetted into one of four tubes filled with 10mL of Chlamydomonas algae. The twenty Daphnia assigned to the medium density group were split into two groups of ten and placed into one of two tubes also filled up to 10mL with Chlamydomonas. The final twenty Daphnia were all placed into a single tube filled with 10mL of the algae. In order to avoid suffocation-related

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