Effects The of Selenastrum Population Growth in Competition with Anabaena and Predation with Daphnia.
Abstract In aquatic ecosystems human development has disturbed natural interactions between species. If these natural interactions can be understood than pollution can be counteracted and we can make advances in the way of ecosystem reconstruction. In this experiment we will work towards this cause by understanding the relationships on competition and predation based on Selenastrum populations. This experiment will work to answer what affect competition between two forms of algae, Selenastrum and Anabaena, has on the Selenastrum population. The Second question to be addressed is what effect predation has on Selenastrum while in the presence of Daphnia. These questions will be answered through the use of model ecosystems, microcosms. Three microcosms will include the single presence of Selenastrum, Selenastrum with Anabaena, and Selenastrum with Daphnia. Over time the Selenastrum population density will be calculated with the help of a Hemacytometer. This data will be statistically analyzed to compare the relative effects. With the completion of this experiment it can be concluded that competition between Selenastrum and Anabaena positively affects Selenastrum populations while predation between Daphnia and Selenastrum negatively affects Selenastrum populations. These conclusions based on controlled environments can allow us to understand real life complex relationships in order to restore the natural balance to aquatic ecosystems.
Introduction Competition occurs when two organisms require the same resource. In such cases the resource availability is then affected. In cases of limited environments such as those with limited space, when population increases the resource availability is decreased. This interspecific competition leads to logistic growth instead of exponential growth which could occur in unbound
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ecosystems. Predation can also affect the impact of competition. If one organism is in competition with another it can be less of a threat for that shared resource if it faces predation as well. The relationships involving competition and predation between organisms are important to understand for all fields of biology. To understand population growth rates as well as natural selection and overall fitness it is important to evaluate competition and predation. This experiment can further the developments of competition and predation specifically relating to specific types of algae. Previous work has concluded that algae and zooplankton similar to the species we are working with are important to ecosystems. Previous experiments and real life history has taught us that human development is destructive to the natural ecosystems of many fish. Human development increases phosphorous runoff into streams, rivers and other waterways. These increased amounts of phosphorous increase algae populations resulting in more food for zooplankton such as Daphnia. However when this phosphorus increases, a different form of algae, blue green, overruns the native green algae. This blue green bacterium reduces oxygen leaving the environment completely changed for fish (Jensen 2007). In relation to the Daphnia the blue green bacteria is actually destructive to the Daphnia population as well. Increased amounts of blue green bacteria can decrease body size, limit growth and decrease birth rates of Daphnia (Gliwicz 1990). Previous research has not determined whether Selenastrum or Anabaena is the strongest competitor. The effects these two algae have on each other remains unknown. The affect of Selenastrum while together with Daphnia is also undetermined. This experiment will ask which form of algae is a stronger competitor. The experiment will explore the competition relationship between these two. In the way of predation this experiment will determine how in a limited
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environment, the prey, (Selenastrum) reacts to the predator, (Daphnia). The hypotheses for this experiment are that in treatment one, the Selenastrum alone, the levels of Selenastrum will grow. This population growth should occur because the Selenastrum species is undisturbed with no predator. For treatment 2 the hypotheses is that the Selenastrum will increase as a result of competition. The Selenastrum will increase because it is a better competitor than the Anabaena in normal conditions. In the third treatment the Selenastrum will decrease as a result of predation. The Daphnia is the predator of the Selenastrum causing the population as a whole to decrease while it is in the presence of a predator. In this experiment the effects of competition are studied in relation to the effect Anabaena has on the growth rate of Selenastrum. Anabaena is blue green algae while Selenastrum is green algae. Further this experiment will explore the effects of Daphnia, an herbivore, on Selenastrum. The comparisons of effects will be utilized using model ecosystems to control extraneous variables. One ecosystem will compare Selenastrum growth populations in their own secluded environment. The other will evaluate Selenastrum in the presence of Anabaena. The last comparison will conclude the effects of Daphnia on Selenastrum. This experiment will answer questions on the relationships between these three organisms as well as their relationships with their environments. These model ecosystems will answer what affects two types of algae have on each other as well as the effect of predation on the Selenastrum. Relationships between herbivores and primary producers will be explored and ecology can then be further understood. Methods This experiment investigated the impact of competition and predation on Selenastrum based on the population growth. First three 600 mL microcosms were set up. In all three systems
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growth medium was added. These three were treatments calculated so that they each contained 150,000 cells/mL Selenastrum. In the first microcosm, just the Selenastrum were present. The second treatment contained Selenastrum and 100 mL of Anabaena in order to measure competition. The third microcosm contained Selenastrum and twenty Daphnia to evaluate predation. In order to evaluate this experiment data was collected in terms of Selenastrum density. Selenastrum density was calculated with the aid of a Hemacytometer. A sample from the microcosm was added to the Hemacytometer and then the number of Selenastrum counted to calculate the density. This was done by calculating an average number of Selenastrum and multiplying by the concentration of cells. The approximate number of Daphnia was also estimated. This was done using an approximate scale in base twenty up to one hundred Daphnia. Data was collected over a two week period. Exact data was recorded on day seven as well as on day fourteen. The class's data for each treatments Selenastrum density was compiled for statistical analysis in order to get an accurate measurement of the densities. This provided a more accurate idea of what the effects of competition and predation were by having a more accurate estimate of the actual densities. The compiled data was then statistically analyzed using the t-test. The data from treatment one and treatment two were compared in order to evaluate competition. This t-test was completed using the day fourteen data for each treatment one and two. The second evaluation was between treatment one and treatment three in order to evaluate predation. The day fourteen data for each of these microcosms were also used in this calculation. Using microcosms to control the experiment competition and predation effects were observed and analyzed statistically through Selenastrum density (Jensen 2007).
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Results Through this experiment, competition between Selenastrum and Anabaena was evaluated by comparing treatment one and treatment two. Using a statistical t-test comparing these two treatments, a t calculated value was found. This value was calculated to be 1.86. The t critical value using the chart and degrees of freedom of 6 was 2.447. Because the t calculated value was lower than the t critical we can retain the null hypothesis. In this case that means that competition of the Anabaena did not have any effect on the Selenastrum population. The data reflects this statistical conclusion in that in the presence of Anabaena the Selenastrum population did not decrease (Figure II). The second comparison was between treatment one and treatment three evaluating predation. The t test calculated a value of 3.06 for this relationship. The t critical value with degrees freedom of 6 was 2.447. In this case the t calculated value is higher than the t critical value so the null hypothesis is rejected. Therefore the Daphnia did have an effect on the Selenastrum population. The data supports this because over time treatment three's Selenastrum density decreased (Figure III). Discussion This experiment evaluated the effects of competition (Selenastrum and Anabaena) and predation (Selenastrum and Daphnia) in ecosystems. Through the use of a controlled environment, microcosms, we could determine to what extent the Selenastrum populations were effected. Previously it was unknown as to what effect Anabaena had on Selenastrum. This experiment proved that Anabaena is a far weaker competitor than Selenastrum. The population of the Anabaena was effected negatively where as it is reflected in the data that the population of Selenastrum was positively affected. No previous work had been done to determine the effect Daphnia had on Selenastrum. This experiment allowed us to see that Daphnia is a very
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successful competitor to Selenastrum. The data supports that while the Daphnia populations continued to grow exponentially the Selenastrum population decreased rapidly as it was preyed upon. These conclusions relate to the general idea of aquatic ecology. As in real life ecosystems the native green algae, in our case Selenastrum, is much stronger in normal settings than the blue green algae, Anabaena. Research has shown us that Anabaena is a better competitor when phosphorous levels are increased however. It was also known that predator prey relationships would decrease prey populations. It was unclear to what extent the Daphnia would have on the Selenastrum population but our study had concluded that in controlled environments the Daphnia can significantly decrease Selenastrum populations. In real life situations these relationships are not as predictable. In stable environments the Daphnia would not run the Selenastrum extinct because of other species interactions. Species Richness would provide predators to the Daphnia as well as other prey for it (Wooton 1992). Ecosystems in action can be thought of as more of a checks and balance system instead of one simple controlled interaction as in our experiment. Future research could analyze in more detail these predation and competition reactions. A future experiment would be helpful if more than one factor was available in a microcosm. In the future studies involving more than one species and each of there population growth would be more helpful to ecology. Other possible studies could include the effect of human destruction as in rising phosphorous levels have on these common species interactions.
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Bibliography Z. Maciej Gliwicz; Winfried Lampert. 1990. Food Thresholds in Daphnia Species in the Absence and Presence of Blue-Green Filaments. Ecological Society of America. 71: 691-702. Jensen, J.S. 2007. Biological Sciences 106. Hayden-McNeil Publishing INC. Plymouth. Wootoon, Timothy J. 1992. Indirect Effects, Prey Susceptibility, and Habitat Selection: Impacts of Birds on Limpets and Algae. Ecology. 73:981-991.
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