Effect of Competition on Population Growth

Population Online Lab


The purpose of this laboratory experiment was to investigate how two species of the freshwater protozoan Paramecium, alone and together, compete for food and how it affects their population growth.


Placing each Paramecium on its own allows them to grow and flourish because they do not have any competition that inhibits their growth. Therefore, both species of the Paramecium will grow to their maximum level. Placing the two protozoans together leads to a competition for food resulting in the faster growth of one species while the other one stops growing and eventually disappears.



The materials used in the experiment included a microscope, three test tubes, two volumetric flasks, two pipettes, rice, Paramecium aurelia, and Paramecium caudatum.


The first procedure involved placing rice on the three test tubes.

The second step of the experiment involved filling the three test tubes with the stock cultures in the flasks. The first test tube was filled with 4 cell/mL of Paramecium aurelia, the second with 4 cell/mL of Paramecium caudatum, while the third test tube was filled with a mixture of both species, each 4 cell/Ml.

The next step involved making the wet mounts of the three cultures and placing them on slides. The wet-mount slides were then placed on the microscope for examination.

The number of cells in each mount was then counted to establish the total number of cells and the data was recorded on the data table.

The process of making of wet mounts slides from each sample was then repeated continuously after every two days and the number of cells were counted and recorded respectively.


The procedure was from day 0, day 2, day 4, day 6, day 8, day 10, day 12, day 14, and to day 16.


I tested my hypothesis by placing in one test tube a stock culture of Paramecium aurelia, the next with Paramecium caudatum, and the third test tube with a mixture of the two species of the Paramecium. wet mount slides were then prepared for each test tube and then observed under the microscope after every two days. The results were recorded on a table and used to test the hypothesis.

The carrying capacity ofParamecium caudatumwhen grown alone was realized on the eighth day and the total population was 28. The carrying capacity is achieved when the population of the organisms stops increasing. From the eighth day to the sixteenth day, the population of the Paramecium caudatum did not grow.

The carrying capacity ofParamecium aureliawas realized on the eighth day with a maximum population of 48. Despite reaching its carrying capacity, the population of the protozoa increased to 50 on the tenth day and 51 on the twelfth day before going back to 48 on the fourteenth and sixteenth days.

The growth patterns among the two species of Paramecium show that Paramecium aurelia is stronger than Paramecium caudatum. Paramecium caudatum growth was slow compared to Paramecium aurelia. The species doubled its numbers daily until it attained it carrying capacity of 28 on the eighth day. On the other hand, aurelia grew at a faster pace by increasing five times from day two and four, and then nearly doubling each day after that until it achieved its carrying capacity of 48 on the eighth day. The growth patterns indicate that Paramecium aurelia makes good use of both food and solar light thus leading to rapid increase in its population.

The experiment proves that no two species can occupy the same niche by showing how Paramecium aurelia overpowers Paramecium caudatum when they are placed in the same test tube. The power of natural selection eventually leads to the extinction of Paramecium caudatum.

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