Population Ecology

Paramecium caudatum feed on bacteria by driving them into the biosphereic presser valve with cilia. Their natural habitat is fresh water. They take in water from the hypotonic environment via osmosis and use bladder-like contractile vacuoles to accumulate excess water from radial canals and periodically expel it through the plasma membrane by contractions of the surrounding cytoplasm. The contractile vacuoles also serve to maintain osmotic pressure. When moving through the water, they follow a spiral path while rotating on the long axis.

Paramecium aurelia are unicellular organisms belonging to the genus of Paramecium of the phylum Ciliophora. They are covered in cilia which help in movement and feeding. Paramecium can reproduce sexually, asexually, or by the process of endomixis. Paramecium aurelia demonstrate a strong “sex reaction” whereby groups of individuals will cluster together, and emerge in conjugant pairs. This pairing can last up to 12 hours, during which the micronucleus of each organism will be exchanged. In Paramecium aurelia, a cryptic species complex was discovered by observation. Since then, some have tried to decode this complex using genetic data.

The following data is the results of a trial of paramecium growth over 16 days, the numbers going in order horizontally P. aurelia grown alone, cells/mL, P. caudatum grown alone, cells/mL, P. aurelia grown in mixed culture, cells/ mL, P caudatum grown in mixed culture, cells/mL.
Day O 1 1 1 1
Day 2 4 5 3 5
Day 4 27 15 16 9
Day 6 43 24 31 10
Day 8 54 28 38 7
Day 10 47 28 45 4
Day 12 48 28 46 1
Day 14 49 28 50 0
Day 16 49 28 47 0

The following questions are questions that I answered that were linked to the lab.

1. What are the objectives for this experiment? (you can summarize)
Demonstrate how competition for a resource can effect population growth and to explain how the availability of resources can be limited for populations.
2. Make a hypothesis about how you think the two species of Paramecium will grow alone and how they will grow when they are grown together.
When the two species of paramecium are separate both will survive, when they are together only one will survive.
3. Explain how you tested your hypothesis.
I created three environments, one with only P. caudatum, one with only P. auralia, and one with both secies to see how they would interact.
4. On what day did the Paramecium caudatum population reach the carrying capacity of the environment when it was grown alone? How do you know?
Day 8 because the days after the same number was repeated.
5. On what day did the Paramecium aurelia population reach the carrying capacity of the environment? How do you know?
Day 14 because the day after, the same number was repeated.
6. Explain the differences in the population growth patterns of the two Paramecium species. What does this tell you about how Paramecium aurelia uses available resources?
In the P. caudatum population they use a larger amount of the available resources and that’s why the is a smaller amount of the of the species, and with the P. auralia a smaller amount of resources is used by each individual and that is why the are many more of the P. auralia specie.
7. Describe what happened when the Paramecium populations were mixed in the same test tube. Do the results support the principle of competitive exclusion? (you may need to briefly explain what competitive exclusion is)
The competitive exclusion principle states that two species competing for the same resources cannot coexist if other ecological factors are constant. Since P. aurelia had the advantage that specie survived and therefore the P. caudatum died off.
8. Explain how this experiment demonstrates that no two species can occupy the same niche.
This experiment demonstrates that no two species can occupy the same niche because when the two species were put together one died off.

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