Reference no: EM133472047

Assignment:

Investigation: Biotic Interactions

Materials Needed:

This Microcosm Model is used to simulate the population growth in Escherichia coli (bacteria), Paramecium aurelia (protists), Paramecium bursaria (protists) and Didinium nasutum (protists).

Procedure: use Microcosm Model and add screenshots of each of the steps.

(modified with permission from Virtual Biology Lab)

The model opens to a virtual petri dish, which is initially filled with sterile nutrient broth. You can add a specified amount of each microbe, and watch them move about the dish. When 'Go' is clicked, the individuals reproduce, feed or die. The volume and light level of the microcosm can be adjusted in the simulation. Take some time to familiarize yourself with the model before beginning the exercise. Clicking on 'Go' a second time stops the simulation, and clicking on 'Setup' resets the simulation. You can speed up the simulation using the slider at the top and you can download your graph using the buttons in the top right corner above the graph.

1. Add the default amount of 200 bacteria into the petri dish. Leave volume and light at their default settings. Select 'Go' to observe the population grow over time. You can stop it when you see no more growth occurring. Record observations about the time it takes for the population to grow, the change in population size, and type of population growth (exponential or logistic). Calculate the average population growth (change in population / change in time).
2. Repeat three more times, once for each protist species and each with an initial population of 20. Record the same observations as above.
3. Next, reset the simulation. Choose two of the three protist populations to study further. Add the bacteria with the first of the two protist populations you chose into the petri dish. Keep all other variables the same, including initial population numbers. Record observations about the time the population grows, the change in population size, and type of population growth. Calculate the average population growth.
4. Repeat step 3 for the bacteria and second protist population you chose.
5. Repeat step 3 for bacteria together with the two protist populations you chose.

Interpretation and Analysis:

Create an observation chart for each of your experiments which answers the questions in the procedure. Include a picture of the graph for each of your studies.

Answer the following analysis questions:

1. When the bacteria and protists were on their own in the dish, what limited the size of each of their populations?
2. Create a food chain to show the relationship between the 3 microorganisms you studied and explain how you came to this conclusion.
3. What types of intra- and interspecific competition are demonstrated in this simulation. Be specific as to which organisms are able to outcompete others.