Species Interactions: Competition – Introduction
How to Proceed
- Read through the introductory materials below.
- Open the Unit 8 Experiment Answer Sheet and complete the following Experiment exercises this unit:
- Experiment 8 Exercise 1 – Species Interactions: Competition (~1.5 hrs)
- Experiment 8 Exercise 2 – Biomes (~30 min)
- Save your completed Unit 8 Experiment Answer Sheet and submit it no later than Sunday midnight (CT).
Species Interactions: Competition – Introduction
This unit we are learning about species-species interactions and how species influence each other (see pp 428-432 and our online lecture). One important interaction is interspecific competition, in which two or more species compete for limited resources. Competition, along with predation and symbioses (e.g., commensalism, mutualism, and parasitism) are important biological interactions that affect the size of species populations.
In the first exercise, we will examine the population growth of two species of freshwater ciliates. Populations of these species initially grow exponentially (see p 408), but the population does not increase in size forever. Eventually it reaches what is known as the carrying capacity of the environment, or the maximum population size the environment can support due to limitations in food, water or other resources.
Competitive exclusion (see p 429) may occur between two species that compete for the same resources. In this situation, only one species will be successful, such that the other species is forced to move elsewhere or die out. This rarely happens in nature though, since the species on the losing end typically switches to an alternate resource. However, under artificial situations, elimination of one species can occur.
The purpose of this exercise is to use a simulation to model competitive exclusion using the microscopic organisms that Gause used to come up with his competitive exclusion principle (see p 429). You will need to use the following website. Be sure you can access it and use it:
Glencoe/McGraw Hill. No date. Population Biology
http://www.mhhe.com/biosci/genbio/virtual_labs/BL_04/BL_04.html (Links to an external site.)
When you are ready to begin, go to the above website and open the Unit 8 Experiment Answer Sheet and follow the instructions.
In Biomes – Introduction
This unit we have learned about the large scale ecosystems called Biomes. They have developed over millions of years and the flora and fauna found in each biome type have adapted to the long term climate conditions (e.g., average rainfall, average temperatures). The purpose of this exercise is to see how well you understand the biotic and abiotic factors that shaped the various biomes. Review pp 384-390 and our online lecture this unit before beginning.
You will need to use the following websites. Be sure you can access them and use them:
NASA. No date. The Great Graph Match
http://earthobservatory.nasa.gov/Experiments/Biome/graphmatch_advanced.php (Links to an external site.)
NASA. No date. To Plant or Not to Plant
http://earthobservatory.nasa.gov/Experiments/Biome/plant_it.php (Links to an external site.)
When you are ready to begin, open the Unit 8 Experiment Answer Sheet to complete this exercise.
WEEK 8 EXPERIMENT ANSWER SHEET Please submit to the Week 8 Experiment dropbox no later than Sunday midnight.
SUMMARY OF ACTIVITIES FOR WEEK 8 EXPERIMENT ASSIGNMENT
· Experiment 8 Exercise 1 – Species Interactions: Competition
· Experiment 8 Exercise 2 – Biomes (Part I and II)
Experiment 8 Exercise 1: Species Interactions: Competition
In this exercise you will be evaluating the effect of competition on the population size of two species of microorganisms. Be sure you have read through the readings for Week 8 as well as the introductory information for the Week 8 Experiment. When you are ready to begin, open in the following website:
Glencoe-McGraw Hill. No date. Population Biology http://glencoe.mcgraw-hill.com/sites/dl/free/0078759864/383928/BL_04.html
Procedure
A. Click on the Information button on the bottom and read through the material before beginning. You will need to scroll down to read all of the information. Close the window when you are done. Note that the two species we will be using will be competing for the same food source; bacteria.
B. First, you need to set up the experiment by distributing the two species to the three test tubes.
a. Click on the pipette (the purple bulb) in the flask containing P. caudatum, fill it and place the contents in Tube #1.
b. Then click on the pipette in the flask containing P. aurelia, fill it and place the contents in Tube #2.
c. Finish by putting a pipette full of both species in the Tube #3.
C. Answer the question below before proceeding.
Question
1. The number of P. caudatum and P. aurelia grown alone would be expected to increase until the population size reaches the carrying capacity of the test tube. What do you think will happen in terms of population growth in Tube #3 that contains both species combined and why (2 pts)?
Procedure (continued)
D. You now need to count the number of organisms in each Tube beginning on Day 0 and continuing every 2 days until you reach Day 16. These values will need to be recorded in Table 1 below (do NOT use the Table provided by the website).
a. Click on the Microscope to get started.
b. Click on Clean microscope slides and then Take Sample.
c. Click on the first slide and drag it on to the microscope. Count the number of P. caudatum (note its shape) and multiply by 2 to get the number of cells per ml (your slide holds 0.5 ml). Record this number in the Table below; this is Day 0.
d. Next, click on the second slide and drag it to the microscope. Count the number of P. aurelia (note its shape), multiply by 2 and record this number in the Table for Day 0.
e. Finally, drag the third slide on to the microscope and count the number of each type of organism, multiply by 2 and enter the data into the Table.
f. Click on Clear Slides (on the bottom) and then on the Calendar that says Day 0 to advance it two days.
g. Repeat steps b – f until you reach 16 days.
h. As the days go on, you will have more and more individuals to count. Click on the Grid On button on the microscope to make them easier to count.
Table 1. Results (4 pts).
| Grown Separately (cells per ml) | Grown Together (cells/ml) | |||
| Day | P. caudatum | P. aurelia | P. caudatum | P. aurelia |
| 0 | ||||
| 2 | ||||
| 4 | ||||
| 6 | ||||
| 8 | ||||
| 10 | ||||
| 12 | ||||
| 14 | ||||
| 16 |
E. Now it is time to analyze your data.
a. You will need to generate two graphs, one which depicts the number of both species per day of culture when grown separately and one that depicts the number of both species per day of culture when grown together.
b. You must use the Scatter type graph in Excel and each graph should have two lines (one for each species).
c. Be sure you label your axes and your series; meaning you will need to indicate which line pertains to P. caudatum and which to P. aurelia.
Paste your two graphs below (4 pts):
Questions
2. What were the carrying capacities (maximum population size) for the two species when grown separately and on what day were they reached (1 pts)?
3. Describe what happened when the two species were grown together and explain why. Be sure to discuss the magnitude and timing of each species’ carrying capacity compared to when they were grown separately (3 pts).
4. Do these results support the principle of competitive exclusion; why or why not? Be sure to cite your sources. (4 pts).
Experiment 8 Exercise 2: Biomes
In these two relatively short exercises, we will be examining the biotic and abiotic factors that define a biome. You should have completed the readings for this week before beginning.
Procedure – Part I: The Great Graph Match
A. Open the following website:
NASA. No date. The Great Graph Match http://earthobservatory.nasa.gov/Experiments/Biome/graphmatch_advanced.php
B. In the Great Graph Match, you will need to match abiotic information (annual rainfall and temperatures) to the appropriate biome. Follow the instructions on the page and fill-in the Table below. For the Explanation column, you need to briefly explain why you chose the biome you did based on the data presented.
C. Be sure to provide complete citations for the sources used.
Table 2. Locations, biomes and explanations (4 pts).
| Location | Biome | Explanation |
| Frogmore, England | ||
| Goteborg, Sweden | ||
| Koombooloomba, Australia | ||
| Barrow, Alaska | ||
| Alice Springs, Australia | ||
| San Bernadino, California | ||
| Centralia, Kansas |
Citations:
Procedure – Part II: To Plant or Not to Plant
A. Open the following website:
NASA. No date. To Plant or Not to Plant http://earthobservatory.nasa.gov/Experiments/Biome/plant_it.php
B. In the To Plant or not to Plant, you will need to determine which in which biomes to plant various plants, based on the information presented. Follow the instructions on the page and fill-in the Table below. For the Explanation column, you need to briefly explain why you chose the biome you did.
C. Be sure to provide complete citations for the sources used.
Table 3. Plants, biomes and explanations (4 pts).
| Plant | Biome | Explanation |
| Creosote bush | ||
| Spruce | ||
| Flowering dogwood | ||
| Orchid | ||
| Lichen | ||
| Bluestem grasses | ||
| White sage | ||
| Saguaro cactus |
Citations:
Week 8 Experiment Grading Rubric
| Component | Expectation | Points |
| Experiment 8 Exercise 1 | Correctly conducts experiment, records data (Table 1) and generates two graphs. | 8 pts |
| Experiment 8 Exercise 1 | Demonstrates an understanding competition between species and the effect it has on population growth (Questions 1-4). | 10 pts |
| Experiment 8 Exercise 2 | Develops an appreciation of the diversity of ecosystems around the globe and understands the environmental conditions that lead to their development (Tables 2 and 3). | 8 pts |
| TOTAL | 26 pts |
Updated October 2013
