Population Biology Report[1]

Deborah Omoyege BIO 1134: Lab Report Lab Time: W 1:00p.m. November 24, 2009 Investigating the Competitive Exclusion Principle

Introduction Gause cultured a few protest species such as Paramecium caudatum and Paramecium Aurelia together, Paramecium caudatum went extinct (McGraw-Hill). Both species utilized bacteria as food but Paramecium Aurelia grew at a rate six times faster than Paramecium caudatum and was better able to convert the food into offspring (McGraw-Hill). However, when Gause cultured Paramecium caudatum and Paramecium bursaria together, neither went extinct simply because the population volumes of both were much less compared to when they were grown alone, because some competition occurred between them (McGraw-Hill). Gause also recognized that Paramecium was better able to utilize the yeast in the lower part of the culture tubes. From these experiments Gause was able to conclude that two species with exactly the same requirements cannot live together in the same place and use the same resources, that is, occupy the same niche (McGraw-Hill). Gause established the competitive exclusion hypothesis, essentially meaning that complete competitors cannot coexist (McGraw-Hill). Competitive exclusion states that when the competition between species is sufficiently strong, only the dominant species survive (Ziyad and Rhouma). In the scientific journal article the writers try to examine the different ways of using harvesting and stocking techniques to prevent the extinction of the weak species in a competitive exclusion environment (Ziyad and Rhouma). This experiment will test whether or not two diverse species of the freshwater protozoan Paramecium can coexist together in the same niche. Methods A study of freshwater protozoan Paramecium was conducted. The methods that were in carrying out this procedure were the use of a microscope, microscope slides, flasks, pipettes, rice, and test tubes. A Pipette filled with Paramecium caudatum was added to the first of three test tubes. Paramecium aurelia was added to the second test tube. The last test tube was composed of both Paramecium caudatum and Paramecium aurelia. Rice is also added to all three test tubes as food for the bacteria, which in turn would be food for the Paramecium. After the test tubes were filled with the necessary stock cultures wet-mounts slides of the samples were prepared. Individually microscope slides were placed on the stage of the microscope. The wet slides were then studied and counted. Wet-mouth slides for each test tube were placed under the microscope and counted. Every two days more wet mount slides from each sample were created for a period of ten days.

Results

The population size of Paramecium aurelia began to grow rapidly over the course of ten days and eventually depleted the Paramecium caudatum stock culture species. Table 1.1 Day 0 2 4 6 8 10 12 14 16

P. caudatum alone, cells/mL

P. aurelia alone, cells/mL

1 4 13 26 28 28 31 31 30

1 6 26 44 46 46 50 49 48

P. caudatum mixed, cells/mL 1 6 18 10 7 3 2 0 0

P. aurelia mixed, cells/mL 1 4 12 33 39 44 48 48 47

The table above shows the number of cells per 0.5 mL that were present on the wet-mouths composed of Paramecium caudatum, Paramecium aurelia, and Paramecium caudatum and Paramecium aurelia combined. The first column shows the number of days that the samples sat being the amount of time two species would have before an extension of one species occurs.

Graph 1.1

Graph 1.2

60 9 50

P. aurelia mixed, cells/mL

8 P. caudatum alone, cells/ mL

40

7

P. aurelia alone, cells/ mL

30

5

P. aurelia alone, cells/mL P. caudatum alone, cells/ mL

3

P. aurelia mixed, cells/ mL

10

P. caudatum mixed, cells/ mL

4

P. caudatum mixed, cells/ mL

20

6

2

Day

1 0 0

5

10

15

20

0

50

Day

40

10

20

30

P. caudatum

Graphalone, 1.3cells/mL

30

P. aurelia alone, cells/mL

20 10 0 1 2 3 4 5 6 7 8 9

P. caudatum… Day

P. caudatum mixed, cells/mL P. aurelia mixed, cells/mL

40

50

Results The competition amongst the species affects population tremendously because of many factors. The genus Paramecium consists of unicellular species of protists that live in freshwater environments (VirtualLab). Under ideal conditions, sufficient food, water, and space, populations of these species grow rapidly and follow a exponential growth pattern that ultimately affect populations size (VirtualLab). Nevertheless, the size of any population can not continue to grow and grow with out depletion. Eventually there will become a strong demand on the resources of that particular niche. Inevitably limitations on food, water, sunlight, and other resources will cause the population to stop increasing (VirtualLab). When a population arrives at the point where its size remains stable, it has reached its carrying capacity (VirtualLab). The competition for resources among members of a single species which is referred to as intraspecific competition, places limits on population size (VirtualLab). In this lab experiement there is a competition for resources among members of two different species; Paramecium caudatum and Paramecium aurelia, places limits on the overall population size that could ever exist. Discussion/ Conclusion In conclusion it is quite impracticable for more than one species to coexist in one given area which can also be referred to as niche, and subsist. As stated above the competition for resources among members of two or more different species greatly affect population size. Earlier along in the lab both the Paramecium caudatum and Paramecium aurelia grew at a very steady rate. As the lab progressed Paramecium aurelia began to grow at a more frequent rate. The fact that Paramecium aurelia grew faster than Paramecium caudatum shows the dominant species between the two. G.F. Gause stated that between two species competing in the same niche for the same food, water, light, etc. the species with a greater percentage of growth rate will prevail over the other. Ziyad and Rhouma of “Coexistence and extinction...” assert that between species, when competition is sufficiently strong, only the dominant species survive. This affirms the results in the lab. The hypothesis was upheld and conclusive. During the course of the lab experiment, as the days progressed the slides with both Paramecium aurelia and Paramecium caudatum began to become very clear. Paramecium aurelia began to significantly outnumber Paramecium caudatum until the point where it was completely eradicated. Thereby proving and concluding that the coexistence of any two species is impossible. There is not enough resources to sustain life such as food, water, light, etc. in a given niche in order for more than one species to survive. Because of this, naturally some species leave and invade unoccupied habitats simply to avoid competing

(VirtualLab). Population Biology is a subject that is always open to more research. Further tests can be done to reassure the simply fact that only one species can coexist in a specific niche. Literature Cited AlSharawi, Ziyad, and Mohamed Rhouma "Coexistence and extinction in a competitive exclusion Leslie/Gower model with harvesting and stocking." Journal of Difference Equations & Applications 15.11/12 (2009): 1031-1053. Academic Search Premier. EBSCO. Web. 22 Nov. 2009. Virtual Lab. McGraw-Hill Higher Education. McGraw-Hill Companies Inc., 1221 Avenue of the Americas. Widmaier, Eric, et al. Biology--Textbook. New York, NY 10020: The McGraw-Hill Companies, Inc., 2008. Print.