Module 9S2 Changes in Populations

4.9.3S2 page 3

Watch and Listen

To review these concepts and understand graphing, watch the following video. You may choose to make notes as you view the presentation:

r and K selection

Self-Check

SC 1.

In this unit, practice problems and graphing are essential. The following self-check is an opportunity to practice your skills.

 

Caribou: Exponential or Logistic?

1. 

   © Clément Billet #2296248/Fotolia LLC

   Caribou live in the arctic and subarctic tundra, feeding on lichens in the winter and willows, grasses and sedges in the summer. Their most important predator is the wolf. The winter migration takes them from the open tundra to the protection of the boreal forests; in spring they return to the calving grounds of the tundra. During the fall ‘rut’ (breeding period) the most dominant male breeds with up to 15-20 females, with one calf born to each mother in the spring. The following data describes caribou reindeer population changes on St. Paul Island, Alaska from 1910 to 1950.
   

   Year	Population (N)
   1910	30
   1920	300
   1930	350
   1940	1200
   1950	0

   
   
   1. Graph the data from the table above. Label axes and provide a title and units.
   2. Considering the information you were given regarding reindeer reproductive habits and predation, would you predict that the population growth curve would be logistic or exponential?
   3. Analyze the graph. In a statement, describe the growth pattern that existed from 1910 to 1950.
   4. Does the data support your prediction from B?
   5. Consider all the information you have been given about caribou populations. Hypothesize as to 2 reasons for the observed growth pattern. Indicate whether each reason is density dependent or density independent.

Bacterial Growth
Answer the following questions and store your answers in your course folder. Remember how important these problem solving and graphing skills are in this unit.

 

In suitable abiotic conditions, and with adequate food, E. coli bacteria (part of your normal intestinal flora) undergo binary fission every 20 minutes. Thus, with each generation, populations double and each generation is only 20 minutes long. Typically, bacteria introduced onto a medium will go through the following phases

• Lag phase: slow growth

• Exponential growth: doubling with each generation

• Death phase: population crashes due to competition for food and accumulation of toxins.

1. Using your calculator (using 2n as a function):
   
   

   • fill out the following table

   • graph the results (it is only necessary to plot every second generation)

   Exponential Population Growth in E.coli Bacteria
   generation #	population (N)
   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   13
   14
   15
   16
   17
   18
   19
   20

   
   Assume the environment (the Petri dish containing the nutrient medium) can only support 1 million bacterial cells.

   
   
   1. At what generation has the population outstripped its environment and will begin to crash? If generation 1 was time 0, at what time did the population crash?
   2. Draw a graph showing the growth curve. Label axes correctly and provide a title. Label the graph with lag phase, exponential phase, and death phase.
   3. With each successive generation, what happens to the difference between N of the previous population and N of the current population?
   4. A population of lilies is growing exponentially with a generation time of 3 days. The water lilies threaten the species living below the surface by cutting off sunlight. At this point in time, the lilies cover half the pond. How long before the whole pond is covered?

 

Discuss

Develop, present, and defend a position on Earth’s carrying capacity of Homo sapiens on the discussion board. Work with other students and your instructor in developing more ideas. File you work in your course folder.

 

Self-Check

1. Which of the following would not be an example of environmental resistance?
   
   
   1. drought
   2. increase in predators
   3. disease due to waste accumulation
   4. lack of food
   5. lack of nesting sites
      
      
2. Exponential growth is found only in
   
   
   1. organisms with a high biotic potential
   2. organisms with a low biotic potential
   3. organisms reproducing at their biotic potential
   4. organisms that have many offspring at a time
3. Match birth rates (b) and death rates (d) to the phases of the logistic growth curve:
   
   
   1. stationary phase: high b, low d
   2. lag phase: low b, high d
   3. exponential phase: high b, low d
   4. lag phase: b and d are equal
4. Which of the following is paired correctly?
   
   
   1. exponential growth – population crash
   2. logistic growth – J curve
   3. exponential growth – carrying capacity
   4. exponential growth – S curve
      
      
5. Look at the graph on page 722 of your text.
   
   What conclusion can you draw from the graph?
   
   
   1. density of hares was highest in the control group
   2. removing predators doubled the population density
   3. when population density rises, environmental resistance offered by lack of food and increased predators are equally important in controlling density
   4. the combined effect of removing both food and predators was greater than the sum of both effects.