Lesson 4.9.3S2

4.9.3S2 page 2

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biotic potential (r): highest per capita growth rate possible

 

exponential growth pattern: exhibited by a population that doubles with each generation; results in a J-shaped curve; begins with a lag phase, followed by a steep rise

 

The term ‘exponential phase’ refers to a section of the logistic growth curve (S) where births exceed deaths. This phase occurs after the lag phase and before the stationary phase.

 

logistic growth: a population increase resulting in an S-shaped curve

 

Begins with slow growth, steepens to exponential growth, and then levels to a carrying capacity due to competition because of environmental resistance.

 

carrying capacity (K): the theoretical maximum population size that the environment can sustain over an extended period of time; may change as the quality of the habitat changes

 

The population is at carrying capacity when it levels off during logistic growth.

 

What factors determine the biotic potential (r) of a species? If you compare the biotic potentials of the mouse and the human reproductive stories above, you should be able to find at least four differences between them that account for the differences in biotic potential. Differences in biotic potential are partly responsible for how fast population numbers change.

 

Read

Do all populations grow in the same way? It would not seem so from the information given about humans and mice!

 

Read p. 709 and 711 on exponential and logistic growth patterns. It is very important to make notes on the characteristics of species that typify these patterns. Draw graphs that show the characteristic shapes of both kinds of growth. Label the 2 graphs with the phases of growth. Save these notes in your course folder. You will note that interpreting graphs is an important skill in biology 30. If you use The Key to prepare for the diploma exam, you will have the opportunity to see many types of questions based on graphs, or you can go to the Government of Alberta Education website to view samples of Diploma exam questions.

 How much growth can an environment sustain without depletion of already scarce resources? In other words, what is the carrying capacity (K) of the environment?

 

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environmental resistance: rhe combined effects of factors that limit population growth; prevents a population from growing at its biotic potential; determines the carrying capacity of the environment

 

density independent factors: abiotic factors that limit a habitat’s carrying capacity (e.g. fire, flood, frost)

 

The impact is not affected by the density of the population.

 

density dependent factors: biotic factors that limit a habitat’s carrying capacity (e.g. parasites, disease, increase in predators, lack of water/food/territory); the impact increases with the density of the population

Read pages 711–712 and make notes on how the concept of carrying capacity applies to exponential and logistic growth patterns. What are the consequences of growth beyond carrying capacity?

 

In one habitat the carrying capacity for white-tailed deer may be very high, and in another, very low. What factors determine how high the carrying capacity of a given environment may be? As populations increase, environmental resistance slows growth rates. Environmental resistance may be due to density independent factors such as climate and natural disasters, but is more likely due to the density dependent effects of population growth, such as lack of food and/or water, high predation, high parasitism, and lack of space.

 

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Read page 712 and look at "Figure 20.5" to make a list of both density dependent factors and density independent factors that cause environmental resistance.

 

Try this Try This

This Population Density Factors activity wll help you sort density-dependent and density-independent factors.

 

Is it possible for a habitat to not have a carrying capacity? Is there a species that is capable of changing its habitat to continually increase the carrying capacity? Is there an upper limit to this carrying capacity? Before you form an answer, check out "Figure 20.22" on page 733 that illustrates the human population curve. Then do the following Try This activity.

 

Try This
  1. Assume species A was introduced into a new environment. Population counts produced the following data:

    Generation

    Population (N)

    1

    2

    2

    3

    3

    4

    4

    8

    5

    15

    6

    31

    7

    32

    8

    33

    9

    33

    Graph the data on the table. Use the graph to answer the following questions?

    1. Is the population above growing in a logistic or exponential pattern? Support your answer. What is the shape of the curve?
    2. What is K (carrying capacity) in this population?
    3. List 4 density dependent factors that could have contributed to environmental resistance.
    4. Provide 2 density independent factors that could affect K in this population. State whether each factor would increase or decrease K.
  2. Regarding "Figure 20.2" on p. 733 of your text:

    1. At approximately what year did the human population enter the exponential growth phase?
    2. Prior to that time, what was the approximate carrying capacity of Earth?
    3. State 4 significant developments that began to increase the carrying capacity from that time.
    4. Provide 2 pieces of evidence that demonstrate how density-dependent factors are contributing to environmental resistance in human populations?
Check your work.