Unit 7 Lesson 1

Populations
returning red salmon
Population of red salmon; ©Alaska Division of Tourism AK Photo Library

Objectives

After completing this lesson you should be able to:
  • distinguish between the "everyday" definitions and the scientific definitions of "ecology" and "environment;"
  • define population in the way a population biologist would;
  • list and define the four rates that determine population size;
  • recognize that the environment may slow or stimulate the growth of a population;
  • classify environmental factors as biotic or abiotic;
  • calculate the size of a population given the mortality, natality, immigration, and emigration rates;
  • use a model to predict the effects of changes in birth rate, death rate, immigration rate, and emigration rate on the size of Alaska's population;
  • give two reasons that populations must disperse;
  • describe two ways in which plant populations disperse; and
  • explain how the non-motile animal coral is able to disperse.

    Alaska State Standards: A12, A14, A15, B1, C2

Key Terms

ecology Ecology is the study of the relationships between organisms and their environment.
 
environment The environment is everything both living and non-living that surrounds and affects an organism.
 
population A population is a group of interbreeding individuals of the same type living in the same place at the same time.
 
natality Natality is another name for birth rate.
 
mortality Mortality is another name for death rate.
 
immigration Immigration occurs when one or more organisms moves into an area. It increases the population.
 
emigration Emigration occurs when one or more organisms leaves an area. It decreases the population.
 
biotic The living part of the environment is called the biotic environment.
 
abiotic The non-living part of the environment is called the abiotic environment.
 
model A model is a representation of an object or system that the scientist is studying in the real world. The model has many of the same properties of the real world object or system that is being studied but also differs in some ways.
 
biological
dispersal		 Biological dispersal refers to movement away from the parent organisms for population maintenance or movement away from an existing population for population expansion.


Activities

Read each paragraph below and follow the directions.

  1. What do the terms "ecology" and "environment" mean to biologists?

    1. Think about what the words "ecology" and "environment" mean to you. How have these terms been used in news articles you have read or on television shows you have watched? Write down on your own paper what these two terms mean to you.

    2. Read the article "Natural environment" found at the Wikipedia web site.

    3. Compare what you wrote in Activity 1a above with the definitions of "ecology" and "environment" found in the Key Terms definitions at the beginning of this lesson. Compare the values that are implicit in the everyday uses of these terms with a scientific understanding of these terms.


       

  2. What do biologists mean by "population?"

    You probably already have learned a definition for the word population. The first definition for population at the Merriam-Webster Online Dictionary is "the whole number of people or inhabitants in a country or region." In ordinary speech, we use the term for people, and indeed we will spend quite a bit of time in this unit studying "people populations." Biologists, however, use the term for other organisms they are studying, too, not just people. For example, fish biologists are interested in knowing about the size of a salmon population and game biologists may be interested in the size of the moose, wolf, and bear populations.

  3. Do population sizes change?

    Study the graph below of the Alaska wolf population from 1912 to 1953. Does the size of the population stay the same? In what year was the population largest? How does the size of the wolf population in 1912 compare with the size in 1953?

    NERC Centre for Population Biology, Imperial College (1999) The Global Population Dynamics Database. http://cpbnts1.bio.ic.ac.uk/gpdd/

     

  4. What are biotic and abiotic factors?

    Think about what kinds of factors in the environment might effect the size of the wolf population: weather, abundance of food, disease, hunters, etc. One way in which biologists classify environmental factors is according to whether or not they are derived from a once-living organism or whether they are non-living. Biotic factors are the parts of the environment that are alive or once were alive. Abiotic factors are non-living. Classify the factors below as biotic or abiotic.

    mosquitoes that bite the wolves abundant pure water to drink
    deep snow (making hunting for prey difficult) human hunters and trappers
  5. How do mortality, natality, immigration, and emigration effect a population?

    1. Think about the following questions and then answer them to the best of your ability. Check your answers.

      1. Why might a population of wolves increase in size?

      2. What might decrease the size of a population of wolves?

    2. Scientists have special terms for possible changes to the size of a population. Read the definitions of "mortality," "natality," "immigration," and "emigration" in the Key Terms definitions above.

    3. Complete the Population Rates activity.

  6. How are population sizes predicted?

    1. Scientists use many different kinds of models to help them better understand the things that they are studying. In this unit, we will be using several kinds of mathematical models on the computer. Study the Mathematical Models activity.

    2. Complete the Predicting Alaska's Population activity.

    3. Write your own scenario for Alaska's population in the future. Tell what social and economic changes you imagine will occur that will change the four rates that affect the size of the population. Tell why these circumstances will affect each rate.

      Give specific values for the:

      1. birth rate,

      2. death rate,

      3. immigration rate, and

      4. emigration rate.

      You will determine the number of people that you believe will live in Alaska in 2029 under this scenario but will NOT post this prediction.

      Other students will read your scenario and post any questions they have about the scenario to this discussion board. They will then e-mail their prediction to you. You will respond to their answer by e-mail.

      You will read the scenario of at least one other person and use your model to make a prediction of Alaska's population in 2029 for their scenario. Post any questions or comments you have, but DO NOT post the prediction on this discussion board. Contact the author of the scenario by e-mail to verify the accuracy of your prediction.

      link to discussion board
      		Click on the Discussion Board icon to the left or on the Discussion Board link in your course menu to post your answer.
  7. How are populations dispersed?

    1. Read the article titled "Biological dispersal," found at the Wikipedia web site.

    2. OPTIONAL: If you have a fast Internet connection, the Missouri Botanical Garden web site has two short video clips showing two different methods of Seed Dispersal.

    3. Answer the following questions about how organisms disperse.

      1. Give two reasons that populations of organisms must disperse.

         

      2. Plants are generally not motile, yet populations of plants are found all over the world. Describe two different ways in which populations of plants are able to disperse.

      3. Explain how the non-motile animal coral is able to disperse.
    8. You have finished this lesson when you have posted your scenario to the discussion board and read and responded to at least one other student.
    This assignment is worth 10 points.