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Module 9S2 Changes in Populations

Lesson 4.9.2S2

4.9.2S2 page 2

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How do field biologists count organisms? One of the biggest problems that field biologists face is how to get accurate population counts. Remember that organisms that swim, run, hide, burrow, fly, are dangerous, or are very small - are of these making them difficult to count, so estimation methods have to be used. In this lesson, you will learn some of the sampling methods used and how to do some of the calculations that give the population numbers meaning to those (like wildlife managers) who analyze the data.

 

Read

density: the number of individuals in a given unit of area (land) or volume (air or water) 

  • Dp = N or Dp = N    
           A            V

growth rate (gr): the change in the number of individuals in a unit of time

  • gr = delta N = final population – initial population  
           delta t                 change in time
  • Gr will be positive if the population size is increasing, and negative if it is decreasing.

per capita growth rate: the rate of change per individual

  • cgr = delta N   or  Nfinal – Ninitial         
               N                Ninitial               
  • Cgr can also be positive or negative depending on whether the initial N is.

 

Read pages 704–705 and 708–709 in the textbook for information on determining the rates of population growth.

 

Pay close attention to the concept of density, growth rate, and per capita growth rate as ways of indicating how much the population has changed. Create a clear and easily accessible table in your course folder for the formulas and their definitions. Remember that in the Diploma exam you will encounter many of these problem-solving situations. Whenever possible, practice solving problems from the text or from this lesson. If you are having any difficulty, consult with your instructor.

 

Read

Read pages 705 and 707 on "Distribution Patterns: Random, Clumped, Uniform."

 

Make notes on the significance of each distribution pattern and what conditions lead to each pattern. Diagrams are also a good way to store this information in your course folder.

 

Self-Check
  1. The population size of microscopic Paramecia in a 1 L hay infusion needed to be determined. By using a depression slide (a microscope slide with a well in the center) at medium power, and averaging the results of 3 1mL samples, it was found that there were on average 4 Paramecia/mL of hay infusion. What was the population (N) in the entire 1 L infusion?
  2. Refer back to Get Focused. Will the lack of competition and natural selection in white-tailed deer populations increase or decrease the genetic diversity of the gene pool? Explain your answer.  
  3. There is a lovely white daisy with fern-like leaves that adds brightness and cheer to the roadside ditches of rural Alberta. Unfortunately, it is an inadvertently introduced species and is very invasive, competing vigorously with indigenous wild species. Your job is to provide data on the spread of the species, beginning with a population count in a 1 km2 parcel of land.
    1. How would you count them? (Refer to samples on page 704-5)
    2. Would you do one sampling or several? Why?
    3. Would it be more informative to express the count as N (population size) or as density (Dp =   #    ) Why or why not?
Check your work.