Properties of Populations

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Properties of Populations
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Properties of Populations

• Two main properties of population that are
  studied by scientists (demographers) are
• Density
• Age Structure

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1. Size/Density

• This is the number of individuals in a given area
• Two main ways to calculate it
• Census
• Literally every individual in an area is counted
• Sample
• Small sections are counted and numbers for the
  whole area are estimated

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2. Age Structure

• This is an account of the number of individuals
  of each gender and/or the number of individuals
  in each defined age group.
• Age structure is usually shown as a graph called
  a population histogram. It is also called a
  population pyramid.

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Properties of Populations

• The histogram can be used by demographers to
  predict future changes in population size and
  provide governments with information on the types
  of changes that might be required in terms of
  social services.

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Properties of Populations

• For example, if there are more children,
• more schools will be needed.

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Three types of Histograms

• Wide Base
• Represents a population that is quickly
  increasing in size
• The large number of births now will result
  in a larger number of females giving birth to new
  offspring in the future.
• The shape of the graph is triangular

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Properties of Populations

• 2. Narrow Base
• Represents a population that is either
  increasing very slowly or is fairly stable with a
  net population growth of close to 0.
• The number of individuals being born is equal
  to the number of individuals dying.
• Shape looks like a high rise building

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Properties of Populations

• 3. Narrow base, narrow top, and wide middle.
• Represents a population that is decreasing in
  size.
• There are less recent births meaning that
  there will be fewer females giving birth to new
  offspring in the future.
• Shape often referred to as Bullet Shaped

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• Made by constructing 2 histograms, one for
  females and one for males
• The 2 histograms sit sideways and next to each
  other, one facing left, the other right

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• Pages 40 41 show you how to make a population
  histogram
• Do the worksheets on pages 42-44

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Answers to p 4344
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• 1. 15-19 Males 3.5 Females 3.3
• 2. 35-39 Females 4.5
• 3. 30-39
• 4. Males 49.2 Females 51.1
• 5. Males 5.3 Females 7.1
• The of females over 65 is greater than the
  of males because females have a longer life
  expectancy
• 6(a) increasing (b) decreasing or stable
• (c) Females are having less babies in 1996
  than they were in 1961