Human Populations and Demographics

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Human Populations and Demographics
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Age Structure Diagrams

• Shows age distribution of a population
• Pre-reproductive, reproductive and
  post-reproductive groups

SLOW GROWTH
ZERO GROWTH
NEGATIVE GROWTH
RAPID GROWTH
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Demographic Transition Model

• Based on historical data from western Europe
• Postulates that as countries become
  industrialized, first death rates drop, then
  birth rates drop

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Demographic Transition Model
Stage 1 Preindustrial
Stage 2 Transitional
Stage 3 Industrial
Stage 4 Postindustrial
relative population size
births
deaths
low
increasing
very high
decreasing
low
zero
negative
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Population Momentum

• Lowering fertility rates cannot immediately slow
  population growth rate
• Why? There are already many future parents alive
• If every couple had just two children, population
  would still keep growing for another 60 years

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Population Size

• N1 N0 (B D I E)
• where
• N0 initial population
• N1 population at a later time
• B birth rate
• D death rate
• I immigration
• E emigration

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Population Doubling Time

• Rule of 70
• 70 divided by net growth rate
• or
• Dt 70 / R0

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So Whats Net Growth Rate?

• Net Growth Rate
• Pop size at a later time / Pop size at initial
  time
• or
• R0 N1 / N0

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Notes on Birth and Death Rates

• B births per 1000
• D deaths per 1000
• Remember to multiply by 1/10 if you want
• Intrinsic rate of increase
• r B D
• This will give of new people per 1000 per year

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Rate of change of population size

• dN change in population (N1-N0)
• dt time period
• rN change of population in of people
• dN/dt rN

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Example 1

• In 1950, the population of a small town was
  20,000. The birth rate was measured at 25 / 1000
  per year, while death rate was 7 / 1000 per year.
  The immigration rate was 600 while the emigration
  rate was 200.
• What was the population size in 1951?
• What was the intrinsic rate of increase?
• What was the rate of change of the population?
• What is the Net Growth rate?
• What would be its Doubling time if the pattern
  continued?

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A population size

• N1 N0 (B D I E)
• N1 20,000 25(20) -7 (20) 600 200
• N1 20,760

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A Intrinsic Rate of Increase

• r B D
• r 25 7
• r 18 new people per year per 1000 population

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A Rate of Change

• dN/dt rN
• (20,760 20,000) / 1 year 760 people per year

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A Net Growth Rate

• R0 N1 / N0
• R0 20,760 / 20,000 1.038

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A Doubling time

• Dt 70 / R0
• Dt 70 / 1.038 67 years

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Example 2

• If a population doubles in about 70 years, it is
  showing what net growth rate?

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A

• Dt 70 / R0
• 70 70 / R0
• R0 70 / 70 1 net growth rate