1. Human Populations and Demographics

2. Age Structure Diagrams
Shows age distribution of a population
Pre-reproductive, reproductive and post-reproductive groups
RAPID GROWTH
SLOW GROWTH
ZERO GROWTH
NEGATIVE GROWTH

3. Demographic Transition Model
Based on historical data from western Europe
Postulates that as countries become industrialized, first death rates drop, then birth rates drop

4. 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

5. 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

6. 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

7. Population Doubling Time
Rule of 70
70 divided by net growth rate or
Dt = 70 / R0

8. So What’s “Net Growth Rate”?
Pop size at a later time / Pop size at initial time or
R0 = N1 / N0

9. 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

10. 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

11. 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?

12. A: population size: N1 = N0 + (B – D + I – E)

13. A: Intrinsic Rate of Increase
r = B – D
r = 25 – 7
r = 18 new people per year per 1000 population

14. A: Rate of Change dN/dt = rN
(20,760 – 20,000) / 1 year = 760 people per year

15. A: Net Growth Rate
R0 = N1 / N0
R0 = 20,760 / 20,000 = 1.038

16. A: Doubling time
Dt = 70 / R0
Dt = 70 / = 67 years

17. Example 2:
If a population doubles in about 70 years, it is showing what % net growth rate?

18. A:
Dt = 70 / R0
70 = 70 / R0
R0 = 70 / 70 = 1% net growth rate