1. Section 1b Age/ sex Structure

2. Learning outcomes To discover how population changes through time in relation to births, deaths and migration How population pyramids present age/ sex structure How population pyramids enable comparisons to be made over time

3. Population changes in time Population is dynamic…. It changes constantly over time and space How? Births Deaths Migration

4. Births, deaths and migration The total population of an area is the balance between two forces of change: natural increase (births- deaths) and migration Crude Birth rate: the number of live births per 1000 people per year Crude death rate: the number of deaths per 1000 people per year

5. Migration Migration does not affect the world population It affects the way in which people are distributed around the world It may lead to an increase or decrease in population in an area.

6. The Demographic Transition model The DTM describes a sequence of changes over a period of time in the relationship between births, deaths and overall population change. It was based on western Europe and USA It suggests that countries follow through a particular cycle

7. Demographic Transition Model Stage 1Stage 2Stage 3Stage 4 TIME BIRTHS AND DEATHS PER 1000 PER YEAR Birth rate Death rate Total population

9. Stage 1 Both death and birth rates are high giving small population growth Examples: Ethiopia, Bangladesh, UK pre 1760

10. Stage 2 Birth rate remain high but death rates fall to about 20 per 1000 Examples: Peru, Sri Lanka, Kenya and UK 1760-1880

11. Stage 3 Birth rates fall rapidly to 0 per 1000 and death rates fall slightly to 15 per 1000. slowly increasing population Examples: China, Cuba and Australia, UK 1880-1940

12. Stage 4 Birth and death rates remain low, fluctuating slightly to give a steady population Examples: Canada, Japan, USA and UK post 1940

13. Stage 5? Birth rates fall below death rates to give a declining population Examples Germany and Sweden

14. Problems with the model Its “Eurocentric”- a lot of the LEDC’s will not pass through all 4 stages Stage 5 is now possible Countries such as Malaysia and Hong Kong developed at a much faster rate than the model suggests

15. Population Pyramids The population structure of a country is best illustrated by a population or age- sex pyramid It is useful as it can predict short and long term changes in the population The DTM shows only natural increase the pyramids show the effects of migration, age and sex of migrants and effects of wars and epidemics.

16. The models are structured to show 'snapshots' of population at four points during its development, which are shown as Stages 1 - 4 in the DTM

17. Population Pyramids of LEDC’s

18. Population Pyramid of MEDC