Population dynamics and structure
How and why population changes, how population structure is shown in pyramids, and how population is distributed around the world.
📌 Key points
- Birth rate is the number of live births per 1000 people per year; death rate is the number of deaths per 1000 people per year.
- Natural increase = birth rate − death rate; a natural increase of 20 per 1000 is the same as 2.0% per year.
- Population change = natural increase + net migration (immigrants − emigrants).
- The Demographic Transition Model has five stages: 1 high birth and death rates; 2 death rate falls quickly, so population grows rapidly; 3 birth rate falls; 4 low birth and death rates; 5 birth rate below death rate, so population declines.
- Death rates fall because of better health care, vaccinations, clean water, sanitation and food supply; birth rates fall because of family planning, education of women, urbanisation and lower infant mortality.
- A population pyramid shows the age and sex structure of a population; a wide base and narrow top shows high birth rates and a young population (typical of LICs).
- An ageing population (more people aged 65 and over) puts pressure on pensions and health care; a youthful population needs schools and future jobs.
- Dependency ratio = (people aged 0–14 + people aged 65 and over) ÷ people aged 15–64 × 100.
- Overpopulation is when there are too many people for the resources and technology available to keep a good standard of living; underpopulation is when there are too few people to use the resources fully.
- Population density = number of people ÷ area (people per km2); dense areas often have flat land, fertile soil, a reliable water supply and jobs, while sparse areas are very cold, dry, mountainous or forested.
📖 Key terms
- Birth rate
- The number of live births per 1000 people per year.
- Death rate
- The number of deaths per 1000 people per year.
- Natural increase
- The birth rate minus the death rate.
- Infant mortality rate
- The number of deaths of children under one year old per 1000 live births per year.
- Life expectancy
- The average number of years a person can expect to live from birth.
- Dependency ratio
- The ratio of dependents (under 15 and 65 or over) to people of working age (15–64).
- Anti-natalist policy
- A government policy to reduce the birth rate, such as China's one-child policy.
- Population density
- The average number of people per square kilometre.
✏️ Worked example
A country has a birth rate of 32 per 1000 and a death rate of 12 per 1000. Calculate its natural increase as a percentage, and suggest which stage of the Demographic Transition Model it is in.
- Natural increase = birth rate − death rate = 32 − 12 = 20 per 1000.
- Convert to a percentage: per 1000 ÷ 10 gives per cent, so 20 ÷ 10 = 2.0%.
- The death rate is low but the birth rate is still high, so the population is growing rapidly.
- This fits stage 2 or early stage 3, when death rates have fallen but birth rates are still high.
- Answer: 2.0% per year; stage 2 to early stage 3 (rapid growth).
When describing a population pyramid, quote figures from the graph (age groups and percentages) and compare the base, middle and top. 'Describe' questions need evidence, not reasons.
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