Geography

Population change and structure

Population numbers change over time, influenced by births, deaths and migration into or out of the area. Global population levels, having grown slowly for most of human history, are now rising.

Global population growth

Population pyramids show the structure of a population by comparing relative numbers of people in different age groups. Population structures differ markedly between LEDCs [LEDC: A Less Economically Developed Country (LEDC) has low levels of development, based on economic indicators, such as gross domestic product (the country's income). ] and MEDCs [MEDC: A More Economically Developed Country (MEDC) has high levels of development based on economic indicators such as gross domestic product (the country's income). ].

Demographic transition models show population change over time - and also show marked differences between LEDCs and MEDCs.

At present the world's population is growing quickly, though this has not always been the case.

  • Until the 1800s the world's population grew slowly for thousands of years.
  • In 1820 the world's population reached one billion.
  • In the early 1970s, the world's population reached three billion.
  • In 1999, less than 30 years later, the population doubled to six billion.
  • The global rate of population growth is now one billion every 15 years.

The graph shows this pattern of accelerating growth (including the predicted population for 2025).

World population growth 500BC - 2025

World population growth 500BC - 2025

Causes and rates of change

The three main causes of population change

  • Births - usually measured using the birth rate (number of live births per 1,000 of the population per year).
  • Deaths - usually measured using the death rate (number of deaths per 1,000 of the population per year).
  • Migration - the movement of people in and out of an area.

Rate of change

Births and deaths are natural causes of population change. The difference between the birth rate and the death rate of a country or place is called the natural increase. The natural increase is calculated by subtracting the death rate from the birth rate.

natural increase = birth rate - death rate

The rate of natural increase is given as a percentage, calculated by dividing the natural increase by 10. For example, if the birth rate is 14 per 1,000 population, and the death rate is 8 per 1000 population, then the natural increase = 14 - 8 = 6. That is 6/1000, which is equal to 0.6 per cent.

Patterns of population growth

Rates of population growth vary across the world. Although the world's total population is rising rapidly, not all countries are experiencing this growth. In the UK, for example, population growth is slowing, while in Germany the population has started to decline. MEDCs [MEDC: A More Economically Developed Country (MEDC) has high levels of development based on economic indicators such as gross domestic product (the country's income). ] have low population growth rates, with low death rates and low birth rates.

Population will decline if death rate is greater than birth rate.

Population will increase if death rate is less than birth rate.

LEDCs [LEDC: A Less Economically Developed Country (LEDC) has low levels of development, based on economic indicators, such as gross domestic product (the country's income). ] have high population growth rates. Both birth rates and death rates in LEDCs tend to be high. However, improving healthcare leads to death rates falling - while birth rates remain high.

The table shows data in selected LEDC and MEDC countries. The figures are per 1,000 of the population per year.

MEDCs

CountryBirth rateDeath rateNatural increasePopulation growth rate (%)
UK111010.1
Canada11740.4
Bulgaria914-5-0.5

LEDCs

CountryBirth rateDeath rateNatural increasePopulation growth rate (%)
South Africa2515101
Botswana312290.9
Zimbabwe292090.9

In Bulgaria, the birth rate is 9/1,000 and death rate is 14/1,000. As birth rate is less than the death rate, Bulgaria has a declining population.

In South Africa, the birth rate is 25/1,000 and death rate is 15/1,000. South Africa has an increasing population with a population growth rate of 1 per cent.

The demographic transition model

The demographic transition model [demographic transition model: A measure of population change over time which tracks birth and death rates. ] shows population change over time. It studies how birth rate and death rate affect the total population of a country.

The five stages of the demographic transition model

  1. Total population is low but it is balanced [balanced: A population is in balance when birth rates equal death rates. ] due to high birth rates and high death rates.
  2. Total population rises as death rates fall due to improvements in health care and sanitation. Birth rates remain high.
  3. Total population is still rising rapidly. The gap between birth and death rates narrows due to the availability of contraception and fewer children being needed to work - due to the mechanisation of farming. The natural increase [natural increase: The natural growth of a population due to the number of births exceeding deaths. ] is high.
  4. Total population is high, but it is balanced by a low birth rate and a low death rate. Birth control is widely available and there is a desire for smaller families.
  5. Total population is high but going into decline due to an ageing population. There is a continued desire for smaller families, with people opting to have children later in life.

As a country passes through the demographic transition model, the total population rises. Most LEDCs [LEDC: A Less Economically Developed Country (LEDC) has low levels of development, based on economic indicators, such as gross domestic product (the country's income). ] are at stage 2 or 3 (with a growing population and a high natural increase). Most MEDCs [MEDC: A More Economically Developed Country (MEDC) has high levels of development based on economic indicators such as gross domestic product (the country's income). ] are now at stage 4 of the model and some such as Germany have entered stage 5.

The demographic transition model

The demographic transition model

As populations move through the stages of the model, the gap between birth rate and death rate first widens, then narrows. In stage 1 the two rates are balanced. In stage 2 they diverge [diverge: Move away from each other. ], as the death rate falls relative to the birth rate. In stage 3 they converge [converge: Move towards each other. ] again, as the birth rate falls relative to the death rate. Finally in stage 4 the death and birth rates are balanced again but at a much lower level.

Limitations of the model

  1. The model was developed after studying the experiences of countries in Western Europe and North America. Conditions might be different for LEDCs [LEDC: A Less Economically Developed Country (LEDC) has low levels of development, based on economic indicators, such as gross domestic product (the country's income). ] in different parts of the world.
  2. The original model doesn't take into account the fact that some countries now have a declining population and a 5th stage. Most texts will now show this stage as it is relevant to an increasing number of MEDCs [MEDC: A More Economically Developed Country (MEDC) has high levels of development based on economic indicators such as gross domestic product (the country's income). ] in the 21st century.

Population structure and population pyramids

Population structure means the 'make up' or composition of a population. Looking at the population structure of a place shows how the population is divided up between males and females of different age groups.

Population structure is usually shown using a population pyramid. A population pyramid can be drawn up for any area, from a whole continent or country to an individual town, city or village.

The following graphs show the population pyramids of an MEDC (the UK) and an LEDC (Mozambique), for 2000 and in 2025 using projected figures. The left side of each pyramid shows the number of men in each age group, the right side shows the number of women in each age group.

Population pyramid for the UK 2000

Population pyramid for the UK 2000

Notice how in the UK 2000 pyramid there is a bulge in the area of the 30-34 and 35-39 age groups, with the numbers thereafter reducing fairly steadily as the ages increase. This matches stage 4 of the demographic transition model.

Projected population pyramid for the UK 2025

Projected population pyramid for the UK 2025

Compare this to the 2025 pyramid, which would be stage 5 in the model. Here the bulge extends much further, covering the age groups 30-64, with the numbers beginning to reduce significantly only after 64.

Now compare the UK population pyramids with those for Mozambique:

Population pyramid for Mozambique 2000

Population pyramid for Mozambique 2000

In this graph, notice that in 2000 the 0-4 age group contained the largest number of people, with the numbers thereafter declining steadily as the ages increase. The graph matches stage 1 in the model.

Projected population pyramid for Mozambique 2025

Projected population pyramid for Mozambique 2025

In the second graph, the largest group in Mozambique in 2025 is still the 0-4 age group, but there are nearly as many people in the 5-29 age groups. Now the population pyramid matches stage 2.

Analysing population pyramids

Key things to know about population pyramids

  • The shape of a population pyramid can tell us a lot about an area's population.
  • It gives us information about birth and death rates as well as life expectancy.
  • A population pyramid tells us how many dependants [dependants: People who rely on others for support (social and economic support). For example, old and young people depend on those of working age. ] there are. There are two groups of dependants; young dependants (aged below 15) and elderly dependants (aged over 65).
  • Dependants rely upon the economically active [economically active: People who are of working age. ] for economic support.
  • Many LEDCs have a high number of young dependants, whilst many MEDCs have a growing number of elderly dependants.

How do pyramids change over time?

  • A population pyramid that is very triangular (eg Mozambique in 2000) shows a population with a high number of young dependants and a low life expectancy.
  • A population pyramid that has fairly straight sides (more like a barrel) shows a population with a falling birth rate and a rising life expectancy.
  • Over time, as a country develops, the shape changes from triangular to barrel-like.
  • Places with an ageing population and a very low birth rate would have a structure that looks like an upside-down pyramid.

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