Geography | Population distribution—changing population

Welcome to Population Dynamics: Understanding Global Change

Hello Geographers! This chapter, Population distribution—changing population, is essential because it forms the foundation of the SL and HL Core: Geographic perspectives—global change. Why do people live where they do? How quickly is the global population changing, and what are the consequences of that change?

Understanding these concepts helps us tackle “wicked problems”—complex issues like sustainable development, resource security, and climate vulnerability—which are all profoundly affected by human numbers and location. Don't worry if some of the statistics seem daunting; we will break them down into clear, manageable steps!

1. Understanding Population Distribution and Density

The first step in studying population is defining where people are located (distribution) and how many people are in a given space (density).

Key Concepts: Distribution vs. Density

• Population Distribution: This describes the pattern of where people live across an area. Is the population clustered in cities, or spread out evenly?
• Population Density: This is a measure of the number of people per unit area. It is usually expressed as people per square kilometre (p/km²).

  Analogy: Imagine a tray of cookies. The pattern of how the cookies are arranged is the distribution. If you count how many cookies are in a specific square inch, that's the density.

Factors Affecting Population Distribution (Why people live where they live)

Population distribution is highly uneven globally, often categorized by physical (natural) and human (socio-economic) factors.

A. Physical Factors (The Natural Environment)

• Relief and Topography: Low-lying, flat areas (plains and valleys) are generally preferred because they are easier to farm, build infrastructure on, and transport goods across. Mountainous areas tend to have sparse populations (e.g., The Himalayas).
• Climate: Temperate climates (moderate rainfall, mild temperatures) are densely populated (e.g., Western Europe). Extreme climates (very hot/cold, very wet/dry) are sparsely populated (e.g., The Sahara Desert or Antarctica).
• Water Supply: Access to reliable, clean water is crucial. River valleys and coastlines tend to attract high densities (e.g., The Nile Valley).
• Soil and Resources: Areas with fertile soil (often volcanic or alluvial) support agriculture and thus denser populations. Areas rich in mineral resources can also become densely settled due to employment opportunities.

B. Human Factors (Socio-Economic and Political)

• Economic Opportunities: Areas with high levels of industrialisation, urban centres, and diverse employment options attract people (e.g., Major global cities like London, Tokyo, or New York).
• Political Stability: Stable governments, lack of conflict, and good governance are powerful pull factors. Conversely, conflict is a major push factor (e.g., large refugee movements out of areas experiencing war).
• Infrastructure and Connectivity: Regions with good transport networks (roads, ports, airports), healthcare, and education facilities generally have higher population densities.
• Historical Factors: Long-established settlements, particularly ancient trading routes or colonial hubs, often maintain high densities today.

2. The Components of Population Change

Population change is driven by three main factors: births, deaths, and migration. The rate at which a population changes is calculated as:
(Births - Deaths) + (Immigration - Emigration)

A. Fertility and Birth Rates

Fertility refers to the actual reproductive performance of a population.

• Crude Birth Rate (CBR): The number of live births per 1,000 people in a population per year.
• Total Fertility Rate (TFR): The average number of children a woman would have over her lifetime if she experienced the current age-specific fertility rates.

The Replacement Level is the TFR needed for a population to replace itself. This is usually about 2.1 children per woman (the 0.1 accounts for infant mortality and women who do not survive to reproductive age).

Factors Influencing High Birth Rates:

• Social: Traditional roles requiring women to have many children; lack of education and status for women.
• Economic: Children are viewed as economic assets (working on farms, supporting parents in old age).
• Health/Survival: High Infant Mortality Rates (IMR) often lead to parents having more children to ensure some survive.

B. Mortality and Death Rates

Mortality refers to the occurrence of death in a population.

• Crude Death Rate (CDR): The number of deaths per 1,000 people in a population per year.
• Infant Mortality Rate (IMR): The number of deaths of children under one year of age per 1,000 live births. (This is an excellent indicator of a country's overall health and development.)

Factors Influencing Declining Death Rates:

The dramatic global fall in CDRs since the 18th century is primarily due to:

• Improvements in Public Health and Sanitation: Cleaner water and better waste disposal.
• Medical Advances: Vaccinations, antibiotics, and better access to healthcare.
• Improved Nutrition: Better food supply and storage (linked to the Green Revolution).

C. Natural Increase and Decrease

The difference between the CBR and CDR gives us the Rate of Natural Change (usually expressed as a percentage).

• If CBR > CDR: The population is experiencing Natural Increase.
• If CDR > CBR: The population is experiencing Natural Decrease (often seen in highly developed nations).

3. The Demographic Transition Model (DTM)

The DTM is a key geographical model that describes the historical shift of birth and death rates from high to low levels in a population. It generally correlates with economic development and industrialisation.

The Five Stages of the DTM

Stage 1: High Fluctuating (Pre-industrial)

• BR: Very High (Lack of family planning, high IMR).
• DR: Very High (Disease, famine, poor sanitation).
• Population: Stable or very slow growth.
• Example: Few, if any, countries remain strictly in Stage 1 today. Historical populations fit this stage.

Stage 2: Early Expanding (LED-Developing)

• DR: Falls rapidly (Improved sanitation, nutrition, and medical care).
• BR: Remains High (Cultural lag, lack of education takes time to change).
• Population: Rapidly increasing (This is the period of 'population explosion').
• Example: Many Least Economically Developed Countries (LEDCs).

Stage 3: Late Expanding (Developing/Transitional)

• BR: Falls rapidly (Increased urbanisation, better status/education for women, desire for smaller families).
• DR: Falls slowly/Plateaus at a low level.
• Population: Growth slows down.
• Example: Many newly industrialising countries (NICs) like Brazil or India.

Stage 4: Low Fluctuating (MEDC-Developed)

• BR: Low and fluctuating (Affluence, high cost of children, family planning is common).
• DR: Low and fluctuating (High life expectancy, good healthcare).
• Population: Stable or slow increase.
• Example: USA, France, UK.

Stage 5: Decline/Contracting (Contested Stage)

• BR: Very Low (often below replacement level, TFR < 2.1).
• DR: Low, but may slightly rise (due to an ageing population structure).
• Population: Natural Decrease/Decline.
• Example: Japan, Germany, Italy.

Critiques and Limitations of the DTM (Crucial for Evaluation)

IB Geography requires critical evaluation. The DTM is a useful framework, but it has flaws:

• It assumes all countries follow the Western path of development (industrialisation leading to falling BR/DR).
• It does not account for the impact of migration (which can significantly affect the growth rate in Stages 4 and 5).
• The BR drop in many developing nations today (Stage 3) has been faster than historically seen in Europe, often due to government intervention (e.g., China’s One-Child Policy).
• It does not easily incorporate reversals caused by disease (like AIDS in Sub-Saharan Africa) or conflict.

4. Population Structure and Ageing Populations

Population Structure refers to the composition of a population, usually described in terms of age and gender. This is visually represented using Population Pyramids.

Population Pyramids: A Visual Tool

Pyramids graph the percentage or number of the population in different age groups (usually 5-year cohorts) by gender. The shape tells us instantly about the country's development stage and its population dynamics.

A. Pyramid Shapes and Development

1. The Pyramid Shape (Stage 2/3):
   • Base: Wide (High BR).
   • Top: Narrow (Low life expectancy).
   • Description: Rapidly expanding population; very high proportion of young dependents.
2. The Column/Beehive Shape (Stage 4):
   • Base: Narrowing (Low BR, near replacement level).
   • Middle: Widening (Large working population).
   • Description: Stable population; slow growth.
3. The Urn/Contracting Shape (Stage 5):
   • Base: Very narrow (BR below replacement level).
   • Top: Widening (High life expectancy).
   • Description: Declining population; high proportion of elderly dependents.

B. Dependency Ratios

Population pyramids allow us to calculate the Dependency Ratio, which compares the non-working population (dependents) to the working population (economically active).

Dependents include the young (0-14 years) and the elderly (65+ years). A high dependency ratio places a significant economic burden on the working population.

• Youth Dependency: High in Stage 2 countries (strain on schools, food supply).
• Elderly Dependency (Ageing Population): High in Stage 5 countries (strain on pensions and healthcare systems).

Managing Ageing Populations (The Challenge of Stage 5)

Many MEDCs (e.g., Japan, Germany) face population ageing—where the median age rises due to falling fertility and rising life expectancy.

• Economic Consequences: Fewer workers, higher taxes, reduced economic output.
• Social Consequences: Increased demand for geriatric care, reduced availability of young caregivers, and potential closure of services geared towards younger populations (e.g., schools).

Policy Response: Governments often attempt to manage this by raising the retirement age, encouraging immigration (selective migration policies), and providing incentives for couples to have children (pro-natalist policies).

5. Migration: The Spatial Component of Change

While births and deaths determine natural change, migration involves the movement of people across a specified boundary. It is essential to recognize the spatial dimension of population change—it changes the distribution, not just the total size.

Key Terms and Types of Migration

• Immigration: Movement into a country/area.
• Emigration: Movement out of a country/area.
• Net Migration: Immigration minus Emigration.
• Internal Migration: Movement within the same country (e.g., rural-to-urban migration).
• International Migration: Movement between countries.

Voluntary vs. Forced Migration

• Voluntary Migration: Occurs when the individual chooses to move, usually for economic reasons (jobs) or lifestyle improvements.
• Forced Migration: Occurs when the individual has no choice but to move due to threat of violence, persecution, environmental disaster, or famine. Examples include refugees and Internally Displaced Persons (IDPs).

Push and Pull Factors (The Why)

These factors explain why people choose to leave (push) or are attracted to (pull) a location.

Socio-economic Impacts of Migration

Migration has major consequences for both the source region (where people leave) and the receiving region (where people arrive).

Impacts on the Source Region (The Leaving Country)

• Positive: Reduction in unemployment and population pressure; remittances (money sent home by migrants) boost the local economy.
• Negative: Brain Drain (loss of skilled workers, e.g., doctors, engineers); loss of young, economically active population; dependency ratio increases.

Impacts on the Receiving Region (The Destination Country)

• Positive: Provides cheap labor to fill low-skill jobs (e.g., agriculture); cultural enrichment; taxes paid by migrants support public services.
• Negative: Potential for social tension or xenophobia; increased strain on public services (schools, housing); increased traffic congestion and pressure on local environments.