🧍 Exam Summary: Human populations
Key Idea: Human population patterns affect resource use, environmental impact, and sustainability. Understanding how populations change helps predict future pressures on ecosystems.
📈 Measuring population change
- Crude birth rate (CBR) and crude death rate (CDR) measure births and deaths per 1,000 people per year
- Natural increase = (CBR − CDR) ÷ 10
- Total fertility rate (TFR) = average number of children per woman (replacement ≈ 2.1)
- Doubling time = 70 ÷ growth rate
📊 Population structure
- Population pyramids show age and sex structure
- Wide base = high birth rate and rapid growth
- Narrow base = ageing or declining population
- Dependency ratio shows economic pressure on the workforce
🔄 Demographic transition model (DTM)
- Stage 2: death rates fall first → rapid growth
- Stage 3: birth rates fall → growth slows
- Stage 4: low birth and death rates → stable population
- Stage 5 (optional): population decline and ageing
🌍 Population & sustainability
- IPAT equation: Impact = Population × Affluence × Technology
- Consumption often matters more than population size alone
- Female education and voluntary family planning are most effective strategies
- Population policies raise ethical issues about rights and equity
Link population → resource use → environmental impact → sustainability. Always support answers with data, trends, or named examples.