3.8: Human population dynamics (& Calculations)

World population

8 billion

US Population

340 million

Calculating a rate

• Rate is interpreted as a percentage, or percent change

  • birth, death, migration, population growth,

  • Percent change = (final - initial) x 100

initial

• Typically to use a rate mathematically divide by 100 (move the decimal two places to the left

Changes in Population Size

Population growth rate = r

Global population growth rate (no migration) = 

birth rate - death rate

National population growth rate = 

(birth rate + immigration) - (death rate + emigration)

Net migration rate

The difference between immigration and emigration in a given year per 1,000 people in a country.

• Both the US and Canada have population growth due to immigration

• Migration because of crisis leads to humanitarian and environmental issues

Crude rates

Crude birth rate (CBR) - The number of births per 1,000 individuals per year.

Crude death rate (CDR) - The number of deaths per 1,000 individuals per year.

• Typically rate, (“r”) is interpreted as a percent (per 100)

Doubling time

Doubling time - The number of years it takes a population to double.

Doubling time (years) = 70 ÷ growth rate

• “Rule of 70”

• Assumes growth rates are constant

Derived from:

N_t = N₀e^rt

Factors that drive population growth

• Changes in population size

• Birth and death rates

• Fertility

• Life expectancy

• Migration