Population Ecology - Section 2: Human Population

Human Population

Demography: The study of human population size, density, distribution, movement, and birth and death rates.
The human population remained fairly stable for thousands of years but has recently increased due to technological advances.
Technology's Impact: Humans have learned to change their environment, increasing the carrying capacity through agriculture, domestication of animals (increased food supply), and advancements in medicine and shelter construction (reduced death rate).
Current Growth Rate: Is just over 80 million people per year.
Expected Population: By 2050, the population is expected to be nine billion.
Slowing Growth Rate: Although the human population is growing, the rate of growth has slowed.
Peak Growth: Human population growth peaked at over 2.2 percent in 1962.
Growth in 2003: By 2003, the rate of growth had dropped to almost 1.2 percent.
Reasons for Decline: The decline in growth is primarily due to diseases such as AIDS and voluntary population control.

Events such as disease and war can change population trends.
Countries with similar economies tend to have similar population growth trends.
Industrially Developed Countries:
- Have advanced industry and technology and a high standard of living.
- The United States is an example.
- Early in its history, the United States had a high birthrate and a high death rate causing many children to die before reaching adulthood.
- Typically, individuals died by their early forties.
- In recent years, the birthrate in the United States has decreased a lot.
- The average lifespan is now more than 70 years.
Demographic Transition: A change from high birth and death rates to low birth and death rates in a population.

The formula for calculating Population Growth Rate (PGR) is: [birthrate - death rate + migration rate]
To get a percentage, divide the final answer by 10 because the rates are calculated per 1000.
Example: United States (2008):
- Birthrate: 14.1 (per 1000)
- Death rate: 8.3 (per 1000)
- Migration rate: 2.9 (per 1000)
- PGR = (14.1 - 8.3 + 2.9) / 10 = 0.87
- PGR: 0.87 percent
Example: Honduras (2008):
- Birthrate: 26.9 (per 1000)
- Death rate: 5.4 (per 1000)
- Migration rate: -1.3 (per 1000)
- PGR = (26.9 - 5.4 - 1.3) / 10 = 2.02
- PGR: 2.02 percent
Zero Population Growth (ZPG): Occurs when the birthrate equals the death rate.
- According to one estimate, the world will reach zero population growth between 2020 and 2029.
- At zero population growth, the number of people in different age groups should be nearly equal.

A population’s age structure is the number of males and females in each of three age groups:
- Pre-reproductive (up to age 20)
- Reproductive (ages 20 through 44)
- Post-reproductive (after age 44)
When the largest portion of the population is in the pre-reproductive stage, the population is growing rapidly (e.g., Kenya).
When the smallest portion is pre-reproductive, the population is decreasing (e.g., Germany).
When the reproductive and pre-reproductive groups are roughly equal, the population is growing slowly (e.g., the United States).

All populations have carrying capacities, including human populations.
Scientists are concerned that the human population might exceed Earth’s ability to support it.
Human overcrowding may lead to disease and starvation.
Family planning is being used in many countries to slow the growth rate.
Individuals in industrially developed countries use far more resources than individuals in developing countries.
As developing countries industrialize, resource use will increase rapidly.