1. Studying Human Populations
Chapter 9
Section 1
Ms. Cuthrell
Ecology
2nd Period

2. The Human Population
The human population has been growing faster and faster in the 20th century.
The rapid growth has led to environmental problems worldwide.
To save our planet and our future, we must study how the human population changes over time to help predict and understand these changes and how they will affect us in years to come.

3. The Human Population
Demography: the study of populations (usually talking about humans).
Demographers study the historical size and makeup of past population to make comparisons and predictions about unique populations around the globe.
They also study properties that affect population growth such as economics and social structure.
Countries are put into two main categories depending on these certain properties: developed or developing countries.

4. Human Population Over Time
In the beginning, the human population grew steadily for thousands of years because of limiting factors humans were exposed to.
Around the 1800’s, the human population exploded because of advances in food production and hygiene caused by the industrial and scientific revolutions.
Populations began to grow exponentially because of these advances, and continue growing in this way today.
It is important to understand that the Earth will not be able to support human exponential growth forever.

5. Forecasting Population Size
Demographers must make predictions about population size and how it will change to decide what amenities and resources that population will need in the future.
Most predictions are inaccurate because of the constant change experienced in human behavior.
Forecasting a population is done by studying its age structure, survivorship, fertility rate, and migration into or out of the population.

6. Age Structure
Age structure is the distribution of ages in a specific population at a certain time.
For example, if there are most older people in the population, the population will be predicted to decrease because there are more people who are closer to the end of their lives who have already reproduced.
Demographers show this using a population pyramid, which is a double-sided bar graph showing male and female age ranges in a specific population.

7. Age Structure
Countries with high growth rates have more young people than older people.
In contrast, countries that have slow growth or no growth usually have an even distribution of ages in the population.

8. Survivorship
Survivorship is the percentage of members of any group that are predicted to live to a certain age.
To determine this, demographers follow a group of individuals born at the same time and notes each time a member of the group dies.
This is plotted using a survivorship curve.

9. Survivorship There are three types of survivorship curves:
Type I: most people live to be very old.
Ex: Japan or Germany
Type II: similar death rate at all age ranges.
Ex: Britain or United States
Type III: very poor populations in which lots of children die.
Ex: India and African tribal countries

10. Fertility Rates
Fertility rate expresses the number of babies born each year per 1,000 women in the population.
Total fertility rate is the average number of children a woman gives birth to in her lifetime.
Replacement level is the total number of children each parent must have in order to “replace” themselves.
This number is slightly higher than 2 in most cases because not all children born will survive to reproduce.

11. Fertility Rates In the United States:
1972: the fertility rate drops below replacement level for the first time in history.
Remained below replacement level for most of the 1990s.
The population continued to grow despite this.
Children of the baby boom grew up and had children.

12. Migration Migration is the movement of individuals between areas.
Population continues to grow in the US even if the fertility rate is below replacement level because increases in immigration.
Movement in = immigration (think “in”)
Movement out = emmigration (think “exit”)
Migration between countries is a significant part of population change.
If not for immigration, the populations of many developed countries would be decreasing.

13. Declining Death Rates
Human populations have dramatically increased over the last 200 years because of a decrease in death rates overall.
This is mainly due to better resources such as food, clean water, and better sanitation/ sewage disposal.
The discovery of vaccines in the 20th century greatly increased the mortality rate for children and infants.
So, how long can an average person live because of these advances?

14. Life expectancy
Life expectancy is the average number of years a person is expected to live.
It is most affected by infant mortality, or the death rate of infants less than a year old.
In 1990, worldwide life expectancy was 40 years with a high infant mortality rate.
By 2000, the infant mortality rate was 1/3 of what it was in 1990.
Presently, the average life expectancy is 67 worldwide and 87 for those in developed countries.

15. Life expectancy
Infant mortality is not just sustained by expensive medical resources, but rather differs greatly among countries, even those having the same annual income.
Infant health is affected by parents’ access to food, education, fuel, and clean water.
In poor areas, it is well understood that babies need to be well fed and kept safe and warm and that if their basic needs are met, they will have a better chance for survival.

16. Life expectancy
New threats to life expectancy arise with the populations of the world becoming more dense in certain areas.
Contagious diseases such as AIDS and tuberculosis are found in great frequency in these areas and can spread quickly if not carefully monitored.
AIDS is one of the biggest treats to the human population, especially in poor countries such as Africa.

17. The Demographic Transition
What happens when a country become developed and their population stops growing?
If there are countries that are no longer growing in population, why is the worldwide population still growing so rapidly?
The answer to this is the demographic transition model that describes how changes occur over the “life” of a population.
This model is based on the belief that a population’s growth depends on the economic and social progress caused by industrialization of a country.

18. The Demographic Transition
Stages of Transition:
Preindustrial Condition – birth and death rate are both high, population size is stable. (Most of the world was in this state before the 1700s.)
Population explosion – death rates decline with increasing technology, birth rates remain high so the population grows rapidly.
Demographic transition – birth rates decrease and population growth slows. As birth and death rates become close to the same, population stabilizes.
Postindistrial – birth rate drops below replacement level, the population begins to decrease.

19. Women and Fertility
Factors that are clearly related to a decline in the birth rate are factors such as increasing education and economic independence for women.
Educated women do not feel the strong urge to have as many children because they fell they can take care of themselves instead of expecting to be cared for by their children.
These women are also participating in family planning which decrease the number of unplanned pregnancies which increases birth rates in underdeveloped countries.
These countries place a priority on education for women to decrease birth rates.

20. Women and Fertility
In communities where it is common for people to have large families, it is valuable to have more children to help provide more income or to take care of an elderly family member.
In more modern countries, where parents work away from home, children must go to child care which is expensive.
These countries have a lower birth rate because of the financial burden that a large number of children can have on a family.
Also, elderly are cared for by other means in developed countries (nursing homes, hospice, etc.)
Total fertility rate in developed countries: 1.6 children per woman.
Total fertility rate in developing countries: 3.1 children per woman.