Population Dynamics

Population Growth• Populations grow exponentially• Exponential growth is an increase by a percentage

– Looks like a curve when graphed– J-CURVE is a special type of exponential growth in which

the percentage changes over time. When graphed, it looks like a “J”

– Example: the human population, insect populations, etc.

• Populations grow until they meet the limits of their resources.

• Carrying capacity (K) is the number of individuals an area can support indefinitely.

The Human Population has a carrying capacity

• Effects of a large human population:– Food and other resource shortages– Job shortages– Increased pollution and habitat disruption– Disease epidemics– Increased crime, war, etc.

Populations in nature fluctuate around their carrying capacity.

• If “K” is exceeded, the population could crash or cease to exist.

• This graph is for a real population of deer in Arizona that was almost wiped out when predators were removed

Populations cannot exceed the carrying capacity

HUMAN POPULATION GROWTH• For most of the history of humans on

earth, the growth rate was about 0.002%. • During late 1800’s, the percentage

changed. • In 1974 it reached its highest growth rate

at 2.78%. • Today the world growth rate is less than

1.17%. • The graph forms a very steep “J”.

Why did the population grow so fast?

• These changes are not due to a change in crude birth rate, but rather a change in the death rate and infant mortality due to:

– BETTER HYGIENE– BETTER NUTRITION– INDUSTRIALIZATION– MECHANIZED FARMING– PESTICIDES TO PROTECT OUR FOOD SOURCES– MEDICINES, ANTIBIOTICS

Why has the population growth decreased since 1970 (from 2.78 to

1.17)?• Decrease in population growth since the

1970’s is mainly due to available birth control and women becoming educated and entering the work force

• The growth rate varies considerably from country to country – China 0.6%– US 1.10%– Kenya 2.79%

What is a demographer?• Demographers study

populations – Collect data on age of

individuals, birth rates, fertility rates, death rates, etc.

– Predict future population growth

• A large proportion of young people indicates future growth

• Which of these two countries will grow quickly in the next several years?

% change = (birth rate + immigration)-(death rate + emigration) X 1001000 People

Demographers measure distribution of birth rate by age group

Fertility Rates• Replacement level fertility is the number of

children a couple must have to replace themselves when they die. Varies due to differences in child mortality.– More developed countries (US, Canada, Australia,

Western Europe, Japan) = 2.1 children per couple– Less developed countries = 2.5 (much higher in some)

• Total fertility rate is the total number of children a woman will have if she survives her childbearing years (age 15-44). Varies due to cultural, religious values.

Global Fertility RatesFertility rates are used by demographers to predict population growth around the world.

Factors Effecting Total Fertility

• Varies in from one population to the next due to:

– EXPENSE OF RAISING A CHILD– EDUCATION OF WOMEN, JOB AVAILABILITY– IMPORTANCE OF CHILDREN TO WORK– AVAILABILITY OF PRIVATE AND PUBLIC

RETIREMENT– AVAILABILITY OF RELIABLE BIRTH CONTROL– CULTURAL REASONS (HAVING SONS, ETC)– AGE OF MOTHER AT HER FIRST CHILD’S BIRTH

Fertility varies among more developed countries

Fertility varies widely among less developed countries.

• Where women are educated, fertility rates are lower.

Demographic Transition:growth rates change as nations

become industrialized.