1. Section 1: How Populations Grow
Chapter 5: Populations
Section 1: How Populations Grow

2. Properties of Populations
Population – a group of organisms of the same species that live in a specific geographical area and interbreed
Population Size – the number of individuals in the population
Population Density – measure of how crowded a population is
the number of individuals per unit of area
Dispersion – the spacing of organisms in a population
clumped
even
random

3. Changes in Population Size
Birth Rate: the number of births occurring in a period of time
in the U.S. there are about 4 million births per year
Death Rate: the number of deaths in a period of time
in the U.S. there are about 2.4 million deaths per year
Growth Rate: birth rate – death rate
depends on birth rate, death rate, emigration, and immigration
Immigration: individuals move into its range from elsewhere
Emigration: individuals move out of the population’s range
Age Structure: the number of males and females of each age a population contains

4. Age Structure

5. Age Structure The shape of the age structure diagram tells you:
if a population is increasing, stable, or shrinking
Population growth momentum; even if people are having less children, the effect won’t take place until much later when the children reach reproductive maturity.
Scientists use age structure diagrams to:
Compare age groups such as pre-reproductive ages
Compare the number of males to females
Scientists use the shape of the graph to determine:
If a population is growing, shrinking, or staying the same
Growth momentum; how soon overpopulation will become a problem

6. Age Structure

7. Population Growth
Exponential Model – a model of growth describing an unrestricted population that increases very rapidly forever
assumes birth rates and death rates are constant with births outnumbering deaths & that there are unlimited resources
not realistic because resources become limited as the population grows

8. Population Growth
Logistic Model – a model of growth describing a population that increase very rapidly but then levels off ; levels off(population stabilizes) at the carrying capacity which is the largest population that an environment can support at any given time
assumes birth rates & death rates are not constant & that birth and death rates vary with population size
the death rate increases when resources become limited
When there is no population
growth the line is horizontal; at this time the number of births and deaths are equal
Logistic Models display in a ‘S”
shape

9. Section 2: Limits to Growth
Chapter 5: Populations
Section 2: Limits to Growth

10. Limiting Factors
Limiting Factor: factor that controls the growth of a population
Acting separately or together, limiting factors determine the carrying capacity of an environment for a species
Charles Darwin recognized the importance of limiting factors (natural selection) in shaping the history of life on Earth

11. Density-Dependent Limiting Factors
Density Dependent Factors – something that affects the population size due to the population density
examples: competition, herbivory, parasitism, disease, and stress from overcrowding
application example: millions of people moving to California will cause a food shortage there

12. Density-Independent Limiting Factors
Density Independent Factors – something that affects the population size regardless of the population density
examples: hurricanes, droughts, or floods and natural disasters such as wildfires
application example: millions of people moving to California won’t cause an earthquake

13. Section 3: Human Population Growth
Chapter 5: Populations
Section 3: Human Population Growth

14. Historical Overview
Human Population Growth – the number of people on the planet is still growing rapidly.
We are now just above 7 billion people.
If our population gets too high, it could put a strain on the environment; the ever growing population is the greatest threat to the world’s future
increased emissions
competition for water, space, food, etc.
destruction of natural habitat

16. Patterns of Human Population Growth
Demography: the scientific study of human populations
Examines characteristics of human populations and attempts to explain how those populations will change over time
Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly
Demographic Transition: a dramatic change from high birthrates and death rates to low birthrates and death rates
US, Japan, & Europe