1. Population Growth Chapter 5
Ecology Notes 5
Population Growth
Chapter 5

2. Graph #1 – Bacterial Growth

3. Graph #2 – Field Mice Growth

4. Graph Questions Questions
How are the two graphs you made similar? Just list characteristics.
How are the two graphs you made different? Just list 2 – 3 characteristics.
Propose 2 hypotheses for the changes in the mouse population growth pattern.

5. Question Answers
Similarities – specific time, monitoring population growth, both line graphs,
Differences – time scale (minutes vs. years), organisms, 1st graph only increases & 2nd graph fluctuates
2 Hypotheses –
Mouse has a predator regulating population size
Mouse might not have regular access to resources like food, water, mates, & habitat space

6. 1. Population Growth
Population Growth - an increase in population size
Population Growth Rate = change in the number of individuals / Time

7. 1. Population Growth Population size is affected by 3 main factors:
Number of Births
Number of Deaths
Number of Immigrants or Emigrants
Immigration – entering a population
Emigration – exiting a population

8. 2. Population Growth Curves
Exponential Growth – occurs when individuals of a population reproduce at a constant rate
There are no factors affecting how quickly this population can increase in size
This is often how populations grow when they first inhabit an environment.
Populations generally cannot maintain exponential growth.

9. 2. Population Growth Curves
Exponential Model of Population Growth
Notice that an Exponential Growth curve has a “J” shape
It is often called a “J Curve”
Exponential Growth # of I N D V U A L S
TIME \

10. 2. Population Growth Curves
Logistic Growth – occurs after exponential growth when a population’s size might slow or stop
Population growth slows when:
Death rate equals or exceeds birth rate
Emigration equals or exceeds immigration
Carrying Capacity for an environment is met

11. 2. Population Growth Curves
Logistic Model of Population Growth
Graph shows indicates carrying capacity
Notice the graph’s “S” shape
This type of graph is often called an “S Curve”
Carrying Capacity
Number of Yeast Cells
Time (hours)

12. 2. Population Growth Curves
Limiting Factors: conditions which control a population’s ability to grow
Carrying Capacity: the limited number of individuals in a population that a particular environment can support

13. 3. Limiting Factors Limiting factors can be:
Density Dependent - affect population members according to density (size in space)
Examples: availability of food, mates, and habitat space; spread of disease
Density Independent Factors - affect population members regardless of how big the population is
Examples: environmental disasters (floods, earthquakes, tornados, human impact, etc)

14. Population Growth With Limiting Factors60
2400 50
2000 40
1600 30
1200 20
800 10
400
1955
1960
1965
1970
1975
1980
1985
1990
1995
Moose
Wolves
This graph shows how predator/prey interactions affect population size of both predators (wolf) and prey (moose).

15. 4. Human Population Growth
How Fast Are We Growing?
Until about 500 years ago, the world’s human population remained fairly stable. Then, as advances in medicine, agriculture, and technology occurred, the human population began growing very rapidly.
Today, the world’s human population is greater than 7 billion people, and it continues to grow, but at a slower rate.

16. 4. Human Population Growth
Industrial
Revolution
begins
Agriculture
begins
Bubonic
plague
Plowing
and
irrigation

17. 4. Human Population Growth
The human population is increasing by about 1.4 percent each year. Assume that the population is 6 billion (6,000,000,000). How large will the population be in one year?
6,000,000,000 X = 84,000,000 people will be added in one year, so the population would be 6.08 billion in one year.