1. How Populations Grow & Limits to Growth

2. Population Growth What is a population?
A group of organisms that all belong to the same species and live in a given area

3. Populations can change by:
Immigration – individuals moving into a population
Increase or decrease?
Emigration – individuals moving out of a population
Increase or decrease
Birth rate
Death rate

4. Population Growth
Two Types:
Exponential Growth
Logistic Growth

5. Exponential Growth
Exponential Growth occurs when organisms are provided with ideal conditions for growth and reproduction
If nothing stops population from growing, it grows faster and faster

6. Exponential Growth

7. Logistic Growth Population begins to grow exponentially
Growth of population slows down
Growth levels out due to deathrate and birthrate equalizing (steady state)

8. Logistic Curve
Carrying capacity
Number of Mice
Time (hours)

9. Quick Think #1
What are the four factors that can affect a change in population?
What are the causes of these factors?

10. What do you think would cause the growth of a population to decrease?
LIMITING FACTORS!
Factors that cause the growth of a population to decrease
Density-dependent factors
Density-independent factors

11. Density Dependent Factors
Affected by other populations
Strongest when population is large and dense
Four Common Types:
Competition
Parasitism
Predation
Disease

12. Density Independent Factors
Not affected by population
Common examples:
Unusual weather
Natural disasters
Seasonal cycles
Human interference

13. Figure 5-7 Wolf and Moose Populations on Isle Royale
Section 5-2 60
2400 50
2000 40
1600 30
1200 20
800 10
400
1955
1960
1965
1970
1975
1980
1985
1990
1995
Moose
Wolves
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14. Quick Think #2
What is the difference between density dependent factors and density independent factors?
Name one density-dependent and one density-independent factor.