1. Bellwork: Describe the conditions under which logistic growth occurs

2. Chapter 5 - populations
5.1 How populations grow

3. How could one harmless plants cause widespread problems

4. In Florida the hydrilla population has got out of control
Why?

5. Fish stocks in New England have plummeted I recent years
Why are fish populations in decline?

6. What do both of these stories have in common?
Both involve dramatic changes in the size of a population
Population – A group of organisms of a single species that live in a given area
Researchers study a population’s
Geographic range
Density
Distribution
Growth Rate
Age Structure

7. Geographic range The area inhabited by a population
Can vary from less than a cubic meter to continents

8. Density and distribution
Population density = Number of individuals per unit area
Different species have different densities – even in the same area

9. Patterns of distribution
How individuals are spaced out

10. Growth rate High growth rate – population size is increasing
Neutral growth rate – constant population size
Negative growth rate – population is in decline

11. Age Structure
Why is it important to know the age structure of a population
Why is it important to know the distribution between male and females?

12. What factors affect population growth?
Birth rate
Death rate
Immigration
Emigration

13. Birth and Death rate
If more people are born than die, a population will grow
If birthrate is higher than it’s death rate
Birth can mean different things to different species
Mammals give birth
Fish hatch from eggs
Some countries have a higher death rate than birth rate

14. Immigration and Emigration
Immigration – influx of organisms moving into an area
Emigration – mass exodus of organisms due to a food shortage or, overcrowding or another reason….

15. Exponential growth
Under ideal condition, with unlimited resources, a population will grow exponentially
Why is this unrealistic?

16. Bacterial growth
If one bacteria can divide every 30 minutes, how many bacteria could you have at the end of 24 hr period?
Answer = 281,474,976,710,656

17. Organisms that reproduce slowly
Example - elephants that were protected from hunting in the kruger national park (South Africa)
Single offspring every 2 – 4 years

18. Organism in new environment
Organisms can sometimes flourish in a new environment - why?
Example – Burmese pythons in florida

19. Why don’t we see many examples of exponential growth?
Many populations start with exponential growth
At some point growth rate will slow down
Increased competition for food, land etc…
At some point growth rate will stop

20. Logistic growth
When a population’s growth slows and then stops following exponential growth
Growth can slow due to
Decreased birth rate
Increased death rate
Immigration decrease
Emigration increase

21. Carrying capacity
When birth rate = death rate, and immigration = emigration, population growth stops
Some small variation, but on the whole stable
Where this line intersects y axis = carrying capacity
Definition = The maximum number of individuals of a particular species that a particular environment can support
A number of factors will stabilize population at this size

22. Writing exercise
How is the carrying capacity of a cities roads similar to the carrying capacity of an ecosystem?