1. Population Growth

2. Population
group of individuals of the same species living in the same area, potentially interacting

3. Population Growth Four factors can affect population size:
Birthrate – number of births
Death rate – number of deaths
Emigration – number of individuals moving away from a population
Immigration – number of individuals moving into a population

4. A population can grow when its birthrate is greater than its death rate.

5. Understanding Exponentials
Put your pens down for a minute & think about this:
An employer offers you two equal jobs for one hour each day for fourteen days.
The first pays $10 an hour.
The second pays only 1 cent a day, but the rate doubles each day.
Which job will you accept? 5

6. Understanding Exponentials
Now, how much would your employer owe you if you stayed at this job for another 2 weeks?
Job 2 lags for a long time before exponential growth kicks in!
What would happen if this type of growth took place within a population?

7. Exponential Growth
Under ideal conditions with unlimited resources, a population will grow exponentially. Exponential growth occurs when the individuals in a population reproduce at a constant rate.

8. Exponential Growth

9. Logistic Growth
As resources become less available, the growth of a population slows or stops.
Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.

10. Logistic growth is characterized by an S-shaped curve.

11. Carrying Capacity (K)
The largest number of individuals of a population that a given environment can support is called its carrying capacity. When a population reaches the carrying capacity of its environment, its growth levels off. The average growth rate is zero.

12. What factors limit population growth?
A limiting factor that depends on population size is called a density-dependent limiting factor.
Density-dependent limiting factors include:
Competition (for food, water space, sunlight and other essentials)
Predation (predator- prey relationships)
parasitism
disease

13. What factors limit population growth?
Density-independent limiting factors affect all populations in similar ways, regardless of the population size.
Examples of density-independent limiting factors include:
unusual weather
natural disasters
seasonal cycles
certain human activities—such as damming rivers and clear-cutting forests

14. Focus Question Monday, October 6th
What are the interactions that occur within communities?

15. Community Interactions
Community interactions, such as competition, predation, and various forms of symbiosis can powerfully affect an ecosystem.

16. Population – group of individuals of the same species living in the same area, potentially interacting.
Community – group of populations of different species living in the same area, potentially interacting.
What are some ecological interactions?

17. Fitness – how well an organism fits in its environment.

18. Why are ecological interactions important?
Interactions can affect distribution and abundance.
Interactions can influence evolution.

19. Types of ecological interactions
competition
predation
parasitism
mutualism
commensalism
symbiosis

21. Competition – two species share a requirement for a limited resource  reduces survival of one or both species

22. Predation – one species feeds on another  enhances fitness of predator but reduces survival of prey
herbivory is a form of
predation

23. Parasitism – one species feeds on another  enhances survival of parasite but reduces fitness of host.

24. Mutualism – two species provide resources or services to each other  enhances survival of both species.

25. Commensalism – one species receives a benefit from another species  enhances survival of one species; no effect on fitness of the other species.

26. Symbiosis – two species live together  can include parasitism, mutualism, and commensalism.

27. Isle Royale near Lake Superior

29. Organizing ecological interactions
effect on species 1
predation
herbivory
parasitism
mutualism + -
commensalism
effect on
species 2
competition

30. Choose an organism and describe the type of community interactions that affect the success of that organism.
List the limiting factors of the carrying capacity of the habitat

31. How would you describe the trends seen within this graph?
Bunny
Fox
Grass
Time (Months)

32. Focus Question Wednesday, October 9th
What types of human activities can disturb an ecosystem and cause succession?

33. Monday October 10th
Write down your answer on a separate piece of paper:
What is the difference between an organism’s habitat and niche?