1. Unit 2: Communities & Populations

2. Change in the community…
Part of ecology is studying the constant cycles of change that occur within an ecosystem
Factors affecting change
Loss of Habitat
Shortage of Resources
Population Growth
Disease

3. Changes in the community…
Succession: a series of predictable changes that occur in a community over time
-can be a drastic change or just a change of
seasons.

4. Succession (cont.)
Primary succession: form of succession where growth begins in an area that had no living organisms
Example: Growth beginning on new land formed by cooling lava.
Pioneer species: 1st species to populate the area in primary succession

5. Succession (cont.)
Secondary succession: when a disturbance changes a community and the community must grow back again
Ex: when land is cleared for farming and then trees are allowed to grow back

6. Primary Succession
Secondary Succession

7. Population Dynamics Characteristics of Populations
Geographic Distribution (where people live)
Density
Growth rate

8. Population Dynamics Factors that affect population growth:
Number of births
Number of deaths
Number of organisms entering or leaving the ecosystem

9. Population Growth Exponential Growth
Reproduction occurs at a constant rate
Growth is unlimited
Forms a J-shaped curve

10. Population Growth Logistic Growth
Growth slows as less resources become available
Carrying capacity: maximum number of organisms the ecosystem can hold
Forms a S-shaped
curve
Number of Yeast Cells
Time (hours)
Carrying capacity

11. Population Growth
Limiting Factors: factors that cause population growth to decrease
Limiting Growth Factors
Amount of nutrients
(food, water, etc.)
Competition
Predation
Disease (Parasitism)

12. Population Growth
Density Dependent Factors: factors that depend on the number of organisms in a population
Examples: competition, predation, parasitism, resource availability

13. Population Growth
Density Independent Factors: factors that affect a population in the same way no matter what size the population is
Examples: Weather, Natural disasters, Human activities

14. Human Population Growth
The human population remained relatively stable until approximately 500 years ago
Advances in medicine, agriculture and technology have increased humans rate of survival
Today the human population is above 6 billion and still growing

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

16. Human Population Growth
Distribution of population by age for industrialized and developing countries
U.S. Population
Rwandan Population
Males
Females

17. Math Connections
The human population increases on average 1.4% every year. If the population is 6 billion now what would the population be next year?
6,000,000,000 x = 84,000,000 people
Next years’ population would be 6,084,000,000
If the human population continues this growth the size would double in the next 50 years!

18. Reflection
What affect might the increase in human population have on the environment and other people?
What will happen when
humans reach their
carrying capacity?
What do you think is the human carrying capacity on Earth?