Andreas Schleicher presents at the launch of What does child empowerment mean...
Poulations.ppt
1. What is a Population?
Population Ecology
- The study of changes in population size and the factors that
regulate it.
Population
- group of individuals of a single species that occupy the
same general area
1. Rely on same resources
2. Influenced by the same biotic and abiotic factors
3. High likelihood of interbreeding
2. How do scientists describe population
growth?
Let’s look at population growth of bacteria starting from a single bacterium
- binary fission every 20 minutes under ideal conditions
Q: How many will there be after 36 hours?
3. How do scientists describe population
growth?
Let’s look at population growth of bacteria starting from a single bacterium
- binary fission every 20 minutes under ideal conditions
Graph it:
Q: How many will there be after 36 hours?
A: 2108 (enough to cover the planet one foot deep)
2n Where n = # of divisions
4. How do scientists describe population
growth?
1. Exponential Growth Model
(J-shaped curve)
Unlimited resources
Absence of predation
No disease
So why is Earth not covered in bacteria?
5. How do scientists describe population
growth?
Ex. Fur seals on St. Paul Island
1. Uncontrolled hunting until 1925
2. Population jumped until 1935
- Almost exponential
3. Population stabilized
- Some hunting
- limited breeding grounds
6. How do scientists describe population
growth?
3. Logistic Growth Model
(S - shaped curve)
Q: How does the logistic model
differ from the exponential model?
7. How do scientists describe population
growth?
Carrying capacity (K)
- The max. population the environment can support.
Determined by:
The species itself and the
environment (resources
available, predation, etc…)
8. How do scientists describe population
growth?
When is growth rate the lowest?
When is it the highest?
What factors would cause a
population to stop growing?
1. When population is small or large
1. Population at intermediate level
relative to carrying capacity.
3. Logistic Growth Model
9. What is a limiting Factor?
2. Population limiting factors
- environmental factors that restrict population growth
There are many factors that limit a population from getting to large.
- Competition for food or space.
- Disease
- Predation
- Stress levels
- Climate/ weather
- Major disasters (freak events)
10. What are some of the factors that limit
population growth?
Population limiting factors
1. Biotic factors
a. Competition among members (intraspecific)
Song Sparrow Population Experiment
(small island in British Columbia)
Fig. 35.4A
- add food
- Clutch size increased
- food supply, water, space, energy
(oil), mates, etc…
11. What are some of the factors that limit
population growth?
Population limiting factors
1. Biotic factors
a. Competition among members (intraspecific)
i. food supply
ii. space (territory)
A. Dispersion patterns
1. clumped
2. uniform
3. random
12. What are some of the factors that limit
population growth?
Dispersion patterns
13. What are some of the factors that limit
population growth?
Population limiting factors
1. Biotic factors
b. Health
- increased spread of disease with increased pop. density
- accumulation of waste
14. What are some of the factors that limit
population growth?
Population limiting factors
1. Biotic factors
c. Predation
Fig. 35.5
“boom-and-bust” cycles
As the hare population increases, so
does the Lynx population, which will
cause the hare population to decrease
and in turn the lynx population
decreases, etc…
15. What is happening to the moose and wolf
populations?
• Red is moose
• Blue is wolves
• 1955 to 1995
16. What are some of the factors that limit
population growth?
Population limiting factors
1. Biotic factors
d. Physiological factors
White-footed mouse experiment
1. Enclose in a small field
2. Reproduce quickly to 30 or 40
3. Reproduction declines and pop. stabilizes
around 40
4. Add more food and water
- no change
RESULT: high population induces stress syndrome (hormonal changes)
- sexual maturity delayed, reproductive organs shrink, depressed immune system
17. What are some of the factors that limit
population growth?
Population limiting factors
2. Abiotic factors
a. Climate and weather
Ex. Aphids
- insects that feed on phloem sap of plants
1. Exponential growth in spring
2. Rapid die out in hot, dry summer
3. A few individuals survive and reproduce
when conditions improve
Fig. 35.4B
18. What are some of the factors that limit
population growth?
Population limiting factors
2. Abiotic factors
b. Fire, flood, etc…
