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?
Where n = # of divisions
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?
A: 2108
(enough to cover the planet one foot deep)
Graph it:

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)
A logistic function or logistic curve is the most common sigmoid curve. It models the "S-shaped" curve (abbreviated S-curve) of growth of some set[1] P, where P might be thought of as population. The initial stage of growth is approximately exponential; then, as saturation begins, the growth slows, and at maturity, growth stops.
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?
3. Logistic Growth Model
When is growth rate the lowest?
1. When population is small or large
When is it the highest?
1. Population at intermediate level relative to carrying capacity.
What factors would cause a population to stop growing?

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)
- food supply, water, space, energy (oil), mates, etc…
Song Sparrow Population Experiment
Clutch size = # of eggs laid
(small island in British Columbia)
- add food
- Clutch size increased
Fig. 35.4A

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
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…
Hare cycles - food shortage from overgrazing, predator-prey,
“boom-and-bust” cycles
Fig. 35.5

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
Range - North East US to SW near Mexico
Food - fruit skins, insects, insect larva
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
Fig. 35.4B
- 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

18. What are some of the factors that limit population growth?
Population limiting factors
2. Abiotic factors
b. Fire, flood, etc…

19. Human population growth Is there a Carrying Capacity for Homo sapiens?
Section 5-3
Industrial
Revolution
begins
Agriculture
begins
Bubonic
plague
Plowing
and
irrigation
The human population growth of the last century has been truly phenomenal. It required only 40 years after 1950 for the population to double from 2.5 billion to 5 billion. This doubling time is less than the average human lifetime. The world population passed 6 billion just before the end of the 20th century.  Present estimates are for the population to reach 8-12 billion before the end of the 21st century. During each lecture hour, more than 10,000 new people enter the world, a rate of ~3 per second!
Of the 6 billion people, about half live in poverty and at least one fifth are severely undernourished. The rest live out their lives in comparative comfort and health.
The factors affecting global human population are very simple. They are fertility, mortality, initial population, and time. The current growth rate of ~1.3% per year is smaller than the peak which occurred a few decades ago (~2.1% per year in ), but since this rate acts on a much larger population base, the absolute number of new people per year (~90 million) is at an all time high. The stabilization of population will require a reduction in fertility globally. In the most optimistic view, this will take some time.