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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
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?
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
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?
How do scientists describe population growth?
Ex. Fur seals on St. Paul Island
1. Uncontrolled hunting until 1925
2. Population jumped until 1935
- Almost exponential3. Population stabilized
- Some hunting- limited breeding grounds
How do scientists describe population growth?
3. Logistic Growth Model
(S - shaped curve)
Q: How does the logistic model differ from the exponential model?
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…)
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
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)
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…
What are some of the factors that limit population growth?
Population limiting factors
1. Biotic factors
a. Competition among members (intraspecific)i. food supplyii. space (territory)
A. Dispersion patterns1. clumped
2. uniform
3. random
What are some of the factors that limit population growth?
Dispersion patterns
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
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…
What is happening to the moose and wolf populations?
• Red is moose
• Blue is wolves
• 1955 to 1995
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 404. Add more food and water
- no change
RESULT: high population induces stress syndrome (hormonal changes)
- sexual maturity delayed, reproductive organs shrink, depressed immune system
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
What are some of the factors that limit population growth?
Population limiting factors
2. Abiotic factors
b. Fire, flood, etc…
Agriculture begins
Plowingand irrigation
Bubonicplague
IndustrialRevolutionbegins
Section 5-3
Human Population GrowthHuman population growthIs there a Carrying Capacity for Homo
sapiens?
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