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Biology
Ch. 4
Population
Ecology
Ch. 4 Population Biology
I.Population Dynamics
Constant Population:
Birth rate = Death rate
Biotic Potential vs.
Environmental Resistance
A. Biotic Potential vs.
Environmental Resistance
1. Biotic Potential:
- factors that increase
population level
a. Birth rate:
- number of births, eggs laid,
seeds or spores
b. Recruitment:
- becoming part of breeding pop.
- Salmon: high birth rate, low
recruitment
- Humans: low birth rate, high
recruitment
Short vs. Long Life History
c. Migration
d. Adaptibility, Defense,
Resistance
- if all conditions are
favorable, a population
explosion (rare) could occur
2.Environmental Resistance:
a. Abiotic factors:
- temperature, water, fire, etc.
b.Biotic factors:
- predators, parasites, disease,
food
- constantly re-adjusting
(dynamic)
3. Exponential Growth
3. Exponential Growth
- population growth pattern
showing an increasing growth
rate
- can result in a population
explosion
3. Exponential Growth
(i) Reproductive Age 4
(ii) Reproductive Age 6
4.Carrying Capacity
Number of Individuals
(environmental resistance)
Carrying Capacity
Equilibrium
(biotic
potential)
Exponential
Growth
Time
4.Carrying Capacity
- the number of organisms
of a species that a
particular habitat can
support
Boom-and-bust Population Cycle
Annual lake algal bloom
Conditions good: Boom; Conditions bad: Bust
Effects of Exceeding Carrying Capacity
1911 - 25 reindeer
introduced
1938 - 2000
reindeer
1950 - 8 reindeer
survived
St. Paul Island, Pribilof, Alaska
Lemming Population Cycles
5. Density Dependent Factors:
- environmental resistance
increases as pop. increases
- predators, disease, parasites,
competition
6.Density Independent Factors:
- drought, fire, tidal waves,
floods, volcanoes, salinity,
comet
B. Mechanisms of Population
Balance
1. Predator/Prey
- lynx vs.hare
2. Host/Parasite:
- similar
- more common
- provides more stability
2. Host/Parasite: weevil vs. wasp
3. Principle of Ecosystem
Stability:
- Species diversity provides
ecosystem stability
- Species diversity provides
ecosystem stability
3. Principle of Ecosystem
Stability:
- Species diversity provides
ecosystem stability
- Natural enemies provide
balance
- Natural enemies provide balance
- Evolved together
3. Principle of Ecosystem
Stability:
- Species diversity provides
ecosystem stability
- Natural enemies provide balance
- Evolved together
- Introduced enemies create
imbalances
II. Human Population Growth
A. Human Population Explosion
A.Human Population Explosion
A. Human Population Explosion
- started around 1830
- 1 billion added every 12 years
- How many can the biosphere
support?
B. Rich Nations vs. Poor Nations
B. Rich Nations vs. Poor Nations
1. Highly Developed
(Industrialized) Countries:
- USA, W. Europe, Japan
- 20% of pop. but 80% of wealth
- pop. growth stabilizing
2. Moderately Developed Countries:
- Latin America, E. Asia, N. & S.
Africa
3.Low Income (3rd World) Countries:
- Ethiopia, Vietnam, C. Africa, China,
India
- 80% world's pop. but only 20% of
world's wealth
- population growing very rapidly
C. Demography
- the study of human population
growth
Pop. Growth Rates:
Developed & Developing Countries
Developing
Countries
Developed Countries
Age-Structure Diagrams
Post-Reproductive
(46-100 y old)
Reproductive
(15-45 y old)
Pre-Reproductive
(0-14 y old)
Expanding
Stable Contracting
Age Structures Developed Country
Age Structures Developing Country
The End
Population Growth by World Regions
World Average 1.4%
Developed
Countries 0.1%
Developing Countries 1.7%
Africa 2.4%
Latin America/Caribbean 1.8%
Asia (excluding China) 1.7%
China 0.9%
USA 0.6%
Europe 10.1%
-0.5
0
0.5
1
1.5
2
Natural Increase (annual %)
2.5
3
U.S. Population Growth
U. S. overconsumes and
over-pollutes
U.S. citizen
uses 6X
energy of
average
world
Effect of Death Rates on
Population Growth
bacteria
No
deaths
10% die
between
doublings
25% die
between
doublings