Ch. 4
Population
Ecology
I. Population Dynamics
- Biological processes constantly
influence a population’s density,
dispersion, and growth rate.
Tent Caterpillars
A. Population Characteristics
1.Population Density
- number of organisms per unit area
2. Spatial Distribution
- uniform, clumped, random
Clumped
Uniform
Random
3. Population Range
- depends on the species’ adaptations
to biotic and abiotic factors
Range of
the Cougar
Range of the
Olympic Marmot
B. Population-Limiting Factors
1. Density-Independent Factors
- affect organisms regardless of
population size
Tsunami
Forest Fire
2. Density-Dependent Factors
- competition, predation, disease and
parasites
Snowshoe hare
160
120
Lynx
9
80
6
40
3
0
0
1850
1875
Year
1900
1925
Lynx population
size (thousands)
Hare population
size (thousands)
Snowshoe Hare
and Lynx
2. Density-Dependent Factors
Host-Parasite Relationship:
Bean Weevil vs. Braconid Wasp
C. Population Growth Rate
- balance between biotic potential and
environmental resistance
Immigration
Births
Births and immigration
add individuals to a
population.
Population
Size
Emigration
Deaths
Deaths and emigration
remove individuals from a
population.
C. Population Growth Rate
- balance between biotic potential and
environmental resistance
- Natality: birth rate
- Recruitment: joining the breeding
population
- Mortality: death rate
- Immigration
- Emigration
1. Exponential Growth
- shows an increasing growth rate
(J-shaped curve)
- results in population explosion
1. Exponential Growth
Elephant Population
8,000
6,000
4,000
2,000
Exponential Growth in the African
Elephant Population of Kruger
National Park, South Africa
0
1900
1920
1940
Year
1960
1980
1. Exponential Growth
2. Logistic Growth
1,000
Number of Daphnia/50 ml
Number of Paramecium/ml
- population growth levels off at
carrying capacity (S-shaped curve)
800
600
400
200
0
0
5
10
15
Time (days)
Paramecium population
180
150
120
90
60
30
0
0
20
40
60
80 100 120 140 160
Time (days)
Daphnia population
3.Boom-and-Bust Population Cycle
- population greatly exceeds carrying
capacity resulting in a population crash
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
food (lichens) overgrazed
St. Paul Island, Alaska
D. Reproductive Patterns
R-strategists
K-Strategists
1. R-Strategists
- adapted to unstable environments
- short life spans
- produce many offspring
Locust Swarm
Chum Salmon
1. R-Strategists
- adapted to unstable environments
- short life spans
- produce many offspring
Dandelion
Chum Salmon
2. K-Strategists
- adapted to more stable environments
- long life spans
- produce fewer offspring
II. Human Population Growth
- Humans are undergoing a
population explosion.
6
4
3
2
The Plague
1
8000
B.C.
4000
B.C.
3000
B.C.
2000
B.C.
1000
B.C.
0
1000
A.D.
0
2000
A.D.
Human population (billions)
5
Human Population Growth
A. Technological advances have
increased carrying capacity for
humans
- agricultural improvements
- advances in sanitation and
medicine
- decrease in childhood mortality
B. Demographic Transition
- shift from high birth and death rates
to low birth and death rate
C. Rate of increase has slowed
Demographic Transition in Sweden and Mexico,
1750–2050 (Data as of 2003)
Birth or death rate per 1,000 people
50
40
30
20
10
Sweden
Birth rate
Death rate
0
1750
1800
Mexico
Birth rate
Death rate
1850
1900
Year
1950
2000
2050
Human Population Growth Rate by Country
Age Structure Pyramids for the Human
Population of Three Countries (2003)
Rapid growth
Afghanistan
Male
Female
8 6 4 2 0 2 4 6 8
Percent of population
Age
85
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Slow growth
United States
Female
Male
8 6 4 2 0 2 4 6 8
Percent of population
Age
85
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
Decreas
e Italy
Female
Male
8 6 4 2 0 2 4 6 8
Percent of population
Age Structure Diagram for Japan
in 1950, 2005, and 2050
1950
2005
2050
Infant Mortality and Life Expectancy at Birth in
Developed and Developing Countries
80
50
Life expectancy (years)
Infant mortality (deaths per 1,000 births)
60
40
30
20
60
40
20
10
0
Developed
countries
Developing
countries
0
Developed
countries
Developing
countries
Ecological Footprint in Relation
to Available Ecological Capacity
Ecological footprint (ha per person)
16
14
12
New Zealand
10
8
Australia
Canada
Netherlands
Norway
Japan
6
Sweden
UK
4
Spain
2
0
USA
Germany
World
China
India
0
2
4
6
8
10
Available ecological capacity (ha
per person)
12
14
16
The
End