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Chapter 36
Population Ecology
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
 Individual emperor penguins face the rigors of the
Antarctic climate and have special adaptations,
including a
– downy underlayer of feathers for insulation and
– thick layer of fat for energy storage and insulation.
 The entire population of emperor penguins reflects
group characteristics, including the
– survivorship of chicks and
– growth rate of the population.
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Introduction
 Population ecologists study natural population
– structure and
– dynamics.
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Figure 36.0_1
Chapter 36: Big Ideas
1985
Male
Population Structure
and Dynamics
Female
The Human Population
Figure 36.0_2
POPULATION STRUCTURE
AND DYNAMICS
© 2012 Pearson Education, Inc.
36.1 Population ecology is the study of how and
why populations change
 A population is a group of individuals of a single
species that occupy the same general area.
 Individuals in a population
– rely on the same resources,
– are influenced by the same environmental factors, and
– are likely to interact and breed with one another.
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36.1 Population ecology is the study of how and
why populations change
 A population can be described by the number and
distribution of individuals.
 Population dynamics, the interactions between biotic
and abiotic factors, cause variations in population
sizes.
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36.1 Population ecology is the study of how and
why populations change
 Population ecology is concerned with
– the changes in population size and
– factors that regulate populations over time.
 Populations
– increase through birth and immigration to an area and
– decrease through death and emigration out of an area.
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36.2 Density and dispersion patterns are
important population variables
 Population density is the number of individuals of
a species per unit area or volume.
 Examples of population density include the
– number of oak trees per square kilometer in a forest or
– number of earthworms per cubic meter in forest soil.
 Ecologists use a variety of sampling techniques to
estimate population densities.
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36.2 Density and dispersion patterns are
important population variables
 Within a population’s geographic range, local
densities may vary greatly.
 The dispersion pattern of a population refers to the
way individuals are spaced within their area.
Video: Flapping Geese (clumped)
Video: Albatross Courtship (uniform)
Video: Prokaryotic Flagella (Salmonella typhimurium) (random)
© 2012 Pearson Education, Inc.
36.2 Density and dispersion patterns are
important population variables
 Dispersion patterns can be clumped, uniform, or
random.
– In a clumped pattern
– resources are often unequally distributed and
– individuals are grouped in patches.
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Figure 36.2A
Figure 36.2A_1
36.2 Density and dispersion patterns are
important population variables
 In a uniform pattern, individuals are
– most likely interacting and
– equally spaced in the environment.
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Figure 36.2B
Figure 36.2B_1
36.2 Density and dispersion patterns are
important population variables
 In a random pattern of dispersion, the individuals in
a population are spaced in an unpredictable way.
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Figure 36.2C
Figure 36.2C_1
36.3 Life tables track survivorship in populations
 Life tables track survivorship, the chance of an
individual in a given population surviving to various
ages.
 Survivorship curves plot survivorship as the
proportion of individuals from an initial population
that are alive at each age.
 There are three main types of survivorship curves.
– Type I
– Type II
– Type III
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Table 36.3
Percentage of survivors (log scale)
Figure 36.3
100
I
10
II
1
III
0.1
0
50
Percentage of maximum life span
100
36.4 Idealized models predict patterns of
population growth
 The rate of population increase under ideal
conditions is called exponential growth. It can be
calculated using the exponential growth model
equation, G = rN, in which
– G is the growth rate of the population,
– N is the population size, and
– r is the per capita rate of increase (the average
contribution of each individual to population growth).
 Eventually, one or more limiting factors will restrict
population growth.
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Figure 36.4A
Population size (N)
500
450
400
350
300
250
200
150
100
50
0
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (months)
Figure 36.4A_1
Population size (N)
500
450
400
350
300
250
200
150
100
50
0
1 2 3 4 5 6 7 8 9 10 11 12
Time (months)
Figure 36.4A_2
Table 36.4A
36.4 Idealized models predict patterns of
population growth
 The logistic growth model is a description of
idealized population growth that is slowed by limiting
factors as the population size increases.
 To model logistic growth, the formula for exponential
growth, rN, is multiplied by an expression that
describes the effect of limiting factors on an
increasing population size.
 K stands for carrying capacity, the maximum
population size a particular environment can sustain.
(K  N)
G = rN
K
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Breeding male fur seals
(thousands)
Figure 36.4B
10
8
6
4
2
0
1915
1925
1935
Year
1945
Breeding male fur seals
(thousands)
Figure 36.4B_1
10
8
6
4
2
0
1915
1925
1935
Year
1945
Figure 36.4B_2
Number of individuals (N)
Figure 36.4C
G
 rN
K
G
0
Time
(K  N)
 rN K
Table 36.4B
36.5 Multiple factors may limit population growth
 The logistic growth model predicts that population
growth will slow and eventually stop as population
density increases.
 At increasing population densities, densitydependent rates result in
– declining births and
– increases in deaths.
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Figure 36.5A
Average clutch size
12
11
10
9
8
0
10
20
30 40 50 60 70 80
Number of breeding pairs
90
36.5 Multiple factors may limit population growth
 Intraspecific competition is
– competition between individuals of the same species for
limited resources and
– is a density-dependent factor that limits growth in natural
populations.
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36.5 Multiple factors may limit population growth
 Limiting factors may include
– food,
– nutrients,
– retreats for safety, or
– nesting sites.
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Figure 36.5B
100
Survivors (%)
80
60
40
20
0
20
40
60
80
100
120
Density (beetles/0.5 g flour)
36.5 Multiple factors may limit population growth
 In many natural populations, abiotic factors such as
weather may affect population size well before
density-dependent factors become important.
 Density-independent factors are unrelated to
population density. These may include
– fires,
– storms,
– habitat destruction by human activity, or
– seasonal changes in weather (for example, in aphids).
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Number of aphids
Figure 36.5C
Exponential
growth
Apr May Jun
Sudden
decline
Jul
Aug Sep Oct Nov Dec
Month
36.6 Some populations have “boom-and-bust”
cycles
 Some populations fluctuate in density with regularity.
 Boom-and-bust cycles may be due to
– food shortages or
– predator-prey interactions.
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160
Snowshoe hare
120
9
Lynx
80
6
40
3
0
0
1850
1875
1900
Year
1925
Lynx population size
(thousands)
Hare population size
(thousands)
Figure 36.6
160
Snowshoe hare
120
9
Lynx
80
6
40
3
0
0
1850
1875
1900
Year
1925
Lynx population size
(thousands)
Hare population size
(thousands)
Figure 36.6_1
Figure 36.6_2
36.7 EVOLUTION CONNECTION: Evolution
shapes life histories
 The traits that affect an organism’s schedule of
reproduction and death make up its life history.
 Key life history traits include
– age of first reproduction,
– frequency of reproduction,
– number of offspring, and
– amount of parental care.
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36.7 EVOLUTION CONNECTION: Evolution
shapes life histories
 Populations with so-called r-selected life history
traits
– produce more offspring and
– grow rapidly in unpredictable environments.
 Populations with K-selected traits
– raise fewer offspring and
– maintain relatively stable populations.
 Most species fall between these two extremes.
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36.7 EVOLUTION CONNECTION: Evolution
shapes life histories
 A long-term project in Trinidad
– studied guppy populations,
– provided direct evidence that life history traits can be
shaped by natural selection, and
– demonstrated that questions about evolution can be
tested by field experiments.
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Guppies:
Larger at
sexual maturity
Experiment:
Transplant
guppies
Results
Pool 3
Pools with killifish
but no guppies
prior to transplant
Pool 2
Predator: Pikecichlid;
preys on large guppies
Guppies: Smaller at
sexual maturity
Hypothesis: Predator feeding preferences caused difference in life history
traits of guppy populations.
Mass of guppies
at maturity (mg)
Pool 1
Predator: Killifish;
preys on
small
guppies
185.6
200
161.5
160
120
80 67.5 76.1
40
Age of guppies
at maturity (days)
Figure 36.7
100
85.7 92.3
80
60 48.5 58.2
40
20
Males
Males
Females
Females
Control:
Guppies from pools with
pike-cichlids as predators
Experimental:
Guppies transplanted to pools
with killifish as predators
Figure 36.7_s1
Pool 1
Predator: Killifish;
preys on
small
guppies
Guppies:
Larger at
sexual maturity
Figure 36.7_s2
Pool 1
Predator: Killifish;
preys on
small
guppies
Guppies:
Larger at
sexual maturity
Pool 2
Predator: Pikecichlid;
preys on large guppies
Guppies: Smaller at
sexual maturity
Hypothesis: Predator feeding preferences caused difference in life
history traits of guppy populations.
Figure 36.7_s3
Pool 1
Predator: Killifish;
preys on
small
guppies
Guppies:
Larger at
sexual maturity
Experiment:
Transplant
guppies
Pool 3
Pools with killifish
but no guppies
prior to transplant
Pool 2
Predator: Pikecichlid;
preys on large guppies
Guppies: Smaller at
sexual maturity
Hypothesis: Predator feeding preferences caused difference in life
history traits of guppy populations.
200
160
120
80
40
185.6
161.5
67.5 76.1
Males
Females
Control:
Guppies from pools with
pike-cichlids as predators
Age of guppies
at maturity (days)
Mass of guppies
at maturity (mg)
Figure 36.7_2
100
80
60
40
20
85.7 92.3
48.5
58.2
Males
Females
Experimental:
Guppies transplanted to pools
with killifish as predators
36.8 CONNECTION: Principles of population
ecology have practical applications
 Sustainable resource management involves
– harvesting crops and
– eliminating damage to the resource.
 The cod fishery off Newfoundland
– was overfished,
– collapsed in 1992, and
– still has not recovered.
 Resource managers use population ecology to
determine sustainable yields.
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Yield (thousands of metric tons)
Figure 36.8
900
800
700
600
500
400
300
200
100
0
1960
1970
1980
1990
2000
THE HUMAN POPULATION
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36.9 The human population continues to increase,
but the growth rate is slowing
 The human population
– grew rapidly during the 20th century and
– currently stands at about 7 billion.
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100
80
10
Population increase
8
60
6
40
4
Total population size
20
1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050
Year
2
0
Total population (in billions)
Annual increase (in millions)
Figure 36.9A
36.9 The human population continues to increase,
but the growth rate is slowing
 The demographic transition
– is the shift from high birth and death rates
– to low birth and death rates, and
– has lowered the rate of growth in developed countries.
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Figure 36.9B
Birth or death rate
per 1,000 population
50
40
30
Rate of
increase
20
10
Birth rate
Death rate
0
1900 1925 1950 1975 2000 2025 2050
Year
36.9 The human population continues to increase,
but the growth rate is slowing
 In the developing nations
– death rates have dropped,
– birth rates are still high, and
– these populations are growing rapidly.
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Table 36.9
36.9 The human population continues to increase,
but the growth rate is slowing
 The age structure of a population
– is the proportion of individuals in different age groups and
– affects the future growth of the population.
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36.9 The human population continues to increase,
but the growth rate is slowing
 Population momentum is the continued growth that
occurs
– despite reduced fertility and
– as a result of girls in the 0–14 age group of a previously
expanding population reaching their childbearing years.
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Age
Figure 36.9C
80
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
1985
Male
2010
Female
6 5 4 3 2 1 0 1 2 3 4 5 6
Population in millions
Total population size  76,767,225
Male
2035
Female
5 4 3 2 1 0 1 2 3 4 5
Estimated population in millions
Total population size  112,468,855
Male
Female
5 4 3 2 1 0 1 2 3 4 5
Projected population in millions
Total population size  139,457,070
Age
Figure 36.9C_1
80
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
1985
Male
Female
6 5 4 3 2 1 0 1 2 3 4 5 6
Population in millions
Total population size  76,767,225
Age
Figure 36.9C_2
80
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
2010
Male
Female
5 4 3 2 1 0 1 2 3 4 5
Estimated population in millions
Total population size  112,468,855
Age
Figure 36.9C_3
80
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
2035
Male
Female
5 4 3 2 1 0 1 2 3 4 5
Projected population in millions
Total population size  139,457,070
36.10 CONNECTION: Age structures reveal
social and economic trends
 Age-structure diagrams reveal
– a population’s growth trends and
– social conditions.
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Figure 36.10
Age
Birth years
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
1985
Male Female
before 1901
1901–1905
1906–10
1911–15
1916–20
1921–25
1926–30
1931–35
1936–40
1941–45
1946–50
1951–55
1956–60
1961–65
1966–70
1971–75
1976–80
1981–85
Birth years
2010
Male Female
before 1926
1926–30
1931–35
1936–40
1941–45
1946–50
1951–55
1956–60
1961–65
1966–70
1971–75
1976–80
1981–85
1986–90
1991–95
1996–2000
2001–2005
2006–2010
12 10 8 6 4 2 0 2 4 6 8 10 12
Population in millions
Total population size  238,466,283
Birth years
2035
Male Female
before 1951
1951–55
1956–60
1961–65
1966–70
1971–75
1976–80
1981–85
1986–90
1991–95
1996–2000
2001–05
2006–10
2011–15
2016–20
2021–25
2026–30
2031–35
12 10 8 6 4 2 0 2 4 6 8 10 12
Estimated population in millions
Total population size  310,232,863
12 10 8 6 4 2 0 2 4 6 8 10 12
Projected population in millions
Total population size  389,531,156
Figure 36.10_1
Age
Birth years
1985
Male Female
before 1901
85
80–84
1901–1905
75–79
1906–10
1911–15
70–74
1916–20
65–69
1921–25
60–64
1926–30
55–59
1931–35
50–54
1936–40
45–49
1941–45
40–44
1946–50
35–39
30–34 1951–55
25–29 1956–60
20–24 1961–65
15–19 1966–70
10–14 1971–75
1976–80
5–9
1981–85
0–4
12 10 8 6 4 2 0 2 4 6 8 10 12
Population in millions
Total population size  238,466,283
Figure 36.10_2
Age
Birth years
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
2010
Male Female
before 1926
1926–30
1931–35
1936–40
1941–45
1946–50
1951–55
1956–60
1961–65
1966–70
1971–75
1976–80
1981–85
1986–90
1991–95
1996–2000
2001–2005
2006–2010
12 10 8 6 4 2 0 2 4 6 8 10 12
Estimated population in millions
Total population size  310,232,863
Figure 36.10_3
Age
Birth years
2035
Male Female
before 1951
85
80–84
1951–55
75–79
1956–60
70–74
1961–65
1966–70
65–69
1971–75
60–64
1976–80
55–59
1981–85
50–54
1986–90
45–49
40–44 1991–95
35–39 1996–2000
30–34
2001–05
25–29 2006–10
20–24 2011–15
15–19 2016–20
10–14 2021–25
5–9 2026–30
0–4 2031–35
12 10 8 6 4 2 0 2 4 6 8 10 12
Projected population in millions
Total population size  389,531,156
36.11 CONNECTION: An ecological footprint is a
measure of resource consumption
 The U.S. Census Bureau projects a global
population of
– 8 billion people within the next 20 years and
– 9.5 billion by mid-21st century.
 Do we have sufficient resources to sustain 8 or 9
billion people?
 To accommodate all the people expected to live on
our planet by 2025, the world will have to double
food production.
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36.11 CONNECTION: An ecological footprint is a
measure of resource consumption
 An ecological footprint is an estimate of the
amount of land required to provide the raw materials
an individual or a nation consumes, including
– food,
– fuel,
– water,
– housing, and
– waste disposal.
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36.11 CONNECTION: An ecological footprint is a
measure of resource consumption
 The United States
– has a very large ecological footprint, much greater than
its own land, and
– is running on a large ecological deficit.
 Some researchers estimate that
– if everyone on Earth had the same standard of living as
people living in the United States,
– we would need the resources of 4.5 planet Earths.
© 2012 Pearson Education, Inc.
Figure 36.11A
Figure 36.11A_1
Figure 36.11A_2
Figure 36.11B
Ecological Footprints
(gha per capita)
0–1.5
1.5–3.0
3.0–4.5
4.5–6.0
6.0–7.5
7.5–9.0
9.0–10.5
 10.5
Insufficient data
You should now be able to
1. Define a population and population ecology.
2. Define population density and describe different
types of dispersion patterns.
3. Explain how life tables are used to track mortality
and survivorship in populations.
4. Compare Type I, Type II, and Type III survivorship
curves.
5. Describe and compare the exponential and logistic
population growth models, illustrating both with
examples.
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You should now be able to
6.
Explain the concept of carrying capacity.
7.
Describe the factors that regulate growth in
natural populations.
8.
Define boom-and-bust cycles, explain why they
occur, and provide examples.
9.
Explain how life history traits vary with
environmental conditions and with population
density.
10. Compare r-selection and K-selection and indicate
examples of each.
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You should now be able to
11. Describe the major challenges inherent in
managing populations.
12. Explain how the structure of the world’s human
population has changed and continues to change.
13. Explain how the age structure of a population can
be used to predict changes in population size and
social conditions.
14. Explain the concept of an ecological footprint.
Describe the uneven use of natural resources in
the world.
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Percentage of survivors
Figure 36.UN01
Few large offspring,
low mortality I
until old age
II
Many small
offspring,
high mortality III
Percentage of maximum life span
Age
Figure 36.UN02
80
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
2010
1985
Male
Female
Male
Female
6 5 4 3 2 1 0 1 2 3 4 5 6
5 4 3 2 1 0 1 2 3 4 5
Population in millions
Total population
size  76,767,225
Population in millions
Total population
size  112,468,855
Figure 36.UN03
(K  N)
G  rN
K
Figure 36.UN04
II
Birth or death rate
I
Time
III
IV
Figure 36.UN05