Download Topic 21-Population Dynamics

Chapter 36
Population Dynamics
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
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The Spread of Shakespeare’s Starlings
• The European Starling
– Has become an abundant and
destructive pest in North America
European
starling
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• Starling populations have become very
successful
– And spread throughout North America
since their introduction in 1890
Current
Current
1955
1955
1945
1935
1925
1945
1905
1915
1935
1925
The spread of starlings across North America
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• Population ecology
– Is concerned with changes in population
size and the factors that regulate
populations over time
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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
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POPULATION STRUCTURE AND DYNAMICS
36. 2 Density and dispersion patterns are
important population variables
• Population density
– Is the number of individuals of a species
per unit of area or volume
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• Environmental and social factors
– Influence the spacing of individuals in
various dispersion patterns: clumped,
uniform, or random
Figure 36.2A
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Figure 36.2B
36.3 Life tables track mortality and survivorship in
populations
• Life tables and survivorship curves
–
Predict an individual’s statistical chance of dying
or surviving during each interval of the
individual’s lifetime
Table 36.3
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• The three types of survivorship curves
Percentage of survivors (log scale)
– Reflect species’ differences in
reproduction and mortality
100
I
10
II
1
III
0.1
0
Figure 36.3
50
Percentage of maximum life span
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100
36.4 Idealized models help us understand
population growth
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The Exponential Growth Model
• Exponential growth
– Is the accelerating increase that occurs
when growth is unlimited
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• The equation G  rN describes this J-shaped curve
–
G  the population growth rate
–
r  an organism’s inherent capacity to
reproduce
–
N  the population size
1
= 20
20
2
= 21
40
4
= 22
60
8
= 23
80
16
= 24
100
32
= 25
120 (= 2 hours)
64
= 26
3 hours
512
29
4 hours
4,096
= 212
8 hours
16,777,216
= 224
12 hours
68,719,476,736
= 236
0 minutes
Figure 36.4A
Number of Cells
=
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70
Number of bacterial cells (N)
Time
60
50
40
30
20
G=rN
10
0
0
20
40
60 80 100
Time (min)
120 140
Limiting Factors and the Logistic Growth Model
• Limiting factors
Breeding male fur seals
(thousands)
– Are environmental factors that restrict
population growth
10
8
6
4
2
0
Figure 36.4B
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1915 1925 1935 1945
Year
• Logistic growth
Is the model that represents the slowing of
population growth as a result of limiting factors
–
Levels off at the carrying capacity, which is the
number of individuals the environment can
support
Number of individuals (N)
–
G=rN
G=rN
K
0
Figure 36.4C
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Time
(K – N)
K
• The equation G  rN(K – N)/K describes a
logistic growth curve
– Where K  carrying capacity and
(K – N)/K accounts for the leveling off of
the curve
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36.5 Multiple factors may limit population growth
• As a population’s density increases
–
Factors such as limited food supply and
increased disease or predation may increase
the death rate, decrease the birth rate, or both
4.0
Clutch size
3.8
3.6
3.4
3.2
3.0
2.8
0
10
20
Figure 36.5A
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30
40
50
Density of females
60
70
80
• Abiotic factors such as weather
– May limit many natural populations
Exponential
growth
Number of aphids
Sudden
decline
Figure 36.5B
Apr
May
Jun
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Jul
Aug
Sep
Oct
Nov
Dec
• Most populations
–
Are probably regulated by a mixture of factors,
and fluctuations in numbers are common
80
Number of females
60
40
20
0
1975
1980
Figure 36.5C
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1985
1990
Time (years)
1995
2000
36.6 Some populations have “boom-and-bust” cycles
• Some populations
Figure 36.6
Snowshoe hare
160
120
Lynx
9
80
6
40
3
0
0
1850
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1875
1900
Year
1925
Lynx population size
(thousands)
Undergo regular boom-and-bust cycles of
growth and decline
Hare population size
(thousands)
–
LIFE HISTORIES AND THEIR EVOLUTION
36.7 Evolution shapes life histories
• An organism’s life history
– Is the series of events from birth through
reproduction to death
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• Populations with so-called r-selection life
history traits
– Produce many offspring and grow rapidly
in unpredictable environments
Figure 36.7A
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• Populations with K-selected traits
– Raise few offspring and maintain
relatively stable populations
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• Life history traits
– Are shaped by natural selection
Experimental
transplant of
guppies
Predator: Killifish;
preys mainly on small,
immature guppies
Guppies: Larger at
sexual maturity than
those in pike-cichlid
pools
Predator: Pike-cichlid;
preys mainly on large,
mature guppies
Figure 36.7B
Guppies: Smaller at
sexual maturity than
those in killifish pools
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CONNECTION
36.8 Principles of population ecology have
practical applications
• Principles of population ecology
– Are useful in managing natural resources
Yield (thousands of metric tons)
900
800
700
600
500
400
300
200
100
0
Figure 36.8
1960
1970
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1980
1990
2000
THE HUMAN POPULATION
CONNECTION
36.9 Human population growth has started to slow after
centuries of exponential increase
• The human population
– Has been growing almost exponentially for
centuries, standing now at about 6.4 billion
5
4
3
2
The Plague
1
Figure 36.9A
8000
B.C.
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4000 3000 2000 1000
B.C. B.C. B.C. B.C.
0
0
1000 2000
A.D. A.D.
Human population size (billions)
6
• The ecological footprint
–
Represents the amount of land per person
needed to support a nation’s resource needs
Ecological footprint (ha per person)
16
14
12
New Zealand
10
Germany
8
Netherlands
Norway
Japan
6
Australia
Canada
Sweden
UK
4
Spain
World
China
India
2
0
0
Figure 36.9B
USA
2
4
6
8
10
12
14
Available ecological capacity (ha per person)
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16
• The ecological capacity of the world
– May already be smaller than the
population’s ecological footprint
Traffic in downtown Cairo, Egypt
Figure 36.9C
Manhattan,
New York City
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Refugee camp in Zaire
36.10 Birth and death rates and age structure affect
population growth
• The demographic transition
–
Is the shift from high birth rates and death
rates to low birth rates and death rates
Birth or death rate per 1,000 population
50
Figure 36.10A
40
30
20
Birth rate
Death rate
10
0
1900
1925
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1950
1975
Year
2000
2025
2050
• The age structure of a population
–
Is the proportion of individuals in different
age-groups
–
Affects its future growth
Age
Rapid growth
Slow growth
Decrease
Afghanistan
United States
Italy
Male
Female
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
Female
Male
Female
Primary
reproductive
ages
8
Figure 36.10B
Male
6
4 2 0 2 4 6
Percent of population
8
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6
4 2 0 2 4 6
Percent of population
6
4
2
0
2
4
Percent of population
6
• Increasing the status of women
– May help to reduce family size
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