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Copyright © 2009 Pearson Education, Inc.
PowerPoint Lectures forBiology: Concepts & Connections, Sixth EditionCampbell, Reece, Taylor, Simon, and Dickey
Chapter 36Chapter 36 Population Ecology
Lecture by Brian R. Shmaefsky
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Introduction: A Tale of Two Fishes
Population ecology is concerned with
– Changes in population size
– Factors that regulate populations over time
It helps explain the biodiversity of an environment
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Ecologists learn the structure and dynamics of natural populations
With this information they are better equipped to
– Develop sustainable food sources
– Assess the impact of human activities
– Balance human needs with the conservation of biodiversity and resources
Introduction: A Tale of Two Fishes
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36.1 Population ecology is the study of how and why populations change
Population
– 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
– Are likely to interact and breed with one another
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A population can be described by the number and distribution of individuals
Population dynamics is the interactions between
– Biotic and abiotic factors
It is the cause of variation in population sizes
– A population increases through birth and immigration
– Death and emigration out of an area decrease the population
36.1 Population ecology is the study of how and why populations change
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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
– The number of oak trees per square kilometer in a forest
– The number of earthworms per cubic meter in forest soil
Ecologists use a variety of sampling techniques to estimate population densities
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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
36.2 Density and dispersion patterns are important population variables
Video: Flapping Geese (clumped)
Video: Albatross Courtship (uniform)
Video: Prokaryotic Flagella (Salmonella typhimurium) (random)
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The dispersion pattern of a population refers to the way individuals are spaced within their area
Dispersion patterns can be
– Clumped
– Uniform
– Random
36.2 Density and dispersion patterns are important population variables
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In a clumped pattern individuals are grouped in patches
36.2 Density and dispersion patterns are important population variables
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In a uniform pattern individuals are equally spaced in the environment
36.2 Density and dispersion patterns are important population variables
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In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way
36.2 Density and dispersion patterns are important population variables
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36. 3 Life tables track survivorship in populations
Life tables track survivorship over the life span of individuals in a population
Survivorship curves plot the proportion of individuals alive at each age
– Type I
– Type II
– Type III
Percentage of maximum life span
Per
cen
tag
e o
f su
rviv
ors
(lo
g s
cale
)
0 50 1000.1
1
10
100
III
II
I
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36.4 Idealized models predict patterns of population growth
Exponential growth model
– The rate of population increases under ideal conditions
– Calculated using the equation G = rN
– G is the growth rate of the population
– N is the population size
– r is the per capita rate of increase
Time (months)
Po
pu
lati
on
siz
e (N
)
0 1 2 3 4 5 6 7 8 9 10 11 120
50
100
150
200
250
300
350
400
450
500
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Logistic growth model
– This growth model takes into account limiting factors
– Limiting factors are environmental factors that restrict population growth
– Formula
36.4 Idealized models predict patterns of population growth
(K N)G = rN
K
Year
Bre
edin
g m
ale
fur
seal
s(t
ho
usa
nd
s)
1915 1925 1935 19450
2
4
6
8
10
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Idealized models describe two kinds of population growth
– Exponential growth
– Logistic growth
36.4 Idealized models predict patterns of population growth
Time
Nu
mb
er o
f in
div
idu
als
(N)
0
K
G = rN
G = rN(K – N)
K
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36.5 Multiple factors may limit population growth
The logistic growth model
– Population growth slows and ceases as population density increases
– Increasing population density results in a decrease in birth rate, an increase in death rate, or both
Density of females
Clu
tch
siz
e
0 10 20 30 40 50 60 70 802.8
3.0
3.2
3.4
3.6
3.8
4.0
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Abiotic factors may reduce population size before other limiting factors become important
36.5 Multiple factors may limit population growth
Apr May Jun Jul Aug Sep Oct Nov Dec
Nu
mb
er o
f ap
hid
s
Exponentialgrowth
Suddendecline
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Most populations fluctuate in numbers
36.5 Multiple factors may limit population growth
Time (years)
Nu
mb
er o
f fe
mal
es
1975 1980 1985 1990 1995 20000
20
40
60
80
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36.6 Some populations have “boom-and-bust” cycles
Some populations fluctuate in density with regularity
Boom-and-bust cycles
– Food shortages
– Predator-prey interactions
Lynx
Snowshoe hare
Ly
nx
po
pu
lati
on
siz
e(t
ho
usa
nd
s)
Ha
re p
op
ula
tio
n s
ize
(th
ou
san
ds)
Year1850 1875 1900 1925
0
40
80
120
160
0
3
6
9
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36.7 EVOLUTION CONNECTION: Evolution shapes life histories
Life history
– Series of events from birth to death
r/K selection
– r-selective traits
– K-selective traits
Males Females
Experimentaltransplant ofguppies
Predator: Killifish; preysmainly on small guppies
Guppies:Larger atsexual maturitythan those inpike-cichlid pools
Pools with killifish,but no guppies priorto transplant
Predator: Pike-cichlid preys mainly on large guppies
Guppies: Smaller at sexual maturity thanthose in killifish pools11 years
later
Mas
s o
f g
up
pie
sat
mat
uri
ty (
mg
)
40
80
120
160
200
67.5 76.1
161.5185.6
Ag
e o
f g
up
pie
sat
mat
uri
ty (
day
s)
Males Females
20
40
60
80100
48.558.2
85.792.3 Control:Guppies from poolswith pike-cichlidsas predators
Experimental:Guppies transplantedto pools with killifishas predators
Predator: Killifish; preysmainly on small guppies
Experimentaltransplant ofguppies
Guppies:Larger atsexual maturitythan those inpike-cichlid pools
Pools with killifish,but no guppies priorto transplant
Predator: Pike-cichlid preys mainly on large guppies
Guppies: Smaller at sexual maturity thanthose in killifish pools
Males Females
Mas
s o
f g
up
pie
sat
mat
uri
ty (
mg
)
Males Females
4080
120160200
67.5 76.1
161.5185.6
Ag
e o
f g
up
pie
sat
mat
uri
ty (
day
s)
2040
60
80100
48.558.2
85.7 92.3 Control:Guppies from poolswith pike-cichlidsas predators
Experimental:Guppies transplantedto pools with killifishas predators
11 yearslater
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36.8 CONNECTION: Principles of population ecology have practical applications
Sustainable resource management
– Maximum sustained yield
1960
Yie
ld (
tho
usa
nd
s o
f m
etri
c to
ns)
1970 1980 1990 20000
100
200
300
400
500
600
700
800
900
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36.9 The human population continues to increase, but the growth rate is slowing
Human population is expected to continue increasing for several decades
95% of the increase is in developing nations
1500
Year
Population increase
Total population size
To
tal p
op
ula
tio
n (
in b
illio
ns
)
1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 20500
2
4
6
8
10
20
40
60
80
100
An
nu
al in
cre
ase
(in
mill
ion
s)
Year
Birth rateDeath rate
Rate of increase (r)
1900 19501925 1975 2000 2025 20500
10
20
30
40
50
Bir
th o
r d
eath
rat
ep
er 1
,000
po
pu
lati
on
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Population momentum of Mexico
36.9 The human population continues to increase, but the growth rate is slowing
0 1 2 3 4 55 4 3 2 1 0 1 2 3 4 55 4 3 2 1
1980
Age
Male Female
80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
Population in millionsTotal population size = 68,347,479
Population in millionsTotal population size = 106,202,903
FemaleMale
2005 2030
FemaleMale
Population in millionsTotal population size = 135,172,155
0 1 2 3 4 55 4 3 2 1
Age
80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
5 4 3 2 1 0 1 2 3 4 5Population in millions
Total population size = 68,347,479
1980
Male Female
5 4 3 2 1 0 1 2 3 4 5
Age
80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
Population in millionsTotal population size = 106,202,903
FemaleMale
2005
5 4 3 2 1 0 1 2 3 4 5
Age
80+75-7970-7465-6960-6455-5950-5445-4940-4435-3930-3425-2920-2415-1910-14
5-90-4
2030
FemaleMale
Population in millionsTotal population size = 135,172,155
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36.10 CONNECTION: Age structures reveal social and economic trends
Age structure diagram
– Reveals a population’s growth trends
Age1980
Birth years Male Female2005 2030
Birth years Male Female Birth years Male Female80+ before 1900 before 1926 before 1951
1951-551926-301901-190575-7970-74 1906-10 1931-35 1956-60
1961-651936-401911-1565-6960-6455-59
1916-20 1941-45 1966-701971-751946-501921-25
50-54 1926-30 1951-55 1976-801981-851956-601931-3545-49
40-44 1936-40 1961-65 1986-901991-951966-701941-4535-39
30-34 1946-50 1971-75 1996-20002001-051976-801951-5525-29
20-24 1956-60 1981-85 2006-102011-151986-901961-6515-19
10-14 1966-70 1991-95 2016-202021-251996-20001971-755-9
0-4 1976-80 2001-2005 2026-30
12 10 8 6 4 2 0 2 4 6 8 10 12Population in millions
Total population size = 363,811,435Population in millions
Total population size = 295,734,134
12 10 8 6 4 2 0 2 4 6 8 10 1212 10 8 6 4 2 0 2 4 6 8 10 12Population in millions
Total population size = 227,726,463
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36.11 CONNECTION: An ecological footprint is a measure of resource consumption
U.S. Census Bureau projection
– 8 billion people within the next 20 years
– 9.5 billion by mid-21st century
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Ecological footprint helps understand resource availability and usage
The United States has a
– Big ecological footprint
– Large ecological deficit
36.11 CONNECTION: An ecological footprint is a measure of resource consumption
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You should now be able to
1. Explain the factors that determine the characteristics of a population
2. Describe exponential growth and the factors that produce logistic growth of a population
3. Explain the limiting factors that influence population growth
4. Distinguish between r- and K-strategies
5. Describe and give examples of the different types of life histories
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6. Explain the factors the determine human population growth
7. Describe the concept of ecological footprint
You should now be able to