Chapter 36 Population Ecology Individual emperor penguins face the rigors of the Antarctic climate...
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Transcript of Chapter 36 Population Ecology Individual emperor penguins face the rigors of the Antarctic climate...
Chapter 36 Population Ecology
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.
© 2012 Pearson Education, Inc.
POPULATION STRUCTURE AND DYNAMICS
Population ecologists study natural 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.
© 2012 Pearson Education, Inc.
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.
36.1 Population ecology is the study of how and why populations change
© 2012 Pearson Education, Inc.
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.
36.1 Population ecology is the study of how and why populations change
© 2012 Pearson Education, Inc.
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.
© 2012 Pearson Education, Inc.
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
© 2012 Pearson Education, Inc.
Dispersion patterns can be clumped, uniform, or random.
– In a clumped pattern
– resources are often unequally distributed and
– individuals are grouped in patches.
36.2 Density and dispersion patterns are important population variables
© 2012 Pearson Education, Inc.
Figure 36.2A Clumped dispersion of ochre sea stars at low tide
In a uniform pattern, individuals are
– most likely interacting and
– equally spaced in the environment.
36.2 Density and dispersion patterns are important population variables
© 2012 Pearson Education, Inc.
Figure 36.2B Uniform dispersion of sunbathers at Coney Island
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
© 2012 Pearson Education, Inc.
Figure 36.2C Random dispersion of dandelions
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
© 2012 Pearson Education, Inc.
Table 36.3
Figure 36.3 Three types of survivorship curves
Percentage of maximum life span50 1000
0.1
1
10
100
III
II
IP
erce
nta
ge
of
surv
ivo
rs (
log
sca
le)
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.
© 2012 Pearson Education, Inc.
Figure 36.4A Exponential growth of rabbits
Time (months)
Po
pu
lati
on
siz
e (N
)
0 1 2 3 4 5 6 7 8 9 1011 120
50
100
150
200
250
300
350
400
450
500
Table 36.4A
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.
36.4 Idealized models predict patterns of population growth
© 2012 Pearson Education, Inc.
G = rN
(K N)
K
Figure 36.4B Logistic growth of a population of fur seals
Year1915 1925 1935 1945
0
2
4
6
8
10B
ree
din
g m
ale
fu
r s
eals
(th
ou
san
ds)
Figure 36.4C Logistic growth and exponential growth compared
G rN
K
0Time
Nu
mb
er o
f in
div
idu
als
(N)
G rN (K N)K
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, density-dependent rates result in
– declining births and
– increases in deaths.
© 2012 Pearson Education, Inc.
Figure 36.5A Declining reproductive success of song sparrows (inset) with increasing population density
Density of females 0 10 20 30 40 50 60 70 80
Data from P. Arcese et al., Stability, Regulation, and the Determination of Abundancein an Insular Song Sparrow Population. Ecology 73: 805–882 (1992).
6
5
4
3
2
1
0Mea
n n
um
be
r o
f o
ffs
pri
ng
per
fe
mal
e
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.
36.5 Multiple factors may limit population growth
© 2012 Pearson Education, Inc.
Limiting factors may include
– food,
– nutrients,
– retreats for safety, or
– nesting or denning sites.
36.5 Multiple factors may limit population growth
© 2012 Pearson Education, Inc.
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).
36.5 Multiple factors may limit population growth
© 2012 Pearson Education, Inc.
Figure 36.5C Weather change as a density-independent factor limiting aphid population growth
Month
Exponentialgrowth
Suddendecline
Apr May Jun Jul Aug Sep Oct Nov Dec
Nu
mb
er o
f ap
hid
s
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.
© 2012 Pearson Education, Inc.
Figure 36.6 Population cycles of the snowshoe hare and the lynx
Snowshoe hare
Lynx
Year1850 1875 1900 1925
0
3
6
9
Lyn
x p
op
ula
tio
n s
ize
(th
ou
san
ds
)
0
40
80
120
160
Har
e p
op
ula
tio
n s
ize
(th
ou
san
ds
)
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.
© 2012 Pearson Education, Inc.
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.
© 2012 Pearson Education, Inc.
36.7 EVOLUTION CONNECTION: Evolution shapes life histories
A long-term project on life histories
– 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.
© 2012 Pearson Education, Inc.
Figure 36.7 The effect of predation on the life history traits of guppies
Pool 1Predator: Killifish;preys onsmallguppies
Guppies:Larger atsexual maturity
Pool 2Predator: Pike-
cichlid;preys on large guppies
Guppies: Smaller atsexual maturity
Hypothesis: Predator feeding preferences caused difference in life historytraits of guppy populations.
Pool 3Pools with killifishbut no guppiesprior to transplant
Results
Experiment:Transplantguppies
Males Females
Males Females
Control:Guppies from pools withpike-cichlids as predators
Experimental:Guppies transplanted to poolswith killifish as predators
92.3
185.6161.5
85.7
76.1
58.248.5
67.5
200160120
8040
4020
6080
100
Ag
e o
f g
up
pie
sat
mat
uri
ty (
day
s)M
ass
of
gu
pp
ies
at m
atu
rity
(m
g)
36.8 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.
© 2012 Pearson Education, Inc.
Figure 36.8 Collapse of northern cod fishery off Newfoundland
1960 1970 1980 1990 20000
100
200
300
400
500
600
700
800
900Y
ield
(th
ou
san
ds
of
met
ric
ton
s)
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.
© 2012 Pearson Education, Inc.
Figure 36.9A Five centuries of human population growth, projected to 2050
Population increase
Total population size
Year1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 2000 2050
0
2
4
6
8
10
To
tal
po
pu
lati
on
(in
bil
lio
ns)
An
nu
al i
ncr
ease
(in
mil
lio
ns)
20
40
60
80
100
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.
© 2012 Pearson Education, Inc.
Figure 36.9B Demographic transition in Mexico
1900 1925 1950 1975 2000 2025 2050Year
Rate ofincrease
Birth rateDeath rate
0
10
20
30
40
50B
irth
or
dea
th r
ate
per
1,0
00 p
op
ula
tio
n
In the developing nations
– death rates have dropped,
– birth rates are still high, and
– these populations are growing rapidly.
36.9 The human population continues to increase, but the growth rate is slowing
© 2012 Pearson Education, Inc.
Table 36.9
The age structure of a population
– is the proportion of individuals in different age groups and
– affects the future growth of the population.
36.9 The human population continues to increase, but the growth rate is slowing
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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.
36.9 The human population continues to increase, but the growth rate is slowing
© 2012 Pearson Education, Inc.
Figure 36.9C Population momentum in Mexico due to increased proportion of women of childbearing age
1989 2012
MaleMale Female
Ag
e
80+75–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–14
5–90–4
6 5 4 3 2 1 0 1 2 3 4 5 6
Population in millionsTotal population size = 83,366,836
5 4 3 2 1 0 1 2 3 4 5 5 4 3 2 1 0 1 2 3 4 5
Estimated population in millionsTotal population size = 114,975,406
Projected population in millions
Total population size = 139,457,070
Adapted from International Data Base, U.S. Census Bureau (2013).
Female Male Female
2035
36.10 Age structures reveal social and economic trends
Age-structure diagrams reveal
– a population’s growth trends and
– social conditions.
© 2012 Pearson Education, Inc.
Figure 36.10 Age structures for the United States in 1985, 2010 (estimated), and 2035 (projected). Baby boom after war (tan) will result in older population structure with stress on social security and medicaid.
1989Male Female
Ag
e
85+
75–7970–7465–6960–6455–5950–5445–4940–4435–3930–3425–2920–2415–1910–14
5–90–4
12 10 8 6 4 2 0 2 4 6 8 10 12
Population in millionsTotal population size = 246,819,230
80–84
Birth years
Data from International Data Base, U.S. Census Bureau website, (2013).
2012Male FemaleBirth years
2035Male FemaleBirth years
Estimated population in millionsTotal population size = 313,847,465
Projected population in millionsTotal population size = 389,531,156
12 10 8 6 4 2 0 2 4 6 8 10 12 12 10 8 6 4 2 0 2 4 6 8 10 12
before 19051905–19091910–14
1915–191920–24
1925–291930–34
1935–391940–44
1945–491950–54
1955–591960–641965–691970–74
1975–791980–84
1985–89
before 19281928–32
1933–371938–42
1943–471948–52
1953–571958–621963–671968–721973–77
1978–821983–87
1988–921993–97
1998–20022003–20072008–2012
before 19511951–55
1956–601961–65
1966–701971–75
1976–801981–85
1986–901991–95
1996–20002001–05
2011–152016–202021–252026–302031–35
2006–10
36.11 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.
© 2012 Pearson Education, Inc.
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.
36.11 CONNECTION: An ecological footprint is a measure of resource consumption
© 2012 Pearson Education, Inc.
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.
36.11 CONNECTION: An ecological footprint is a measure of resource consumption
© 2012 Pearson Education, Inc.
Figure 36.11B
Worldaverage
Earth’s biocapacity
Afghan
ista
n
Haiti
India
Colom
bia
Uzbek
ista
n
China
South A
frica
Argen
tina
Mex
ico
United K
ingdom
Austra
lia
United S
tate
s
Adapted from Living Planet Report 2012: Biodiversity, Biocapacity, and Better Choices, World Wildlife Fund (2012).
Ec
olo
gic
al F
oo
tpri
nt
(glo
bal
hec
tare
s p
er
per
so
n)
8
7
6
5
4
3
2
1
0