Chapter 52

Report
Chapter 52 (pgs. 1151- 1172)
Population Ecology
AP minknow
•How density, dispersion, and demographics can
describe a population.
•The differences between exponential and logistic
models of population growth.
•How density-dependent and density-independent
factors can control population growth
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Characteristics of Populations
1.Define the scope of population ecology
2.Define and distinguish between density and dispersion.
3.Explain how ecologists measure the density of a species.
4.Describe conditions that may result in the clumped dispersion,
uniform dispersion, and random dispersion of populations.
• 5.Describe the characteristics of populations that exhibit Type I,
Type II, and Type III survivorship curves.
• 6.Describe the characteristics of populations that exhibit Type I,
Type II, and Type III survivorship curves.
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Life History Traits
7.Define and distinguish between semelparity and iteroparity.
8.Explain how limited resources affect life histories.
9.Give examples of the trade-off between reproduction and survival.
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Population Growth
10.Compare the geometric model of population growth with the logistic
model.
11.Explain how an environment's carrying capacity affects the intrinsic rate
of increase of a population.
12.Distinguish between r-selected populations and K-selected populations.
13.Explain how a "stressful" environment may alter the standard r-selection
and K-selection characteristics.
Population-Limiting Factors
14.Explain how density-dependent factors affect population growth.
15.Explain how density-dependent and density-independent factors may
work together to control a population's growth.
16.Explain how predation can affect life history through natural selection.
17.Describe several boom-and-bust population cycles, noting possible
causes and consequences of the fluctuations.
Human Population Growth
18.Describe the history of human population growth.
19.Define the demographic transition.
20.Compare the age structures of Italy, Kenya, and the United States.
Describe the possible consequences for each country.
21.Describe the problems associated with estimating Earth's carrying
capacity.
• Population ecology is
the study of
populations in
relation to
environment
– Including
environmental
influences on
population density
and distribution, age
structure, and
variations in
population size
52.1: Dynamic biological processes influence population
density, dispersion, and demography
A population
• A population
– Is a group of
individuals of a
single species
living in the same
general area
Density and Dispersion
• Density
– Is the number of individuals per unit area
or volume
• Dispersion
– Is the pattern of spacing among
individuals within the boundaries of the
population
Density: A dynamic perspective.
• Determining the density of
natural populations
– Is possible, but difficult to
accomplish
Births and immigration
add individuals to a
population.
Births
Immigration
• In most cases
– It is impractical or impossible to
count all individuals in a
population
PopuIation
size
• Density is the result of a
dynamic interplay
– Between processes that add
individuals to a population and
those that remove individuals
from it
Emigration
Deaths
Deaths and
emigration remove
individuals from a
population.
Patterns of Dispersion
• Environmental and
social factors
– Influence the spacing
of individuals in a
population.
– There are three
different Patterns of
Dispersion
• Clumped Dispersion
• Uniform Dispersion
• Random Dispersion
• A clumped dispersion
– Is one in which individuals aggregate in
patches
– May be influenced by resource availability and
behavior
(a) Clumped.
For many animals, such as these
wolves, living in groups increases the
effectiveness of hunting, spreads the work of
protecting and caring for young, and helps
exclude other individuals from their territory.
Figure 52.3a
• A uniform dispersion
– Is one in which individuals are evenly
distributed
– May be influenced by social interactions
such as territoriality
(b) Uniform.
Birds nesting on small islands,
such as these king penguins on South
Georgia Island in the South Atlantic
Ocean, often exhibit uniform spacing,
maintained by aggressive interactions
between neighbors.
Figure 52.3b
• A random dispersion
– Is one in which the position of each individual
is independent of other individuals
Figure 52.3c
(c) Random. Dandelions grow
from windblown seeds that land
at random and later germinate.
Life Tables
• A life table
– Is an age-specific summary of the survival pattern of a
population
– Is best constructed by following the fate of a cohort
Survivorship Curves
•
A survivorship curve
– Is a graphic way of representing the data in a life table
Number of survivors (log scale)
1000
100
Females
10
Males
1
0
2
4
6
Age (years)
Figure 52.4
8
10
• Survivorship curves can be classified into
three general types
Number of survivors (log scale)
– Type I, Type II, and Type III
1,000
I
100
Many species fall
somewhere between
these basic types of
survivorship curves.
II
10
III
1
0
Figure 52.5
50
Percentage of maximum life span
100
Some invertebrates,
such as crabs, show a
“stair-stepped” curve,
with increased mortality
during molts.
52.2
Life histories are highly diverse, but
they exhibit patterns in their variability.
•
Life histories entail three basic
variables:
– when reproduction begins
– how often the organism reproduces
– how many offspring are produced
during each reproductive episode.
• These histories are evolutionary
outcomes reflected in the
development, physiology, and
behavior of an organism.
•
Some organisms, such as the agave
plant, exhibit semelparity. Big Bang
Production. (then death)
•
By contrast, some organisms exhibit
iteroparity.
– They produce only a few offspring
during repeated reproductive
episodes.
• Some plants produce a large number of
small seeds
– Ensuring that at least some of them will grow
and eventually reproduce
(a) Most weedy plants, such as this dandelion, grow quickly and produce a large
number of seeds, ensuring that at least some
will grow into plants and eventually produce seeds themselves.
Figure 52.8a
• Other types of plants produce a moderate
number of large seeds
– That provide a large store of energy that will
help seedlings become established
(b) Some plants, such as this coconut palm, produce a moderate number of very
large seeds. The large endosperm provides
nutrients for the embryo, an adaptation that helps ensure the success of a
relatively large fraction of offspring.
Figure 52.8b
What factors contribute to the evolution of
semelparity versus iteroparity?
• In other words, how much does an individual
gain in reproductive success through one
pattern versus the other?
• The critical factor is survival rate of the offspring.
• When the survival of offspring is low, as in highly
variable or unpredictable environments, bigbang reproduction (semelparity) is favored.
• Repeated reproduction (iteroparity) is favored in
dependable environments where competition for
resources is intense.
• In such environments, a few, well-provisioned offspring have
a better chance of surviving to reproductive age.
Population Growth is measured by
Per Capita Rate of Increase
• If immigration and emigration are ignored
– A population’s growth rate (per capita
increase) equals birth rate minus death rate
Growth rate = rN
It can be found using the
equation---
dN
dt
 rN
Exponential Population Growth
•Exponential population growth
Is population increase under idealized conditions
•Under these conditions
•The rate of reproduction is at its maximum, called
the intrinsic rate of increase
• Exponential
population growth
– Results in a Jshaped curve
dN 
dt rmaxN
Figure 52.9
Population size (N)
2,000
dN 
dt 1.0N
1,500
dN 
0.5N
dt
1,000
500
0
0
10
5
Number of generations
15
The J-shaped curve of exponential
growth
• Is characteristic of some populations that are
rebounding
Elephant population
8,000
6,000
4,000
2,000
0
1900
Figure 52.10
1920
1940
Year
1960
1980
52.4: The logistic growth model includes
the concept of carrying capacity
Exponential growth
–
Cannot be sustained
for long in any
population
• A more realistic
population model
–
Limits growth by
incorporating
carrying capacity
• Carrying capacity (K)
–
Is the maximum
population size the
environment can
support
The Logistic Growth Model
• In the logistic population growth model
– The per capita rate of increase declines as
carrying capacity is reached
Maximum
Per capita rate of
increase (r)
We construct the logistic
model by starting with the
exponential model
And adding an
expression that reduces
the per capita rate of
increase as N increases
Positive
0
NK
Negative
Population size (N)
The logistic growth equation
Includes K, the
carrying
capacity
(K  N)
dN
 rmax N
dt
K
Table 52.3
• The logistic model of population growth
– Produces a sigmoid (S-shaped) curve
2,000
dN
dt
Population size (N)
1,500
 1.0N
Exponential
growth
K  1,500
Logistic growth
1,000
dN
dt
 1.0N
1,500  N
1,500
500
0
0
Figure 52.12
5
10
Number of generations
15
2. As N approaches K for a certain
population, which of the following is
predicted by the logistic equation?
–
–
–
–
–
The growth rate will not change.
The growth rate will approach zero.
The population will show an Allee effect.
The population will increase exponentially.
The carrying capacity of the environment will
increase.
The Logistic Model and Real
Populations
Number of
Paramecium/ml
1,000
• The growth of
laboratory populations
of paramecia
– Before settling down to
a relatively stable
density
• Some populations
– Fluctuate greatly
around K
400
200
0
0
5
10
Time (days)
15
0 20 40 60 80 100 120 140 160
Time (days)
80
60
Number of
females
• Some populations
overshoot K
600
Number of
Daphnia/50 ml
– Fits an S-shaped curve
180
150
120
90
60
30
0
800
40
20
0
1975
1980
1985
1990
Time (years)
1995
2000
The Logistic Model and Life
Histories
• Life history traits favored by natural selection
– May vary with population density and
environmental conditions
• K-selection, or density-dependent selection
– Selects for life history traits that are sensitive
to population density
• K-selection tends to maximize population size
and operates in populations living at a density
near K.
• r-selection, or density-independent selection
– Selects for life history traits that maximize
reproduction
• r-selection tends to maximize r, the rate of
increase, and occurs in environments in which
population densities fluctuate well below K, or
when individuals face little competition.
Controversy
52.5: Populations are regulated by a complex interaction of
biotic and abiotic influences
• In density-independent populations
– Birth rate and death rate do not change with population density
• In density-dependent populations
– Birth rates fall and death rates rise with population density
• Determining equilibrium for population density
Density-dependent birth
rate
Birth or death rate per
capita
Density-dependent birth
rate
Densitydependent death
rate
Equilibrium
density
Population density
(a) Both birth rate and death rate change with
population density.
Figure 52.14a–c
Density-dependent
death rate
Densityindependent
death rate
Equilibrium
density
Densityindependent
birth rate
Equilibrium
density
Population density
Population density
(b) Birth rate changes with population
density while death rate is constant.
(c) Death rate changes with population
density while birht rate is constant.
Density-Dependent Population
Regulation
• Density-dependent birth and death rates
– Are an example of negative feedback that regulates
population growth
– Are affected by many different mechanisms
•
•
•
•
•
Competition for Resources
Territoriality
Health (Disease/Parasites)
Predation
Toxic Wastes (think bacteria)
Competition for Resources
• In crowded populations, increasing population
density
– Intensifies intraspecific competition for resources
4.0
3.8
Average clutch size
Average number of seeds
per reproducing individual
(log scale)
10,000
1,000
100
3.6
3.4
3.2
3.0
2.8
0
0
10
100
Seeds planted per m2
(a) Plantain. The number of seeds
produced by plantain (Plantago major)
decreases as density increases.
0
10
20
30
40
50
60
70
Density of females
(b) Song sparrow. Clutch size in the song sparrow
on Mandarte Island, British Columbia, decreases
as density increases and food is in short supply.
80
Territoriality
• Cheetahs are highly territorial
– Using chemical communication to warn other
cheetahs of their boundaries
Figure 52.16
Population Dynamics
• The study of population dynamics
– Focuses on the complex interactions between
biotic and abiotic factors that cause variation
in population size
Stability and Fluctuation
• Long-term
population
studies
FIELD STUDY
Researchers regularly surveyed the population of moose on
Isle Royale, Michigan, from 1960 to 2003. During that time, the lake never froze
over, and so the moose population was isolated from the effects of immigration
and emigration.
RESULTS
Over 43 years, this population experienced
two significant increases and collapses, as well as several less severe
fluctuations in size.
2,500
2,000
Moose population size
– Have
challenged the
hypothesis that
populations of
large
mammals are
relatively
stable over
time
Steady decline probably
caused largely by wolf
predation
1,500
1,000
Dramatic collapse caused by severe winter
weather and food shortage, leading to
starvation of more than 75% of the
population
500
0
1960
1970
1980
Year
1990
2000
CONCLUSION
Figure 52.18
The pattern of population dynamics observed
in this isolated population indicates that various biotic and abiotic factors can
result in dramatic fluctuations over time in a moose population.
Extreme fluctuations in population size
Are typically more common in invertebrates
than in large mammals
Fluctuating
Wind pushing
eggs out to
sea
Cannibalism
Commercial catch (kg) of male crabs
(log scale)
730,000
100,000
10,000
1950
Figure 52.19
1960
1970
Year
1980
1990
Metapopulations and
Immigration
• Metapopulations
• High levels of
immigration combined
with higher survival
– Can result in greater
stability in populations
– Are groups of
populations linked by
immigration and
emigration
50
Number of breeding females
– Are groups of
populations linked by
immigration and
emigration
60
40
Mandarte
island
30
20
10
Small
islands
0
1988
1989
1990
Year
1991
Population Cycles
• Many populations
– Undergo regular boom-and-bust cycles
Three main hypotheses have
been proposed to explain the
lynx/hare cycles.
•The cycles may be affected by
a combination of food resource
limitation and excessive
predation.
Snowshoe hare
160
120
Lynx
80
6
40
3
0
0
1850
Figure 52.21
9
1875
1900
Year
1925
Lynx population size
(thousands)
•The cycles may be due to
predator-prey interactions.
Hare population size
(thousands)
•The cycles may be caused by
food shortage during winter.
Limiting Factors
Density
Dependant
Factors
Density Independent
Factors
52.6: Human population growth has slowed
after centuries of exponential increase
• No population can grow indefinitely
– And humans are no exception
The Global Human Population
5
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)
6
Increased
relatively
slowly until
about 1650
and then
began to
grow
exponentially
Global population Growth Rate
• Though the global population is still growing
– The rate of growth began to slow approximately
40 years ago
2.2
2
Percent increase
1.8
1.6
2003
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1950
Figure 52.23
1975
2000
Year
2025
2050
Age Structure
• One important demographic factor in present and future growth
trends
– Is a country’s age structure, the relative number of individuals at
each age
– Usually presented in Pyramids
Rapid growth
Afghanistan
Male
Female
Slow growth
United States
Male
Female
Decreas
e Italy
Female
Male
Age
Age
85
85
80–84
80–84
75–79
75–79
70–74
70–74
65–69
65–69
60–64
60–64
55–59
55–59
50–54
50–54
45–49
45–49
40–44
40–44
35–39
35–39
30–34
30–34
25–29
25–29
20–24
20–24
15–19
15–19
10–14
10–14
5–9
5–9
0–4
0–4
8 6 4 2 0 2 4 6 8
8 6 4 2 0 2 4 6 8
8 6 4 2 0 2 4 6 8
Percent of population
Percent of population
Percent of population
Figure 52.25
Infant Mortality and Life
Expectancy
• Infant mortality and life expectancy at birth
– Vary widely among developed and developing countries but do
not capture the wide range of the human condition
80
50
Life expectancy (years)
Infant mortality (deaths per 1,000 births)
60
40
30
20
40
20
10
0
0
Developed
countries
Figure 52.26
60
Developing
countries
Developed
countries
Developing
countries
Global Carrying Capacity
• Just how many humans can the biosphere support?
• It is complex and we just don’t know, but we have….
• The ecological
footprint concept
Ecological footprint (ha per person)
Ecological Footprint
16
14
12
10
New Zealand
USA
Germany
– Summarizes the
Australia
8
Netherlands
Japan
Canada
Norway
aggregate land and
6
Sweden
UK
water area needed
4
Spain
World
2
China
to sustain the
India
0
people of a nation
4
2
6
8
10
12
0
Available ecological
capacity (ha per person)
– Is one measure of
how close we are to Figure 52.27
At more than 6 billion people
the carrying
The world is already in
capacity of Earth
ecological deficit
14
16

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