Transcript Population Ecology (Part 2)

Population Growth Models
• Carrying Capacity
 The maximum number of individuals of a species
the environment can continuously support
• The closer the population to the carrying capacity, the
more likely its resources will become scarce and that
biotic effects such as competition and predation will
become apparent
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44.4 Regulation of Population Size
• Density-independent Factors
– The population density does not influence the
intensity of the factor’s effect
• Natural disasters
• Density-dependent Factors
– The percentage of the population affected
increases as the population density increases
• Competition
• Predation
• Parasitism
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Density-independent Effects
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a. Low density of mice
b. High density of mice
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Density-dependent Effect
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Number of Reindeer
2,000
1,500
decline as
a result
of sudden
resource
depletion
exponential
growth
1,000
500
0
1910
1920
1930
1940
1950
© Paul Janosi/Valan Photos
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Density-dependent Effects -- Competition
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a. Low density of birds
b. High density of birds
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Density-dependent Effects -- Predation
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a. Low density of mice
b. High density of mice
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44.5 Life History Patterns
• Life histories contain characteristics of a population
such as
–
–
–
–
The number of births per reproduction
The age of reproduction
The life span
The probability of an individual living the entire life span
• Each population distributes energy among its life
span, reproduction events, and care of offspring.
• Related species may have different life history
patterns.
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Parental Care Among Frogs and Toads
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a. Mouth-brooding frog,
Rhinoderma darwinii
b. Strawberry poison arrow frog,
Dendrobates pumilio
c. Midwife toad, Alyces obstetricans
(a): © Michael Fogden/Animals Animals; (b): © Michael Fogden/Animals Animals;
(c): © Tom McHugh/Photo Researchers, Inc.
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Life History Patterns
• r is the rate of natural increase of a population.
• K is the carrying capacity of the environment.
• Some populations are subject to r-selection,
and other populations are subject to Kselection.
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Life History Patterns
• r - Selection
 In unstable or predictable environments, population growth
is controlled by density-independent factors.
 Population size is low relative to K.
• r - Strategists (opportunistic species)






Produce large numbers of offspring
Have a small body size
Mature early
Have a short life span
Do not invest energy in parental care
Tend to be good dispersers and colonizers
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Life History Patterns
• K - Selection
 In stable, predictable environments, population size is
controlled by density-dependent factors.
 Population size tends to be near K.
• K - Strategists (equilibrium species)






Produce small numbers of offspring
Have a large body size
Mature late
Have a long life span
Invest energy in parental care
Tend to be strong competitors
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Life History Strategies
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Opportunistic Species
(r-strategist)
• Small individuals
• Short life span
• Fast to mature
• Many offspring
• Little or no care of
offspring
• Many offspring die
before reproducing
• Early reproductive age
Equilibrium Species
(K-strategist)
• Large individuals
• Long life span
• Slow to mature
• Few and large offspring
• Much care of offspring
• Most young survive to
reproductive age
• Adapted to stable
environment
(dandelions): © Ted Levin/Animals Animals; (bears): ©Michio Hoshino/Minden Pictures
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Ecology Focus: When a Population
Grows Too Large
• White-tailed deer are prolific breeders
– Female deer breed their first year, and once they start
breeding, produce about two young each year of life.
• A century ago, the white-tailed deer population was
less than half a million
• Today, it is well over 200 million
• Natural predators of deer, such as wolves and
mountain lions, are now absent from most regions.
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Ecology Focus: When a Population
Grows Too Large
• Populations that are too large may suffer from
starvation as they deplete their own food
supply
• For example, after deer hunting was banned
on Long Island, New York, the deer population
quickly outgrew available food resources
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White-tailed Deer
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a.
b.
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(a): © Tony Campbell/Shutterstock Images; (b): © Altrendo Images/Getty Images
44.6 Human Population Growth
• The human population is undergoing exponential
growth
 Present size is 6.7 billion people
• The doubling time of the human population is
currently estimated at 52 years
• Population Size




1800
1930
1960
2012
1 Billion
2 Billion
3 Billion
6 Billion
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Human Population Growth
• More-Developed Countries (MDCs)
– North America, Europe, Japan, and Australia
– Slow population growth
– High standard of living
– A demographic transition (decreased death rate
followed by decreased birth rate) has occurred, so
population growth has stabilized.
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Human Population Growth
• Less-Developed Countries (LDCs)
–
–
–
–
Latin America, Africa, and Asia
Rapid population growth
Low standard of living
Strategies to reduce population growth
• Family planning programs
• Social progress, which may reduce the desire for large families
• Delay the onset of childbearing
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World Population Growth
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12
10
highest growth
lowest growth
Billions of People
8
6
4
less-developed countries
2
more-developed countries
0
1750
1800
1850
1900
1950
2008
2250
Year
a.
b.
b(Top): © The McGraw-Hill Companies, Inc./Jill Braaten, photographer; b(Bottom): © Robert Harding/Robert Harding World Imagery/Corbis
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Human Population Growth
• Age Distributions
– Populations of MDCs and LDCs can be divided into
three age groups
• Prereproductive
• Reproductive
• Postreproductive
– MDCs and LDCs have different age structure
diagrams
• Many MDCs have a stable age structure
• Most LDCs have a youthful profile and are experiencing
population growth
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Age Structure Diagrams
Age (in years)
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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
postreproductive
reproductive
prereproductive
Millions
Age (in years)
a. More-developed countries (MDCs)
80+
75–79
70–74
65–69
60–64
55–59
50–54
45–49
postreproductive
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
reproductive
300 250 200 150 100
50
0 50 100 150 200 250 300
Millions
b. Less-developed countries (LDCs)
c.
c: © Still Pictures/Peter Arnold, Inc.
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Human Population Growth
• Population Growth and Environmental Impact
– Environmental impact of a population is measured
in terms of:
• Population size
• Resource consumption per capita
• Resultant pollution due to resource consumption
– There are two types of overpopulation
• Overpopulation due to population growth
• Overpopulation due to increased resource
consumption
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Environmental Impact Caused by
MDCs & LDCs
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Population
Hazardous Waste Production
Consumption
LDCs
40%
LDCs
10%
MDCs
22%
fossil fuels
paper
LDCs
25%
MDCs
60%
metals
MDCs
75%
LDCs
78%
a.
MDCs
90%
LDCs
20%
b.
MDCs = more-developed countries
LDCs = less-developed countries
MDCs
80%
c.
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