1. Biology Sylvia S. Mader Michael Windelspecht
Chapter 44
Population Ecology
Lecture Outline
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2. Outline 44.1 Scope of Ecology 44.2 Demographics of Populations
44.3 Population Growth Models
44.4 Regulation of Population Size
44.5 Life History Patterns
44.6 Human Population Growth 2

3. 44.1 Scope of Ecology Ecology
The study of the interactions of organisms with
Other organisms and the physical environment
Habitat - Place where an organism lives
Population - All the individuals of a species within a particular space
Community – Various populations of multiple species interacting with each other
Ecosystem - Community interacting with the environment
Biosphere - All the communities on Earth whose members exist in air and water and on land

4. © David Hall/Photo Researchers, Inc.
Ecological Levels
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Organism
Population
Community
Ecosystem
© David Hall/Photo Researchers, Inc.

5. 44.2 Demographics of Populations
Demography is the statistical study of a population
Demography includes
Population density
Population distribution
Growth rate of a population 5

6. Demographics of Populations
Density and Distribution
Population Density - Number of individuals per unit area
Population Distribution - Pattern of dispersal of individuals across an area of interest
Limiting factors are environmental aspects that particularly determine where an organism lives

7. Distribution Patterns of the Creosote Bush
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Young, small
shrubs
a. Mature desert shrubs
Medium
shrubs
b. Clumped
c. Random
Large
shrubs
d. Uniform
(a): © The McGraw Hill Companies, Inc. Evelyn Jo Johnson, photographer

8. Demographics of Populations
Population Growth
The rate of natural increase depends on
The number of individuals born each year, and
The number of individuals who die each year

9. Demographics of Populations
Population Growth (continued)
Biotic Potential
The maximum rate of natural increase for a population that can occur when resources are unlimited
Biotic potential depends on factors that influence the population’s reproduction, including
The usual number of offspring surviving to reproductive age
The amount of competition within the population
Age of and number of reproductive opportunities
Presence of disease and predators 9

10. Biotic Potential
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b.
(mice): © E. R. Degginger/Photo Researchers, Inc.; (rhinos): © Corbis RF

11. Demographics of Populations
Mortality Patterns
A cohort
Composed of all the members of a population born at the same time
Life tables demonstrate how many members of a cohort are still alive after certain intervals of time
Survivorship
The probability that newborn individuals of a cohort will survive to a particular age
Survivorship Curves
A plot of the number of organisms surviving at each age

12. A Life Table for a Bluegrass Cohort

13. Demographics of Populations
Survivorship Curves
Type I
Characteristic of a population in which most individuals survive past the midpoint of the life span and death does not come until the end of the life span
Type II
Death is linear over time (unrelated to age)
Type III
Typical of a population in which most individuals die very young

14. Survivorship Curves 1,000 1,000 I Death occurs after midpoint. 100 100
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1,000
1,000 I
Death occurs after midpoint.
100
100 I II
Death unrelated to age. II
Number of Survivors
III
Number of Survivors 10 10
III
Death comes early on. 50
100 50
100
Percent of Life Span
Percent of Life Span a.
b. Bluegrasses
1,000
1 million
100
10,000
Number of Survivors 10
100
Number of Survivors 50
100 50
100
Percent of Life Span
Percent of Life Span
c. Lizards
d. Mosquitoes
b: © Holt Studios/Photo Researchers, Inc.; c: © Bruce M. Johnson; d: © Digital Vison/Getty RF Images

15. Demographics of Populations
Age Distribution
The proportion of the population that falls into various age categories
There are three major age groups
Prereproductive
Reproductive
Postreprodutive
At least three age structure diagrams are possible
Increasing population
Stable population
Decreasing population

16. Age Structure Diagrams
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Age Structure
Postreproductive Ages
Reproductive Ages
Prereproductive Ages
Increasing Population
Stable Population
Decreasing Population

17. 44.3 Population Growth Models
Two working models for population growth:
Semelparity
Members of a population have only a single reproductive event in their lifetime
Ex: insects
Iteroparity
Members of the population experience many reproductive events throughout their lifetime
Ex: most vertebrates, shrubs, and trees 17

18. Patterns of Reproduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b.
a: © Breck P. Kent/Animals Animals/Earth Scenes; b: © Doug Sokell/Visuals Unlimited

19. Population Growth Models
Exponential Growth
Rate of population growth increases as the total number of females increases
Biotic potential is having full effect and birthrate is a maximum during exponential growth
Phases of an exponential growth curve
During the lag phase, growth is small because the population is small.
During the exponential growth phase, growth is accelerating. 19

20. Model for Exponential Growth
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Generation
Population
Size
Number of
Females
10.0 5 1
24.0 12 2
57.6
28.8 3
138.2
69.1 4
331.7
165.9 5
796.1
398.1 6
1,910.6
955.3 7
4,585.4
2292.7 8
11,005.0
5502.5 9
26,412.0 10
63,388.8 a. 70 60
R = 2.4 50 40
exponential growth
Population (thousands) 30 20 10
lag 1 2 3 4 5 6 7 8 9 10
Generations b.
To calculate population size from year to year, use this
formula:
Nt+1 = RNt
Nt = number of females already present
R = net reproductive rate
Nt+1 = population size the following year c.

21. Population Growth Models
Logistic growth
Occurs when limiting environmental factors oppose growth
Phases of a logistic growth curve
During the lag phase, growth is slow because the population is small.
During the exponential growth phase, growth is accelerating.
During the deceleration phase, growth slows down.
During the stable equilibrium phase, there is little if any growth.

22. Model for Logistic Growth
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Growth of Yeast Cells in Laboratory Culture
Time (t )
(hours)
Number of
individuals (N)
Number of individuals
added per 2-hour period
D N
D t
9.6 2
29.0
19.4 4
71.1
42.1 6
174.6
103.5 8
350.7
176.1 10
513.3
162.6 12
594.4
81.1 14
640.8
46.4 16
655.9
15.1 18
661.8
5.9 a.
700
600
deceleration
stable
equilibrium
phase
500
Number of Yeast Cells
400
exponential
growth
300
200
lag
100 2 4 6 8 10 12 14 16 18
Time (hours) b.
To calculate population growth as time passes, use this
formula: N
= rN
K – N t K
N = population size
N/t = change in population size
r = rate of natural increase
K = carrying capacity
K – N = effect of carrying capacity on population growth K c.

23. 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

24. 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

25. Density-independent Effects
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a. Low density of mice
b. High density of mice

26. Density-dependent Effect
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2,000
decline as
a result
of sudden
resource
depletion
1,500
exponential
growth
Number of Reindeer
1,000
500
1910
1920
1930
1940
1950
© Paul Janosi/Valan Photos

27. Density-dependent Effects -- Competition
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a. Low density of birds
b. High density of birds

28. Density-dependent Effects -- Predation
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a. Low density of mice
b. High density of mice

29. 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.

30. 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.

31. 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 K-selection. 31

32. 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 32

33. 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

34. Life History Strategies
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Opportunistic Species
(r-strategist)
Equilibrium Species
(K-strategist)
• Small individuals
• Large individuals
• Short life span
• Long life span
• Fast to mature
• Slow to mature
• Many offspring
• Few and large offspring
• Little or no care of
offspring
• Much care of offspring
• Most young survive to
reproductive age
• Many offspring die
before reproducing
• Adapted to stable
environment
• Early reproductive age
(dandelions): © Ted Levin/Animals Animals; (bears): ©Michio Hoshino/Minden Pictures

35. 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.

36. 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

37. White-tailed Deer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b.
(a): © Tony Campbell/Shutterstock Images; (b): © Altrendo Images/Getty Images

38. 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
Billion
Billion
Billion
Billion

39. 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.

40. 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 40

41. World Population Growth
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highest growth
lowest growth 8
Billions of People 6 4
less-developed countries 2
more-developed countries
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

42. 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

43. Age Structure Diagrams
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80+
75–79
70–74
65–69
postreproductive
60–64
55–59
50–54
45–49
Age (in years)
40–44
35–39
30–34
reproductive
25–29
20–24
15–19
10–14
prereproductive
5–9
0–4
Millions
a. More-developed countries (MDCs)
80+
75–79
70–74
65–69
postreproductive
60–64
55–59
50–54
45–49
Age (in years)
40–44
35–39
30–34
reproductive
25–29
20–24
15–19
10–14
5–9
0–4
300
250
200
150
100 50 50
100
150
200
250
300
Millions
b. Less-developed countries (LDCs)
c: © Still Pictures/Peter Arnold, Inc. c.

44. 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

45. Environmental Impact Caused by MDCs & LDCs
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Population
Hazardous Waste Production
Consumption
fossil fuels
paper
LDCs
40%
LDCs
10%
LDCs
25%
MDCs
22%
MDCs
60%
metals
MDCs
75%
LDCs
78%
MDCs
90%
LDCs
20%
MDCs
80% a. b.
MDCs = more-developed countries
LDCs = less-developed countries c.