1. Chapter 36
Population Ecology

2. Figure 36.0_2
Emperor penguins
Figure 36.0_2 Emperor penguins 2

3. Introduction
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. 3

4. Introduction Population ecologists study natural population
Population ecologists study natural population
structure and
dynamics.
© 2012 Pearson Education, Inc. 4

5. Population Structure and Dynamics The Human Population
Figure 36.0_1
Chapter 36: Big Ideas
1985
Male
Female
Figure 36.0_1 Chapter 36: Big Ideas
Population Structure
and Dynamics
The Human Population 5

6. POPULATION STRUCTURE AND DYNAMICS
POPULATION STRUCTURE AND DYNAMICS
© 2012 Pearson Education, Inc. 6

7. 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A mark-recapture method not specifically addressed in this chapter can be used to estimate the size of a population. The following can serve as a demonstration or an activity for students working in small groups:
a. Provide each group with an opaque bag (brown paper lunch bags work well) of about 200 dried lima beans (or any inexpensive small item that can be marked).
b. Have each group draw out 40 beans.
c. Mark each bean with a distinct pencil or ink mark.
d. Return these marked beans back to the bag.
e. Mix the beans in the bag by shaking or turning the bag. Note: Thorough mixing and random selection is essential to the mark-recapture method. You may wish to note here that this research method does not work well for wildlife populations that are territorial and thus do not mix.
f. Draw out another 40 beans and count the number of marked beans in the sample.
g. The formula for calculating the population size is as follows: The number of marked beans in the first sample  the total number in the second sample  the number of recaptures in the second sample = the population size. Thus, if you started out with exactly 200 beans, sampled 40, marked them, and resampled 40 beans, we would expect that you would recapture 8 marked beans, based on the equation 40  40  8 = 200.
© 2012 Pearson Education, Inc. 7

8. 36.1 Population ecology is the study of how and why populations change
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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A mark-recapture method not specifically addressed in this chapter can be used to estimate the size of a population. The following can serve as a demonstration or an activity for students working in small groups:
a. Provide each group with an opaque bag (brown paper lunch bags work well) of about 200 dried lima beans (or any inexpensive small item that can be marked).
b. Have each group draw out 40 beans.
c. Mark each bean with a distinct pencil or ink mark.
d. Return these marked beans back to the bag.
e. Mix the beans in the bag by shaking or turning the bag. Note: Thorough mixing and random selection is essential to the mark-recapture method. You may wish to note here that this research method does not work well for wildlife populations that are territorial and thus do not mix.
f. Draw out another 40 beans and count the number of marked beans in the sample.
g. The formula for calculating the population size is as follows: The number of marked beans in the first sample  the total number in the second sample  the number of recaptures in the second sample = the population size. Thus, if you started out with exactly 200 beans, sampled 40, marked them, and resampled 40 beans, we would expect that you would recapture 8 marked beans, based on the equation 40  40  8 = 200.
© 2012 Pearson Education, Inc. 8

9. 36.1 Population ecology is the study of how and why populations change
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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A mark-recapture method not specifically addressed in this chapter can be used to estimate the size of a population. The following can serve as a demonstration or an activity for students working in small groups:
a. Provide each group with an opaque bag (brown paper lunch bags work well) of about 200 dried lima beans (or any inexpensive small item that can be marked).
b. Have each group draw out 40 beans.
c. Mark each bean with a distinct pencil or ink mark.
d. Return these marked beans back to the bag.
e. Mix the beans in the bag by shaking or turning the bag. Note: Thorough mixing and random selection is essential to the mark-recapture method. You may wish to note here that this research method does not work well for wildlife populations that are territorial and thus do not mix.
f. Draw out another 40 beans and count the number of marked beans in the sample.
g. The formula for calculating the population size is as follows: The number of marked beans in the first sample  the total number in the second sample  the number of recaptures in the second sample = the population size. Thus, if you started out with exactly 200 beans, sampled 40, marked them, and resampled 40 beans, we would expect that you would recapture 8 marked beans, based on the equation 40  40  8 = 200.
© 2012 Pearson Education, Inc. 9

10. 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A simple application of the dispersion pattern of a population would be to apply the concept to the population of humans on your college or university campus. Would students consider the distribution of people to be clumped, uniform, or random? Most campuses would likely represent a clumped pattern. It might be fun to discuss when, if ever, the human population on your campus represents a uniform or random pattern.
© 2012 Pearson Education, Inc. 10

11. 36.2 Density and dispersion patterns are important population variables
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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A simple application of the dispersion pattern of a population would be to apply the concept to the population of humans on your college or university campus. Would students consider the distribution of people to be clumped, uniform, or random? Most campuses would likely represent a clumped pattern. It might be fun to discuss when, if ever, the human population on your campus represents a uniform or random pattern.
© 2012 Pearson Education, Inc. 11

12. 36.2 Density and dispersion patterns are important population variables
Dispersion patterns can be
clumped,
uniform, or
random.
In a clumped pattern
resources are often unequally distributed and
individuals are grouped in patches.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A simple application of the dispersion pattern of a population would be to apply the concept to the population of humans on your college or university campus. Would students consider the distribution of people to be clumped, uniform, or random? Most campuses would likely represent a clumped pattern. It might be fun to discuss when, if ever, the human population on your campus represents a uniform or random pattern.
© 2012 Pearson Education, Inc. 12

13. Clumped dispersion of ochre sea stars at low tide
Figure 36.2A
Clumped dispersion of ochre sea stars at low tide
Figure 36.2A Clumped dispersion of ochre sea stars at low tide 13

14. Clumped dispersion of schooling fish
Figure 36.2A Clumped dispersion of schooling fish.

15. 36.2 Density and dispersion patterns are important population variables
In a uniform pattern, individuals are
most likely interacting and
equally spaced in the environment.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A simple application of the dispersion pattern of a population would be to apply the concept to the population of humans on your college or university campus. Would students consider the distribution of people to be clumped, uniform, or random? Most campuses would likely represent a clumped pattern. It might be fun to discuss when, if ever, the human population on your campus represents a uniform or random pattern.
© 2012 Pearson Education, Inc. 15

16. Uniform dispersion of nesting king penguins
Figure 36.2B Uniform dispersion of nesting king penguins.

17. 36.2 Density and dispersion patterns are important population variables
In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
A simple application of the dispersion pattern of a population would be to apply the concept to the population of humans on your college or university campus. Would students consider the distribution of people to be clumped, uniform, or random? Most campuses would likely represent a clumped pattern. It might be fun to discuss when, if ever, the human population on your campus represents a uniform or random pattern.
© 2012 Pearson Education, Inc. 17

18. 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
The Centers for Disease Control provide information and life tables for people living in the United States at their website,
© 2012 Pearson Education, Inc. 18

19. Table 36.3
Table 36.3 Life Table for the U.S. Population in 2004 19

20. 36.3 Life tables track survivorship in populations
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
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
The Centers for Disease Control provide information and life tables for people living in the United States at their website,
© 2012 Pearson Education, Inc. 20

21. Percentage of survivors (log scale)
Figure 36.3
100 I 10
Percentage of survivors (log scale) II 1
III
Figure 36.3 Three types of survivorship curves
0.1 50
100
Percentage of maximum life span 21

22. 36.4 Idealized models predict patterns of population growth
There are two models of population growth
The exponential growth model
The logistic growth model
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
Exponential growth in a population is like compounded interest on a bank account. The growth of the account is initially small, but as the interest earns interest, the growth expands. $1,000 invested at 7% interest is worth more than $30,000 in 50 years. Consider assigning students to calculate the value of an interest-bearing investment over a set period of years, as in the example just noted. Many online financial calculators can perform this task.
© 2012 Pearson Education, Inc. 22

23. 36.4 Idealized models predict patterns of population growth
The exponential growth model
Explains the rate of population increase under ideal conditions.
It can be calculated using the following 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
Exponential growth in a population is like compounded interest on a bank account. The growth of the account is initially small, but as the interest earns interest, the growth expands. $1,000 invested at 7% interest is worth more than $30,000 in 50 years. Consider assigning students to calculate the value of an interest-bearing investment over a set period of years, as in the example just noted. Many online financial calculators can perform this task.
© 2012 Pearson Education, Inc. 23

24. Exponential growth of rabbits
Figure 36.4A
Exponential growth of rabbits
500
450
400
350
Population size (N)
300
250
200
Figure 36.4A Exponential growth of rabbits
150
100 50 1 2 3 4 5 6 7 8 9 10 11 12
Time (months) 24

25. Table 36.4A
Table 36.4A Exponential Growth of Rabbits, r  0.3 25

26. 36.4 Idealized models predict patterns of population growth
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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
Exponential growth in a population is like compounded interest on a bank account. The growth of the account is initially small, but as the interest earns interest, the growth expands. $1,000 invested at 7% interest is worth more than $30,000 in 50 years. Consider assigning students to calculate the value of an interest-bearing investment over a set period of years, as in the example just noted. Many online financial calculators can perform this task.
© 2012 Pearson Education, Inc. 26

27. Breeding male fur seals
Figure 36.4B 10 8
Growth of a population of fur seals
Breeding male fur seals
(thousands)
Figure 36.4B Growth of a population of fur seals 6 4 2
1915
1925
1935
1945
Year 27

28. Logistic growth and exponential growth compared
Figure 36.4C
Logistic growth and exponential growth compared G rN   G rN
(K  N) K K
Number of individuals (N)
Figure 36.4C Logistic growth and exponential growth compared
Time 28

29. Table 36.4B
Table 36.4B Effect of K on Growth Rate as N Approaches K, K  1,000, r  0.1 29

30. 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.
Multiple factors may limit population growth
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
It is typically easier for students to understand a concept when the examples are familiar. Consider the biology of your region and identify a population that is likely to be well-known by your students, for instance the population of squirrels on your campus. Challenge your students to identify limiting factors for that particular population.
© 2012 Pearson Education, Inc. 30

31. Figure 36.5A
Decreasing birth rate with increasing density in a population of great tits 12 11 10
Average clutch size 9 8
Figure 36.5A Decreasing birth rate with increasing density in a population of great tits 10 20 30 40 50 60 70 80 90
Number of breeding pairs 31

32. 36.5 Multiple factors may limit population growth
Limiting factors may include food, nutrients, retreats for safety, or nesting sites.
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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
It is typically easier for students to understand a concept when the examples are familiar. Consider the biology of your region and identify a population that is likely to be well-known by your students, for instance the population of squirrels on your campus. Challenge your students to identify limiting factors for that particular population.
© 2012 Pearson Education, Inc. 32

33. Figure 36.5B
Decreasing survival rates with increasing density in a population of flour beetles
100 80 60
Survivors (%) 40 20
Figure 36.5B Decreasing survival rates with increasing density in a population of flour beetles 20 40 60 80
100
120
Density (beetles/0.5 g flour) 33

34. 36.5 Multiple factors may limit population growth
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).
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
It is typically easier for students to understand a concept when the examples are familiar. Consider the biology of your region and identify a population that is likely to be well-known by your students, for instance the population of squirrels on your campus. Challenge your students to identify limiting factors for that particular population.
© 2012 Pearson Education, Inc. 34

35. Figure 36.5C
Weather change as a density-independent factor limiting aphid population growth
Exponential
growth
Sudden
decline
Number of aphids
Figure 36.5C Weather change as a density-independent factor limiting aphid population growth
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Month 35

36. 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
Consider challenging your class to explain why the lynx-and-hare cycle does not result in the elimination of one or both of the species. Why don’t we see hares hunted to extinction? Students may not have considered that predators encounter greater difficulty in finding prey when prey populations are low. This permits the recovery of the hare population, which in turn supports the recovery of the lynx population.
© 2012 Pearson Education, Inc. 36

37. Population cycles of the snowshoe hare and the lynx
Figure 36.6
Population cycles of the snowshoe hare and the lynx
160
Snowshoe hare
120 9
Lynx population size
(thousands)
Hare population size
(thousands)
Lynx 80 6
Figure 36.6 Population cycles of the snowshoe hare and the lynx 40 3
1850
1875
1900
1925
Year 37

38. 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
Compromise is a key principle of biology. No adaptation can be perfect, and no reproductive strategy can maximize all types of efforts. As the text notes, an organism cannot have a great number of offspring and invest great amounts of parental care in each one. Resources, including time, are limited. Have students imagine how different their lives would have been if they had been born as one of a set of quadruplets—or if they themselves were faced with the task of rearing four children at once!
© 2012 Pearson Education, Inc. 38

39. 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.
Student Misconceptions and Concerns
Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
Teaching Tips
Compromise is a key principle of biology. No adaptation can be perfect, and no reproductive strategy can maximize all types of efforts. As the text notes, an organism cannot have a great number of offspring and invest great amounts of parental care in each one. Resources, including time, are limited. Have students imagine how different their lives would have been if they had been born as one of a set of quadruplets—or if they themselves were faced with the task of rearing four children at once!
© 2012 Pearson Education, Inc. 39

40. 36.8 CONNECTION: 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.
Student Misconceptions and Concerns
1. Many students who are not biology majors have trouble thinking about the evolution of systems. One analogy that can be developed, especially for economically minded students, is the parallel to the “evolution” of businesses. Consider the introduction and expansion of McDonald’s restaurants in the United States over the last 50 years. When McDonald’s restaurants were just starting out, they experienced little competition, with access to many customers. The “population” of McDonald’s restaurants in the United States grew exponentially (or nearly so), with few density-dependent factors. However, today McDonald’s restaurants in the United States must compete with each other, as well as with many other fast-food restaurants, such as Burger King and Taco Bell. The population of McDonald’s restaurants in the United States has stabilized because of this competition for customers, a density-dependent factor. A graph of the growth of McDonald’s restaurants in the United States would likely resemble the lazy “S” shape.
2. Students often expect that spraying insecticides or using various killing devices (such as bug zappers) will make a significant impact in a pest population. As noted in Module 36.8, many pesticides kill both pests and their predators. Furthermore, most pest populations are r-selective and capable of recovering quickly, perhaps more quickly than their predators. Such considerations provide a classic illustration of the complexities inherent in biological systems and the often unexpected consequences of change.
Teaching Tips
1. Consider a class assignment exploring the collapse of the northern cod fishery and identifying other fish species in danger of overharvesting, as well as strategies to prevent this. As emphasized in Module 36.4, harvesting a population down to intermediate levels maximizes the sustained yield.
2. The sustainable management of the Alaska fisheries is a good lesson in responsible resource management. Considering learning more about the management of halibut populations around Alaska as a positive example.
© 2012 Pearson Education, Inc. 40

41. Collapse of northern cod fishery off Newfoundland
Figure 36.8
Collapse of northern cod fishery off Newfoundland
900
800
700
600
Yield (thousands of metric tons)
500
400
300
200
Figure 36.8 Collapse of northern cod fishery off Newfoundland
100
1960
1970
1980
1990
2000 41

42. THE HUMAN POPULATION
© 2012 Pearson Education, Inc. 42

43. 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.
Student Misconceptions and Concerns
Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
Teaching Tips
The U.S. government’s Census Bureau sponsors a U.S. and World Population Clock at It might be of special interest to see if we have reached a world population of 7 billion people (as predicted for 2012).
© 2012 Pearson Education, Inc. 43

44. Annual increase (in millions) Total population (in billions)
Figure 36.9A
100 10
Population increase 80 8 60 6
Annual increase (in millions)
Total population (in billions) 40 4
Total population size 20 2
Figure 36.9A Five centuries of human population growth, projected to 2050
1500
1550
1600
1650
1700
1750
1800
1850
1900
1950
2000
2050
Year 44

45. 36.9 The human population continues to increase, but the growth rate is slowing
The demographic transition
Is the shift in population
from high birth and death rates
to low birth and death rates, and
has lowered the rate of growth in developed countries.
Student Misconceptions and Concerns
Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
Teaching Tips
The U.S. government’s Census Bureau sponsors a U.S. and World Population Clock at It might be of special interest to see if we have reached a world population of 7 billion people (as predicted for 2012).
© 2012 Pearson Education, Inc. 45

46. Demographic transition in Mexico
Figure 36.9B
Demographic transition in Mexico 50 40 30
Rate of
increase
per 1,000 population
Birth or death rate 20
Birth rate 10
Death rate
Figure 36.9B Demographic transition in Mexico
1900
1925
1950
1975
2000
2025
2050
Year 46

47. 36.9 The human population continues to increase, but the growth rate is slowing
In the developing nations
death rates have dropped,
birth rates are still high, and
these populations are growing rapidly.
Student Misconceptions and Concerns
Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
Teaching Tips
The U.S. government’s Census Bureau sponsors a U.S. and World Population Clock at It might be of special interest to see if we have reached a world population of 7 billion people (as predicted for 2012).
© 2012 Pearson Education, Inc. 47

48. Table 36.9
Table 36.9 Population Changes in 2009 (Estimated) 48

49. 36.9 The human population continues to increase, but the growth rate is slowing
The age structure of a population
is the proportion of individuals in different age groups and
affects the future growth of the population.
Student Misconceptions and Concerns
Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
Teaching Tips
The U.S. government’s Census Bureau sponsors a U.S. and World Population Clock at It might be of special interest to see if we have reached a world population of 7 billion people (as predicted for 2012).
© 2012 Pearson Education, Inc. 49

50. 36.9 The human population continues to increase, but the growth rate is slowing
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.
Student Misconceptions and Concerns
Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
Teaching Tips
The U.S. government’s Census Bureau sponsors a U.S. and World Population Clock at It might be of special interest to see if we have reached a world population of 7 billion people (as predicted for 2012).
© 2012 Pearson Education, Inc. 50

51. 36.10 CONNECTION: Age structures reveal social and economic trends
Age-structure diagrams reveal
a population’s growth trends and
social conditions.
Student Misconceptions and Concerns
Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
Teaching Tips
Module provides a wonderful opportunity to discuss the social impact of human population changes in the United States. As noted in Module 36.10, Medicare and Social Security will be increasingly impacted as the U.S. population ages. You might want to discuss the occupational outlook for professions that will address the needs of the growing elderly population, and the opportunity to invest in companies that will capitalize on these changes.
© 2012 Pearson Education, Inc. 51

52. Figure 36.10
Age structures for the United States in 1985, 2010 (estimated), and 2035 (projected)
1985
2010
2035
Birth years
Male
Female
Birth years
Male
Female
Birth years
Male
Female
85
before 1901
before 1926
before 1951
80–84
1901–1905
1926–30
1951–55
75–79
1906–10
1931–35
1956–60
70–74
1911–15
1936–40
1961–65
65–69
1916–20
1941–45
1966–70
60–64
1921–25
1946–50
1971–75
55–59
1926–30
1951–55
1976–80
50–54
1931–35
1956–60
1981–85
Age
45–49
1936–40
1961–65
1986–90
40–44
1941–45
1966–70
1991–95
35–39
1946–50
1971–75
1996–2000
30–34
1951–55
1976–80
2001–05
25–29
1956–60
1981–85
2006–10
20–24
1961–65
1986–90
2011–15
15–19
1966–70
1991–95
2016–20
10–14
1971–75
1996–2000
2021–25
5–9
1976–80
2001–2005
2026–30
0–4
Figure Age structures for the United States in 1985, 2010 (estimated), and 2035 (projected)
1981–85
2006–2010
2031–35 12 10 8 6 4 2 2 4 6 8 10 12 12 10 8 6 4 2 2 4 6 8 10 12 12 10 8 6 4 2 2 4 6 8 10 12
Population in millions
Total population size  238,466,283
Estimated population in millions
Total population size  310,232,863
Projected population in millions
Total population size  389,531,156 52

53. Population in millions Total population size  238,466,283
Figure 36.10_1
1985
Birth years
Male
Female
85
before 1901
80–84
1901–1905
75–79
1906–10
70–74
1911–15
65–69
1916–20
60–64
1921–25
55–59
1926–30
50–54
1931–35
45–49
1936–40
Age
40–44
1941–45
35–39
1946–50
30–34
1951–55
25–29
1956–60
20–24
1961–65
Figure 36.10_1 Age structure for the United States in 1985 (part 1)
15–19
1966–70
10–14
1971–75
5–9
1976–80
0–4
1981–85 12 10 8 6 4 2 2 4 6 8 10 12
Population in millions
Total population size  238,466,283 53

54. Estimated population in millions Total population size  310,232,863
Figure 36.10_2
2010
Birth years
Male
Female
85
before 1926
80–84
1926–30
75–79
1931–35
70–74
1936–40
65–69
1941–45
60–64
1946–50
55–59
1951–55
50–54
1956–60
45–49
Age
1961–65
40–44
1966–70
35–39
1971–75
30–34
1976–80
25–29
1981–85
20–24
1986–90
Figure 36.10_2 Age structure for the United States in 2010 (estimated) (part 2)
15–19
1991–95
10–14
1996–2000
5–9
2001–2005
0–4
2006–2010 12 10 8 6 4 2 2 4 6 8 10 12
Estimated population in millions
Total population size  310,232,863 54

55. Projected population in millions Total population size  389,531,156
Figure 36.10_3
2035
Birth years
Male
Female
85
before 1951
80–84
1951–55
75–79
1956–60
70–74
1961–65
65–69
1966–70
60–64
1971–75
55–59
1976–80
50–54
1981–85
Age
45–49
1986–90
40–44
1991–95
35–39
1996–2000
30–34
2001–05
25–29
2006–10
20–24
2011–15
Figure 36.10_3 Age structure for the United States in 2035 (projected) (part 3)
15–19
2016–20
10–14
2021–25
5–9
2026–30
0–4
2031–35 12 10 8 6 4 2 2 4 6 8 10 12
Projected population in millions
Total population size  389,531,156 55

56. 36.11 CONNECTION: 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.
Student Misconceptions and Concerns
1. Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
2. Students are often frustrated by the long list of environmental problems caused by humans, and students may begin to feel helpless as coverage of the issues goes on. You might consider directing them to specific websites for basic suggestions on what they can do to make a difference. A Google search for “What you can do environment” should yield many potentially good sites.
Teaching Tips
Module notes that the United States has an ecological footprint greater than the land area of the United States. Consider asking your class to explain how this is possible and what this means to other countries. The authors further note that the world’s richest countries, with 15% of the global population, account for 36% of humanity’s total footprint.
© 2012 Pearson Education, Inc. 56

57. 36.11 CONNECTION: An ecological footprint is a measure of resource consumption
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.
Includes how much cropland, Grazing Lands, Forests, Fishing grounds, etc. are required
Student Misconceptions and Concerns
1. Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
2. Students are often frustrated by the long list of environmental problems caused by humans, and students may begin to feel helpless as coverage of the issues goes on. You might consider directing them to specific websites for basic suggestions on what they can do to make a difference. A Google search for “What you can do environment” should yield many potentially good sites.
Teaching Tips
Module notes that the United States has an ecological footprint greater than the land area of the United States. Consider asking your class to explain how this is possible and what this means to other countries. The authors further note that the world’s richest countries, with 15% of the global population, account for 36% of humanity’s total footprint.
© 2012 Pearson Education, Inc. 57

58. Ecological Footprints
Source: Global Footprint Network

59. 36.11 CONNECTION: An ecological footprint is a measure of resource consumption
Unites States has a huge ecological foot print
The United States gha per person.
India – less than 0.9 ha per person
US can support only 5 gha per person.
Thus US has a large ecological deficit
Student Misconceptions and Concerns
1. Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
2. Students are often frustrated by the long list of environmental problems caused by humans, and many begin to feel helpless as coverage of the issues goes on. You might consider directing them to the following websites for basic suggestions on what they can do to start to make a difference.
Teaching Tips
1. Module notes that the United States has an ecological footprint greater than the land area of the United States. Consider asking your class to explain how this is possible and what this means to other countries. The authors further note that only 14% of the global resources are available for 80% of the world’s population.
Copyright © 2009 Pearson Education, Inc.

60. 36.11 CONNECTION: An ecological footprint is a measure of resource consumption
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.
Student Misconceptions and Concerns
1. Some students may not understand the impact of delayed reproduction on population growth. Working through the following example in class might help. Refer back to the text example of exponential growth in a population of bacteria (Module 36.4). What if one population reproduced every 20 minutes and another population reproduced every 40 minutes? Clearly, the 20-minute cycle would increase the population faster.
2. Students are often frustrated by the long list of environmental problems caused by humans, and students may begin to feel helpless as coverage of the issues goes on. You might consider directing them to specific websites for basic suggestions on what they can do to make a difference. A Google search for “What you can do environment” should yield many potentially good sites.
Teaching Tips
Module notes that the United States has an ecological footprint greater than the land area of the United States. Consider asking your class to explain how this is possible and what this means to other countries. The authors further note that the world’s richest countries, with 15% of the global population, account for 36% of humanity’s total footprint.
© 2012 Pearson Education, Inc. 60

61. Figure 36.11A
Figure 36.11A Families in India (left) and the United States (right) display their possessions 61

62. Figure 36.11A_1
Figure 36.11A_1 A family in India displays their possessions (part 1) 62

63. Figure 36.11A_2
Figure 36.11A_2 A family in the United States displays their possessions (part 2) 63

64. Ecological Footprints
Figure 36.11B
Ecological Footprints
(gha per capita)
0–1.5
1.5–3.0
3.0–4.5
4.5–6.0
Figure 36.11B Ecological footprints around the world
6.0–7.5
7.5–9.0
9.0–10.5
 10.5
Insufficient data 64

65. Environmental Bankruptcy
“Environmental bankruptcy, as with corporate bankruptcy, can happen very slowly, then all of a sudden. This is what we face unless we slow down, then reverse the damage. We’re running short on fresh water, topsoil, fisheries, wetlands – all our planet’s natural systems and resources that support business, and life, including our own.
We’re now using the resources of one-and-a-half planets on our one and only planet”
-Advertisement on Patagonia Jacket

66. Ecological Footprint assignment
If everyone in the world lived your lifestyle, how many earths would we need??
Your Ecological Footprint assignment will give you the answer ?