Chapter 36 Population Ecology Lecture by Brian R. Shmaefsky.

Chapter 36 Population Ecology Lecture by Brian R. Shmaefsky

Introduction: A Tale of Two Fishes
Population ecology is concerned with Changes in population size Factors that regulate populations over time It helps explain the biodiversity of an environment Copyright © 2009 Pearson Education, Inc.

Introduction: A Tale of Two Fishes
Ecologists learn the structure and dynamics of natural populations With this information they are better equipped to Develop sustainable food sources Assess the impact of human activities Balance human needs with the conservation of biodiversity and resources Copyright © 2009 Pearson Education, Inc.

Nile perch.

Fish market on Lake Victoria beach.

Fishing boats on Lake Victoria.

POPULATION STRUCTURE AND DYNAMICS
POPULATION STRUCTURE AND DYNAMICS Copyright © 2009 Pearson Education, Inc.

36.1 Population ecology is the study of how and why populations change
Population 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 Are likely to interact and breed with one another 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 parallels 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 U.S. 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 1. Use of the mark-recapture method to estimate the size of a population is discussed in the Applying the Concepts section at the end of Chapter 36. The following can serve as a demonstration of the mark-recapture method 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. Copyright © 2009 Pearson Education, Inc.

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 is the interactions between Biotic and abiotic factors It is the cause of variation in population sizes A population increases through birth and immigration Death and emigration out of an area decrease the population 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 parallels 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 U.S. 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 1. Use of the mark-recapture method to estimate the size of a population is discussed in the Applying the Concepts section at the end of Chapter 36. The following can serve as a demonstration of the mark-recapture method 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. Copyright © 2009 Pearson Education, Inc.

36.2 Density and dispersion patterns are important population variables
Population density is the number of individuals of a species per unit area or volume Examples of population density The number of oak trees per square kilometer in a forest The number of earthworms per cubic meter in forest soil Ecologists use a variety of sampling techniques to estimate population densities 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

Within a population’s geographic range, local densities may vary greatly The dispersion pattern of a population refers to the way individuals are spaced within their area 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 parallels 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 U.S. 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 1. 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. Video: Flapping Geese (clumped) Video: Albatross Courtship (uniform) Video: Prokaryotic Flagella (Salmonella typhimurium) (random) Copyright © 2009 Pearson Education, Inc.

Figure 36.2A Clumped dispersion of schooling fish. Figure 36.2B Uniform dispersion of nesting king penguins. Figure 36.2C Random dispersion of dandelions.

The dispersion pattern of a population refers to the way individuals are spaced within their area Dispersion patterns can be Clumped Uniform Random 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

In a clumped pattern individuals are grouped in patches 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 36.2A Clumped dispersion of schooling fish.

In a uniform pattern individuals are equally spaced in the environment 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 36.2B Uniform dispersion of nesting king penguins.

In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

Figure 36.2C Random dispersion of dandelions.

36. 3 Life tables track survivorship in populations
Life tables track survivorship over the life span of individuals in a population Survivorship curves plot the proportion of individuals alive at each age Type I Type II Type III 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 parallels 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 U.S. 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 1. The Centers for Disease Control provide information and life tables for people living in the United States at their website, Copyright © 2009 Pearson Education, Inc.

Table 36.3 Life Table for the U.S. Population in 2003.

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

36.4 Idealized models predict patterns of population growth
Exponential growth model The rate of population increases under ideal conditions Calculated using the equation G = rN G is the growth rate of the population N is the population size r is the per capita rate of increase 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 parallels 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 U.S. 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 1. 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 a simple interest-bearing investment over a set period of years, as in the example just noted. Many online financial calculators can perform this task. Copyright © 2009 Pearson Education, Inc.

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

Table 36.4A Exponential Growth of Rabbits, r = 0.3.

Logistic growth model This growth model takes into account limiting factors Limiting factors are environmental factors that restrict population growth Formula 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 parallels 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 U.S. 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 1. 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 a simple interest-bearing investment over a set period of years, as in the example just noted. Many online financial calculators can perform this task. Copyright © 2009 Pearson Education, Inc.

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

Figure 36.4B Growth of a population of fur seals.

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

Idealized models describe two kinds of population growth Exponential growth Logistic growth 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 parallels 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 U.S. 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 1. 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 a simple interest-bearing investment over a set period of years, as in the example just noted. Many online financial calculators can perform this task. Copyright © 2009 Pearson Education, Inc.

Number of individuals (N)
G = rN (K – N) K G = rN Number of individuals (N) K Figure 36.4C Logistic growth and exponential growth compared. Time

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

36.5 Multiple factors may limit population growth
The logistic growth model Population growth slows and ceases as population density increases Increasing population density results in a decrease in birth rate, an increase in death rate, or both 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

4.0 3.8 3.6 Clutch size 3.4 3.2 Figure 36.5A Decrease in song sparrow clutch size as population density increases. 3.0 2.8 10 20 30 40 50 60 70 80 Density of females

Abiotic factors may reduce population size before other limiting factors become important 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

Exponential growth Sudden decline
Number of aphids Figure 36.5B The effect of an abiotic factor (climate) on aphid population size. Apr May Jun Jul Aug Sep Oct Nov Dec

Most populations fluctuate in numbers 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

80 60 40 Number of females Figure 36.5C Fluctuations in a song sparrow population, with periodic catastrophic reductions due to severe winter weather. 20 1975 1980 1985 1990 1995 2000 Time (years)

36.6 Some populations have “boom-and-bust” cycles
Some populations fluctuate in density with regularity Boom-and-bust cycles Food shortages Predator-prey interactions For the BLAST Animation Population Dynamics, go to Animation and Video Files. 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 parallels 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 U.S. 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 1. 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. Copyright © 2009 Pearson Education, Inc.

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

36.7 EVOLUTION CONNECTION: Evolution shapes life histories
Life history Series of events from birth to death r/K selection r-selective traits K-selective traits 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 parallels 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 U.S. 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 1. 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 both 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! Copyright © 2009 Pearson Education, Inc.

Predator: Killifish; preys mainly on small guppies
Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Pools with killifish, but no guppies prior to transplant Guppies: Larger at sexual maturity than those in pike-cichlid pools Predator: Pike-cichlid preys mainly on large guppies Guppies: Smaller at sexual maturity than those in killifish pools Figure 36.7 Effect of predation on life history traits of guppies. 11 years later 200 185.6 100 Control: Guppies from pools with pike-cichlids as predators 161.5 85.7 92.3 160 80 120 Age of guppies at maturity (days) 60 58.2 48.5 Mass of guppies at maturity (mg) 80 67.5 76.1 40 Experimental: Guppies transplanted to pools with killifish as predators 40 20 Males Females Males Females

Predator: Killifish; preys mainly on small guppies
Experimental transplant of guppies Predator: Killifish; preys mainly on small guppies Pools with killifish, but no guppies prior to transplant Guppies: Larger at sexual maturity than those in pike-cichlid pools Figure 36.7 Effect of predation on life history traits of guppies. Predator: Pike-cichlid preys mainly on large guppies Guppies: Smaller at sexual maturity than those in killifish pools

11 years later Control: Guppies from pools with pike-cichlids
as predators 200 185.6 100 92.3 85.7 161.5 160 80 Mass of guppies at maturity (mg) Age of guppies at maturity (days) 120 58.2 60 48.5 80 76.1 67.5 40 Experimental: Guppies transplanted to pools with killifish as predators 40 20 Figure 36.7 Effect of predation on life history traits of guppies. Males Females Males Females

36.8 CONNECTION: Principles of population ecology have practical applications
Sustainable resource management Maximum sustained yield 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 parallels 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 U.S. 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 changes. 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 36.8, harvesting a population down to intermediate levels maximizes the sustained yield. Copyright © 2009 Pearson Education, Inc.

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

36.9 The human population continues to increase, but the growth rate is slowing
Human population is expected to continue increasing for several decades 95% of the increase is in developing nations 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. Teaching Tips 1. You might surprise your class by noting that the majority of the people who have ever lived in the history of the human race are alive today. An examination of Figure 36.9A reveals how this could be true. 2. The U.S. government’s Census Bureau sponsors a U.S. and world population clock at Copyright © 2009 Pearson Education, Inc.

Annual increase (in millions) Total population (in billions)
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

Table 36.9 Population Changes in 2006.

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

36.9 The human population continues to increase, but the growth rate is slowing
Population momentum of Mexico 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. Teaching Tips 1. You might surprise your class by noting that the majority of the people who have ever lived in the history of the human race are alive today. An examination of Figure 36.9A reveals how this could be true. 2. The U.S. government’s Census Bureau sponsors a U.S. and world population clock at Copyright © 2009 Pearson Education, Inc.

Figure 36.9C Population momentum in Mexico.
Age 80+ 1980 2005 2030 75-79 70-74 Male Female Male Female Male Female 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 Figure 36.9C Population momentum in Mexico. 5 4 3 2 1 1 2 3 4 5 5 4 3 2 1 1 2 3 4 5 5 4 3 2 1 1 2 3 4 5 Population in millions Population in millions Population in millions Total population size = 68,347,479 Total population size = 106,202,903 Total population size = 135,172,155

Population in millions Total population size = 68,347,479
Age 80+ 1980 75-79 70-74 Male Female 65-69 60-64 55-59 50-54 45-49 40-44 35-39 30-34 25-29 20-24 Figure 36.9C Population momentum in Mexico. 15-19 10-14 5-9 0-4 5 4 3 2 1 1 2 3 4 5 Population in millions Total population size = 68,347,479

36.10 CONNECTION: Age structures reveal social and economic trends
Age structure diagram Reveals a population’s growth trends 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. Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

1980 2005 2030 Age Birth years Male Female Birth years Male Female Birth years Male Female 80+ before 1900 before 1926 before 1951 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 Figure Age structures for the United States in 1980, 2005, and 2030 (projected). 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 Population in millions Population in millions Total population size = 227,726,463 Total population size = 295,734,134 Total population size = 363,811,435

1980 Age Birth years Male Female 80+ before 1900 75-79 70-74 65-69 60-64 55-59 50-54 45-49 40-44 35-39 30-34 25-29 20-24 Figure Age structures for the United States in 1980, 2005, and 2030 (projected). 15-19 10-14 5-9 0-4 12 10 8 6 4 2 2 4 6 8 10 12 Population in millions Total population size = 227,726,463

36.11 CONNECTION: An ecological footprint is a measure of resource consumption
U.S. Census Bureau projection 8 billion people within the next 20 years 9.5 billion by mid-21st century 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.

36.11 CONNECTION: An ecological footprint is a measure of resource consumption
Ecological footprint helps understand resource availability and usage The United States has a Big ecological footprint 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.

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

Figure 36.11A A family in India display their possessions.

Figure 36.11A A family in the United States display their possessions.

> 5.4 global ha per person 3.6–5.4 global ha per person
North America Europe Asia Africa > 5.4 global ha per person 3.6–5.4 global ha per person 1.8–3.6 global ha per person South America Figure 36.11B World map with area corresponding to ecological footprint. 0.9–1.8 global ha per person Australia < 0.9 global ha per person Insufficient data

Few large offspring, low mortality until old age I Percentage of survivors Many small offspring, high mortality II III Percentage of maximum life span

(K  N) G = rN K

I II III IV Birth or death rate Time

You should now be able to
Explain the factors that determine the characteristics of a population Describe exponential growth and the factors that produce logistic growth of a population Explain the limiting factors that influence population growth Distinguish between r- and K-strategies Describe and give examples of the different types of life histories Copyright © 2009 Pearson Education, Inc.

Chapter 36 Population Ecology Lecture by Brian R. Shmaefsky.

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Chapter 36 Population Ecology Lecture by Brian R. Shmaefsky.

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