1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 52 Population Ecology

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Earth’s Fluctuating Populations To understand human population growth – We must consider the general principles of population ecology

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population ecology is the study of populations in relation to environment – Including environmental influences on population density and distribution, age structure, and variations in population size

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The fur seal population of St. Paul Island, off the coast of Alaska – has experienced dramatic fluctuations in size Figure 52.1

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.1: Dynamic biological processes influence population density, dispersion, and demography A population – Is a group of individuals of a single species living in the same general area Density Density – Is the number of individuals per unit area or volume Dispersion – Is the pattern of spacing among individuals within the boundaries of the population

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density: A Dynamic Perspective Determining the density of natural populations – N/A or N/V – Is possible, but difficult to accomplish In most cases – It is impractical or impossible to count all individuals in a population – Quadrat method, mark and recapture

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density is the result of a dynamic interplay – Between processes that add individuals to a population and those that remove individuals from it Figure 52.2 Births and immigration add individuals to a population. BirthsImmigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population.

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Patterns of Dispersion Environmental and social factors – Influence the spacing of individuals in a population

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A clumped dispersion – Is one in which individuals aggregate in patches – May be influenced by resource availability and behavior Figure 52.3a (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A uniform dispersion – Is one in which individuals are evenly distributed – May be influenced by social interactions such as territoriality Figure 52.3b (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

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12. A random dispersion – Is one in which the position of each individual is independent of other individuals Figure 52.3c (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

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14. Demography Demography is the study of the vital statistics of a population – And how they change over time Death rates and birth rates – Are of particular interest to demographers

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life Tables A life table – Is an age-specific summary of the survival pattern of a population – Is best constructed by following the fate of a cohort

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The life table of Belding’s ground squirrels – Reveals many things about this population Table 52.1

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Survivorship Curves A survivorship curve – Is a graphic way of representing the data in a life table

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The survivorship curve for Belding’s ground squirrels – Shows that the death rate is relatively constant Figure 52.4 1000 100 10 1 Number of survivors (log scale) 0 2 46 810 Age (years) Males Females

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Survivorship curves can be classified into three general types – Type I, Type II, and Type III Figure 52.5 I II III 50 100 0 1 10 100 1,000 Percentage of maximum life span Number of survivors (log scale)

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21. Reproductive Rates A reproductive table, or fertility schedule – Is an age-specific summary of the reproductive rates in a population

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A reproductive table – Describes the reproductive patterns of a population Table 52.2

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.2: Life history traits are products of natural selection Life history traits are evolutionary outcomes – Reflected in the development, physiology, and behavior of an organism

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life History Diversity Life histories are very diverse

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species that exhibit semelparity, or “big-bang” reproduction – Reproduce a single time and die Figure 52.6

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species that exhibit iteroparity, or repeated reproduction – Produce offspring repeatedly over time

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings “Trade-offs” and Life Histories Organisms have finite resources Figure 52.7 Researchers in the Netherlands studied the effects of parental caregiving in European kestrels over 5 years. The researchers transferred chicks among nests to produce reduced broods (three or four chicks), normal broods (five or six), and enlarged broods (seven or eight). They then measured the percentage of male and female parent birds that survived the following winter. (Both males and females provide care for chicks.) EXPERIMENT The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents. CONCLUSION 100 80 60 40 20 0 Reduced brood size Normal brood size Enlarged brood size Parents surviving the following winter (%) Male Female – Which may lead to trade- offs between survival and reproduction RESULTS

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why do reproducing female red deer show a higher mortality rate? Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 52.5

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some plants produce a large number of small seeds – Ensuring that at least some of them will grow and eventually reproduce Figure 52.8a (a) Most weedy plants, such as this dandelion, grow quickly and produce a large number of seeds, ensuring that at least some will grow into plants and eventually produce seeds themselves.

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other types of plants produce a moderate number of large seeds – That provide a large store of energy that will help seedlings become established Figure 52.8b (b) Some plants, such as this coconut palm, produce a moderate number of very large seeds. The large endosperm provides nutrients for the embryo, an adaptation that helps ensure the success of a relatively large fraction of offspring.

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parental care of smaller broods – May also facilitate survival of offspring

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.3: The exponential model describes population growth in an idealized, unlimited environment It is useful to study population growth in an idealized situation – In order to understand the capacity of species for increase and the conditions that may facilitate this type of growth

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Per Capita Rate of Increase If immigration and emigration are ignored – A population’s growth rate (per capita increase) equals birth rate minus death rate

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Intrinsic rate of growth of a population: b–m = r. Zero population growth – Occurs when the birth rate equals the death rate – b-m=0=r The population growth equation can be expressed as dN dt  rN

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential Growth Exponential population growth – Is population increase under idealized conditions Under these conditions – The rate of reproduction is at its maximum, called the intrinsic rate of increase

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The equation of exponential population growth is dN dt  r max N

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential population growth – Results in a J-shaped curve Figure 52.9 0 5 1015 0 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt  1.0N dN dt  0.5N

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The J-shaped curve of exponential growth – Is characteristic of some populations that are rebounding Figure 52.10 1900 1920194019601980 Year 0 2,000 4,000 6,000 8,000 Elephant population

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.4: The logistic growth model includes the concept of carrying capacity Exponential growth – Cannot be sustained for long in any population – Due to finite resources A more realistic population model – Limits growth by incorporating carrying capacity

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Carrying capacity (K) – Is the maximum population size the environment can support

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Growth Model In the logistic population growth model – The per capita rate of increase declines as carrying capacity is reached

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings We construct the logistic model by starting with the exponential model – And adding an expression that reduces the per capita rate of increase as N increases Figure 52.11 Maximum Positive Negative 0 N  KN  K Population size (N) Per capita rate of increase (r)

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic growth equation – Includes K, the carrying capacity dN dt  ( K  N ) K r max N

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A hypothetical example of logistic growth Table 52.3

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic model of population growth – Produces a sigmoid (S-shaped) curve Figure 52.12 dN dt  1.0N Exponential growth Logistic growth dN dt  1.0N 1,500  N 1,500 K  1,500 0 51015 0 500 1,000 1,500 2,000 Number of generations Population size (N)

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 52.13a 800 600 400 200 0 Time (days) 05 10 15 (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment. 1,000 Number of Paramecium/ml The Logistic Model and Real Populations The growth of laboratory populations of paramecia – Fits an S-shaped curve

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations overshoot K – Before settling down to a relatively stable density Figure 52.13b 180 150 0 120 90 60 30 Time (days) 0 160 140120 80 1006040 20 Number of Daphnia/50 ml (b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size.

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations – Fluctuate greatly around K Figure 52.13c 0 80 60 40 20 1975 19801985 1990 19952000 Time (years) Number of females (c) A song sparrow population in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model.

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic model fits few real populations – But is useful for estimating possible growth

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Model and Life Histories Life history traits favored by natural selection – May vary with population density and environmental conditions

51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic population growth model and life histories. – This model predicts different growth rates for different populations, relative to carrying capacity. Resource availability depends on the situation. The life history traits that natural selection favors may vary with population density and environmental conditions.

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings K-selection, or density-dependent selection – Selects for life history traits that are sensitive to population density r-selection, or density-independent selection – Selects for life history traits that maximize reproduction

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The concepts of K-selection and r-selection – Are somewhat controversial and have been criticized by ecologists as oversimplifications

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.5: Populations are regulated by a complex interaction of biotic and abiotic influences There are two general questions we can ask – About regulation of population growth

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What environmental factors stop a population from growing? Why do some populations show radical fluctuations in size over time, while others remain stable?

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Characteristics of K Selected Species Population grows to near carrying capacity and fluctuates around K. Population usually limited by density dependent factors Good competitors Low r Large size Examples: moose, bear, tigers, eagles

57. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings K-selected Reproductive Strategy K-selected Species: – occur near carrying capacity – experience effects of population density – have low reproductive rates, high parental care – have type I survivorship curves.

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Characteristics of r selected species Large r Population does not usually reach carrying capacity Lives in unstable environment Shows boom/bust growth curve Density independent factors usually limits growth Small in size ex: mosquitoes, rabbits, sparrows

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings r-selected Reproductive Strategy r-selected Species: – have high reproductive rates – tend to occur in unpredictable environments – typically have type III survivorship curves

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Change and Population Density In density-independent populations – Birth rate and death rate do not change with population density In density-dependent populations – Birth rates fall and death rates rise with population density

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Determining equilibrium for population density Figure 52.14a–c Density-dependent birth rate Density- dependent death rate Equilibrium density Density-dependent birth rate Density- independent death rate Equilibrium density Density- independent birth rate Density-dependent death rate Equilibrium density Population density Birth or death rate per capita (a) Both birth rate and death rate change with population density. (b) Birth rate changes with population density while death rate is constant. (c) Death rate changes with population density while birht rate is constant.

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density-Dependent Population Regulation Density-dependent birth and death rates – Are an example of negative feedback that regulates population growth – Are affected by many different mechanisms

63. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competition for Resources In crowded populations, increasing population density – Intensifies intraspecific competition for resources Figure 52.15a,b 100100 0 1,000 10,000 Average number of seeds per reproducing individual (log scale) Average clutch size Seeds planted per m 2 Density of females 0 7010 2030 40506080 2.8 3.0 3.2 3.4 3.6 3.8 4.0 (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.

64. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Territoriality In many vertebrates and some invertebrates – Territoriality may limit density

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cheetahs are highly territorial – Using chemical communication to warn other cheetahs of their boundaries Figure 52.16

66. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oceanic birds – Exhibit territoriality in nesting behavior Figure 52.17

67. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Owls have a limited amount of breeding territory because of limits of food in their environment – Density Dependent or Independent?

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69. Health Population density – Can influence the health and survival of organisms In dense populations – Pathogens can spread more rapidly

70. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Predation As a prey population builds up – Predators may feed preferentially on that species

71. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Toxic Wastes The accumulation of toxic wastes – Can contribute to density-dependent regulation of population size

72. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Intrinsic Factors For some populations – Intrinsic (physiological) factors appear to regulate population size

73. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Dynamics The study of population dynamics – Focuses on the complex interactions between biotic and abiotic factors that cause variation in population size

74. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stability and Fluctuation Long-term population studies – Have challenged the hypothesis that populations of large mammals are relatively stable over time Figure 52.18 The pattern of population dynamics observed in this isolated population indicates that various biotic and abiotic factors can result in dramatic fluctuations over time in a moose population. Researchers regularly surveyed the population of moose on Isle Royale, Michigan, from 1960 to 2003. During that time, the lake never froze over, and so the moose population was isolated from the effects of immigration and emigration. FIELD STUDY Over 43 years, this population experienced two significant increases and collapses, as well as several less severe fluctuations in size. RESULTS CONCLUSION 1960 197019801990 2000 Year Moose population size 0 500 1,000 1,500 2,000 2,500 Steady decline probably caused largely by wolf predation Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population

75. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Extreme fluctuations in population size – Are typically more common in invertebrates than in large mammals Figure 52.19 1950 19601970 1980 Year 1990 10,000 100,000 730,000 Commercial catch (kg) of male crabs (log scale)

76. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metapopulations and Immigration Metapopulations – Are groups of populations linked by immigration and emigration

77. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings High levels of immigration combined with higher survival – Can result in greater stability in populations Figure 52.20 Mandarte island Small islands Number of breeding females 198819891990 1991 Year 0 10 20 30 40 50 60 One isolated island less stable

78. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Cycles Many populations – Undergo regular boom-and-bust cycles Figure 52.21 Year 1850187519001925 0 40 80 120 160 0 3 6 9 Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare

79. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Boom-and-bust cycles – Are influenced by complex interactions between biotic and abiotic factors

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81. Concept 52.6: Human population growth has slowed after centuries of exponential increase No population can grow indefinitely – And humans are no exception

82. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Global Human Population The human population – Increased relatively slowly until about 1650 and then began to grow exponentially Figure 52.22 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. 0 The Plague Human population (billions) 2000 A.D. 0 1 2 3 4 5 6

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84. Though the global population is still growing – The rate of growth began to slow approximately 40 years ago Figure 52.23 1950 19752000 2025 2050 Year 2003 Percent increase 2.2 2 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1.8

85. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regional Patterns of Population Change To maintain population stability – A regional human population can exist in one of two configurations

86. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zero population growth = High birth rates – High death rates Zero population growth = Low birth rates – Low death rates

87. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The demographic transition – Is the move from the first toward the second state Figure 52.24 50 40 20 0 30 10 1750 1800 1850 1900 1950 2000 2050 Birth rate Death rate Birth rate Death rate Year SwedenMexico Birth or death rate per 1,000 people

88. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The demographic transition – Is associated with various factors in developed and developing countries

89. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age Structure One important demographic factor in present and future growth trends – Is a country’s age structure, the relative number of individuals at each age

90. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure – Is commonly represented in pyramids Figure 52.25 Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Male FemaleMale Female Age 864202468864202468864202468 Percent of population 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19 80–84 85  75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19

91. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure diagrams – Can predict a population’s growth trends – Can illuminate social conditions and help us plan for the future

92. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Infant Mortality and Life Expectancy Infant mortality and life expectancy at birth – Vary widely among developed and developing countries but do not capture the wide range of the human condition Figure 52.26 Developed countries Developing countries Developed countries Developing countries Infant mortality (deaths per 1,000 births) Life expectancy (years) 60 50 40 30 20 10 0 80 60 40 20 0

93. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Global Carrying Capacity Just how many humans can the biosphere support?

94. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Estimates of Carrying Capacity The carrying capacity of Earth for humans is uncertain

95. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Footprint The ecological footprint concept – Summarizes the aggregate land and water area needed to sustain the people of a nation – Is one measure of how close we are to the carrying capacity of Earth

96. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological footprints for 13 countries – Show that the countries vary greatly in their footprint size and their available ecological capacity Figure 52.27 16 14 12 10 8 6 4 2 0 0 2 4 68 1214 16 New Zealand Australia Canada Sweden World China India Available ecological capacity (ha per person) Spain UK Japan Germany Netherlands Norway USA Ecological footprint (ha per person)

97. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At more than 7 billion people – The world is already in ecological deficit