1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Biology 102 Week 9 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 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 density and distribution, age structure, and population size The fur seal population of St. Paul Island, off the coast of Alaska, has experienced dramatic fluctuations in size

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5. 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

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density and Dispersion 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

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density: A Dynamic Perspective Determining the density of natural populations is difficult In most cases, it is impractical or impossible to count all individuals in a population Density is the result of an interplay between processes that add individuals to a population and those that remove individuals

8. LE 52-2 Population size Emigration Deaths Immigration Births

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

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a clumped dispersion, individuals aggregate in patches A clumped dispersion may be influenced by resource availability and behavior Video: Flapping Geese (clumped) Video: Flapping Geese (clumped)

11. LE 52-3a 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.

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A uniform dispersion is one in which individuals are evenly distributed It may be influenced by social interactions such as territoriality Video: Albatross Courtship (uniform) Video: Albatross Courtship (uniform)

13. LE 52-3b 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.

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In a random dispersion, the position of each individual is independent of other individuals Video: Prokaryotic Flagella (Salmonella typhimurium) (random) Video: Prokaryotic Flagella (Salmonella typhimurium) (random)

15. LE 52-3c Random. Dandelions grow from windblown seeds that land at random and later germinate.

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

17. 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 It is best made by following the fate of a cohort The life table of Belding’s ground squirrels reveals many things about this population

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19. Survivorship Curves A survivorship curve is a graphic way of representing the data in a life table The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate

20. LE 52-4 Males Females 10 Age (years) Number of survivors (log scale) 4 6 8 0 2 1,000 100 10 1

21. 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

22. LE 52-5 III II 100 Percentage of maximum life span Number of survivors (log scale) 0 50 1,000 100 10 1 I

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive Rates A reproductive table, or fertility schedule, is an age-specific summary of the reproductive rates in a population It describes reproductive patterns of a population

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25. 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

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life History Diversity Life histories are very diverse Species that exhibit semelparity, or “big-bang” reproduction, reproduce once and die Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly

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28. “Trade-offs” and Life Histories Organisms have finite resources, which may lead to trade-offs between survival and reproduction

29. LE 52-7 Female Parents surviving the following winter (%) Normal brood size 100 80 60 0 Reduced brood size Enlarged brood size Male 40 20

30. 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

31. LE 52-8a 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.

32. 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

33. LE 52-8b 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.

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In animals, parental care of smaller broods may facilitate survival of offspring

35. 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 Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth

36. 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

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zero population growth occurs when the birth rate equals the death rate Most ecologists use differential calculus to express population growth as growth rate at a particular instant in time: dN dt  rN

38. 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

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Equation of exponential population growth: dN dt  r max N

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential population growth results in a J- shaped curve

41. LE 52-9 Number of generations Population size (N) 2,000 = 1.0N 1,000 1,500 500 0 15 10 5 0 dN dt = 0.5N dN dt

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The J-shaped curve of exponential growth characterizes some rebounding populations

43. LE 52-10 Year Elephant population 8,000 4,000 6,000 2,000 0 1980 1960 1940 1920 1900

44. 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 A more realistic population model limits growth by incorporating carrying capacity

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

46. 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 We construct the logistic model by starting with the exponential model and adding an expression that reduces per capita rate of increase as N increases

47. LE 52-11 Population size (N) Per capita rate of increase (r) Maximum Positive Negative N = K 0

48. 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

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50. The logistic model of population growth produces a sigmoid (S-shaped) curve

51. LE 52-12 Number of generations Population size (N) K = 1,500 1,500 2,000 1,000 500 15 10 5 0 0 Logistic growth Exponential growth = 1.0N dN dt = 1.0N dN dt 1,500 – N 1,500

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Model and Real Populations The growth of laboratory populations of paramecia fits an S-shaped curve

53. LE 52-13a Time (days) Number of Paramecium/mL 1,000 0 400 5 200 10 0 15 800 600 A Paramecium population in the lab

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations overshoot K before settling down to a relatively stable density

55. LE 52-13b Time (days) Number of Daphnia/50 mL 180 0 90 20 60 40 0 60 150 120 A Daphnia population in the lab 30 80 100 120140 160

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations fluctuate greatly around K

57. LE 52-13c Time (years) Number of females 80 1975 1980 40 1985 0 1990 60 A song sparrow population in its natural habitat 20 1995 2000

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

59. 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 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

60. 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

61. 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 about regulation of population growth: – What environmental factors stop a population from growing? – Why do some populations show radical fluctuations in size over time, while others remain stable?

62. 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

63. LE 52-14 Population density Equilibrium density Density- independent birth rate Density-dependent death rate Population density Equilibrium density Density- independent death rate Density-dependent birth rate Population density Equilibrium density Density- dependent death rate Density-dependent birth rate per capita Birth or death rate

64. 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 They are affected by many factors, such as competition for resources, territoriality, health, predation, toxic wastes, and intrinsic factors

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competition for Resources In crowded populations, increasing population density intensifies intraspecific competition for resources

66. LE 52-15 10,000 Average number of seeds per reproducing individual (log scale) 1,000 100 10 1 Plants per m 2 (log scale) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply. Average clutch size 2.8 80 Females per unit area 3.0 3.8 4.0 3.4 3.6 3.2 60 70 50 30 40 20 0 10

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

68. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cheetahs are highly territorial, using chemical communication to warn other cheetahs of their boundaries

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70. Oceanic birds exhibit territoriality in nesting behavior

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72. Health Population density can influence the health and survival of organisms In dense populations, pathogens can spread more rapidly

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

74. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Toxic Wastes Accumulation of toxic wastes can contribute to density-dependent regulation of population size

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

76. 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

77. 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

78. LE 52-18 1960 Year Moose population size 2,500 Steady decline probably caused largely by wolf predation 2,000 1,500 1,000 500 0 1970 1980 1990 2000 Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population

79. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Extreme fluctuations in population size are typically more common in invertebrates than in large mammals

80. LE 52-19 1960 Year Commercial catch (kg) of male crabs (log scale) 730,000 100,000 10,000 1970 1980 1990 1950

81. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metapopulations and Immigration Metapopulations are groups of populations linked by immigration and emigration High levels of immigration combined with higher survival can result in greater stability in populations

82. LE 52-20 1988 Year Number of breeding females 60 1989 1990 1991 Small islands Mandarte Island 50 40 30 20 10 0

83. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many populations undergo boom-and-bust cycles Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors

84. LE 52-21 Year Hare population size (thousands) 1850 Snowshoe hare 0 1875 1900 1925 40 80 120 160 Lynx population size (thousands) Lynx 0 3 6 9

85. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 52.6: Human population growth has slowed after centuries of exponential increase No population can grow indefinitely, and humans are no exception

86. 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

87. LE 52-22 8000 B.C. Human population (billions) 6 5 4 3 2 1 0 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. The Plague 0 1000 A.D. 2000 A.D.

88. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Though the global population is still growing, the rate of growth began to slow about 40 years ago

89. LE 52-23 Annual percent increase 2.2 2 1.8 1.6 1.4 1.2 1 2003 2050 Year 2025 2000 1975 1950 0.8 0.6 0.4 0.2 0

90. 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: – Zero population growth = High birth rate – High death rate – Zero population growth = Low birth rate – Low death rate The demographic transition is the move from the first state toward the second state

91. LE 52-24 Birth or death rate per 1,000 people 50 40 30 20 10 Sweden 2050 Year 20001900 1950 1850 0 1800 1750 Birth rate Death rate Mexico Birth rate Death rate

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

93. 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 Age structure is the relative number of individuals at each age It is commonly represented in pyramids

94. LE 52-25 Rapid growth Afghanistan Age Male Percent of population Female 86 42 24 68 0 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 Slow growth United States Age Male Percent of population Female 6 42 24 68 0 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 8 Decrease Italy Male Percent of population Female 6 42 24 68 0 8

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

96. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Infant Mortality and Life Expectancy Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition

97. LE 52-26 Infant mortality (deaths per 1,000 births) 50 40 30 20 10 0 Developed countries 60 Developing countries Life expectancy (years) 80 40 20 0 Developed countries 60 Developing countries

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

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

100. 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 It is one measure of how close we are to the carrying capacity of Earth Countries vary greatly in footprint size and available ecological capacity

101. LE 52-27 Ecological footprint (ha per person) 14 12 10 8 6 4 16 0 2 0 24 6 8 1012 14 16 Available ecological capacity (ha per person) New Zealand Australia Canada Sweden World China India Spain UK Japan Germany Norway USA Netherlands

102. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At more than 6 billion people, the world is already in ecological deficit