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 (Campbell) Chapter 45

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What is Ecology? Is the study of the interactions of organisms with one another and with the physical and chemical environment.

3. 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 – No population, including the human population, can continue to grow indefinitely

4. 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

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The fur seal population of St. Paul Island, off the coast of Alaska – Is one that has experienced dramatic fluctuations in size Figure 52.1 Human predation is one of reasons for the population to grow and decline

6. 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

7. 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

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

9. 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 (immigration) and those that remove individuals from it (emigration) Figure 52.2 Births and immigration add individuals to a population. BirthsImmigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population.

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

11. 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 – Plants and fungi are often found together because it favors soil conditions and other environmental factors 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.

12. 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 – Some plants produce chemicals to inhibit the germination and growth of nearby individuals that compete for resources. 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.

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

14. 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

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 – Survivorship Curve can be classified in three types Type I is flat at the start, reflecting low death rates during early and middle life and drops steeply as many older individuals die – Humans and large mammals are this curve because produce few individuals are provide good care

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Continue… Type II: Constant death over an individual life span – Examples: rodents, invertebrates, some plants Type III: drops sharply at the start, reflecting very high death rates for the young, but flattens out as death rate declines for those individuals that survived to a certain critical period

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)

20. 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 – Type II Survivorship Curve Figure 52.4 1000 100 10 1 Number of survivors (log scale) 0 2 46 810 Age (years) Males Females

21. 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

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 – Three basic variable: When reproduction begins, how often an organism reproduces, and how many offspring are reproduce

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 Example: agave or century plant

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 – Showed that survival was cost to parents caring for their young. RESULTS

28. 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.

29. 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.

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

31. 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

32. 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

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zero population growth – Occurs when the birth rate equals the death rate The population growth equation can be expressed as dN dt  rN

34. 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

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

36. 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

37. 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

38. 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

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

40. 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

41. 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)

42. 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

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

44. 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)

45. 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

46. 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.

47. 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.

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

49. 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

50. 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 Example: Parasitism and Predation r-selection, or density-independent selection – Selects for life history traits that maximize reproduction Example: Seasonal changes and Natural distribances

51. 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 of the variation seen in the natural histories of species

52. 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

53. 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?

54. 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

55. 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.

56. 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

57. 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.

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

59. 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

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oceanic birds – Exhibit territoriality in nesting behavior Figure 52.17 Gannets nest virtually a peck apart and defend their territories by calling and pecking at one another.

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Health Population density – Can influence the health and survival of organisms In dense populations – Pathogens can spread more rapidly

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

63. 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

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

65. 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

66. 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

67. 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)

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

69. 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

70. 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

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

72. 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

73. 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

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

75. 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

76. 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

77. 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

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

79. 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

80. 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

81. 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

82. 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

83. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Global Carrying Capacity Just how many humans can the biosphere support? Estimate today is: 1 billion to over 1,000 billion (1 trillion) people, with an over of 10-15 billion.

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

85. 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

86. 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) Two conclusion were found in this graph” 1-countries vary greatly in their individual footprint size and in their available ecological capacity (the actual resource based of each country). 2- The world was already in ecological deficit when the study was conducted Overall analysis suggest that he world is not at or slightly above its carrying capacity

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