1. Chapter 52 Population Ecology

2. 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

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

4. 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.

5. 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.

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

7. 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

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

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

10. 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

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

13. 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.

14. 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.

15. In animals, parental care of smaller broods may facilitate survival of offspring

16. Carrying capacity (K) is the maximum population size the environment can support

17. 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

18. Territoriality In many vertebrates and some invertebrates, territoriality may limit density

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

22. Predation As a prey population builds up, predators may feed preferentially on that species

23. Toxic Wastes Accumulation of toxic wastes can contribute to density-dependent regulation of population size

24. 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. Human Population Growth

25. 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

26. 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

27. 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

28. 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

29. Age structure diagrams can predict a population’s growth trends They can illuminate social conditions and help us plan for the future

30. 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

31. 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

32. 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

35. Competition Interspecific competition occurs when species compete for a resource in short supply Strong competition can lead to competitive exclusion, local elimination of a competing species

36. The Competitive Exclusion Principle The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place

37. LE 53-2 Chthamalus fundamental niche High tide Low tide Ocean Chthamalus realized niche High tide Low tide Ocean Balanus realized niche Chthamalus Balanus

38. Resource Partitioning Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community

39. LE 53-3 A. insolitus usually perches on shady branches. A. ricordii A. insolitus A. christophei A. cybotes A. etheridgei A. aliniger A. distichus perches on fence posts and other sunny surfaces.

40. Predation Predation refers to interaction where one species, the predator, kills and eats the other, the prey Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison

41. Prey display various defensive adaptations Behavioral defenses include hiding, fleeing, self- defense, and alarm calls Animals also have morphological and physiological defense adaptations

42. Cryptic coloration, or camouflage, makes prey difficult to spot Video: Seahorse Camouflage Video: Seahorse Camouflage

43. Animals with effective chemical defense often exhibit bright warning coloration, called aposematic coloration Predators are particularly cautious in dealing with prey that display such coloration

45. In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model

46. LE 53-7 Hawkmoth larva Green parrot snake

47. In Müllerian mimicry, two or more unpalatable species resemble each other

48. LE 53-8 Cuckoo bee Yellow jacket

49. Herbivory Herbivory refers to an interaction in which an herbivore eats parts of a plant or alga It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores

50. Parasitism In parasitism, one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process Parasitism exerts substantial influence on populations and the structure of communities

51. Disease Effects of disease on populations and communities are similar to those of parasites Pathogens, disease-causing agents, are typically bacteria, viruses, or protists

52. Mutualism Mutualistic symbiosis, or mutualism, is an interspecific interaction that benefits both species Video: Clownfish and Anemone Video: Clownfish and Anemone

54. Commensalism In commensalism, one species benefits and the other is apparently unaffected Commensal interactions are hard to document in nature because any close association of two species likely affects both

56. LE 53-12 Quaternary consumers Tertiary consumers Carnivore Secondary consumers Carnivore Primary consumers ZooplanktonHerbivore Primary producers Phytoplankton Plant A terrestrial food chain A marine food chain

57. LE 53-13 Euphausids (krill) Carnivorous plankton Phyto- plankton Copepods Squids Elephant seals Fishes Birds Crab-eater seals Leopard seals Sperm whales Smaller toothed whales Baleen whales Humans

58. LE 53-14 Zooplankton Fish larvae Fish eggs Sea nettle Juvenile striped bass

59. Keystone Species In contrast to dominant species, keystone species are not necessarily abundant in a community They exert strong control on a community by their ecological roles, or niches

60. LE 53-16 Without Pisaster (experimental) With Pisaster (control) 1963 ’64’65 ’66 ’67 ’68’69 ’70 ’71 ’72 ’73 20 15 10 5 0 Number of species present

61. LE 53-21 Before a controlled burn. A prairie that has not burned for several years has a high propor-tion of detritus (dead grass). During the burn. The detritus serves as fuel for fires. After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.

62. LE 53-22 Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance. One year after fire. This photo of the same general area taken the following year indicates how rapidly the com-munity began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.

63. Human Disturbance Humans are the most widespread agents of disturbance Human disturbance to communities usually reduces species diversity Humans also prevent some naturally occurring disturbances, which can be important to community structure

64. Ecological Succession Ecological succession is the sequence of community and ecosystem changes after a disturbance Primary succession occurs where no soil exists when succession begins Secondary succession begins in an area where soil remains after a disturbance

65. Early-arriving species and later-arriving species may be linked in one of three processes: – Early arrivals may facilitate appearance of later species by making the environment favorable – They may inhibit establishment of later species – They may tolerate later species but have no impact on their establishment

66. LE 53-24 Pioneer stage, with fireweed dominant Dryas stage Spruce stage Nitrogen fixation by Dryas and alder increases the soil nitrogen content. Successional stage DryasPioneer Alder Spruce Soil nitrogen (g/m 2 ) 60 50 40 30 20 10 0

67. LE 54-2 Microorganisms and other detritivores Tertiary consumers Secondary consumers Detritus Primary consumers Sun Primary producers Heat Key Chemical cycling Energy flow

68. Decomposition Decomposition connects all trophic levels Detritivores, mainly bacteria and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs

70. Pyramids of Production A pyramid of net production represents the loss of energy with each transfer in a food chain

71. LE 54-11 1,000,000 J of sunlight 10,000 J 1,000 J 100 J 10 J Tertiary consumers Secondary consumers Primary consumers Primary producers

72. Pyramids of Biomass In a biomass pyramid, each tier represents the dry weight of all organisms in one trophic level Most biomass pyramids show a sharp decrease at successively higher trophic levels

73. LE 54-12a Trophic level Dry weight (g/m 2 ) Tertiary consumers Secondary consumers Primary consumers Primary producers 1.5 11 37 809 Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida.

74. Certain aquatic ecosystems have inverted biomass pyramids: Primary consumers outweigh the producers

75. LE 54-12b Trophic level Dry weight (g/m 2 ) Primary consumers (zooplankton) Primary producers (phytoplankton) 21 4 In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton).

76. Pyramids of Numbers A pyramid of numbers represents the number of individual organisms in each trophic level

77. LE 54-13 Trophic level Number of individual organisms Tertiary consumers Secondary consumers Primary consumers Primary producers 3 354,904 708,624 5,842,424

78. LE 54-17a Transport over land Precipitation over land Evaporation from ocean Precipitation over ocean Net movement of water vapor by wind Solar energy Evapotranspiration from land Runoff and groundwater Percolation through soil

79. LE 54-17b Cellular respiration Burning of fossil fuels and wood Carbon compounds in water Photosynthesis Primary consumers Higher-level consumers Detritus Decomposition CO 2 in atmosphere

80. LE 54-17c Assimilation N 2 in atmosphere Decomposers Nitrifying bacteria Nitrifying bacteria Nitrogen-fixing soil bacteria Denitrifying bacteria Nitrification Ammonification Nitrogen-fixing bacteria in root nodules of legumes NO 3 – NO 2 – NH 4 + NH 3

81. LE 54-17d Sedimentation Plants Rain Runoff Weathering of rocks Geologic uplift Soil Leaching Decomposition Plant uptake of PO 4 3– Consumption

82. Agriculture and Nitrogen Cycling Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

83. Toxins in the Environment Humans release many toxic chemicals, including synthetics previously unknown to nature In some cases, harmful substances persist for long periods in an ecosystem One reason toxins are harmful is that they become more concentrated in successive trophic levels In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

84. LE 54-23 Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Lake trout 4.83 ppm Smelt 1.04 ppm Herring gull eggs 124 ppm Concentration of PCBs

85. Depletion of Atmospheric Ozone Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere Satellite studies suggest that the ozone layer has been gradually thinning since 1975

86. LE 54-26 Ozone layer thickness (Dobson units) 350 300 250 200 150 100 50 0 1960 1965 1970 19751980 1985 1990 1995 2000 2005 Year (Average for the month of October) 1955

87. Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity

88. LE 54-27 Chlorine atoms O3O3 Chlorine Cl 2 O 2 CIO O2O2 O2O2 Chlorine from CFCs interacts with ozone (O 3 ), forming chlorine monoxide (CIO) and oxygen (O 2 ). Sunlight causes Cl 2 O 2 to break down into O 2 and free chlorine atoms. The chlorine atoms can begin the cycle again. Two CIO molecules react, forming chlorine peroxide (Cl 2 O 2 ). Sunlight

89. LE 54-28 October 1979 October 2000