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Chapter 8 Population Ecology. Chapter Overview Questions What are the major characteristics of populations? What are the major characteristics of populations?

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Presentation on theme: "Chapter 8 Population Ecology. Chapter Overview Questions What are the major characteristics of populations? What are the major characteristics of populations?"— Presentation transcript:

1 Chapter 8 Population Ecology

2 Chapter Overview Questions What are the major characteristics of populations? What are the major characteristics of populations? How do populations respond to changes in environmental conditions? How do populations respond to changes in environmental conditions? How do species differ in their reproductive patterns? How do species differ in their reproductive patterns?

3 Updates Online The latest references for topics covered in this section can be found at the book companion website. Log in to the books e-resources page at to access InfoTrac articles. InfoTrac: One Hatchling at a Time. Brownsville Herald (Brownsville, TX), July 2, InfoTrac: One Hatchling at a Time. Brownsville Herald (Brownsville, TX), July 2, InfoTrac: Where the Cattle Herds Roam, Ideally in Harmony With Their Neighbors. Jim Robbins. The New York Times, July 11, 2006 pF3(L). InfoTrac: Where the Cattle Herds Roam, Ideally in Harmony With Their Neighbors. Jim Robbins. The New York Times, July 11, 2006 pF3(L). InfoTrac: A nudge for nature. Milwaukee Journal Sentinel, July 10, InfoTrac: A nudge for nature. Milwaukee Journal Sentinel, July 10, Earth Island Institute Earth Island Institute Environmental Defense: Creating a Conservation Community in Oregons Williamette Valley Environmental Defense: Creating a Conservation Community in Oregons Williamette Valley Marine Bio: Habitat Conservation Marine Bio: Habitat Conservation

4 They were over- hunted to the brink of extinction by the early 1900s and are now making a comeback. They were over- hunted to the brink of extinction by the early 1900s and are now making a comeback. Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction? Figure 8-1

5 Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction? Sea otters are an important keystone species for sea urchins and other kelp- eating organisms. Sea otters are an important keystone species for sea urchins and other kelp- eating organisms. Figure 8-1

6 POPULATION DYNAMICS AND CARRYING CAPACITY Most populations live in clumps although other patterns occur based on resource distribution. Most populations live in clumps although other patterns occur based on resource distribution. Figure 8-2

7 Fig. 8-2a, p. 162 (a) Clumped (elephants)

8 Fig. 8-2b, p. 162 (b) Uniform (creosote bush)

9 Fig. 8-2c, p. 162 (c) Random (dandelions)

10 Changes in Population Size: Entrances and Exits Populations increase through births and immigration Populations increase through births and immigration Populations decrease through deaths and emigration Populations decrease through deaths and emigration

11 Age Structure: Young Populations Can Grow Fast How fast a population grows or declines depends on its age structure. How fast a population grows or declines depends on its age structure. Prereproductive age: not mature enough to reproduce. Prereproductive age: not mature enough to reproduce. Reproductive age: those capable of reproduction. Reproductive age: those capable of reproduction. Postreproductive age: those too old to reproduce. Postreproductive age: those too old to reproduce.

12 Limits on Population Growth: Biotic Potential vs. Environmental Resistance No population can increase its size indefinitely. No population can increase its size indefinitely. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat. Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

13 Exponential and Logistic Population Growth: J-Curves and S-Curves Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off. Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off. Figure 8-4

14 Fig. 8-3, p. 163 Environmental Resistance Time (t) Population size (N) Carrying capacity (K) Exponential Growth Biotic Potential

15 Animation: Exponential Growth PLAY ANIMATION

16 Exponential and Logistic Population Growth: J-Curves and S-Curves As a population levels off, it often fluctuates slightly above and below the carrying capacity. As a population levels off, it often fluctuates slightly above and below the carrying capacity. Figure 8-4

17 Fig. 8-4, p. 164 Carrying capacity Year Number of sheep (millions) Overshoot

18 Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. Figure 8-6

19 Fig. 8-6, p. 165 Number of reindeer Population overshoots carrying capacity Carrying capacity Year Population Crashes

20 Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Over time species may increase their carrying capacity by developing adaptations. Over time species may increase their carrying capacity by developing adaptations. Some species maintain their carrying capacity by migrating to other areas. Some species maintain their carrying capacity by migrating to other areas. So far, technological, social, and other cultural changes have extended the earths carrying capacity for humans. So far, technological, social, and other cultural changes have extended the earths carrying capacity for humans.

21 How Would You Vote? Can we continue to expand the earth's carrying capacity for humans? Can we continue to expand the earth's carrying capacity for humans? a. No. Unless humans voluntarily control their population and conserve resources, nature will do it for us. a. No. Unless humans voluntarily control their population and conserve resources, nature will do it for us. b. Yes. New technologies and strategies will allow us to further delay exceeding the earth's carrying capacity. b. Yes. New technologies and strategies will allow us to further delay exceeding the earth's carrying capacity.

22 Population Density and Population Change: Effects of Crowding Population density: the number of individuals in a population found in a particular area or volume. Population density: the number of individuals in a population found in a particular area or volume. A populations density can affect how rapidly it can grow or decline. A populations density can affect how rapidly it can grow or decline. e.g. biotic factors like diseasee.g. biotic factors like disease Some population control factors are not affected by population density. Some population control factors are not affected by population density. e.g. abiotic factors like weathere.g. abiotic factors like weather

23 Types of Population Change Curves in Nature Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. Stable: fluctuates slightly above and below carrying capacity. Stable: fluctuates slightly above and below carrying capacity. Irruptive: populations explode and then crash to a more stable level. Irruptive: populations explode and then crash to a more stable level. Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles. Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles. Irregular: erratic changes possibly due to chaos or drastic change. Irregular: erratic changes possibly due to chaos or drastic change.

24 Types of Population Change Curves in Nature Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. Figure 8-7

25 Fig. 8-7, p. 166 Population size (thousands) Year Lynx Hare

26 Animation: Capture-Recapture Method PLAY ANIMATION

27 Case Study: Exploding White-Tailed Deer Populations in the United States Since the 1930s the white-tailed deer population has exploded in the United States. Since the 1930s the white-tailed deer population has exploded in the United States. Nearly extinct prior to their protection in 1920s. Nearly extinct prior to their protection in 1920s. Today million white-tailed deer in U.S. pose human interaction problems. Today million white-tailed deer in U.S. pose human interaction problems. Deer-vehicle collisions (1.5 million per year). Deer-vehicle collisions (1.5 million per year). Transmit disease (Lyme disease in deer ticks). Transmit disease (Lyme disease in deer ticks).

28 REPRODUCTIVE PATTERNS Some species reproduce without having sex (asexual). Some species reproduce without having sex (asexual). Offspring are exact genetic copies (clones). Offspring are exact genetic copies (clones). Others reproduce by having sex (sexual). Others reproduce by having sex (sexual). Genetic material is mixture of two individuals. Genetic material is mixture of two individuals. Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly. Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly. Major advantages: genetic diversity, offspring protection. Major advantages: genetic diversity, offspring protection.

29 Sexual Reproduction: Courtship Courtship rituals consume time and energy, can transmit disease, and can inflict injury on males of some species as they compete for sexual partners. Courtship rituals consume time and energy, can transmit disease, and can inflict injury on males of some species as they compete for sexual partners. Figure 8-8

30 Reproductive Patterns: Opportunists and Competitors Large number of smaller offspring with little parental care (r- selected species). Large number of smaller offspring with little parental care (r- selected species). Fewer, larger offspring with higher invested parental care (K-selected species). Fewer, larger offspring with higher invested parental care (K-selected species). Figure 8-9

31 Fig. 8-9, p. 168 r species; experience r selection Time Number of individuals K Carrying capacity K species; experience K selection

32 Reproductive Patterns r-selected species tend to be opportunists while K-selected species tend to be competitors. r-selected species tend to be opportunists while K-selected species tend to be competitors. Figure 8-10

33 Fig. 8-10a, p. 168 Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species r-Selected Species Cockroach Dandelion

34 Fig. 8-10b, p. 168 Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species K-Selected Species SaguaroElephant

35 Survivorship Curves: Short to Long Lives The way to represent the age structure of a population is with a survivorship curve. The way to represent the age structure of a population is with a survivorship curve. Late loss population live to an old age. Late loss population live to an old age. Constant loss population die at all ages. Constant loss population die at all ages. Most members of early loss population, die at young ages. Most members of early loss population, die at young ages.

36 Survivorship Curves: Short to Long Lives The populations of different species vary in how long individual members typically live. The populations of different species vary in how long individual members typically live. Figure 8-11

37 Fig. 8-11, p. 169 Percentage surviving (log scale) Age Early loss Late loss Constant loss

38 Animation: Life History Patterns PLAY ANIMATION

39 Video: Coral Spawning PLAY VIDEO

40 Video: Kelp Forest (Channel Islands) PLAY VIDEO

41 Video: Salmons Swimming Upstream PLAY VIDEO


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