Chapter 8 Population Ecology

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

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. Figure 8-1

Southern Sea Otter Figure 5.1 An endangered southern sea otter in Monterey Bay, California (USA) uses a stone to crack the shells of clams that it feeds on (left). It lives in a giant bed of seaweed called kelp (right). Fig. 5-1, p. 102

Core Case Study: Southern Sea Otters - A Species in Recovery Live in giant kelp forests By the early 1900s they had been hunted almost to extinction Partial recovery since 1977 Why care about sea otters? Ethics Tourism dollars Keystone species

Chapter Objectives What are the major characteristics of populations? How do populations regulate their size? How do species differ in their reproductive patterns?

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

What are some advantages to living in clumps? Disadvantages? Figure 5.14 Three general habitat dispersion patterns for a population’s individuals. a. Clumped (elephants) Fig. 5-14a, p. 112

b. Uniform (creosote bush) Figure 5.14 Three general habitat dispersion patterns for a population’s individuals. b. Uniform (creosote bush) Fig. 5-14b, p. 112

Figure 5.14 Three general habitat dispersion patterns for a population’s individuals. c. Random (dandelions) Fig. 5-14c, p. 112

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

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

Exponential and Logistic Population Growth: J-Curves and S-Curves The intrinsic rate of increase (r) Slope Rise over run. Figure 8-4

Exponential and Logistic Population Growth: J-Curves and S-Curves Europeans landed in Tasmania 1642. Guns, Germs, and Steel. Tasmania isolated 10,000 years ago. Figure 8-4

Reindeer introduced to small Bering Sea island of St. Paul. 1910. Lichens, mosses,and other food sources plentiful. Easter Island Figure 8-6

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment. 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. b. Yes. New technologies and strategies will allow us to further delay exceeding the earth's carrying capacity.

Population Density and Population Change: Effects of Crowding Population density: the number of individuals in a population found in a particular area or volume. e.g. biotic factors like disease e.g. abiotic factors like weather

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

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. Figure 8-7

Density-Dependent Factors Wolf and Moose Populations on Isle Royale The relationship between moose and wolves on Isle Royale illustrates how predation can affect population growth. In this example, the moose population was also affected by changes in food supply, and the wolf population was also affected by disease. Moose Wolves Copyright Pearson Prentice Hall

White-Tailed Deer Populations What should we do? Figure 5-17: White-tailed deer populations in the United States have been growing. Fig. 5-17, p. 115

Case Study: Exploding White-Tailed Deer Populations in the United States Nearly extinct prior to their protection in 1920’s. Lack of predators (wolf, cougar, bear) Today 25-30 million white-tailed deer in U.S. pose human interaction problems. Deer-vehicle collisions (1.5 million per year). Injure 14,000 and kills 200 $1.1 billion in damages Transmit disease (Lyme disease in deer ticks). Eat native vegetation Suburbs in Forest expansion and habitat loss

More than nine out of 10 of the species recently caught were too young to have reproduced, meaning they may have been the last generation of the bluefin tuna.

Chapter Objectives What are the major characteristics of populations? How do populations regulate their size? Humans must manage populations in the future. How do species differ in their reproductive patterns?

REPRODUCTIVE PATTERNS Asexual. Offspring are exact genetic copies (clones). Sexual. Genetic material is mixture of two individuals. Courtship and mating rituals can be costly. Because there is variation in a population…………….

Sexual Reproduction: Courtship consume time and energy, transmit disease, inflict injury. picking the most fit for next generation is worth the risk Figure 8-8

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

Little or no parental care and protection of offspring r-Selected Species Cockroach Dandelion 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 Figure 8.10 Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes. Fig. 8-10a, p. 168

Fewer, larger offspring High parental care and protection of offspring K-Selected Species Elephant Saguaro 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 Figure 8.10 Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes. Fig. 8-10b, p. 168

Survivorship Curves: Short to Long Lives The way to represent the age structure of a population.

Percentage surviving (log scale) Late loss Constant loss Percentage surviving (log scale) Figure 8.11 When does death come? Survivorship curves for populations of different species, show the percentages of the members of a population surviving at different ages. Most members of a late loss population (such as elephants, rhinoceroses, and humans) live to an old age. Members of a constant loss population (such as many songbirds) die at all ages. In an early loss population (such as annual plants and many bony fish species), most members die at a young age. These generalized survivorship curves only approximate the realities of nature. Early loss Age Fig. 8-11, p. 169

TYING IT ALL TOGETHER Southern Sea Otters and Sustainability p. 117

Figure 5.B Changes in the population size of southern sea otters off the coast of the U.S. state of California, 1983–2012. Changes in the population size of southern sea otters off the coast of the U.S. state of California, 1983–2012. How do we determine delisting threshold? Fig. 5-B, p. 114

What term is used for the maximum population of a given species that a particular habitat can sustain indefinitely? range of tolerance carrying capacity population density environmental resistance

Biotic potential and ______ determine ______. Environmental resistance; intrinsic rate of increase Intrinsic rate of increase; carrying capacity Carrying capacity; environmental resistance Environmental resistance, carrying capacity

A J-shaped curve is characteristic of Zero population growth Logistic growth A population that has overshot its carrying capacity Exponential growth

True or false? Humans throughout history have been exempt from the effects of population overshoots and diebacks. True False

What term is used for the maximum population of a given species that a particular habitat can sustain indefinitely? range of tolerance carrying capacity population density environmental resistance

Biotic potential and ______ determine ______. Environmental resistance; intrinsic rate of increase Intrinsic rate of increase; carrying capacity Carrying capacity; environmental resistance Environmental resistance, carrying capacity

A J-shaped curve is characteristic of Zero population growth Logistic growth A population that has overshot its carrying capacity Exponential growth

Generally, a species with a high intrinsic rate of increase will r-selected K-selected Be a specialist Reproduce late in life

True or false? Humans throughout history have been exempt from the effects of population overshoots and diebacks. True False

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