Chapter 8

1. Chapter 8 Population Ecology

2. 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

3. 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

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

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

6. 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.

7. Limits on Population Growth: Biotic Potential vs. Environmental Resistance • 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. • Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

8. 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. Figure 8-4

9. 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. Figure 8-4

10. 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. Figure 8-6

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

12. What do you think? • 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.

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

14. 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.

15. 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

16. 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. • Nearly extinct prior to their protection in 1920’s. • Today 25-30 million white-tailed deer in U.S. pose human interaction problems. • Deer-vehicle collisions (1.5 million per year). • Transmit disease (Lyme disease in deer ticks).

17. REPRODUCTIVE PATTERNS • Some species reproduce without having sex (asexual). • Offspring are exact genetic copies (clones). • Others reproduce by having sex (sexual). • 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. • Major advantages: genetic diversity, offspring protection.

18. 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. Figure 8-8

19. Reproductive Patterns:Opportunists and Competitors • 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

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

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

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