Population Ecology

1. Population Ecology

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

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

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

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

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

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

8. 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.

9. 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

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

11. 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

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

13. 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

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

15. 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

16. 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.

17. 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

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

19. 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).

20. 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

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

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

23. 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 Fig. 8-10a, p. 168

24. 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 Fig. 8-10b, p. 168

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

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

28. Animation: Life History Patterns PLAY ANIMATION