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Population Ecology

Population Ecology. Study of populations in relation to environment. Environmental influences on: population density population distribution (dispersion) age structure. Definition of Population:.

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Population Ecology

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  1. Population Ecology

  2. Study of populations in relation to environment • Environmental influences on: • population density • population distribution (dispersion) • age structure

  3. Definition of Population: • Group of individuals of a single species living in a specific geographic region at the same time

  4. Density: A Dynamic Perspective • Determining the density of natural populations is possible, but difficult to accomplish • In most cases it is impractical or impossible to count all individuals in a population • How do wildlife biologists approximate populations?

  5. Estimating Wildlife Population Size Defined Populations -complete counts -incomplete counts -indirect counts Undefined Populations Mark and Recapture

  6. Births and immigration add individuals to a population. Births Immigration PopuIationsize Emigration Deaths Deaths and emigration remove individuals from a population. • Density is the result of a dynamic interaction of processes that add individuals to a population and those that remove individuals from it • How do these factors • Contribute to Population Size?? • Births • Deaths • Immigration • Emigration

  7. Patterns of Dispersion • Environmental and social factors influence the spacing of individuals in a population

  8. Clumped Dispersion • Individuals aggregate in patches • May be influenced by resource availability and behavior

  9. Uniform Dispersion • Individuals are evenly distributed • May be influenced by social interactions such as territoriality

  10. Random Dispersion • Position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

  11. Life history traits are products of natural selection • Life history traits are evolutionary outcomes • Reflected in the development, physiology, and behavior of an organism

  12. Semelparity: Big Bang • Reproduce a single time and die • putting all available resources into maximizing reproduction at the expense of future life 

  13. Iteroparity – Repeated Reproduction • produce offspring repeatedly over time • increased parental care along with enhanced energetic investment per offspring

  14. 100 Male Female 80 60 Parents surviving the following winter (%) 40 20 The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents. CONCLUSION 0 Reduced brood size Normal brood size Enlarged brood size “Trade-offs” and Life Histories • Which may lead to trade-offs between survival and reproduction • Organisms have finite resources RESULTS • Kestrels: • Produce a few eggs? • Can invest more into each, ensuring greater survival • Produce many eggs? • Costly but if all survive, fitness is better

  15. More is Better? • Some plants produce a large number of small seeds • Ensuring that at least some of them will grow and eventually reproduce

  16. Fewer is Better? • Other types of plants produce a moderate number of large seeds • That provide a large store of energy that will help seedlings become established

  17. Demography • Study of the vital statistics of a population • And how they change over time • Death rates and birth rates • Zero population growth • Occurs when the birth rate equals the death rate

  18. Exponential Population Growth Population increase under idealized conditions No limits on growth • Under these conditions • The rate of reproduction is at its maximum, called the intrinsic rate of increase

  19. Example-understanding growth Question: I offer you a job for 1 cent/day and your pay will double every day. You will be hired for 30 days. Will you take my job offer? Answer: If you said YES, you will have made $~21 million dollars for 30 days of work. How is this possible?????

  20. Amount of Pay/Day # of Days 1ST DAY OF WORK: 1 cent pay/day 30TH DAY OF WORK: ~10.2 million/day How is this possible?????

  21. dN  rmaxN dt Exponential Growth Model *Idealized population in an unlimited environment *Very rapid doubling time; steep J curve *r=N=(b-d)N t r=instrinsic rate of growth

  22. 8,000 6,000 Elephant population 4,000 2,000 0 1900 1920 1940 1960 1980 Year Exponential Growth in the Real World • Characteristic of some populations that are rebounding • Cannot be sustained for long in any population

  23. Logistic Population Growth • A more realistic population model • Limits growth by incorporating carrying capacity

  24. Logistic Population Growth • Carrying capacity (K) • Is the maximum population size the environment can support • In the logistic population growth model • The per capita rate of increase declines as carrying capacity is reached

  25. 2,000 dN  1.0N Exponential growth dt 1,500 (K  N) K  1,500 dN  rmax N Logistic growth dt K Population size (N) 1,000 dN 1,500  N  1.0N dt 1,500 500 0 0 5 10 15 Number of generations Logistic Population Growth • Produces a sigmoid (S-shaped) curve Figure 52.12

  26. 1,000 800 600 Number of Paramecium/ml 400 200 0 0 5 15 10 Time (days) (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment. The Logistic Model and Real Populations • The growth of laboratory populations of Paramecium • Fits an S-shaped curve

  27. 180 150 120 90 Number of Daphnia/50 ml 60 30 0 160 0 40 60 100 120 140 20 80 Time (days) (b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size. Logistic Growth and The Real World • Some populations overshoot K • Before settling down to a relatively stable density What type of feedback loop is this?

  28. 80 60 40 Number offemales 20 0 1995 2000 1980 1985 1990 1975 Time (years) (c) A song sparrowpopulation in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model. Logistic Growth and the Real World • Some populations • Fluctuate greatly around K

  29. The Logistic Model and Life Histories • Life history traits favored by natural selection • May vary with population density and environmental conditions

  30. Natural selection (diverse reproductive strategies) a) Relatively few, large offspring (K selected species) b) Many, small offspring (r selected species) (K selected species) (r selected species)

  31. Populations Regulated Biotic and Abiotic Factors Two general questions we can ask about regulation of population growth • What environmental factors stop a population from growing? • 2. Why do some populations show radical fluctuations in size over time, while others remain stable?

  32. 4.0 10,000 3.8 3.6 Average number of seeds per reproducing individual (log scale) 1,000 3.4 Average clutch size 3.2 3.0 100 2.8 0 0 40 50 60 80 20 30 10 70 0 10 100 Seeds planted per m2 Density of females (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply. Competition for Resources • In crowded populations, increasing population density • Intensifies intraspecific competition for resources

  33. Many vertebrates and some invertebrates are territorial • Territoriality may limit density • Cheetahs are highly territorial • Using chemical communication to warn other cheetahs of their boundaries

  34. Territoriality: Ocean birds • Exhibit territoriality in nesting behavior

  35. Health • Population density • Can influence the health and survival of organisms • In dense populations • Pathogens can spread more rapidly

  36. 730,000 100,000 Commercial catch (kg) of male crabs (log scale) 10,000 1990 1950 1980 1960 1970 Year Figure 52.19 Fluctuations in Population Size • Extreme fluctuations in population size • Are typically more common in invertebrates than in large mammals

  37. Metapopulations and Immigration • Metapopulations • Groups of populations linked by immigration and emigration

  38. 60 50 40 Mandarte island Number of breeding females 30 20 Small islands 10 0 1991 1988 1989 1990 Year Immigration- Movement Into a Population • High levels of immigration combined with higher survivalcan result in greater stability in populations Figure 52.20

  39. Snowshoe hare 160 120 Lynx 9 Lynx population size (thousands) Hare population size (thousands) 80 6 40 3 0 0 1850 1875 1900 1925 Year Population Cycles • Many populations undergo regular boom-and-bust cycles • Influenced by complex interactions between biotic and abiotic factors

  40. Human Populations 6 5 4 Human population (billions) 3 2 The Plague 1 0 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. 2000 A.D. 0 Figure 52.22 • No population can grow indefinitely and humans are no exception

  41. Global Carrying Capacity • Just how many humans can the biosphere support? • Carrying capacity of earth is unknown…. http://www.youtube.com/watch?v=9_9SutNmfFk http://www.youtube.com/watch?v=UUOEcNomakw&feature=rec-LGOUT-exp_fresh+div-1r-8-HM http://www.youtube.com/watch?v=4B2xOvKFFz4&feature=related

  42. Age Structure • One important demographic factor in present and future growth trends • Is a country’s age structure, the relative number of individuals at each age

  43. Rapid growth Afghanistan Decrease Italy Slow growth United States Male Female Female Male Male Age Age Female 85 85 80–84 80–84 75–79 75–79 70–74 70–74 65–69 65–69 60–64 60–64 55–59 55–59 50–54 50–54 45–49 45–49 40–44 40–44 35–39 35–39 30–34 30–34 25–29 25–29 20–24 20–24 15–19 15–19 10–14 10–14 5–9 5–9 0–4 0–4 8 8 8 6 6 6 4 4 4 2 2 2 0 0 0 2 2 2 4 4 4 6 6 6 8 8 8 Percent of population Percent of population Percent of population Figure 52.25 • Age structure is commonly represented in pyramids

  44. 60 80 50 60 40 Infant mortality (deaths per 1,000 births) Life expectancy (years) 40 30 20 20 10 0 0 Developed countries Developed countries Developing countries Developing countries Figure 52.26 Infant Mortality and Life Expectancy • Infant mortality and life expectancy at birth • Vary widely among developed and developing countries but do not capture the wide range of the human condition

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