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Chapter 53 Population Ecology

Chapter 53 Population Ecology. Population Ecology. Study of the factors that affect population size and composition. Individuals of a single species that occupy the same area. Population. Important Characteristics. 1. Density 2. Dispersion. Density.

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Chapter 53 Population Ecology

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  1. Chapter 53 Population Ecology

  2. Population Ecology • Study of the factors that affect population size and composition.

  3. Individuals of a single species that occupy the same area. Population

  4. Important Characteristics 1. Density 2. Dispersion

  5. Density • Number of individuals per unit area or volume. • Ex: • Diatoms - 5 million/m3 • Trees - 5,000/km2 • Deer - 4/km2

  6. Dispersion • Pattern of spacing among individuals. • Types: 1. Clumped 2. Uniform 3. Random

  7. Clumped Dispersion • May result form a patchy environment. • May increase chances for survival. • Ex: • Schooling behavior • Flocks of birds

  8. Uniform Dispersion • Often the result of antagonistic interactions between individuals. • Ex: • Territories • Spacing between desert plants

  9. Random Dispersion • Often the result of the absence of strong attractions or repulsions between individuals. • Not a common pattern.

  10. Demography • The study of the vital statistics that affect population size. • Ex: Birth and Death rates

  11. Demographic Factors • Age structure of the population. • Birth and Death rates. • Generation time. • Sex ratio and reproductive behavior.

  12. Life Tables • Mortality summary for a cohort of individuals. • First developed from life insurance studies.

  13. Life Tables Show • Mortality rate per year. • Life span of the organism. • Fecundity (birth rate).

  14. Survivorship Curve • Plot of the numbers of a cohort still alive over time. • Curve Types: • Type I • Type II • Type III

  15. Type I • Low early deaths. • High late deaths. • Ex: • Humans • Other large mammals

  16. Type II • Constant death rate. • Ex: • Annual plants • Many invertebrates

  17. Type III • High early deaths. • Low late deaths. • Ex: • Trees • Oysters

  18. Comment • Curve type may change between young and adults. • Ex: Nestlings - Type III Adult Birds- Type II

  19. Life History Strategies 1. "r" or Opportunistic species 2. "k" or Equilibrial species

  20. "r" Species • Increase fitness by producing as many offspring as possible. • Do this by: • Early maturation • Many reproductive events • Many offspring

  21. Result • Maximize reproduction so that at least a few offspring survive to the next generation. • Most offspring die (Type III curve).

  22. "k" Species • Increase fitness by having most offspring survive. • Do this by: • High parental care • Late maturation • Few reproduction events • Few offspring.

  23. Result • Maximize survivorship of each offspring. • Few offspring, but most survive (Type I curve).

  24. What is the strategy • For a weed? • For an endangered species? • For Garden Pests?

  25. Population Growth • DN/Dt = b - d • Where: • N= population size • t = time • b = birth rate • d = death rate

  26. Rate of Increase • r = difference between birth rate and death rate. • r = b - d

  27. Equation: • DN/Dt = rN • N = population size • t = time • r = rate of increase

  28. From Calculus • The equation DN/Dt = rN becomes: • dN/dt = rmax N • rmax = intrinsic rate of increase

  29. Exponential Growth • dN/dt = rmax N • Characteristic of "r" species. • Produces a “J-shaped” growth curve. • Only holds for ideal conditions and unlimited resources.

  30. Logistic Growth • dN/dt = rmax N K-N K • K = carrying capacity

  31. Result • “S-shaped” growth curve. • Characteristic of “k" species. • Common when resources are limited.

  32. Comment • K is not a constant value. • Populations often oscillate around “K” as the environment changes.

  33. Additional Comments • Populations often overshoot “K”, then drop back to or below “K”. • AP Exam rarely asks you to work the equations, but you should be able to give them.

  34. Regulation of Population Size 1. Density- Dependent Factors 2. Density- Independent Factors

  35. Density-Dependent • Affect is related to N. • As N increases, mortality increases. • Ex: Food, nesting space, disease

  36. Density-Independent • Affect is not related to N. • Mortality not related to population size. • Ex: Weather and climate

  37. Population Cycles • Cyclic changes in N over time. • Often seen in predator/prey cycles. • Ex: Snowshoe Hare - Lynx

  38. Causes • Density dependent factors. • Chemical cycles. • Saturation strategy to confuse predators.

  39. Age Structure Diagrams • Show the percent of a population in different age categories . • Method to get data similar to a Life Table, but at one point in time.

  40. Importances • Can be used to predict future population growth trends, especially for long lived species.

  41. Exponential Growth • Produces age structures that are a triangle or pyramid shape.

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