Population Ecology

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Population Ecology

Population Ecology

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  • 1. Ecology I Population Ecology
  • 2.
    • Why is it important?
            • assessing health of population
            • determining endangered or threatened status
            • predicting population dynamics
  • 3. Population size
    • … is the number of individuals present at a given time.
    The passenger pigeon was once North America’s most numerous bird, but it is now extinct.
  • 4. Population density
    • … is the number of individuals per unit area.
    In the 19th century, the flocks of passenger pigeons showed high population density.
  • 5. Population distribution
    • … is the spatial arrangement of individuals.
    • Random
    • Uniform
    • Clumped
  • 6. Population growth
    • Populations grow, shrink, or remain stable, depending on rates of birth, death, immigration, and emigration.
    • (crude birth rate + immigration rate) –
    • (crude death rate + emigration rate)
    • = growth rate
  • 7. Two Modes of Population Growth
    • Exponential growth
    • Logistic growth
    • Represent two different growth patterns or Strategies of populations
  • 8. Exponential Growth
      • Also known as a J-curve
      • Growth is a fixed percentage of the whole (e.g., 10% per day or year)
      • Population is growing at its full biotic potential
  • 9. Exponential growth in a growth curve
    • Population growth curves show change in population size over time.
    • Scots pine shows exponential growth
  • 10. Biotic Potential
    • Maximum possible growth rate of a population.
      • Absence of limitations to growth
    • Example :
      • 2 cats plus all their kittens make how many cats in 10 years?
        • 2 litters/year
        • 2.8 surviving kittens per litter
        • Breeds for 10 years (“breeding life”)
    (Drum roll…)
  • 11. ANSWER:
    • 80,399,780 cats!!!
    Do you need a cat?
  • 12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Biotic Potential J curve Time Population Carrying Capacity
    • Carrying Capacity:
    • MAXIMUM number of individuals that can be supported
      • in a given AREA.
      • FOREVER.
    Can Populations Grow Forever?
  • 13.
    • Oscillations :
      • Populations overshoot the carrying capacity and experience a dieback
      • Can be regular or irregular
      • Overshoot When a population surpasses the carrying capacity of its environment or population explosion
      • Dieback Population crash
  • 14. Population growth: Oscillations
    • Some populations fluctuate continually above and below carrying capacity, as with this mite.
  • 15. Population growth: Dampening oscillations
    • In some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle.
  • 16. r-Selected Species
    • r = Growth rate
      • Reproduce young
      • High reproductive rates
      • Many small offspring
      • Short-lived
      • Found in unstable or unpredictable environments
  • 17. Examples of r-Selected Species
    • Weeds, bacteria, insects, algae, small mammals
  • 18. Logistic Growth
      • Also known as S-curve
      • Growth slows as the population approaches Carrying Capacity
      • Populations stabilize at carrying capacity
  • 19. K-Selected Species
    • K = Carrying Capacity
      • Reproduce later in life
      • Low reproductive rates
      • Fewer large offspring
      • Long-lived
      • Stable or predictable environments
  • 20. Examples of K-Selected Species
    • Elephants, great apes, hippopotamus, whales, humans (?)
  • 21. What Determines Population Size or Carrying Capacity?
    • Environmental Resistance
      • All the limiting factors that tend to reduce population growth rates
    • Balance between biotic potential & environmental resistance determines growth rate
  • 22. Environmental resistance Carrying capacity Stabilized population size Exponential growth Limiting factors: Water Space Food Predators Disease LE 4-11
  • 23. Predator – prey cycles
    • Population dynamics of predator – prey systems sometimes show paired cycles: ups and downs in one drive ups and downs in the other.
  • 24. QUESTION: Review
    • Which is a K-selected species?
      • a. A dragonfly that lays 300 eggs and flies away
      • b. An oak tree that drops its acorns each year
      • c. A bamboo plant that flowers only once every 20 years
      • d. A human who raises three children
      • e. A fish on the second trophic level
  • 25. QUESTION: Review
    • How can you tell that this population growth curve shows exponential growth?
      • a. Population is increasing.
      • b. Data points match curve closely.
      • c. Population is rising by the same number during each interval.
      • d. Population is rising by the same percentage during each interval.
  • 26. QUESTION: Review
    • This shows growth ending at a(n) .
      • a. exponential… carrying capacity
      • b. intrinsic… equilibrium
      • c. logistic… carrying capacity
      • d. runaway… equilibrium
      • e. logistic… extinction