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Population Ecology
 

Population Ecology

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Population Ecology

Population Ecology

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    Population Ecology Population Ecology Presentation Transcript

    • Ecology I Population Ecology
      • Why is it important?
              • assessing health of population
              • determining endangered or threatened status
              • predicting population dynamics
    • 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.
    • Population density
      • … is the number of individuals per unit area.
      In the 19th century, the flocks of passenger pigeons showed high population density.
    • Population distribution
      • … is the spatial arrangement of individuals.
      • Random
      • Uniform
      • Clumped
    • 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
    • Two Modes of Population Growth
      • Exponential growth
      • Logistic growth
      • Represent two different growth patterns or Strategies of populations
    • 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
    • Exponential growth in a growth curve
      • Population growth curves show change in population size over time.
      • Scots pine shows exponential growth
    • 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…)
    • ANSWER:
      • 80,399,780 cats!!!
      Do you need a cat?
    • 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?
      • 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
    • Population growth: Oscillations
      • Some populations fluctuate continually above and below carrying capacity, as with this mite.
    • Population growth: Dampening oscillations
      • In some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle.
    • r-Selected Species
      • r = Growth rate
        • Reproduce young
        • High reproductive rates
        • Many small offspring
        • Short-lived
        • Found in unstable or unpredictable environments
    • Examples of r-Selected Species
      • Weeds, bacteria, insects, algae, small mammals
    • Logistic Growth
        • Also known as S-curve
        • Growth slows as the population approaches Carrying Capacity
        • Populations stabilize at carrying capacity
    • K-Selected Species
      • K = Carrying Capacity
        • Reproduce later in life
        • Low reproductive rates
        • Fewer large offspring
        • Long-lived
        • Stable or predictable environments
    • Examples of K-Selected Species
      • Elephants, great apes, hippopotamus, whales, humans (?)
    • 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
    • Environmental resistance Carrying capacity Stabilized population size Exponential growth Limiting factors: Water Space Food Predators Disease LE 4-11
    • 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.
    • 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
    • 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.
    • 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