Population Growth Curves and Carrying Capacity · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Boom, Brake, Balance

Science · Organisms & Life Processes · ages 17-18
Name ______________________   Date ____________

  1. What is carrying capacity?

    • The maximum number a habitat can support over time
    • The number of young born in the whole habitat each year
    • The speed of the exponential phase

  2. Put these three named phases of a closed microbial culture in their usual order.

    • Exponential, lag, stationary
    • Lag, exponential, stationary
    • Stationary, lag, exponential

  3. Under stable conditions, a population grows and levels off as shown in the yearly bars. Estimate its carrying capacity.

    Year 130Year 270Year 3160Year 4260Year 5330Year 6360Year 7370Year 8370
    • About 260, where the bars climb fastest
    • About 30, the starting count
    • About 370, where the bars level off

  4. Which described effect is density-independent?

    • Disease spreads faster per animal when more animals share the same area
    • Predators take a larger fraction of prey when more prey share the same area
    • A flood gives each animal the same death risk at low and high density

  5. Which described effect is density-dependent?

    • Food competition reduces survival more as animals crowd together
    • An eruption kills more animals in a denser population, but the fraction killed is unchanged
    • Frost survival per animal is unchanged when more animals occupy the same area

  6. For populations starting well below K, how do ideal exponential and logistic growth models differ on a graph?

    • Exponential is S-shaped toward K; logistic is J-shaped
    • Exponential is J-shaped; logistic is S-shaped toward K
    • Both are S-shaped and approach the same fixed value of K

  7. In equal-sized fields, a frost kills the same fraction of a population of ten voles as of ten thousand. Its effect is density-dependent.

    Circle one:   True   False

  8. A deer herd stops growing while grass still covers the fields. Which explanation could account for this?

    • Grass covers the fields, so food quality must be adequate and food cannot limit the herd
    • Food quality, disease, and predators may limit growth
    • Births always stop as soon as any crowding begins, even with plentiful resources
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Boom, Brake, Balance W1-mt_KX6rhHF5kj-s1

  1. The maximum number a habitat can support over time · Carrying capacity, labelled K, is the maximum population of a species that the habitat can support over time with its available resources.
  2. Lag, exponential, stationary · The culture starts with a lag while cells adjust, grows exponentially, then reaches a stationary phase as growth becomes limited.
  3. About 370, where the bars level off · Under the stated stable conditions, the later counts suggest K is about 370. They rise from 360 to 370 and then remain at 370.
  4. A flood gives each animal the same death risk at low and high density · In the stated flood example, each animal's death risk is unchanged by density. The disease and predation effects increase with crowding.
  5. Food competition reduces survival more as animals crowd together · Food competition reduces survival more with crowding. The eruption kills an unchanged fraction, and frost survival per animal is unchanged. Those stated environmental effects are density-independent.
  6. Exponential is J-shaped; logistic is S-shaped toward K · The ideal exponential model has a J-shaped rise without a resource limit. Logistic growth slows toward K, giving an S-shaped curve from a low starting population.
  7. False · The equal-sized fields have different vole densities, but the fraction killed is the same. The stated frost effect is density-independent.
  8. Food quality, disease, and predators may limit growth · Visible grass and open space do not rule out poor food quality, disease or predation. These are possible limits, but the observation alone does not identify the cause.
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