Demography: Life Tables, Age Structure and What They Predict · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Life tables: reading the future of a population

Science · Ecology & Conservation · ages 20-21
Name ______________________   Date ____________

  1. Which pair shows a Type I survivorship curve?

    • Humans and elephants
    • Fish and orchids
    • Small birds at steady risk

  2. What group does a life table follow?

    • Many mixed generations at once
    • One cohort born together
    • Only the oldest adults

  3. A net reproductive rate above one means the population grows.

    Circle one:   True   False

  4. Birds face about the same risk at every age. Which curve fits them?

    • Early crash of Type III
    • Late drop of Type I
    • Steady fall of Type II

  5. A cohort starts with 1000 newborns. At age two, 400 survive. What is the survival rate to age two?

    Answer: ______________

  6. Salmon release masses of eggs they abandon, while elephants raise one calf for years. What does this contrast show?

    • One lifetime budget spent two ways
    • Identical survival at every age
    • Equal birth rates per adult

  7. Two populations each hold 500 animals. One is mostly young, one mostly old. Which grows faster next generation?

    • Neither, since the sizes match
    • The old one, with longer lived adults
    • The young one, with breeders arriving

  8. A student says a net reproductive rate of 0.7 means growth. What is wrong?

    • Below one means shrinking, not growth
    • Rates below one are impossible
    • Growth needs a rate of exactly one
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Answer key

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

Life tables: reading the future of a population W1-mt_raWfdLLACU-s1

  1. Humans and elephants · Type I stays high then drops late, since the young are well protected.
  2. One cohort born together · A life table tracks one cohort born together across the ages.
  3. True · Above one replaces each individual with more than one descendant.
  4. Steady fall of Type II · Equal risk at every age removes a steady share, giving the Type II slope.
  5. 0.4 · Divide survivors by the starting number: 400 out of 1000 is 0.4.
  6. One lifetime budget spent two ways · One limited budget buys either many uncared young or few well cared ones.
  7. The young one, with breeders arriving · Size misleads; the age structure decides how many births arrive next.
  8. Below one means shrinking, not growth · Each individual replaces itself with less than one descendant, so numbers fall.
Worksheet · LightMySky