Competition, Niches and What Allows Coexistence · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why rivals can share one world

Science · Ecology & Conservation · ages 20-22
Name ______________________   Date ____________

  1. How do warblers divide a single tree?

    • By feeding at different heights in separate zones
    • By taking turns across different centuries
    • By eating rocks instead of insects

  2. What has to be true for two competing species to coexist?

    • One species must stop reproducing entirely
    • Each species must limit itself more than it limits the other
    • Both species must eat exactly the same food

  3. Two species compete for one scarce resource. Which one usually wins?

    • The fastest breeder, whatever it needs
    • The one that persists on the scarcest supply of the limiting resource
    • The largest species, whatever it eats

  4. You remove one competitor and the other expands its diet. What did the removal reveal?

    • Removals always poison the remaining species
    • The removed species had been denying that diet through competition
    • Diets never change, so the observation is impossible

  5. Desert rodents divide seeds by size. What is the mechanism?

    • Each species harvests the seed sizes the other leaves
    • All rodents eat identical seeds at identical times
    • Rodents stop eating seeds during droughts

  6. A weak competitor persists only where a predator eats its dominant rival. Why?

    • The predator feeds the weak species directly
    • The weak species hides inside the predator
    • Holding the dominant down frees resources the weaker needs

  7. Two species using the same limiting resource always coexist peacefully.

    Circle one:   True   False

  8. A plant with nitrogen fixing partners thrives on poor soils where rivals starve. What does this show?

    • Competition never matters whenever partners exist
    • Fixing nitrogen poisons every rival plant
    • Partners can unlock resources a species could not use solo
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Answer key

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

Why rivals can share one world W1-mt_VS9Yud3rCQ-s1

  1. By feeding at different heights in separate zones · Height zones split one insect supply into separate shares. Each warbler harvests its own floor.
  2. Each species must limit itself more than it limits the other · Self crowding must strike before victory. That balance stops either side from excluding the other.
  3. The one that persists on the scarcest supply of the limiting resource · Scarcity decides: the thriftiest user outlasts the rest when the resource runs short.
  4. The removed species had been denying that diet through competition · Expansion after release exposes the denied niche. The experiment separates competition from preference.
  5. Each species harvests the seed sizes the other leaves · Size division splits one seed supply into complementary shares. Naming the split names the mechanism.
  6. Holding the dominant down frees resources the weaker needs · Predation taxes the winner and subsidizes the loser indirectly. The balance tilts toward coexistence.
  7. False · Sharing one limit without separation ends in exclusion. The stronger displaces the weaker.
  8. Partners can unlock resources a species could not use solo · Allies reshape niches by unlocking supplies. Coexistence belongs to the whole web, not the pair.
Worksheet · LightMySky