Optimal foraging and the currency of a behavioural decision · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
En anglais

Eating smart against the clock

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

  1. An animal can take only one prey before leaving. Big prey offers 2 net energy units per handling minute; small prey offers 4. Both are available now, with no further search and other costs equal. Which offers the higher rate?

    • Big prey, at 2 net energy units per handling minute
    • Both prey, at 3 net energy units per handling minute
    • Small prey, at 4 net energy units per handling minute

  2. In an energy-rate foraging model, which quantity is maximised?

    • Food energy gained per prey item before subtracting energetic costs
    • Net energy gained per unit of total search, travel and handling time
    • Prey captures per minute without weighting their energy content

  3. Under the marginal-value model, when should a forager leave a patch with declining returns?

    • When the patch's marginal gain rate equals the attainable long-run rate
    • When the patch's remaining energy equals the energy spent travelling to it
    • When its marginal gain rate reaches zero after the food supply is depleted

  4. An energy-only model predicts use of a food-rich open patch. Foragers avoid it, and predator attacks are more frequent there. Which omitted cost does this evidence suggest?

    • Higher risk of being attacked while feeding in the open
    • Longer handling of prey while feeding in the open
    • Lower energy content of prey available in the open patch

  5. A focal patch's declining return curve stays unchanged, but the attainable long-run rate elsewhere rises. Why does the marginal-value model predict an earlier exit?

    • The patch's food supply declines faster as the other patches improve
    • The unchanged declining rate reaches the new, higher benchmark earlier
    • The higher outside rate reduces travel time, shifting the patch's return curve

  6. Prey A gives 30 net energy units in 15 handling minutes; B gives 16 in 4. Each is encountered separately. Rejecting either permits continued foraging at 3 units per minute, including search. With other costs equal, what does the rate model predict?

    • Accept A and reject B, comparing total prey energy
    • Reject A and accept B, comparing each rate with 3
    • Accept both prey, comparing each gain with zero

  7. One disagreement between an energy-rate model and observed foraging proves that energy per time is useless for every foraging decision.

    Circle one:   True   False

  8. A distant patch gives 60 net energy units in 10 feeding minutes plus 10 travel minutes. A nearby patch gives 48 units in 12 total minutes. Using the same visit boundary, which has the higher net-energy rate?

    • Distant patch, at 6 units per minute when travel time is excluded
    • Distant patch, because 60 units gained exceeds the nearby total of 48
    • Nearby patch, at 4 units per minute across the full 12-minute visit
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Answer key

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

Eating smart against the clock W1-mt_9iNYB7d1Rh-s1

  1. Small prey, at 4 net energy units per handling minute · Small prey offers 4 units per handling minute, compared with 2 for big prey. The stated conditions make this a direct rate comparison.
  2. Net energy gained per unit of total search, travel and handling time · The model divides net energy gained by all search, travel and handling time.
  3. When the patch's marginal gain rate equals the attainable long-run rate · Compare the gain rate from staying a little longer with the best attainable long-run rate across patch visits, including travel.
  4. Higher risk of being attacked while feeding in the open · The attack evidence suggests a survival cost omitted from the energy-only model. This explanation still needs testing.
  5. The unchanged declining rate reaches the new, higher benchmark earlier · An unchanged declining return curve reaches a higher rate before it reaches a lower one.
  6. Reject A and accept B, comparing each rate with 3 · A gives 2 units per handling minute, below the alternative rate of 3. B gives 4, above it. Reject A and accept B.
  7. False · One discrepancy does not establish that universal claim. Check assumptions and test alternatives; repeated contrary evidence can still challenge the currency.
  8. Nearby patch, at 4 units per minute across the full 12-minute visit · The distant visit gives 60/(10 + 10) = 3 units per minute. The nearby visit gives 48/12 = 4.
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