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.

Eating smart against the clock

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

  1. Big prey pays 2 per minute and small prey pays 4 per minute. Which should the forager take?

    • The big prey, since the richest item always wins
    • Neither, since both rates are too low to bother
    • The small prey, since its rate per minute is higher

  2. What currency does optimal foraging maximize?

    • The biggest single bite, whatever the time cost
    • Energy gained per unit of time, counting travel and handling
    • The number of prey caught, whatever their energy

  3. When should a forager leave a patch?

    • When the patch return drops to the habitat average including travel
    • When the patch is fully empty, whatever the habitat offers
    • After a fixed number of minutes, whatever the returns

  4. Foragers avoid the richest patch, which sits in the open. Which missing cost best explains it?

    • Predation risk, since feeding in the open can get them eaten
    • Laziness, since foragers prefer to rest all day
    • Poor eyesight, since foragers cannot see rich food

  5. Why are patch stays shorter in a rich habitat?

    • Predators force every forager to leave early
    • The habitat average is high, so a patch drops below it sooner
    • Rich habitats have no travel time at all

  6. New prey A gives 30 energy for 15 minutes of handling. Prey B gives 16 for 4 minutes. Which should be taken?

    • Prey A, since 30 beats 16 in total energy
    • Prey B, since 4 per minute beats 2 per minute
    • Both equally, since handling time does not matter

  7. If foragers ignore the richest prey, the energy currency is useless and should be dropped.

    Circle one:   True   False

  8. A distant patch is twice as rich, but the trip is long. When is the trip worth it?

    • Always, since richer patches are always worth any trip
    • Never, since travel time always ruins every patch
    • Only if the patch surplus beats the travel bill
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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. The small prey, since its rate per minute is higher · The higher rate wins even when the bite is smaller. Four per minute beats two.
  2. Energy gained per unit of time, counting travel and handling · Time is a budget like energy. Rate per minute beats size per bite.
  3. When the patch return drops to the habitat average including travel · The habitat average is the opportunity cost of staying. Leaving at that line maximizes the rate.
  4. Predation risk, since feeding in the open can get them eaten · The richest patch is worthless if feeding there gets you eaten. Safety trades against food.
  5. The habitat average is high, so a patch drops below it sooner · A high average sets a high bar. Each patch sinks below it quickly, so moving on pays.
  6. Prey B, since 4 per minute beats 2 per minute · Work the rates: 30 over 15 is 2 per minute, while 16 over 4 is 4. Higher rate wins.
  7. False · A miss names a hidden cost to add, such as risk. The best model is the simplest one whose failures stop.
  8. Only if the patch surplus beats the travel bill · Travel is a cost like any other. The surplus must cover the bill or staying home wins.
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