Foraging

1
Foraging

• Psychology 3107

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Introduction

• Animals face a number of problems when it comes
  to getting food
• What should be eaten
• Deciding to eat
• Is it worth it?
• Deciding what to eat
• Deciding when to stop
• Might make sense to go somewhere else
• Finding food
• May be hidden

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Introduction

• There has been a lot of success recently using
  Optimality Models
• Same sort of thing that we talked about when we
  looked at mobbing in the Adaptation section
• Optimality models are all about costs and benefits

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How do they work?

• A Decision is Identified
• Where should an animal feed
• How long should it stay
• What food should it eat?
• Could be a choice or it could be an
  evolutionary decision
• Decide to leave an area
• Decide to evolve the means to de-toxify a plant
• Decide how long chewing teeth should be

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Optimality Models The Saga Continues

• Assumptions are made about the currency
• What fitness correlated variable is important?
• Maximize energy gain?
• Minimize travel time?
• P(Survival until nightfall)
• Calories/hour

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And finally

• Assumptions are made about the constraints
• What fixed properties of the animal or the
  environment affect the decision
• How much energy can you get out of a food item
• What is the encounter rate?
• How quickly do nectar sources renew themselves?
• How often will I encounter a giant man eating
  shark?

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The Goal.

• Determine what decision, given the constraints,
  maximizes the Currency
• Note that the model will be quantitative
• The model will make precise, testable predictions
• Who says evolutionary theory does not lead to
  testable hypotheses?

8
Belovsky and the Moose

• Belovsky has done a bunch of work on many
  different species
• Question, how much aquatic vegetation should a
  moose eat?
• Constraints include sodium and rumen size

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Marginal Value Theorem

• Charnov (1976)
• If P e / h
• Where P is Profitability, e is energy and h is
  handling time
• An animal should leave a food patch when
  P(current patch) (P(all patches)) / number of
  patches

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For the mathematically inclined

• You can see that calculus would play a big role
  here
• It is about slopes of curves at given points

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Assumptions

• Animal should know P for every patch in the
  environment
• Animal must know P, e and h for each patch!
• How do they do this?
• Rules of thumb
• Giving up time
• ROBL

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Whats a psychologist to do?

• The foraging models lead to precise predictions
  about results
• They can give clues about what an animal should
  do
• The Psychologists task is to look at the
  mechanisms (we have the training)
• Cognitive and behavioural ways that help an
  animal reach optimality

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Dont Get Confused!

• OFT is about function
• Cognitive mechanisms are about cause
• You can look at times when OFT makes one sort of
  prediction and animal cognition make different
  predictions (Shettleworth, 1989, 1993)
• REMEMBER THAT THESE ARE NOT COMPETING EXPLANATIONS