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Foraging

Foraging. Psychology 3106. 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. Introduction.

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Foraging

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  1. Foraging Psychology 3106

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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?

  7. 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

  9. 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

  10. For the mathematically inclined • You can see that calculus would play a big role here • It is about slopes of curves at given points

  11. 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

  12. What’s a psychologist to do? • The foraging models lead to precise predictions about results • They can give clues about what an animal ‘should’ do • The Psychologist’s task is to look at the mechanisms (we have the training) • Cognitive and behavioural ways that help an animal reach optimality

  13. Don’t 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

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