Foraging

Psychology 3906

Introduction

• Foraging has been looked at from a functional angle for a long time

• Optimality models etc

• Then you have to look at what mechanisms might make such behaviour possible

How do optimality models 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

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

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?

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?

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

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

For the mathematically inclined

• You can see that calculus would play a big role here

• It is about slopes of curves at given points

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

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

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

One mechanism may be…

• The matching law

• Basically the animal matches response rates to reinforcement rates

• They probably do this by encoding the time between reinforcers

• This leads in fact to roughly optimal foraging.

Conclusion

• This is probably the first place the psychologists and the biologists came together.

• Each must recognize the that other’s explanation is just fine

• Lots of awesome research here