ForagingForaging

Psychology 3106Psychology 3106

IntroductionIntroduction

Animals face a number of problems when Animals face a number of problems when it comes to getting foodit comes to getting food What should be eatenWhat should be eaten Deciding to eatDeciding to eat

Is it worth it?Is it worth it? Deciding what to eatDeciding what to eat Deciding when to stopDeciding when to stop

Might make sense to go somewhere elseMight make sense to go somewhere else Finding foodFinding food

May be hiddenMay be hidden

IntroductionIntroduction

There has been a lot of success recently There has been a lot of success recently using Optimality Modelsusing Optimality Models Same sort of thing that we talked about when Same sort of thing that we talked about when

we looked at mobbing in the Adaptation we looked at mobbing in the Adaptation sectionsection

Optimality models are all about costs and Optimality models are all about costs and benefitsbenefits

How do they work?How do they work?

A Decision is IdentifiedA Decision is Identified Where should an animal feedWhere should an animal feed How long should it stayHow long should it stay What food should it eat?What food should it eat? Could be a ‘choice’ or it could be an Could be a ‘choice’ or it could be an

evolutionary decisionevolutionary decisionDecide to leave an areaDecide to leave an area

‘‘Decide’ to evolve the means to de-toxify a plantDecide’ to evolve the means to de-toxify a plant

‘‘Decide’ how long chewing teeth should beDecide’ how long chewing teeth should be

Optimality Models – The Saga Optimality Models – The Saga ContinuesContinues

Assumptions are made about the currencyAssumptions are made about the currency What fitness correlated variable is important?What fitness correlated variable is important?

Maximize energy gain?Maximize energy gain?

Minimize travel time?Minimize travel time?

P(Survival until nightfall)P(Survival until nightfall)

Calories/hourCalories/hour

And finally……And finally……

Assumptions are made about the Assumptions are made about the constraintsconstraints What fixed properties of the animal or the What fixed properties of the animal or the

environment affect the decisionenvironment affect the decisionHow much energy can you get out of a food itemHow much energy can you get out of a food item

What is the encounter rate?What is the encounter rate?

How quickly do nectar sources renew themselves?How quickly do nectar sources renew themselves?

How often will I encounter a giant man eating How often will I encounter a giant man eating shark?shark?

The Goal….The Goal….

Determine what decision, given the Determine what decision, given the constraints, maximizes the Currencyconstraints, maximizes the Currency

Note that the model will be quantitativeNote that the model will be quantitative

The model will make precise, testable The model will make precise, testable predictionspredictions Who says evolutionary theory does not lead Who says evolutionary theory does not lead

to testable hypotheses?to testable hypotheses?

Belovsky and the MooseBelovsky and the Moose

Belovsky has done a Belovsky has done a bunch of work on bunch of work on many different many different speciesspecies

Question, how much Question, how much aquatic vegetation aquatic vegetation should a moose eat?should a moose eat?

Constraints include Constraints include sodium and rumen sodium and rumen sizesize

Marginal Value TheoremMarginal Value Theorem

Charnov (1976)Charnov (1976)

If P = e / h If P = e / h Where P is Profitability, e is energy and h is Where P is Profitability, e is energy and h is

handling timehandling time

An animal should leave a food patch when An animal should leave a food patch when P(current patch) = (P(all patches)) / P(current patch) = (P(all patches)) / number of patchesnumber of patches

For the mathematically inclinedFor the mathematically inclined

You can see that calculus would play a big role You can see that calculus would play a big role herehere

It is about slopes of curves at given pointsIt is about slopes of curves at given points

AssumptionsAssumptions

Animal should ‘know’ P for every patch in Animal should ‘know’ P for every patch in the environmentthe environment

Animal must ‘know’ P, e and h for each Animal must ‘know’ P, e and h for each patch!patch!

How do they do this?How do they do this? Rules of thumbRules of thumb

Giving up timeGiving up time

ROBLROBL

What’s a psychologist to do?What’s a psychologist to do?

The foraging models lead to precise The foraging models lead to precise predictions about resultspredictions about results

They can give clues about what an animal They can give clues about what an animal ‘should’ do‘should’ do

The Psychologist’s task is to look at the The Psychologist’s task is to look at the mechanisms (we have the training)mechanisms (we have the training)

Cognitive and behavioural ways that help Cognitive and behavioural ways that help an animal reach optimalityan animal reach optimality

Don’t Get Confused!Don’t Get Confused!

OFT is about functionOFT is about function

Cognitive mechanisms are about causeCognitive mechanisms are about cause

You can look at times when OFT makes You can look at times when OFT makes one sort of prediction and animal cognition one sort of prediction and animal cognition make different predictions (Shettleworth, make different predictions (Shettleworth, 1989, 1993)1989, 1993)

REMEMBER THAT THESE ARE NOT REMEMBER THAT THESE ARE NOT COMPETING EXPLANATIONSCOMPETING EXPLANATIONS