PredationPredation

Psychology 3106Psychology 3106

IntroductionIntroduction

You hear quite a bit about foragingYou hear quite a bit about foraging

Foraging is a two way streetForaging is a two way street There has to be a ‘foragee’ as wellThere has to be a ‘foragee’ as well

Just as foragers have evolved strategies, Just as foragers have evolved strategies, so have preyso have prey

Possible StrategiesPossible Strategies

Live in a groupLive in a group

CamouflageCamouflage

ArmourArmour

Fight backFight back

Don’t taste good!Don’t taste good!

AposematismAposematism

Some insects taste Some insects taste bad and are obvious bad and are obvious about itabout it

Usually have a diet of Usually have a diet of plants that does not plants that does not taste good to the taste good to the predatorpredator

The Monarch butterfly The Monarch butterfly is great exampleis great example

Questions, Questions, Questions, Questions, Questions…..Questions…..

Two evolutionary questions can be askedTwo evolutionary questions can be asked

1) How did distastefulness evolve?1) How did distastefulness evolve?

2) Why are distasteful prey so obvious about 2) Why are distasteful prey so obvious about it?it?

Question 1Question 1

Well, it should increase the probability of Well, it should increase the probability of the prey survivingthe prey surviving

But, the predator has to sample a prey But, the predator has to sample a prey item in order to learn that it will get sickitem in order to learn that it will get sick

How does the fitness of the prey item How does the fitness of the prey item increase if it has been eaten?increase if it has been eaten?

Species level?Species level? Not a chance in hell…..Not a chance in hell…..

So How then?So How then?

Well, here’s a hint: Usually aposematic Well, here’s a hint: Usually aposematic bugs are gregariousbugs are gregarious

Usually they are surrounded by siblingsUsually they are surrounded by siblings

If only a few of the brood are eaten then If only a few of the brood are eaten then the frequency of the distasteful gene will the frequency of the distasteful gene will spreadspread

(Fisher, 1958) one of the first kin selection (Fisher, 1958) one of the first kin selection modelsmodels

Why be so obvious then?Why be so obvious then?

First off, not all distasteful prey are First off, not all distasteful prey are obviousobvious

Most are thoughMost are though

Two possible explanationsTwo possible explanations Contrast with the background makes learning Contrast with the background makes learning

easier than learning about cryptic preyeasier than learning about cryptic prey Gibson (1974)Gibson (1974)

Blue, green or red millet on a green dot Blue, green or red millet on a green dot backgroundbackground

Gibson (1974)Gibson (1974)

Feeding platform dropped when red Feeding platform dropped when red ‘aposematic’ grain was eaten‘aposematic’ grain was eaten

The birds stopped eating red seeds, still The birds stopped eating red seeds, still ate the blue and greenate the blue and green

Can’t be the background then, as the Can’t be the background then, as the cryptic ones were still eatencryptic ones were still eaten

Gittleman and Harvey (1980)Gittleman and Harvey (1980)

Chicks fed two grain Chicks fed two grain typestypes

Colour did not matter Colour did not matter on its ownon its own

Distastefulness and Distastefulness and colour are the keycolour are the key

Shettleworth (1972)Shettleworth (1972)

Chicks learned to avoid Chicks learned to avoid unpalatable water if it was unpalatable water if it was a novel colour (other than a novel colour (other than what they were raised on)what they were raised on)

Novelty is the key, not Novelty is the key, not contrastcontrast

So, could be that the prey So, could be that the prey evolved a strategy of evolved a strategy of being different as being different as possible possible

Kin SelectionKin Selection

Aposematism must have Aposematism must have evolved through kin evolved through kin selectionselection

Aposematic butterflies Aposematic butterflies are gregariousare gregarious

Cryptic butterflies are not!Cryptic butterflies are not!

Aposematic live longer Aposematic live longer than crypticthan cryptic

They could still ‘teach a They could still ‘teach a lesson’lesson’

Other characteristicsOther characteristics

They have smaller territoriesThey have smaller territories

They roost communallyThey roost communally

They have delayed sexual maturityThey have delayed sexual maturity

So, because they live longer they can So, because they live longer they can teach the lesson more easilyteach the lesson more easily

MimicryMimicry

Some insects are Some insects are aposematic and aposematic and successful, why not successful, why not copy?copy? Batesian mimicryBatesian mimicry

Colouration is similar Colouration is similar to toxic species, but to toxic species, but the prey item is not the prey item is not toxictoxic

Mullerian MimicryMullerian Mimicry

In Mullerian mimicry, In Mullerian mimicry, all species that share all species that share a colouration are a colouration are dangerousdangerous

Many snakes use thisMany snakes use this

Also may have Also may have characteristics that characteristics that make prey look like a make prey look like a predator!predator!

ConclusionsConclusions

Evolution is basically an arms raceEvolution is basically an arms race

As fast as aposematism or crytic As fast as aposematism or crytic colouration evolve, species learn to detect colouration evolve, species learn to detect the preythe prey Learn evolutionarily or in the real senseLearn evolutionarily or in the real sense