Animal Communication

Dilution Effect

•     Hypothesis

–   Ravens call to attract others

–   Reduced the risk of predation

•     Prediction:

–   Once a group had been assembled and feeding begun

–   Ravens should stop calling

•     Observations:

–   Ravens continue calling even after a feeding party has been assembled

Residents and Wanderers

•     Two distinct groups of ravens at carcasses

–   Residents = adult

•   Individuals or pairs

•   Defended any carcass in their territory.

•   Did not call

–   Wanderers = juveniles.

•   Larger numbers

•   Call and attract others

Gang up of Territorial Residents

•     Hypothesis: Wanderers attract others so that they can gang up on a territorial pair

•     Predictions:

–   Residents should never yell

–   Non-residents should yell

–   Yelling should facilitate a mass assault on a carcass

–   Residents should be unable to repel a massed assault

–   Carcass should be eaten either by a resident pair or a mob of ravens

Communication

•     Action or cues given by one organism (sender)

•     Intended to influence the behavior of another organism (receiver)

•     Adaptive to one or both participants

Cumulative Selection

•     Richard Dawkins

•     Incremental layering of one modification on top of preceding ones

An Example

•     Phrase “METHINKS IT IS LIKE A WEASEL”

•     28 letters and spaces

•     What is the probability that a computer could produce this combination of letters and spaces by chance?

•     Are you kidding?!?

Same Example, New Rules

•     Start with a random sequence

•     “SWAJS MEIRNZMMVASJDNA YPQZK”

•     Copy phrase above but occasionally insert a new letter into one position

•     From the list of phrases, pick the one that is closest to desired phrase

•     Repeat process

True Communication

•     Both sender and receiver benefit

•     Honest signal = conveys accurate information

•     Male red deer

European Toads

•     Males compete for receptive females

•     When male finds another male - tries to push male off

•     Mounted male croaks

•     Other male concedes defeat

•     Why would a rival toad give up a chance to mate (decrease fitness) based on a single croak?

Origins of Sensory Signals

•     Sensory exploitation = biased effects of existing perceptual mechanisms

•     For example: water mites

Illegitimate Receivers

•     Use information from the signals to the detriment of legitimate signalers and receivers

•     For example: bird predators that listen in on begging calls

Begging Calls

•     Cost associated with begging

–   May attract a passing predator

•     Artificial nests containing eggs = play begging calls in half of nests

–   Eggs taken from noisy nests while quiet nests left untouched

Túngara Frogs

•     Males give a special call to attract mates

•     Males give two calls

–   Whining call with chucks

–   Whining call without chucks

Predators

•     Fringe-lipped bat

•     Illegitimate receiver - homes in on frog call

Predictions

•     Bats should be attracted to signals of frogs

•     Bats should be more attracted to the whine-chuck calls than just the whine calls

•     When risk of predation is lower, frogs should be more likely to give riskier whine-chuck calls (dilution effect)

Manipulation or Deceit

•     Sender benefits, receiver is unaffected or harmed

•     Illegitimate signalers

•     “Femme Fatale” fireflies

Novel Environment Theory

•     Maladaptive response is caused by a proximate mechanism that once was adaptive

•     Environmental conditions changed too fast for response to evolve

Exploitation Theory

•     Maladaptive response caused by a proximate mechanism that is adaptive in its sum

–   Only exploited by some individuals

–   Average fitness loss reduced but not eliminated