Forelesning 11/11

Signals and communication

Most interactions between individuals involve communication

  • offspring ask for food from their parents

  • bees “dance” to show the direction and distance to nectar

  • poisonous larvae warn predators with vibrant colors

Some signals are honest while others are dishonest and developed in order to “trick” the receiver

The difference between cues and signals

cues:

The receiver uses a characteristic or feature of the sender to control their own behavior. The feature of the sender has not evolved to have this function.

  • the rustling sound of a mouse looking for food on the ground is not a signal. The sound is a byproduct of looking for food. The sound is not formed through natural selection to convey information.

signals:

behavior/actions or structures produced by the sender

  • changes the behavior in the receiver

  • evolved because they have that effect. They are effective because the receiver has developed the response through evolution.

they are developed through natural selection to communicate something

Signals

To important points:

  1. signals can be distinguished from cues in that they are selected based on their effect on others

  2. if the response in the receiver is selected, then the response represents a benefit (if it wasn’t, this response wouldn’t be selected)

    • the benefit applies broadly (“on average”) to both parties. There are individuals/species that will send out misleading/dishonest/manipulative signals or exploits the honest signaling by others

What is a signal?

Broadly speaking:

A signal is a property of the sender that changes the behavior of a receiver:

  • the receiver’s response can be immediate and obvious (as when a male firefly flies towards a flashing female)

  • the response may be subtle and difficult to detect (when a male antelope changes direction to avoid an odor-marked territorial boundary)

  • the response may be delayed (as when the ovaries of a female budgie develop gradually due to the male’s song)

  • the response can also be sporadic (as when a territorial male blackbird sings for several hours, but only one or two intruders hear the song and retreat)

Signals are shaped by the environment

The effectiveness of a signal is weakened by forest, water, noice, etc.

  • certain modalities are better suited to transmit signals, e.g. sound in dense forest or over a distance in water

  • the duration of the signals: light is short-lived and suitable for scaring or alarming, while chemical signals are more permanent and suitable for marking the area/territory

The Lombard effect: birds increase the volume of their singing in noisy environments.

  • birds can also change e.g. frequency depending on noise in the surroundings.

The diversity of signals

Signals are diverse: they can be visual, auditory, chemical, electrical, or tactile

  • they vary in function

  • how they affect the receiver’s behavior

  • when (immediately or eventually) they affect the receiver’s behavior

Two important questions when we observe dishonest signals

  1. is it a signal system that is about to collapse, or is it a stable balance between honest and dishonest signals?

    If individuals always lied and exaggerated:

    • the signals would not carry useful information

    • there would be no benefit in paying attention to such signals

    • the signal system will collapse

  2. if there is a stable balance, what keeps the dishonest signals at a low enough level to prevent the system from breaking down?

    Why does the receiver allow themselves to be fooled, why not just ignore such false signals?

    • the signals manipulate the behavior in the receiver that is adaptive on average: wasp-like flying creatures are usually wasps, not hoverflies.

    Why aren’t all signals dishonest? Why are they not exploited more? What prevents senders from exaggerating or lying? What processes ensure that the signals are honest?

    • because dishonest signals can involve a cost/consequence for the sender that limits them

Dishonest signals must be seen in the light of adaptation for both the sender and the receiver

For the signal system to remain evolutionary stable:

  1. on average, it must contain more useful information so that receivers benefit from paying attention to the signals rather than ignoring them. This gives senders room for a certain degree of dishonesty that can be exploited.

  2. Dishonest signals have a cost for the sender that limits dishonesty.

Animal signals (Laidre, 2013)

Five factors that ensure that signals remain reliable despite conflict of interest between signaler and receiver.

  1. Index

    • the signals are “unforgeable” because they are linked to an animal’s anatomy or physiology

    • allows receivers to assess the signal'er’s strength/resources

    • the cost that stabilizes reliability is paid through the development of the signal

  2. Quality handicap

    • the signals have a cost that stabilizes honesty

    • the signals “use up” the quality advertised (often because they are energy-intensive)

    • only “high-quality” individuals can afford them

  3. General handicap

    • the signals have a production cost that is the same for all signalers

    • what distinguishes the signalers is the benefits they get by succeeding in eliciting a response with the signal. Signalers who will benefit more (e.g. hungrier offspring) will be more likely to signal (e.g. beg more often for food from their parents), which indicates their greater need.

  4. Convention and vulnerability

    • the signals are produced with minimal cost and negligible difficulty

    • reliability is ensured by receivers often testing signalers for weaknesses

    • the signals can trigger an attack/test and potentially result in serious injury

  5. Reputation