Download Alcock Chapter 6 - “Behavioral Adaptations for Survival”. Really

Alcock Chapter 6 - “Behavioral Adaptations for
Survival”.
Really about predator/prey relationships.
In the larger context, this is one aspect of
Behavioral Ecology
1
There are different interactions between
organisms -predator-prey
parasite-host
symbiosis
mutualism
The interactions relative to predatory-prey
and parasite-host involve communication.
It is often interesting to analyze whether
the communication is honest or deceitful.
2
Cryptosis & mimicry. These anti-predator
strategies may involve one or more forms of
biological deceit -- that is, you attempt to
portray yourself as something different from
reality.
cryptosis
• hiding
• mimicry
• camouflage
3
Biston betularia
(camo moth)
Question:
What does the previous example (Figure 6.16
in the text) have to do with behavior?
5
Skipper butterfly caterpillars that eject feces
from their hiding spots....
6
6.21 Personal hygiene by a skipper butterfly larva may be an
antipredator adaptation
Trachops finds dinner
Deception is also prevalent with parasitehost interactions. Consider the famous case
of Oropendolas and Cow birds...
22
Oropendola
… and nest
Cowbird
Bot flies and a squirrel with an infestation.
A deceptive mimic -- The fly mimics the very
predator that is after it.
fly
jumping spider
On the other hand, there can be honest signals
used as anti-predator devices:
Stotting in
Springboks/
Gazelles
Hypotheses for why stotting occurs:
1.  Alarm signal: Warn neighbors who are related to you.
2.  Social cohesion signal: Do it to bring group together.
3.  Confusion effect: Predator will be confused by odd
behavior and go after someone else in the group.
4.  Honest signal of unprofitability: Anyone who can jump
that high can outrun me, says the predator, I better pick
a different target.
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Predictions from each hypotheses
You honestly communicate to the predator that you are the
most costly prey item. Of course this strategy only works if you
are in a group, and the predator has the sophistication to get
the point!
So the behavior works…
For stotting to work, first there had to be herding.
Why is there herding behavior? Or schooling behavior?
Many individuals moving in a coordinated way
become a large visual mass. That is, the predator
doesn’t see many fish, the predator sees a large
undulating “whale”.
Hypothetically, a gene shows up that causes one
individual to prefer hanging close to a con-specific. A
predator eats your neighbor, and you leave more
genes in the next generation. So the “grouping” gene
becomes fixed.
Everyone trying to hide behind everyone else
makes an instant herd
As a corollary, the most aggressive and
strongest individuals should successfully
compete for the best position in the herd (the
center).
Individuals in large groups have lower predation risk
Anolis doing a push-up
Smaller fish are more likely
to be attacked
From electric fish behavior study we learn that there is a
preferred prey size.
In one sense, this is obvious. You have to be physically
adapted to capture, eat prey of a certain size, or
toughness, etc.
This begs the question, though, of whether predators
forage optimally, or just settle for anything that is
acceptable.
The term “optimal” is not the best. It implies some animals
or groups make bad choices if they are not optimizing their
food selection.
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Eat anything
that vaguely
resembles food.
Continuous Range
Very selective
about what to
grab, eat.
Each strategy across range can be equally “optimal”.
Being “efficient” as a predator is not always the best
way to leave more genes in the next generation.
Crows prefer large whelks
The large ones only have to be dropped from 5 meters.
Almost no drops of large whelks from > 5 m.
A higher proportion of the smaller whelks are dropped from a
higher point (more energy to fly higher).
When there are multiple selection pressures,
there is no one best strategy for foraging.
Recall Tungara frog: There was no one best
strategy for mate advertisement.
Similarly, for foraging, skinks trade off the
distance they will travel from shelter for good
food vs the need to avoid snake predation…
Also, what is optimal at one time of day (or
season, etc) is not necessarily optimal at other
times…
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• The most efficient foraging by ants in colony with head sizes 2.2-2.6 mm.
• These larger ants are more likely to be preyed upon by parasitic flies.
• The flies are only active during the day.
• So colony sends out smaller foragers during day, and “optimal” foragers at night.
The classical prisoner's dilemma (PD; see text pg 469, 9th edition text):"
Two accomplices, Fluffy and Prunella, are going to rob a bank. Beforehand, they
agree that if they are caught each should remain silent and not rat out the other.
Neither really trusts the other, however."
Well Fluffy and Prunella are caught, and held in separate cells. The police have
insufficient evidence for a conviction, but they offer each the same deal: "
If one testifies for the prosecution against the other (rats), and the other remains
silent, the betrayer goes free = the temptation. The silent accomplice receives
the “sucker” payoff, a full 10-year sentence. "
If both stay silent, both prisoners are sentenced to only six months in jail for a
minor charge. "
If each betrays or rats out the other, each receives a five-year (reduced)
sentence for cooperating. "
Each prisoner must make the choice of whether to betray the other or to remain
silent. The dilemma is that neither prisoner knows for sure what the other
prisoner will do. "
Prunella Stays Silent Fluffy
Stays
Silent
Prunella betrays or defects and
rats out Fluffy
Fluffy = Minor sentence, serves six months
Fluffy = Sucker payoff, serves ten years Prunella = Minor sentence, serves six
months
Fluffy
Betrays
Fluffy = Temptation payoff, goes free
or defects
and rats
Prunella = Sucker payoff, serves ten years
out
Prunella
Prunella = Temptation payoff, goes free
Fluffy = Reduced sentence of five years
Prunella = Reduced sentence of five years
Given these payoff values: Temptation > Minor > Reduced > Sucker
What do you do?
If you know your accomplice will remain silent, it is in your best interest to
remain silent too. Since you are unsure, however, the best strategy is to defect,
avoid the sucker payoff and accept the reduced sentence.
Prunella Stays Silent Fluffy
Stays
Silent
Prunella betrays or defects and
rats out Fluffy
Fluffy = Minor sentence, serves six months
Fluffy = Sucker payoff, serves ten years Prunella = Minor sentence, serves six
months
Fluffy
Betrays
Fluffy = Temptation payoff, goes free
or defects
and rats
Prunella = Sucker payoff, serves ten years
out
Prunella
For Prunella = 50% chance
of getting 6 months and
50% chance of worst
sentence!
Prunella = Temptation payoff, goes free
Fluffy = Reduced sentence of five years
Prunella = Reduced sentence of five years
For Prunella = 50% chance of
getting best deal (go free) and
50% chance of reduced
sentence. No chance of worst
sentence!
Terns can either hunt for fish, or steal fish from their neighbors. If
you know your neighbor will go and hunt, your best strategy is to
save your energy, wait for your neighbor to return with a fish, and
steal it.... but you don’t know.
The neighbor is making the same assessment of you.
So the “evolutionarily stable strategy” is for both to hunt and both
to steal when they can, even though the payoff for hunting + stealing
is less than for just stealing.
tern B hunts
tern B hunts & steals
tern A hunts
each tern gets two fish,
but high energetic cost
tern A gets zero fish
tern B gets two fish tern A hunts & steals
tern A gets two fish tern B gets zero fish
Each tern gets one fish