Biology 360: February 5, 2007
Adaptation and Anti-predator behavior
Switching our focus back to ultimate hypotheses:
I.
Comparative approach to animal behavior (overview) [Fig. 6.7]
A.
Comparisons are made among closely related species (or even
subspecies/populations) in different habitats
1.
Adaptationist hypothesis (divergent evolution): Behavioral differences
in these related species have evolved due to differences in environment
rather than simply due to random mutation, genetic drift, and other
mechanisms that could create differences not due to natural selection.
B.
Comparisons are made among very distant relatives in similar habitats.
1.
Adaptationist hypothesis (convergent evolution):
Behavioral
similarities in these non-related species evolved because a similar
environment led to selection for similar traits; these traits arose
independently.
C.
Benefits of this approach: generate ecologically-relevant hypotheses
D.
Limitations of this approach: show correlation, not causation
II.
Example of comparative approach: Comparison of several behaviors of ground
nesting vs. cliff nesting gull species (related to predator avoidance, survival)
A.
Video: comparison of a variety of behaviors (fighting, shells in nest,
appeasement, nest structure, mating posture, fight practice of young, mobbing
behavior)
III.
The prey’s perspective: Individual adaptations for avoiding predation (briefly)
A.
Avoid detection
1.
Camouflage and cryptic behavior (very common)
a)
See examples in PowerPoint
2.
(Avoid dangerous habitat): we didn’t go into this, but many obvious
examples such as animals that live in cracks and crevices, making it
difficult for predators to reach them…
B.
Advertise inedibility/or uncatchability (i.e. “I am not worthwhile prey to
pursue.”)
1.
Warning coloration [Fig. in PP]
a)
Bright colors/distinctive patterns are coupled with toxicity

Poison arrow frog

Nudibranch
2.
Mimicry [Fig. in PP]
a)
Mullerian (Example: cuckoo wasp and yellow jacket)
b)
Batesian (deceptive): hawkmoth and snake
3.
Push-up displays by anoles: honest signals of fitness and ability to
flee? [Fig. 6.27]
C.
Stopping a pursuer
1.
Use of toxins and other deterrents
a)
Example: gacking in giant petrel chicks
2.
Evasion
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a)
IV.
Moths and crickets can detect bat sonar and will react by
changing their flight path [Fig. 4.18].
b)
Schools of fish confuse the predator by flashing and making it
difficult to hone in on a single fish.
3.
Fighting back when captured
Prey perspective: focus on group defense mechanisms
A.
Mobbing [Fig. 6.1]
1.
Description (in blackheaded gulls and others)
2.
Adaptive value (for black-headed gull)
a)
Experiment with unguarded eggs placed from outside to inside
territory (Kruuk) [Fig. 6.3]

Description/key result
3.
Costs?
a)
South polar skuas and penguin colonies…
B.
Stotting behavior in Thomson’s gazelles (generally found in herds)
1.
Description of stotting
2.
Hypotheses for the value of this behavior/Predictions to differentiate
among hypotheses [Table 6.2]
a)
Be sure you understand the basics of each hypothesis and
prediction
b)
Which hypothesis is supported by the actual data? [Table 6.2;
Fig. 6.26]
C.
Vigilance and the value of groups
1.
Goshawk and wild wood pigeons
a)
Method: Kenword used a hungry, trained goshawk and released
it at a standard distance away from flocks of wild wood pigeons
b)
Result: Larger flocks responded to the threat by taking flight
more quickly (when the hawk was further away) than smaller
groups. Also, the hawk was much less successful in making a
kill from the larger flock [PP only]
2.
Half brain sleep (ducks, dolphins)
D.
Dilution effect: The greater the number in a group, the greater the odds of
survival (for a given number of predators). Predators become satiated.
1.
Example: mayflies [Fig. 6.11]
a)
How was the data collected for this graph?
b)
What is the key result of this study? Does it support the concept
of the dilution effect/predator satiation?
2.
Example 2: mud-puddling behavior in butterflies [Fig. 6.10]
a)
Value of mud-puddling for butterflies
b)
What is the key result related to dilution effect/predator
satiation?
E.
Selfish herd hypothesis: There are particular locations within a group that
are safe locations, with chances of survival much greater for those animals that
are able to make it to the safest position than if the entire group was spaced
out evenly
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1.
2.
3.
Paradox of herding and schooling behavior
a)
Being spaced out as individuals often makes individuals less
conspicuous and more difficult to find. Predators often prefer
to prey on larger groups [PP, Predation on whirligig beetles
1]
b)
But each individual within a group often has less of a chance of
being attacked, just as seen for mayflies and butterflies [PP,
predation on whirligig beetles 2]
c)
Why do we see these types of results

Numbers game (the odds…)

Vigilance

Confusion effect (as for schools of fish)
Evolution of selfish herds (hypothesis)
a)
Selfish individuals could exploit the ones that space themselves
out by orienting close to another and essentially using it as “as
a shield”.
b)
If that selfish trait helps the animal survive and reproduce, and
it is heritable, exploiters will leave more offspring than the
ones that space themselves out, and the selfish gene will
spread, causing larger aggregations,
c)
Not all positions are equal: dominant animals move to the
safest place in the crowd.
What is the best position within a group? Is it preferable to be part of
the group even if you are in an inferior position?
a)
Adelie penguin “line”
b)
Bluegill nests (depression in lake bottoms) [PP].
c)
NOTE: Interestingly, predators tend to aim toward the center
of a group, but it is those on the outside that end up having a
higher rate of predation.
Study questions (see also the questions in the body of the outline above.)
1.
For the comparative approach to animal behavior:
a.
Of what value are comparisons among closely related groups in different
environments/habitats?
Be sure you know/understand the adaptationist
hypothesis for differences seen among closely related species found in different
environments.
b.
Of what value are comparisons among species that are only very distantly related
but found in similar environments/habitats? Be sure you know/understand the
adaptationist hypothesis for differences seen among distantly related species
found in similar environments.
2.
Describe some key benefits as well as the key limitation of the comparative approach.
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3.
Use the example of ground-nesting gulls vs. cliff-nesting gulls to describe some
differences in behavior that appear to have evolved as the result of differences in
environment. You should be able to describe/discuss several of these behaviors.
(NOTE: This was in the video “Signs and Signals”; I’ve listed the key types of
behaviors in the outline above to help jog your memory.)
4.
Provide at least one real example for each of the following (from lecture or your own
knowledge.) Be sure you are familiar with the examples given in lecture.
a.
Adaptations for avoiding detection
b.
Adaptations that advertise inedibility/uncatchability
c.
Adaptations that help an animal deter the pursuer
d.
Adaptations that help an animal evade the pursuer
5.
Warning coloration
a.
What is meant by “warning coloration”?
b.
What is the value of pairing bright coloration with toxins?
c.
Are all animals with warning coloration toxic? If not, how could warning
coloration benefit animals without toxins?
d.
What is a Batesian mimic? Provide at least one example.
6.
How could push-ups in anoles (a type of lizard) serve as an honest signal of fitness?
7.
Mobbing behavior:
a.
Provide a basic description of mobbing behavior.
b.
Discuss the potential adaptive value of this behavior.
c.
Describe Kruuk’s experiment and key result.
d.
Discuss whether Kruuk’s experiment is a realistic way to test the benefits of
mobbing behavior. (In other words, point out both positive and problematic
aspects of the experimental design as described in the text and lecture.)
e.
Describe at least one possible cost of this behavior. (HINT: Think about my
description of Adelie penguins “mobbing” South polar skuas.)
8.
Stotting in Thomson’s gazelles
a.
Provide a basic description of stotting behavior
b.
List/briefly explain the four hypotheses used to explain stotting.
c.
List/briefly explain the four predictions used to differentiate among the
hypotheses.
d.
Discuss whether their “expected results” for each predicted behavior (the “yes”
vs. “no” in the table) make sense for each of the four hypotheses. Why or why
not?
e.
Discuss whether the data presented in Fig. 6.26 really supports the “signal of
unprofitability” hypothesis. (Play devil’s advocate here: make your best
argument for one of the other hypotheses…)
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9.
If predators often prey on larger groups in preference to small ones, why should
animals (prey) ever hang out in groups? Provide at least three advantages of
grouping for the individuals in the group.
10.
Vigilance and the value of groups.
a.
Provide a basic description of the experiment done to generate the data in the two
pigeon-related PowerPoint slides.
b.
State the key results of the graphs as they relate to vigilance and the value of
groups.
11.
What is meant by the dilution effect? Provide a real example of the dilution effect
(lecture or text). (Be sure you are familiar with examples given in lecture.)
12.
Mayfly study
a.
Describe the basic data collection method for this study, as discussed both in
lecture and the text. In other words, be sure you can explain how they estimated
“mayflies emerging per day” as well as “total predation” for Fig. 6.11.
b.
Discuss problematic aspects of the data collection method (we discussed this in
class, but you should also brainstorm on your own.)
c.
Describe, in words, the key result of Fig. 6.11.
13.
Use the example/data for of fish predation on whirligig beetles to explain the “paradox”
of herding and schooling behavior with respect to risk of being eaten alone vs. in a
group.
14.
Explain how selfish behavior could lead to the evolution of aggregation as a protective
strategy.
15.
Use the table “Predation Pressure on bluegill nests in relation to nest position” to
discuss the best position to be located within a bluegill sunfish colony.
NOTE: The exam is likely to include graphs similar to those provided throughout this
lecture. You may be asked to describe the key result indicated by the graph as well as explain
which hypothesis the data supports (or whether it supports or contradicts a particular
hypothesis.)
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