Transcript L4Methodscont`d copy

Biology 441: 9/17/07
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Last time
Types of questions (Proximate vs. Ultimate)
 Behavioral research methods
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Today
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Behavioral methods cont’d
Crickets
Infanticide discussion
Next time
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Development of Behavior
[http://research.amnh.org/~krussell/professional/teaching.htm]
Behavioral Research Methods
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2. Experimental Methods
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Manipulating something (independent variable) and
measuring its affect on something else (dependent
variable) while holding other factors constant
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Best suited for lab situations; psychology
Behavioral Research Methods
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2. Experimental Methods
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Example: Method of isolation
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Bird song in white-crowned sparrows
Behavioral Research Methods
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2. Experimental Methods
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Problems with laboratory studies
Difficult to
generalize
 Artificial situation
affects behavior
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Behavioral Research Methods
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2. Experimental Methods
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Example of field study
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Wasp nest location & landmarks (Tinbergen)
Example:
Tinbergen and beewolf wasps
• Wasp hunts bees to provision their young
• Young are reared in burrows
• Burrows occur in groups
• Burrows entrances are buried when the wasp leaves to hunt
• Wasps can relocate their nests quickly
Example:
Observation
• Wasps were marked to allow recognition of individuals
• Wasps returned to same nest and only constructed one nest
• Wasps would circle their nest before departing to hunt
Example:
Hypothesis (possible explanation; educated guess)
• Tinbergen’s hypothesis - wasps used landmarks to locate
their nests
Example:
Experiment
• Tinbergen cleared possible landmarks from around the nest
• When the wasps returned, they circled but could not locate the nest site
• Does this prove Tinbergen’s hypothesis correct?
• Can this result be explained in other
ways?
Example:
Experiment (additional experiment)
• Tinbergen shifted landmarks from around the nest to a site close by
• He wanted to see if the wasps could be trained to the landmarks
• When the wasps returned, they landed within the landmarks
Landmarks (pinecones)
around nest
Landmarks shifted to new
site
Example:
Experiment (additional experiment)
• Tinbergen shifted landmarks from around the nest to a site close by
• He wanted to see if the wasps could be trained to the landmarks
• When the wasps returned, they landed within the landmarks
• Does this prove Tinbergen’s hypothesis correct?
• Can this result be explained in other ways?
Behavioral Research Methods
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2. Experimental Methods
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Problems with field studies
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Lack of control; inability to hold certain variables
constant
Behavioral Research Methods
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3. Correlational Methods
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Measurable changes in animals behavior that are
predictable from some other variable that we can
measure
Behavioral Research Methods
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3. Correlational Methods
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Measurable changes in animals behavior that are
predictable from some other variable that we can
measure
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E.g., temperature and activity
Behavioral Research Methods
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3. Correlational Methods
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Problem: cannot infer causation
Behavioral Research Methods
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3. Correlational Methods
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Problem: cannot infer causation
Solution? Manipulate potential causal factor
(experimental)
Behavioral Research Methods
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3. Correlational Methods
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Problem: cannot infer causation
Solution? Manipulate potential causal factor
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Not possible for study of human behavior
Behavioral Research Methods
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4. The Comparative Method
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Comparisons of behavior within species or between
species
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Idea that animals are optimally adapted to their
environment
Behavioral Research Methods
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4. The Comparative Method
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Comparisons among living species
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Different strategies in different habitats
Behavioral Research Methods
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4. The Comparative Method
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Comparisons among living species
Different strategies in different habitats
 Different strategies in same habitat
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E.g., Agelenopsis aperta & anti-predator behavior
Behavioral Research Methods
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4. The Comparative Method
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Comparisons among living species
Different strategies in different habitats
 Different strategies in same habitat
 Related species: differences in life styles related to
habitat
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E.g. Kittiwake vs. black-headed gulls
Behavioral Research Methods
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4. The Comparative Method
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Fossils (ancestors)
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Clues about behavior
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Teeth marks, aggregation, nesting, etc.
Behavioral Research Methods
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5. Cost-Benefit Analysis
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Behavior is examined in terms of cost to animal vs.
gain to animal
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Assumption that animals behave to maximize gains and
minimize costs
Behavioral Research Methods
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5. Cost-Benefit Analysis
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Example: Tinbergen (again) and black-headed gulls
Behavioral Research Methods
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5. Cost-Benefit Analysis
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Example: Tinbergen (again) and black-headed gulls
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Observations:
Gulls remove eggshells from nest 1 hour after
hatching
Cost? Energy/time spent moving shells; leaving the
nest (predation risk)
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Behavioral Research Methods
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5. Cost-Benefit Analysis
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Example: Tinbergen (again) and black-headed gulls
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Observations:
Gulls remove eggshells from nest 1 hour after
hatching
Cost? Energy/time spent moving shells; leaving the
nest (predation risk)
Benefit?
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Behavioral Research Methods
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5. Cost-Benefit Analysis
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Example: Tinbergen (again) and black-headed gulls
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More information:
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Nest in open
Numerous nest predators
Nests are unguarded while parents forage
Cryptic nest, offspring, and eggs
Inside of egg is white
Hypothesis?
Behavioral Research Methods
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5. Cost-Benefit Analysis
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Example: Tinbergen (again) and black-headed gulls
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Hypothesis? (ultimate cause)
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Removal of egg shells decreases likelihood of
predation
Test?
Behavioral Research Methods
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5. Cost-Benefit Analysis
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Example: Tinbergen (again) and black-headed gulls
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Hypothesis? (ultimate cause)
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Removal of egg shells decreases likelihood of
predation
Test?
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Establish artificial nests
Place eggshells at 15 cm, 100cm and 200cm
Behavioral Research Methods
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5. Cost-Benefit Analysis
Example: Tinbergen (again) and black-headed gulls
 Steps to address ultimate causes
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Question: Why had black-headed gulls evolved a special response
to eggshells in their nest
Hypothesis: Eggshell removal had become common because it
helped gulls conceal their offspring
Prediction: Predators would use eggshell as a cue for finding eggs
Experiment: Find out what predators did
Conclusion: Match data to hypothesis
Percent depredated
Results:
50
42
40
32
30
21
20
10
0
15
100
200
Distance from nest (cm)
Do these data support the idea that eggshell
removal is reproductively advantageous?
Black-headed Gulls
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Experimental method
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Nests with eggshells near them more likely to
predated
Comparative method
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The Kittiwake ignores shells; has no nest predators
Black-headed Gulls
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Next Question:
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Why wait 1 hour to remove shells?
Cost: increased likelihood of predation
 Benefit?
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Black-headed Gulls
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Next Question:
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Why wait 1 hour to remove shells?
Cost: increased likelihood of predation
 Benefit?
 More info:
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Chicks easier to eat when plumage wet
Cannibalism likely (neighbors)
Black-headed Gulls
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Next Question:
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Why wait 1 hour to remove shells?
Cost: increased likelihood of predation
 Benefit? Avoid predation by neighbors if wait
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Black-headed Gulls
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Next Question:
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Why wait 1 hour to remove shells?
Cost: increased likelihood of predation
 Benefit? Avoid predation by neighbors if wait
 Comparative Method:
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Oystercatcher chicks
not in danger of predation
by neighbors
 Parents remove egg
shell immediately
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Behavioral Research Methods
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SUMMARY
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1.
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3.
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5.
Observation method
Experimental method
Correlational method
Comparative method
Cost-benefit analysis
Discussion Questions
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Which of the two articles is most persuasive, and why?
How does progress in science arise from controversies of
this sort?
Can you link the opposing interpretations of these two
studies to our discussion of ultimate and proximate
causation of
behavior?