Biology 441: 9/17/07 Last time Types of questions (Proximate vs. Ultimate) Behavioral research...

Biology 441: 9/17/07

Last time Types of questions (Proximate vs. Ultimate) Behavioral research methods

Today Behavioral methods cont’d Crickets Infanticide discussion

Next time Development of Behavior

[http://research.amnh.org/~krussell/professional/teaching.htm]

Behavioral Research Methods

2. Experimental Methods Manipulating something (independent variable) and

measuring its affect on something else (dependent variable) while holding other factors constant

Best suited for lab situations; psychology


2. Experimental Methods Example: Method of isolation

Bird song in white-crowned sparrows


2. Experimental Methods Problems with laboratory studies

Difficult to

generalize Artificial situation

affects behavior


2. Experimental Methods Example of field study

Wasp nest location & landmarks (Tinbergen)

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

Example:

Landmarks (pinecones) around nest

Landmarks shifted to new site

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?

Example:


2. Experimental Methods Problems with field studies

Lack of control; inability to hold certain variables constant


3. Correlational Methods Measurable changes in animals behavior that are

predictable from some other variable that we can measure


3. Correlational Methods Measurable changes in animals behavior that are

predictable from some other variable that we can measure

E.g., temperature and activity


3. Correlational Methods Problem: cannot infer causation


3. Correlational Methods Problem: cannot infer causation Solution? Manipulate potential causal factor

(experimental)


3. Correlational Methods Problem: cannot infer causation Solution? Manipulate potential causal factor

Not possible for study of human behavior


4. The Comparative Method Comparisons of behavior within species or between

species Idea that animals are optimally adapted to their

environment


4. The Comparative Method Comparisons among living species

Different strategies in different habitats



Different strategies in different habitats Different strategies in same habitat

E.g., Agelenopsis aperta & anti-predator behavior



Different strategies in different habitats Different strategies in same habitat Related species: differences in life styles related to

habitat E.g. Kittiwake vs. black-headed gulls


4. The Comparative Method Fossils (ancestors)

Clues about behavior Teeth marks, aggregation, nesting, etc.


5. Cost-Benefit Analysis Behavior is examined in terms of cost to animal vs. gain

to animal Assumption that animals behave to maximize gains and

minimize costs


5. Cost-Benefit Analysis Example: Tinbergen (again) and black-headed gulls



Observations: Gulls remove eggshells from nest 1 hour after hatchingCost? Energy/time spent moving shells; leaving the nest

(predation risk)



Observations: Gulls remove eggshells from nest 1 hour after hatchingCost? Energy/time spent moving shells; leaving the nest

(predation risk)Benefit?



More information: Nest in open Numerous nest predators Nests are unguarded while parents forage Cryptic nest, offspring, and eggs Inside of egg is white

Hypothesis?



Hypothesis? (ultimate cause) Removal of egg shells decreases likelihood of predation

Test?



Hypothesis? (ultimate cause) Removal of egg shells decreases likelihood of predation

Test? Establish artificial nests Place eggshells at 15 cm, 100cm and 200cm


5. Cost-Benefit Analysis Example: Tinbergen (again) and black-headed gulls Steps to address ultimate causes

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

21

32

42

0

10

20

30

40

50

15 100 200

Distance from nest (cm)

Percent depredated

Results:

Do these data support the idea that eggshell removal is reproductively advantageous?

Black-headed Gulls

Experimental method Nests with eggshells near them more likely to predated

Comparative method The Kittiwake ignores shells; has no nest predators

Black-headed Gulls

Next Question: Why wait 1 hour to remove shells?

Cost: increased likelihood of predation Benefit?

Black-headed Gulls


Cost: increased likelihood of predation Benefit? More info:

Chicks easier to eat when plumage wet Cannibalism likely (neighbors)

Black-headed Gulls


Cost: increased likelihood of predation Benefit? Avoid predation by neighbors if wait

Black-headed Gulls


Cost: increased likelihood of predation Benefit? Avoid predation by neighbors if wait Comparative Method:

Oystercatcher chicks not in danger of predation by neighbors Parents remove egg shell immediately


SUMMARY 1. Observation method 2. Experimental method 3. Correlational method 4. Comparative method 5. Cost-benefit analysis

Discussion Questions 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?

Biology 441: 9/17/07 Last time Types of questions (Proximate vs. Ultimate) Behavioral research...

Documents

Transcript of Biology 441: 9/17/07 Last time Types of questions (Proximate vs. Ultimate) Behavioral research...