Transcript Scientific Laws

Announcements
Seminar:
How development has influenced morphologic
evolution in mammals:
Evidence from the lab and fossil record
Karen Sears, University of Colorado
B102 CLSL
Basic Scientific Principles
Scientific method.
Form and test hypotheses.
Approaches to studying behavior.
Limitations of science.
Scientific Thinking
Science — A process used to solve problems or
develop an understanding of nature that involves
testing possible answers.
Scientific Method — Gaining information about the
world by forming possible solutions to questions,
followed by rigorous testing to determine if the
proposed solutions are valid.
Scientific Method
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Presumptions
 Specific
causes for observed events.
 Causes can be identified.
 General rules can describe observations.
 Repeated events have same cause.
 Perceptions are not individualistic.
 Fundamental rules of nature are universal.
Scientific Method
Hypothesis — Logical statement that potentially
explains an event, or answers a question.
A good hypothesis will:
take into account all known facts
be as simple as possible
be testable and falsifiable
Scientific Method
Test Hypothesis
Theoretical approach
Comparative approach
Experimental approach
Scientific Method
Test Hypothesis
Theoretical approach
Comparative approach
Experimental approach
Use models and simulations to make
predictions. Input should come from best
available data.
Scientific Method
Test Hypothesis
Theoretical approach
Comparative approach
Experimental approach
Gather information from different groups
(individuals, species, sites) that vary in as
few factors as possible. For example,
juveniles vs adults in a population.
Scientific Method
Test Hypothesis
Theoretical approach
Comparative approach
Experimental approach
For comparisons among species, need to
control for independent evolutionary events
(the comparative method).
Sp. A
Sp. B
present
Speciation
event
past
ancestor
Phylogeny’s allow for comparisons among species while controlling for
evolutionary independent events (comparative method of independent
contrasts)
Trap-jaw ant (Odontomachus bauri)
Photo - Alex Wild
Scientific Method
Test Hypothesis
Theoretical approach
Comparative approach
Experimental approach
Devise a manipulative experiment. Predict
the outcome of the experiment if the
hypothesis is correct.
Scientific Method
Manipulative experiment — experimental factors
are varied to test hypothesis.
Important features of manipulative experiments:
Control – Separate variables and divide experiment into
experimental and control groups. There should be only one
difference between the experimental and control groups.
Replication — Experiment is repeated to eliminate
unconscious bias or a spurious correlation.
R. Wehner
How do they find
their way back to
the nest?
Wittlinger, Wehner and Wolf. 2006. Science
Scientific Method
Conclusion — statement if the hypothesis has been
supported or not by the results of the test.
If results match predictions, then hypothesis
supported.
If results to not match predictions, then
hypothesis not supported.
Hypotheses are never “proven” true!!
Statistics
A branch of applied mathematics concerned
with the collection and interpretation of
quantitative data.
Probability
How likely are your results true?
Our ability to accept or reject a hypothesis will be based
on the accuracy and precision of our measurements.
Accuracy - an
estimate of nearness to
the truth or the true value
Precision -
the
repeatability of reproducibility
of a measurement
Quantitative vs. Qualitative data
Quantitative data: Based on numerical data - can be
precise. (descriptive of size, magnitude or degree)
example - the number of species in a community
Qualitative data: A general description of properties
that often cannot be written in numbers and may be
subjective. (descriptive of kind, type or direction)
example - aggressiveness
Much of what we measure in Animal Behavior is
qualitative - often poses problem for statistical
analysis.
The ethogram, a graph of the time course or switch
points in a sequence of behaviors, became a way of
categorizing species-typical behaviors.
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Behavioral scientists often convert qualitative data
into quantitative data.
Place behaviors into discrete categories.
Assign relative values to different behaviors
(e.g. scales of aggression or attraction)
Example: Measuring intraspecific aggression in ants.
After two individuals come in contact, many behaviors can occur.
1. Place these behaviors into discrete categories.
2. Record the amount of time spent doing each behavior.
Touch - contacts that include antennation, grooming and
trophallaxis.
Avoid - contacts that resulted in one or both of the ants
retreating in opposite directions.
Aggression - head biting, leg biting, leg pulling, or charging.
Fighting - prolonged aggression, often consisted of ants locking
mandibles, grappling, or death.
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1 = touch
2 = avoid
3 = aggression
4 = fighting
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Lake Skinner A
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Y = 8.227 - 7.044 * X; R2 = 0.58
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Correlation of hydrocarbon
profiles between nests
Example of hypothesis testing:
Niko Tinbergen observed that
digger wasps could return to their
exact nest location after
spending considerable time away
(ignoring the 100s of other nests
at the same location).
Observation: Wasps can relocate their inconspicuous
nests.
Question: How do digger wasps relocate their nests?
Question: How do digger wasps relocate their nests?
Hypotheses:
The wasp returns to any nest.
The wasp uses chemical scents to relocate the nest.
The wasp uses visual landmarks to relocate the nest.
Question: How do digger wasps relocate their nests?
Hypotheses:
The wasp returns to any nest.
The wasp uses chemical scents to relocate the nest.
The wasp uses visual landmarks to relocate the nest.
Tinbergen further observed that when wasps left
the nest, they spent time flying back and forth
around the nest entrance.
Question: How do digger wasps relocate their nests?
Hypotheses:
The wasp returns to any nest.
The wasp uses chemical scents to relocate the nest.
The wasp uses visual landmarks to relocate the nest.
Tinbergen further observed the when wasps left
the nest, they spent time flying back and forth
around the nest entrance.
Null hypothesis: visual landmarks are not used to
relocate the nests.
Tests & Predications:
1. If I modify the visual landmarks around the
nest, the wasp will not be able to find it.
2. If I move the landmarks (keeping them
intact), the wasp will return to the wrong
location.
3. If I give the wasp landmarks (pine cones),
she will use them to relocate her nest.
Important to only manipulate one thing at a time!!
Results:
1. Wasps took much longer to find their nests if
landmarks were manipulated.
2. If landmarks were moved to a new location (intact),
the wasp searched for her nest in that new location.
3. Experimental manipulation of landmarks allowed us
to predict where the wasp would look for her nest.
Conclusions:
The wasp probably uses visual landmarks to
relocate the nest.
Why say probably?
Was this an example of a proximate or
ultimate question?
Another example of hypothesis testing:
Observation: Adult black-headed gulls remove
broken egg shells from their nests.
Question: Why do gulls remove broken egg shells?
Tinbergen was not interested in the mechanisms
of egg shell removal (how they were
recognized), but why they were removed (in an
evolutionary sense)
Question: Why do gulls remove broken eggshells?
Hypothesis:
Broken egg shells attract predators to the nest.
Tests & Predications:
The presence of broken egg shells increases the
probability of nest predation.
Results:
The presence of egg shells near the nest increased
the probability of predation.
Conclusions:
Black-headed gulls (or some ancestor) likely
evolved the behavior of removing eggs shells to
reduce the probability of their nests being located
by predators.
Why say probably?
What are some alternative testable hypotheses?
Scientific Method
Humans have been using this method in some
form for a long time.
Blurton-Jones (1976) documented Kalahari
bushmen’s (!Kung) knowledge of animal behavior
Hunter-gatherer society, similar to most of human’s
history.
- Discriminated data
from theory
- Developed
hypotheses
- Used reasoned
skepticism
“When asked whether newborn cape
buffaloes stayed with their mothers or
were kept hidden, one man replied that
he had not looked ‘since buffaloes kill
you, you don’t go after them.’
However, he then suggested that since
buffaloes are like cows, and newborn
calves stay with their mothers, the same would be true of buffaloes.
Or, that since newborn buffaloes are large and conspicuous, the
option of trying to stay hidden wouldn’t work very well.”
These are examples of comparative (behavior same as
similar species - phylogenetic) and ecological (based on
interactions with the environment) hypotheses.
Limitations of Science
- Restricted to those things that can be logically
tested and falsified.
- More than one hypothesis can predict the same
outcome of a test.
- Results can be interpreted in different ways,
leading to different conclusions.
- Hypotheses constantly being reevaluated and
modified as more results and information are
gained.
Next time:
Proximate vs Ultimate causes of behavior.