what is science?
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What is science?
Science is our effort to understand the world around us, using observable physical evidence.
Science is done through observation and experimentation
What is ecology?
Simple answer:
the study of how organisms interact with each other and their environment
Long answer:
“Ecology is the scientific study of the processes regulating the distribution and abundance of organisms and the interactions among them, and the study of how these organisms in turn mediate the transport and transformation of energy and matter in the biosphere (i.e., the study of the design of ecosystem structure and function).” (Krebs 1972)
What is ecology?
Ecology is by nature multi-disciplinary
Evolution
Physiology
Chemistry
Behavior
Genetics
Geology
Physics
Hydrology
moss grows on north side of treesYou notice:
Why?????
Pattern
Process
moss grows on north side of trees
microclimate is cooler on north side and more favorable to moss
deer live in groupsYou notice:
Why?????
Pattern
Process
deer live in groups
reduces susceptibility to predation
Alternative hypothesis
OR…groups to more easily find mate
Science is detecting interesting patterns and asking
WHY?????
Pattern
Process
Non-random outcome or event that begs an explanation
Mechanism causing a natural pattern
Or the Popperian method (after Karl Popper)
There is an ongoing debate though, on how science should be done
Philosophy of science
This method of scientific inquiry called
HYPOTHETICO-DEDUCTIVE REASONING
What is a hypothesis?
HYPOTHESIS
Reasonable explanationTestable
statement
Asks how? or why? Usually an
if / then statement
Challenge statement:
You can prove a hypothesis true.
Agree or disagree? Why?
Case study
Betholdia trigona (tiger moth) – emits a particularly dense series of ultrasonic clicks
Eptesicus fuscus (big brown bat) – eats tiger moths. Finds using sonar.
From Corcoran et al. Science 2009
You know:
WHY?
Hypothesis 1:
are blocking the sonar of
have a warning effect on
From Corcoran et al. Science 2009
Hypothesis 2 (or alternative hypothesis):
(telling them they taste bad)
How can you test this???????
If moths are blocking sonar, naïve bats should startle
and stop attack.
Won’t affect subsequent attack.
If moths have a warning effect (say they taste
bad), then naïve bats should complete attack but
not attack againFrom Corcoran et al. Science 2009
Hypothesis 1:
Hypothesis 2 (or alternative hypothesis):
As an if / then statement:
Now it’s testable
Experiment
Silence some moths
Leave some alone
Tether moths and watch how bats react when attack
From Corcoran et al. Science 2009
Results
Stopped attack on normal moths, but didn’t avoid moths in future
Bats caught silenced moths
From Corcoran et al. Science 2009How can you interpret????
Interpretation
Alternative hypothesis of being distasteful and giving a warning is disproven
Moths are obstructing the bats sonar, allowing them to escape being eaten
From Corcoran et al. Science 2009
Back to hypothetico-deductive approach
Formulates a hypothesis from observation – then tries
to nullify alternatives
Never really proves the hypothesis, just disproves the
alternatives
Eliminates alternatives within a certain degree of error
Observation
Argentine ants are successful invaders of native California ant habitats
Jeanna Bryner
Hypothesis
Argentine ants don’t fight amongst themselves, but do fight with other species (observation)
Hypothesis: if / then
If Argentine ants are more genetically similar, they will fight more with native species than with their own
Alternative hypothesisIf predators prefer native species but don’t eat Argentine ants, native species will suffer reduced populations relative to Argentine ants
Experiment
Check genetic similarity between native species and Argentine ants and among themselves
Feeding experiments – which species do predators prefer
BUT, even if predators prefer the natives, does that affect their population numbers?
Hypothesis:
Alternative hypothesis
Results
Hypothesis:
Alternative hypothesis
Argentine ants are very similar genetically to other Argentine ant nests – the same is not true of native ants
Predators prefer native ants, but predation is probably less important in structuring community than competition
Interpretation
Argentine ants represent a “supercolony” – individuals from
nearby nests recognize each other as siblings rather than
intraspecific competitors.
Tools
Statistics are a tool scientists use to see patterns and test hypotheses.
Average trait
All individuals
There is considerable variation in traits among individuals of the same species
Wing length (mm)
Correlation between spot length and wing length of Anopheles darlingi from the Amazon (open circles) and Mato Grosso (closed circles)
From Charlwood 1996
What does each point represent?
Variation
Biological variability: differences in individuals
MeanThe average. But it’s also important how much the data vary around the mean
5 5 5 5 5
7 1 5 3 9
average
average
5
5
0
10
variance
CONTROL GROUP EXPERIMENTAL GROUP
“normal” The altered group
No special conditions “abnormal”
Reference point With special condition you’re interested in
Plants in field Plants with added nitrogen
Number of seeds per plant
Grow plants with other plants and count seeds
Independent variable
Difference between control and experimental groups
Factor being tested
Can be different levels (e.g. different time points, different amount of nutrients
Sometimes call treatment
Cause
Dependent variable
Factor assume will be affected
Factor being measured
Factor that depends on the treatment
e.g. Plant growth, seed production, number of offspring, growth rate
Effect
Scatter plot
The scatter plot shows the hours of study and
test scores of 20 students
As the number of hours of study increases, the
marks scored tend to increase
So, the scatter plot describes a positive trend
Independent variable
Depe
nden
t var
iabl
e
Positive correlation
Independent variable
Depe
nden
t var
iabl
e
Negative correlation
Independent variableDe
pend
ent v
aria
ble
No correlation
Scatter plot
Scatter plot with error bars
Controls
Experiments that are testing a treatment should also have a control with the exact same conditions as the treatments, without the treatment.
Hypothesis: If nitrogen is a limiting nutrient for a certain plant community, then adding nitrogen will lead to increased growth of the plants in the community.
Add N Add N Control
Control Add N Control
Add N Control Control
Control Add N Add N
Hypothesis: If nitrogen is a limiting nutrient for a certain plant community, then adding nitrogen will lead to increased growth of the plants in the community.
What would the results graph look like???
Independent variable?Amount of Nitrogen added
Dependent variable?
Measure of plant growth
Kinds of data
Discrete Continuous
• Also called categorical
• Data have clear beginning
and end
e.g. Food in a diet (seed, plant,
animal)
• Usually a measurement
• Usually numeric data
e.g. the number of seeds per
plant or dry weight of a plant
Visual representations
Discrete Continuous
Histogram,Frequency distributionBar graph
Scatter plot
Histogram
Challenge statement
Correlation implies causation
Correlation and Causation
Pattern Correlation Describes the relationship between two variables
Process Causation Describes cause and effect
Case studyRead the article: Want a Higher G.P.A.? Go to a Private
College by C. Rampell, printed in the NY Times
1. What are the variables being compared (look at the title of the article)
2. Which is the dependent variable? The independent variable?
3. Does the headline indicate correlation or causation between the two variables?
4. Study claims following causal relationships:
• Students at private schools started receiving significantly higher grades than equally
qualified students (based on SAT scores) in public schools around the 1950’s
• All schools inflate grades, but private schools inflate more
• Admissions officers at top medical, business and law schools and some PhD.
programs are fooled by private school students’ inflated grades
• Lower grades in the sciences discourage American students from studying such
disciplines
Which, if any, claim is supported by the study? Explain.
Correlation and Causation
Sudden Oak Death (SODS)
First observed in the mid-1990’s in Marin County
On a slope near Mt. Tamalpais, facing SF Bay, where cool, moist fog bathes the hillsides
Correlation and Causation
Hikers noticed several clusters of tan oaks had turned brown and died
Tan oak (Lithocarpus densiflorus), not a true oak, but a close relative
Arborists also reported dying tan oaks elsewhere with unusually large swarms of three common bark beetles on he trunks, attracted to cankers
Sudden Oak Death
All trees that were sick or died had a beetle infestation
These beetles were known to burrow and tunnel in trunks of dead trees to nest and reproduce
Sudden Oak Death
Pathogen in Dutch elm epidemic was transmitted by insects, so assumed that they played the same role in this disease
Fungus transmitted by elm bark beetle
Sudden Oak Death
Because of testing of alternatives, we now know that it’s Phytophthora ramorum,in genus of Oomycetes (water molds), like a fungus
Hypothesis: beetles were transmitting the pathogen causing SODS
Many trees had large weeping cankers, swarms of beetles and green to black fruiting bodies of Hypoxylon fungus
This fungus is believed to be in the tree when it is healthy, and to break out and grow in areas of sapwood that die
What is a Scientific theory?
What is a theory?
THEORY
Offers a tested mechanism for
this phenomena
A phenomena based on a
group of observations
Close to a scientific law Derived from work
of multiple scientists
Ecology is hierarchical
Different levels of organization (scale):
Landscape
Ecosystem
Community
Population
Individual
Scal
e
Hierarchies in ecology
1. How do individuals affect and are affected by the environment?
2. How are individuals adapted to the environment?
3. How does an individual make a living?
4. What are the limiting factors for an individual’s reproduction and growth?
Individual
Hierarchies in ecology
1. What causes the presence or absence of a particular species?
2. What do we know about the species’ abundance or rarity?
3. Are there trends and fluctuations in their numbers?
4. What are their characteristics?
• Life histories
• Genetics
• Competition among each other
Population
Hierarchies in ecology
1. What structures communities?
2. What can we say about interactions among species?
• Predation
• Competition
• Parasitism
• Mutualism
Community
Hierarchies in ecology
1. How does energy and nutrients move through ecosystems?
2. How does this flux influence species?
Ecosystem
Hierarchies in ecology
1. How does energy and nutrients flow between ecosystems?
2. How are ecosystems connected?
3. What determines the presence and absence of species on a large scale?
Landscape
Kinds of ecological studies
Observational
Comparative
Theoretical
Experimental
Observe natural phenomena
No experiments or manipulations
Manipulate a microcosm
Isolate a portion, limit factors, manipulate conditions
May be based on data (or not)
e.g. mathematical models that describe ecosystem interactions
From literature and / or previously collected data
Meta-analysis
Reading literature
1. What is the problem?
2. What is the hypothesis of the researchers?
3. What are the alternative hypotheses?
4. How did they gather evidence?
5. Does the evidence support the hypothesis?
6. How does this fit in with the larger issues in ecology?
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