what is science?

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


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


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


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:


Results

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


Depe

nden

t var

iabl

e

Positive correlation


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.


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


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


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


1. What structures communities?

2. What can we say about interactions among species?

• Predation

• Competition

• Parasitism

• Mutualism

Community


1. How does energy and nutrients move through ecosystems?

2. How does this flux influence species?

Ecosystem


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?

what is science?

Documents

philosophy of science

hypothesis true

normal moths

silenced moths

alonetether moths

bats sonar

scientific study

attackfrom corcoran