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BIOL 2322 Ecology > Lecture 4: Experimental Design > Flashcards

Lecture 4: Experimental Design Flashcards

1
Q

What are the 3 ways we quantify ecology/measure interactions between organisms and their environment?

A
  1. formulate questions and hypotheses about observations
  2. design experiments and collect data to test hypotheses
  3. analyze data and interpret results in order to draw conclusions
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2
Q

What are the 8 components of experimental design?

A
  1. independent variable
  2. dependent variable
  3. groups in the experiment (treatment vs control)
  4. standardized variables
  5. replication
  6. data collection
  7. statistical analysis
  8. conclusion
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3
Q

What is the independent variable?

A

the variable that is intentionally different among the experimental groups

It is the variable that is manipulated by the researcher

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4
Q

what is the dependent variable?

A

the variable that is measured by the researcher

it is the one we expect to be affected by the changes the researcher makes

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5
Q

What is the first step in an experimental design?

A

making observations

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6
Q

What is an example of an observation?

A

most green frogs, Rana clamitans, reproduce in early march

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7
Q

What is the second step in an experimental design?

A

Formulating a scientific question

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8
Q

What are the 2 types of scientific questions in an ecological experimental design?

A
  1. proximate questions

2. ultimate questions

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9
Q

Describe proximate questions

A

They ask “HOW does it happen?”

What is causing this to happen?

They are based on immediate cause

the physiological, genetic, hormonal, motor responses to environmental stimulus

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10
Q

Describe ultimate questions

A

they ask “WHY does it happen?”

Considers evolutionary explanations; relationship to fitness (survival or reproductive success)

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11
Q

Give an example of a PROXIMATE question for the observation that most green frogs reproduce in early March

A

Does the warming water temperature in early March affect the timing of frog reproduction?

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12
Q

Give an example of a ULTIMATE question for the observation that most green frogs reproduce in early March

A

Does the warming water temperature in early March affect reproductive success in frogs?

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13
Q

Define null hypothesis

A

Statement that the independent variable will not have an effect on the dependent variable

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14
Q

Define alternative hypothesis

A

Statement that the independent variable will have an effect on the dependent variable

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15
Q

Which hypothesis is tested in an experimental design? Why?

A

the NULL hypothesis

We always assume the null is true until we have statistically significant data that allows us to reject the null hypothesis

By testing the null, it avoids introducing biases into the experiments

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16
Q

Which is the INDEPENDENT variable in this null hypothesis example: Water temperature does not have an effect on the reproductive success of green frogs

A

Water temperature

it is what can be manipulated

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17
Q

T or F: in all cases you can manipulate your independent variable for your experiment

A

FALSE.

Sometimes you can, other times you have to work with the natural variation

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18
Q

Which is the DEPENDENT variable in this null hypothesis example: Water temperature does not have an effect on the reproductive success of green frogs

A

the reproductive success

it is what will be measured

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19
Q

T or F: this null hypothesis: “Water temperature does not have an effect on the reproductive success of green frogs” example provides enough detail about the dependent variable for the experimental design?

A

FALSE.

reproductive success (dependent variable) can be measured in a lot of ways, this statement is not detailed enough

20
Q

What are 4 ways to measure reproductive success in frogs?

A
  1. egg production
  2. fertilization success
  3. hatching success
  4. offspring survival
21
Q

What else needs to be considered when deciding how to measure a dependent variable?

A

the difficulty of collect the data and how useful it will be in answering the question

ex. later life stages are harder to measure, but better estimators of reproductive success

22
Q

What 4 elements does a formal hypothesis include?

A
  1. independent variable
  2. dependent variable
  3. units of measurement for both ^^
  4. the scientific name of the study species
23
Q

Give a more formal null hypothesis for the example of the green frogs and water temperature

A

Water temperature (degrees C), does not have an affect on egg production (#eggs/egg mass) of green frogs, Rana clamitans.

24
Q

Give a more formal alternative hypothesis for the example of the green frogs and water temperature

A

Water temperature (degrees C), does have an affect on egg production (#eggs/egg mass) of green frogs, Rana clamitans.

25
Q

After making the hypotheses, what comes next?

A

You have to make a prediction of the results you would expect to see if the ALTERNATIVE HYPOTHESIS IS SUPPORTED

26
Q

Give an example of a prediction for the green frogs and water temperature hypotheses

A

If water temperature (degrees C), does have an affect on egg production (#eggs/egg mass) of green frogs, Rana clamitans, THEN

the number of eggs produced per egg mass should be positively correlated with water temperature

27
Q

Describe positive correlation

A

one variable increases as the other increases

28
Q

Describe negative correlation

A

One variable decreases as the other increases

29
Q

T or F: when describing your experiment, you need to explain how you will collect the data so that someone else can replicate your experiment

A

TRUE

30
Q

What are the 3 types of experiments in ecology?

A
  1. Natural/observational experiments
  2. manipulative experiments
  3. mathematical model
31
Q

Describe natural experiments

A

rely on natural variation in the environment so that researchers do not manipulate groups in the experiment

32
Q

Give 4 reasons why we might use a natural experiment

A
  1. working with endangered species (cannot manipulate environment, collect offspring)
  2. working in parks (organisms are protected against manipulation)
  3. Some manipulations would harm the organisms
  4. Always do this as a first step to ensure a relationship actually exists
33
Q

Why are natural experiments not always the best choice?

A

Because it is difficult to isolate the exact cause and affect

34
Q

Describe manipulative experiments

A

test hypotheses by artificially changing the factor that is hypothesized to be the underlying cause of a phenomenon

  • essentially applying treatments to test groups

Control groups are usually required

35
Q

Why are control groups required in addition to treatment groups for manipulative experiments?

A

to demonstrate that the manipulation did not have any unintended effects on the results

36
Q

Give 3 reasons to do a manipulative experiment

A
  1. to isolate specific variables to determine cause and effect
  2. natural variation with population is too low
  3. there is no barrier to doing so, there is much more power in the results
37
Q

Describe mathematical models and give an example

A

represent a system with a set of equations representing hypothesized relationships between components of the system

  • write a model predicting the hatching success in frogs given different values for several environmental conditions
  • then measure conditions and hatch success in the field to verify the accuracy of the model
38
Q

When are mathematical models useful?

A
  1. to answer theoretical questions

2. to predict outcomes in response to multiple scenarios

39
Q

What are the disadvantages of natural experiments?

A

difficult to isolate variables

correlation does not equal causation

40
Q

What are the disadvantages of manipulative experiments?

A

creates simplified environments with potential of lab effects (ie, testing outside of natural conditions can remove confounding variables)

41
Q

What are the disadvantages of mathematical modelling?

A

it introduces assumptions that may or may not be correct

42
Q

T or F: it is best to pick one type of experiment

A

False. They all have their limitations so it is best to use multiple approaches

43
Q

From this example:

“Observe frog reproduction from and measure egg masses daily from first to last date of reproduction. Collect all new egg masses daily and record water temperature at time and location of collection. Gently spread each egg mass out on a tray and count and record number of eggs. Return all egg masses to original location in pond immediately after counting.”

Which type of experiment was done? how can you tell?

A

Natural because the dependent variable (water temperature) was not altered

44
Q

What is the purpose of scatterplots to show results?

A

They show the correlation between 2 variables

if the dots are centred around a non-horizontal line, the variables are correlated

if the line is horizontal and the dots are everywhere, there is no correlation

45
Q

On a scatterplot, what does the ‘r’ value represent?

A

r value = correlation

r = 0 = no correlation = horizontal graph

r = +1 = positive correlation = line with positive slope

r = -1 = negative correlation = line with negative slope

46
Q

On a scatterplot, what does the ‘p’ value represent?

A

significance levels

significance = 0.05

less than 0.05 = statistically significant results

more than 0.05 = no statistically significant effect

47
Q

What is the hypothetico-deductive/scientific method? What are the steps?

A
  1. question
  2. form hypotheses
  3. prediction
  4. test hypotheses
  5. if you fail to reject the null hypothesis - look at the experiment and see if there are problems
  6. if you reject the null hypothesis, formulate other questions that could further the research

BIOL 2322 Ecology (13 decks)

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