EXPERIMENTAL

DESIGN

Sam Stynen

• First year grad student at Kellogg Biological Station (KBS)

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• From Nevada were I studied butterflies and taught middle school.

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• I like arts and crafts, music, and learning new instruments

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• I study how climate impacts butterfly morphology.

Ashley Darst

• Second year PhD student at Michigan State University
• From Minnesota, love to hike/canoe!
• Research how pollinators are affected by human-caused changes (like pollution)

Robin Waterman

• 5th year PhD student at MSU’s Kellogg Biological Station
• Grew up in Connecticut
• Research how weedy plants evolve in response to agriculture and pollinators
• For fun I hike with my dog, ski, play board games, and ballroom dance

Reproducibility

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Experimental

Design

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Variables

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Experimental Design

Experimental design is the part that happens BEFORE you carry out an experiment.

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It is the process of planning and structuring experiments to answer an inquiry question by manipulating independent variables and observing their effect on dependent variables.

Experimental Design

Key Terms:

• Independent variable
• Dependent variable
• Controlled variables
• A control group

In the following example, identify the independent and dependent variable

Do sunflowers grow taller in the sun or shade?

Independent Variable: The amount of sunlight

(Sun vs Shade)

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Dependent Variable: The height of the sunflower plant

What might be some variables that we would need to control in this experiment?

• Amount of water
• Type of soil
• Temperature of the air
• Ruler used to measure plant height

Controlled Variables

Sam’s Example

How does temperature impact butterfly body size?

How does temperature impact butterfly body size?

Heating Chamber

Independent variable:

• Temperature via heating chamber

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Dependent variables:

• Body size, survival, lifespan

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Controlled variables:

• Plant, location, nectar

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A control group:

• Wild caught individuals

Higher temperature parents

Current temperature parents

Wild Caught individuals

Ashley Darst

• Second year PhD student at Michigan State University
• From Minnesota, love to hike/canoe!
• Research how pollinators are affected by human-caused changes (like pollution)

Ashley’s Example

Independent variable:

Dependent variable:

Independent variable: salt vs no salt

Dependent variable:

Independent variable: salt vs no salt

Dependent variable: number of pollinators

Salt applied to plots every other week (plants moved salt from soil into nectar)

Pollinators surveyed daily

Controlled variables:

Controlled variables:

• Plot orientation
• Plot size
• Pollinator survey length and time of day
• Habitat type

butterfly/moth

honey bee

wasp

sweat bee

butterfly/moth

honey bee

wasp

sweat bee

Butterflies / moths visited MORE salty flowers

butterfly/moth

honey bee

wasp

sweat bee

Butterflies / moths visited MORE salty flowers

Honey bees visited MORE salty flowers

butterfly/moth

honey bee

wasp

sweat bee

Butterflies / moths visited MORE salty flowers

Honey bees visited MORE salty flowers

Wasps visited LESS salty flowers

butterfly/moth

honey bee

wasp

sweat bee

Butterflies / moths visited MORE salty flowers

Honey bees visited MORE salty flowers

Wasps visited LESS salty flowers

Sweat bees visited THE SAME number of salty/not salty flowers

butterfly/moth

honey bee

wasp

sweat bee

For what pollinator groups was our hypothesis supported?

For what groups was it not supported?

Robin Waterman

• 5th year PhD student at MSU’s Kellogg Biological Station
• Grew up in Connecticut
• Research how weedy plants evolve in response to agriculture and pollinators
• For fun I hike with my dog, ski, play board games, and ballroom dance

Robin’s Example

Adaptation of weeds to agricultural environments

Robin’s Example

Question: Does GA impact the life cycle of horseweed plants?

Hypothesis: Horsweed plants with more GA will have an accelerated summer annual life cycle

Observation: Some horseweed individuals have a winter annual life cycle, while others have a summer annual life cycle.

Prior research: In other species, the growth hormone Gibberellic Acid (GA) causes plants to grow faster and flower sooner

Independent variable: GA level (added vs. not added)

Leaves sprayed weekly from emergence to flowering

• Growth rate
• Flowering time
• Leaf shape

Dependent variables:

Summer annual

Winter annual

Question: Does GA impact the life cycle of horseweed plants?

What should the control group be?

What could I measure to answer my question?

Independent variable:

Dependent variables:

• Growth rate
• Flowering time
• Leaf shape

Greenhouse pot arrangement options:

Grouped

Random

All other conditions are controlled

• Soil
• Genetics
• Temperature
• Light

Question: Does GA impact the life cycle of horseweed plants?

vs.

Independent variable:

Dependent variables:

• Growth rate
• Flowering time
• Leaf shape

Greenhouse pot arrangement options:

Random

All other conditions are controlled

• Soil
• Genetics
• Temperature
• Light

Question: Does GA impact the life cycle of horseweed plants?

vs.

Water

GA

Hypothesis: Horsweed plants with more GA will have an accelerated summer annual life cycle

Do these data provide evidence to support my hypothesis?

Thank you!

Questions?