Featured scientist:
Dr. Sarah W. Davies from UT Austin
Won’t you be my Urchin?
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Imagine you are snorkeling on a coral reef where you can see many species living together. They all depend on the coral to survive.
Who is your favorite Finding Nemo character?
Some animals in coral reefs, like sharks, are predators that eat other animals.
Other species, like anemones and clown fish are mutualists and they work together to increase their chance of survival.
Herbivores like sea urchins, eat plants and algae that grow on the coral reef.
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Herbivore: primary consumers, eat producers
Predator: an animal that consumes other animals
Mutualists: organisms that help each other in a mutually beneficial relationship.
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Corals are the animals that build coral reefs. They are very sensitive and can be hurt by human activity, like boating and pollution.
Corals reef ecosystems are also in danger from warming waters due to climate change.
List three pressures that impact a population of coral.
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Three selective pressures that impact a population of coral:
Corals compete with certain types of algae for space to grow on the reef. If there is too much algae, corals have no place to attach and grow.
Here are two pictures of algae overtaking coral.
Corals and algae are competitors. What do they compete for?
Considering that corals compete with algae for space to grow. What is a possible way we can help a struggling coral population?
Did you think of introducing an herbivore that eats the algae?
That is what Sarah W. Davies, then a graduate student at UT Austin, thought.
Sea urchins are important herbivores and one of the species like to eat algae on coral reefs.
The vegetarian sea urchin Diadema antillarum.
Sarah predicted that if urchins are present on the reef, the corals might have less competition from algae for space, and thus more room to grow.
A sea urchin (a primary consumer) having a delicious algae feast.
What was Sarah’s hypothesis ( if...then...because…)
Dr. Sarah W. Davies sharing her love of the sea with her daughter.
Sarah wondered:
Could adding urchins to a coral reef help the coral population grow?
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Sara’s hypothesis:
If urchins are present then corals populations will grow,
because the corals will have less competition for space.
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Of course, is is not enough to just come up with a hypothesis-- as scientists, we have to TEST IT OUT!
She was a post-doctoral student at UT and she chose the Gulf of Mexico to do her experiments.
Have you ever been to the Gulf of Mexico? Did you imagine there were scientists doing experiments out there under the waves?
Would you like to have a job where you get to scuba dive in coral reefs?
She and her team set 8 bins with coral out on the reef.
Into half of the bins, Sarah added urchins.
In the other half she did not place any urchins.
Why did Sarah set out bins without any urchins?
There are more than 8 bins in this picture because other scientists are also doing research in the same location.
Experimental Set-up:
The independent variable has been manipulated (urchins.)
Control Set-up:
No urchins- everything else the same.
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Adding bins that are identical, but without any urchins is important because then any difference in the number of coral could be attributed to the presence of urchins.
Because it is the only difference!
It is the only Maniupulated Variable.
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Check for Understanding:
What was Sarah’s Independent (Manipulated) Variable?
What one condition did she intentionally change (manipulate)
in order to test her hypothesis?
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Sarah manipulated (changed) only one condition:
Adding sea urchins in the bins of coral.
This is her INDEPENDENT VARIABLE (IV)
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After a few months, Sarah returned to collect data. She counted how many corals were growing on each tile and recorded her results.
These are two coral species Sarah studied.
What do you predict she found in the bins?
Check for Understanding
What was Sarah’s dependendent (responding) variable?
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Sarah’s dependendent (responding) variable:
the number of coral that grew on each tray
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The number of coral that grew was DEPENDENT on if there were urchins in the bin (the independent variable!)
The coral that grew in the bin RESPONDED to the presence of urchins (the manipulated variable.)
Writing the scientific question
“What is the effect of ____ on _____?”
Scientific Question:
What is the effect of introducing sea urchins on the number of corals that grow?
Sarah took the data back to her lab and started processing!
Experimental Set-up:
The independent variable has been manipulated (urchins.)
Control Set-up
The independent variable has NOT been introduced (no urchins.)
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Sarah returned to the bins in a few months and collected data.
It is hard to count on here as they are crowded!
The actual data table is on the next slide.
Raw Data (Data Table)
Calculate: Find the Average number of coral in the bins with sea urchins present by adding the numbers in the four bins and dividing by 4. Round to the nearest whole number.
Write it in the table below.
Repeat with the number of coral in the bins with NO sea urchins present.
| Average number of coral |
Sea Urchins Present | |
No Sea Urchins | |
Use the text tool to add the averages to the data table.
The effect of sea urchins on the number of coral
Time to Graph!
Make a bar graph on the paper provided that shows the average number of coral in the bins with and without sea urchins.
Use your graphing resources that you pasted into your science journal. If you do not have them please ASK.
Close up your computer once you have gone back to make any corrections. There is an information sheet in your packet you can use to review important information from the study.
Optional…
Want to read the scientific paper Dr. Sarah published?
What is Dr. Sarah W. Davis up to now?
PRINCIPAL INVESTIGATOR Boston University
Sarah hails from Canada and her path to Boston University took her through University of Victoria, University of Calgary, UT Austin and, UNC Chapel Hill. She is largely interested in understanding why some organisms are winners and others are losers, and what this means in the context of rapidly changing environments. Sarah lives for travel, nerding out, Halloween, brewery tastings, and now she enjoys experiencing all of these things (minus the beer) with her daughters Kingsley and Kennedy.
Email: daviessw@bu.edu