SimBio Virtual Labs®
EcoBeaker®: The Barnacle Zone
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This workbook accompanies the SimBio Virtual Labs® The Barnacle Zone laboratory. Only registered subscribers are authorized to use this material. Laboratory subscriptions may not be shared or transferred.
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SimBio Virtual Labs®: EcoBeaker® The Barnacle Zone
Background
When we tell our kids about different species and where they live, we naturally start talking about weather and the physical environment. Camels are adapted to life in the desert and can go a long time without water. Polar bears live in the Arctic and are adapted to cold with their thick layers of insulation. A polar bear wouldn’t be very happy in the desert, and a camel would have a hard time in the Arctic (though a herd of camels pulling a sled over the ice is an amusing image). The underlying idea is that in order to be adapted to one environment, you necessarily give up the ability to live in other environments. But is this true for most species? Do species live where they do primarily because of their adaptations to the physical environment, or might the other species in the environment also be important?
The intertidal zone of rocky coastlines makes an interesting natural laboratory in which to explore these questions. First, the physical environment itself is challenging. The intertidal zone is that portion of the shore that is covered during high tide and exposed to air during low tide. If you think about how rocks would be covered and exposed as tides come in and out (twice a day on average), you can see that, the higher an organism lives on the rocks, the more time it will spend exposed to the air. You would expect, therefore, that organisms living in the upper intertidal zone would need very different adaptations than those living in the lower intertidal. In addition to including a range of physical environments, the intertidal zone is home to many different kinds of organisms who spend their time either stuck to the rocks or moving slowly around them. This makes it a great habitat in which to study how organisms interact with one another and whether or not those interactions shape organisms’ distributions.
This lab simulates life on the side of a rock along the rocky intertidal coast of Scotland. Our simulated rock is inhabited by two species of barnacles, small animals that, as adults, have shells that are shaped like little volcanoes. Although they don’t look like it in their adult stages, barnacles are crustaceans, related to crabs and lobsters. As adults, barnacle shells are cemented to a rock or other hard object, so that an adult barnacle can’t move anywhere. When a barnacle is submerged, it opens its shell and uses its feathery legs to filter the water for food particles. When the tide recedes and a barnacle is exposed to the air, it closes its shell tightly to keep itself from drying out. Although the adult barnacle can’t move, it makes larvae that can swim around in the water in search of appropriate places to settle and live out their adult lives. © 2013, SimBio. All Rights Reserved. 1
SimBio Virtual Labs® | The Barnacle Zone
Two common species of barnacle live on the Scottish coast; one is Semibalanus balanoides (formerly Balanus balanoides) and the other is Chthamalus montagui (formerly Chthamalus stellatus) When you walk along the shore, you can see that above a certain height, the rocks are covered by Chthamalus but have very few Semibalanus individuals. (Note: This lab refers to the two barnacle species by their Genera names.) Lower on the rock, the pattern is reversed, with Semibalanus abundant and Chthamalus rare. In the early 1960s, a researcher named Joseph Connell decided to investigate the cause of this pattern. He knew that one important determinant of where intertidal organisms live is how much they are exposed to air. Connell wanted to know whether exposure to air was the only condition that governed which species of barnacle lived where, or whether some interaction between the two species of barnacles also had something to do with it. In this lab, you’ll repeat some of Connell’s experiments.
Outline of This Lab
This lab takes you on a virtual field trip to the coast of Scotland. While exploring the marine life along the shore, you encounter the side of a large rock upon which you find Chthamalus and Semibalanus, the two types of barnacles described previously.
In this simulated system, the depth of the water covering the rock decreases each day when the tide goes out, exposing barnacles on the upper part of the rock to air. This exposure may be difficult for barnacles on the upper part of the rock to endure. On the other hand, being submerged underwater for too long may be challenging to barnacles on the lower part of the rock. Competition may also present a life-threatening challenge, as a larval barnacle may be able to settle next to or on top of a stationary adult barnacle, and then grow over the top of it. Barnacles may also kill their neighbors in some way, perhaps through a poison or by some form of fighting. Some combination of these effects is responsible for the distribution of the two species of barnacles on our simulated rock wall.
Note: In the real world, new individuals of both barnacle species settle on rocks continuously throughout their reproductive periods. In this simulated system, once barnacles settle, they grow up right away, and no individuals die of old age.
Your first challenge will be to come up with a set of hypotheses for why Chthamalus lives high on the rock and Semibalanus lives lower down. Next, you will design and carry out experiments to test your hypotheses. SimBio Virtual Labs includes tools that will allow you to replicate some of Connell’s experiments, including removing barnacles, transplanting barnacles, and sampling barnacle populations at different heights on the rock. Your final task will be to write a scientific report summarizing your findings. © 2013, SimBio. All Rights Reserved. 2
SimBio Virtual Labs® | The Barnacle Zone
Exercise 1: Exploring the System
In this exercise, you will observe the settlement and distribution patterns of barnacles on a rock face in the intertidal zone. You will also study the tide cycle and its relationship to barnacle distribution. Along the way, you’ll become familiar with the simulation and some of its tools.
[1] If you haven’t already, start SimUText® by double-clicking the program icon on your computer or by selecting it from the Start menu. When the program opens, enter your Log In information and select the Barnacle Zone lab from your My Assignments window. You will see a number of different panels on the screen; these will be described as needed for the exercises in the lab.
[2] The top menu bar has a drop-down menu from which you will select individual exercises as you proceed through the lab. Be sure that Exploring the System is selected.
[3] Buttons on the right will provide information about organisms in the lab. Click buttons for Semibalanus and Chthamalus and read the descriptions. Use the information to answer the following question:
[ 3.1 ] Which barnacle species ranges into the warmest water?
[4] Click the TIDES button in the Library Panel. Use the entry to complete the following questions: [ 4.1 ]
[ 4.2 ]
[ 4.3 ]
On average, how many high and low tides will a given spot on the coast experience in a day, and why?
What is a spring tide and when does it occur?
What is a neap tide and when does it occur?
[5] The large panel on the left represents the vertical rock face where you’ll do your experiments. The rock is initially devoid of life, as it might be after a major storm. The lower blue/green part of the rock is under water. The ruler on the left marks off the vertical range of your study area in meters. Note that “0 m” simply represents the lowest point you are studying, not the bottom of the rock. © 2013, SimBio. All Rights Reserved. 3
SimBio Virtual Labs® | The Barnacle Zone
[ 6 ]
[ 7 ]
Click the GO button in the Control Panel at the bottom of the screen to start the simulation. The tide will begin coming in and going out and Chthamalus and Semibalanus will begin settling on the rock. (The virtual barnacles are drawn much larger than actual barnacles; you can imagine that each virtual barnacle represents 50-100 individuals.) The Tide Clock above the rock face tracks daily high and low tides and the Time Elapsed monitor above the rock tracks days passed.
[ 6.1 ] How many high and low tides are there each day?
Click the RESET button, and then the STEP 7 button to run the simulation for 7 days. This time, pay attention to the graph on the right as it plots each high and each low tide each day. Click the STEP 7 button again to complete the 14-day tidal cycle.
[ 8 ]
Click the RESET button to wipe the rock face clean. In the next set of simulation runs, focus on the barnacles. Use the STEP 7 button to run the simulation for seven days at a time.
[ 7.1 ]
[ 7.2 ]
[ 7.3 ]
[ 7.4 ]
What is the height of each of the following in your study area? Spring high tide:
Spring low tide:
Neap high tide:
Neap low tide:
If you are an organism that must remain submerged at all times, what is your maximum height on the rock? Explain.
During approximately which days in the 14-day tide cycle do organisms living low on the rock experience their greatest potential exposure to air? Explain.
During approximately which days in the 14-day tide cycle do organisms living on the upper part of the rock face their greatest potential exposure to air? Explain. © 2013, SimBio. All Rights Reserved. 4
SimBio Virtual Labs® | The Barnacle Zone
[ 9 ]
Develop a hypothesis for the patterns of distribution for Chthamalus and Semibalanus that you observed.
[ 9.1 ] Hypothesis:
[ 10 ]
Click the TEST YOUR UNDERSTANDING button in the bottom right corner of the screen and answer the question in the window that pops up.
[ 8.1 ]
Briefly describe what you notice about the distribution patterns for each species on the following days. Do both species settle on the same parts of the rock face? Do their distribution patterns of the rock face change over time?
Days 1–7:
On day 28:
General observations: © 2013, SimBio. All Rights Reserved. 5
SimBio Virtual Labs® | The Barnacle Zone
Exercise 2: Counting Barnacles
Connell studied many aspects of barnacle biology to address his question about their distributional patterns. He started out by making (and quantifying) some basic observations. Connell did A LOT of barnacle-counting by hand. Fortunately, you have some handy tools to simplify this process. This exercise will introduce you to your virtual SAMPLING tool, which creates a sampling transect. In this type of sampling, the investigator establishes a line of fixed length and counts the organisms of interest along (or within a fixed distance from) that line. [ 1 ] [ 2 ]
[ 3 ]
Your first task will be to quantify the barnacles’ vertical distribution. Select the Counting Barnacles exercise and click the STEP 7 button twice to run the simulation for 14 days.
The SAMPLING tool is at the far right of your Tools panel; it looks like a red and white bordered grid. Select it, and then move your cursor over to the rock face. The cursor determines the lower boundary of your transect. Click a few places along the rock face to see how the transect is established. Observe that the transect height is 0.2 m. Your sampling results are displayed numerically and graphically in the Sampling Results panel to the right. Once you understand how to place the transect and read the results, click the CLEAR SAMPLES button at the bottom of the Sampling Results panel.
Quantify the distribution of barnacles at approximately 1-m intervals up the rock face, starting with a transect whose top edge is around the 1 meter mark.
[ 3.1 ] Record your results in the first (Sample 1) row of Data Table 1, below.
DATA TABLE 1: VERTICAL DISTRIBUTION OF BARNACLE
DEPTH AT SAMPLE BOTTOM 1M2M3M4M5M SAMPLE S C S C S C S C S C 1 2 3 Range Average [ 4 ]
As you’ve likely noticed, the number of barnacles at any one place on the rock changes over time, even if the overall distribution pattern is consistent. Just like real intertidal systems, the simulation includes random variability. A proper sampling procedure would sample several rock faces and use the average and range of values to describe the barnacle distribution. You can achieve this by re-running the simulation and sampling again—each run is the equivalent of looking at a different rock face. © 2013, SimBio. All Rights Reserved. 6
SimBio Virtual Labs® | The Barnacle Zone
[ 5 ]
RESET the simulation, then run for 14 days and repeat your sampling. Enter the data in the table. Repeat this process for a third sample; then fill in the range and average values.
[ 5.1 ] Using your numerical results, describe the vertical distribution of barnacles on the rock face.
[ 6 ]
RESET the simulation to clear the rock face. Another interesting pattern to quantify is how the number of organisms in one place changes over time.
[ 6.1 ] Select a height between 1 and 4 m that you think would be interesting to sample over time. Based on your hypothesis and the observations you’ve made so far, how do you predict the distribution of the two species would change over time at the depth you will be sampling? Explain.
Using the STEP 1 button, advance the simulation two days.
[ 7.1 ] Record the number of individuals of each species in the first (Sample 1) row of Data
Table 2 below.
Then advance the simulation 2 more days and record your data. Continue until the Sample 1 row is complete. [Optional] If you want to conduct more thorough sampling, you can repeat your measurements with an additional simulation run and record data in the Sample 2 row of Table 2.
DATA TABLE 2: CHANGE IN BARNACLE NUMBER OVER TIME AT _______ M
DAY
SAMPLE 2 4 6 8 10 12 14
[ 7 ]
[ 8 ] S
C
S
C
S
C
S
C
S
C
S
C
S
C
1 2 © 2013, SimBio. All Rights Reserved. 7
SimBio Virtual Labs® | The Barnacle Zone
[8.1] Using your numerical results, describe the temporal pattern of barnacle distributions
[ 9 ]
In light of the observations you’ve made in this exercise, do you need to revise your hypothesis, either to change your explanation or to make it more specific? If so, write your revised hypothesis below.
[ 9.1 ] Revised hypothesis: you observed.
[8.2] Were your expectations from Question 6.1 met? Explain, using numerical results.
[8.3] In what ways do you think your results would have been different if you had sampled at a different height on the rock? Explain. © 2013, SimBio. All Rights Reserved. 8
SimBio Virtual Labs® | The Barnacle Zone Exercise 3: Wet and Dry
This exercise introduces some of Connell’s experimental approaches. You will apply various techniques to investigate how individuals of the two species interact with one another and how they interact with their physical environment. (Later on in the lab, you’ll get to design and conduct your own experiments.) [ 1 ]
Select the Wet and Dry exercise. First you will conduct a classic exclusion experiment—keeping one species off the rock and seeing what happens with the other. Exclusion experiments allow researchers to examine the effects of the physical environment alone and are often a first step in examining distribution patterns.
[ 1.1 ] What do you predict will happen to Chthamalus if you exclude Semibalanus from settling on the rock? Explain.
To prevent Semibalanus from settling, click on the EXCLUDE SEMIBALANUS button in the Exclusions panel on the right. RUN for around 28 days.
[ 2.1 ] In the absence of Semibalanus, at what height in your plot does Chthamalus settle? Give its distribution range in meters.
[ 2.2 ] Did you predict correctly? Explain.
[ 2 ]
[3]
Another important tool for studying species distributions is direct observation of species interactions. Specifically, Connell wanted to know if individuals of either species commonly killed individuals of the other species. Barnacles kill one another by overgrowing (growing on top © 2013, SimBio. All Rights Reserved. 9
SimBio Virtual Labs® | The Barnacle Zone of) and undercutting (wedging underneath and displacing) each other. In the simulation, one
[ 4 ]
[ 5 ] barnacle kills another if the first overlaps the second and the second disappears.
[ 3.1 ] Based on your hypothesis, do you predict that Semibalanus is capable of overgrowing and killing Chthamalus? Explain.
Uncheck the EXCLUDE SEMIBALANUS button so that both barnacles species can settle again. Then click the RESET button to clear your rock of barnacles. RUN the simulation for 14 days to allow barnacles to settle.
Select an individual Chthamalus from the 0.5–1.6m range to observe. Use the STEP 1 button to advance the simulation slowly as you observe what happens. If your Chthamalus is overgrown, select another to observe. Continue your observations for at least 20 days.
[ 5.1 ] Is Semibalanus capable of overgrowing and killing Chthamalus? Explain.
[ 5.2 ] Did you predict correctly? Explain.
Another common experimental technique in ecology is transplantation—moving individuals from one area to another without removing all individuals of the other species that might be present. With mobile species, this can be extraordinarily difficult. For Connell, transplanting barnacles meant chiseling up a piece of rock with barnacles on it and tethering the rock in a new spot. It will be even easier for you!
Click the RESET button. Look at the selection of Tools to the lower right of the rock. The fifth button from the left—the one with the picture of barnacles on it—is the ADD ORGANISMS tool. By clicking on the drop-down arrow, you can select a species for transplantation. For now, click on Semibalanus (the default button). Move your cursor back to the rock, and then click, hold, and drag the cursor anywhere on the rock to transplant Semibalanus (individuals of either species that were already established are removed during this process). Your transplantation area is marked with a rectangle for easier viewing. Try this a few times.
[ 7.1 ] Based on your hypothesis, what do you predict will happen if you transplant a group of Semibalanus to a section of rock in the 1.5–2.5m range, with Chthamalus present?
[ 6 ]
[ 7 ] © 2013, SimBio. All Rights Reserved. 10
SimBio Virtual Labs® | The Barnacle Zone
[8]
Click the RESET button to clear the rock. Run the simulation for 14–28 days. Use the ADD ORGANISMS tool to create a patch of 40–50 Semibalanus in the 1.5–2.5m range. Run the simulation and observe what happens.
[ 8.1 ] What happened to the transplanted barnacles?
[ 8.2 ] Did you predict correctly? Explain.
Just as you can transplant a group of barnacles to a new place on the rock amidst other barnacles, you can remove some individuals from an area that still contains other individuals. This kind of small-scale exclusion experiment can be very informative, and the simulation allows you to conduct a few different variations of it.
[ 9.1 ] Based on your hypothesis, if you cleared an area in the center of the rock face, do you predict that Semibalanus will settle in the new open space (i.e., will any land and attach to the rock in that space)? Why or why not?
[ 9.2 ] Based on your hypothesis, if any Semibalanus do settle in the new open space, do you predict that they would persist there (i.e., stick around for a while)? Explain.
Click the RESET button, then run the simulation for 14–28 days. Find and click the skull and crossbones button (the DELETE ORGANISMS tool) next to the ADD ORGANISMS tool. Move the cursor to a spot roughly in the center of the rock, then click, hold, and drag to create a “dead zone” approximately 1 m square. When you release the cursor, all organisms in that area will be removed, but the surrounding individuals will be left in place.
[ 9 ]
[ 10 ] © 2013, SimBio. All Rights Reserved. 11
SimBio Virtual Labs® | The Barnacle Zone
[ 11 ]
RUN the simulation long enough for a clear result to emerge. [ 11.1 ] What did you observe?
[ 11.2 ] Did you predict correctly? Explain.
Another way you can use the DELETE ORGANISMS tool is to remove individuals one at a time from an area. This allows you to create new spacing patterns, for example, or to remove individuals of one species from an area, allowing individuals of another species to grow there. You can try this technique on your own if it is useful for testing your hypothesis.
Recall the barnacle distribution pattern you’re trying to explain. In light of the observations you’ve made throughout this exercise, do you need to revise your hypothesis for why the two barnacle species are distributed as they are, either to change your explanation or to make it more specific? If so, write your revised hypothesis below.
[ 13.1 ] Revised hypothesis:
[ 12 ]
[ 13 ] © 2013, SimBio. All Rights Reserved. 12
SimBio Virtual Labs® | The Barnacle Zone Exercise 4: On Your Own
Now it’s your turn. You have developed a hypothesis based on a number of different observations and experiments. Your job now is to use your new tools to further test and refine your hypothesis. To accomplish this, you will make a set of predictions derived from your hypothesis, design and conduct a series of experiments to test your predictions, record and analyze your data, and write a report based on your findings. You might want to do each experiment a few times to make sure that your results aren’t due to chance. If you want to modify your original hypotheses and experiments based on the results you have so far, that is fine as well, but be sure to indicate your new hypotheses in your report. [ 1 ] [ 2 ]
Select the On Your Own exercise.
To organize your work, begin by examining your hypothesis and deriving predictions from it. Remember that predictions generally take the form of if-then statements: “If my hypothesis is correct and I (perform this experiment/make this observation), then I should find (find a specific result). Or: “If my hypothesis is correct, then I should find (specific result) when I (perform this experiment/make this observation). You, of course, have to fill in the experiment, observation, and result!
[ 2.1 ] List your initial predictions here:
[ 3 ]
Your predictions themselves indicate the experiments/observations you will perform. Before you conduct your experiments/observations, make sure you have thought about experimental controls, replication and/or sample size, and how you will record your data.
[ 3.1 ] Briefly describe your experiments/observations. On a separate sheet or sheets of paper, prepare any data tables you will need. Be sure to label them correctly. © 2013, SimBio. All Rights Reserved. 13
SimBio Virtual Labs® | The Barnacle Zone
[4] Once you’ve conducted your experiments, analyze your data in light of your predictions and, in turn, your hypothesis. Do you need to revise your hypothesis? Can you identify other experiments and/or observations that would help clarify it? If time permits, revise the hypothesis and test it with the new experiments and/or observations. If not, include them as potential future studies in your report.
[5] Write your report. Be sure to consider how best to display your data (tables, graphs) so you can use the data to support your findings. Identify new questions that may have popped up as you conducted your experiments as well as new research that might provide additional information about this system. © 2013, SimBio. All Rights Reserved. 14
SimBio Virtual Labs® | The Barnacle Zone Exercise 5: Snails Rule
You may have noticed a LIBRARY button for Nucella, a species which has not yet appeared on the rock face. Nucella is a species of snail that crawls around on the rock, eating barnacles. It does not exist in all locations along the Scottish coast, but where it does exist it can have a significant effect on the distribution of barnacles. This exercise explores why. [ 1 ]
Select Snails Rule from the drop-down menu. Run the simulation for 14–28 days.
[ 2 ]
You have available all the tools you’ve worked with before, as well as the ability to exclude, transplant, and sample Nucella. Use these tools to test your hypothesis and write a report about your findings, following the basic instructions from the previous exercise.
[ 1.1 ]
[ 1.2 ]
What do you observe about the distribution of Nucella on the rock face? Be as specific as possible.
How is the distribution of barnacles different in the presence of Nucella than it was when Nucella was absent?
Develop and present one or two hypotheses to explain your observations:
[ 1.3 ] © 2013, SimBio. All Rights Reserved. 15
SimBio Virtual Labs® | The Barnacle Zone Graded Questions
[ 1 ] Use the SELECT AN EXERCISE menu to launch “Graded Questions”.
[ 2 [ Enter your answers for each of the questions and click the SUBMIT ALL button. NOTE: You must answer all of the questions before you click the SUBMIT ALL button. © 2013, SimBio. All Rights Reserved. 16
SimBio Virtual Labs® | The Barnacle Zone Wrap-Up
The intertidal area of the ocean has been an excellent place to find out how species interact with each other and with their physical environment, and how these interactions determine species distributions. Connell’s work with barnacles provided some of the first really good field evidence that competition between species can be important. It also showed very clearly that there are tradeoffs in the way species are constructed. One barnacle may be able to out compete another, but can’t survive in as many environments. This type of trade-off is quite common. You never find a single species that is good at everything.
Another lesson we learn from this lab is that just looking is often not enough. You must also do experiments. Without the experiments that you conducted here, you couldn’t know whether the two species of barnacles lived where they did simply because one liked air and the other liked water, or whether they actually competed with each other. Only through experimentation were you able to figure out which hypothesis is right. This is true in general—it’s very hard to do ecology without experiments, and if you don’t experiment, then many times you will arrive at the wrong answer.