Guidelines and stipulations for the use of self-print labs from SimBiotic Software

Transcription

1 Guidelines and stipulations for the use of self-print labs from SimBiotic Software We offer the text that accompanies our computer laboratories in this digital ( self-print ) format to provide instructors with flexibility to: (1) modify exercises to meet their specific course objectives; (2) incorporate our laboratories directly into lab manuals or course packs; (3) alter formatting to complement other course materials, and (4) offer our labs at minimal cost. Please make note of the following guidelines and stipulations before altering or reproducing this document. [We advise printing this page for your records before you delete it from the document file.] 1. Text and formatting in this document may be added, deleted, or modified with the exception of the copyright information that appears on the bottom of each page of the laboratory instructions. SimBiotic Software s copyright information must remain as a footer on each page of the laboratory instructions. 2. Please contact SimBiotic Software if this document will be incorporated into course packs or manuals that will be used for more than one academic term. The accompanying software is updated at least once a year, sometimes including changes that must be reflected in the laboratory text. It is important to make sure that the laboratory text being provided to students will coincide with the software being implemented in their classrooms. 3. Please do not produce more copies of this document than permitted by licensing agreements, which must be renewed each time this material is to be used in a course. 4. Any questions or problems should be directed to: Dr. Ellie Steinberg SimBiotic Software eks@simbio.com (406)

2 Barnacles and Tides 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 we find species where they are primarily because of their adaptations to the physical environment, or might other species present also be important? This lab simulates life on the side of a rock along the rocky intertidal coast of Scotland. The rock is inhabited by two species of barnacles. Barnacles are small animals that as adults have shells that are shaped like a little volcano. The shells are cemented to a rock or other hard object, so that an adult barnacle can t move anywhere. Inside the shell is a mouth, out of which come feathery legs that the barnacle uses to filter the water for food particles. 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. Two common species of barnacle live on the Scottish coast; one is called Balanus balanoides and the other is Chthamalus stellatus. When you walk along the shore, you can see that above a certain line, the rocks are covered by Chthamalus but have very few Balanus individuals. However, below this line the pattern is reversed, with Balanus covering the lower rocks. In the early 1960s a researcher named Joseph Connell decided to investigate the cause of this distributional pattern. He knew that one important determinant of where intertidal organisms live is how much they are exposed to air. Twice a day (on average) the tide goes out and many rocks are left exposed. Species that can t handle exposure to air have trouble surviving on the upper parts of these rocks. 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. EcoBeaker 2.5 Barnacles & Tides 1

3 Outline of This Lab This lab takes you on a virtual excursion to the coast of Scotland where, while exploring the marine life along the shore you encounter the side of a large rock upon which you find the two species of barnacles, Chthamalus and Balanus, described above. New individuals of both barnacle species are continually settling on the rock surface; in this model, once they settle, they grow up right away. None of the barnacles in the model die of old age, but they can die of several other causes. In the model, each day the depth of the water covering the rock decreases when the tide goes out, exposing barnacles in the upper part of the rock to air. It is possible that this exposure may be difficult for barnacles to endure. It is also possible that 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 rock wall. Your job is to come up with a set of hypotheses for why Chthamalus lives high on the rock, and Balanus lives lower down. Then you will design and carry out experiments to test these hypotheses. EcoBeaker 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. At the end you will write a scientific report summarizing your findings. EcoBeaker 2.5 Barnacles & Tides 2

4 The Lab 1. First read the introductory sections of the workbook. 2. Start EcoBeaker by double-clicking on the EcoBeaker icon on your computer or by selecting it from the Start menu. Double-click anywhere on the opening screen with the rolling credits to expose the main Home view. 3. Load the Barnacles and Tides lab by double-clicking Barnacles in the Available Labs panel located on the lower left corner of the Home view or from the Labs pull-down menu at the top of your screen. 4. Several panels will appear on the screen. On the left is a window labeled Intertidal Rock Face, giving a view of the rock face where you ll do your experiments. The slab of rock you picked is perfectly vertical in the water, and its top is just at the level of the high tide, so at high tide the rock is submerged under water. The rock face is initially devoid of life (representing how it might look after a major storm). To the right of the rock face a panel labeled Species lists the species in the model in the same color that they will be on the rock face (i.e. Chthamalus will be brown and Balanus will be black). The third species on the list (Nucella) will be explained later. The Links panel includes general instructions on starting up and running EcoBeaker labs. At the bottom of the screen the Control Panel includes the buttons that start and stop the simulation, the Speed Slider allows you to adjust how fast the model runs, and the Time-counter keeps track of virtual time (which in this lab is measured in days). 5. Run the simulation by clicking on the GO button (the green arrow button) in the Control Panel at the bottom of the screen. You will see brown Chthamalus and black Balanus settling on the rock. [Note: if you have trouble distinguishing the species by color, stop the model by clicking on the STOP button (the red stop sign). Then click on the INFO button (the question mark) and next click on an individual; its position and species name will appear in a pop-up window. When you have figured out which icon goes with which species, you can start the model again with the GO button again.] Every day the tide comes in and out, and this is represented by air (colored white) coming down from the top of the rock and displacing the blue water. The height of the tide has a 14-day cycle (caused by the moon), so that for each of 7 days the low tide will get successively lower and for the next 7 days the tide will rise. 6. Approximately how many rows of barnacles are exposed during the lowest tides? Make sure you can see the top of the rock (the scroll bar to the right of the window should be as high as possible.) You may need to watch several complete tidal cycles to get this right. Use the tick marks on the right-hand side of the rock face to count down rows, and then write down your answer here [NOTE - this is the low-tide line ]: EcoBeaker 2.5 Barnacles & Tides 3

5 7. Continue to watch the simulation until you see a very clear distribution of the two barnacle species. Then stop the model with the STOP button (the red stop sign). In the space below, provide a short description of this distribution. 8. Now write down two hypotheses for why you see the two species of barnacles distribute themselves as they do. If you are having trouble thinking of hypotheses, go back and re-read the introduction, which mentions several factors that may be important to these barnacles. Hypothesis 1: Hypothesis 2: Joseph Connell also had hypotheses that were probably similar to yours. To distinguish between them, Connell conducted a number of studies including: Looking for barnacles dying Looking for whether individual barnacles ever were overgrown by other barnacles Moving (transplanting) barnacles from one place to another Removing barnacles from different areas of rocks Counting the number of barnacles at different heights of the rock EcoBeaker 2.5 Barnacles & Tides 4

6 The EcoBeaker program provides tools that you can use to simulate Connell s experiments. Follow the instructions below to experiment with these tools. Barnacle death and overgrowth 9. Reset the model by clicking on the RESET button (the circular arrow to the right of the STOP button). 10. Start the model running again by clicking on the GO button. Let the model run for about 50 days (as indicated by the Time Counter to the right of the Speed bar). 11. Then click on the STOP button to stop the model. 12. Find a cluster of 4 adjacent Chthamalus individuals (in a line or in a 2x2 square) towards the bottom of the rock (below the low tide line). 13. While watching those barnacles, click on the STEP button (the red/green arrow to the right of the GO button). If a barnacle disappears, it means it died. If a Balanus individual appears in the cluster, it means the Chthamalus individual previously in that spot was displaced. 14. Continue stepping the model forward for at least 20 days, watching the cluster of barnacles. Then try observing a cluster towards the top of the rock face (above the low tide line, using the scroll bar if necessary). 15. In the space below, write down what you observed and whether your results provide any clues about your hypotheses. Transplanting barnacles Observational studies can be more informative when combined with a manipulation of the system, such as a transplant experiment. 16. To do a transplant, click on the PAINT button (the paintbrush) in the Control Panel. This puts the mouse into Painting Mode. [Note: if the model is running, stop it first with the STOP button.] EcoBeaker 2.5 Barnacles & Tides 5

7 17. Once in Painting Mode, to transplant Chthamalus, click on Chthamalus in the Species panel to the left of the rock. To transplant Balanus, click on Balanus in the Species panel. 18. Next, move the mouse pointer over the position on the rock where you want to add barnacles. Click on that spot once to add a single barnacle. This will also kill anything else that was in that spot (such as another barnacle). 19. To add a whole swath of barnacles, click and hold down the mouse button. Then drag the mouse down and to the left. You will see a rectangle that expands out with the mouse. When the rectangle covers the area into which you want to transplant, let go. The whole area will be filled with new barnacles (sometimes it can take a few seconds so be patient). [NOTE: it is usually easier to do your transplants with the method in step 19. However, for some tests (such as whether adult barnacles fight in some way with their neighbors) you may want to transplant individual barnacles as in steps ] 20. To practice transplanting, try placing a bunch of Chthamalus below the low-tide line (i.e. low enough on the rock that they will never be exposed to air). Then run the model for a few tidal cycles (at least 30 days) and watch for barnacle death and overgrowth. 21. Stop the model. In the space below, write down what you observed and whether your results provide any clues about your hypotheses. Removing Barnacles 22. Creating bare patches can also provide some clues. To do so, again click on the PAINT button (the paintbrush) in the Control Panel. Instead of clicking on a species name, click on Rock in the Species panel. 23. Click and hold down the mouse button and drag the mouse to make a rectangular area. Then let go of the mouse button. Everything within this area will be removed, leaving bare rock. 24. As practice, try clearing the rock of barnacles below the low tide line. Then watch what happens over the next few tidal cycles either by stepping or running EcoBeaker 2.5 Barnacles & Tides 6

8 the model. In the space below, write down what you observed and whether your results provide any clues about your hypotheses. Sampling [Note: To keep a species out of an area for a period of time, click once on any barnacle individuals of the offending species that have moved into your cleared area. For instance, to keep an area clear of Balanus, stop the model every few days and click on each Balanus individual that entered the area during that time interval.] You can make your observations more quantitative by counting how many barnacles there are in different places after different manipulations. You can do this by looking and counting by hand (the way Connell did). But EcoBeaker makes it convenient for you to count in a more automated way. 25. To set up your automated sampler, click on the Setup pull-down menu at the top of your screen, and from there, select Model. 26. Click on the Sampling tab from the Setup window that opens. In the lower left hand corner of this window, find Quadrat Width and set it to 40. Quadrat Height should be set to 1; this will allow you to sample all of the individuals in one row (i.e. at one height) of the rock. When you are done, click the Set button on the right and then close the Setup window. [NOTE: when you are ready to do your own experiments, feel free to experiment with other sampling schemes.] 27. To sample the number of barnacles of each species at a certain height on the rock, click on the SAMPLE button (the butterfly net) in the Control Panel. 28. Move your mouse on top of the rock. As you move your mouse up and down, a transect line will follow it. When the transect line is over the height you want to sample, click on your mouse. A window will appear reporting the number of barnacles counted along that transect. Click on the OK button to close the window and take another sample. 29. As practice (and to provide data for your report) try quantifying the distribution of barnacles from top to bottom of the rock. Sample the top 3, the middle 3 and EcoBeaker 2.5 Barnacles & Tides 7

9 the bottom 3 rows using the SAMPLE button. Use the table provided at the top of the next page to record your data. Top of Rock Face Middle of Rock Face Bottom of Rock Face Sample Number Chth. Bal. Chth. Bal. Chth. Bal SUM: 30. Now plot the totals (in a bar graph using different shading for the bars representing each barnacle species) using the axes below. Be sure to indicate which shading represents which species. Individuals Top Middle Bottom [Note: for your report, you may want to try sampling and creating graphs for different times during the colonization process.] EcoBeaker 2.5 Barnacles & Tides 8

10 Your turn 31. Now it is up to you. You already have some information from the your trial experiments. After looking over those data and your hypotheses, design a series of experiments to test whether your hypotheses are likely to be right. Then perform those experiments. 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. Also be sure to record all of your results so you will have data to report. 32. Write a short report (on separate paper) describing your study and results, being careful to describe the hypotheses you were testing, the experiments you performed, and your conclusions. More Things to Try You may have noticed that there is a third species called Nucella, which did not appear on the rock above. Nucella is a species of snail that crawls around below the level of the tide, eating barnacles. It does not exist in all locations along the Scottish coast, but where it does exist it can have a large effect on the distribution of barnacles. To see this, try adding in the snails. You can do this the same way you added in barnacles, by painting in a snail or two. Watch what happens for a little while. You can come up with hypotheses as to why the snail has the effect it does, and test these hypotheses with similar experiments to those you have already used. EcoBeaker 2.5 Barnacles & Tides 9

11 Notes and Comments The intertidal area of the ocean has been a really useful 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 thing we learn from this lab is that just looking is often not enough. You must also do experiments. Without the experiments that you did 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 the experiments 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. References This lab was loosely based on the following paper: Connell, J. H The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus stellatus. Ecology 42: EcoBeaker 2.5 Barnacles & Tides 10