ECOBEAKER: BARNACLES
Name: _______________________
Background
Different species live in different places, but why a particular species lives one place
and not another is often hard to figure out. One explanation is that the species is
adapted to a particular environment. It might not be able to live outside a certain range
of temperatures, rainfall levels, or other abiotic factors. A second explanation is that
interactions with other species, biotic factors, limit where the species can live.
One of the founding experiments of modern ecology was an attempt to tease apart what
set the boundaries for each species in one community. In the 1950’s, an ecologist
named Joseph Connell decided to study two common barnacle species along the coast
of Scotland. Barnacles are small animals whose adults live in hard shells cemented to
a rock. Unlike the adults, larval barnacles can swim around looking for a nice rock to
settle on. When you walk along a Scottish beach, you can see that, above a certain
line, the rocks are covered by a barnacle called Chthamalus but have very few of
another barnacle called Balanus. However, below this line you find mostly Balanus and
hardly any Chthamalus. Connell did a series of experiments to determine why each
species is found where they are found. In this computer lab activity, you will develop
your own hypotheses, and design and perform experiments to determine the factors
involved.
Objective
1. You should be able to apply your knowledge of the design of hypothesis-based
experiments to study the ecology, abiotic and biotic interactions, in an simplified
community.
Procedure
1. Through the “start” and “programs” menus, navigate to the “Ecobeaker HS” software
icon, and select it.
2. When the software opens, click on the middle box so it will close, revealing the
contents of ecobeaker.
3. Double click on the “Barnacles” selection from the Available Labs shown in the lower
left-hand corner of the display. If you just click once it will tell you about the lab
without pulling up the actual software.
4. Scroll through the information displayed until you reach the “More information on
topics related to this laboratory” and click the links appropriate for answering
questions 1 and 2.
5. Scroll down and read exercise 1 and complete exercise 2 (distribution of species).
When finished completing exercise through and thinking through the questions the
lab asked, answer questions 3 and 4.
6. Scroll down and read exercise 3 (watching, transplanting, and removing barnacles).
Reset and run the simulation watching, transplanting, and removing barnacles to see
if each of the species dies or is overgrown, and answer question 5 and 6.
7. Scroll down and read exercise 4 (sampling and slowing the simulation) and answer
question 7.
8. Now that you have the background knowledge of the software, and two hypotheses,
design an experiment to test one of your hypotheses, complete the experiment, and
make appropriate conclusions by answering questions 8, 9, and 10.
9. Finally, complete exercise 5 to learn about the influence of a third species on this
ecological community of the intertidal zone and answer question 11.
Questions
1. Draw and describe what a barnacle looks like, name the taxonomic group to which it
belongs and is related to, and describe its life cycle.
2. Explain the occurrence of the tides over the course of a day.
3. Describe your observations of the distribution of the Chthamalus (brown) and
Balanus (black) species of barnacles on the rock.
4. Write two hypotheses explaining possible cause and effect relationships that could
explain the distribution of barnacles you witnessed in the exercise. One hypothesis
should be based on an “abiotic” factor, while the other should be based on a “biotic
factor”.
After you write your hypotheses, identify the independent variable
associated with each hypothesis.
Abiotic Hypothesis
Independent Variable
Biotic Hypothesis
Independent Variable
5. Describe your observations of whether or not the species are dying or are being
overgrown by each other. Make sure to record your observations for each species.
Chthamalus
Balanus
6. After these additional observations, does one of the hypotheses seem more
supported? Explain.
7. Describe how you can use the software to count the number and type of barnacles on
a particular portion of the rock.
8. Describe the design of your experiment, including how you will manipulate the
independent variable and measure the dependent variable (collect data).
9. Record your observations and the data you collected.
10. Make conclusions based on your observations and the data that you collected
above.
11. How does the addition of the predatory snail Nucella, influence the distribution of the
two barnacle species in the intertidal zone?