Course: Life Science, Integrated Science, STEM
Unit: Ecological Networks Part 1- Network interactions
What Students Learn:
- Energy flows in one direction and is stored in matter.
- Trophic levels indicate an organism’s position on a food chain.
- The amount of available energy decreases as it progresses through food chains; the total amount of available energy in a trophic level is less in higher trophic levels than in lower trophic levels.
- Identify the interdependent relationships between populations, communities, ecosystems and the biosphere (EALR 1.2 and 1.3).
- Analyze the effects of natural events and human activities on the earth’s capacity to sustain biological diversity (EALR 1.3).
- Explain how organisms can sustain life by obtaining, transporting, transforming, releasing, and eliminating matter and energy (EALR 1.3).
What Students Do:
- Focusing on the Great Salt Lake Ecological Network, students will describe energy relationships, emphasizing the concept of interdependence, between the different components, both abiotic and biotic, of an ecological network.
- Analyze how an ecological disturbance in a single abiotic or biotic factor could affect an entire ecosystem. In this analysis, recognize the components, structure, and organization of systems and the interconnections within and among them.
Warm Up: Verify student understanding and foster higher level thinking by checking students’ comprehension. Write these questions on the board and have students answer them in their notebooks: “Why do halobacteria grow better in high salt solutions than in low salt solutions? As a single celled organism, what happens to Halo when they are placed in a test tube of 1) distilled water, 2) low salt water, and 3) high salt water? Draw a picture showing what happens in each of these three cases.” Walk through classroom to check in students drawings. Discuss answers.
These questions should elucidate students’ understanding on how organisms sustain life through homeostasis and on osmosis in general. This article from NASA, Secrets of a Salty Survivor, can give more insight into how Halobacterium survive in a dynamic environment. Their internal, salty composition makes them well suited for high salt water environments such as the Great Salt Lake and the power of osmosis and active transport allow them to survive in low salt environments.
Next, link students back to the Cell Phone and Cytoscape activities to foster further development of systems.
Important Note: Activity 2 is very important to link the data from the halobacteria investigation back to the GSL ecosystem and network concepts from the entire unit. Depending on how foodwebs, matter cycles, and ecosystem concepts were taught, teachers may choose to do both activities below or only activity 2 and certain parts of Activity 1.
ACTIVITY 1 (OPTIONAL): Creating a Food Web Network of the Great Salt Lake Ecosystem
Say to the students “Now that we have explored extremophiles and specifically investigated the effect of salinity on the growth of Halobacterium we will now focus on the entire Great Salt Lake ecosystem. We will focus on the abiotic and biotic factors within the network and explore how humans have impacted the entire system.”
- For a class of 30, divide students into 6 groups with 5 students each.
- The teacher should ask students to recall the cell phone activity and review what a network is, what the components of a network are, and why networks are useful visualization tools. Explain networks are really important to visualizing systems in Biology and today they will be creating a biological network, a food web!
- Review with students about food webs. Distribute the student activity sheet (GSLfoodwebworksheet.doc (Google Doc | Word Doc) and read through the introduction as a class. Have the students complete the pre-activity questions individually of with a small group.
- Read through the first two procedure steps as a class (below).
- You will be working with your assigned group to learn about some of the organisms that live in the Great Salt Lake.
- As a group, you will need to answer the following four questions about each of your assigned organisms. Each group member must write down the answers to the questions in the table provided below.
- On the Smartboard or overhead using the table from student sheet 2b, model one organism with which students are familiar such as a fox.
Ask the students what the fox eats. The students can use the food web in the example to determine that a fox eats snakes, raccoons, mice, etc. Ask the students what waste is produced? The students should determine that carbon dioxide is one of the waste products. Ask the students what abiotic or environmental factors the fox needs to survive. Possible student responses may include oxygen, water, sunlight, etc. Finally, ask the students to explain the process by which the fox obtains its energy and whether the fox is a heterotroph or an autotroph? Students should say the fox is a heterotroph because it consumes food and obtains its energy from consuming other organisms.
- Explain that each group will be responsible for researching 2-3 organisms living in the Great Salt Lake. Give the students time (15- 20 minutes) in their groups to research their organism and complete the table provided on the student sheet.
Assign each group 3-4 of the following organisms (you may assign more than one group the same organism):
- Migrating Birds
- Marsh Hawk
- Brine Shrimp
- Brine Flies
- Meadow Vole
- Salt Grasses
- After students have gathered their information, have them number off 1-5. Go over the remainder of the procedures with the class (below).
- Next, you will be assigned to a different group in which you will share your information. Together you will create a food web network showing the relationships existing in this ecosystem. Use circles (nodes) to represent the organisms and any abiotic factors and arrows (edges) to represent the relationship between the organisms. Remember the arrow always points toward the consumer (to show the transfer of energy from one to another)!
- Use your food web to answer the questions on the worksheet (Google Doc | Word Doc).
An alternative, more computer-based approach to step 7:
- Rather than hand-drawing the network, you could have students create a network using a modeling tool such as Cytoscape (https://cytoscape.org/) or Loopy (https://ncase.me/loopy/).
- If using Cytoscape, show the students how to use it by using the prepared PowerPoint and materials from Lesson 2 of Introduction to Networks. In order to have the most authentic modeling experience, students should create a sif file and then use it to create a network in Cytoscape rather than adding their nodes and edges to the system one at a time.
- If using Loopy, go back to the instructions in the Systems are Everywhere module or on the Loopy website for a refresher on how to use Loopy.
- Have all the 1’s meet together, all the 2’s meet together, etc to create a food web network and answer the associated questions.
ACTIVITY 2: Salinity Effect on Halobacterium PowerPoint
- Say to students: Now that we have explored the effect of salinity on the growth of Halobacterium and designed a food web network with our Great Salt Lake organisms, we will now use all of this knowledge to explore a detailed PowerPoint simulation of the Great Salt Lake Ecological Network. In this network, we will consider how an ecological disturbance could affect an entire ecosystem (both abiotic and biotic factors).
- Start PowerPoint (salinity_effect_on_halobacterium.ppt (Google Slides | PowerPoint) Description slides below to conduct a class discussion. Do not rush through the slides, encourage all students to participate. You may want to have printed copies of the effect of salinity on the growth of Halobacterium graphs for students to refer to.
- Slide 1: This is the static network of the GSL. You have discovered a relationship between salinity and Halobacterium growth. We will now see how that relationship will be visualized in the network. Please note: students have data only for the effect of salinity on Halobacterium growth and they do not have knowledge about other quantitative relationships. Please be sure to distinguish hypothesis from fact.
- Slide 2: First you started with a salinity of 2.5M –what was the effect on the growth of halo?
- Slide 3: Students should observe that Halo did not grow at all
- Slide 4: At a salinity of 3.0M –what was the effect on growth of halo?
- Slide 5: Students should observe that Halo showed moderate growth
- Slide 6: At a salinity of 3.5M –what was the effect on growth of halo?
- Slide 7: Students should observe that Halo grew even better
- Slide 8: At a salinity of 4.0M –what was the effect on growth of halo?
- Slide 9: Students should observe that Halo grew extremely well
- Slide 10: At a salinity of 4.5M –what was the effect on growth of halo?
- Slide 11: As a reminder from the lab activities ask the students: What overall observation about Halobacterium growth can we make regarding the different salinities? Observation: Halo growth was less relative to growth at 4.0M; 4.5M is approximately the salinity of the North arm of the lake.
- Slide 12: Great Salt Lake Food networks in North and South Arms
Students Hypothesize about the Great Salt Lake Network in the North arm
- Slide 13: Observation: Halo growth was less relative to growth at 4.0M; 4.5M is approximately the salinity of the North arm of the lake.
Students should HYPOTHESIZE what will happen to rest of the network in the North arm of the lake (remind them of salinity-4.5M). Students can write their hypotheses in journals, or they can be discussed in small groups and then shared with the whole class. Students should draw a sketch of how salinity affects the network.
- Before going to slide 14, ask students which nodes are directly affected by salinity. Students should respond by saying that the algae, brine shrimp, and salt grasses nodes will decrease in size. This hypothesis should be based on the information learned in the PowerPoint before the lab on how most organisms cannot thrive/live in a salt environment.
- Slide 14: Observation: Halo growth was lower relative to growth at 4.0M; 4.5M is approximately the salinity of the North arm of the lake. Salt grasses, algae, and brine shrimp population nodes have decreased in size due to the increase in salinity.
- Before going to slide 15 ask students which nodes are indirectly affected by salinity. Students should respond demonstrating that the migrating bird, meadow vole, and marsh hawk nodes (populations) will decrease because their energy source (brine shrimp and salt grasses) is depleted.
- Slide 15: Observation: Halo growth was less relative to growth at 4.0M; 4.5M is approximately the salinity of the North arm of the lake. Migrating birds and meadow vole populations have decreased because their food source populations have decreased.
- Slide 16: Observation: Halo growth was less relative to growth at 4.0M; 4.5M is approximately the salinity of the North arm of the lake. The Marsh Hawk node has decreased in size because its energy source (meadow voles and migrating birds) is depleted.
Students draw conclusions about how ecological disturbance affected the Great Salt Lake Network in its entirety.
- Show slide 17 and ask students to think about the Great Salt Lake network in its entirety. Thinking back to the lesson objectives, ask students, “What is the ecological disturbance that we are referring to here?” (Human impact by building the causeway in 1952.) Ask students to summarize how this ecological disturbance affected the entire ecosystem. Students should either draw the GSL showing how the causeway resulted in different ecological networks for the north and the south arm, or they can write about it in paragraph form.
Ask for students to share their conclusions with the entire class.
- Use slide 18 to support student conclusions about how the building of the causeway resulted in an ecological network in the north arm that is different than the network in the south arm.
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Have students discuss the benefits and risks for trying to undo this alteration to the Great Salt Lake. Are there any solutions? Should there be a solution?
Have the students explore a problem or situation in their local environment, such as the removal of a dam, in order to describe the process as well as the advantages and disadvantages of using a systems approach to solving the problem.