The World of Lichens Part of: Joint Science Education Project at Dartmouth Developed by: Ruth Heindel, Earth Sciences Department, Dartmouth College Overview Lichens are incredible symbiotic organisms that can survive in some of the harshest environments on Earth. Lichens serve important roles in ecosystems as pioneering species, and they are used by earth scientists to learn about the timing of past events and to monitor pollution. This module introduces students to the world of lichens through a student-driven project and gives students hands-on practice with the scientific method. Science Standards Disciplinary Core Ideas: -LS2.C: Ecosystem Dynamics, Functioning, and Resilience -LS4.D: Biodiversity and Humans -ESS3.C: Human Impacts on Earth Systems -ESS2.E: Biogeology Science and Engineering Practices: -Asking Questions and Defining Problems -Planning and Carrying out Investigations -Analyzing and Interpreting Data Cross-Cutting Concepts: -Patterns -Stability and Change Focus Questions What are lichens, and how do they interact with their environment? What can lichens tell us about the environment in which they grow? Objectives Through this lesson, students will: -Learn to appreciate the diversity of lichens and the roles lichens play in ecosystems -Generate their own scientific question and hypothesis -Record field observations about the abundance, size, and type of lichens in different environmental settings. -Analyze data and re-evaluate their hypothesis Background Lichens are symbiotic organisms made up of a fungus (providing structure) and an algae or cyanobacteria (providing nutrients through photosynthesis). Lichens are pioneering species and are often the first to colonize bedrock or bare soil after a disturbance. Lichens are distributed widely across the earth and can survive in many of the harshest conditions. In ecology, lichens play important roles in soil stabilization and development, nutrient cycling, and succession. In earth sciences, scientists make use of lichens to monitor pollution and to estimate the age of rock surfaces.
Vocabulary Lichen: A symbiotic organism that is made up of a fungus and an algae or cyanobacteria. Symbiosis: An interaction between two different organisms living in close physical association; a mutualism is a type of symbiotic relationship that is beneficial to both organisms. Fungi: The kingdom Fungi contains a diverse group of eukaryotic heterotrophs that are neither animals nor plants. Yeast, mold, mushrooms, and the structural component of lichens are all part of the kingdom Fungi. Algae: A large, diverse group of simple photosynthetic eukaryotic organisms that lack stems, leaves, roots, or vascular tissue. Often the photobiont in a lichen. Cyanobacteria: A phylum of photosynthetic bacteria, sometimes called blue-green algae (but are prokaryotic). Sometimes the photobiont in a lichen. Mycobiont: The fungal component of a lichen. Photobiont: The photosynthetic component of a lichen, either an alga or a cyanobacterium. Ecological succession: The process of change in species structure of an ecological community over time, often following a disturbance. Lichens are some of the first successional species. WARM-UP: LET S EXPLORE THE WORLD OF LICHENS! (Prior to main lesson, optional) Goal: Gain hands-on appreciation for the diversity and abundance of lichens. -Accompanying video -Notebook for recording lichen types -Camera for recording lichen types (optional) -Container for lichen collection (optional) Preparation Find a good outdoor location with many lichen species where students can collect samples without harming the environment. A variety of surfaces (trees, rocks, soil) will increase the number of lichen species that students can find. Procedure Give a brief description of what a lichen is, and show a few examples of what lichens look like. Show accompanying lichen video: https://youtu.be/vvhbag4upt8 This is a short (3-min) personal video that I created about my own experience with lichens in Greenland, where I conducted my dissertation research. With this video, students will gain a personal introduction to lichens and the challenges and joys of studying them. In addition, students are introduced to Greenland, somewhere lichens thrive despite cold and dry conditions. Divide students into groups, and give each group a camera and container (optional). Give the students 5-10 minutes (longer or shorter depending on your schedule) to find, record, and/or collect as many lichen species as possible. The group with the most lichen species wins!
Keep the collected lichens for a discussion of the types of lichens during the main lesson. MAIN LESSON: LICHENS AND THEIR ROLE IN ECOSYSTEMS Goal: Learn about lichen biology and ecology. -PowerPoint presentation (accompanying materials) -Lichens collected during the warm-up (or a range of lichen types collected from the area) Topics Covered This lesson is meant to be a basic introduction to lichens. The PowerPoint covers the following four topics, which can also be used independently as needed: -What is a lichen? Symbiosis, Fungus, Photobiont -What are the different types of lichens? Macro/micro, fruticose/foliose/squamulose/crustose -Where do lichens grow? Ability to survive in harsh conditions -Roles in ecosystems: Succession, rock weathering and soil formation, nutrient cycling -Roles as indicators: Pollution monitoring, lichenometry Detailed Slide Notes 1 Title Slide 2 What is a lichen? Have students come up with ideas on their own. What do they think of when they hear the word lichen? 3 What is a lichen? This image is a schematic of a cross-section through a lichen. The photobiont lives in a thin layer protected by a layer of fungus (the upper cortex). If you slice through an actual lichen, you can actually see a thin green layer. 4 Where do lichens grow? Ask students to think about where they have seen lichens growing. 5 Where do lichens grow? Lichens grow everywhere, on many substrates. Have students brainstorm why lichens may be better adapted to harsh conditions than vascular plants. Lichens require very little nutrients and water. Since they are low-lying, they are not as exposed to wind. Lichens can enter a dormant stage in order to survive without moisture. 6 What are the different types of lichens? Using the lichens collected during the warmup, have students come up with their own categories of lichens. In small groups, students could be tasked to come up with 2-4 categories of lichens. After 5-10 minutes, each group could present their categories (along with their reasoning). 7 What are the different types of lichens? Lichenologists (people who study lichens) use growth form to categorize lichens. These three categories are not completely distinct. Lichens can be intermediate, or may tend toward one growth form in a certain environment. After introducing the different growth forms, students can revisit their lichen collections and sort them based on growth forms. 8 What roles do lichens play in ecosystems? Have students brainstorm ideas. 9 What roles do lichens play in ecosystems? By photosynthesizing carbon and fixing nitrogen, lichens contribute to nutrient cycling. In harsh environments like the Arctic,
lichens can be important in contributing nitrogen to the ecosystem. Crustose lichens that grow on rocks can help to break them apart, contributing to rock weathering and erosion. Crustose lichens that grow on soils can help to stabilize soil and prevent soil erosion. Lichens are important parts of biological soil crusts that stabilize soils in desert and dryland environments. Lichens are often early successional organisms, colonizing bare land after any kind of disturbance. 10 How can lichens be used as indicators? Have students brainstorm ideas. 11 How can lichens be used as indicators? I highlight two ways lichens can be used as indicators. First, lichens can be used to estimate the age that a substrate was exposed to air. Certain lichens (the genus Rhizocarpon is used most frequently) grow radially at a known rate. Lichens larger in diameter are older, and indicate that a substrate is older. For instance, a gravestone erected in 1850 will likely have larger lichens growing on it than a gravestone erected in 1950. Lichens can also be used as indicators of pollution, since lichens readily absorb substances from the atmosphere. Scientists have measured the amount of mercury, lead, sulphur dioxide, and other substances in lichens in order to understand how much pollutant is in the atmosphere. Additional Resources https://www.anbg.gov.au/lichen/what-is-lichen.html PRACTICING THE SCIENTIFIC METHOD: OBSERVATIONS Goal: Make observations about the diversity and abundance of lichens. -Guiding Questions handout (at the end of this document) appropriate for working in a graveyard with trees, could be adapted for other environments. Expects students to be familiar with the different types of lichens. -Notebook for recording observations Preparation This lesson is best conducted in a graveyard, so students can use gravestones of different ages as part of their study design. However, the lesson plan could be modified for any natural setting. Before bringing the students to the graveyard, make sure that there are plenty of lichens on gravestones, trees, and soil to make the activity worthwhile. Procedure Before going into the graveyard, have a brief discussion about the importance of respect when working in a sacred place. Discuss appropriate behavior. Break students into groups and give each group a Guiding Questions handout. Have them spend time in the graveyard (15-20 minutes, shorter or longer depending on your schedule) making observations and answering the questions on the handout.
If you only have a brief amount of time to make observations, have each group pick the handout section (Lichen Growth Forms, Lichen Diversity, Lichen Substrates, Substrate Age) that interests them the most. PRACTICING THE SCIENTIFIC METHOD: GENERATING A HYPOTHESIS Goal: Articulate a specific hypothesis about lichen diversity. -Generating Hypothesis handout (at the end of this document) -Examples of measurement tools ruler, gridded transparencies (for measuring lichen coverage) Procedure After coming inside from the Observation part of the lesson, have groups work through their Generating Hypothesis handout. At some point, demonstrate the use of gridded transparencies to estimate percent lichen coverage of a surface. If time allows, each group could share their hypothesis with the class at the end of the class period. PRACTICING THE SCIENTIFIC METHOD: DATA COLLECTION Goal: Collect data to answer the question identified during the previous activity. -Notebook to record data -Rulers, tape measures -Gridded transparencies (for measuring lichen coverage) Procedure Return to the graveyard and have groups collect data to answer the question they generated during the previous activity. This part of the activity can take however long your schedule allows. PRACTICING THE SCIENTIFIC METHOD: DATA ANALYSIS (Optional) Goal: Analyze data collected during the previous activity and re-evaluate the original hypothesis. This part of the activity depends on the students familiarity with spreadsheets and basic statistics. If students are familiar with Excel, they can enter their data into a spreadsheet and calculate some basic statistics (for instance, the average number of lichen species growing on gravestones versus the average number of lichen species growing on trees). If students are not familiar with Excel, they can use calculators and draw a graph by hand.
Lichen Observations: Guiding Questions Handout 1. Lichen Growth Forms Can you find examples of all the lichen growth forms (fruticose, foliose, squamulose, and crustose)? Do certain lichen growth forms seem more common on certain substrates (rock, tree, soil, etc.)? Why do you think different lichen growth forms might prefer different habitats? 2. Lichen Diversity How many different colors of lichens can you find? Is there a color that seems to be most common? Do different gravestones have different numbers of lichen species? Is there one species that seems to dominate? Where would you look to find the highest lichen diversity? 3. Lichen Substrates How many different lichen substrates can you find? Are there any surfaces or substrates where you don t see any lichens? How do different lichen substrates differ in terms of lichen growth forms or the number of lichen species? 4. Substrate Age What are the oldest and youngest gravestones you can find? Do they look different in terms of the lichen coverage or number of lichen species? What s the diameter of the largest lichen you can find? What can you say about the age of this lichen? What s the diameter of the smallest lichen you can find? What can you say about the age of this lichen.
Group name: Date: Generating a Lichen Hypothesis Handout 1. Pick a topic In your group, decide which topic (growth forms, diversity, substrates, or substrate age) interests you the most. Topic: 2. Pick a question Now come up with a specific question related to your topic that you want to answer. If you re having trouble, you might think about the following questions: What observation was the most surprising/interesting? What was the clearest pattern that you observed? Question: 3. Write a hypothesis What do you think the answer to your question is? Why is that the case? When you can answer both of those questions, you have a hypothesis! Are there any different scenarios you can imagine? Hypothesis: Different Scenarios:
4. Develop a method How are you going to answer your question? What do you need to measure? How many measurements will you need to take? What materials will you need? Come up with a plan with your group members. needed: Plan: 5. Anticipate your results What do you expect your results to be? What are other possibilities? Write a few sentences describing your expected results.