Puget Sound Food Web

Transcription

1 Puget Sound Food Web Exploring a Local Ecosystem Students will build an estuary food chain and web, following the instructions adapted from the USDA classroom activity Weaving the Web. Students will discover how living parts of an ecosystem are interconnected by the flow of energy through their food web, and how those organisms are dependent upon the abiotic (non-living) parts of their ecosystem. Suggested for grades: 2 5 Estimated Time: minutes Objectives: Students will be able to: 1. Build a food chain and explain how energy flows through the chain 2. Combine several food chains to represent a food web 3. Explain how all living things in the ecosystem depend on producers for their food 4. Explain how all living things in the ecosystem need or use the non-living parts of their ecosystem 5. Discuss possible effects from disruptions to one or more parts of an ecosystem Materials Needed: 1. Ball of yarn 2. Scissors 3. Estuary Ecosystem Cards 4. Hole punch & string to make the cards into necklaces 5. Space for the class to form a large circle Background: Ecosystems contain both living and non-living parts (ex. plants/animals & water/rocks). The living things, or organisms, need food energy. Living Things Need Energy From Food Energy can be defined as the capacity for change. Living things need energy for everything they do. For example, a butterfly needs energy to change position when it flies, and a daffodil needs energy to change size as it grows and blooms. Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 1

2 All living things get energy from food. Green plants use energy from the sun to make their food. Plants use the food they make for energy to grow. Animals get energy by eating plants or other animals. The Sun is the Source The energy in living things originates from the sun. Producers, such as green plants, algae and certain bacteria, are the only living organisms that can use energy from the sun to make food. Although many children know that the sun keeps plants healthy, they may not know that plants rely on the sun s energy to make food, or that this food can be used by the plant itself or by animals that eat the plant. For example, a sugar maple tree uses the sun s energy to make sugar, a food, in its leaves. The tree uses the sugar for energy to grow and stay alive. If people eat maple syrup, they get energy from the sugar in the tree. But people cannot hold out their hands to the sun and make food in the same way that a maple tree can make food in its leaves. Children may think that the sun is important because it keeps animals warm. The sun does provide warmth to the animals, but, more importantly, the sun provides the energy that green plants use to produce food. Animals get this energy when they eat the plants. To help students understand that animals depend on the sun for food energy, have them think about how long a deer could live if it only basked in the sun and did not eat green plants. The relationship between the sun s energy and the energy required by living things will become clearer as the children learn about food chains and webs. Children may cling to the idea that plants draw in usable food from the soil through their roots. It is true that plants absorb water and essential minerals from the soil and that they need water to make food. Food contains energy, however, and the water and minerals in the soil do not contain energy. So plants use the energy from the sunlight plus water and minerals along with carbon dioxide from the air to produce food that contains energy. Food Chains A food chains energy is transferred in sequence. For example, energy comes from the sun, to green plants, to animals that eat plants, and to animals that eat other animals. Green plants use the sun s energy directly to make food. When animals eat green plants and other animals eat those animals, the energy moves from one living thing to another along the food chain. Animals that eat plants are called herbivores, animals that eat both plants and animals are called omnivores, and animals that eat only other animals are called carnivores. Ultimately, all members of a food chain depend on the energy from the sun that green plants transform into food energy. Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 2

3 - The above diagram illustrates a food chain that might be found in the prairie. Arrows indicate the transfer of energy from one organism to another. The sun provides energy for the grass, the grass for the caterpillars that eat the grass, and so on. Students may want to use arrows to show animals moving toward their food. It may be necessary to help students recognize their thinking, as in the following example: Does your arrow show that the frog hops toward the fly to get food? Now, can you draw the arrow to show which way the food energy is going? Does eating the fly give energy to the frog? As they draw food chains in this unit, the students will better understand how the sun s energy passes through food chains. Food Webs Food webs are more complex than food chains. They consist of many food chains that are interconnected. The following example is a series of food chains, which together make a food web. sun grass grasshopper blue jay owl sun grass rabbit hawk sun clover caterpillar snake hawk Vocabulary/Glossary abiotic non-living carnivore an animal that eats only animals community all the plants and animals that live in one place, and that interact and depend on one another decomposer an organism that primarily eats dead plants and animals, releasing their nutrients back into the system Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 3

4 detritus decaying or rotting bits of dead plants and animals ecosystem a natural system that includes the plants and animals interacting with each other and with their non-living components, such as soils, water, and nutrients that support the organisms living within them energy the capacity for change: all living things need energy from food to live and grow estuary An estuary is a body of water formed where freshwater from rivers and streams flows into the ocean, mixing with the seawater. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them. ( food chain transfer of energy in sequence, for example, from green plants, to animals that eat plants, to animals that eat other animals food web a network of food chains that are interconnected within a particular community herbivore an animal that eats only plants interact to influence one another omnivore an animal that eats both plants and animals Estuary Food Web Activity 1. Copy Estuary Ecosystem Card sheets and cut apart. Have students fold and tape each card together to create a front & back. Punch one or two holes at the top of each card and string up to make necklaces. 2. Distribute cards to students, making sure to include the sun, producers, herbivores, carnivores, omnivores and detritus. (Hold the abiotic/non-living cards aside.) ***Suggestion, particularly for smaller groups: although the cards include many different organisms, the energy cycle and effects from ecosystem disruptions may unfold more clearly and simply if you use a smaller subset of the cards. For example, make two or three copies of one or two producers (to represent their greater proportional presence in the system), and then use only a few chains radiating from those producers. a. Have students read their cards to learn about their diets, predators and other needs. Answers are on the backs of their cards. **Anyone can give energy to the detritus player. Some eelgrass will go directly to detritus. Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 4

5 b. Ask them to walk around and introduce themselves to the other organisms that they eat, or are eaten by, so that they will begin to think about how they are all connected. Tell them that they are meeting each other for the first time so they must tell all about themselves to the other organism. Suggest that they ask the following questions: i. What do you eat? ii. Do you eat me? iii. Am I the only thing you eat? 3. Once they feel pretty familiar with each other have them work together to form food chains. Explain that many food chains linked together will form a food web. 4. Tell the students that they will make a food web. Have them stand in a circle. The student with the sun picture should stand in the center. They should look around and ask themselves: a. Who in the circle could I give my energy to? (Who might eat me?) b. Who in the circle could give me energy? (Whom could I eat?) 5. The sun starts things off, holding the end of the yarn and passing the ball to a producer (green card player). 6. Weave the estuary food web, using the prairie food web example on the next page as a guide (excerpted from USDA Weaving the Web, **You can try different ways of web weaving a ball of intact yarn: a. Start off with the sun, and then weave throughout the circle without breaking the string. After top predators, the ball can be passed to bacteria or back to the sun to start again. b. Broken strings/individual chains: start off with the sun, and then pass the ball through one full chain, cutting the string after a top predator. Pass the ball back to the sun and start a new chain. How is it different if you continue some chains by passing the ball to bacteria after a top predator (instead of back to the sun)? Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 5

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8 7. Now, to emphasize the importance of the non-living elements, hold each abiotic card up in turn and ask: a. Will anyone who needs sand please shake a leg? b. Will anyone who needs mud please jump up and down? c. Will anyone who needs brackish water please do a wiggle dance? (How many players responded to each element?) 8. See what happens to each chain and web overall if any individual link is wiped out. For example, imagine that clams and oysters are completely overharvested and disappear. Those students pull on their strings. Who feels the tug? A disease kills off the amphipods or midges; amphipods/midges pull their strings whoever feels the tug is affected and then pulls their own strings. Who else now feels the tug? What would happen if all the producers died? (Nothing else in the food web could survive.) 9. Ask: a. How could we show what could happen if one kind of plant, such as all the eelgrass died? (The student representing eelgrass could pull out his or her pieces of yarn and sit down.) b. If all the eelgrass is gone, who may have trouble getting enough food? (Identify all the animals that were in food chains that included eelgrass. Whoever had yarn pulled out of their hands might have trouble getting enough food without the eelgrass.) c. What happened to our food web? (It is much thinner, less complex, and less strong.) d. Why should we be concerned about each kind of plant or animal? (Because other plants and animals in the food web may depend on it.) 10. You can emphasize that each group is important and applaud each in turn. a. Will the carnivores please show their teeth? b. Will the omnivores please shake a leg? c. Will the herbivores please wink an eye? d. Will the only living things that can make food using the sun s energy producers please take a bow? Extensions: Now that students have an understanding of interdependence and energy flow through the food web, challenge their thinking with a series of change scenarios. 1. As more and more people move into neighborhoods near the estuary, they bring pets and don t always clean up after them. Pet waste washes into nearby streams, then into the estuary, causing nitrogen levels to rise, which triggers a huge overgrowth of algae. Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 8

9 The algae take up a lot of the dissolved oxygen in the brackish water, leaving an oxygenstarved environment. Who would be affected? a. Producers, fish and any organism that depends on them for energy 2. Puget Sound enjoys a year with an unusually high number of clear-sky, sunny days. This boosts the amount of phytoplankton and zooplankton in the estuary. How might that impact the food web? a. This can be beneficial at first until the plankton die off. This can cause an over concentration of decaying organism which will affect the water quality. Some detritus (decaying plants and animals) but too much makes for unhealthy water and lower levels of oxygen. 3. A large neighborhood is built along the estuary. Developers construct a seawall to protect the houses from flooding. The wall bounces waves back into the estuary, ripping up eelgrass beds. Who would be affected? Is this a fast or slow change? a. Eel grass and anyone dependent on eel grass. 4. Summer arrives, and people living in nearby homes spray fertilizers and pesticides on their lawns. What might happen to the estuary habitat? Who would be impacted? a. Everything! The producers absorb the toxins and those toxins will move up each food chain. b. Organisms that live in the water will be exposed to the toxins through their skin and gills. 5. Citizens have noticed that an invasive plant species is taking over territory in the estuary, choking out the native eelgrass. They plan several community events where people remove the invasive species and plant eelgrass. How would those actions change the estuary ecosystem? a. Habitat restoration! Yay! b. Visit pugetsound.org for information about local projects 6. With climate change, ocean temperatures rise. This changes the ocean ph to be more acidic. Higher ocean acidity makes it harder for shellfish to grow shells, so shells become thinner offering less protection from predators. Who would this affect? a. Anything with a shell (including zooplankton, many of which are the larvae of crabs, clams, octopuses, other invertebrates. b. Anything that eats anything with a shell. c. Anything that eats anything that eats something that has a shell. Have students identify food chains from other ecosystems (forest, prairie, marine, etc.) and make pictures of the plants and animals from that ecosystem, using arrows to indicate the flow of energy. **For an additional challenge, identify the cross-over Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 9

10 species which link more than one eco-system together (such as SALMON). How are all of those ecosystems impacted by disturbances to those keystone species? Students can learn about the plant or animal they represented in the food web activity and write a report, tell a story, or make an illustration about the plant or animal to share with the class. Adapted from Project LEAP: Learning about Ecology, Animals, and Plants, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY What are some actions that students can take to preserve their local estuary or other ecosystem? Examples: Check local storm drains to see if they are marked with no dumping signs, and send a request to city officials if not. Students could do a fundraiser for a local conservation/preservation group. Students could ask parents about any chemicals used on their lawns/landscaping and discuss alternatives. Make pledge cards to help pick up after their pets. Develop an education campaign to make other students or local residents aware that everything eventually washes into Puget Sound. Point Defiance Zoo & Aquarium ~ Tacoma, Washington ~ pdza.org Page 10