Ecosystems are complex and mysterious. Plants and animals interact with each other and with the non-living components of their environment in ways we humans are just beginning to understand, though scientists have given us some helpful categories for understanding basic roles that are needed for ecosystems to function well.
Plants and animals are sometimes labeled according to their role in transferring the sun’s energy through the ecosystem. As described in this chapter, producers gather the sun’s energy and convert it into sugar. Primary consumers eat plants and thereby gain energy/sugar. Secondary and tertiary consumers eat other consumers and thereby gain energy. Decomposers gain energy eating dead producers and consumers. Alternately, organisms may also be classified according to what they eat, be they herbivores (plant eaters), carnivores (meat eaters) or omnivores (eaters of both plants and meat).
In addition to word labels, ecosystem relationships can be depicted visually. The overall ecological structure of an area, with multiple possibilities for who eats whom and how energy flows, might be illustrated in food web. However, each form of life has its own food chain – where it got its food from and where its energy will end up.
In this activity, participants will first attempt to observe a variety of species in one ecosystem, then identify and illustrate their ecological relations hips. The activity requires participants to observe first hand any species included in the diagram. However, they are not required to observe the species in the act of eating another species to record that energy-transfer relationship in their diagram. Participants may need to gather information from field guides or other sources to learn or confirm what eats what.
1. Select one outdoor location to observe and diagram. You may choose an aquatic or terrestrial location. Spend time as a group observing several plant and animal species living in or using that location.
2. Introduce the terms producer, consumer, decomposer. Explain how the energy from the sun travels through the ecosystem. Show simple food chain and food web diagrams.
3. Instruct participants to search for several examples of each type of species: producer, consumer, and decomposer. Which type is hardest to see? Now construct a simple food chain. Select one organism and figure out what it eats and who eats it. In the interest of expediency, the instructor may want to simply tell the participants who eats whom while looking for examples. Later, the participants can do their own research. On paper, participants should draw these food relationships using arrows that represent the sun’s energy traveling from producer to consumer to decomposer. Participants may draw several food chains, but only include species they actually observe themselves.
4. Instruct students to combine their food chains into a food-web diagram representing the relationships among observed species in the ecosystem. Which consumers eat which producers? Do some consumers consume more than one type of producer ? Do some consumers consume other consumers? Draw the arrows to indicate what each species eats, making sure the arrows reflect the flow of the sun’s energy through the ecosystem. If participants observe a species and aren’t sure of its role, instruct them to write it down and follow up with further reading; they can add arrows later. Advise participants to consider how the non-living components of the ecosystem, such as soil or water, influence the ecosystem. Discuss as a group. As participants more closely observe the ecosystem in the location they have chosen, they should add more species and arrows to their diagram. This could occur over the space of 30 minutes or many weeks.
5. Encourage participants to fully illustrate their diagrams; they might draw each observed species or add clip art later. Label each organism or component with its name and ecological role.
For younger audiences: Make this activity more concrete using yarn instead of pencil and paper. Provide each student with three lengths of bright-colored yarn at least four feet long each. Instruct students to use the yarn gently to connect ecosystem components that rely on each other in some way. Be sure you define a specific area in which the students should stay. Students might tie a tree to the soil, or lay one end of the yarn on a leaf and let the other end hang in the open to represent the air. Call everyone together and survey the activity area. Comment on all the connections going this way and that and discuss how many more connections exist that we didn’t mark with yarn. Everything really is connected, even if we can’t see it! Tour the activity area while each student takes a turn explaining the connections they “tied.” Be sure to gather all the yarn lengths before departing the area.