Observing the Nutritional Relationships in an Ecosystem

What fifth grader isn't fascinated by bobcats eating bunnies, crows eating caterpillars, and pill bugs eating poop? Food webs are an interesting topic and include the learning of new and notable vocabulary, such as predators, parasites, scarcity, scavengers, composers, and decomposers.

There is a tremendous variety of options to help engage learners in this topic. Below, I have chosen a few resources that, in my opinion, are exemplary and should be examined before deciding what approach will work best for your class.

Survival of the Fittest

Before reaching fifth grade, students should be able to explain how organisms with similar needs compete with one another for resources, such as food, space, water, air, and shelter. Building on this knowledge, we next want them to investigate different nutritional relationships among organisms in an ecosystem.

Understanding these nutritional relationships will lead, in later grades, to examining the roles of consumers, producers, and decomposers in a biological community. Building on this knowledge will also lead to describing how matter and energy are transferred through an ecosystem, drawing conclusions from data about interactions between the biotic and abiotic elements of a particular environment, and analyzing the environments and the interdependence among organisms found in the world’s major biomes.

All About Food 

Food webs, or food chains, and related concepts are very commonly found on standardized tests because this domain of topics is straightforward, concrete, and indicative of both breadth and depth of learning at the fifth grade level. Such test items typically look at basic comprehension and understanding of the concepts, as well as application of the concepts to illustrations or diagrams. Sometimes the questions will ask pupils to trace matter or energy across categories.

Because of the importance of this topic to testing, here is a list of the key concepts you would want to cover:

• Transfer of Energy: sun to plants, plants to animals, animals to parasites and decomposers. (Advanced: Decomposers store some of the energy and carbon in their waste products, which can become fossil fuels which provide energy to humans.)
• Living things interact in a variety of ways to obtain materials needed for energy, growth, and repair.
• Plants (or plankton) are producers that manufacture their own food.
• All animals are consumers that obtain food by eating other organisms or their products.
• Herbivores eat only plants, carnivores eat only animals, and omnivores consume both plant and animals.
• Decomposers, such as bacteria and fungi, obtain food from the breakdown of dead plants or animals.
• Scavengers depend on dead or decaying material from plants and animals for food.
• Predators have a negative effect on their prey since they capture and feed upon them.
• Parasites have a negative effect on the hosts upon or within which they live, feed, and sometimes reproduce.
• Some relationships among species are mutually beneficial (symbiosis).
• When depicting the transfer of matter among organisms, arrows point downward in a direction that illustrates what eats what.
• When depicting energy transfer among organisms, arrows point upward toward the organisms to whom energy is being transferred.

Resources for Further Investigation:

• Energy Flow: Here you will find a video showing the energy flow through an energy pyramid.
• Energy Pyramid: A visual tutorial explaining the different trophic levels of an energy pyramid in several ecosystems.
• Creating Food Webs: This website, developed by the Gould League, provides an interactive learning experience where learners build four different food webs for four distinct ecosystems (Australian Grassland-African Grassland-Marine-Antarctic). They identify organisms as producers or consumers (herbivores, carnivores, or omnivores) and place pictures of those various organisms into the appropriate trophic levels.  Once the organisms are correctly sorted, they can view the overall food web and observe the energy flow between trophic levels.
• Bill Nye on the Food Web: This 8-minute video describes how all organisms are connected back to plants.

Resources for Teachers:

Wetlands Are Wonderlands!

In the first two lessons provided here, pupils explore how energy travels through the wetlands. The third lesson requires access to a picture book.

Weave an Aquatic Food Web

Pupils describe all organisms in terms of their roles as part of interconnected food webs. They visualize concrete images of species interaction. This is a good launch point for discussions about ecosystems and a good way to synthesize information regarding food webs and chains.

How Does an Organism Obtain its Energy?

This lesson explains how organisms obtain energy. Your class can explore and analyze how energy is passed from one organism to another in food webs, chains, and the energy pyramid.