Backyard Islands

By Venita Bright

Energy in the form of food must be available for an environment to sustain life. In most communities, plants supply the primary food energy to the system. Plants are called producers; animals that eat plants are called consumers. While consumers are typically found in places where producers grow, Dr. Polis' exploration shows that this is not always the case. Sometimes food energy is carried out of one ecosystem and into another. Often this food energy is in the form of dead plants or animals.

Look carefully at the ground, and you will likely find dead leaves, insect shells, and other organic matter generally called detritus. In some ecosystems, detritus is a major source of energy. Transport of food and energy does not only occur from ocean to islands. What about leaves that blow into a schoolyard from a nearby wood? Or raccoons that eat from a stream and defecate on land?

Materials Needed: Meter sticks, metric rulers, poster board, markers, photographs of ecosystems.

  • Think about what you know about food webs in your area. Use free association to come up with a list of at least 20 components within their food webs. Do some areas of the schoolyard support more life than others?

  • Select two 1-square-meter areas in your backyard, schoolyard, or neighborhood to study. The study areas should be near each other, but in two different habitats (e.g. on a sidewalk and in the grass; or just inside a forest and in a clearing).

  • Observe and record all organisms in the air space above and within this study area. Which organisms are producers? Which are consumers? Which eat detritus (these are called "detritovores")? How do the number of producers (number of individuals and number of species), consumers, and detritovores compare? Devise a system for estimating the number of something too great to count, like the number of grass individuals in your study area.

  • Make predictions about which study area might depend more on food energy from adjacent habitats. Which study area will produce more energy for adjacent habitats?

  • Devise methods to test your predictions. This might include categorizing different species as "visitors" and "residents." Are the "visitors" bringing food energy into a study area? Taking it away? How will you measure the flow of detritus?

  • After the data are collected, graph your findings and write about what you learned. Send us your results at:

    Dragonfly
    Miami University
    Oxford, OH 45056

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