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Destination: Galapagos Islands Cyber Field Trip

Cyber Field Trip Student Activity
Backyard Science: How Ecosystems Work

Safety Precautions
Critical Thinking Questions


The word ecology is derived from the Greek word oikos, meaning "place to live" or "house." Ecology is the study of how organisms interact with one another and their physical and chemical environments. In other words, it is the study of how things are interconnected in nature. Because the delicate ecosystems found in the Galapagos Islands exist nowhere else on Earth and are, in some areas, largely undisturbed by humans, the islands are a great place to make ecological observations.


Use the glossary to define any unfamiliar terms:


  • 3 x 5 index cards
  • Colored pencils or markers
  • Calculator
  • Meter stick
  • String
  • Wooden stakes
  • Plant and insect field guides


  • When working in the field, follow all safety precautions given by your teacher.
  • Be especially cautious of poisonous plants and stinging or biting animals.


One way to measure the population density of an organism is to divide a large area into smaller sections, count the number of organisms in each section, add the numbers together and divide by the total area of all the sections. The best size for the individual section depends on the relative size of the organism you're studying. For soil-dwelling organisms or insects, the section can be extremely small, while for mammals, the section should be much larger. This activity can be accomplished even if you do not know the names of the organisms. You must only be able to distinguish one species from another.
  1. Designate an area of study that is one square meter by marking it off with string and wooden stakes.

  2. Identify three different types of plants in this area to use for your population density study.

  3. Sketch each plant and, if possible, use a field guide to identify its common name. If you are unable to identify the plants, simply label your sketches A, B and C.

  4. Now divide the area into ten equal sections and mark each with string.

  5. Count and record the number of each of your selected plants in the first section. Repeat the procedure for the other nine sections. Finally, record the total population of each plant for the entire area.

  6. Have one student record the class totals for each plant on the Data Chart (copy or print out the chart below).

    Data Chart
    Section Organism A Organism B Organism C
    Section 1      
    Section 2      
    Section 3      
    Section 4      
    Section 5      
    Section 6      
    Section 7      
    Section 8      
    Section 9      
    Section 10      

  7. Divide each total by the number of students in your class to calculate the population density for each of the three plants. Your answers should be in the form, "There are n [name of plant] per square meter."

  8. Create an ecological pyramid of organisms found in your area, using the format below.

    ecological pyramid

  9. Calculate the amount of biomass (organic matter) stored in each organism in the pyramid using the following rules:

    • Herbivores store about 15% of the previous trophic level's biomass.

    • Carnivores store about 10% of the previous trophic level's biomass.

  10. After completing your ecological pyramid, answer the following questions:

    • Which organism is the primary consumer? The secondary consumer? The tertiary consumer?

    • Is there a top carnivore in your pyramid? If so, what organism occupies this position? On which trophic level is the secondary consumer? The tertiary consumer?

    • Calculate the amount of biomass in percent for each trophic level.


  • Identify three abiotic factors that might exist in any ecosystem.

  • Identify three biotic factors that might exist in any ecosystem.

  • Explain the difference between population and species.

  • Identify specific problems relating to indigenous wildlife that are caused by introduced species.

  • What is the difference between a food chain and a food web?

  • What impact have introduced species had on Galapagos Island ecosystems?

  • Diagram a four-level pyramid illustrating a food chain that might exist in the Galapagos Islands. Differentiate between and label the trophic levels and the producer(s) and primary, secondary and tertiary consumers. What percent biomass would be available to each trophic level?


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.