Interactions in an Open Ecosystem
In nature, there is a constant interaction among animals, plants, fungi, protists—microorganisms not easily classified as fungi, plant or animal—and their environment. In this ecosystem, there is a direct relationship between the community of living organisms and its surroundings. The organisms affect their physical surroundings just as they are affected by them.
In this project, you will observe some of these interactions in an open ecosystem and investigate populations within a sector. You will also determine populations of organisms by using the technique of random sampling.
Purpose: To select and layout a study area.
- measuring tape
- 12 wooden or metal tent stakes
- 300 yards (300 m) of cord
- graph paper
- Select a study area that has a variation of plant life. (A wooded area was chosen by the author, but any ecosystem can be used.)
- Use the compass to determine which direction is north.
- With the measuring tape, measure an area 30 × 30 yards (30 × 30 m). The plot of ground should be measured so that it is aligned in a north-to-south direction.
- At each of the four corners of the plot, hammer one stake into the ground, leaving about 6 inches (15 cm) of the stake aboveground.
- Attach the end of the cord to one stake, loop it around the other stakes, and tie it to the starting stake to enclose the plot.
- Use the measuring tape to divide the sides of the plot into 10-yard (10-m) sections.
- Drive one stake into the ground at each 10-yard (l0-m) interval along all sides of the plot (see Figure 23.1).
- Using cord to join opposite stakes, divide the plot into nine equal subplots.
- On graph paper, sketch the plot Identify each subplot with a number. Indicate the compass directions with arrows on the sketch.
- Make separate sketches of each subplot Note prominent land features such as trails, open areas, erosion, and streams.
A sampling plot of ground is selected, measured, and subdivided. A general description of prominent land features is noted.
The sampling plot allows you to sample and study biotic factors (relationships among organisms) and abiotic factors (the physical aspects of an environment; temperature, erosion, the slope of the land). In this field study, measurements of physical factors and organisms can be taken. Separate information taken from each subplot, when studied as a whole, provides a clear picture of the ecological community (interaction of living organisms with their environment) within the plot and gives clues to the surrounding ecosystem (ecological community).
Try New Approaches
- Construct and use an Abney level to measure the angle of the slope of the land of each subplot Make the level by using masking tape to attach a protractor to the center of a yardstick (meterstick). Tie a 12-inch (30-cm) piece of string to the center of the protractor and attach a washer to the free end of the string (see Figure 23.2). Hold the measuring stick parallel to the ground of each subplot while a helper reads the angle on the protractor made by the hanging string. When the slope is zero, the string hangs straight down across the 90° mark. To determine the angle of slopes, subtract the angle reading from 90°. For example, if the protractor reads 50°, the angle of the slope is 90° – 50°, or 40°.
- Observe the types of plants in each subplot. The four types of plants that you may find and their typical description within each subplot are as follows:
- herbaceous (nonwoody) plants—vegetation such as fern, grass, weeds, moss, lichen, and fungi.
- woody plants—shrubs with two or more main stems.
- trees—woody plants with one main stem.
- Record the actual presence or indications of the presence of animals. Note the presence of tracks, holes, sounds, claw marks, hair, nests, and so on. Cautiously turn over rocks and logs to discover insects, reptiles, and amphibians. Remember that you are an observer and do not want to change this ecosystem, so return rocks and logs to their original positions.
- Make an insect net by bending a coat hanger into a hoop. Attach smallholed netting sewn in the shape and size of a pillowcase to the hoop (or a pillowcase can be used instead). Secure the ends of the hoop to a broom handle. Walk across each subplot in a straight line. Sweep the net back and forth as you walk across each plot Close the net Empty the contents of the net into a jar and secure the lid. Label the jar with the plot number. Collect insects in each plot Record the number and type of insects found in each plot. Science Fair Hint: Display the collected insects in small baby food jars containing rubbing alcohol. Place identification labels on each jar.
- Determine the number and identity of arthropods (joint-legged animals) in leaf litter found on the ground in each subplot. Use your hands to remove the leaf litter from a 10-×-10-inch (25-×-25-cm) sampling area. Pour the leaf litter into a funnel (some will fall through, but most will pack and stay in the open funnel). Push a paper towel around the top surface of the litter to prevent organisms from crawling out. Stand the funnel in a jar with about 2 inches (5 cm) of alcohol in it. Place a desk lamp above the funnel. As the leaf litter heats and dries, the organisms will crawl to the bottom and fall into the alcohol. This may take several days, so add alcohol as it evaporates.
- Beneath the leaf litter in each subplot, collect a baby-food-size jar full of soil. Analyze soil samples for organisms by lining a food colander with fine-mesh screen. Support the colander with a bucket. Spread the soil sample over the mesh screen. Slowly pour water over the soil until the soil washes away. Turn the screen over on a paper towel and use tweezers or forceps to sort through the material. Use a dissecting microscope, if available, to observe and identify macrofauna (larger than 1 cm), mesofauna (0.2 to 1 cm), and microfauna Oess than 0.2 cm) present.
Count and record the number of each type of plant found within the sampling area of each subplot. Use these numbers and sample problems from Appendix 3 to determine the abundance and frequency percentages as well as the density for each plant type.
CAUTION: Alcohol is flammable. Do not use it near an open flame. Wash your hands after using alcohol.
Design Your Own Experiment
- Collect leaf samples from the plants and, using plant field guides, identify the types of each plant present. You could display photographs of the plants along with preserved samples of the leaves or leaf rubbings. See Appendix 4 for techniques for preserving plants and making rubbings.
- Make molds of tracks by pouring plaster of paris into the tracks. Mix this liquid by following the directions on the box of plaster of paris. You could use the molds as part of a project display.
Get the Facts
- When an organism feeds upon another living thing, there is a transfer of materials and energy. This transfer from organism to organism is called a food chain. Find out more about the food chain. What is a food web? What is a pyramid of energy and a pyramid of numbers? Use the information collected in your plot to construct a pyramid of numbers.
- Energy is constantly lost in an ecosystem and has to be replaced by sunlight. There is also a fixed amount of matter within the system. Find out how matter is recycled in an ecosystem.
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.