BIOLOGICAL SUCCESSION IN A KNOWN MICROECOSYSTEM

The desert soil succession activity will yield various types of organisms depending upon eggs and cysts present in the soil collected.

This activity also deals with succession in a microsystem. However, this time all the organisms present in the microecosystem will be known, because they will be added from pure cultures provided by the teacher.

By manipulating environmental factors such as temperature, light, and food, students are able to see in a matter of weeks the results of change that can take years in larger ecosystems in nature.


Background Information:

Teacher notes:

Allow one lab period for students to observe the organisms in the "pure" cultures so that they become familiar with the appearance of each type. Set up the culture dishes and add the various organisms prior to the beginning of the actual sampling. Allow at least a span of 4 to 6 weeks sampling time.

A set of six dishes is needed for each lab group, but remember that the same sets can be used for different classes. Be sure the water is conditioned, either tap water left out over night or boiled water.

Make a picture key of the various organisms available for the students. They sometimes forget what the "critters" look like since the sampling dates are a week apart.

Student requirements:

Students are responsible for collecting data and reporting group averages to the teacher on each sampling day. Students prepare a formal lab report, complete with graphs of data collected. This is used as the evaluation tool for this activity.

In this investigation, you are to set up six culture dishes containing various protozoans. You are able to place these dishes in areas of specific temperature and light conditions. Over a period of time, you are to determine the order of the stages of succession in the dishes. You are to describe succession as it occurred in each dish.

Purposes:

  1. To observe the order of stages of succession in cultures containing bacteria, protists, and microinvertebrates.
  2. To determine the factors causing succession.
  3. To learn population sampling techniques.
  4. To observe food chains in a microecosystem.

Materials:
  • Medium size culture dishes - 6
  • Conditioned water
  • Droppers - 6
  • Cooked wheat grain
  • Stereomicroscope
  • Microscope (compound light)
  • Glass Slides
  • Cover slips
  • Graph paper
  • Paramecium culture
  • Mixed rotifer culture
  • Blepharisma culture
  • Eudorina culture
  • Peranema culture
  • Euglena culture
  • Amoeba culture

Procedure:

Food and Environmental Conditions for Each Culture Dish
Culture DishFood Environmental Conditions
A3 grainsUnlighted refrigerator (remove bulb)
B3 grainsLighted shelf in classroom (18-27 0C)
C3 grainsLighted incubator (28-32 0C)
DnoneUnlighted refrigerator
E noneLighted shelf in classroom
FnoneLighted incubator


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