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Students estimate a nonmobile population by using a quadrat sampling technique in the field or in a tabletop simulation. A mobile population is simulated and counted using a mark and recapture technique. Students use class data to determine mean, standard deviation, and percent (%) error. Data for cell density of Acanthamoeba is plotted on arithmetic and semilog graph paper. Students can use a microcomputer program to explore growth curves.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Balances, 0.01 g sensitivity Microcomputer with population growth software	2/lab 1/lab or group
MATERIALS
Books, identification of common weeds Map, sampling area Chart, pairs of random numbers Bags, 6" x 8" plastic or paper Wooden pegs or applicator sticks String, 40 cm and 4 m Examples of plants to be found in sampling area—grass, weeds, wild flowers, trees, other Coffee can, 3 lb with lid Jar, half-pint with lid Box or tray, 8" x 10" x 1" (to hold captured beads for counting) Beads Tabletop Quadrat Simulation Pine boards, 6 cm wide x 1 m long Pine boards, 6 cm wide x 1.01 m long Paper, 1 m x 1 m ruled in 10 cm grid 500—600 beads	Display 8/lab 8/lab 8/lab 8/bag 1 each/bag 8/lab 8/lab 8/lab 300 one color, 1000 another color 2/setup 2/setup 1/setup

*Please refer to the Appendix for name and address of supplier.

PREPARATION

Week before Lab

1. Survey the local area for a lawn or field with a variety of features. Avoid areas with only one kind of vegetation. Select two to three different areas and draw a map for the students to use in their field study.
2. Measure the lengths of string and pack two lengths into each bag with the sticks (pegs), a chart, and the map.
3. Fill each 3 lb can with one-250 ml beaker measure of beads. This should yield approximately 1000 beads. (Exact count is not necessary or desirable.) Fill the half-pint jar with beads of a different color. The following chart can be posted for collection of data:

One to Two Days before Lab

NOTES

Many good books are available to identify the common weeds. Local agricultural extension specialists and botanists can provide references on local flora.

CLASSROOM SUGGESTIONS

1. Successful results for the mark-recapture trials are best obtained when a large number of students perform the exercise. To prevent mistakes and boredom, the class could be divided into groups so that each group need only perform two aspects of the test for the actual population. In graphing the results, students will see that the more marked and recaptured, the lower the % error from the actual population.
2. This exercise provides the student with a good opportunity to investigate ways to graphically represent data collected in the laboratory. Transparencies can be made of arithmetic and semilog graph paper. These can assist in illustrating some simple data to the entire class prior to students’ plotting of the Acanthamoeba cell growth.
3. Lab can be completed in two hours if outside sampling is not done.
4. Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/ You will find useful materials for developing your lab introduction or summary, and in some cases, you may want to tell students to connect to a particular site for further information.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. Non-random laying out of quadrats can lead to either an over or under estimation.
   Clumped distributions of certain species may lead to erroneous results.
2. Birth rate is influenced by climatic and soil conditions that influence seed production and seed germination. Herbivores grazing on fruits, nuts or cones will reduce the number of seeds. Forest fires can kill seeds. Diseases may influence seed set on trees. Crowding and shading can reduce germination rates. Chemicals produced by some plants inhibit seed germination in others. Death rate is influenced by disease, fire, and climatic conditions. Herbivorous insects can denude trees.
3. Food productivity is only increasing linearly and at some point the needs of an exponentially growing population will outstrip what can be supplied through agriculture. As the population increases the need for housing and living space increases exponentially as well. Natural resources are finite and the needs of an expanding population will inevitably outstrip what is available. Energy is a crucial resource in modern living. With increased population comes an increased production of waste which may choke and foul the planet. Diseases may become more common.

SUPPLEMENTAL MATERIALS