INTRODUCTION
The biotic factors of an environment are all organisms found within that environment. Organisms are divided into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. A group of organisms of the same species found within the same environment is called a population.
Populations of different species sharing the same area and interacting with each other make up a community. One way of studying the interactions of organisms in a community is by taking an inventory of all the species in the area and comparing the sizes of their populations.
In this investigation, you will observe the abiotic factors of a study site and classify the species of plants and animals in that site. You will then measure randomly chosen quadrats within the site and count the individuals of each poulation located within each quadrat. With this data, you will estimate the sizes of plant and animal populations within the community.
Before scientists can design an experiment, they must first make observations on which to base their hypotheses. Scientists have many different methods of collecting this data. The task of taking an inventory of the different kinds of organisms and their population sizes in an environmental site can be very difficult, especially if the area is teeming with life. Since it would be impractical, if not impossible, to count each individual organism in a large area, ecologists randomly choose small portions of the whole area and classify and count the organisms in each small portion. They can then estimate the size of each population in the larger community. This process is called the quadrat method .
The goal of the quadrat method is to estimate the population density of each species in a given community. Population density is the number of individuals of each species per unit area. Small square areas, called quadrats, are randomly selected to avoid choosing unrepresentative samples.
Once the population densities for all quadrats are determined, the population size within the larger area can be estimated.
For example, if a 10 m x 10 m (100 m perhaps 1 m x 1 m (1 m 2 ), might be selected at random. If the population densities of a particular species at the three quadrats are 10, 12, and 14 individuals per m
+ 14/3 = 12 individuals per m 2 area of each quadrat (100 m 2 /1 m 2
2 ) site is being surveyed, three quadrats of a smaller size,
2 , an average is taken [(10 + 12
]. That number is multiplied by the ratio of the larger area to the
) to calculate the estimated population size within the site (12 x
100 = 1200 individuals). This process is repeated for all species in the community.
You all should already be familiar with how to keep records of an experiment in a databook. For review, see the Lab Investigation Handout that I have given you. Of particular note - when making entries in a databook, remember that this information is not just for you, but for anyone else who may need to use it. All material should be presented in a clear and concise manner that can be understood even by those who are not in the class.
PURPOSE : To estimate the population sizes of various species of organisms using the quadrat method.
HYPOTHESIS : If the quadrat method is used, then the population sizes of various species of organisms can be estimated.
MATERIALS : ruler, beans, straws, scissors, tape

PROCEDURE :
1) Using the ruler, mark off a square 60 cm by 60 cm on each side and use tape to create margins. Use the corner of your notebook as a right triangle to make the square as precise as possible.
2) Take your cup of beans and randomly dump them onto sample area being careful to not spill them onto floor.
3) Using straw create a 6 cm by 6 cm quadrat by cutting and taping.
3) Select at random an area within the site to be your first quadrat. To do this, close your eyes and toss the straw quadrat into the square.
4) Record in your data table the number of organisms of each plant or animal species within the quadrat.
5) Repeat steps 3 and 4 a total of 10 times.
6) For each species, add the number of organisms found in all 10 quadrats and average them to calculate the average population density per 6 cm 2 .
7) For each species, multiply the population density by _____ to estimate the total number of organisms in the larger site. Record the estimated population sizes in your data table.
DATA:
You should have all the observations and measurements requested in the procedure. A convenient way to present some of your data would be as follows:
SPECIES NO. IN
QUAD
1
NO. IN
QUAD
2
NO. IN
QUAD
3
AVERAGE
POP.
DENSITY
EST.
POP.
SIZE
IN
SITE
GRAPH:
Graph the estimated population for each “species” found in your site.

CONCLUSION:
Answer the following questions -
1) Why was it necessary to close your eyes before choosing the quadrat?
2) Which was the dominant “species” within the site?
3) How do your averages compare to the population densities of the individual quadrats? Were the populations spread out evenly over the site?
4) Using the quadrat method, how could you better estimate the actual population sizes of species within the site?
5) How is the sampling of animal populations more difficult than that of plant populations?
6) Predict how the removal of the dominant plant species from the site would affect the population sizes of the other organisms. Explain.
*Adapted from Environmental Science Laboratory Manual, Addison-Wesley Pub. Co., 1995.