Prairie Populations

Lesson Introduction

To study the population of a species in an area or to assess the biodiversity of an area, biologists must figure out how many individuals the area supports. One way would be to count each one. That might take a long time, but the result would be precise. This approach may be unrealistic if the area is very large, say a 5000-acre prairie, or if the individuals of the species are too numerous, like the grass in the school yard. To solve this problem, scientists often take a sample. They count the individuals of a species within a smaller area to get an estimate of the total. An area is divided into square sections and each individual plant in that area is counted. This method is called a quadrat survey.

After a survey has been completed of an area, the biologist will count the number of each individual species and multiply that number by the number of squares it would take to cover the whole study area. For example, if the schoolyard is 200 square meters, and the study area is 6 square meters, a population of 20 dandelions in the study area is multiplied by 33 (200 sq. meters divided by 6 sq. meters) to get an estimated 660 dandelions in the school yard.

Illinois State Goal	Standard	Learning Benchmarks
12	B	5a: Understand the fundamental concepts, principles and interconnections of the life, physical and earth/space sciences. Know and apply concepts that describe how living things interact with each other and with their environment. Analyze and explain biodiversity issues and the causes and effects of extinction.

Lesson Objectives

The students will:

• learn the Quadrat Survey Technique to analyze the biodiversity of a local plant community.
• compare its biodiversity with the documented changes in biodiversity of the tallgrass prairie over time.
• answer discussion questions about the extinction of tallgrass prairie species.

Advance Preparation

Time Allotment

Three 40 minute class periods (one for learning the survey technique, one for conducting the survey, and one for analyzing the data and comparing it to the Midewin area)

Materials

• an outdoor yard or access to a natural area
• clipboards
• graph paper
• examples of quadrat surveys
• 9 metal tent stakes
• 100 yards of twine or string
• field guides to the local plants
• access to information about the tallgrass prairie and biodiversity (books or web sites)

PROCEDURE

Tap Prior Knowledge

1. Have your students discuss the definitions of diversity, biodiversity and extinction.

Share with Neighbor

2. Have students work in pairs to compare the area of plants growing around the school, or in a select natural area. How many different species grow there? Have the students consider the species within a tallgrass prairie like the Midewin site? More species or less?

Hands-on Activity

3. Using stakes and a compass, mark out the four corners of your study area, oriented north. Tie rope to the corners. Measure off 6 squares at 2 meter intervals and put a stake at each point. Tie rope vertically and horizontally across the area. This should produce a 6 meter square area divided into 2 meter squares.

4. Assign each group of 3 students to a 2 meter square.

5. Each group should first identify each type of plant in their square. It is not important what the real name is, just that each type is given an identity. For each type of plant, create some symbol to be used in mapping the plant's locations in the square.

6. Permanent abiotic features such as a sidewalk should be mapped in as landmarks. map the locations in the square of each type of plant. Grass and clover can be mapped in 10cm squares rather than each individual plant.

7. Have each group collect a specimen of each type of plant in the plot and organize them into one list of species. Then, each group will count the number of each species in their square. For grass and clover, estimate the number in each 5 cm square and multiply by 60 (300 sq. cm / 5 sq. cm).

8.As a class, add each group's estimates and record the number of each species in the entire 4 meter square area.

9.Determine an approximate size of the school grounds (how many 6 meter squares would fill the entire space around the school, including the park). Record the estimates for each species.

Introduce Scientific Principle/Environmental Issue

11. All life on earth is part of one great, interdependent system. It interacts with, and depends on, the non-living components of the planet: atmosphere, oceans, freshwaters, rocks, and soils. Humanity depends totally on this community of life--this biosphere--of which we are an integral part. Biological diversity, or biodiversity, is the variety of the world's organisms, including their genetic diversity and the assemblages they form. It is the blanket term for the natural biological wealth that undergirds human life and well-being. The breadth of the concept reflects the interrelatedness of genes, species, and ecosystems.

Biodiversity and the causes of extinction are well defined in several articles by the Defenders of Wildlife: What is Biodiversity? and A History of Extinction.

The biodiversity of the tallgrass prairie and the threats to it are well described by Ken Robertson on his web page The Tallgrass Prairie in Illinois: Biodiversity and Prairie Settlement.

Relate Activity and Concept

12. Have students answer the following questions: Do the estimates from the study seem high or low? Some species, like trees or shrubs may be few enough to count every individual. If most of the land does not have trees, this method may produce wildly inaccurate results, so use common sense.

Is the quadrat area too different from the rest of the area? A prairie garden in one small area will not have the same species as the rest of the 200 square meter yard. Again, common sense will tell you if the survey gives an accurate account of biodiversity. A survey like this one, however is still useful when the number of individuals is too high to count of the area is too large.

How many species of plants do they think can be found on a healthy tallgrass prairie?

How have humans affected the biodiversity of tallgrass prairies?

Learning Outcomes

Students will:

• conduct a quadrat survey
• compare the relative biodiversity of different places based on such survey data
• understand what biodiversity means
• understand the causes of extinctions in general and in the tallgrass prairie in particular

Internet Resources

Biodiversity

Biodiversity Information Networks and Interest Sites
Yahoo! Search Results -- "biodiversity"
Biodiversity (World Resources Institute)
The Biodiversity Center - Defenders of Wildlife
What is Biodiversity? - Biodiversity Center - Defenders of Wildlife
WRI Article: "A History of Extinction"

Tallgrass Prairie