Procedure:
Work with the class to phrase a question about population size that can be answered through scientific investigation. The question should be along the lines of How many objects of a certain type are there in an area of known size? Discuss with the class types of questions can be answered through scientific investigation and what types of questions are more difficult to answer.

Take the students outside to a big area or field.

Look around and decide on an object whose population you will measure. It may be rocks, plants (all plants or a specific type), sticks, etc. Sample areas won’t be large, so don’t select full-sized trees.

Discuss with the students how they might design and conduct an investigation answering their population size question. If an area is too large to count every object, how might they estimate the population anyway? Scientists use a method known as field sampling. They carefully count all the objects in a small, manageable area or a series of areas and then make an estimate from those sampling areas to the entire area.

As a class decide the extent that you would like your population estimate to cover. For instance, a soccer field, a playground, the parking lot, etc.

Sometimes science requires only simple tools and instruments. In this investigation, use a tape measure to mark off at least five different sampling areas that are a meter square. Select sampling areas that represent the variety within your larger area.

You may split your class into five groups and have each group count all of the specified objects in that sampling square. If the object is numerous or difficult to see, you can have each member of the group count separately, and see if they arrive at the same number, and use the mean as the number of individuals.

Record the number of individual objects within each of the one-meter squares.

Determine the average (mean) number of individuals per square meter by using the information collected from each of the sample areas. Use the following as an example for the calculations.

The class now has a measure of the average number of individuals per square meter. This number is known as a population density.

To determine the total population, calculate the area of your complete population extent, e.g., the field or playground. (For younger students, remind them how to calculate area by measuring the long side and short side of a rectangle and multiplying.)

Multiply the density per square meter times the total area in square meters to determine the total population estimate.

Scientists review each others' work by asking questions about how they did their research, and what conclusions they draw from their research. Have the students brainstorm a list of questions to ask each other about their techniques and conclusions. You can do this as a class, and have the students answer them together as a class, or students can brainstorm in their small groups and then ask them of another group which must answer the questions.

Scientists make their results public. Have the students make a presentation of their research methodology and results for the public. They can do this as individuals or in their small groups. Create a small poster that describes the question to be answered, the methodology used, the data, the results, and the conclusions they can draw from those results. These can be presented to the class or put on display in the hall.

Discussion Questions:

1. Is the total population estimate the true number of individuals in the area?
   
   
2. If you sampled another square meter area, would you get the same population density?
   
   
3. If the objects you were counting were very much larger (trees) or smaller (grains of sands) how would you need to adapt your research design?
   
   
4. Was it difficult to know which objects to count? Were some objects similar but not to be included? (For instance, if you are counting pebbles, when is an object a pebble and when is it sand or rock? If you are counting leaves how small can a leaf fragment be before it is no longer considered a leaf?)
   
   
5. How might wildlife researchers counting populations in a large habitat area decide where and when to sample?

Extensions:

• Students can discuss the various habitat needs for each population and then draw their needs on the mural. For example, squirrels need trees for food and shelter so the students would draw or cut out pictures of trees for their squirrel population.
  
  
• Students could collect various materials from the local area and glue them to the mural (i.e. tundra, grass, rocks, needles).

Suggested Assessment:
Ask the students if a population can include two or more different kinds of animals (Answer: no).

Give the students a worksheet with pictures or drawings of animals. Ask them to state the size of each population.

Credit:
Adapted from Population Posters, Wildlife for the Future - Alaska Wildlife Curriculum, Teacher’s Guide K-8. Alaska Department of Fish and Game.