Lab Exercise

# Biology Lab: Population Density

Concept: Energy flows from sun to plants to animals, with decreasing amounts reaching each successive level.

AP Exam preparation -- Doing the AP version of this lab:

Please read through the 2012 AP Biology Lab Manual, Investigation #10: Energy Dynamics. This lab requires you to grow plants and raise butterflies, then monitor their behavior, so you must plan on at least two weeks to carry out this investigation. Of course, if you are able to arrange to perform the AP lab with a local homeschool group or a biology tutor, then you should do so.
If you are unable to do AP lab #10 as written, you may perform the alternative population density study below.

## Goal: To determine the population density of a given area for two species, plant and animal

### Equipment:

• Measuring stick or tape
• String and sticks
• Field Guide

### Procedure:

1. Select the area for your survey. Try to avoid yards, which tend to be landscaped; if possible, use a natural area. Be sure that you can work in it undisturbed for several hours.
2. Mark the boundaries of your survey by placing sticks at the corners and wrapping string between them. You should try for an area about10 meters by 10 meters, if possible. It does not have to be a perfect square -- but 100 square meters is a good sample area.
3. Survey your area. Select a single plant that occurs throughout the area. [If you are stuck with the front lawn, weeds are a good choice.]
4. Watch your area for awhile, and select an animal that you find there. Insects like beetles, or small mollusks such as snails are good choices for a yard.
5. Perform a sample counting survey of 10 1-meter square areas for your plant.
6. Determine the density of the plant, and its dispersion pattern.
7. Choose a DIFFERENT set of 10 1-meter square areas and count your plant again. Do the results radically change? Why? In particular, consider
• variations in sunlight (energy) available in each area due to direction of slope or shade.
• variations in water available due to slope (drainage) or other plants (trees may drain water out of the soil)
• competition from other plants
• human or wild animal traffic through the area
8. Survey your area for your animal (this may be a lot harder). If you have permission to trap and can do so without hurting the subject, use the mark and recapture method. If not, take your samples at dawn or dusk and at midday. You will have to determine the number and location of the regions based on the terrain.
9. Determine the population density and dispersion pattern of your animal. Does dispersion for your animal appear to depend on the same factors as the dispersion pattern for your plant?

### Report

1. Describe your experimental setup, especially if you needed to improvise.
2. Present your data in tabular format, organized so that the reader can see how you did your calculations for density.
3. How is the dispersion pattern and density of each species affected by the terrain?