Natural Science - Year II

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Lab for Unit 57

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# Unit 57 Laboratory Activity: Field Observations

## Goal: Field studies of an area.

### Materials

• Study area
• Materials for recording observations (pen/pencil, paper, camera)
• String and measuring tape

### Procedure

1. Chose a natural or mostly natural area to which you can have access at least twice for up to an hour during your study period.
2. Measure an area 6 feet by 6 feet (or 2 meters by 2 meters). Place sticks in the ground at the corners and use your string to mark the boundary.
3. Count EVERY non-microscopic organism you can observe in the area.
1. If necessary for certain organisms, use a sampling technique. For example, for blades of grass, count the number of blades in a 2" x 2" area, and repeat for 5-10 areas (until your patience runs out). Determine the total number counted and the total area included in your count.
2. Figure out what proportion of your total field area (6x6 ') your sample area covers. For example, if you have a 6x6' area, you have a 72x72 inch area or 5184 inches. If you counted 152, 79, 331, 16, and 222 blades of grass in 5 2*2" areas, you have a total of 800 blades of grass in 5 * 4 sq. inches= 20 square inches. The ratio of grass to inches is 800/20 and this proportion should hold true (assuming similar conditions throughout your area) throughout the whole area. So you have 800/20 = x/52200. x = 55184* 800/20, or 207360 blades of grass in your sample area (which is why you don't want to count the whole thing).
3. Estimate the accuracy of your sampling. Since in this particular case, we had a wide variation in sample counts, the result is probably not very good. If our sample counts had been 157, 163, 159, 161, 160, for example, we could have assumed a more uniform distribution of our 800 leaves of grass and a high accuracy of our total for the whole area.
4. Use this method for other populations as necessary. [I used this method the last time I turned the compost heap and came up with approximately 20,000 sow bugs in my compost, based on the surface concentration when I first opened the lid and the volume of the bin. However, the population density of the sow bugs was much less in the middle of the compost, so it only looked really awful. It was actually merely mildly awful.]
4. Repeat counts for at least two species at another time of day at least two days after your first observations.