Oct. 12, 2011

Field Problem: Variation Within a Population

by Coastal Studies for Girls

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By Nell and Loraine, Coastal Studies for Girls


Last Monday, Coastal Studies for Girls took a field trip to the shore by Wolfe’s Neck Farm to do some research in the field and look at variation within a population. The goal was to collect smooth periwinkles (Littorina obtusata) and record data on the snails. The original aim was to collect 195 individuals and to measure size and color for each.

Smooth periwinkles, Littorina obtusata

We worked together to find the height, width, mass, and color of each individual snail. Although we did not collect all 195 individuals, we still gathered a large amount of data, and had plenty of individuals to determine average characteristics and observe variability.

When we first arrived at the rocky intertidal zone, we used a sight level and meter stick to determine tidal height, and to divide the rock ledge into three horizontal sections of rocky intertidal habitat. Next, we set loose in teams -- one team in each section. We collected dozens and dozens of snails. Then we quickly and efficiently measured the periwinkles with a compass and ruler. We found their masses using an electronic balance. Last, but certainly not least, we identified the shade of the periwinkles using a color wheel that we had numbered for recording purposes.

This field problem was designed mostly to study biological variation within populations in the environment. By keeping data on traits of periwinkles from each section of tidal height, we can test whether traits vary with height in the tidal column. This gives us a close-up look at the raw material that natural selection acts upon.

When we continue to work on this lab in class this week, we will discuss what the average size/color is, how it differs from section to section, and why this may be. Hopefully when we do some tests with these data, this field problem will give us an even better understanding of natural selection at work and the range of biological variation.

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Coastal Studies for Girls is the country’s only residential science and leadership semester school for 10th grade girls. CSG is dedicated to girls who have a love for learning and discovery, an adventurous spirit, and a desire to challenge themselves.

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Coastal Studies for Girls is the country’s only residential science and leadership semester school for 10th grade girls.

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