Snail shell temperature


Use this diagram to explain that pairing reduces the effect of variability between individuals. State that the two distributions overlap considerably because of the variability in the exposure to sunlight in the different sites.

Click on individual crosses. Although the yellow shell is sometimes a little warmer, the brown shell is usually considerably warmer.

Click Show Pairing. Most lines are sloped upwards and most differences are positive — much clearer evidence that the mean temperature is higher for the brown shells.

A land snail (Ceaea nemoralis) is more often brown-shelled than yellow-shelled in cooler areas. Pairs of shells were exposed to sunlight at the same time and in the same orientation. Temperatures in degrees Celsius are shown.