Crab spiders use camouflage to hide on flowers while lying in wait to prey on other insects. Ecologists theorize that this natural camouflage also enables the spiders to hide from their own predators, such as birds and lizards. Researchers at the French Museum of Natural History conducted a field test of this theory and published the results in Behavioral Ecology (Jan. 2005). They collected a sample of 10 adult female crab spiders, each sitting on the yellow central part of a daisy.
The chromatic contrast between each spider and the flower it was sitting on was measured numerically with a spectroradiometer, on which higher values indicate a greater contrast (and, presumably, easier detection by predators). The data for the 10 crab spiders are shown in the following table and saved in the SPIDER file.
a. Summarize the chromatic contrast measurements for the 10 spiders with a stem-and-leaf display.
b. For birds, the detection threshold is 70. (A contrast of 70 or greater allows the bird to see the spider.) Locate the spiders that can be seen by bird predators by circling their respective contrast values on the stem-and-leaf display.
c. Use the result of part b to make an inference about the likelihood of a bird detecting a crab spider sitting on the yellow central part of a daisy.

  • CreatedMay 20, 2015
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