Question: Are insects more attracted to male plants? Some scientists wanted to determine whether there are gender-related differences in the level of herbivory (insects munching on plants) for the jack-in-the-pulpit, a spring-blooming perennial plant common in deciduous forests. A study was conducted in southern Maryland at forests associated with the Smithsonian Environmental Research Center (SERC).20 To determine the effects of flowering and floral characteristics on herbivory, the researchers altered the floral shape of male and female plants. The three levels of floral characteristics were as follows:
(1) the outside part of the flower (spathe) was completely removed;
(2) in females, a gap was created in the base of the spathe, and in males, the gap was closed;
(3) plants were not altered (control).
The percent of leaf area damaged by thrips (an order of insects) between early May and mid-June was recorded for each of 30 plants per combination of sex and floral characteristic. A table of means and standard deviations (in parentheses) follows:
(a) Give the degrees of freedom for the F statistics that are used to test for gender, floral characteristic, and the interaction.
(b) Describe the main effects and interaction using appropriate graphs.
(c) The researchers used the natural logarithm of percent area as the response in their analysis. Using the relationship between the means and standard deviations, explain why this was done.