Homework #7

PCB 6466: Homework 7
DUE TUE Oct 20
1. A classical, agricultural experiment (the yields.txt data set) grew a variety of wheat with
the same fertilizer amounts and water, but in three different soils, where randomlyselected fields were in either sandy, clay, or loam soils. Did soil type significantly affect
wheat yield (bushels/acre)? If so, which treatments differed from which other treatments
and by how much, on average?
2. Tannins are a complex mix of organic compounds produced by plants. One hypothesis is
that they are just waste products. Another is that they combat predators, such as
caterpillars. An experiment was conducted by feeding artificial diets dosed with different
levels of tannins to caterpillars raised under the same conditions (tannins.txt). The
experiment did not have replicates of each tannin level but did have a control. The
hypothesis was that more tannin led to less caterpillar growth. Was the hypothesis
supported? If so, how much effect did tannin have on growth?
3. Some plant extracts may be anti-cancer agents (or may have no real effect). An
experiment was conducted with 3 plant extracts (Drugs A, B, & C) and controls (the same
drug that would be used as a placebo. Cultures of cancer cells were dosed with the same
concentrations of all drugs and then the percent of dead cells was counted (cancer.txt).
Did plant extracts cause significant cancer cell death? If so, which treatment worked
4. Competition by exotic species may inhibit success of threatened species. An experiment
(competition.txt) first heat-treated soils to kill most seeds, then mixed the soil and seeded
random plots with a threatened species by itself (solo), or together with one of three
exotic species. All plots had the same initial total number of seeds. At the end of the
growing season the biomass (dry weight) of the threatened species was measured. Did
exotic species significantly inhibit growth of the threatened species? If so, how would
you rank the exotics for their inhibitory effect on the threatened species?