Refer to Exercise 16.23. Biologists have noted that in many environments the annual precipitation is not the crucial factor in the survival of many types of foliage; rather, it is the amount of precipitation during the dry season. Repeat Exercises 16.23 and 16.24 using the dry season precipitation in place of the annual precipitation. Are there any differences in your conclusions?
Pyke et al. (2001) describe a study that deals with the floristic composition of lowland tropical forest in the watershed of the Panama Canal. The following variables were measured on 45 plots in five regions: Stems—number of tree stems; Species—number of tree species; Fisher’s alpha and Shannon index (H), which are measures of biodiversity of the foliage; Topography—l 5 level terrain, 2 5 sloping, 3 5 irregular; Age—1 5 secondary forest, 2 5 mature secondary, 3 5 old growth, primary forest; Ppt 5 annual precipitation (mm); PptDry 5 dry season precipitation (mm).
a. Is there significant evidence of a difference among the three age classifications of the forests relative to their biodiversity as measured by Fisher’s alpha. Use annual precipitation to adjust for differences in the five regions.
b. Provide a grouping of the three age classifications based on their adjusted mean Fisher’s alpha.
c. Using residual plots, evaluate whether the conditions needed to properly answer parts (a) and (b) are valid for this data set.