This lecture is based on the research, ongoing, of a group of ecologists at the U. of Minn., headed by David Tilman. I've taken most of these data from a 1994 publication. Before looking at Tilman's data, we need to go over some basic definitions from ecology.
Diversity is estimated by sampling.
It is important to note that good sampling proceedures are very important in determining diversity, because most communities have a few very common species, and many, more rare, species. In this case, diversity is necessary because it makes communities more stable. In this case, diversity is not necesssary for stability as long as some members of each functional group are present. Many, many years of observational data grew into these two competing models, and we are not going to consider these histories. Instead, we will look at an early result from Tilman's continuing research.