Species Diversity in Lacustrine Phytoplankton. I. The Components of the Index of Diversity from Shannon's Formula

Abstract

Seasonal observations on the diversity of phytoplankton communities were made in three lakes in Wisconsin. Extremes in nutrient availability and morphometry in the lakes yielded a range in diversity indexes calculated from Shannon's formula. Examination of the relative importance of the two components in the index indicated that the variability of the index can in large part be attributed to the component of equitability as expressed in the 10 to 15 most abundant species. It appears that with additional species, the positive effect of the component of species richness is countered by the negative effect of the equitability component. Species of low abundance appear to have a minor effect on the index of diversity. The response of the components is discussed in terms of interactions, relationships, and problems associated with estimating the diversity of indefinitely large communities.