Species Diversity Indices

The concept of'biological diversity' has become popularized and is often thought to be a measure of species variety. Nothing could be further from the truth. The Biological Diversity Convention clearly defines biological diversity in terms of the variety at all levels of biological organization. This includes species diversity. However, measures of species diversity have been used for a long time and well before the concept of biological diversity was popularized by way of the 1992 Convention on Biological Diversity.

Species richness is simply the number of species in a certain area or sample. Species richness is a measure of the variety of species and is based simply on a count of the number of species in a particular sample.

Species diversity can be calculated in many ways and can be expressed in different ways. There are therefore many indices of species diversity. Some are calculated in a very simple manner while others are based on some interesting mathematics. An index of species diversity can be calculated by either using a combination ofspecies richness and species composition or can be based on a combination of species richness and the relative abundance of each species. For example, one simple measure or plant species diversity is based on percentage cover as a measure of abundance and is expressed as follows:

P x2

where D is the index ofdiversity and x is a measure ofthe abundance of the species.

In simple terms, maximum diversity (equitability) exists if each individual belongs to a different species. Minimum diversity exists if all individuals belong to one species.

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