Measurements of biodiversity

A variety of objective measures have been created in order to empirically measure biodiversity. The basic idea of a diversity index is to obtain a quantitative estimate of biological variability that can be used to compare biological entities, composed of direct components, in space or in time.

Three sorts of indices can be distincted:

1. Species richness indices: Species richness is a measure for the total number of the species in a community but in practice is the actual number of the species in the community usually immeasurable.

2. Evenness indices: Evenness expresses how evenly the individuals in a community are distributed over the different species.

3. Taxonomic indices: These indices look after the taxonomic relation between different organisms in a community, for example the mean taxonomic distance between two organisms. Taxonomic diversity can be visualized by the distance to connect two organisms along the branches of a phylogenetic tree.

These indices can be used on different spatial scales:

• Alpha diversity refers to diversity within a particular area, community or ecosystem, and is measured by counting the number of taxa within the ecosystem (usually species)

• Beta diversity is species diversity between ecosystems; this involves comparing the number of taxa that are unique to each of the ecosystems.

• Gamma diversity is a measure of the overall diversity for different ecosystems within a region.