Calculating diversity

Abundance: The actual number of organisms of a species per unit of area or volume (Density).

Relative Abundance: The proportion or percentage of all organisms in a community or sample that are a particular species (Species Eveness).

Sampling effort: With a “small” sample rare species are not likely to be included. With a larger sample, rare species are more likely to be included.

Species Diversity: Two factors define species diversity. Species Richness, which is the number of species in community and Species Evenness, which is the Relative Abundance of the species.

Diversity: A community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance. As species richness and evenness increase, so diversity increases.

Simpson's Diversity Index: The Simpson's Index (D) is a measure of diversity which takes into account both richness and evenness. Simpson's Index (D) measures the probability that two individuals randomly selected from a sample will belong to the different species (or some category other than species). The formula for calculating D is

D = 1- [Sum(n / N)²]

n = the total number of organisms of a particular species

N = the total number of organisms of all species

The value of D ranges between 1 and 0. With this index, 1 represents infinite diversity and 0, no diversity. That is, the bigger the value of D, the greater the diversity.