Glossary:

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.


Shannon-Weaver Diversity Index: Shannon-Weaver Index combines the number of species present and evenness into a single index:  D = -Σ p_i ln p_i
University of Hawaiʻi at Manoa Biology 301 & 301L Marine Ecology and Evolution and Center for Earth and Environmental Science Indiana University ~ Purdue University, Indianapolis ARBOR Project - BIRD BIODIVERSITY

• n_i  The number of individuals in species i; the abundance of species i.
• S The number of species. Also called species richness.
• N The total number of all individuals
• p_i The relative abundance of each species, calculated as the proportion of individuals of a given species to the total number of individuals in the community: 

The value of D The value of D is highest when species are equally abundant.