Definitions

species richness: the number of species in an area
evenness: all species have the same number of individuals

Calculation

Biodiversity consists of the above two elements, richness and evenness. Richness is the easiest to visualize. Think of two hoola hoops on the ground. If there is only one species inside the first one and four species inside the second one, the second is more diverse. Say there were a third hoola hoop on the ground and it had four species like the second one. However the second hoola hoop may have one individual of each species and the third hoop may have four individuals of the third species and one individual in each of the other species. The second hoop would still contain a more diverse area because none of the plants were dominating. Evenness is considered important in biodiversity, but not as important as richness, both are combined in the Shannon-Weaver index that this site uses. That equation is displayed below.

What are those symbols?

H is the Shannon-Weaver index

The wierd looking E is a greek symbol called sigma used to indicate that the function to the right will be calculated several times and the results added together.

s is the total number of times that the equation is calculated, once for each species.

i indicates which time the equation is calculated.

P is the proportion of individuals out of the total number of individuals.

ln() is the natural log.