Measuring Biodiversity

It is important to take into account that when measuring biodiversity it is being tried to describe the relationship between individuals of varying subspecies within a zone. There are three most common ways of measuring biodiversity.

Species richness (S)

This is one of the most common ways. It Works by counting the subspecies diversity in a specific community. However, this method doesn’t indicate the proportion nor how the species are distributed or organized.

Simpson’s Index (D)

Simpson created this method in 1949, and it’s similar to the previous one. This one works by counting the subspecies (richness) and it also measures the proportion.

The first step to calculate the Index, is calculation Pi which is the abundance of a certain subspecies in a certain zone, divided by the total number of subspecies in the same zone.

Simpson's index: D

D = sum(Pi2)

This one calculates the probability of two randomly selected organisms in the zone, belong to the same species

Simpson’s Index of diversity: 1 – D

This one is the contrary of the previous one: the probability of two randomly selected organisms in the zone, do not belong to the same species.

Simpson’s reciprocal index: 1/D

The last one calculated the amount of equally common subspecies that will produce the observed Simpson’s index.

Like already said, Simpson’s index may be affected by the richness and the equitability of percent of each species present. When talking about the richness, D will decrease as the percentage of species is more equitable.

Shannon-Wiener Index (H)

The last one works with the number of individuals observed for each subspecies located in a sample plot.

This works similarly like the previous one. First, it is necessary to calculate Pi for each category of subspecies. Then, you need to multiply the logarithm of Pi base 10. Then the index is computed with a negative sum. Here is the formula:

H = -sum(Pilog[Pi]) 


Important fact: Knowing the Shannon-Wiener Index and species richness, it may be known the eveness. But, what is eveness? Eveness is the measure of how similar the abundances of different species are. When the evenness is one, it means that they have similar proportions. But when the abundance isn’t similar, the value tends to increase.

"Biodiversity Measures." Raytheon Employees Wildlife Habitat Committe. REWHC, 2000. Web. 18 Aug 2010. <http://www.rewhc.org/biomeasures.shtml>.