Biodiversity Indices

Question 1

Shannon- Wiener diversity index

Answer 1

H = -Σpi * ln(pi)

where:
Σ: A Greek symbol that means “sum”
ln: Natural log
pi: The proportion of the entire community made up of species i

The higher the value of H, the higher the diversity of species in a particular community. The lower the value of H, the lower the diversity. A value of H = 0 indicates a community that only has one species.

Question 2

Simpsons diversity index

Answer 2

Simpson’s Diversity Index -
Where:

D= 1-Σ (ni/ N)^2

D= Diversity
S= no. of species.
ni = number of individuals of species i
N = total number of individuals of all species.

Simpsons diversity index is probability that any two individual randomly selected from a large communtiy will belong to the same species.

There are variations on this theme, e.g. where 1- D is NOT calculated, so index is opposite- higher the value, lower the diversity.

Question 3

Problems with diversity indices

Answer 3

• Diversity cant be estimated in an unbiased way based on a random sample from a community,
• Most species are rare- sampling efforts often dont detect rare species.
• Other methods may be used to measure and equalize sample completeness.
• Some ecologists prefer measuring species richness instead of diversity, but this is still sensitive to relative abundance.