Measuring Diversity

Community A Community B

Species diversity

• Often defined as a combination of the number of species and their relative abundance.

Diversity Divisions

• Alpha diversity refers to species richness

• Beta diversity describes the degree of change in species richness from one habitat to another.

• Gamma diversity relates to the total regional species diversity that results from the number of habitats present.

Diversity Divisions

• Alpha diversity refers to species richness

• Beta diversity describes the degree of change in species richness from one habitat to another ~ habitat patchiness

• Gamma diversity relates to the total regional species diversity that results from the number of habitats present.

Diversity Divisions

• Alpha diversity refers to species richness

• Beta diversity describes the degree of change in species richness from one habitat to another.

• Gamma diversity relates to the total regional species diversity that results from the number of habitats present.

Number of species

• Species richness– Method – simply count the number of different

species you observe, regardless of abundance. – Therefore, if a species occurs 1 or 100 times, its

richness is still 1.

Community A Community B

Relative Abundance

• Species evenness = assesses the relative numerical importance of each species– the contribution of each species to the total

number of individuals in the community

Relative Abundance

• Method – count up the number of each individual observed or collected and divide by the total number observed or collected.– RA = n/N

• the percent contribution made by each species to the community

Community A Community B

Simpson Index

• A measurement that accounts for the richness and percent of each species from a biodiversity sample within a community.

Simpson Index

• This index assumes that the proportion of individuals in an area indicates their importance to diversity.

• So, it measures not only diversity but dominance as well.

Simpson Index

• Can actually refer to any one of 3 closely related indices.– Simpson's Index (D) measures the probability

that two individuals randomly selected from a sample will belong to the same species

• Ranges between 0 and 1, the lower the value, the greater the sample diversity

Simpson Index

• Simpson's Index of Diversity 1 – D measures the probability that two individuals randomly selected from a sample will belong to the same species– Ranges between 0 and 1, the greater the value,

the greater the sample diversity

Simpson Index

• Simpson's Reciprocal Index 1 / D provides the number of equally common categories (e.g., species) that will produce the observed Simpson's index.

– Ranges between 0 and total # species collected, the higher the value, the greater the diversity

Species Number (n) n(n-1)

Woodrush 2 2

Holly (seedlings) 8 56

Bramble 1 0

Yorkshire Fog 1 0

Sedge 3 6

Total (N) 15 64

D = 0.3 (Simpson's Index)

OR:Simpson's Index of Diversity 1 - D = 0.7Simpson's Reciprocal Index 1 / D  = 3.3

Simpson Index

• Simpson's Index gives more weight to the more abundant species in a sample. The addition of rare species to a sample causes only small changes in the value of D

Species Number (n) n(n-1)

Woodrush 2 2

Holly (seedlings) 8 56

Bramble 1 0

Yorkshire Fog 1 0

Sedge 3 6

Total (N) 15 64

Shannon-Wiener index

• Also been called the Shannon index and the Shannon-Weaver index.

• Used to compare diversity, doesn’t give a measure of dominance.

• Similar to Simpson's Index, this measure takes into account species richness and proportion of each species within a community.

where H = Information content of sample, Index of species diversity, or Degree of Uncertainty, s = Number of species pi = Proportion of total sample belonging to ith species

IN EXCEL = LN (pi) will give you the natural log

H' = -Σ{ pi*ln(pi)}

Species Name # Found Pi Pi

2 Piln[Pi] Measure Value

Species 1 40 0.2 0.04 -0.322 S 5Species 2 40 0.2 0.04 -0.322 D 0.2Species 3 40 0.2 0.04 -0.322 1 - D 0.8Species 4 40 0.2 0.04 -0.322 1/D 5Species 5 40 0.2 0.04 -0.322 H 1.609Totals 200 1

Species Name # Found Pi Pi

2 Piln[Pi] Measure Value

Species 1 1 0.005 0 -0.026 S 5Species 2 1 0.005 0 -0.026 D 0.96Species 3 196 0.98 0.961 -0.02 1 - D 0.04Species 4 1 0.005 0 -0.026 1/D 1.041Species 5 1 0.005 0 -0.026 H 0.126Totals 200 1

Shannon-Wiener index

• Unlike the Simpson index, H is interpreted that the higher the score the more diverse.

What does diversity tell us?

• Comparison purposes

• Recovery purposes

• Community interaction

• Community summary