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 Holly (seedlings) 8 56 Bramble 1 Yorkshire Fog Sedge 3 6 Total (N) 15 64

D = 0.3 (Simpson's Index) OR: Simpson's Index of Diversity 1 - D = 0.7 Simpson'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 Holly (seedlings) 8 56 Bramble 1 Yorkshire Fog 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.

H' = -Σ{ pi*ln(pi)} 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

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