Measuring Diversity Community A Community B Species diversity

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. 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 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.

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