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Measuring 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

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Measuring Diversity

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  1. Measuring Diversity

  2. Community A Community B

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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Community A Community B

  9. 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

  10. 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

  11. Community A Community B

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

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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

  18. D = 0.3 (Simpson's Index) OR: Simpson's Index of Diversity 1 - D = 0.7 Simpson's Reciprocal Index 1 / D  = 3.3

  19. 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

  20. 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

  21. 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.

  22. 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

  23. Shannon-Wiener index • Unlike the Simpson index, H is interpreted that the higher the score the more diverse.

  24. What does diversity tell us? • Comparison purposes • Recovery purposes • Community interaction • Community summary

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