Simpson index

simpson biodiversity index used to measure species richness and evenness of an area

1. WELCOME

2. BY PRIYANKA KUJUR M.SC. ZOOLOGY EVALUATION OF DOMINANCE INDEX

3. Number and variety of organisms within a particular area. 3 main components : Species diversity = no. of different species and no. of individuals of each species within any one community. Ecosystem diversity = diversity of ecosystems within an area. Genetic diversity = genetic variability of species. BIODIVERSITY

4. Using functional categories ecosystem, species, genetic Using theoretical categories Alpha Beta Gamma How do we measure biodiversity ?

5. α diversity : diversity within one habitat. β diversity : diversity along environmental gradient. Diversity comparable between 2 adjacent ecosystems. γ diversity : diversity of the whole landscape.

6. To get a better description of the community we need to get a measure of species richness and evenness of their distribution. Over 60 indices are used in ecology to measure biodiversity. Indices are used to measure proportional abundance. Two major forms : Dominance Indices ( eg . Simpson index) Information Indices ( eg . Shannon Weiner index) DIVERSITY INDICES

7. The Simpson index was introduced in 1949 by  Edward H. Simpson. 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’s index considered a dominance index because it weights towards the abundance of the most common species. SIMPSON INDEX

8. 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. There are two versions of the formula for calculating  D . SIMPSON INDEX D = (n / N) 2 n = the total number of organisms of a particular species N = the total number of organisms of all species  

9. The value of  D  ranges between 0 and 1. With this index, 0 represents infinite diversity and 1, no diversity. That is, the bigger the value of D, the lower the diversity. This is neither intuitive nor logical, so to get over this problem, D is often subtracted from 1 to give: SIMPSON INDEX

10. Simpson's Index of Diversity  (1 -  D) The value of this index also ranges between 0 and 1, but now, the greater the value, the greater the sample diversity. This makes more sense. In this case, the index represents the probability that two individuals randomly selected from a sample will belong to different species. SIMPSON INDEX

11. Simpson's Reciprocal Index (1 / D) It provides the number of equally common categories (e.g., species) that will produce the observed Simpson's index. Ranges between 0 and total no. of species collected. The higher the value, the greater the diversity. SIMPSON INDEX

12. The diversity of the ground flora in a woodland. Example : Species Number (n) n(n-1) Woodrush 2 2 Holly (seedlings) 8 56 Bramble 1 Yorkshire Fog 1 Sedge 3 6 Total ( N ) 15 64

13. Putting the figures into the formula for Simpson's Index                   D = 0.3   (Simpson's Index) Then: Simpson's Index of Diversity 1 - D = 1 - 0.3 = 0.7 Simpson's Reciprocal Index 1 / D  = 1 / 0.3 = 3.3

14. Low species diversity suggests: Relatively few successful species in the habitat. The environment is quite stressful with relatively few ecological niches and only a few organisms are really well adapted to that environment. Food webs are relatively simple. Changes in the environment would probably have quite serious effects.

15. High species diversity suggests: A greater number of successful species and a more stable ecosystem. More ecological niches are available and the environment is less likely to be hostile. Complex food webs. Environmental changes is less likely to be damaging to the ecosystem as a whole.

16. Does not require all species be represented. Measures chance that two individuals are from same species Sensitive to changes in common species Weighted towards most abundant species Opposite of dominance Advantages and Disadvantages of Simpson’s Index

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