Simpson’s Diversity Index To measure the diversity in an ecosystem

Simpson’s Diversity Index Attempts to quantify the diversity (variety) of an ecosystem. There are two components: Evenness Richness

Evenness Evenness is a measure of the relative abundance of the different species within an area. (Same amount of each kind of organism) When the numbers of each type of species is even, the value for the Simpson Diversity Index will be larger.

Richness = variety Richness is a measure of the number of kinds of species More species is “richer” so the value for the index will be higher.

High Richness Native Valdivian Temperate Rainforest

Low richness (Pinus Radiata forest)

The equation D = N(N - 1)  n(n -1) D = diversity index   D = N(N - 1)  n(n -1) D = diversity index N = total number of organisms of all species found n = number of individuals of a particular species

How to Calculate D: D = N(N – 1)  n(n -1) Record the numbers of each species Calculate n-1 for each species Find the total number of organisms, N Calculate the Simpson Diversity Index D = N(N – 1)  n(n -1)

Let’s Try an Example n You have studied a specific site, and have counted the individuals of five different species. n is the total number of organisms of a particular species. Species A 12 Species B 3 Species C 7 Species D 4 Species E 9 Page 11 Teacher Zone nature.ca/education

Simpson’s Index n n - 1 n(n - 1) ∑ n(n - 1) = 264 ∑ n(n - 1) = D Species A 12 11 132 Species B 3 2 6 Species C 7 42 Species D 4 Species E 9 8 72 ∑ n(n - 1) 264 ∑ n(n - 1) D = N(N - 1) ∑ n(n - 1) = 264 Page 12 Teacher Zone nature.ca/education

N = total number of all individuals = 35 Simpson’s Index ∑ n(n - 1) 264 D = = N(N - 1) N(N - 1) N = total number of all individuals = 35 N - 1 = 34 N(N - 1) = 1190 264 D = = 0.22184 1190 This area would score 0.22184 on the Simpson’s Index. The scale ranges from 0–1, with 1 representing the lowest biodiversity. Therefore, the score for this area indicates a high level of biodiversity. Page 13 Teacher Zone nature.ca/education

Calculate the Simpson’s Diversity Index for each sample Compare the evenness and richness of each sample.

Answers Sample One: 2.99 Sample Two: 1.15 Both have the same richness as there are three species in each area. Sample One is more even because the numbers of each kind of species are nearly the same.

A high value of D suggests a stable, complex and diverse ecosystem.

A low value of D could suggest pollution, recent colonization or agricultural management. Eukalyptus plantation Deforestation in Chile

The lowest value of D is 1.0 (monoculture)

Compare Simpson’s Diversity Index for a tropical rainforest vs a desert

Biodiversity at Sites in Honduras The following calculations are based on sampling conducted in Honduras by Canadian Museum of Nature research scientist Bob Anderson. Site N N(N - 1) ∑ n(n - 1) D Species Richness Cerro Montecristo 2996 7 120 892 1 600 002 0.2247 61 El Pital 2050 m 233 54 056 6856 0.1268 22 El Pital 2650 m 5411 29 273 510 12 873 694 0.4398 46 Cerro Puca 311 96 410 19 126 0.1984 27 Santa Barbara 839 703 082 55 514 0.0789 44 Page 14 Teacher Zone nature.ca/education

Biodiversity at Sites in Honduras Which site has the highest species richness? Which site is the most diverse according to the Simpson’s Index? (HINT: Has the lowest D). Do any sites have both a low Simpson’s Index and high species richness? Which one(s)? Page 15 Teacher Zone nature.ca/education