Exercise 1: Caleulating Species Diversity Ecologists agree that communities with
ID: 209862 • Letter: E
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Exercise 1: Caleulating Species Diversity Ecologists agree that communities with more species and greater evenness have higher species diversity. To quantify the species diversity of a community, we need a method of calculating a single value for species diversity. Over the years, numerous indices of species diversity have been created. We will consider the two that are most common and equally valid: Simpson's index and Shannon's index. Both indices incorporate species richness, which we abbreviate as S, and evenness. However, they do so in different ways. To see how we calculate species diversity with either iridex, we can begin with data from three communities for which we have the absolute abundance for each of the species. From these data we can then calculate relative abundance for each of the fivespecies in the community, which is denoted Pi. With these relative abundance data, we can calculate both Simpson's index and Shannon's index Table 1: The abundance of different mammal species in three communitiess Co Community B Absolute Relative Absolute Relative Absolute Relative (p) abundance abundance (p) abundance abundance (p) Species abundance Mouse Chipmunk Squirrel 24 16 0.24 0.16 Shrew0.08 0.34 20 23 100 34 VoleTotal100 0.18 1.0 1.0 0.99 abundance 100 Simpson's index (D),ameasurement of species diversity, is given by the following formula: In words, this formula means that we square each of the relative abundance values sum these squared values, and then take the inverse of this sum. For example, for Community A, Simpson's index of species diversity is: (0.24) + (0.1 6) + (0.08)2 +(0.34% + (0.18) 4.21 Simpson's index can range from a minimum value of 1, which occurs when a community only contains one species, to a maximum value equal to the number of species in the community. This maximum value only occurs when all the species in the community have equal abundances.Explanation / Answer
Simpson's index:
For B, D = 1 / (0.18)^2 + (0.22)^2 + (0.20)^2 + (0.17)^2+ (0.23)^2 = 4.936
For C, D = 1 / (0.33)^2 + (0.33)^2 + (0.33)^2 + (0)^2+ (0)^2 = 3
Shannon's index :
For B, H' = - [ (0.18)ln(0.18) + (0.22)ln(0.22) + (0.20)ln(0.20) + (0.17)ln(0.17) + (0.23)ln(0.23)] = - [-0.309 - 0.333 - 0.322 - 0.301 - 0.338] = 1.603
For C, H' = - [ (0.33)ln(0.33) + (0.33)ln(0.33) + (0.33)ln(0.33)] = 1.098
As species richness and evenness increase, diversity also increases. Simpson's Diversity Index and Shannon's Index too is a measure of diversity which takes into account both richness and evenness. Thus more the Simpson's Diversity Index / Shannon's Index more is species evenness and richness.
Species Community B Community C Relative abundance Relative abundance Mouse 0.18 0.33 Chipmunk 0.22 0.33 Squirrel 0.20 0.33 Shrew 0.17 0 Vole 0.23 0Related Questions
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