Master Advanced Placement (AP) with Fun Quizzes & Brain Teasers!
Environmental scientists are often interested in evaluating both species richness and species evenness, so they have come up with milesspecies diversity that take both measures into account. One commonly used index is Shannon's index of biodiversity. To calculate this index,we must know the total number of species in the community (s) and, for each species, the proportion of the individuals in the community thatrepresents that species (p). Once we have the information, we can calculate Shannon's index of diversity (H) by taking the product of eachproportion (0) and its natural log (In ()) and then summing these products, as indicated by the summation symbol (E):H-- pin(p)whereH = the Shannon index valueP, = the proportion of individuals found in the ith speciesIn = the natural logarithmS = the number of species in the communityThe minus sign makes the index a positive number. Higher values of Hindicate higher diversityNote: the book uses "n" and the formula I found online uses "s" for the number of species in the community.Imagine a community of 100 individuals that are evenly divided among four species, so that the proportions () of the species all equal 0.25.We can calculate Shannon's index as follows: H = -((0.25 x In 0.25) + (0.25 x In 0.25) + (0.25 x In 0.25) + (0.25 x in 0.25)] H-[(-0.35)+(-0.35) + (-0.35) + (-0.35)] 1.40Now imagine another community of 100 individuals that also contains four species, but in which one species is represented by 94 indiviudalsand the other three species are each represented by 2 indivudals. We can calculate Shannon's index to see how this difference in speciesevenness affects the value of the index: H = -[(0.94 x in 0.94)+ (0.02 x In 0.02) + (0.02 x In 0.02) + (0.02 x in 0.02)] H=-[(-0.06) + (-0.08) + (-0.08) + (-0.08)] 0.30Because this value of His lower than the value we calculated for the first community, we can conclude that the second community has lowerdiversity. Note that the total number of indiiduals does not affect Shannon's index of diversity, only the the number of species and theproportion of individual within each species matters.Your TurnImagine a third community of 100 individual in which those indviduals are distributed evenly among all the species, but there are only twospecies, not four. Calculate shannon's index to see how different in species richness affects the value of the indexShannon's index.HeKif the answer is less than tha Zero belongs in front of the decimall