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Ch. 54 - Community Ecology
Chapter 54, Problem 9

Community 1 contains 100 individuals distributed among four species: 5A, 5B, 85C, and 5D. Community 2 contains 100 individuals distributed among three species: 30A, 40B, and 30C. Calculate the Shannon diversity (H) for each community. Which community is more diverse?

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1
Calculate the proportions of each species in each community. For Community 1: pA = 5/100 = 0.05, pB = 5/100 = 0.05, pC = 85/100 = 0.85, pD = 5/100 = 0.05. For Community 2: pA = 30/100 = 0.3, pB = 40/100 = 0.4, pC = 30/100 = 0.3.
Apply the Shannon diversity index formula: H = -\sum (p_i \times \ln(p_i)), where p_i is the proportion of each species.
Calculate H for Community 1: H1 = -(0.05\ln(0.05) + 0.05\ln(0.05) + 0.85\ln(0.85) + 0.05\ln(0.05)) = 0.544.
Calculate H for Community 2: H2 = -(0.3\ln(0.3) + 0.4\ln(0.4) + 0.3\ln(0.3)) = 1.029.
Compare the Shannon diversity indices: H1 = 0.544 and H2 = 1.029. Community 2 is more diverse than Community 1.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Shannon Diversity Index

The Shannon Diversity Index (H) is a mathematical formula used to quantify the diversity of a community. It takes into account both the number of species and the evenness of their distribution. The formula is H = -Σ(p_i * ln(p_i)), where p_i is the proportion of individuals belonging to species i. A higher H value indicates greater diversity.
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Species Richness

Species richness refers to the number of different species present in a community. It is a simple count of species and does not consider the abundance of each species. In the context of the question, Community 1 has four species while Community 2 has three, which contributes to the overall diversity assessment.
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Evenness

Evenness measures how evenly individuals are distributed among the different species in a community. It is an important component of diversity, as communities with a few dominant species and many rare ones have lower evenness. In calculating the Shannon diversity, both species richness and evenness are considered to determine which community is more diverse.
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