Food chains are sometimes short because a. only a single species of herbivore feeds on each plant species. b. local extinction of a species causes extinction of the other species in its food chain. c. most of the energy in a trophic level is lost as energy passes to the next higher level. d. most producers are inedible.
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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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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Textbook Question
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Textbook Question
Which of the following could qualify as a top-down control on a grassland community? a. limitation of plant biomass by rainfall amount b. influence of temperature on competition among plants c. influence of soil nutrients on the abundance of grasses versus wildflowers d. effect of grazing intensity by bison on plant species diversity
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Textbook Question
The most plausible hypothesis to explain why species richness is higher in tropical than in temperate regions is that a. tropical communities are younger. b. tropical regions generally have more available water and higher levels of solar radiation. c. higher temperatures cause more rapid speciation. d. diversity increases as evapotranspiration decreases.
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