ENVS-438,538 Lecture 5 - Measuring Diversity Measuring...

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Measuring Diversity
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The methods we will discuss potentially apply to many levels of biodiversity, but we will focus on the species level. The general approach of these methods is to test whether the number of species observed in a set of samples corresponds to some other factor of interest. Examples: Sites / locations Latitudes Seasons Ecosystems Measuring Diversity
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Measuring species diversity Species richness = a count of the number of species that occur within the community Relative abundance = the percentage that each species contributes to the total number of individuals of all species in a community. Rank abundance diagram : Species ranked most to least abundant on x-axis, with relative abundance for each on y- axis Rank abundance curves for two forest communities in West Virginia where one has greater species richness.
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Approximately the same number of trees were counted in each forest First forest had 24 species, the second forest had only 10 tree species. Species evenness: the distribution of individuals among species in a community. The first forest had greater species evenness.
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Methods of assessing biodiversity Ex) Two college campuses surveybird species: •To measure species diversity, need to incorporate both o Number of species o Proportions ofspecies Type of Bird Campus A Campus B Starling 96 20 American robin 1 20 Blue jay 1 20 Common grackle 1 20 House sparrow 1 20
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Shannon Diversity Index (H) P indicates the percent presence of a species. Take natural logofeach species’ presence, multiplybyoriginal value and sum between the whole communityto get H One species, H = 0 Maximum H = ln (sample size)
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Ln (5) = 1.61 Thus, Campus B is as diverse as a five-species community can possibly be! Type of Bird Campus A Campus B Starling 96 20 American robin 1 20 Blue jay 1 20 Common grackle 1 20 House sparrow 1 20 H 0.223 1.610 Shannon Diversity Index (H)
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Simpson’s index (D) measures the probability that two individuals randomly selected from a sample will belong to the same species. The number D decreases as diversity increases. Consequently the usual way this Simpson’s index is expressed is as the inverse (1/D). The lowest possible value is 1, which is a community of just one species.
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Fundamental Empirical Observations: The more we sample, the more species we observe (“accumulate”). In general, the rate of recording new species decreases with sampling effort. Species accumulation curves generally approach an upper limit or asymptote. The relationship of diversity to sampling effort is not constant across sites.
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Fundamental Empirical Observations: This means we need special statistical tools to analyze and compare species diversity across samples. MEASURING AND ANALYZING SPECIES ACCUMULATION
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SPECIES ACCUMULATION CURVES
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EstimateS software EstimateS 8.2 User's Guide Last Revised July 20, 2009 Copyright 2009 by Robert K. Colwell , Department of Ecology & Evolutionary Biology, University of Connecticut, Storrs, CT 06869-3043, USA Website: or
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A worked example of analyzing Species richness data: Bird-army ant interactions in Costa Rican montane forest
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Army ant bivouac Swarm pattern Raid party
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Bird flocks form at army ant swarm fronts Birds feed on prey that is fleeing the ants
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Multiple bird species attend raids together Birds interact at raids, and may affect each other’s foraging
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