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Biol 201 4-18-2011

Biol 201 4-18-2011 - of land • How to quantify diversity...

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Community: all the organisms in a defined area (all individuals of all species). We usually talk about Guilds, which is a group of organisms which inhabit a same habitat. Community Structure: Species richness: number of species Species composition: identity of species Species relative abundances o Animas-usually numbers o Plants-usually biomass. Most species are intermediate abundance: percent cover vs number of species of log scale looks like a bell curve or log normal. How to quantify the relative abundance of species? o Look at the evenness: pick a plot of land and measure the distribution in this plot
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Unformatted text preview: of land. • How to quantify diversity: o There are many quantitative measures o Shannon-Wiener index o Maximized for a given S when species are even. H’= -, where s is relative species richness. P i will get close to 1. If one community has a P i = 5/25, 5/25, 5/25, 5/25, 5/25= 0.2, then H’=5 (.2) ln(.2)= ln(.2) = 1.609 Visualizing diversity: species richness: • The flatter the slope of abundance rank vs proportional pulation, the more rich it is. What causes diversity? Communities that have more realized niches have more diversity. • Competition • Disturbance • Predation, mutualism…...
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