Lab 09 Community Measures

Lab 09 Community Measures - COMMUNITY MEASURES Lab 9...

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COMMUNITY MEASURES Lab 9 9-1 Reminders ! Memory Stick or Floppy Disk Calculator Key Concepts Community Species Richness Species Evenness Species Diversity Community Similarity I. COMMUNITY A community is the assemblage of interacting populations inhabiting the same area. In general terms, an ecological community includes all species within an area; however, ecologists are often interested in addressing hypotheses about specific groups of species (e.g. birds or plants), therefore terms like “bird community” are common in ecology. A community should not be confused with an ecosystem. An ecosystem is comprised of one or more communities and their physical environment. Ecosystem studies are usually specifically focused on energy flow or nutrient cycling, while community studies usually focus on specific groups of species. Communities can be characterized by their species richness, species evenness, species diversity, relative species abundance, and trophic structure. Today we will focus on richness, evenness, and diversity. We will also use measures of community similarity to quantify how similar (or different) the communities are in your plots on Wa’ahila Ridge. II. SPECIES DIVERSITY Species richness is simply a count of the number of species in a community. Species richness may be a good initial descriptor of community diversity, but it tells us nothing about the relative abundance of different species in a community. For example, consider two communities, A and B, which each contain 10 species. 99% of the individuals in Community A are from one species, and 1% of the individuals are from the remaining nine species. When walking through community A, you will probably see only one species, unless you look very carefully for the other nine rare species. Community A is not very diverse. In Community B, each species comprises 10% of all individuals. Community B has higher diversity because the species abundances are more even. Walking through community B, you would probably find all 10 species within an arms reach. Species diversity is a combined measure of species richness and abundance. High species diversity is associated with both high species richness and evenness. In order to calculate such measures of diversity, we first need to determine the proportional representation of each species in the community – the relative density or relative % cover (see lab 4). Density refers to the number of individuals of a species per unit area. Relative density is useful for calculating diversity when species in the community are similar in size. Relative percent cover is the fraction of area in a community (not counting bare areas) that is covered by a given species. If you are considering different sized organisms, like grasses, herbs, and trees, then percent cover gives a better idea of what a community looks like than does density. A drawback of percent cover is that such data can usually only be obtained for species that do not
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This note was uploaded on 04/10/2008 for the course BIO 265L taught by Professor Fukami during the Fall '07 term at Hawaii.

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Lab 09 Community Measures - COMMUNITY MEASURES Lab 9...

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