Ch 7 - Study Guide Chapter 7 Study Guide Chapter 7 The book talks about the American alligator as a keystone species because of its pivotal role in

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Study Guide - Chapter 7 Study Guide – Chapter 7 The book talks about the American alligator as a keystone species because of its pivotal role in the ecosystems in which it lives. We talked about the importance of keystone species; these are organisms that we must identify and conserve because their activities have such an important impact on the structure and function of the entire biotic community. Communities are often identified based on dominant species that create the habitat, e.g., an oak-hickory community, or a Spartina marsh community. Obviously there are hundreds of other species of plants and animals present, but identifying the visually dominant species will often tell us quite a lot about the other types of organisms that make up that community. The book talks about edge , where two communities meet, e.g., when a forest becomes grassland. We will talk more about edge later, as it has some important effects on wildlife. If it is a natural edge, it is much like the ecotone we discussed in class, which may have unique flora and fauna that are not abundant in either of the other two community types. We can use species diversity to describe a biological community, and diversity is composed of richness , the number of species, and evenness , which is the abundance of individuals within each species. On page 145, I believe the authors made a mistake. In paragraph 3, the book gives and example of a community composed of 10 individuals within each of 20 species, versus a community with 10 species each containing 2 individuals and 10 other species containing 18 individuals. Each community has 20 species and 200 individuals, and the book asks which has the highest richness. Both communities have 20 species, so the richness is the same, so unless the book was trying to be clever, a better question is which community has more evenness? Even if you do not know how evenness is calculated, by the nature of the term, a community in which all species are equally abundant would be as even as you could get. The book is in error at the bottom of the first column on p. 145, which talks about a high richness (lots of species) community with each species having few individuals as low evenness; this is not correct – evenness refers to the relative abundance among species, not their absolute abundance. If each species in a community has the same number of individuals, high or low, then the evenness is high . Community dominance is a similar concept but is the opposite of evenness, and is easier to understand. If we have a community with 10 species, 9 of which have 1 individual, and one that has 91 individuals, this is high dominance and low evenness. If, however, each species has 10 individuals, this is low dominance and high evenness. Communities are also characterized by a
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This note was uploaded on 04/07/2008 for the course RNR 1001 taught by Professor W.kelso during the Spring '08 term at LSU.

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Ch 7 - Study Guide Chapter 7 Study Guide Chapter 7 The book talks about the American alligator as a keystone species because of its pivotal role in

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