Chapter 4 - Chapter 4: evolution, biological communities,...

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Chapter 4: evolution, biological communities, and species interactions Key definitions Evolution – genetic changes with a population over time Natural selection – differential reproductive success Mutations – random changes in DNA Adaptation – genetic trait that confers a selective advantage in a given environment Critical Limits All species have environmental limits - Von Liebig: a single factor in shortest supply determines species distribution - Shelford: expanded idea to tolerance limits (high or low) beyond which a particular species cannot survive Generally no single limited factor, but the interaction of several factors, determines species distribution Species requirements and tolerances can also be used as useful indicators Darwin’s theory of Natural Selection Four conditions are necessary for evolution to occur: 1. Variation in traits in a population 2. traits must affect reproductive success 3. traits must be inheritable 4. some selective pressure must favor these traits differentially - …2, 3, and 4 happen naturally, once you have variation How does variation occur in population in the first place? - Mutation of DNA - Random errors in replication - Radiation - Chemicals
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- Absorption of other DNA Selective Pressure - Natural selection modifies populations so that they are better suited to their environment Different types of natural selection: - Directional – environmental gradient pushes to one side - Stabilizing – - Disruptive – more than one way a species can survive in an ecosystem Resource partitioning – disruptive selection can lead to specialized groups Radiative evolution – if these groups cannot interbreed anymore, then new species result (species can interbreed) Reproductive isolation
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This note was uploaded on 04/28/2008 for the course ENVS 1000 taught by Professor Neff,jason during the Spring '07 term at Colorado.

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Chapter 4 - Chapter 4: evolution, biological communities,...

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