PLB 115 1st edition Evolution Lecture 19Outline of Last LectureI. Communitya. Complexity & StabilityII. Dynamic CommunitiesIII. The Niche ConceptIV. The Habitat ConceptV. Kinds of Organism InteractionsVI. CompetitionVII. Competition & Natural SelectionVIII. Examples of Competitive ExclusionIX. PredationX. Predation’s Effects on PreyXI. Symbiotic RelationshipsXII. ParasitismXIII. Styles of ParasitismXIV. Parasitic Life CyclesXV. CommensalismXVI. MutualismXVII. Types of CommunitiesXVIII. Biomes of the WorldXIX. Temperate Deciduous ForestXX. Temperate Grassland (Prairie)XXI. Temperate RainforestXXII. Boreal Coniferous ForestXXIII. TundraXXIV. Mediterranean Shrublands (Chaparral)XXV. DesertXXVI. SavannaXXVII. Tropical Dry ForestXXVIII. Tropical RainforestXXIX. Influence of Precipitation & Temperature on VegetationXXX. The Relationship Between Elevation and ClimateOutline of Current NotesI. EvolutionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Early Thinking About EvolutionIII. Theory of Natural SelectionIV. The Role of Natural Selection in Evolutiona. UpdateV. Reproductive SuccessVI. Common Misunderstandings About Natural SelectionVII. Importance of Excess ReproductionVIII. Importance of Genetic DiversityIX. Mechanisms that Affect Genetic DiversityX. Differential SurvivalXI. Darwin’s finchesXII. Herbicide-Resistance WeedsXIII. Differential Reproductive RatesXIV. Differential Mate ChoiceXV. Patterns of SelectionXVI. Stabilizing SelectionXVII. Directional SelectionXVIII. Disruptive SelectionCurrent NotesEvolutionEvolution: the change in the frequency of genetically determined characteristics within a population over timeMicroevolution: changes in allele frequencies between populations of same speciesMacroevolution: major genetic changes that occur over long periods of time that generate new species- Mechanisms of both are the sameEarly Thinking About EvolutionMid 1700s- (Buffon) observed fossils were so different from modern animals, implying that animals have changed over time Early 1800s- (Lamarck) suggested a process by which the changes could occur- Acquired characteristics could be passed on to offspringo Example: Giraffes have long necks because their ancestors stretched to reach leaves in trees. Lamarck was wrong, but his ideas stimulated thought about evolutionTheory of Natural Selection1858- Darwin and Wallace suggested the theory of natural selection as a mechanism for evolution- Darwin wrote Origin of Species by Means of Natural SelectionThe idea that some individuals with favorable genetic combinations are more likely to survive, reproduce, and pass their genes on to the next generation than others that have unfavorable genetic combinations- All organisms produce more offspring than can survive- No two organisms are exactly alike- Among organisms, there is a constant struggle for survival- Individuals that possess favorable characteristics for their environment have a higher rate of survival and produce more offspring- Favorable characteristics become more common in the specieso Unfavorable characteristics are lost over time Darwin and Wallace’s theories were not immediately accepted because meiosis, genes, and inheritance were poorly understood Mendel’s discovery provided an explanation for how characteristics could be transmittedfrom one generation to the next Knowledge of mutation, gene flow, and reproductive isolation supported Darwin/Wallace’s theoryUpdate- An organism’s ability to overproduce results in surplus organisms- Due to mutation, new traits enter the gene pool and due to meiosis new combinations of alleles can be generated- Resources such as food, soil nutrients, water, etc., are in short supply, so some individuals will not survive- Disease, predators, etc., will also affect survivalo These are called selecting agentso Allele combinations that favor survival and reproduction will be more commonin a populationThe Role of Natural Selection in EvolutionNatural selection will select for individuals with certain alleles- When allele frequencies change over time, evolution has occurred- Natural selection works on individuals, but only populations evolve- Three factors work together to determine how a population changes over timeo Environmental factors that affect individualso Sexual reproduction among the individualso Genetic diversity within the gene poolReproductive Success- Individuals that have the combinations of alleles that allow them to successfully reproduce will pass on their alleleso This success is measured as fitnesso Fitness is a relative measure- An individual can successfully reproduce, but be less fit than another individualo Involves the number of offspring produced and their viabilityCommon Misunderstandings About Natural SelectionSurvival of the fittest- Individual survival is not as important as reproductive success (# of descendants)Struggle for life- Does not refer to conflict- Refers to finding and utilizing resourcesThe significance of acquired characteristics- Phenotypes acquired during the life of the individual will not be passed onImportance of Excess Reproduction- Successful organisms reproduce at a rate in excess of that necessary to merely replace them when they die- However, population size remains relatively constanto A high death rate offsets the high reproductive ratesImportance of Genetic Diversity- A large gene pool with great genetic diversity is more likely to contain genetic combinations that will allow some individuals to adapt to changing environmentsMechanisms that Affect Genetic Diversity- Natural selection cannot occur in a population in which all of the individuals are genetically identicalGenetic diversity is essential for natural selection- Several mechanisms generate genetic diversity in a populationo Mutation, migration, and sexual reproductionDifferential Survival“Survival of the fittest” - Survival is a prerequisite of reproduction- Individuals that do not survive cannot reproduceDarwin’s finches- The finch’s beak size correlated with the type of seeds they ateo Small beaks - softer seedso Larger beaks - harder seeds- During drought, as soft seeds became scarce, only birds with larger beaks survivedHerbicide-Resistant Weeds- Only the individual plants that are resistant will survive- As these reproduce, more and more individuals in the species are resistant to