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ISU BSC 101 - Speciation and Extinction

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BSC 101 1st Edition Lecture 6Outline of Last Lecture I. Section 2.3: Domain Eukaryaa. Animal Cellb. Plant Cellc. Fungid. ProtistsII. Section 2.4: Bacteria and Archaea are ProkaryoticIII. Section 3.2: Genetic Variationa. Sexual Reproductionb. Mutationc. Migration and DispersalIV. Terms to KnowOutline of Current Lecture I. Section 3.3: Selection Pressuresa. Sexual Selectionb. CoevolutionII. Section 3.4: Speciationa. Reproductive Isolationb. Reproductive BarriersIII. Section 3.5a: Species Unique Evolutionary HistoryIV. Section 3.5.b: Adaptive RadiationV. Section 3.5c: ExtinctionCurrent LectureSection 3.3: Selection PressuresSelection Pressures: Conditions that exert natural selection on an organism at its particular stage of life.o Examples… Temperature Concentration of oxygen Amount of moisture and lightThese 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. Competition with other organisms for resources Predatorso Genotypes determine traits and capabilities.o Selection pressures change with the life stage of an organism (just because their traits were adaptive in their earlier stages of life doesn’t mean they will be in their late stages)o Natural selection gets rid of the least fit organisms.Sexual Selection: Pressures that favor particular traits that attract a mate.o Favors traits that increase reproductive success.o Example; a mating call or dance or two males fighting to the death to attract a female.o If you don’t have what it takes to attract a mate, you can’t reproduce and your traits won’t be passed on.Coevolution: process that occurs when two or more organisms interact and exert selection pressures on each other to produce adaptations.o Example; the long curved bill of a sunbird fits perfectly into the long tubular flower of a sticky-tube heather.o Leads to greater fitness and adaptation of those species involved.Random events are nonselectiveand do not produce better adapted organisms – they favor or eliminate individuals regardless of their fitness.Section 3.4: SpeciationSpeciation: the process that produces new species.o Species are members of a population that can interbreed in nature by sharing a similar set of genes.1. Populations diverge from an ancestral population. Speciation occurs when an ancestral population diverges into new habitats underdifferent selection pressures. As they diverge, they first become races, then species.Races: two different populations of the same species that can interbreed, but display different phenotypes and appearances.Reproductive isolation: when a race or population accumulates enough phenotypic and genetic differences and are unable to interbreed, leading to separate species. Drives speciation.2. Reproductive barriers isolate populations and drive speciation.Reproductive barriers: conditions that prevent two organisms or populations from breeding. Two categories… Those that prevent fertilization (pre-mating) Those that prevent the fertilized egg from developing (post mating)Geographical Barrierso Pre-mating barriero Keep races apart.o No gene flow between them.o Example; mountains, oceans, lakes, ect.Temporal Barrierso Pre-mating barriero Both organisms have a different time period in the reproductive cycle.o Example; if one breeds early in the year and one breeds late in the year, they cannot breed together.Mechanical Barrierso Pre-mating barriero Genitals don’t fit together to allow mating.SHIT DON’T FIT.o Example; Dragonflies.Behavioral Barrierso Pre-mating barriero The organism doesn’t do the mating dance/call/courtship ritual right and cannot get a mate.Hybrid Inviabilityo Post mating barriero Early death of the embryo because of genetic incompatibility.o Miscarriage.Hybrid Sterilityo Post mating barriero Infertile organisms so they can’t mate at all.o Example; a mule (the offspring of a horse and a donkey)Section 3.5a: Species Unique Evolutionary Historyo Example; trilobites have diversified into 17,000 species.o Some species diversify extensively while others survive millions of years with little change. Example; horseshoe crabs today look almost identical with those found 150 million years ago. Populations under intense selection pressure maintain a constant phenotype. An especially stable and constant environment drives against genetic variation. Constraints by development  no room to develop any further. Reproductive barriers might have been very strong and created many isolated populations.Section 3.5.b: Adaptive RadiationAdaptive Radiation: species have branched or radiated into numerous lineages each with many species.o Not a needs driven process where organisms evolve adaptive structures in response to environmental demands; rather adaptations evolve because traits were selected for their fitness.Section 3.5c: Extinctiono In face of change, a species faces three possible outcomes…1. Genetic variation and natural selection will shape the future population to become better adapted.2. Individuals will migrate and colonize new or more stable habitats.3. The species will fail to adapt quickly enough, decline, and become extinct.o 99.9% of all species once alive are now extinct.o Extinction can be caused in two ways…1. Species is replaces by a species better adapted to change.2. Mass extinction: the death of all individuals comprising a species; elimination of a species in a relatively short period in geologic time.o Local extinction: when a species dies out in a region but not


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