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15,16,17,18,19 lecture notes

15,16,17,18,19 lecture notes - Species Concepts How do you...

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Species Concepts: How do you know it is a species -Descriptive- Identifying/classifying species Phylogenetic species concept Evolutionary species concept -Explanatory-Why a species evolves Ecological species concept Biological species concept Phylogenetic Spcies Concept: Unique set of features Morphological, physiological, cellular structure, DNA sequences Can be applied to all types of organisms/situations -But- how many traits should be used? -How dissimilar do populations have to be? Evolutionary Species Concept: Unique genetic history-lineage Focus is on the pathway that has lead to the formation of species Problems with determining a criterion for what is different Used frequently in determining if species that are already considered distinct are closely or distantly related evolutionarily Ecological Species Concept: Do populations utilize different aspects of their environment? Are the ‘ecological niches’ the same or different? -ecological niche— *habitat (microhabitat) to which a population is adapted *What it eats *What eats it *When & where it is active (Different niches > different selective pressures) (Different adaptations > different species) Biological Species Concept: (classic type) Reproductive isolation -Do not mate/ do not produce fertile offspring -lack of genetic mixing (gene flow) Reproductive isolating mechanisms -Barriers to successful reproduction -Prevent genetic exchange between species -Prezygotic barriers -Postzygotic barriers The biological species concept cannot be applies to all situations… Hybridization (e.g. in orioles)
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-may not provide information about close evolutionary ties Organisms that are asexual -reproductive isolation is meaningless Extinct organisms -do not know anything about gene flow Allopatric (geographically isolated) populations -would they reproduce IF they came in contact? Reproductive Isolation: -First two species concepts (Descriptive two: phylogenetic and evolutionary) say nothing about why or how species are different, just that they are different enough. -What keeps them from blurring into one big group? (A: Isolation) -Biological Species Concept defines a species based upon its isolation from other pops of source species. -The others just have to have something keeping species separate…Many of the same mechanisms apply to different species concepts, just not required. -General isolation can be as simple as allopatric speciation, or ecological differentiation (using different resources so they don’t come in contact) Prezygotic Isolating Mechanisms: -prevents formation of zygote (fertilization) Allopatric speciation o Physically located in different place, still is sorta’ prezygotic isolating… Ecological niche partitioning (e.g. ecological species concept; Anolis lizards) Live and “work” in different areas, so unlikely to ‘date’ in a different place.
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