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Adaptive Radiation rapid speciation after new characters arise (e.g., photosynthesis, flight), a new habitat is occupied (e.g., terrestrial), a new area is colonized (oceanic islands), or following mass extinctions. |
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Character Displacement variation of traits due to the presence of competing species. Example, three species of finches have different beak sizes on 4 different islands (A-D) where the other species are present (Lack, 1947). |
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Cladogenesis the formation of lineages (phylogenies) through progressive speciation, diversification, and extinction. The vertical axis is time and the horizontal axis is the range of a trait. |
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Convergence the formation of similar organs, structures, or morphology in response to selection pressures. Example, penguins, ichthyosaurs, dolphins. |
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Directional Selection process by which one state or value of a trait becomes more common in a population. |
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Disruptive (Diversifying) Selection process by which more than one trait of a population is selected, possibly leading to two different species. |
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Founder Event dispersal of a few individuals of a population, with only a small portion of the genetic diversity of the population, potentially resulting in speciation. |
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Gradualistic Evolution
cladogenisis characterized by gradual changes in the frequency
of traits in a population, sometimes leading to speciation. ex. Dinos |
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Inversion A chromosomal mutation caused by the reversal of the genetic sequence in a chromosome. A barrier to reproduction with organisms with normal (non-inversion) chromosome because it inhibits the pairing of homologous chromosomes during fertilization and meiosis. |
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Phyletic Speciation speciation through time, without branching via. directional selection. "d e f" and "i j k" are series of plyletic species. The vertical axis is time & the horizontal axis is a trait. |
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Punctuated Equilibrium evolution (cladogenisis) characterized by speciation events (punctuation) and otherwise, relatively few changes in traits (stasis). |
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Reticulate Evolution evolution (cladogenisis) characterized by occasional hybridization and combination of two species. |
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Selection Pressure the environmental force altering the frequency of traits in a population. The S+ selective pressure is stronger than the S+ pressure, so its trait becomes more common. Selection may be for or against (S-) traits. |
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Stabelizing Selection process by which extreme traits of a population are elimintated. |
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Trait any physical characteristic of an organism: size, color, life-span. The blue curve represents the frequency (vertical axis) of a range of traits (horizontal axis) in a population. |
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Translocation A chromosomal mutation caused by the exchange of genetic material among non-homologous chromosomes. A barrier to reproduction with organisms with normal (non-inversion) chromosome because it inhibits the pairing of homologous chromosomes during fertilization and meiosis. |
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Vicariant Event
historical appearance of a barrier* to genetic exchange, which
separates a population, potentially resulting in speciation. *river, mountain, desert etc. where the population cannot exist |
Lack, D. 1947. Darwin's finches. Cambridge Univ. Press. |
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