BIOLOGY 1M03 Lecture Notes - Dusky Seaside Sparrow, Species Problem, Phylogenetic Tree

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Populations can be recognized as distinct species if they are reproductively isolated from each other, if they have distinct morphological characteristics, or if they form independent branches on a phylogenetic three, Populations can become genetically isolated from each other if they occupy different geographic areas, if they use different habitats within the same area or if one population is polypoid and cannot breed with the other. When populations that have diverged come back into contact, several outcomes are possible (fusion, reinforcement, through pre and post zygotic isolation, development or hybrid zones, extinction and speciation by hybridization). When gene flow is reduced between populations, they may then diverge genetically as a result of any among the other 4 factors (most remarkably natural selection, genetic drift, or mutation). This genetic divergence may eventually lead to speciation. Speciation: the evolution of two or more distinct species from a single ancestral species. (figure 26. 1) Species: an evolutionary independent population or group of populations.

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