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Concepts |
Media Resources |
16.1 The Species Concept |
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1. Linnaeus's species designations helped scientists communicate. Darwin added evolutionary meaning and Mayr added the requirement for reproductive isolation to define biological species.
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Art Quiz
Taxonomic Hierarchy | |
2. Diagrams of branching lines represent evolutionary relationships among species. Such evolutionary trees are called phylogenies. Speciation is the formation of a new species.
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Essential Study Partner
Speciation | |
3. Comparing sequences of mtDNA is increasingly being used to clarify and supplement species relationships based on visible characteristics.
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16.2 Reproductive Differences Distinguish Species |
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4. Prezygotic reproductive isolation occurs before or during fertilization. It includes obstacles to mating in space, time, and behavior; molecular mismatches between gametes; and incompatible chromosomes.
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5. Postzygotic reproductive isolation results in weak or infertile offspring, or may act more gradually by disrupting beneficial gene linkages.
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16.3 Speciation and Space |
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6. Allopatric speciation occurs when a geographic barrier separates populations, which then diverge genetically to the point that members of the two populations can no longer produce fertile offspring together.
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Essential Study Partner
Allopatric Speciation | |
7. Parapatric speciation occurs when two populations live in neighboring areas but share a border zone. Genetic divergence between the two groups exceeds gene flow, driving speciation.
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8. Sympatric speciation enables populations that occupy the same area to diverge, via drastic genetic change such as polyploidy or the use of different resources.
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Essential Study Partner
Sympatric Speciation |
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16.4 Speciation and Time |
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9. Evolutionary change occurs at many rates, from slow and steady gradualism, to the "leaps and starts" of punctuated equilibrium.
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Essential Study Partner
Evolutionary Trends
Art Quiz
Evolutionary Pace | |
10. In adaptive radiation, an ancestral species rapidly branches into several new species, reflecting sudden availability of new habitats or resources or a particularly beneficial adaptation. A group of species related by recent common descent is a clade.
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16.5 Extinctions |
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11. Extinction is the disappearance of a species.
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Essential Study Partner
Extinctions | |
12. Decreased genetic diversity may lead to extinction of populations and possibly species.
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13. Background extinctions are ongoing losses of species on a local scale. Mass extinctions result from global changes.
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