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Ch. 27.4- Speciation

Ch. 27.4- Speciation. Target #36- I can define species. Species: defined as a group of subpopulations that are capable of interbreeding and are isolated reproductively from other species Different species do not exchange genes

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Ch. 27.4- Speciation

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  1. Ch. 27.4- Speciation

  2. Target #36- I can define species • Species: defined as a group of subpopulations that are capable of interbreeding and are isolated reproductively from other species • Different species do not exchange genes • Known as reproductive isolation can occur before fertilization can take place or after

  3. Speciation • When one species gives rise to two species • Each continues its own evolutionary pathway • Occurs when reproductive isolation develops between two formerly interbreeding groups of populations • Isolation can occur in the following ways • differing habitats • Change in reproductive season • Courtship behavior changes • Mechanical changes in reproductive organs Target #37- I can explain speciation and how it occurs within populations

  4. Target #38- I can differentiate between allopatric and sympatric speciation • Allopatric speciation • Occurs when gene flow is no longer possible • Geographic isolation could occur, separating populations • Groups of organisms may be exposed to different environmental pressures, resulting in other isolating influences

  5. Target #38- cont. • Sympatric speciation • A single population could suddenly divide into two reproductively isolated groups without being geographically isolated • Example • Chromosomal differences in plants prevent them from reproducing with each other

  6. Target #39- I Can explain adaptive radiation by using the galapagos finches as an example • Adaptive Radiation the proliferation of a species by adaptation to different ways of life • The finches found on the Galapagos Islands were thought to have descended from mainland finches that migrated to one of the islands • It is possible that as the founding group grew in number, some individuals would have dispersed to other islands • Would have promoted divergent feeding habits • The birds physically resemble each other, but have variations in beaks to accommodate different resources

  7. Two hypotheses describe the pace at which speciation can occur • Phyletic gradualism states that change is very slow but steady within a lineage before and after splitting of the line of descent • Not shown in fossil record • Fossil record records when a new species evolves and displaces the existing species • Punctuated equilibrium long periods of stasis, or no visible change, are followed by rapid periods of speciation • Could explain why few transitional links are found • Mass extinction events are often followed by rapid periods of speciation Target #40- I can state the two hypotheses which describe the pace in which speciation occurs

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