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A.P. Biology Ch. 24
The Origin of Species
| Question | Answer |
|---|---|
| Speciation | The process by which one species splits into two or more species. |
| Microevolution | Changes over time in the allele frequencies within a population. |
| Macroevolution | The broad pattern of evolution over long time spans. |
| Biological Species Concept | The primary definition of species invented by Ernst Mayr. |
| Species | A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but cannot produce viable and fertile offspring with members of other such groups. |
| Reproductive Isolation | The existence of biological factors that serve as barriers, which impede members of two species from producing viable, fertile, hybrid offspring. |
| Hybrid | The offspring of two organisms of different species. |
| Prezygotic Barrier | An example of reproductive isolation that impedes fertilization, including, habitat, temporal, behavioral, mechanical, and gametic isolation |
| Postzygotic Barrier | An example of reproductive isolation that impedes the development of the hybrid, after fertilization, including reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown. |
| Habitat Isolation | Two species that occupy different habitats within the same are may encounter each other rarely, if at all, even though they are not isolated by obvious physical barriers, such as a mountain range. |
| Temporal Isolation | Species that breed during different times of day, seasons or years cannot mix gametes. |
| Behavioral Isolation | Courtship rituals, such as mate recognition, that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. |
| Mechanical Isolation | Mating is attempted, but morphological differences prevent its successful completion. |
| Gametic Isolation | The sperm of one species may not be able to fertilize the eggs of another species because they may be unable to survive in the reproductive tract or penetrate the membrane surrounding the egg. |
| Reduced Hybrid Viability | The genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment. |
| Reduced Hybrid Fertility | When chromosome number of the two parent organisms differ, meiosis in the hybrid fails to produce normal gametes, so the hybrid is sterile. |
| Hybrid Breakdown | When the hybrids mate with one another or with either parent species, the offspring of the next generation are feeble or sterile. |
| What are the limitations of the biological species concept? | It provides no way to evaluate the reproductive isolation of fossils, account for asexual reproduction, and species are designated by the absence of gene flow. |
| Morphological Species Concept | A characterization of different species based on body shape and structural features, so it applies to any kind of reproduction, regardless of gene flow, but it does not provide a brightl-ine for which structural features distinguish species. |
| Ecological Species Concept | A characterization of species in terms of their ecological niche, the sum of how members of the species interact with the living and nonliving parts of their environment, which accounts for all kinds of reproduction and disruptive natural selection. |
| Phylogenetic Species Concept | A species is the smallest group of individuals that share a common ancestor, forming one branch on the tree of life, which accounts for distinguishing differences, but there is no bright-line for the degree of difference required to determine a species. |
| Allopatric Speciation | When the gene flow is interrupted because a population is divided into geographically isolated subpopulations. |
| What is the process of allopatric speciation? | Geographic speciation, mutations, natural selection, genetic drift, and reproductive isolation result in allopatric speciation. |
| Sympatric Speciation | Speciation that occurs in populations that live in the same geographic area, which can occur if a gene flow is reduced by such factors as polyploidy, habitat differentiation, and sexual selection. |
| Polyploidy | The condition in which there are extra sets of chromosomes because of an accident during cell division. |
| Autopolyploid | An individual that has more than two chromosome sets that are all derived form a single species. |
| Allopolyploid | A hybrid individual that is fertile when mating with others of their kind, but cannot interbreed with either parent species, so they are a new species. |
| Hybrid Zone | A region in which members of different species meet and mate, producing at least some offspring of mixed ancestry. |
| How is a hybrid zone formed? | Populations of species are connected by gene flow, a barrier to gene flow is established, a population diverges, speciation is nearly complete, and the gene flow is re-established in the hybrid zone. |
| What are the possible outcomes for hybrids in the hybrid zone? | Reinforcement, fusion or stability. |
| Reinforcement | The reproductive barriers are reinforced and will be stronger between sympatric species than allopatric species, so the hybrids will eventually cease to be formed. |
| Fusion | The reproductive barriers are weakened, so the hybrid and the original species will fuse in a reversal of the speciation process. |
| Stability | The reproductive barriers remain consistent, so the hybrids will continue to be produced. |
| Punctuated Equilibria | Periods of apparent stasis punctuated by sudden change, which can be seen through the fossil record and was suggested by Niles Eldredge and Stephen Jay Gould. |
| What does punctuated equilibria imply about the rate of speciation? | Once the process begins, speciation can be completed relatively rapidly. |
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