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Speciation and Evolution

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Describes and analyzes speciation, including the processes of adaptive change, adaptive radiation, phyletic gradualism, and punctuated equilibrium

Describes and analyzes speciation, including the processes of adaptive change, adaptive radiation, phyletic gradualism, and punctuated equilibrium

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  • 1. Speciation and Evolution: The Processes
  • 2. Defining Species: Review
    • Evolution involves populations, not Individuals
    • Species is a population of organisms whose members can interbreed under natural circumstances and reproduce fertile (viable) offspring
  • 3. How Do New Species Arise?
    • Two fundamental processes give rise to new species:
    • Cladogenesis: The splitting off of one species into two clades , usually because of geographical isolation, but also because of reproductive isolation.
    • Two kinds of species develop by cladogenesis:
    • Sympatric Species : Those whose speciation is the product of geographical isolation
    • Allopatric Species : Those whose speciation is the product of reproductive isolation of population in the same region.
    • Anagenesis: The replacement of an ancestral species by a daughter species over time; the ancestral species become extinct.
  • 4. Speciation: Evolution Through Cladogenesis
    • Cladogenesis:
    • Time I: Genes flow freely in region
    • Time II: Barrier separates two populations
    • Time III: Mutations change genotype and phenotype of 2 populations
    • Time IV: Two populations cannot interbreed even with removal of barrier
    • Definition: Branching of one species into two
    • From clade (“branch”) or group with common evolutionary ancestry.
  • 5. Speciation: Allopatric Species
    • Allopatric speciation occurs when two populations are separated by a geographical barrier (river, mountain range)
    • In this example, three species of fish have evolved in separate zones
  • 6. Speciation: Sympatric Species
    • Sympatric species are those that are separated by a reproductively isolation mechanism
    • Speciation occurs among three populations of fish even though the different species occupy the same region
    • There are several ways for subspecies to become reproductively isolated
  • 7. Modes of Reproductive Isolation In Sympatry
    • Ecological Isolation: Different populations are separated by occupy a slightly different niche
    • Seasonal Isolation: The breeding season of two closely related populations do not match.
    • Sexual Isolation: One or both sexes of a species initiate mating behavior that does not act a stimulus to the opposite sex of a closely related population
    • Mechanical isolation: Populations do not mate because of an incompatibility of the male and female sex organs of the individuals (extreme example: wolves and Chihuahuas)
    • Gamete Isolation : Incompatibility of sex cell with bodily environment
    • Hybrid Infertility or Sterility: Hybrids do not survive or reproduce (mules)
  • 8. Speciation: Role of Micromutation
    • Micromutation: Mutations with
    • extensive or important phenotypic results
    • Example: Axolotl (species of salamander)
    • This salamander starts life as tadpole-like larvae, as do other salamanders
    • Axolotl, however, never grows up—doesn’t sprout mature legs, keeps its gills, remains aquatic existence.
    • Injection of a hormone enables maturity and to live on land, so that one mutation can and does create major change
  • 9. Adaptive Radiation Defined
    • Definition: Evolution and spreading out of related species into new niches
    • Niche: An environment in which an organism is found and its adaptive response to that environment
    • Generalized Adaptive Radiation: The adaptation of a species to a wide range of niches. Homo sapiens is an example.
    • Specialized Adaptive Radiation: The adaptation of a species to a narrow range of niches.
  • 10. Adaptive Radiation: Favorable Conditions
    • Absence of similar and therefore competing species
    • Occurrence of extensive extinction, thereby emptying an environment of competitors
    • Adaptive generalization of new group of related species which enable it to occupy several niches and displace species already there.
  • 11. Adaptive Radiation: Absence of Competing Species
    • Example : Darwin’s finches on Gal ápagos Islands who were blown there by winds from mainland Ecuador
    • Niches opened up for 13 varieties with different bills, including those that feed on cactus or eat specific insects in trees
    • Others use twig or cactus spine to probe for insects
    • A vampire finch sucks blood from larger birds
  • 12. Finches and Their Adaptive Radiation
    • Ground finches ( Geospiza) who are seed and cactus eaters;
    • Tree finches ( Camarhynchus ), who are insect and bud eaters
    • Warbler finches ( Certhidea ) who vary by color.
  • 13. Adaptive Radiation: Specialization
    • Definition: Adaptation of a species to a narrow range of environmental niches
    • Example: Again, some species of Darwin’s finches on Gal ápagos Islands are examples.
    • Medium ground finch was nearly wiped out in the 1977 drought
    • Sudden change could eliminate this or others of these genera and species of finches
    • Example: prosimians adapt on in habitats afforded by Madagascar and are close to extinction.
  • 14. Adaptive Radiation: Generalization
    • Definition: Adaptation of a species to a wide range of environmental niches
    • Examples:
    • Mammals spread after the disappearance of dinosaurs 65 m.y.a. and occupied innumerable niches, from grassland (ungulates) to trees (bats)
    • Monkeys with a mixed diet occupied diverse arboreal (tree) habitats; they displaced the prosimians
    • Humans: from frozen north to tropical rainforest or desert—thanks to culture—are the most generalized primate
  • 15. Types of Evolution: Darwinian or Phyletic Gradualism
    • Definition:
    • Slow, step-by-step changes over time
    • Intermediate forms assume “missing links”
    • Darwin postulated this model
    • Examples : From monkeys to apes; apes to hominins (e.g. Lucy); and from early hominins to modern Homo sapiens
  • 16. Problems with Gradualism
    • Fossil record does not reveal fine gradations from one lifeform to a descendant life form: no “missing links.”
    • Bipedalism occurred quickly as the fragmentary fossil record shows.
    • Reproductive advantage: do slight changes bestow this advantage?
    • Continuum question: at which point does a population become two species?
    • Sometimes, change can take place rapidly, either through oscillating selection or punctuated equilibrium
  • 17. Types of Evolution: Oscillating Selection
    • Definition: Adaptive variation around a norm rather than direction in response to environmental variation
    • Example: Medium and small ground finch lacked a bill strong enough to crack tough seeds
    • Occurrence of drought selected plants whose seeds had a tough exterior
    • Survival of large, longer-billed finches
    • Smaller, shorter-billed finches returned after the climate returned to normal,
    • Shifting bill size and lengths reflected the oscillation of the environmental conditions.
  • 18. Types of Evolution: Punctuated Equilibrium
    • Definition : Species tend to remain stable over time, then, evolutionary changes occur suddenly (in terms of centuries or millennia)
    • Causation: Populations may become fragmented and isolated, and from there new forms arise
    • Small, new populations may invade a region, and through the founder effect and better adaptation, create and spread a new species
    • Example: Archaeopteryx (ancient bird), a dinosaur with feathers: suddenly appears and may have created a new class known as Aves (birds)
  • 19. Phyletic Gradualism and Punctuated Equilibrium
    • A summary of gradualism and punctuated equilibrium
  • 20. Pseudoscience and Creationism
    • Pseudoscience consists of scientifically testable ideas in form that are taken on faith even after they are proven as false
    • (Scientific) Creationism is the belief in a literal biblical interpretation of the creation of earth in six days 6,000 to 10,000 years ago
    • The claim is testable, has been tested, and has been demonstrated to be false.
  • 21. Counterevidence to Creationism
    • Existence of strata, such as the Grand Canyon, accumulated over 2 billion years falsifies the claim that the earth is only a few thousand years old
    • Presence of extinct lifeforms, from fossil fish to dinosaurs, demonstrate that other forms existed at one time but are now extinct
    • Presence of ancient hominins establish extinct humanlike creatures that look like us but are not us.
    • Both kinds of evidence are abundant
  • 22. Conclusion
    • Species is unit of evolution
    • Evolutionary change is more random than progressive
    • Speciation is the basic process of evolutionary change
    • Changes may be gradual or rapid
    • Scientific rule: follow the evidence
    • Evidence for evolution is overwhelming in the form of geological strata and fossil lifeforms

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