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Speciation and Evolution

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

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Speciation and Evolution

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