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Speciation and Extinction

Speciation and Extinction. Biogeography October 29 - Nov 2. Defining a species Morphological definition Biological definition Subspecies Mechanisms of Speciation Genetic drift Natural selection Gene flow Types of Speciation Allopatric speciation Sympatric speciation. Other Issues

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Speciation and Extinction

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  1. Speciation and Extinction Biogeography October 29 - Nov 2

  2. Defining a species Morphological definition Biological definition Subspecies Mechanisms of Speciation Genetic drift Natural selection Gene flow Types of Speciation Allopatric speciation Sympatric speciation Other Issues Convergent evolution Parallel evolution Coevolution Punctuated equilibrium Extinction Probability of extinction Recent extinctions Fossil extinctions Speciation and Extinction

  3. Defining a Species • Morphologically • Species are morphologically distinct • Biologically • Reproductively isolated (geologically or biol) • Subspecies • Populations that are morphologically (and therefore presumably) genetically distinct

  4. Mechanisms of Speciation • Genetic Drift • Changes in genetic characteristics of population due to pure chance • Founder Effect • Natural Selection • Change in population (genetic/morphological) resulting from expression of genetic characteristics by individuals in population that enhances their survival • Gene Flow • Change in genetics of population due to introduction of genetic materials from outside the population

  5. Types of Speciation • Allopatric Speciation • occurs when pops are geographically isolated so gene flow b/w pops cannot occur • Vicariance events • Disperal/Founder events • Peripatric • Peripheral populations are geog. isolated from main population and thus genetic divergence is accelerated (form of Adaptive Radiation)

  6. Types of Speciation • Sympatric Speciation • Speciation occurring within spatially contiguous populations • Parapatric • evolutionary divergence (speciation) in populations that occupy different habitat in the same geographic area (sympatric form of adaptive radiation) • Chromosomal changes • Polyploidy in plants

  7. Other Issues • Convergent Evolution • Unrelated species separated geographically evolve similar traits

  8. Other Issues • Parallel Evolution • Descendants of an ancestor now isolated evolve in a similar fashion

  9. Other Issues • Coevolution • Mutualistic associations • Punctuated Equilibrium • Long periods with no change followed by severe environmental changes • As compared to phyletic gradualism

  10. Extinction • “ The ultimate fate of every species is extinction.” Brown and Lomolino 2000 • RED QUEEN HYPOTHESIS “A species must continually evolve in order to keep pace with an environment that is perpetually changing, because all other species are evolving, altering the availability of resources and the nature of biotic interactions.” Van Valen 1973

  11. The Probability of Extinction • Taxon level • individuals • subspecies • species • more inclusive taxon levels • trophic cascades

  12. The Probability of Extinction • Ecological Groups • Large body size • Upper trophic levels • Highly specialized • Specifc habitats

  13. Population Size Birth rates Death rates Carrying capacity Small populations Intrinsic demographic events Extrinsic ecological events MVP = Minimum Viable Population The Probability of Extinction

  14. The Probability of Extinction (Quammen 1996: Song of the Dodo, p. 295)

  15. Recent Extinctions • Passenger Pigeon • Barro Colorado Island • Gray Whale

  16. Fossil Extinctions • Mass extinctions • Permian-Triassic (225 mybp) • Pleistocene megafauna (10-12K ybp) • Overkill hypothesis • Climate hypothesis • Cretaceous-Tertiary (65 mybp)

  17. Millenium Ecosystem Assessment 2005

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