Speciation and Breeding

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  • Speciation and Breeding
    • Allopatric speciation
      • Populations of a species become geographically isolated. (More common than sympatric)
      • Selection and genetic drift will act differently creating genetic differences between the two new species
      • The 'Island Rule'
        • Island endemics: species unique to a particular island
        • Gigantism & Dwarfism (smaller species evolve larger bodies and vice versa)
        • Factors effecting immigration / extinction: island size & distance from mainland
      • Population divergence: geographical barrier, population come together again but do NOT interbreed (now 2 new species)
      • Environmental gradients: gradual change in abiotic factors over space (or time)
        • Ecotypes - genetically distinct population within a species which is adapted to specific env. conditions - ultimatley can become their own species
          • e.g. Festuca ovina (grass) Gwynedd, Wales and Dorset, England
      • Mountain diversity: Species migration limited by several factors - area, rainfall, resource diversity, productivity, temperature etc.
        • e.g. Arctic - Alpine taxon (Ben Lawes)
    • Sympatric speciation
      • Polyploidy
        • Offspring produced with twice the normal number of chromosomes
        • More common in plants than animals
        • Tetraploid individual cannot mate with diploid individual creating reproductive isolation
        • Tetraploidy can fertilize itself and create offspring e.g.
        • Autopolyplody & Allopolyploydy
      • Populations of a species that share the same habitat become reproductively isolated from each other
      • Host shiftt
    • Parapatric Speciation
      • Extremely rare
      • Populations separated by an extreme change in habitat
      • Ranges do NOT significantly overlap but are immediatley adjacent to each other - do not occur together except in a narrow contact zone
      • Geographical distribution as oppose to sympatry (same area) and allopatry (two cases of distinct areas)

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