HL 2 Biology

D.2b: Allopatric Speciation

<<Species and Species Formation>> (p.312)

Evolution: the cumulative change in the heritable characteristics of population; a change in allele frequency over time

Species: a group of potentially interbreeding populations, with a common gene pool that is reproductively isolated from other populations

Biological species concept difficult to apply since: 

  • some species only reproduce asexually
  • some species occasionally mate to produce hybrids
  • some species cannot interbreed but they are close in appearance that they’re difficult to tell apart (sibling species)

Speciation: formation of a new species by the splitting of an existing species

  • occurs when barriers isolate the gene pool of one population from another population

Allopatric Speciation: isolation occurring because of geographic separation of species

  • e.g. fluctuations in water levels; can lead to isolation of population = results in new species
  • sympatric speciation: isolation of population within the same habitat


(p. 312)

a) Three morphological differences between the two species of treecreeper are the patterns on their back, their tails and the size of their beaks.  

b) Although the C. brachydactyla and C. familiaris are similar in appearance, they are two different species because they are considered sibiling species which are species that cannot interbreed but are close in appearance.  The two species may have been separated through allopatric speciation or by isolation within the same geographic area.

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