[18.5] isolation and speciation

the formation of new species from pre-existing species over time as a result of changes to gene pools from generation to generation

genetic isolation between the new population and the pre-existing species population

when two populations can no longer interbreed successfully to produce fertile offspring

• allopatric speciation • sympatric speciation

two populations of a species are separated by a geographical barrier and become genetically isolated from each other

two populations of species are living in the same area, experiencing similar environmental selection pressures but still become genetically isolated from each other

individuals within the two separate populations can no longer freely interbreed

when the change in allele frequencies in the population is due to random chance, rather than environmental selective pressures

• reproductive isolation so no interbreeding between populations • variations due to mutations occurring separately in the different populations • different selective pressures acting on the different populations • differential reproductive success in the populations • leads of different changes in allele frequency in each population • eventually, members of the two populations become so different they are unable to reproduce to produce fertile offspring

• geographical • ecological • temporal • behavioural • mechanical • gametic • hybrid sterility