Isolating Mechanisms
Speciation – the splitting of a genetically similar population into two or more populations that
undergo genetic differentiation and eventually reproductive isolation leading to the
production of two or more new species
Species – a group of similar organisms which can interbreed to produce fertile offspring
Allopatric (Geographical) Isolation
Formation of two or more different species from one original species due to
geographical isolation
Geographical features separate two groups within a species:
o Lakes and Rivers
o Mountains and Valleys
o Oceans and Seas (e.g. when on Islands)
Each group is subject to different selection pressures so natural selection favours
different traits in each group
As a result of natural selection, each group becomes adapted to its environment and
eventually become distinct species
Example: Galapagos Island Finches have different beaks on each island due to different
food sources
Sympatric (Reproductive) Isolation
Formation of two or more different species from one original species due to
reproductive isolation
Populations inhabit the same geographical location
Biological and behavioural changes in a population may lead to reproductive isolation
Changes to courtship behaviour (e.g. songbirds from cities may be louder and rural birds
don’t recognise the song)
Mutations affecting when an individual is ready to mate
Mutations to reproductive organs
Mutations leading to a change in activity (e.g. foraging) may cause diurnal animals
(active in the day) to become nocturnal (active at the night) or crepuscular (active at
dawn or dusk) or vica-versa
Speciation – the splitting of a genetically similar population into two or more populations that
undergo genetic differentiation and eventually reproductive isolation leading to the
production of two or more new species
Species – a group of similar organisms which can interbreed to produce fertile offspring
Allopatric (Geographical) Isolation
Formation of two or more different species from one original species due to
geographical isolation
Geographical features separate two groups within a species:
o Lakes and Rivers
o Mountains and Valleys
o Oceans and Seas (e.g. when on Islands)
Each group is subject to different selection pressures so natural selection favours
different traits in each group
As a result of natural selection, each group becomes adapted to its environment and
eventually become distinct species
Example: Galapagos Island Finches have different beaks on each island due to different
food sources
Sympatric (Reproductive) Isolation
Formation of two or more different species from one original species due to
reproductive isolation
Populations inhabit the same geographical location
Biological and behavioural changes in a population may lead to reproductive isolation
Changes to courtship behaviour (e.g. songbirds from cities may be louder and rural birds
don’t recognise the song)
Mutations affecting when an individual is ready to mate
Mutations to reproductive organs
Mutations leading to a change in activity (e.g. foraging) may cause diurnal animals
(active in the day) to become nocturnal (active at the night) or crepuscular (active at
dawn or dusk) or vica-versa
