Transcript E9 Natural selection and geographical isolation can lead

E9 Natural selection and
geographical isolation can lead to
speciation
E9.1 Explain how geographical separation of
populations may result in the divergence of each
subgroup, so that the interbreeding is no longer
possible
speciation
 A species (if you recall ) is when an organisms
can interbreed with the rest of its population
to produce fertile offspring
 Sometimes certain organisms look to be
slightly different but are still the same speciesCrimson, yellow and Adelaide Rosellas in E1.2
 Speciation is when indeed a new species has
been formed – initiated by geographic
isolation
Geographic Isolation
 Geographical barriers such as mountain ranges, grasslands,
deserts or similar separate groups of the same population.
 Separation then isolates the gene flow from one group to
another
 Changes can accumulate in each isolated group due to
different selective pressures (different abiotic/biotic
factors)
 Genetic differences accumulate
 Gives rise then to reproductive isolation
 No more gene flow- over time a new species has formed
unable to mate with the original population from which it
came
 SPECIATION has occurred.
Galapagos Islands
 The finch species on the Galapagos Islands- several
species – thought to be a result of the process of
speciation
 An ancestral form from the mainland of South
America is believed to have flow to an islandflourished and spread to the other islands-as the
ocean rose/separated or isolated the island further
again-different conditions on each island/selective
pressures-the species became more and more diverse
on the islands from beak shape and size related to
each islands food resources- speciation occurred
Pangaea
 Past history it was thought that there existed
one land mass- Pangaea
 Australia thought to have separated 40 million
years ago-supported by geological and fossil
evidence
 Continents are still moving
 When the break occurred-both marsupials and
placental mammals existed on our continentapart from bats placental mammals failed to
survive
 Page 217 read about the frog in Australia
And then………….
 Geographical isolation led the plants and
animals on Australia to develop differently
 Evolution of the kangaroo, koalas, wallabies,
wombats, platypuses, possums and echidnas
 Evolution in Australia has meant adaptations
to Arid conditions-poor nutrient levels, fire
and high salinity levels
 Long process-usually
 Some models suggest speciation can occur
without geographical isolation and quickly
Speciation summarised
 Geographical feature-isolation /separation of a
population
 Different environmental conditions-different
selective pressures in the environments
 As a result of natural selection in each
environment certain features are selected and
are reproductively and advantage and slowly
become part of the species- the gene pools of
each group developing quite differently- lack
of gene flow between the two
 Reproductive isolation occurs- then can no
longer breed together to produce fertile
offspring