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 species Crimson, 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 island flourished 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 continent apart 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