Isolation and the evolution of new species
B2 6.4Speciation
Text page 208
Syllabus content
• New species arise as a result of:• Isolation – 2 populations of a species become
separated e.g. geographically• Genetic variation – each population has a wide range
of alleles that control their characteristics• Natural selection – in each population the alleles that
control the characteristics which help the organism survive are selected
• Speciation – the populations become so different that successful interbreeding is no longer possible
Starter: Aussies only, please
• List animals which only exist in Australia• Why don’t these occur anywhere else?
Answer - Geographical isolation
• There was a geographical barrier i.e. it is an island• Australia separated from the rest of the continents
over 5 million years ago – marsupials were isolated from other mammals
• Many different marsupials evolved from kangaroos to koalas
Reminder – what is a species?
• A group of organisms that are very similar• They can breed together to produce fertile
offspring
Endemics
• If a new species evolves and is only found in 1 place in the world it is known as an endemic
• Many new endemics are being discovered in Borneo –one of the largest islands in the world
Environmental isolation
• This is another kind of isolation, where the climate changes in one area where an organism lives e.g. if the climate becomes warmer, plants may flower earlier than normal
• The breeding times of the plants and the animals linked with them may change
• This could lead to new species emerging
Summary - How do new species arise?
• Isolation of 2 populations of a certain species• They will have different alleles and there will
be slightly different living conditions• This means that different characteristics will
be selected by natural selection• Over time the 2 populations become so
different that they can no longer interbreed• A new species is formed
A Madagascan mystery
• Read the purple box about speciation on page 209 and the extension worksheet about Madagascar
• Make a flow chart to explain how 50 different species of lemurs evolved in Madagascar
Evolution is happening all the time
• There are natural cycles of new species appearing and other species becoming extinct
• What do you think happens after a mass extinction event?
Answer
• Many niches become available and there may be very rapid speciation as these niches become filled by new species
Practice questions
• Answer question 5 page 210 giving as many examples as you can
• Workbook pages 95-96
Plenary - discussion
• Imagine a future global disaster, where humans have been wiped out. How might evolution fill the gap?
• Make a glossary or play hangman with the words used in this topic
evolution – The development of new species as a result of natural selection.
extinction – The complete disappearance of a species due to changes in its environment that reduce its ability to survive and reproduce.
fossil – The preserved remains, impressions or traces of an organism that lived millions of years ago.
natural selection – The process where individuals that are well adapted to their environment survive and reproduce at the expense of less well-adapted individuals.
trait – A distinguishing and inheritable characteristic of an organism.
variation – The natural differences between individual members of a species.
Glossary
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