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