Populations, fossils and extinction

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Presentation transcript:

Populations, fossils and extinction Make sure you revise: Distribution of organisms Sampling methods Fossils Extinction New species

Populations Physical factors that may effect organisms are: Temperature Availability of nutrients Amount of light Availability of water Availability of oxygen and carbon dioxide Limits of Population

Collecting environmental data To sample randomly: Choose area to sample Place quadrat randomly onto area Count number of species within quadrat Repeat 5 times To sample along a transect: Choose a straight line through the area Place quadrat at one end of the line Repeat at 5 set intervals along the line

Fossils and exctinction Evidence for early life forms comes from fossils Fossils are the remains of dead plants and animals which lived millions of years ago. They are found in rocks. Fossils may be formed in various ways: - from the hard parts of animals that do not decay easily - as preserved traces of organisms, eg footprints, burrows and rootlet traces.

Fossils and exctinction Fossils show us how much or how little different organisms have changed as life developed on Earth. Many early life forms were soft-bodied... which means that they have left few traces behind....what traces there were have been mainly destroyed by geological activity.

Fossils and exctinction Extinction may be caused by: - changes to the environment over geological time - new predators - new diseases - new, more successful, competitors - a single catastrophic event, eg massive volcanic eruptions or collisions with asteroids - through the cyclical nature of speciation.

Fossils and exctinction New species arise as a result of: isolation – two populations of a species become separated, eg geographically HT only: 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 to survive are selected speciation – the populations become so different that successful interbreeding is no longer possible.