Stage 2 Biology – Ecosystems Notes
E9. Natural
selection and geographical isolation can lead to speciation
·
Speciation – the process that gives rise to the
origin of new species
o
Usually caused by geographic isolation
§
Geographical barriers = seas, lakes, mountain
ranges, grasslands, deserts
§
Separate groups of individuals from one another
§
Prevent flow of genes between populations
§
Changes accumulate in each population
o
Environments have different biotic and abiotic
factors
o
Forces of natural selection act differently in
each area
o
As a result of different natural selection,
genetic differences may occur between the populations
o
May give rise to reproductive isolation
§
Populations are now so different from one
another, that even if they mixed, interbreeding would not be possible, or the
offspring would be sterile or not survive
o
When differences accumulate, speciation is said
to have occurred
·
Speciation was proposed to explain the several
finch species noted by Darwin in the Galapagos
o
An ancestral form migrated to an island
o
Then spread to other islands
o
Ocean isolated the populations – different
selective pressures
o
Different beak shapes/sizes were related to the
food source on each island
·
Frogs in Western Australia and Eastern states
o
Level of similarity suggests a common ancestor
o
Conditions have changed over time (Nullabor
Plain was once habitable)
o
Arid climate isolated the frogs into two groups
o
Different selective pressures – now the two
groups differ in appearance and mating calls
·
Pangaea
o
At one time in history, all continents were
joined together as Pangaea
o
Over 150 million years ago the land fragmented
o
Australia has been separated for at least 40
million years – supported by fossil evidence
·
Australia
o
Natural selection has led to evolution of
species with adaptations to arid conditions, poor nutrient levels, fire, high
salinity
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