Evolution and Speciation. Species A group of organisms that breed with one another and produce...
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Transcript of Evolution and Speciation. Species A group of organisms that breed with one another and produce...
Isolating Mechanisms
• Reproductive Isolation: As new species evolve, populations become reproductively isolated from each other
Behavioral Isolation
• Two populations may be able to interbreed, but do not recognize courtship rituals or reproductive strategies– Different songs of the
Eastern and Western Meadowlark whose habitats overlap
Geographic Isolation
• Two populations are separated by geographic barriers– Rivers– Mountains– Bodies of water
Two gene pools eventually form
If they are re-introduced and cannot interbreed they are 2 separate species
Temporal Isolation
• Reproducing at different times– Orchids in the same rain
forest may release pollen at different times
– Each species releases pollen only on one single day
– Three species release on three different days so they cannot pollinate one another
Darwin’s Finches
• Speciation in the Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population’s gene pool, reproductive isolation and ecological competition.
Founders Arrive
• Species A flew or were blown to one of the Galapagos Islands
• They do not fly far over open water
• Once they arrived, they survived and reproduced
Geographic Isolation
• Some birds from Species A cross to another island
• They rarely go over open water, so the two populations were essentially isolated and no longer share a gene pool
Changes in Gene Pool
• Populations on each island adapt to local environment
• Food sources produced different seed types
• Natural Selection puts pressure on the ideal size beak for the food source
Reproductive Isolation
• Imagine that a few birds from the second island cross back to the first island.
• They most likely will NOT interbreed because birds prefer mates with a similar beak size to their own
Ecological Competition
• More specialized birds have less competition for certain foods
• During the dry season individuals that are the most different have the highest fitness
• As differences increase, another species ma evolve