Evolution and Speciation

Species A group of organisms that breed with one another and produce fertile offspring

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

Continued Evolution The process of isolation on different islands, genetic change and reproductive isolation repeated itself several times across the Galapagos Over many generations there are now 13 different species of finch there today