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