Speciation - Cloudfront.net

Formation of Species
grp. of organisms that look alike & interbreed to produce fertile offspring
Subspecies-(they can be broken down into subspecies-distinct from each
other, but can interbreed-usually don’t)
to form a new species• need isolation from gene pool!! (Ex: Finches on
A new species has formed:
• produce fertile offspring
• Offspring develop completely
 offspring live to reproductive age
3 Isolation Mechanisms
1. Geographic isolation =
population separated by physical barriersEx: island formation, a
canyon/river forms
2. Behavioral isolation =
differ in courtship rituals or don’t respond to mating signals Ex: Birds using
different songs to attract mates
3. Temporal isolation =
species reproduce at different times of the yearEx: organisms mate in
autumn vs. spring
Rates of Speciation – Two Hypotheses:
1. Gradualism –
speciation occurs through a SLOW change of adaptations2. Punctuated
Equilibrium –
speciation occurs in BURSTS w/ long periods of no change in between *
Fossil evidence for both but remember not everything is fossilized!