Speciation
Speciation
• Speciation = formation of new species
• Species = group of organisms that breed with one
another and produce fertile offspring in nature (share a
common gene pool)
Speciation can happen in two
modes
• Modes of
speciation:
– Sympatric: new
species develop in
same geographic
region
• Sym= same
– Allopatric: new
species develop in
separate regions
• allo= other
Isolation isn’t always bad…
• As new species evolve, populations become
reproductively isolated from each other: When 2
populations cant breed and produce fertile offspring,
resulting in separate gene pools
– Behavioral isolation: Capable of breeding, but have
different courtship rituals or behaviors
– Geographic isolation: Separate by geographic barriers
– Temporal isolation: Reproduce at different times
Geographic Isolation (allopatric)
• Two populations are separated by geographic
barriers. Over time different pressures result in
distinct species
– Rivers, mountains, bodies of water, glaciers, deserts
Behavioral
Isolation
• Differences in the behavior
of two populations prevent
mating
• Because there is no gene
exchange between
populations, evolution
occurs
• Behaviors:
– Mating rituals
– Mate preference
– Mate calling
Behavioral Isolation (sympatric)
Temporal Isolation (sympatric)
• Two or more populations are separated by the time
of year/day that reproduction occurs
– Nocturnal vs Diurnal mating
– Seasonal mating differences
Speciation can happen at two
different rates
• Gradualism: Evolution occurs
slowly, gradually and
continuously
• Punctuated Equilibrium:
Species remain unchanged for
long periods of time. During
certain events, species undergo
rapid evolution.
• Both of the processes above
have likely happened
Speciation of Darwin’s Finches
• Speciation in the Galapagos finches occurred by:
– Founding a new population: A small population of finches
migrates to a different island
– Geographic isolation: Finches don’t usually fly over open water,
so stayed on own island (separate gene pool)
– Changes in the new population’s gene pool: Adapted to new
environment (directional selection) to be more fit
– Reproductive isolation: Differences in phenotypes and mating
rituals may turn different finches off to one another
– Ecological competition: Similar finches compete, so individuals
that are most different from each other have the highest
fitness, because less competition.
– Continued Evolution: Process repeats and over many
generations, it produced the 13 different finch species