Download Evolution Part 3: Speciation

Speciation Drives Evolution
Unit 6: Evolution
Ch. 16-3
Speciation
 Speciation: changes that lead to the
formation of a new species
 Isolation often drives speciation
 Species are individuals who can
successfully reproduce
 Species share the same gene pool (alleles)
 When 2 animals cannot mate, they are
considered different species
Reproductive Barriers
 A. Pre-zygotic Barriers: isolating
mechanism that prevent mating from
happening at all (5 Types)
 1. Geographic Isolation- population
is separated by geographic barriers
 Mountains, rivers, oceans, etc.
 Ex: 2 squirrel species separated at the
Grand Canyon
Although they are in the same region, the white tailed
antelope squirrel inhabits desert to the north of the
canyon, while Harris’s antelope squirrel (above) has a
more limited range to the south.
 2. Habitat Isolation- Population uses
different parts of the habitat
 EX: One species of bird lives on the
ground and the other lives in the trees
 3. Temporal Isolation- Individuals
reproduce at different times
 When some are ready to reproduce,
others are not
 EX: Squirrels reproducing at different
times
 4. Mechanical Isolation- individuals
physically do not fit together to mate
 anatomy does not correspond
 EX: If a beetle’s reproductive organs
(male & female) do not fit
 5. Behavioral Isolation- changes in
courtship rituals cause indviduals
not to breed
 change in song or dance- they don’t
recognize it so they don’t mate
 EX: Grebes (birds) must dance together
before they accept each other to mate
Let’s Dance!
Blue-footed
boobies display
their blue feet
when courting
potential
mates.
Red-footed boobies are not
impressed by the display.
 B. Post-zygotic Barriers: after
reproduction occurs, this prevents a
hybrid offspring from surviving or
reproducing
 EX: A mule (horse x donkey) is sterile,
cannot produce offspring
 EX: A liger (lion x tiger) never stops
growing and will die
Types of Speciation
 1. Sympatric Speciation: organisms
live in same geographic area and
speciation occurs due to genetic
changes
 2. Allopatric Speciation: organisms
live in different areas and speciation
occurs due to geographic isolation
Speciation & Evolution
 Speciation drives evolution.
 Microevolution is small changes in a
species over time
 DNA changes are used as evidence
 Macroevolution is major changes in
the history of live on Earth over
millions of years
 Due to microevolution over long period
of time
 Fossils are used as evidence
Mass Extinctions
 Mass extinction is when a whole
species goes extinct
 Due to rapid, global environmental
changes like ice ages, comet impacts,
etc…
 Adaptive radiation: after a mass
extinction there are many new niches
open to be filled by survivors
 EX: After dinosaurs went extinct,
mammals evolved relatively quickly by
using the new habitats and resources
available and many new species arose