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Speciation
Formation of New Species
Read
notes
under
the
slides
Formation of Species
• Formation of new
species is called
speciation.
• Two or more new
species arise
from a previous
species.
Darwin’s Finches of the Galapagos islands
Morphological Concept of
Species
– Based on similar
structures
(morphology)
– Older definition
of species.
– Not used today.
how many
species do you
see?
Biological Concept of Species
– A population of
organisms that can
successfully
interbreed.
Panthera uncia
– The same
population cannot
interbreed with
other populations
successfully.
Leopards
Panthera pardus
Isolating Mechanisms
• Speciation begins with separation and
isolation of a single population into two
separate populations
Geographic isolation
• A physical
separation.
• Referred to as a
barrier
– Canyons
– Rivers
– freeways
What other types of
animals might be
geographically isolated?
California Newt, 3
subspecies
separated by
mountains and
waterways
Reproductive Isolation
– Reproductive barriers prevent portions of a
population from interbreeding.
– Prezygotic isolation: sperm and egg cannot reach
each other.
• Ecological isolation: same region different
habitat
• Temporal isolation: Mate during different
seasons
• Behavioral isolation: different mating ritual (bird
song, dance, pheromones)
Pollen grains: the shape of the grain can
only fit in the same species of flower like
the toy to the left. (prezygotic isolation)
Temporal
Ecological
Behavioral
Postzygotic Isolation
– Fertilization occurs but zygote does not
survive or offspring cannot reproduce.
– Offspring cannot compete successfully for
resources.
Horse
Donkey
Mule
Summary review
1.
2.
3.
4.
What is speciation?
Give your own examples of geographic
isolation and prezygotic isolation and
explain how they can lead to speciation.
What is postzygotic isolation?
What kind of speciation is shown in the
cartoons below?