Transcript 17.3 The Process of Speciation

What is Speciation?
Speciation is the formation of
new biological species,
usually by the division of a
single species into two or
more genetically distinct
one.
Four Types of Isolating Mechanisms
Reproductive Isolation
Behavioral Isolation
Temporal Isolation
Geographic Isolation
Reproductive Isolation
 Reproductive Isolation is the separation of a
species or population so that they no longer
interbreed and evolve into two separate
species.
 Members of a certain species share a
common gene pool. Over time, genes are
shared by interbreeding.
 Over time, isolated gene pools diverge into
separate species.
Behavioral Isolation
 Behavioral Isolation is a form of reproductive isolation
in which two populations develop differences in
courtship rituals or other behaviors that prevent them
from breeding.
 Example: Eastern and Western Meadowlark
 The populations of the two subspecies overlap in the
midwest.
Behavioral Isolation
 Male birds sing a mating song that females like,
East and West have different songs. Females only
respond to their subspecies song.
Temporal Isolation
 Temporal Isolation is a form of reproductive isolation
in which two or more species reproduce at two
separate times.
 Example: Northern Leopard Frog
& North American Bullfrog
 Mates in April
Mates in July
Geographic Isolation
 Geographic Isolation is a form of reproductive
isolation in which two populations are separated by
geographic barriers such as rivers, mountains or
bodies of water, leading to the foundation of two
separate subspecies.
 Example: 10,000 years ago the Colorado River
separated two squirrel populations.
Geographic Isolation

Kaibab Squirrel Albert Squirrel
 This resulted in a subspecies, but did not result in
speciation because the two can still mate if
brought together
Convergence
 Convergence occurs when species
evolve into a common phenotypic
form due to a common need.
 For example the diagram portrays a
shark, ichthyosaurus, a penguin and
a dolphin. These are fish, reptile.
bird and mammal respectively .
They all have a torpedo body shape,
pectoral, caudal and dorsal fins.
This is based on their common need
to swim rapidly in an aquatic
environment.
Divergent Evolution and
Adaptive Radiation
 Divergence occurs when
species evolve in several
directions away from a
common ancestor. This
happens usually to fill a
vacant ecological niche.
Also known as adaptive
radiation.
Convergent or Divergent Evolution?
Convergent or Divergent Evolution?
 What process is shown in diagram A? Explain
 Divergent Evolution or Adaptive Radiation. It is because one
ancestral species has given rise to many new species
 Why do the animals in diagram A look different from each
other?
 They have evolved to fit different niches.
 What process is shown in diagram B? Explain
 Convergent Evolution. It is because the three organisms look
similar but have been produced by separate evolutionary
lines.
 Why do the animals in Diagram B look similar to one another?
 They have evolved to fit similar niches.