Download The Origin of Species

The Origin
of Species
CHAPTER 24
YOU MUST KNOW
The biological concept of species
 Prezygotic and postzygotic barriers that maintain reproductive isolation in
natural populations
 A description of similar species that are maintained separate by each type
of isolating barrier
 How allopatric and sympatric speciation are similar and different
 How a change in chromosome number can lead to sympatric speciation
 Why speciation rates are often rapid in situations when adaptive radiation
occurs or in times of ecological stress
 The connection between a change in gene frequency, a change in the
environment, natural selection, or genetic drift and speciation
 How punctuated equilibrium and gradualism describe two different tempos
of speciation

I. Speciation and Reproductive Isolation
A.
Speciation – process by which new species arise
1. Biological Species
Concept – a species is a
group of populations
whose individuals have
the potential to interbreed
in nature and produce
viable (healthy and fertile)
offspring
https://www.youtube.com/watch?v=2oKlKmrbLoU
B.
Microevolution – change in the genetic makeup of a
population from generation to generation (confined to a
single gene pool)
C. Macroevolution – broad pattern of evolutionary change
above the species level, such as the appearance of
feathers, used to define higher taxa
D.
Reproductive Isolation – biological barriers that prevent
members of two species from producing viable offspring
1.
Prezygotic Mechanisms– occur before a zygote can be
created
a.
Geographic/Habitat isolation – do not live in the
same place
b.
Behavioral isolation – mating signals are not the same
c.
Temporal isolation – different mating seasons
d.
Mechanical isolation – anatomically incompatible
e.
Gametic isolation – gametes will not fuse together (common
in sea creatures that use external fertilization – sea cucumbers,
sea urchins, etc.)
2.
Postzygotic barriers – zygote
may be formed, but offspring
does not develop into a fertile
adult
a.
Reduced hybrid viability –
zygote forms but does not
develop
b. Reduced hybrid fertility –
zygote develops, but is
sterile
c. Hybrid breakdown – develop
into adults, can mate, but produce
weak or sterile offspring
II. Types of Speciation
A.
Allopatric speciation – new species forms because it is
geographically isolated from parent population
1. Can occur because of geologic events – emergence of
a mountain range, formation of a land bridge,
evaporation of a lake
2. Smaller populations more likely
to undergo speciation
3. Speciation confirmed when
individuals from new population
cannot mate successfully with
individuals from parent
population
B.
Sympatric Speciation
1.
Small portion of the population forms a new species
without being geographically isolated from parent
population
2. Change in habitat, food source, or accident in cell
division resulting in change in chromosome number
a. Polyploidy – nondisjunction resulting in extra sets of
chromosomes – can no longer breed with diploid
plants
C.
Adaptive Radiation
1.
Many new species arise from one ancestral species
2.
Each one fills its own niche
III. Rate of Speciation
A.
Gradualism – species descend from a
common ancestor and gradually diverge
more and more in morphology
B. Punctuated Equilibrium – describes periods of
apparent stasis punctuated by sudden change
observed in the fossil record