1. Chapter 16:
The Origin of Species

2. Species: Groups of interbreeding natural populations that are
Chapter 16: Origin of Species
Species: Groups of interbreeding natural populations that are
reproductively isolated from other groups
Biological-species Concept
What about asexually reproducing species?
Speciation: Process by which new species form (Ernst Mayer s)
Require:
1) Isolation of populations (restricted gene flow…)
2) Genetic divergence (evolve genetic differences…)
Unable to produce vigorous, fertile offspring

3. Mechanisms of Speciation:
Chapter 16: Origin of Species
Mechanisms of Speciation:
1) Allopatric Speciation:
Populations are geographically separated from one
another
Impassible Barrier Forms
(e.g. mountains, river, ocean)
Gene Flow

4. Mechanisms of Speciation:
Chapter 16: Origin of Species
Mechanisms of Speciation:
Major Mechanism of speciation
among animals
1) Allopatric Speciation:
Populations are geographically separated from one
another
Impassible Barrier Forms
(e.g. mountains, river, ocean)
Time Passes
Gene Flow
Species 1

5. Allopatric Speciation:
Chapter 16: Origin of Species
Allopatric Speciation:
(Figure 16.2)

6. Mechanisms of Speciation:
Chapter 16: Origin of Species
Mechanisms of Speciation:
2) Sympatric Speciation:
Populations share the same geographic area
Gene
Flow

7. Mechanisms of Speciation:
Chapter 16: Origin of Species
Mechanisms of Speciation:
Polyploidy is a common mechanism
of speciation among plants
2) Sympatric Speciation:
Populations share the same geographic area
Why is gene flow reduced?
A) Ecological Isolation:
Gene
Flow
Two distinct habituate types
in the same geographic area
leads to habitat specialization
Time Passes
B) Chromosome Aberrations:
Changes in chromosome #s
can cause reproductive isolation
Polyploidy: Acquisition of multiple
copies of each chromosome

8. Sympatric Speciation:
Chapter 16: Origin of Species
Sympatric Speciation:
(Figure 16.2)

9. Speciation “Produces” Evolutionary Trees:
Chapter 16: Origin of Species
Lines that reach
the top represent
extant species
Speciation “Produces” Evolutionary Trees:
Lines that don’t reach
the top represent
extinct species
Vertical slopes
represent slow
changes in form
Forks represent
speciation events
Horizontal slopes
represent rapid
changes in form
Each line represents
a species

10. + = Species: Groups of interbreeding natural populations that are
Chapter 16: Origin of Species
Species: Groups of interbreeding natural populations that are
reproductively isolated from other groups
Isolating Mechanisms:
Structural and / or behavioral modifications
that prevent interbreeding
Table 16.1
Adaptive Value:
Prevent “wasting” of reproductive effort
by producing unfit / sterile offspring + =

11. Mechanisms of Reproductive Isolation:
Chapter 16: Origin of Species
Mechanisms of Reproductive Isolation:
1) Premating Isolating Mechanisms: Incompatibilities that
prevent mating events
A) Geographical Isolation: The separation of two species
by a physical barrier
B) Ecological Isolation: The separation of two species
occupying separate niches

12. Mechanisms of Reproductive Isolation:
Chapter 16: Origin of Species
Mechanisms of Reproductive Isolation:
1) Premating Isolating Mechanisms: Incompatibilities that
prevent mating events
C) Temporal Isolation: The separation of two species
due to different breeding seasons
Pond
Spring
Autumn
D) Behavioral Isolation: The separation of two species
due to different courtship rituals
croak… croak...
clack… clack...

13. Mechanisms of Reproductive Isolation:
Chapter 16: Origin of Species
Mechanisms of Reproductive Isolation:
1) Premating Isolating Mechanisms: Incompatibilities that
prevent mating events
E) Mechanical Incompatibility: The separation of two species
due to differences in reproductive
structures
Tailed Frog
Tree Frog

14. + Mechanisms of Reproductive Isolation:
Chapter 16: Origin of Species
Mechanisms of Reproductive Isolation:
2) Postmating Isolating Mechanisms: Incompatibilities that
prevent production of
vigorous, fertile offspring
A) Gamete Incompatibility: Sperm from one species are
unable to fertilize eggs from
another species
B) Hybrid Inviability: Hybrid offspring survive poorly +
C) Hybrid Infertility: Hybrid offspring unable to reproduce

15. Extinction: The death of all members of a species
Chapter 16: Origin of Species
Extinction: The death of all members of a species
99.9% of all species ever existing are extinct (fossil record)
Cause of Extinction = Environmental Change
Species Vulnerable to Extinction Display...
1) Localized Distribution
(susceptible to localized catastrophes)
2) Overspecialization
(susceptible to minute changes)

16. Environmental Changes Driving Species to Extinction:
Chapter 16: Origin of Species
Environmental Changes Driving Species to Extinction:
1) Competition With Other Species:
Competitors evolve superior adaptations that
allow them to out-compete a species
2) Introduction of Parasites / Predators:
Predators / Parasites prey upon naïve species
3) Habitat Change / Destruction:
Single greatest cause of extinctions