Z333 Lecture

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Chapter 16 The Origin of Species
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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 - 1930s)

• Require

• 1) Isolation of populations (restricted gene
  flow)
• 2) Genetic divergence (evolve genetic
  differences)
• Unable to produce vigorous, fertile offspring

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Chapter 16 Origin of Species
Mechanisms of Speciation
1) Allopatric Speciation

• Populations are geographically separated from
  one
• another

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Chapter 16 Origin of Species
Mechanisms of Speciation
Major Mechanism of speciation among animals
1) Allopatric Speciation

• Populations are geographically separated from
  one
• another

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Chapter 16 Origin of Species
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Chapter 16 Origin of Species
Mechanisms of Speciation
2) Sympatric Speciation

• Populations share the same geographic area

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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?
Gene Flow
A) Ecological Isolation

• Two distinct habituate types
• in the same geographic area
• leads to habitat specialization

B) Chromosome Aberrations

• Changes in chromosome s
• can cause reproductive isolation

• Polyploidy Acquisition of multiple
• copies of each chromosome

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Chapter 16 Origin of Species
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Chapter 16 Origin of Species
Speciation Produces Evolutionary Trees
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Chapter 16 Origin of Species
Species Groups of interbreeding natural
populations that are reproductively
isolated from other groups
Adaptive Value Prevent wasting of reproductive
effort by producing unfit / sterile offspring
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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
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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
D) Behavioral Isolation The separation of two
species due to different courtship
rituals
croak croak... croak croak...
clack clack... clack clack...
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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
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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
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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)
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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

• Single greatest cause of extinctions