Chapter 16 The Origin of Species 16.1 What is a species? 16.2 How do new species form? 16.3 How is...
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Transcript of Chapter 16 The Origin of Species 16.1 What is a species? 16.2 How do new species form? 16.3 How is...
Chapter 16The Origin of Species
• 16.1 What is a species?
• 16.2 How do new species form?
• 16.3 How is reproductive isolation maintained?
• 16.4 What causes extinction?
16.1 What Is a Species?
• Biologists need a clear definition of species
• Species are groups of interbreeding populations (biological species concept)
• Morphological species concept is often used
• But, appearance can be misleading
The cordilleran flycatcher and the Pacific-slope flycatcher are different species
The myrtle warbler and the Audubon’s warbler are the same species
16.2 How Do New Species Form?
• Isolation of populations
• Genetic divergence of populations
• Allopatric speciation - different fatherland
• Sympatric speciation – same fatherland
reproductive isolation reproductive isolation
genetic divergence genetic divergence
geographical isolation ecological isolation
Allopatric speciation Sympatric speciationtimeoriginal population original population
Copyright © 2005 Pearson Prentice Hall, Inc.
Copyright © 2005 Pearson Prentice Hall, Inc.
Kaibab SquirrelNorth Rim
Abert SquirrelSouth Rim
Copyright © 2005 Pearson Prentice Hall, Inc.
Incipient Speciation
Partly formed new species
16.2 How Do New Species Form?
• Changes in Chromosome Number Can Lead to Sympatric Speciation– Speciation by polyploidy– This type of speciation can happen in one
generation– Plants can do this because they can self
fertilize and/or reproduce asexual– This is so common in plants that half of all
flowering plants are polyploid
fertilization
meiosis
meiosis fails;no viable gametes
viable, diploid gametes
Case 1: Self-fertilization
Case 2: Breeds withnormal diploid parentmeiosis
Tetraploid (4 copies of each chromosome instead of 2)
16.2 How Do New Species Form?
• Change over time within a species can cause apparent “speciation” in the fossil record
• Paleontologist use the morphological species concept (even though your book doesn’t call it that)
present
change in form
past
time
Copyright © 2005 Pearson Prentice Hall, Inc.
16.2 How Do New Species Form?
• Under some conditions, many new species may arise– Adaptive radiation
Adaptive Radiation
Figure 16-12 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.
How Is Reproductive Isolation Between Species Maintained?
• Premating isolating mechanisms prevent mating between species– Different species may be prevented from
meeting– Different species may occupy different
habitats (ecological isolation)– Different species may breed at different
times (temporal isolation)
Bishop & Monterey Pine coexist but only produce fertile offspring in the laboratory
How Is Reproductive Isolation Between Species Maintained?
• Premating isolating mechanisms prevent mating between species (cont.)– Different species may have different
courtship rituals
– Species’ differing sexual organs may foil mating attempts
Figure 16-7 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc.
16.3 How Is Reproductive Isolation Between Species Maintained?
• Postmating Isolating Mechanisms Limit Hybrid Offspring– One species’ sperm may fail to fertilize another
species’ eggs– Hybrid offspring may survive poorly– Hybrid offspring may be infertile
16.4 What Causes Extinction?
• 99.9% of all species that have ever existed are extinct
• Localized distribution and overspecialization make species vulnerable in changing environments
Very localized distribution can endanger a species
Extreme specialization places species at risk
16.4 What Causes Extinction?
• Interactions with other organisms may drive a species to extinction
• Habitat change and destruction are the leading causes of extinction
• (With invasive species and global warming also causing large problems)