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)