Speciation and Extinction Chapter 14 Speciation and Extinction Island: ©Morandi Bruno/Hemis/Corbis Copyright © McGraw-Hill Education.  All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

What Is a Species? Countless small evolutionary changes have accumulated through the last 3.8 billion years, leading to today’s great diversity of life. How do small mutations, even if numerous, produce new species? First, we must explore what defines a species. Section 14.1 Figure 14.1 Bacteria: ©S. Lowry/University Ulster/Getty Images; Tree: ©Corbis RF; Bird: ©IT Stock/PunchStock RF

What Is a Species? In the 1700s, Carolus Linnaeus defined species by appearance. He also created a naming scheme for species. Each species’ name combines the broader classification genus with the term species. The scientific name for humans, for example, is Homo sapiens. More recently, the biological species concept defines species based on their potential to interbreed and produce fertile offspring. Section 14.1 Figure 14.3 Butterfly collection: ©IT Stock Free/Alamy RF

What Is a Species? Speciation, the formation of new species, occurs when some individuals can no longer interbreed with the rest of the group. Section 14.1 Figure 14.3 Butterfly collection: ©IT Stock Free/Alamy RF

Clicker Question #1 The biological species concept cannot be applied to humans. plants. extinct organisms. organisms that look alike. Flower: © Doug Sherman/Geofile/RF

Clicker Question #1 The biological species concept cannot be applied to humans. plants. extinct organisms. organisms that look alike. Flower: © Doug Sherman/Geofile/RF

Reproductive Barriers Cause Speciation If the potential to interbreed defines species, reproductive isolation results in new species. Section 14.2 Figure 14.5

Reproductive Barriers Cause Speciation Prezygotic reproductive barriers occur before the formation of the zygote, or fertilized egg. They prevent fertilization. Section 14.2 Figure 14.4

Reproductive Barriers Cause Speciation Postzygotic reproductive barriers reduce the fitness of offspring produced by members of two different species. They prevent the development of fertile offspring. Section 14.2 Figure 14.4

Reproductive Barriers Cause Speciation Section 14.2 Stilts: ©Tim Fitzharris/Minden Pictures; Sperm: ©Francis Leroy, Biocosmos/Science Source; Chick: ©S. Alden/PhotoLink/Getty Images RF; Stilt: USDA Natural Resources Conservation Service Figure 14.24

Clicker Question #2 Which of the following is an example of a postzygotic reproductive barrier? A cross between a horse and a donkey produces an infertile mule. Two types of fireflies lure mates with different flash patterns. Bees pollinate one Mimulus plant species; hummingbirds pollinate another. Pine sperm cannot fertilize spruce eggs. Flower: © Doug Sherman/Geofile/RF

Clicker Question #2 Which of the following is an example of a postzygotic reproductive barrier? A cross between a horse and a donkey produces an infertile mule. Two types of fireflies lure mates with different flash patterns. Bees pollinate one Mimulus plant species; hummingbirds pollinate another. Pine sperm cannot fertilize spruce eggs. Flower: © Doug Sherman/Geofile/RF

Spatial Patterns Define Three Types of Speciation Reproductive barriers arise in three ways, depending on spatial patterns: Section 14.3 Figure 14.5

Spatial Patterns Define Three Types of Speciation In allopatric speciation, a barrier physically separates a population into two groups that cannot interbreed. With no gene transfer between the two populations, each proceeds down its own evolutionary line. Eventually, genetic differences between the populations give rise to one or more reproductive barriers. Section 14.3 Figure 14.5

Spatial Patterns Define Three Types of Speciation For example, Galápagos tortoises diverged into several subspecies on different islands. Section 14.3 Figure 14.7 Left & right tortoise: ©Tui De Roy/Minden Pictures

Spatial Patterns Define Three Types of Speciation In parapatric speciation, part of a population enters a new habitat bordering the range of the parent species. Mating can occur between populations, but most individuals mate with their own population. Genetic differences accumulate between the populations, which may make interbreeding less likely. Section 14.3 Figure 14.5

Spatial Patterns Define Three Types of Speciation Parapatric speciation may be occurring in little greenbuls. Section 14.3 Figure 14.8

Spatial Patterns Define Three Types of Speciation In sympatric speciation, populations diverge genetically while sharing a habitat. Section 14.3 Figure 14.5

Spatial Patterns Define Three Types of Speciation Cichlid fish have diversified into several species in a small African lake. Each species specializes in a unique micro-environment, leading to reproductive isolation and speciation. Section 14.3 Figure 14.9

Spatial Patterns Define Three Types of Speciation Sympatric speciation also occurs when gametes unite to form polyploid offspring with more chromosomes than either parent. Section 14.3 Figure 14.10

Spatial Patterns Define Three Types of Speciation A polyploid organism might form when gametes from two species unite, producing the first cell of a new species. Section 14.3 Figure 14.10

Clicker Question #3 About 3 million years ago the Isthmus of Panama closed, forming a land bridge connecting North and South America. Snapping shrimp collected from water on one side of the isthmus look similar to those on the other side, but they cannot interbreed. What has occurred? allopatric speciation parapatric speciation sympatric speciation Flower: © Doug Sherman/Geofile/RF

Clicker Question #3 About 3 million years ago the Isthmus of Panama closed, forming a land bridge connecting North and South America. Snapping shrimp collected from water on one side of the isthmus look similar to those on the other side, but they cannot interbreed. What has occurred? allopatric speciation parapatric speciation sympatric speciation Flower: © Doug Sherman/Geofile/RF

The fossil record supports two hypotheses about the pace of evolution: The Pace of Speciation The fossil record supports two hypotheses about the pace of evolution: Gradualism Punctuated equilibrium Section 14.4 Figure 14.11

The Pace of Speciation Gradualism suggests that evolution proceeds in small, incremental changes over many generations. Section 14.4 Figure 14.11

The Pace of Speciation Punctuated equilibrium suggests that long periods of little change are interrupted by bouts of rapid change. Section 14.4 Figure 14.11

The Pace of Speciation Bursts of speciation occur during adaptive radiation: a population inhabiting a patchy or heterogeneous environment gives rise to multiple specialized forms in a relatively short time. Section 14.4 Figure 14.11

The Pace of Speciation An adaptive radiation might occur when a key adaptation arises. The first flowering plants, for example, diversified quickly, as flowers provided a new options for reproduction. Section 14.4 Figure 14.11

The Pace of Speciation Evolution might also occur quickly following a mass extinction. The surviving organisms exploit new resources in the changed environment. Section 14.4 Figure 14.13

14.4 Mastering Concepts Describe the theories of gradualism and punctuated equilibrium. Island: ©Morandi Bruno/Hemis/Corbis

Extinction Marks the End of the Line A species is extinct when all of its members have died. Section 14.5 Figure 14.13

Extinction Marks the End of the Line Most extinctions occur as part of the background extinction rate, the pace at which species go extinct due to gradually changing environments. Section 14.5 Figure 14.13

Extinction Marks the End of the Line Earth has witnessed five mass extinctions in the last 600 million years. During these periods, many species went extinct in a short time. Section 14.5 Figure 14.13

Extinction Marks the End of the Line Impact theory suggests that meteorites or comets caused some mass extinctions. The debris suspended in the atmosphere after a collision dramatically changed the environment, leading to the extinction of many species. Section 14.5 Figure 14.12 Rock: ©Francois Gohier/Science Source

Extinction Marks the End of the Line Plate tectonics (Earth’s shifting land masses) also might explain mass extinctions. Section 14.5

14.5 Mastering Concepts Distinguish between background extinction and mass extinctions. Island: ©Morandi Bruno/Hemis/Corbis

Biological Classification Systems Are Based on Common Descent Taxonomy is the science of describing, naming, and classifying species. Section 14.6 Figure 14.15

Biological Classification Systems Are Based on Common Descent The taxonomic hierarchy organizes species into progressively larger groups. Section 14.6 Figure 14.15

Biological Classification Systems Are Based on Common Descent The more features two organisms have in common, the more taxonomic levels they share. Section 14.6 Squid: ©Frank & Joyce Burek/Getty Images RF; Fly: ©Kimberly Hosey/Getty Images RF; Orangutan: ©MedioImages/SuperStock RF; Chimp: ©Anup Shah/Getty Images RF Figure 14.16

Biological Classification Systems Are Based on Common Descent Phylogenetics is the study of evolutionary relationships among species. Section 14.6

Biological Classification Systems Are Based on Common Descent Species 1 Phylogenetic trees depict evolutionary relationships based on descent from common ancestors. Common ancestor of species 1-4 Species 2 Species 3 Species 4 Species 5 Species 6 Common ancestor of species 6 & 7 Species 7 Species 8 Species 9 Common ancestor of species 1-10 Species 10 Section 14.6

Biological Classification Systems Are Based on Common Descent A cladogram is a type of phylogenetic tree. Clades Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent A clade is a group of organisms consisting of a common ancestor and all of its descendants. Clades Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent Tracing taxa back to their common ancestor reveals evolutionary relatedness. Clades Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent According to this cladogram, a bird is more closely related to a dinosaur than a crocodile. Clades Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent We also know that turtles are more closely related to lizards than to mammals. Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent Trace lineages from right to left until they intersect to find their common ancestor. Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent Trace lineages from right to left until they intersect to find their common ancestor. Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent The common ancestor that appears farther to the right arose more recently. Section 14.6 Figure 14.17

Biological Classification Systems Are Based on Common Descent A recent common ancestor means that turtles and lizards are more closely related than turtles and mammals. Section 14.6 Figure 14.17

Clicker Question #4 What is the most recent common ancestor of species 7, 8, and 9? Species 1 Species 2 Species 3 A Species 4 Species 5 Species 6 B Species 7 Species 8 Species 9 D C Species 10 E Flower: © Doug Sherman/Geofile/RF

Clicker Question #4 What is the most recent common ancestor of species 7, 8, and 9? Species 1 Species 2 Species 3 A Species 4 Species 5 Species 6 B Species 7 Species 8 Species 9 D C Species 10 E Flower: © Doug Sherman/Geofile/RF

A Cladogram Can Be Drawn in Several Ways These cladograms all show the same evolutionary relationships. Section 14.6 Figure 14.18

Identifying Groups in Cladograms A clade is also called a monophyletic group. Section 14.6 Figure 14.21

Identifying Groups in Cladograms A paraphyletic group excludes some of the descendants of an ancestor. See how birds are excluded? Section 14.6 Figure 14.21

Identifying Groups in Cladograms A polyphyletic group excludes the most recent common ancestor of its members. Birds and mammals are endotherms, but their common ancestor was not endothermic. Section 14.6 Figure 14.21

Clicker Question #5 Using the phylogenetic tree below, is “Protista” a clade? Yes, because they all share a common ancestor. No, because not all descendants from a common ancestor are included in the group. Flower: © Doug Sherman/Geofile/RF

Clicker Question #5 Using the phylogenetic tree below, is “Protista” a clade? Yes, because they all share a common ancestor. No, because not all descendants from a common ancestor are included in the group. Flower: © Doug Sherman/Geofile/RF