ix
4-4 How Do Speciation, Extinction, and Human
Activities Affect Biodiversity? 86
SCIENCE FOCUS We Have Developed Two Ways
to Change the Genetic Traits of Populations 88
4-5 What Is Species Diversity and Why Is
It Important? 89
SCIENCE FOCUS Species Richness on Islands 90
4-6 What Roles Do Species Play in Ecosystems? 91
CASE STUDY Cockroaches: Nature’s Ultimate
Survivors 92
CASE STUDY Why Are Amphibians Vanishing? 93
CASE STUDY Why Should We Protect Sharks? 96
REVISITING The American Alligator and
Sustainability 975 Biodiversity, Species Interactions,
and Population Control 100
CORE CASE STUDY Southern Sea Otters:
Are They Back from the Brink of
Extinction? 100
KEY QUESTIONS AND CONCEPTS 101
5-1 How Do Species Interact? 101
SCIENCE FOCUS Why Should We Care About
Kelp Forests? 104
5-2 How Can Natural Selection Reduce
Competition between Species? 1075-3 What Limits the Growth of Populations? 108
SCIENCE FOCUS Why Are Protected Sea Otters
Making a Slow Comeback? 110
CASE STUDY Exploding White-Tailed Deer
Populations in the United States 114
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental
Conditions? 115
SCIENCE FOCUS How Do Species Replace One
Another in Ecological Succession? 118
REVISITING Southern Sea Otters and
Sustainability 1196 The Human Population
and Its Impact 122
CORE CASE STUDY Are There Too Many
of Us? 122
KEY QUESTIONS AND CONCEPTS 123
6-1 How Many People Can the Earth
Support? 123
SCIENCE FOCUS How Long Can the Human
Population Keep Growing? 124
6-2 What Factors Influence the Size of the
Human Population? 125
CASE STUDY The U.S. Population Is Growing
Rapidly 126
CASE STUDY The United States: A Nation
of Immigrants 129Photo 4 Temperate deciduous forest, winter, Rhode Island (USA)Paul W. Johnson/Biological Photo Service
Photo 5 Sea star species helps to control mussel populations in
intertidal zone communities in the U.S. Pacific northwest.Thomas Kitchin & Victoria Hurst/Tom Stack & Associates