viii
2-4 What Is Energy and How Can It Be
Changed? 40
2-5 What Are Systems and How Do They Respond
to Change? 44
SCIENCE FOCUS The Usefulness of Models 44
REVISITING The Hubbard Brook Experimental
Forest and Sustainability 473 Ecosystems: What Are They
and How Do They Work? 50
CORE CASE STUDY Tropical Rain Forests
Are Disappearing 50
KEY QUESTIONS AND CONCEPTS 51
3-1 What Is Ecology? 51
SCIENCE FOCUS Have You Thanked the Insects
Today? 54
3-2 What Keeps Us and Other Organisms Alive? 54
3-3 What Are the Major Components of an
Ecosystem? 57
SCIENCE FOCUS Many of the World’s Most
Important Species Are Invisible to Us 61
3-4 What Happens to Energy in an Ecosystem? 61
3-5 What Happens to Matter in an Ecosystem? 65
SCIENCE FOCUS Water’s Unique Properties 67
3-6 How Do Scientists Study Ecosystems? 72
REVISITING Tropical Rain Forests and
Sustainability 744 Biodiversity and Evolution 77
CORE CASE STUDY Why Should We Care
about the American Alligator? 77
KEY QUESTIONS AND CONCEPTS 78
4-1 What Is Biodiversity and Why Is It
Important? 78
4-2 Where Do Species Come From? 80
CASE STUDY How Did Humans Become Such
a Powerful Species? 83
4-3 How Do Geological Processes and Climate
Change Affect Evolution? 84
SCIENCE FOCUS Earth Is Just Right for Life
to Thrive 86Photo 2 Homeless people in Calcutta IndiaHartmut Schwartzbach/Peter Arnold, Inc.Photo 3 Endangered ring-tailed lemur in MadagascarSuperStock