What is the key concept for this section? Define and distinguish between biological extinction and mass extinction. What is the background extinction rate? What percentage of the world’s identified...

What is the key concept for this section? Define and distinguish between biological extinction and mass extinction. What is the background extinction rate? What percentage of the world’s identified species is likely to become extinct primarily because of human activities during this century? How many of the earth’s 24 major ecosystem services are in decline? Give three reasons why many extinction experts believe that projected extinction rates are probably on the low side. Explain how scientists estimate extinction rates and describe the challenges they face in doing so. Distinguish between endangered species and threatened species and give an example of each. List four characteristics that make some species especially vulnerable to extinction.