Inspire Biology

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Extinction Rates

Species become extinct because they can no longer survive and reproduce in an environ-

ment. If members cannot adjust to change that is too fast or drastic, the opportunity for

the species to evolve is lost. Many species that lived on Earth millions of years ago have

become extinct. Paleontologists study fossils of those species. Not all species that have

become extinct have been gone long enough to leave fossils. Several species of amphibi-

ans, insects, and even mammals have become extinct over the past several decades. The

gradual process of species becoming extinct is known as

background extinction.

Stable

ecosystems can be changed by the activity of other organisms, climate changes, or natural

disasters. This natural process of extinction is not what concerns scientists. Instead, many

worry about a recent increase in the rate of extinction. Some scientists predict that

between one-third and two-thirds of all plant and

animal species will become extinct during the

second half of this century. Most of these extinc-

tions will occur near the equator, and affect

organisms like the frog in

Figure 9

Some scientists estimate that the current rate of

extinction is about 1000 times the normal back-

ground extinction rate. They think that we are

witnessing a period of mass extinction.

Mass

extinction

is an event in which a large percentage

of all living species become extinct in a relatively

short period of time. The last mass extinction

occurred about 65 million years ago, as illustrated

Table 1

on the next page.

Figure 9

Animals that live in the tropical rain forests, like

the blue poison frog, are more likely to go extinct than

animals in other areas.

LESSON 2

THREATS TO BIODIVERSITY

FOCUS QUESTION

How can the decline of a single species affect an entire

ecosystem?

Disciplinary Core Ideas

Crosscutting Concepts

Science & Engineering Practices

3D THINKING

COLLECT EVIDENCE

Use your Science Journal to

record the evidence you collect as

you complete the readings and

activities in this lesson.

INVESTIGATE

GO ONLINE

to find these activities and more resources.

Applying Practices:

Evaluating Impacts of Environmental Change on

Populations

HS-LS4-5.

Evaluate evidence that supporting claims that

changes in environmental

conditions

may result in:

(1) increases in the number of individuals of some species, (2) the

emergence of new species over time, and (3) the extinction of other species.

Lesson 2 • Threats to Biodiversity

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