Cause & Effect Review

Cause & Effect Review

Cause & Effect: What's the difference?

To find a cause, look for why something happened. To find the effect, look for the result, or what happened.

Subject | Subject

South America's frog populations are on the decline. That spells trouble for the environment.

The mountains and thick forests of Ecuador, in South America, are home to 417 types of frogs and toads. Tiny red-eyed tree frogs hide inside flowers. Bumpy-skinned toads use their sticky tongues to catch mosquitoes and other prey. Colorful poison dart frogs rest on tree branches. These brightly colored frogs are packed with poison, which protects them from their enemies.

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Frogs at Risk

​Now, many species, or types, of frogs and toads in Ecuador are at risk of dying out. According to a recent report by the group NatureServe, eight frogs have become extinct, or died out, in North and South America in the last 100 years. "It's the same magnitude event as the extinction of the dinosaurs," says scientist Luis Coloma.

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What Are Amphibians?

Salamanders, frogs, and toads are all amphibians. Amphibians are animals with backbones that spend part of their life in water and part on land. Frogs and toads lay jellylike eggs in water. The eggs hatch into tadpoles, which breathe through gills. As the tadpoles grow into frogs or toads, they develop lungs and live on land.

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Like reptiles, such as lizards and snakes, amphibians are cold-blooded. That means their body temperature depends on the environment. Unlike reptiles, amphibians lack protective scales. Amphibians must live near water so that their skin stays moist.

​Vanishing Species

Over the last 50 years, many amphibian species have become extinct. Two of every five of the 3,046 species that live in North and South America are at risk of vanishing.

Why are these creatures in trouble? Their habitat is being destroyed as loggers cut down trees to make room for farms and roads. A habitat is a place in nature where a plant or an animal makes its home. Disease, weather changes, and pollution are other causes of the decline in amphibian populations.

Scientists are concerned about the decrease in the number of frogs. The health of frogs is closely linked to the health of the environment. "Amphibian extinction is an indicator of [a problem with the environment]," scientist Jonathan Campbell told Weekly Reader.

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Because amphibians breathe through their skin, they easily absorb pollution. They are usually the first to disappear when the environment is under threat. As a result, some frogs are born with deformed, or wrongly shaped, body parts, such as extra legs and eyes. When frogs with strange body parts are found in an area, it is a clue that the environment is polluted or suffering.

​What Can Be Done?

Scientists are fighting to save amphibians. Some scientists believe that South America's poison dart frogs have chemicals in their body that can be used to treat diseases, such as cancer. The scientists want governments to pass laws that will reduce pollution and to create parks that protect the amphibians' habitat.

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"Almost half of the extinctions are happening for unknown reasons," scientist Robert Kaplan told Weekly Reader. "Scientists have a lot of work to do, and quickly."

​Endangered Amphibians

Here are some of Ecuador's threatened frogs and toads.

• Splendid leaf frogs live in top layers of trees and come down to the ground only once a year, on a moonless night, to lay eggs.

• Giant glass frogs live in trees and have translucent, or almost see-through, skin. The creature's red heart is visible from the outside.

• Harlequin toads have colorful, smooth skin, often with spots or streaks of orange, red, yellow, blue, or green.

Multiple Choice

According to the passage, there has been a decrease in the number of frogs in Ecuador. Which of the following is not a cause of the drop in Ecuador’s frog populations?

• pollution

• drought

• habitat loss

• disease

Multiple Choice

The reader can conclude that if Ecuador’s frog environment were healthy, then

• reptile populations would become extinct

• frog populations would decrease further

• reptile populations would also drop

• frog populations would increase

Multiple Choice

Read the following sentence from the passage:

“The scientists want governments to pass laws that will reduce pollution and to create parks that protect the amphibians’ habitat.”

In this sentence, the word reduce means

• spread

• share

• lessen

• increase

Multiple Choice

What is the main idea of this passage?

• Many different types of frogs live in South America.

• Scientists are working to save amphibians.

• Frogs are amphibians that breathe through their skin.

• South America’s frogs are dying out.

Multiple Choice

Tadpoles breathe through gills because

• they are cold-blooded.

• they are hatched in water and have no lungs.

• they are the offspring of frogs and toads.

• they are amphibians.

Multiple Choice

The danger of extinction is due to

• pollution or disease.

• weather changes.

• destruction of habitat.

• all of the above.