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Section 30-1

Nonvertebratechordates

FishesAmphibians

ReptilesBirds

Mammals

Invertebrate ancestor

Chordate Cladogram

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Interest Grabber

Declining Numbers of Frogs

Ecologists have recently noticed declining numbers of certain types of amphibians in a variety of places. Some scientists have hypothesized that this decline might be a result of toxins in the environment. Work with a partner to discuss and answer the questions that follow.

Section 30-3

1. What characteristics of amphibians might make them more susceptible to environmental toxins than other types of animals?

2. Frogs reproduce in water. Why might toxins in aquatic ecosystems affect the reproductive success of frogs?

3. Can you think of any other possible explanations for the reduced numbers of amphibians observed?

Interest Grabber Answers

1. What characteristics of amphibians might make them more susceptible to environmental toxins than other types of animals?

Amphibians live both in water and on land, have moist skins that allow the exchange of substances, and do not have protective scales or a thick impermeable skin.

2. Frogs reproduce in water. Why might toxins in aquatic ecosystems affect the reproductive success of frogs?

Eggs and tadpoles may be more sensitive to toxins in the water during these developmental stages.

3. Can you think of any other possible explanations for the reduced numbers of amphibians observed?

Possible answers: more predators; presence of a viral, bacterial, or fungal infection; decreasing food supply; and normal fluctuations in population size.

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Section Outline

AmphibiansA. What Is an Amphibian?

B. Evolution of Amphibians

C. Form and Function of Amphibians

1. Feeding

2. Respiration

3. Circulation

4. Excretion

5. Reproduction

6. Movement

7. Response

D. Groups of Amphibians

1. Salamanders

2. Frogs and Toads

3. Caecilians

E. Ecology of Amphibians

Section 30-3

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that allow for

are

that providethat allow

are

and have special adaptations such as

larvæ they live in adults they live on

Section 30-3

means

as

Concept Map

Efficientmovement

Breathingair

Support andprotection

Bones Lungs Ribs

Amphibians

Water Land

“Double life”

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Section 30-3

Adult FrogAdult Frog

Young FrogYoung Frog

Fertilized EggsFertilized Eggs

TadpolesTadpoles

Adults are typically ready tobreed in about one to two years.Adults are typically ready tobreed in about one to two years.

Frog eggs are laid in water andundergo external fertilization.Frog eggs are laid in water andundergo external fertilization.

The eggs hatch into tadpoles a few days to several weeks later.

The eggs hatch into tadpoles a few days to several weeks later.

Tadpoles gradually grow limbs, lose their tails and gills, andbecome meat-eaters as they develop into terrestrial adults.Tadpoles gradually grow limbs, lose their tails and gills, andbecome meat-eaters as they develop into terrestrial adults.

The Life Cycle of a Frog

Video

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