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Frog Footprints

Lesson at a glance:

Students will follow the life cycle of a frog and become aware of some of the threats it faces as it matures.

Relevant National Curriculum Standards and Benchmarks:

Standard: Knows about the diversity and unity that characterize life

Benchmark: Upper Elementary (Grades 3-5): Knows that plants and animals progress through life cycles of birth, growth and development, reproduction, and death; the details of these life cycles are different for different organisms.

Standard: Understands how species depend on one another and on the environment for survival

Benchmark: Upper Elementary (Grades 3-5): Knows that the behavior of individual organisms is influenced by internal cues (e.g., hunger) and external cues (e.g., changes in the environment), and that humans and other organisms have senses that help them to detect these cues.
Benchmark: Upper Elementary (Grades 3-5): Knows that an organism's patterns of behavior are related to the nature of that organism's environment (e.g., kinds and numbers of other organisms present, availability of food and resources, physical characteristics of the environment).
Benchmark: Upper Elementary (Grades 3-5): Knows that changes in the environment can have different effects on different organisms (e.g., some organisms move in, others move out; some organisms survive and reproduce, others die).

Standard: Understands the cycling of matter and flow of energy through the living environment

Benchmark: Primary (Grades K-2): Knows that plants and animals need certain resources for energy and growth (e.g., food, water, light, air).
Benchmark: Upper Elementary (Grades 3-5): Knows that the transfer of energy (e.g., through the consumption of food) is essential to all living organisms.
Benchmark: Upper Elementary (Grades 3-5): Knows the organization of simple food chains and food webs (e.g., green plants make their own food with sunlight, water, and air; some animals eat the plants; some animals eat the animals that eat the plants).

These national standards and benchmarks are summarized at http://www.mcrel.org/standards-benchmarks/

Materials:

• One sheet of 2’ x 3’ poster board per game
• One brad per game
• Glue
• Scissors
• A hole punch
• One copy per game of the spinner, game board diagram and clues
• Tokens for students or teams (can be anything)

Background:

What is an Amphibian?

Poison dart frogs, Western toads, rough-skinned newts and woodland salamanders are all members of the class amphibia. The word amphibian means "double life" and refers to the life cycle of these animals. Most adult amphibians spend part of the year on land but return to lakes and ponds to breed. It also refers to the transformation of an aquatic tadpole into a terrestrial frog, toad or salamander.

Amphibians share the following characteristics, most of which allow them to live both on land and in the water:

• They are cold blooded.
• Most change from an aquatic larval stage to a terrestrial adult form (called metamorphosis).
• They have moist, smooth thin skin with no scales.
• Feet, if present, are webbed, and the toes lack claws.
• They use gills, lungs and skin to respire.
• The larvae have two-chambered hearts, and the adults have three-chambered hearts.
• The eggs lack shells and are usually laid in water or in a moist environment and fertilized externally.
• They generally have four legs (except for the wormlike caecilians and the sirens).

An amphibian’s naked skin is one of its most important adaptations they lack the scales, feathers or hair that grows from the skin of other vertebrates for protection. Instead they have three kinds of glands to help protect them. The first set of glands is found on the top side of the animal and often produces a poisonous secretion, which deters predators. A second set of glands is spread evenly over the entire body and produces a thin mucus. On land, its main purpose is to keep the skin moist and allow respiration to take place through the skin (this could not happen through a dry skin surface). In the water, it helps to maintain the salt and water balance in the body fluids and acts as a lubricant during swimming. "Mixed" glands produce both mucus and poison secretions and are located over almost the entire body of the amphibian.

Frogs and Toads

Frogs and toads belong to the order Anura, meaning the animals "without tails"; the order includes over 3,800 living species. These animals have enlarged back limbs to hop or jump. Frogs and toads can be distinguished from each other by how they look and move:

Both frogs and toads return to water to reproduce. In nearly all species, eggs are fertilized externally, and the swimming larval form that hatches from an egg is called a tadpole. Most tadpoles are herbivorous, feeding on green algae and bacteria.

As frogs and toads begin the process of metamorphosis (the transformation of an aquatic tadpole to a terrestrial frog or toad), many changes must occur. At hatching, tadpoles have a large, round body and a long tail fin. As they develop, the following changes occur:

• Their back legs grow, followed shortly by the growth of their front legs.
• The gills are absorbed and lungs develop.
• The tail is absorbed.
• The eyelids appear.
• The digestive tracts and mouths of the plant-eating tadpoles change into the mouths and carnivorous digestive tracts of frogs and toads.

The period between hatching and metamorphosis typically lasts two to four months, but in some species, such as the tailed frog, it may take up to four years.

The case of the disappearing amphibians

With over 5,000 living species worldwide, amphibians play an important role in many ecosystems as both predator and prey. Over the past 20 years, scientists have recorded a decline in many of the world’s amphibian populations, and these animals are considered to be indicators of the health of an ecosystem. Several characteristics make them especially vulnerable to decline:

• Amphibians have permeable skin, which make them susceptible to pollutants and toxins in the ecosystem.
• Their high position in the food chain may increase environmental effects.
• They can be further threatened by urbanization, acid rain, soil and water pollution, habitat destruction, forestry, development, farming and possibly the thinning ozone layer.
• In Asia, amphibians are collected, dried and ground up to use as aphrodisiacs and cures for medical problems.
• Amphibians are also over-collected for pets, medical research and live bait for fishing in many countries, including the United States.

The introduction of non-native amphibians also affects amphibian populations. For example, native Northwest amphibians, as well as reptiles, birds and small mammals, are all threatened by the introduction of the bullfrog from the eastern United State. First brought to the West because of its tasty legs, the adaptable, prolific and voracious bullfrog is proving to be the top competitor against native amphibians and is a major factor in their decline. It not only thrives in their habitat, but eats native amphibians and their food sources as well.

Activity:

1. Before class, copy the spinner, arrow, game board and clues for each game you will be making.
2. Cut out the spinner and arrow. Glue them onto the poster board or laminate them. Punch a hole in the center of the spinner and the arrow and insert a brad. Adjust the brad so that the arrow spins.
3. Glue the game board onto a piece of poster board.
4. Cut out the clues and glue them near the corresponding number on the game board.
5. Choose tokens for use in the game and give one to each student. Students could draw or create their own frog game tokens with their name on them.
6. Divide your students into groups of 4-6.
7. Explain the following directions to the class:

• Put your frog on start.
• Spin the spinner and hop ahead that number of spaces
• Follow the directions on the square you land on.
• Now let the next person take their turn.
• Continue taking turns until your frog makes it to the finish.

Summary:

With your students, discuss the following questions:

1. What types of predators tried to eat the frogs? Which predators were native to the ponds? Which predators were introduced?
2. Name two natural occurrences that affected your frog.
3. Name three factors that prevented all of the eggs from hatching.
4. Name two things that caused the adult frogs to die or disappear.
5. How did humans affect the frogs?
6. Why do frogs lay so many eggs?
7. Describe frog metamorphosis.

Extensions:

• Have the students write a research report on a species of frog. Have them include where their animal lives, what and how it eats, and other interesting information. Have them share it with the class.
• Once the animals are researched, have the students create a mural showing where their frog lives.

Game Clues

1. You are one egg in a cluster of hundreds. Some hungry fish are hanging around. Don’t wiggle in your see-through egg and maybe they won’t eat you.
2. The sun has moved over the pond. Half of the egg cluster is sitting in the sun. Some of the eggs do not survive. Hop back one space.
3. You hatch safely into a tadpole. Move ahead two more spaces.
4. The sun has caused algae to grow in the pond. You have plenty of fresh, slimy green algae to eat. Move ahead one space.
5. You grow legs, lose your tail and crawl out of the water. Hop ahead two more spaces.
6. A big bullfrog hops out near you. Freeze! (If you move it might eat you.)
7. The trees are cut down on one side of the pond. The water starts to dry up. You move to the other side of the pond. Hop ahead one space.
8. El Niño changes the weather pattern. It’s too hot and dry for you to eat. You lose weight. Hop back one space.
9. The weather pattern changes again. Heavy rains put more water in your pond. Hop ahead one space.
10. Heavy rains wash oil into the pond. It kills some of your friends. You survive. Hop ahead one space.
11. You move to a new pond. Winter turns to spring. As the temperature warms up, you begin to practice your croaking.
12. The mosquitoes are beginning to hatch. You’re looking forward to a huge meal. Hop ahead one space.
13. You’re so full of tasty mosquitoes that you take time to rest on a lily pad.
14. A pesticide truck sprays your pond to kill the mosquitoes. The spray burns your sensitive skin and leaves you without food. Hop back one space.
15. You and your friends decide to move to another pond. Migrating across the road, five of your friends are run over. But you make it across. Hop ahead one space.
16. Suddenly a whole bunch of people with nets are wadding through the pond. They are collecting your friends and putting them in containers with lids. You dive to the bottom of the pond. Stay put and you won’t be caught.
17. Thank goodness you won’t be frog legs on someone’s plate! The frog hunters are gone. You croak with joy. Hop ahead two spaces.
18. Your singing helps you find a mate. You lay and fertilize 350 eggs. Take a break.
19. El Niño strikes again. It’s a dry summer and only a few of your eggs survive.
20. The eggs shaded by the brush and huge pine trees survive and escape damage from ultraviolet rays. Hop ahead one more space.
21. It’s a nice warm day. Rest on your lily pad.
22. Fish, salamanders and bullfrogs eat more than half of your eggs. Hop back one space.
23. The warm weather makes the mayflies hatch. You eat a dozen in just a few minutes. You’re too full to move. Stop and digest them.
24. A group of local citizens keep your pond form being drained for a housing development. Hop ahead one more space.
25. Finally 75 of your eggs survive and hatch into tadpoles. Hop ahead one more space.
26. A group of school children catch some of your tadpoles. They bring them back to school and put them in a tank. After watching them metamorphose into frogs, they release them back into the pond. Hop ahead two spaces.
27. Thirty of your tadpoles escape being eaten by an alligator someone released into the pond. Hop ahead one space.
28. A protected wetland filters out pollution before it washes into your pond. Hop ahead one space.
29. You dodge the beak of a hungry great blue heron. Dive to the bottom and hide.
30. Suddenly, a human hand grabs you from the water. After giving you a kiss, they gently place you in the water. Thank goodness their hands were wet and they didn’t hurt your sensitive skin. Swim away and take a rest.
31. Twenty of your 350 tadpoles finally grow legs and leave the water. Hop ahead one more space.
32. Congratulations! You’ve completed the life cycle!

© 1998 Oregon Coast Aquarium. All rights reserved.