Materials Included In Kit

Safety Precautions

The materials in this activity are considered nonhazardous. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Disposal

All materials may be saved for future classroom use.

Teacher Tips

• Enough materials are provided in this kit for five groups of students. All materials are reusable. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period.
• The “frog” beads may be placed in the simulated frog pond containers and covered with the lids for extended storage.
• One Frog Pond Population Graph paper sheet is provided. Make a copy of this sheet for each student or student group as needed.
• The decline of amphibians is a complex issue that involves many environmental factors. This activity gives students the basic understanding of how populations fluctuate naturally and under human influence in the wild.
• Have students brainstorm other factors that could affect a frog population and make additional frog pond population cards to add to the provided card sets.
• This activity could be used before performing a class monitoring project of a nearby water source.

Sample Data

Part I. Natural Factors

Answers to Questions

1. Describe any overall changes or trends in the frog population in Part I.

   The frog pond population increased and decreased depending on the factor that was introduced. One mutation was seen in the population. In the end, after all the cards were drawn, the frog pond population returned to the original level.

2. Compare and contrast your graph from Part I to another group’s graph. What factors may explain any similarities or differences in the graphs?

   Results will vary depending on the order the cards are drawn from the card deck.

3. How did the “human influences” added in Part II affect the frog population?

   The population of the frogs in the pond was dramatically reduced or eliminated the frog population. An increased amount of mutations were also observed.

4. Did your frog population in Part II become extinct? Explain.

   Results will vary. The frog population in Part II will most likely become extinct.

5. How did the deformity counts between Parts I and II differ? Why?

   The deformity rates in Part II were higher than what was seen in Part I. The increased amount of human environmental intervention caused the higher deformity rates.

6. Discuss some general measures that humans can take to protect frog and other amphibian populations so they do not become extinct.

   Reduce the amount of habitat destruction, reduce the amount of chemical pollution, support population restocking efforts, etc.

7. How could the number of frog deformities be reduced?

   Decrease the amount of parasites in the population, reduce chemical pollution, decrease the rate of reduction of the ozone layer, etc.

References

Schnake Greene, J. and Tamme, T. Science Activities—Ups and Downs of Frogs; Washington, DC; 2001; Vol. 38, Number 2, pp 12–16.

Introduction

The decline in amphibian populations and increase in amphibian deformity rates throughout the world has become an issue of great concern. In this activity, a card game will be played to simulate the frog population of a local pond under both natural- and human-influenced situations.

Concepts

• Amphibians
• Deformities
• Population cycles
• Environmental factors

Background

Scientists have been observing a worldwide decline in amphibian populations. Although it is not clear if this decline is a long-term trend or natural fluctuations in populations, most scientists agree that something serious is happening. Some species of amphibians are showing no decline, while other species, such as the golden toad and harlequin frog, from relatively undisturbed pristine habitats, are rapidly declining.

Cyclic fluctuations in amphibian populations occur normally in nature. Short-term population studies may show that the population of a certain species appears to be in a rapid decline while, in fact, the species may be undergoing a normal population decrease. To better understand a species population it is imperative that long-term studies be performed. By studying amphibian populations, a greater understanding of the variety of environmental issues that influence all animal populations may be obtained.

Amphibians, such as frogs, have several unique characteristics which make them very susceptible to changes in the environment. Their moist thin skin is in constant contact with their surrounding environment—directly exposing them to pollution. Many amphibians live the beginning stages of their lives in water and their adult lives on land. This exposes them to both aquatic and terrestrial environmental factors. Frogs and toads generally feed on plant material in their larval stages and become carnivores as adults—introducing them to a wide variety of food sources. Amphibians also tend to stay in one general area throughout their lives. Since they stay near their birthplaces, amphibian populations do not usually become replenished by means of immigration. The colors, shapes, sizes, reproduction methods, behaviors and habitats of amphibians across the world vary dramatically. This wide diversity makes it difficult to isolate one single reason why amphibian or frog populations are dwindling. It is most likely that a combination of environmental factors are leading to amphibian declines.

In 1995, a middle school class in Le Sueur, Minnesota came upon a large population of deformed leopard frogs while on a biology field trip. It was later determined that 30 to 40 percent of the frogs in the pond were deformed. At the same time, scientists were discovering that amphibian deformities were occurring not just in Minnesota—they began to receive reports of mass deformities from around the world. Reported deformities included extra limbs, extra eyes, missing eyes, misshaped limbs, missing limbs and limbs growing in incorrect locations. Although deformities of species occur normally in nature, the widespread occurrence and high numbers of deformities (as high as 60 percent in some populations) of amphibians suggest that other environmental issues were responsible.

Deformities, like the overall amphibian decline problem, are likely to be a result of multiple causes—many related to human-induced environmental changes. Factors such as increased levels of ultraviolet (UV) radiation, chemical contamination, and parasitic infection are currently being studied as causes of amphibian deformations. It is possible that the observed deformities are resulting from several different factors, acting alone or in combination with one another.

Experiment Overview

A card game will be played to simulate the frog population of a specific pond. In Part I, the population of the frog pond with little to no human intervention will be simulated, modeled and graphed. In Part II, human-induced factors will be introduced to the pond and their impact on the frog population will be further investigated.

Materials

Safety Precautions

The materials in this activity are considered nonhazardous. Please follow all laboratory safety guidelines.

Procedure

Part I. Natural Factors

1. Obtain 75 green beads, 25 blue beads, a simulated frog pond container, a die and a set of the Natural Factor Game Cards.
2. Count out and place 50 green beads in the frog pond container. Each green bead represents a healthy individual frog. Record the original number of frogs in the pond on the worksheet.
3. Shuffle the green Natural Factor Game Cards and place them face-down in a pile on the tabletop.
4. Draw the top card on the pile. Read the card and see how the factor affected the frog population in the pond that year.
5. The number on the card represents the number of frogs that should be added or subtracted from the frog pond. Add the number of healthy frogs (green beads) or randomly remove the required number of frogs from the simulated pond container. Record the factor and number of frogs added or subtracted from the pond on the worksheet. Note: Do not return the game card to the pile.
6. If the card states that a deformity of the frogs has occurred, roll the die to see how many frogs have become deformed. Remove this number of healthy frogs (green beads) from the frog pond and replace them with the same number of deformed frogs (blue beads). Shake the container of beads to “disperse” the population. Record the number of deformed frogs on the worksheet.
7. Repeat steps 4–6 until all of the Natural Factor Cards have been read. Each card represents what has happened to the frog population in one year. Remember that if frogs are to be removed from the pond, remove the frogs randomly (without looking at the color of the bead). This ensures that both healthy frogs (green beads) and deformed frogs (blue beads) may be removed from the population.
8. Graph the overall frog population and the number of deformed frogs per year for Part I on the Frog Pond Population graph paper. Use different colored pencils on different symbols to graph the results.

Part II. Human-Induced Factors

9. Remove the beads from the simulated frog pond container.
10. Count out and place 50 healthy frogs (green beads) into the container.
11. Add the purple Human-induced Factor cards to the Green Natural Factor Card deck.
12. Reshuffle the cards.
13. Repeat steps 4 through 6 in Part I until all the cards have been read or the frog population becomes extinct.
14. Graph the frog population and the number of deformed frogs for Part II on the Frog Population graph paper. Use different colored pencils on different symbols to graph the results.
15. Answer the Post-Lab Questions.

Student Worksheet PDF

12691_Student1.pdf