Where have all the gopher frogs gone? A scientist's froggy love led him to wonder why gopher frogs in one half of a local forest had disappeared.

Bruce Means graduated from kindergarten a long time ago, but he still likes to splatter in mud puddles and scour the woods for critters. One of the 62-year-old scientist's favorite haunts is the Apalachicola National Forest near his home in Tallahassee, Florida. "Florida is a biologist's paradise," Means says. "We have more frogs and snakes than any place in the U.S. and Canada!"

For more than 25 years, Means has scouted for frogs at a particular spot within the national forest called Munson Sand Hills. "It's about 5 miles wide by 10 miles long," he says. "And it's sprinkled full of little ponds--frog-breeding ponds."

One fascinating resident: Rana capito, known as the gopher frog. "It's a very rare animal," says Means. The gopher frog spends its adult life in this unique ecosystem, or community of diverse plants and organisms--pine forests that grow in large coastal sand deposits in the Southeastern U.S. But in recent years, Means noticed that gopher frog populations in one half of the forest seemed to have plunged. And he felt compelled to find out: Was this true?

RESEARCH STEP-BY-STEP

For scientists, a question leads naturally to an experiment. And to conduct an experiment, scientists turn to the scientific method, a step-by-step process of doing research. "It may sound scary and boring," says Means, "but the scientific method is just a logical pattern of asking questions and coming up with answers."

* The first step is observation. "It all comes from curiosity," Means says. His observation: There seemed to be fewer gopher frogs living in one half of the Munson Sand Hills.

* To verify his observation, Means did background research. This tells him if other scientists have made similar observations of conducted similar experiments. What did he find? Historical records and published studies showed that gopher frogs once thrived throughout the entire forest in Munson Sand Hills. So what might have caused the frog's numbers to drop?

Determined to find out, Means took a hard look at the Munson Sand Hills. One discovery: In the frog-deprived area, a paper company had planted a farm of sand pines where native longleaf pine trees once grew. "The sand pines grow well here, but they're alien to this region," says Means.

* This discovery allowed Means to formulate a hypothesis, an educated guess about what the answer to his question might be. Though he suspected recently planted sand pines had some effect on the frogs' decline, he couldn't be sure. "For all I know, tadpoles [premature frogs] in those ponds could have been killed off by some chemical, of perhaps someone had fished up all the tadpoles for bait." So in this case, Means found it easier to reject his educated guess rather than prove it. That's why he framed his hypothesis this way: Sand-pine tree farms in the surrounding breeding ponds do not harm the gopher frog. {This is also known as a null hypothesis.)

HOPPING EXPERIMENT

Next, Means had to come up with a carefully designed experiment to test his hypothesis. A well-designed experiment has a procedure--a step-by-step plan (see page 14). It must contain a set of clear-cut instructions to test the effect of one or more variables, or characteristics, on another. Means's experiment, for example, tested the effects of two different forest conditions on the gopher frog's ability to survive (see photo, above).

In any experiment there are two major types of variables: independent and dependent variables. The independent variable is the one you change, or adjust on purpose: In Means's case, the forest conditions that surround frog-breeding ponds--which changed when a sand-pine plantation replaced the native longleaf pine forest.

The characteristic that responds to the change is the dependent variable. In Means's study, this was the number of frogs surrounding the breeding ponds.

Armed with a precise plan of action to compare the above variables, Means set out to collect data, or information. First, he searched for historical records that traced gopher-frog numbers in both forest areas, including prior to the planting of sand pines. Then he used dipnets (handheld nets) and seines (hanging nets) to look for tadpoles in the breeding ponds of both pine forests. This allowed him to survey their numbers. After a year of collecting data, Means was ready to analyze them.

He compared the proportion of ponds with frogs in the native longleaf pine forest with the ponds in the sand-pine plantations. His finding: Gopher frogs were much more common in the longleaf pine ponds than in the sand-pine ponds. This allowed Means to reject his null hypothesis. In other words, sand-pine tree plantations do harm the gopher frog.

But how?

Means then formed a new hypothesis: "Gopher frogs ate harmed because sand pines grow so densely. Thus they eliminate the ground-cover plants that provide food and shelter for the gopher frog in its longleaf-pine habitat."

What happens after you reach a conclusion? Scientists usually publish their work to share the findings with other scientists and the world at large. "My passion is to help get people to care for nature," Means says. "Wrecking an ecosystem causes many species to decline. Since we all live in the same world, this will eventually come back to harm us."

THE SCIENTIFIC METHOD: By the Numbers

1 Base your idea for an experiment on an observation.

2 State your purpose. Usually the purpose of an experiment is stated in the form of a research question: What is the effect of (your independent variable) on (your dependent variable)?

3 Do background research to find out what is already known about your topic.

4 State your hypothesis, an educated guess about what the result will be.

5 design a detailed procedure (see p. 14).

6 Carry out your experiment and collect data.

7 Record your results. In many cases you can present your results in charts, pictures, or graphs (see p. 18).

8 Draw a conclusion from your results. Did your hypothesis prove true? Or were you able to reject your hypothesis?

THE SCIENTIFIC METHOD: The Lingo

Variables: Characteristics in an experiment that change or could be changed.

Independent Variable: Variable you change on purpose; also called manipulated variable.

Dependent Variable: Variable that responds to a change in the independent variable; also called responding variable.

Hypothesis: Educated guess about how changing the independent variable will affect the dependent variable.

Constants: Characteristics in an experiment that are kept unchanged in all trials.

Control: Standard for comparison in an experiment.

Trials: Number of times an experiment is repeated for each level, or value, of the independent variable. The more trials, the more reliable your results.

It's Your Choice

After reading the article, choose the correct answer to these questions.

1 Bruce Means's first educated guess about the cause of declining gopher frogs in Munson Sand Hills is called a(n)

A. observation.

B. manipulated variable.

C. responding variable.

D. null hypothesis.

2 The independent variable of Bruce Means's experiment is the

A. age of original longleaf pine trees.

B. paper company that planted sand pines.

C. changing forest conditions.

D. total number of gopher frogs.

3 An ecosystem is a community of

A. plants.

B. animals.

C. microorganisms.

D. all of the above

WILD SCIENTIST

NAME: Bruce Means

JOB: Biologist and chief of the Coastal Plains Institute and Land Conservancy in Tallahassee, Florida

WHY DO YOU STUDY ANIMALS? I've been fascinated with them since I was a kid. We lived in the Santa Monica mountains in California. And I would run into the woods every day after school. Hours later I would come back out with scorpions, centipedes, and tarantulas. My mom allowed me to keep them in jars in my room. But she drew the line at bringing snakes into the house.

WERE YOU A GOOD STUDENTS? I wasn't exceptionally good. I was interested in a lot of things and couldn't pay attention. But I love knowledge and found that whenever I applied myself, I did really well. Since nobody in my family went to college, going was a driving ambition. I started as a math major because I thought that would help me make good money. But I hated it! So I switched to physics. Ha! I wound up floundering for six years.

HOW DID YOU WIND UP A SCIENTIST? Instead of doing my homework, I would procrastinate by learning about wildlife. It never occurred to me that my interest in the outdoors could turn into a career. Eventually I graduated with a degree in biology from Florida State University. Then a masters and a Ph.D. in ecology followed.

SCIENCE PROJECT ADVICE: Figure out what you enjoy doing. Don't be afraid to ask questions. And just go for it. In fact, I'm doing exactly the same thing as I did as a kid. But now I have the tools to do more sophisticated experiments. Most importantly, I'm still having fun!

ANSWERS

1. d 2. c 3. d

For more on Bruce, check out: www.brucemeans.com