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."