Why is a butterfly like a steel rivet?
Jasper Ridge, Stanford, Calif. — Until I met Paul Ehrlich I never could fathom why ecologists made such a fuss over environmental esoterica like the snail darter, the shiny pig-toed pearly mussel, and furbish lousewort.
i was never quite sure which of these endangered species with the jabberwocky names were animal and which vegetable (which is a confession, not a criticism). Furthermore, I couldn't comprehend why they were important enough to be stopping hydroelectric projects and the like.
Bald eagles, blue whales, timber wolves, and trumpeter swans were a whole different story, as far I was concerned. They were the stuff of presidential seals, fairy tales, and team mascots. But who could picture a squadron of pom-pom, girls on the 50-yard line cheering "Go Humpback Chubs! Go, fight, win!"?
Paul Ehrlich set me straight in an afternoon on Jasper Ridge, wandering among the Euphydryas editha.m More on that little creature in a minute. First, meet Professor Ehrlich.
One of the world's most renowned population biologists, he teaches at Stanford University. Much of his reputation rests on his series of best-selling books dealing with problems of population growth and diminishing resources: "The Population Bomb" (1968), "The End of Affluence" (1974), and "Ecoscience: Population, Resources, Environment" (1977).
He is a rail-thin man, armed with a quick wit and skeptical of easy answers. His beard has an angular, Abe Lincoln look, and his deep nasal voice resonates as if it's been recycled through a rain barrel. The day we met, Ehrlich was dressed in hiking boots, clip-on dark glasses, a blue work shirt with a pocketful of pens and a cloth army hat. The hat's brim was coming unstuck in back and gave it a coonskin-cap effect. The professor carried a butterfly net.
In the shade of an oak grove, he sat munching the contents of a sack lunch and sipping unfiltered apple juice. He was comfortable and had an audience. Not one to pass up an opportunity to preach his environmental gospel, Professor Ehrlich offered his own fable for out time, "The Jetliner and Its Rivets," before we hiked the ridge.
"Suppose you had to fly back East," he began. "So you go down to San Jose to catch a flight on Growthmania, that well-known airline whose profits increase every year forever until it fills the whole universe. But as you're walking out on the tarmac to Growthmania's 707, you see a guy up on a ladder, and he is prying rivets out of the wing. Naturally, you are curious, and you saunter over to ask:
"'Hey, buddy! What are you doing?'
"'Cant' you see?' he replies somewhat impatiently. 'I'm prying rivets out of the wing.'
"'That isn't too smart, is it?' you tell him.
"'Sure it is. Growthmania gives me two bucks for each rivet I take out and they sell them for three bucks. So everybody is happy.'
"'But that's likely to damage a wing, and sooner or later it will fall off.'
"'Are you kiddin'? I've taken hundreds of rivets out of this wing. Nothing has happened yet. There's a lot of redundancy built into these planes.'"
Ehrlich settles back, takes another guzzle of apple juice and continues.
"As the guy on the ladder is speaking, you think to yourself, 'Sure, this plane might fly another 10 years with 50 rivets missing. But it's also possible that an hour after takeoff we may hit a thunderstorm, pull six Gs and have the wing snap off.' You finally realize that no person in his right mind would get on that plane, so you walk into the terminal and ask the FAA to life Growthmania's license."
The professor's forehead furrows. He musters all the fire and brimstone necessary to drive home the moral of the story.
"What we're doing with the environment is prying rivets out all over the place. You will never succeed, arguing for the environment rivet by rivet. You can never prove that destroying the snail darter or the furbish lousewort will cause the collapse of the ecological system any more than you could argue (and I'm a pilot) that a jetliner's wing would snap off because of the loss of one rivet.
"The problem is that the missing rivets are building up and eventually the wing will come off. Society is simply unwilling to face what it is up against, and hopes to push it off on the future. But I'm afraid that we, and not our grandchildren, will pay the price of prying out the rivets."
Paul Ehrlich has devoted 21 years of his life to studying one of nature's "rivets," the checkersport butterfly, entomologically known as E. editha.m This species of checkerspot, named for its checkered pattern of blacks, reds, and yellows, ranges from Canada to northern Baja, and as far east as the Rocky mountains. Though it can survive in habitats as diverse as desert and mountain, the checkerspot is a sedentary insect, never traveling more than a few hundred yards from its food plant. The Monarch butterfly, in contrast, migrates as much as 3,000 miles.
Of the 14 colonies of E. editham that lived in the mid-1960s along the penninsula region between San francisco and San Jose, 11 have been driven into extinction with the construction of freeways and subdivisions. This checkerspot is expected by biologists to go on the endangered species list within the next several years. The delicate little creature has become immensely important in the construction of new theories of genetics and evolution, as well as in the development of schemes for ensuring the survival of endangered species like the blue whale.
Largely as a result of Professor Ehrlich's research over the last two decades -- the longest study of its type ever conducted on an insect -- scientists know more about the population biology, the ecology and genetics of E. editham than of any other nonhuman organism. His butterfly study has become a model for long-term environmental research and has revolutionized scientific thinking about the interaction between insects and plants.Ehrlich, who coined the term "coevolution" for his approach, has broken new ground in the field of population structure, reproductive biology, and gene flow between different populations. From his study of the checkerspot's behavior, scientists can extrapolate new ways to boost agricultural production to help solve the food and population problems of which he has so frequently written.
Ehrlich's laboratory is Stanford's 1,300-acre Jasper Ridge Biological Preserve. It is the largest and most biologically-diverse preserve on any American university campus. The ridge borders on the crowded, urbanized region between San Francisco and San Jose, one of the fastest-growing regions in the country.
Jasper Ridge is a veritable archive of natural history, with 120 native herbs , 20 kinds of trees, 46 shrubs, 49 grasses, 79 varieties of sunflower along with rattlesnakes, bobcats, and rare horned toads. The first doctoral thesis using Jasper Ridge was submitted in 1897. Since then about a student a year has earned his PhD on Jasper Ridge. At present, 18 undergraduate courses visit the preserve to inspect everything from chert and Franciscan greenstone to asbestos veins.
Ehrlich commands a small army of graduate students and undergraduates who stalk the checkerspot on the ridge. As we emerge from the chaparral into a meadow, I spot the undergraduate battalion in shorts and track shoes bounding knee-deep through sunflowers and serpentine grass, scooping the air with butterfly nets. It is the checkerspot's mating season, and on this hot afternoon the coldblooded critters refuse to sit still for their captors. Ehrlich informs me these students are part of his "mark-release-recapture" program. When a student nets a checkerspot, he marks the underside of the wing with a felt-tip pen, much like biologists tag dolphins and migrating birds. When his students are through, Ehrlich has a meadow of flapping abacuses, from which he can chart the butterfly's movement.
Meanwhile, another group of undergraduates is on hands and knees and appears to be sniffing sunflowers, like so many oversized honeybees collecting nectar. Still another team carries stopwatches to record the flight patterns of individual adult butterflies for as long as a student can pursue the bug. A journal entry from an afternoon's odyssey might read ". . . three seconds probing on lasthenia,m flies six meters, lands on grass stalks, spends 8 seconds, flies 3 meters, then probes, apparently drinking. . . ." When this season is finished, Ehrlich will have 2 million seconds of probing, flying, landing, and apparently drinking, which he will ask a computer to make sense of.
"Butterflies are ideal for research," he says. "their genetics are displayed in two dimensions on the wings. When you capture fruit flies, you can get back to the lab and find under the microscope you've got 25 different varieties, 24 of which you don't want. Butterflies are relatively easy to catch. Very few organisms can you sample as easily as butterflies, one species at a time. They're easily bred in the laboratory and happen to be the best known group of herbivores [plant-eating animals.]"
When Ehrlich came to Stanford in 1959 from the University of Kansas where he earned his PhD, he realized he was sticking his neck out by undertaking a comprehensive study of the checkerspot. As an untenured assistant professor, he was urged not to gamble on long-term research but to obey immediately the academic edict "publish or perish." Most junior faculty members prefer research projects which turn outquick results and please promotion committees. Ehrlich straightened his spine and marched off to Jasper Ridge.
His conviction paid immediate dividends. After a few months on the ridge, he discovered that, contrary to popular thinking, there was not just one population of checkerspots but three. While all three groups inhabited the serpentine meadow, each was a distinct, independent demographic unit of the species -- much like three separate branches of the Jones family living in three different New York neighbor-hoods but never visiting each other.
Furthermore, he found that the population of each colony changed in different directions. While one was increasing, another might be decreasing; while one was booming, another was becoming extinct. Ehrlich realized that trying to generalize about the dynamics of checkerspots on Jasper Ridge without measuring population shifts of each individual colony was "like trying to evaluate the function of thermostats in several different aquaria by taking water samples from each, dumping them in a common container, and measuring the temperature of the mixture."
The uneducated response to Ehrlich's discovery might well be "So what?" But the principle he uncovered has broad meaning. In essence, it renders useless any schemes for "regulating" animal populations -- from commercial fisheries to endangered whales -- which do not first consider separate demographic units involved. One of the problems for designing a harvesting strategy, he says, for the Peruvian anchoveta fishery (which, at its height, supplied 13 million metric tons of fish, nearly 17 percent of the world's total marine fisher harvest) is that no one really knows whether there are one, two, or three populations.
He offers another example: "Suppose there were 2,000 blue whales left in the world, and they were all one population mixed together. You might be able to take 500 whales per generation without pushing down its size. But if there are four different populations of 500 each, you couldn't take nearly as many out without doing permanent damage."
Having distinguished the three separate populations of checkerspots, Ehrlich set out to solve the next mystery: What was controlling the fluctuations in their population size? Recalls the professor: "We couldn't figure it out, but we knew it had something to do with the caterpillar stage in the cycle."
Every spring on Jasper Ridge, adult checkerspots lay masses of eggs on Plantego erecta,m a native annual plantain. The caterpillars (or larvae) hatch, eat the plantego, and go into a resting period during the dry California summer. In the winter months the rains return, the plantego blooms, and the larvae "wake up" and feed. They form their pupae in the early spring, hatch, mate, lay eggs. And so the cycle continues.
During the winter "caterpillar season," soggy Jasper Ridge is unbearably soggy and offers three distinct varieties of mud to choose from. Hip boots are advisable. "I decided if I was going to solve the caterpillar mystery I had to find a graduate student pre-adapted to the climate," says Ehrlich. "I chose Michael Singer from England, where it's muddy most of the time. He went out and lay around in the mud for two years on Jasper Ridge, and came back with the answer."
The news Singer brought back was simple but starling. He found that although the checkerspots laid their eggs on plantego and were raised in the lab on plantego, the vast majority of the caterpillars which reached adulthood did so by switching in the summer to an owl's-clover, Orthocarpus densiflorus.m "I had been fooled all along," says Ehrlich, who had puzzled over why the checkerspots around Stanford were found only around the serpentine soil when the plantego, the checkerspots' food plant, was found elsewhere. The answer: the owl's-clover , the secondary food source, was restricted to the serpentine soil.
This revelation and others led Ehrlich to focus on something he called "coevolution," which he defines as "the reciprocal evolution of two or more ecologically intimate species." For example, a predator evolves better ways to catch its prey, while the prey evolves better ways to escape. In the case of Jasper Ridge, his term refers to the complex cat-and-mouse interplay between the checkerspots and the plants they feed on.
The ramifications of the "coevolution" principle in world food production are revolutionary. Traditionally, agriculturalists have believed that if they could keep one side of the food equation constant, by creating a pestless "miracle" crop or finding the ultimate pesticide, their problems were over. Ehrlich's "coevolution" principle holds that both sides of the equation are constantly in flux, and that maximum-yield agriculture is achieved by constantly selecting new strains of crops in response to the evolution of new strains of pests. According the Ehrlich, there are no long-term "miracles" in agriculture.
"The cotton industry is working to artificially create a cotton plant that will be forever pest-resistant. But if you know how plants and insects interact , you know it's only a matter of time before a new pest evolves. the average life of a new wheat strain in the West is five to six years. Almost every time a new pesticide is made, it promotes a new organism to pest status. Now, DDT won't kill anything. In fact, insects love it," says Ehrlich.
"The easy tricks for increasing food production have gone by the board. Since 1970, we haven't managed to increase food production at all. The peak year for ocean fisheries was 1971. Ever since, there has been a continuous slide in the per capita availability of protein."
In addition to not increasing food production, agriculturalists' attempts to create "miracle" crops have put the world in a precarious, all-eggs-in-one-basket predicament, says Ehrlich. "The green revolution distributed all over the world high-yeild strains of crops, but in Turkey, for instance, where there used to be 30 to 40 strains of wheat, there is now only one, and it was produced at the Center for the Development of Wheat and Maize, in Mexico. In the United States, the National Academy [of Sciences] was so worried that a few years ago it published a booklet, called the 'Genetic Vulnerability of American Crops.'"
"What concerns population biologists more than anything else," he says, "is the steady erosion of the variety of species and the disappearance of the ecosystem by the nation's massive assault on its fuel resources. Studies show that Sweden uses about half of the per capita energy we do and still generates a per capita gross national product, if that's what you want to generate, larger than ours. We're terribly inefficient."
Ehrlich recently expanded his study of the checkerspots on Jasper Ridge to tropical butterflies, Costa Rican Euptychia,m feeding on grasses ("the most important human food"), and Colorado's blue butterflies, Lycenids,m feeding on legumes ("the second most important food"). By studying the interaction between butterflies and these plants he hopes to answer such questions as: "How can we design our agricultural systems so that we keep the pest suppressed and don't destroy the world with pesticides?" "How do insects become resistant to insecticides?" "How do plants develop natural defense compounds?" As Ehrlich hones his theories and continues to punch holes in time-honored assumptions about plants and insects, he admits that most answers to the "big questions" are still elusive, and will demand decades' more study of the butterflies on the Ridge.
Meanwhile, Ehrlich faces the problem of the extinction of the very species on which he has based his life's work. Of the three original colonies of checkerspots on Jasper Ridge, one is already extinct. Another population of checkerspots which he had studied since 1960 on a grassy knoll in nearby Woodside, Calif., was becoming extinct the very afternoon we spoke, sacrificed to make way for luxury condominiums.
After an afternoon of surveying Jasper Ridge, he hopped into his vintage Dodge, the chrome trim coming unstuck like the brim of his hat, and headed for Woodside to show me the destruction. When we arrived, there was not a single blade of grass left standing on the knoll, not a solitary butterfly in sight. Only the fleet of yellow bulldozers leveling the hill.
"You're witnessing extinction," shouted Ehrlich over the drone of the earthmoving equipment. Visibly distraught, he fought to hold back his rage. "This is what's happening all over the world. Irreplaceable organisms being plowed under in the name of progress with a capital 'P.'"
Ehrlich moves closer to the excavation site to snap a few pictures. A paunchy bulldozen operator shakes his fist at the professor. "It's not his fault," says Ehrlich. "He's a guy who's got to make a living. And the way this system works, what choices does he have? It's not him. It's not individuals doing this. He doesn't know better. He views me as being after his job. I view what he's doing as being after all of our lives."