Why is a butterfly like a steel rivet?
(Page 3 of 5)
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.Skip to next paragraph
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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.