Naturalist 25th Anniversary Edition

by Edward O. Wilson

  We were both a little crazy in those days. As stronger gusts of wind and rain blew in, and the streets began to empty of traffic, we drove to Key Biscayne and hiked into a patch of red mangrove swamp along the bay shore facing Miami. The eye of the hurricane was now passing up the west coast on its way toward landfall in northwest Florida. The gusts on Key Biscayne reached sixty miles an hour, gale but not hurricane force. I was disappointed. The wind was not strong enough to tear insects and other small creatures from the trees. They all stayed hunkered down safely on the branches and leaves as the rain-soaked winds roared through. We saw not a single animal blow by. Nor could we find animals struggling in the water at the edge of the swamp. I said, Well, let’s see what would happen if an animal were blown free. Would the storm-tossed waves carry it out toward a distant shore? I caught an anole lizard and tossed it ten feet or so out into the water. To my dismay, it popped to the surface, swam expertly back to the shelter of the trees, and climbed up a mangrove trunk. Well, I continued, suppose a full hurricane blew an anole so far away on open water it couldn’t get back. Our little experiment shows that it could swim to the nearest islet if it were not too far away. Dan, rainwater streaming from his hat, allowed that the notion was plausible. Our excursion was not a complete loss, but in later years we agreed we were lucky that Alma only brushed Miami. Otherwise we ourselves might have been washed to a distant shore, proving our own hypothesis in extremis.

  A month later, I joined Steve Tendrich and a crew from National Exterminators on a trip into Florida Bay to spray the first two islets, “Experimental 1” and “Experimental 2,” E1 and E2 for short. Simberloff was busy at another location preparing additional islets. We loaded a rented barge with equipment and set forth from a marina on Sugarloaf Key. Halfway out we came upon a stalled sports-fishing cruiser. Observing the law of the sea even in this relatively safe stretch of water, we took the captain and his two fisherman guests on board and back to Sugarloaf. Then we headed forth again. This time we reached E1 and sprayed the little island with parathion. The next morning we proceeded to E2. Here we spotted several nurse sharks, one nearly four feet in length, cruising the shallow waters around the islet. Trouble! The workmen refused to get off the barge. But I knew that nurse sharks never attack people unless hooked or seized by the tail and hauled from the water by the occasional reckless fisherman. They live on a diet of shellfish, crustaceans, and other small bottom-dwelling animals. So I volunteered to stand guard waist deep and drive the sharks away with an oar. Impressed by my specious bravery and with their male pride challenged, the crew got into the water and sprayed E2.

  Several days later, after I had returned to Cambridge, Simberloff called with mixed news about E1 and E2. He had made a close inspection of the islets and found that the kill of the arthropods living on the surface of the vegetation had been total. But some beetle larvae living deep in the wood of dead branches survived. We realized we had no way of knowing what other creatures might still live in these deeper spaces. So we quickly agreed that spraying with parathion or some other short-lived insecticide was not enough. In order to run a proper experiment, we had to start with islets scourged of all animal life, with no exception. It would be necessary to fumigate the islets with a poisonous gas, one that penetrates every crack and crevice.

  I called Steve Tendrich: could National Exterminators fumigate an island? The ever-resourceful Tendrich responded in his usual positive manner: why not? It was common practice in Miami, he said, to cover entire houses with a rubberized nylon tent and fumigate the interior in order to remove all termites and other insect pests, no matter how deeply hidden in the woodwork. To transfer the method to a large object surrounded by water would be tricky, of course. The crew would need to erect a scaffolding around the islet as a frame for the tent. We couldn’t just lay the cover on top of the fragile branches. And something else: the dosage of the gas must be set just right, high enough to kill all the animals but low enough to leave the mangrove trees undamaged. To study a ghost island of dead wood and fallen leaves would have no meaning, I agreed. Not least, I had promised the National Park Service that we would preserve the live vegetation.

  So it was to be poison gas. But what kind? We considered and quickly discarded hydrogen cyanide. It was too dangerous for the crew to use under these uncertain conditions, over water with possible stiff winds. Even if we could apply it safely, hydrogen cyanide is water-soluble and would probably kill the marine communities around the mangrove prop roots, an unacceptable side effect. Methyl bromide, Tendrich ventured, might fill the bill, if he could get the dosage just right. Tendrich immediately set up trials, using small mangrove trees in the swamps near Miami. Meanwhile Simberloff collected cockroach egg cases from mangrove swamps for Tendrich to test with various dosages. If these highly resistant insect life stages could be killed without damage to the vegetation, methyl bromide might work.

  The window between insect kill and tree kill using methyl bromide was narrow, but Tendrich found it. On October 11, 1966, we all gathered for the first trial on an islet in the shallow waters of Harnes Sound, on the mainland side of Key Largo and a relatively short ride down U.S. I from Miami. As the men loaded the gear, we saw ospreys and pelicans flying nearby and herons spearing fish in the shade of the mangrove fringes along walls of barnacles and green algal mats stranded by a dropping tide. Somewhere close by, we had been told, was a nest of bald eagles. The men got the scaffolding up and closed the tent around it without mishap. They pumped the prescribed dose of methyl bromide through a flap-covered opening in the side, in the same manner used to fumigate a small house, then pulled the tent away, allowing the gas to dissipate quickly to harmless levels.

  The next day we searched the islet thoroughly and found no trace of animal life. Even the deep-boring insects had been killed. Our colonization experiment was under way at last.

  Tendrich, however, was not entirely satisfied with the procedure. It had worked all right at Harnes Sound a hundred yards from the highway, but the metal rods used to create the frame were heavy and clumsy and might be very difficult to transport to the more remote and less accessible mud-flat sites. He began to search for alternative techniques of scaffolding. One day as he drove through Miami he spotted a steeplejack working on a tower atop a hotel, and inspiration struck. Steve stopped the car, took an elevator to the hotel roof, and waited for the man to come down. He asked the steeplejack, whose name was Ralph Nevins, whether it might be possible to erect a small tower like that in the middle of a mangrove swamp, then drape a tent over the guy wires. Sure, Nevins replied—another optimist—why not? Would it be very difficult? Don’t think so. Tendrich hired him on the spot. And so it was done thereafter. The rest of our islets were fumigated beneath tents wrapped around the guy wires of a tower raised by Ralph Nevins.

  Simberloff continued to carry the main burden of monitoring. He was tied for months to a physically demanding routine of travel, search, and identification. When I found time I came down from Cambridge, and we worked together. Within weeks it was apparent that the project was going to be a success. The recolonization by arthropod species was already well under way. Moths, bark lice, and other flying insects appeared early, at first in small numbers but accumulating and reproducing as time passed. Winged ant queens, newly inseminated during their nuptial flights, landed, shed their wings, and started colonies. Spiders came early in abundance; some were wolf spiders the size of silver dollars. How were they crossing the water? Since there had been no major storms, we guessed that they used ballooning. Many kinds of spiders, when crowded or short of food, prepare to emigrate by standing in exposed places on leaves and twigs and letting out threads of silk into the wind. As the strands lengthen, the drag increases, until the spiders have difficulty holding themselves in place. Finally they let go, allowing the wind on the strands to pull them up and away. With luck they come down again on land, and best of all in some place like a distant mangrove island with few other spiders and an abundance of prey. Tho
se that hit water instead soon become fish food.

  Toward the end of the year following the defaunations, a pattern in the colonization began to emerge. With so much of our time invested, we now began to worry that a hurricane might strike, perturbing the new faunas and ruining the continuity of the experimental run. Fortunately, none came close to Florida. In fact no major storm struck the area again until Andrew devastated South Miami and the northern keys in 1992. After a while, we relaxed a bit and broadened our attention to include other aspects of local ecology.

  Our first major project was to launch a survey of the arthropods of all the mangrove swamps, in order to gain a picture of the pool of all possible emigrants to the experimental islets. I hired Robert Silberglied, a graduate student working in entomology under my direction, to commence a general survey of the surrounding keys. Bob was a gifted naturalist and a polymath taxonomist who could on sight identify species from a wide array of animal groups. The challenge of a complete arthropod survey was made to order for his talents. He worked tirelessly from island to island, building a large reference collection of insects and other arthropods. His impressive potential was destined never to flower into a full career, however. On January 13, 1982, he died with others in the Potomac River crash of an Air Florida airliner on the outskirts of Washington, D.C. A winter storm was in progress, and the accident was later blamed on wing icing. The flight was to have been the first leg of a flight to Panama, where Bob had planned to continue research on tropical ecology.

  Our interest in the Florida Keys, as our research moved onward into 1967, also extended to include conservation. Silberglied and Simberloff heard rumors that Lignumvitae Key, a 280-acre island on the bay side close to Lower Matecumbe Key and its transecting segment of U.S. I, was an unspoiled paradise covered by large hardwood trees. Undisturbed forest other than mangrove was a rarity in the Keys, and worth investigation. Few people had set foot on Lignumvitae to that time. One was Konrad Lorenz, who later opened his influential book On Aggression with a description of the coral reefs there and on nearby Key Largo.

  When Silberglied and Simberloff put ashore, they were met by the caretakers, Russell and Charlotte Niedhauk, an elderly and reclusive couple who lived on the island alone. The Niedhauks were suspicious of all visitors, and rudely chased most away. But when Bob and Dan revealed that they were biologists interested in conservation of the island, they were given a warm welcome. As they walked inland from the caretakers’ house, they confirmed the rumor: almost all the land was covered by a mature tropical hardwood forest. They were thrilled to find themselves in a near-primeval habitat that once predominated in the high islands of the Keys but had been almost completely obliterated by the 1960s. Huge mahogany and gumbo-limbo, including the largest individual of the latter species in the United States, towered over wild lime, torchwood, Jamaica dogwood, boxleaf stopper, strangler fig, and the only large stand of holywood lignum vitae in Florida. Sixty-five species of trees and woody shrubs, all tropical and subtropical, composed the woody flora. The fauna was also a remnant of the old Keys. Candy-striped tree snails hung like grapes from the trunks and branches. Large butterflies, including showy dagger wings, purple wings, and swallowtails, darted and floated back and forth above the shaded trails. Bald eagles, at that time nearly extinct in the eastern United States, were occasional visitors, and Bahama bananaquits were seen from time to time. Later, after he had visited the island, Archie Carr, the great expert on Caribbean natural history, reminded me that the Lignumvitae forest was a tropical West Indian lowland forest of a quality no longer found in the West Indies themselves. The chances of finding stands of old mahogany and lignum vitae on the islands were close to zero.

  The Niedhauks were almost paranoid about the future of Lignumvitae Key. It was owned, they explained, by a private consortium of wealthy Floridians who were planning to convert it into a community of expensive vacation residences. All the owners cared about, they said and I later confirmed, was a financial killing. Could the visitors help find a way to preserve the island in its natural state? Bob and Dan conveyed this information to me as soon as they returned to their base. Soon afterward, I visited the island and was similarly enchanted, and fearful. I invited Thomas Eisner, my old friend on the Cornell faculty, to join me on a second visit. Together we prepared an article for Natural History about Lignumvitae and its plight. While our effort was under way, I spoke at a meeting of the Florida Audubon Society in Miami on the subject, and to my delight an elderly couple living in Coral Gables pledged $100,000 toward the purchase of the island. It was a big first step toward saving Lignumvitae. But we needed more; the owners had set the tentative price at over $2 million. Their spokesman, a septuagenarian Miami dentist, was gleeful that conservationists had entered the bidding. He made it clear that the final price would be raised as high as the owners could make it. He would love to see his beautiful island saved in its natural state, he claimed, but if we did not act soon the land would go to developers. The Lignumvitae ecosystem, in short, had been placed in ransom.

  I contacted Thomas Richards, president of The Nature Conservancy, in hopes of pressing the campaign to a successful conclusion. TNC was, as it remains today, famous for its policy of purchasing environmentally important land for preservation in the public domain. After a visit of his own, Richards committed his organization to the effort. He then approached Nathaniel Reed, an influential administrator in Florida’s park system, for further assistance. In the end, after long negotiation, a reasonable price was agreed upon. The island was purchased with funds from The Nature Conservancy and the State of Florida, and Lignumvitae Key was turned into a fully protected State Botanical Site. Today visitors walk along trails where tree snails still decorate the gnarled old lignum vitae trees and dagger wings alight among their delicate blue flowers and petard-shaped yellow fruits. The public can in perpetuity, I trust, witness the Florida Keys as they were in prehistory.

  Meanwhile, our experimental project continued to move swiftly forward. By the fall of 1967, a year after we fumigated the islets, the results were all but conclusive. In a formal article published two years later, Simberloff and I summarized the events of recolonization and the reattainment of equilibria:

  By 250 days after defaunation, the faunas of all the islands except the distant one (“E1”) had regained species numbers and composition similar to those of untreated islands even though population densities were abnormally low … The colonization curves plus static observation on untreated islands indicate strongly that a dynamic equilibrium number of species exists for any island.*

  At least the cruder predictions of the theory of island biogeography had been met. The closest island, as expected, had the largest number of species before fumigation, forty-three to be exact, and it regained approximately that number within the year. The most distant island, E1, had the smallest number, twenty-six, and climbed back close to that after defaunation. The other islands, at intermediate distances, had intermediate numbers before fumigation and also returned to their original levels afterward. Two years later, in 1968, these various levels still held.† The turnover in species was very rapid, also as expected from island biogeographic theory applied to small, swiftly occupied islands. In the course of our studies we added many observations on the dispersal and early colonization of various groups of arthropods, including spiders, mites, ants, earwigs, bark lice, crickets, and many others. Dan completed his Ph.D. thesis in the spring of 1968. It had taken us only three years to create miniature Krakataus, in replicate with controls, and follow their histories to an early form of equilibrium.

  In 1971 Simberloff and I received the Mercer Award of the Ecological Society of America for our research, a welcome recognition. We had risked a new approach to biogeography, a subject still considered outside the mainstream of ecology, and succeeded. From many employment opportunities open to him, Dan accepted an assistant professorship at Florida State University, in order to be within easy distance of field sites. In time he became
an ecologist of international stature. He conducted additional experiments with mangrove islets, varying their size and shape. He expanded his activities to include field studies on other ecosystems, and used his mathematical skills to conduct critiques of ecological theory and to develop new approaches in quantitative modeling. In time his university appointed him to the Robert O. Lawton Distinguished Professorship.

  I did not return to the Florida Keys, and my dream of converting them into a natural laboratory languished. A new possibility—a different opening to the future—had seized my imagination. I wanted to make sociobiology into a single science, one that ranged from ants to chimpanzees.

  *“Experimental Zoogeography of Islands: The Colonization of Empty Islands,” Ecology 50(2) (1969): 278-295.

  †“Experimental Zoogeography of Islands: A Two-Year Record of Colonization,” Ecology 51(5) (1970): 934-937.

  chapter fifteen

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