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TO

THOMAS G. SAVAGE, S.J.

1926-1975

VIVID IN MEMORY

CONTENTS

THIRTY-SIX PERSIAN THROW RUGS

1

LET’S START indoors. Let’s start by imagining a fine Persian carpet and a hunting knife. The carpet is twelve feet by eighteen, say. That gives us 216 square feet of continuous woven material. Is the knife razor-sharp? If not, we hone it. We set about cutting the carpet into thirty-six equal pieces, each one a rectangle, two feet by three. Never mind the hardwood floor. The severing fibers release small tweaky noises, like the muted yelps of outraged Persian weavers. Never mind the weavers. When we’re finished cutting, we measure the individual pieces, total them up—and find that, lo, there’s still nearly 216 square feet of recognizably carpetlike stuff. But what does it amount to? Have we got thirty-six nice Persian throw rugs? No. All we’re left with is three dozen ragged fragments, each one worthless and commencing to come apart.

Now take the same logic outdoors and it begins to explain why the tiger, Panthera tigris, has disappeared from the island of Bali. It casts light on the fact that the red fox, Vulpes vulpes, is missing from Bryce Canyon National Park. It suggests why the jaguar, the puma, and forty-five species of birds have been extirpated from a place called Barro Colorado Island—and why myriad other creatures are mysteriously absent from myriad other sites. An ecosystem is a tapestry of species and relationships. Chop away a section, isolate that section, and there arises the problem of unraveling.

For the past thirty years, professional ecologists have been murmuring about the phenomenon of unraveling ecosystems. Many of these scientists have become mesmerized by the phenomenon and, increasingly with time, worried. They have tried to study it in the field, using mist nets and bird bands, box traps and radio collars, ketamine, methyl bromide, formalin, tweezers. They have tried to predict its course, using elaborate abstractions played out on their computers. A few have blanched at what they saw—or thought they saw—coming. They have disagreed with their colleagues about particulars, arguing fiercely in the scientific journals. Some have issued alarms, directed at governments or the general public, but those alarms have been broadly worded to spare nonscientific audiences the intricate, persuasive details. Others have rebutted the alarmism or, in some cases, issued converse alarms. Mainly these scientists have been talking to one another.

They have invented terms for this phenomenon of unraveling ecosystems. Relaxation to equilibrium is one, probably the most euphemistic. In a similar sense your body, with its complicated organization, its apparent defiance of entropy, will relax toward equilibrium in the grave. Faunal collapse is another. But that one fails to encompass the category of floral collapse, which is also at issue. Thomas E. Lovejoy, a tropical ecologist at the Smithsonian Institution, has earned the right to coin his own term. Lovejoy’s is ecosystem decay.

His metaphor is more scientific in tone than mine of the slicedapart Persian carpet. What he means is that an ecosystem—under certain specifiable conditions—loses diversity the way a mass of uranium sheds neutrons. Plink, plink, plink, extinctions occur, steadily but without any evident cause. Species disappear. Whole categories of plants and animals vanish. What are the specifiable conditions? I’ll describe them in the course of this book. I’ll also lay siege to the illusion that ecosystem decay happens without cause.

Lovejoy’s term is loaded with historical resonance. Think of radioactive decay back in the innocent early years of this century, before Hiroshima, before Alamogordo, before Hahn and Strassmann discovered nuclear fission. Radioactive decay, in those years, was just an intriguing phenomenon known to a handful of physicists—the young Robert Oppenheimer, for one. Likewise, until recently, with ecosystem decay. While the scientists have murmured, the general public has heard almost nothing. Faunal collapse? Relaxation to equilibrium? Even well-informed people with some fondness for the natural world have remained unaware that any such dark new idea is forcing itself on the world.

What about you? Maybe you have read something, and maybe cared, about the extinction of species. Passenger pigeon, great auk, Steller’s sea cow, Schomburgk’s deer, sea mink, Antarctic wolf, Carolina parakeet: all gone. Maybe you know that human proliferation on this planet, and our voracious consumption of resources, and our large-scale transformations of landscape, are causing a cataclysm of extinctions that bodes to be the worst such event since the fall of the dinosaurs. Maybe you are aware, with distant but genuine regret, of the destruction of tropical forests. Maybe you know that the mountain gorilla, the California condor, and the Florida panther are tottering on the threshold of extinction. Maybe you even know that the grizzly bear population of Yellowstone National Park faces a tenuous future. Maybe you stand among those well-informed people for whom the notion of catastrophic worldwide losses of biological diversity is a serious concern. Chances are, still, that you lack a few crucial pieces of the full picture.

Chances are that you haven’t caught wind of these scientific murmurs about ecosystem decay. Chances are that you know little or nothing about a seemingly marginal field called island biogeography.

THE MAN WHO KNEW ISLANDS

2

BIOGEOGRAPHY is the study of the facts and the patterns of species distribution. It’s the science concerned with where animals are, where plants are, and where they are not. On the island of Madagascar, for instance, there once lived an ostrichlike creature that stood ten feet tall, weighed half a ton, and thumped across the landscape on a pair of elephantine legs. Yes, it was a bird. One thousand pounds of bone, flesh, feathers. This is no hypothetical monster, no implausible fantasy of Herodotus or Marco Polo. In a ramshackle museum in Antananarivo, I’ve seen its skeleton; I’ve seen its two-gallon egg. Paleontologists know it as Aepyornis maximus. The species survived until humans reached Madagascar, just within the last few millennia, and began hunting it, harrying it, transforming the ecosystem it was part of, scrambling those bounteous eggs. A thousand years ago, Aepyornis maximus existed only on that single island; now it exists nowhere. To say so is the business of biogeography.

As practiced by thoughtful scientists, biogeography does more than ask Which species? and Where? It also asks Why? and, what is sometimes even more crucial, Why not?

Another example. The island of Bali, a small mound of volcanic rock and elaborate rice terraces just off the eastern tip of Java, in Indonesia, once supported a unique subspecies of tiger. Panthera tigris balica, it was called. Java itself had a different subspecies, Panthera tigris sondaica. Meanwhile the island of Lombok, just east of Bali across a twenty-mile stretch of ocean, had no resident tigers at all. Today the Balinese tiger exists nowhere, not even in zoos. It was driven extinct by an intricate combination of the usual factors. The Javanese tiger is probably also extinct, though some people cherish a feeble hope. Sumatra still has a few tigers, and again those belong to a distinct subspecies. Tigers can also be found in certain regions of mainland Asia, but not in the northwestern part of the continent, nor in Africa, nor in Europe. Once they existed as far west as Turkey. Not anymore. And Lombok, no smaller than Bali, with forests no less inviting, is still as tigerless as ever.

Why, why not, why? These facts, and their explanations, represent biogeography. When the same sort of attention is focused specifically on islands, it becomes island biogeography.

Island biogeography, I’m happy to report, is full of cheap thrills.

Many of the world’s gaudiest life forms, both plant and animal, occur on islands. There are giants, dwarfs, crossover artists, nonconformists of every sort. These improbable creatures inhabit the outlands, the detached and remote zones of landscape and imaginability; in fact, they give vivid biological definition to the very word On Madagascar lives a species of chameleon barely more than an inch long, the smallest chameleon (among the smallest land vertebrates of any sort, actually) on the planet. Madagascar was also the home of a pygmy hippopotamus, now extinct. On the island of Komodo lurks that gigantized lizard we’ve all heard of, hungry for flesh and plausibly nicknamed a dragon. In the Galapagos an ocean-going iguana grazes underwater on seaweed, flouting the usual limits of reptilian physiology and behavior. In the central highlands of New Guinea you can catch sight of the ribbon-tailed bird of paradise, no bigger than a crow but dragging a pair of grossly elongated tail feathers, white streamers like the tail on a kite, as it swims heavily through the air of a clearing. On a tiny coral island called Aldabra, in the Indian Ocean, lives a species of giant tortoise less famous though no less imposing than the Galápagos tortoises. On Saint Helena there existed, at least until recently, a species of giant earwig—the world’s largest and no doubt most repulsive dermapteran insect. Java has its own species of rhinoceros, another pygmy. Hawaii has its honeycreepers, a whole group of bizarre birds seen nowhere else. Australia has its kangaroos and other marsupials, of course, while the island state of Tasmania has its devil, its bettong, its pademelon, and its spotted-tailed quoll, marsupials too peculiar even for mainland Australia. The island of Santa Catalina, in the Gulf of California, has a rattleless rattlesnake. New Zealand has the tuatara, the last surviving species of an order of beaky-faced reptiles that flourished in the Triassic period, before the peak of the dinosaurs. Mauritius, until Europe invaded, had the dodo. The list could go on, with no diminution of weirdness. The point is that islands are havens and breeding grounds for the unique and anomalous. They are natural laboratories of extravagant evolutionary experimentation.

That’s why island biogeography is a catalogue of quirks and superlatives. And that’s why islands, those outlands, have played a central role in the study of evolution. Charles Darwin himself was an island biogeographer before he was a Darwinist.

Some of the other great pioneers of evolutionary biology—notably Alfred Russel Wallace and Joseph Hooker—also gathered their best insights from fieldwork on remote islands. Wallace spent eight years collecting specimens in the Malay Archipelago, the empire of islands (and therefore of biological diversity) that now goes by the name Indonesia. Hooker, like Darwin, was lucky and well connected enough to get a place on board one of Her Majesty’s ships. It was the Erebus, sent off (like Darwin’s Beagle) on a round-the-world charting expedition, from which Hooker went ashore on Tasmania, New Zealand, and an interesting little nub called Kerguelen Island, halfway between Antarctica and nowhere. Decades later, Hooker was still publishing studies of the plants of New Zealand and his other island stops.

The trend started by Darwin, Wallace, and Hooker has continued throughout this century, with important studies done in New Guinea, in the southwestern Pacific, in Hawaii, in the West Indies, and on Krakatau after the big eruption. It came to a culmination of sorts—or at least to a turning point—in a dense little volume titled The Theory of Island Biogeography, published in 1967. The Theory of Island Biogeography was a daring, fruitful, and provocative attempt by two young men to merge biogeography with ecology and transform them into a mathematical science. Wherever we wander in this book, you and I, we’ll never be far from that one. The two young men were Robert MacArthur and Edward O. Wilson. They derived their theory in part from the patterns of distribution of ant species that Wilson had found among the islands of Melanesia.