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Gone: Mass Extinction and the Hazards of Earth's Vanishing Biodiversity

By the end of the century, half of all species on Earth may be extinct due to global warming and other causes. Who will survive the world's dwindling biodiversity, and why?

BIODIVERSITY IS DEFINED as the sum of an area's genes (the building blocks of inheritance), species (organisms that can interbreed), and ecosystems (amalgamations of species in their geological and chemical landscapes). The richer an area's biodiversity, the tougher its immune system, since biodiversity includes not only the number of species but also the number of individuals within that species, and all the inherent genetic variation—life's only army against the diseases of oblivion.

Yet it's a mistake to think that critical genetic pools exist only in the gaudy show of the coral reefs, or the cacophony of the rainforest. Although a hallmark of the desert is the sparseness of its garden, the orderly progression of plants, the understated camouflage of its animals, this is only an illusion. Turn the desert inside out and upside down and you'll discover its true nature. Escaping drought and heat, life goes underground in a tangled overexuberance of roots and burrows reminiscent of a rainforest canopy, competing for moisture, not light. Animal trails crisscross this subterranean realm in private burrows engineered, inhabited, stolen, shared, and fought over by ants, beetles, wasps, cicadas, tarantulas, spiders, lizards, snakes, mice, squirrels, rats, foxes, tortoises, badgers, and coyotes.

To survive the heat and drought that killed the lost hiker, desert life pioneers ingenious solutions. Coyotes dig and maintain coyote wells in arroyos, probing deep for water. White-winged doves use their bodies as canteens, drinking enough when the opportunity arises to increase their body weight by more than 15 percent. Black-tailed jackrabbits tolerate internal temperatures of 111 degrees. Western box turtles store water in their oversized bladders and urinate on themselves to stay cool. Mesquite grows taproots more than 160 feet deep in search of perennial moisture.

These life-forms and their life strategies compose what we might think of as the "body" of the desert, with some species acting the role of the lungs and others the liver, the blood, the skin. The trend in scientific investigation in recent decades has been toward understanding the interconnectedness of the bodily components, i.e., the effect one species has on the others. The loss of even one species irrevocably changes the desert (or the tundra, rainforest, prairie, coastal estuary, kelp forest, coral reef, and so on) as we know it, just as the loss of each human being changes his or her family forever.

Nowhere is this better proven than in a 12-year study conducted in the Chihuahuan Desert by James H. Brown and Edward Heske of the University of New Mexico. When a kangaroo rat guild composed of three closely related species was removed, shrublands quickly converted to grasslands, which supported fewer annual plants, which in turn supported fewer birds. Even humble players mediate stability. So when you and I hear of this year's extinction of the Yangtze River dolphin, and think, how sad, we're not calculating the deepest cost: that extinctions lead to co-extinctions because most every living thing on Earth supports a few symbionts and hitchhikers, while keystone species influence and support a myriad of plants and animals. Army ants, for example, are known to support 100 known species, from beetles to birds. A European study finds steep declines in honeybee diversity in the last 25 years but also significant attendant declines in plants that depend on bees for pollination—a job estimated to be worth $92 billion worldwide. Meanwhile, beekeepers in 24 American states report that up to 70 percent of their colonies have recently died off, threatening $14 billion in U.S. agriculture. And bees are only a small part of the pollinator crisis.

One of the most alarming developments is the rapid decline not just of species but of higher taxa, such as the class Amphibia, the 300-million-year-old group of frogs, salamanders, newts, and toads hardy enough to have preceded and then outlived most dinosaurs. Biologists first noticed die-offs two decades ago, and since have watched as seemingly robust amphibian species vanished in as little as six months. The causes cover the spectrum of human environmental assaults, including rising ultraviolet radiation from a thinning ozone layer, increases in pollutants and pesticides, habitat loss from agriculture and urbanization, invasions of exotic species, the wildlife trade, light pollution, and fungal diseases. Sometimes stressors merge to form an unwholesome synergy; an African frog brought to the West in the 1950s for use in human pregnancy tests likely introduced a fungus deadly to native frogs. Meanwhile, a recent analysis in Nature estimates that in the last 20 years at least 70 species of South American frogs have gone extinct as a result of climate change.

In a 2004 analysis published in Science, author Lian Pin Koh and colleagues predict that an initially modest co-extinction rate will climb alarmingly as host extinctions rise in the near future. Graphed out, the forecast mirrors the rising curve of an infectious disease, with the human species acting all the parts: the pathogen, the vector, the Typhoid Mary who refuses culpability, and, ultimately, one of up to 100 million victims.

 

IT'S ONE OF SCIENCE'S GREAT IRONIES that many of today's feel-good nature stories come from researchers scrambling to catalog Earth's life-forms before they disappear. Breaking through the daily news of war and politics are the quiet announcements of novel species, including truly startling finds: a new catlike mammal in Borneo, a new phylum of wormlike creature, a new songbird in India, a snake that changes colors. Most astounding are the marine discoveries, including an average of three new species of fish a week since 2000.

The discovery of novel oceanic life-forms comes thanks to the Census of Marine Life, a network of 2,000 researchers in more than 80 nations engaged in a 10-year initiative to assess ocean life and its changes over time. The census is a veritable factory of revelations: life-forms thriving in 765-degree-Fahrenheit thermal vent waters in the Atlantic; species surviving below 2,300 feet of ice off Antarctica; a living shrimp believed extinct for 50 million years; pairs of mated seabirds flying 44,000-mile, figure-eight loops in the 200 days between nesting seasons, only occasionally resting on the waves; a fish school 20 million strong, the size of Manhattan, swimming off New Jersey.

The quest reveals a startling truth about our planet: that life thrives even in "lifeless" conditions, harvesting energy from sources we thought were ours alone—radioactive uranium, hydrogen, hydrogen sulfide, and methane—in places no one ever thought to look before, including between the crystals in rock. Some (archaea, bacteria, fungi) live nearly two miles below the Earth's surface. Some (cyanobacteria) in Antarctica live inside quartz clear enough to allow them to perform photosynthesis while escaping the weather. We call these organisms extremophiles because their worlds are uninhabitable to us, although many dwell in conditions that mimic what we know of the first life on Earth—in the eons before photosynthesizing plants freed oxygen from water to make our atmosphere.

On Hydrate Ridge 50 miles off the coast of Oregon, the mud on the bottom of the sea is more alive than dead. Thousands of feet below the surface, under pressures that would crush you and me, in temperatures that would turn our blood to sludge, worms, crustaceans, snails, bacterial filaments, and other life-forms as yet undescribed thrive in an environment largely devoid of oxygen and toxic with hydrogen sulfide and methane. This is the world of a cold seep, a seafloor ecosystem not discovered until 1984, where hydrocarbon-rich fluids bubble from the bottom to support unique biological communities fundamentally different from our own.

Seep life is driven not by photosynthesis (where plants use sunlight to power the food web) but chemosynthesis, whereby single-celled organisms use methane and hydrogen sulfide to fuel a gas-powered food web. The process also creates underwater reefs of carbonate rocks, something like coral reefs, which shelter otherworldly communities, including tubeworms with minimum life spans of 170 years. Scattered erratically across the bottom, cold seeps and their cousins, the hydrothermal vents, are the ocean's deepest, farthest flung, and perhaps most ancient communities.

Among their more enduring mysteries are exactly how these ecosystems become populated with life. There's evidence that whale falls act as critical steppingstones, or once did. In preindustrialized whaling days, when millions of behemoths were alive at any given time, their carcasses—which may endure and produce gases for up to a century—would have abounded in the deep, providing oases for the drifting larvae of seep organisms.

Most of the extremophile life-forms living at Hydrate Ridge are invisible to the naked eye—though through the dissecting microscope they're mind-bendingly huge: translucent worms with blood cells chasing each other through their vessels; miniature crustaceans like the alien from Alien. The mud from the seep reeks of sulfur. In fact the whole ship, the hardworking, far-sailing research vessel Atlantis, is full of mud that stinks of rotten eggs and flatulence. The goop comes aboard via the submersible Alvin, which cruises 2,500 feet below in a world so remote and so unwelcoming that only three people at a time can get to it in undersea assignments as coveted as space shuttle berths.

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