The Next Species: The Future of Evolution in the Aftermath of Man (7 page)

He told me how difficult it was to discover a new species. It was not like “Hallelujah! We’ve just found a new species!”; it was more like “We’ve just been through every similar-looking plant in the entire herbarium and can’t find anything that looks like this.” To declare something a new species requires a lot of work. Nevertheless he held up a tiny orchid a short while later and declared, “I’ll bet a case of beer that’s never been described before.”

The rains carved the valleys that surround Vilcabamba, making it a de facto island, but not all lands are so easily separated. It took the massive forces of earth’s molten core to break up Pangaea and to spread the continents wide. But now, through mass transportation, man has destroyed much of this hard-won separation. Similarly, as boats, trains, cars, and planes have spread across the land, so have the mammals, insects, reptiles, and crustaceans that have hidden in the bilges, trunks, and storage facilities of these vehicles. This has destroyed much of the isolation that created these many species, taking them to places where their presence can be ruinous to the resident
animals.

In the United States the resultant spreading of some of these displaced species has been purposeful if not downright ridiculous. In 1890 an eccentric Shakespeare fanatic, Eugene Schieffelin, decided to introduce
all the birds mentioned in Shakespeare’s plays to the United States. Schieffelin released sixty starlings one fateful day in New York’s Central Park, and from that introduction, the US now has 200 million.

These starlings, as well as sparrows and pigeons, make up the majority of the birds Americans see most days in urban environments. Yet none of these birds is native to the United States. “Invasives,” as we call these exotic plants and animals, compete for food with true natives like eastern bluebirds and purple martins. Since local birds tend to migrate south for the winter, while invasives stay home, there is little nesting space available when the native birds return. And this is all because some dutiful citizen felt the New World would be more civilized if it were populated with the Bard’s birds.

Invasive plants often flourish outside their native habitats because the insects, diseases, and animals that naturally check their growth at home are not present in their new digs.

The spread of an invasive species can also be caused by the inability of local animals to deal with new immigrants.
The brown tree snake had such a free rein when it was introduced to Guam from the Solomon Islands after World War II. Scientists speculate that the snake probably snuck onto Guam inside the wheel well of an airplane, since Guam has an active air base. The brown tree snake spread across the island’s jungles over the last sixty years and is responsible for the extinction or severe reduction of a number of native species that had no defense against the snake. Biologists recently attempted to control the snakes by air-dropping into the jungle dead mice laced with about 80 milligrams of acetaminophen—equal to a child’s dose of Tylenol, all that’s needed to kill an adult brown tree snake. The results are not yet conclusive.

Similarly, licensed and unlicensed animal traders over the last couple of decades brought
Burmese pythons into Florida. When pet
owners found that the snakes either took up too much space or tried to swallow the family dog, they let them go in local and national parks. Since 2002, more than 1,800 pythons have been removed from Everglades National Park and the surrounding areas in Florida. Now the US Fish and Wildlife Service reports that northern and southern African pythons, reticulated pythons, boa constrictors, and four species of anaconda have joined the Everglades pythons. Biologists believe that tens of thousands of these snakes now live in the park.

Invasive species can come from afar or they may grow up locally and penetrate spaces formally occupied by other species when the right conditions arise. Native woody shrubs and trees are invading semiarid grasslands in the US, South America, Africa, and Australia as a result of overgrazing, fire suppression, and climate change.

When animal grazing is controlled, grasses grow up naturally and provide kindling for natural or man-made fires, which stimulate more grasses but suppress the growth of woody shrubs. The control of woody shrubs, which inhibit grasses, is critical to pastoral communities on arid and semiarid lands, which make up 35 percent of the earth’s people. They must balance the need for grasses to feed their cattle, sheep, and goats, with the need for fires to control woody vegetation.

To get a look at how shrubs outcompete grasses, I followed Rob Jackson, a professor of environmental earth system science at Stanford University, on a warm afternoon, down a tall ladder
into the underground caverns of Powell’s Cave, about 150 miles (240 kilometers) west of Austin, Texas. We entered a world of stalactites and stalagmites in the porous limestone bedrock of the Edwards Plateau in west-central Texas. I scurried after Jackson through a maze of caverns and tight crawl spaces, over slippery pathways, and into rooms filled with glistening multicolored limestone structures, all carved by nature. We arrived at a point about sixty feet (eighteen meters) below the ground, where an underground stream gushes from the rock.

Like the British geologists who went underground to look for evidence of glaciers, Jackson went deep to try to explain how native juniper trees on the Edwards Plateau have invaded grasslands and are taking over. He showed me several thick tree roots that appeared to burst from the limestone walls, reach down into the stream, and suck water out of it. He explained to me: “A single taproot can provide a third or more of the tree’s water during a drought.”

Junipers put out roots along the full depths of their root systems so that they can get water from deeper roots in times of drought, and from shallower roots in times of rain. This gives them an advantage over grasses, which can pull only from their shallow roots no matter what the weather.

Woody shrubs and trees like junipers have invaded arid and semiarid grasslands and savannas in the US. Their presence limits the grass available for land managers, ranchers, and wildlife. Studies show that increased shrub and tree growth can rob from one-third to two-thirds of the stream water.

Juniper, mesquite, creosote, and Chinese tallow are problem plants in different parts of the US, particularly in the southern regions—the Great Plains, the Southwest, and the Gulf Coast. These plants existed here before, but overgrazing, fire suppression, and climate change have allowed plant populations to explode. Their increased presence has led to
thickets that don’t allow enough light or room for other plants or grasses. “Thicketization” was what Steve Archer, a professor at the School of Natural Resources at the University of Arizona, Tucson, called it when I met him at an Ecological Society of America conference in Austin, Texas. Archer studies the ecology, management, and restoration of rangelands, which are any extensive area of land occupied by native vegetation that is grazed by domestic or wild animals that eat plants.

When huge herds of cattle were introduced to the western United States in the late 1800s, they devastated the grasses. This reduced the fuel for grass fires, and in their absence woody plants got better established. In earlier times, Indians regularly burned the grassy meadows
here to clear brush and trees and open them up for hunting. Today fire suppression is one of the problems promoting the juniper invasion. Without grass fires, woody plants spread unabated.

But it’s more than a recent problem. It goes all the way back fifteen thousand years ago to Ice Age hunters, who wiped out the large animals that once ate the woody plants in the grasslands of North America. In East Africa, they still have elephants that control woody plants, one of their natural foods. But the US no longer has wildlife populations that can do the job, so woody vegetation grows uncontrolled.

Woody plants in the US can be bad for ranchers, farmers, and wildlife. Black-capped vireos and golden-cheeked warblers, both considered endangered in Texas, are two species that need a mixed landscape of forest
and
open grassland to thrive. Woody vegetation suppresses the grasses and the open space that comes with them.

An example of the woody plant problem can be found at the
Tallgrass Prairie Preserve near Pawhuska, Oklahoma, the largest protected area of tallgrass prairie in North America. Tallgrass prairies once spread throughout the Midwest, supporting enormous buffalo herds, and though there are still buffalo here, their numbers are small. Private ranches surround the preserve, and land managers at these ranches find that if they don’t burn grassland areas every year, woody vegetation forms canopies, which makes them immune to future fires.

Woody vegetation is also invading normally bald mountaintop environments in New Mexico as well. Here, bighorn sheep typically gather because they can see mountain lions approaching and escape. But as woody vegetation moves into these formerly bald areas, it allows mountain lions some cover from which to attack, wreaking havoc on bighorn populations.

“Climate change, increasing atmospheric carbon dioxide, and on-the-ground changes like fire suppression and cattle grazing should speed the global transition to woody species,” says Jackson. “It’s not just a problem in Texas, but in South America, Africa, and Asia as well.”

Climate change, its causes and effects, is another issue Jackson is going underground to work out. He is currently looking at problems with natural gas, which was once thought to be an ideal solution for some of our greenhouse problems, since it burns cleaner. It’s certainly a cleaner fuel than coal or oil, but Jackson is concerned with leaks that occur in transport. Belowground fracking can result in leakage into groundwater on the extraction side and old pipes can sprout leaks into urban soils on the delivery side.

Jackson and the Boston University professor Nathan Phillips found natural gas (methane) escaping from more than 3,300
leaks in Boston’s underground pipelines, where there is a record of natural gas blowing up homes, regularly sending manhole covers into the sky, and killing trees.

Still, despite all the importance given to greenhouse gases, Jackson thinks the spread of invasive species across the globe is more permanent and perhaps a more serious threat to our environment. We can reverse climate change in one thousand to ten thousand years, but the plague of invasives and the mixing of species worldwide is not one we
are likely to recover from.

T
HE AUTHOR OF MOST
of our conflicts with nature is our own species. But it wasn’t always that way. For an idea of how we once coexisted with the land and its animals, we visited Olduvai Gorge, part of the African Rift Valley near the Tanzanian border with Kenya. The gorge is a place where many have come to understand
how man developed intelligence, learned to talk, and eventually spread over the world, his numbers exploding in recent years. The idea of a future species of man seems fanciful to many now, but in or near Olduvai there is evidence of three other species of hominids distinct from
Homo sapiens
:
Paranthropus boisei, Homo habilis
, and
Homo erectus
. Their existence shows not only how we got here but how a world of one hominid may not be that natural after all.

A giant plume of magma pushes the land upward, lifting Olduvai Gorge to an elevation of four thousand feet. Even though it is close to the equator, the weather here is mild. In late June, it ranges from daytime highs in the seventies to nighttime lows in the fifties and sixties, which is typical even into the dry season.

The morning after my arrival the sun broke over low shrubs, thorny trees, and savanna grasslands that cover the dry landscape.
Most of the vegetation here evolved with large animals and early man, and brandished nasty spikes or spines to discourage plant eaters. I was with a group of anthropologists, geologists, and paleontologists at a field camp hosted by the University of California, Berkeley. I emerged from my Quonset hut in the former camp of the notable anthropologists Louis and Mary Leakey, among the many scientists who have studied here.

There were field camps from various international institutions here. The Leakey family made Olduvai Gorge famous beginning in the 1930s with unique findings of various species of hominids. Much of the attention devoted to this place was brought by those hoping to find similar fossils and similar fame.

At our camp, scientists from all over the globe rose with me to welcome the sun and start the workday. Our field site comprised a number of corrugated metal buildings and tents that were the base camp for about twenty anthropologists and paleontologists and their Maasai tribal assistants. We consumed a hearty breakfast of millet, porridge, eggs, fresh-baked bread, assorted fruits, and lots of coffee before we got into a half dozen safari vehicles and headed out for the day.

Leslea Hlusko, a professor of paleontology at the University of California, Berkeley, drove our safari vehicle in a caravan with several others past the field site of the Spanish scientists, who waved at our car. The Spaniards acted friendly, but Hlusko assured me there was a competitive fervor among the various international groups at Olduvai. Everyone wants to make a difference, but with the history of historic finds credited to this place, it is hard to find room in the spotlight.

Hlusko is codirector of the Olduvai Vertebrate Paleontology Project, which is trying to develop an online database of fossils so that scientists can readily access past projects and know where fossils are stored. “We want to make the data from the projects available to everyone, and also let them know where the fossils are located, whether they be in a museum in London or in someone’s basement in Florida,” said Hlusko.

Hlusko was also trying to identify the genetics in the fossils, utilizing a unique reverse analysis. Part of her past work had been with captive groups of baboons in the United States,
studying their teeth and then identifying what genes were responsible for their placement, size, enamel, and dental surfaces. Hlusko hoped to study the fossils here and then to determine the genes behind the baboon teeth, including complementary characteristics in other parts of the body that those genes might have turned on. “We know a lot of hominids and early primates just by their teeth or some part of the jaw—particularly as you go further back in time,” Hlusko pointed out.