The Next Species: The Future of Evolution in the Aftermath of Man (28 page)

The size of the fecal pellets is
an indication of pack rat size and diet. Researchers are able to characterize body and genetic responses to climate in populations of pack rats spread out over thousands of years.

Today, Death Valley holds the record for the hottest and driest place on earth, but during the last ice age, Death Valley was covered by Lake Manly, a hundred miles long and six hundred feet deep. The climate was 11 to 18 degrees Fahrenheit (6 to 10 degrees Celsius) cooler. But as the valley began to warm, pack rats adapted and slowly moved upslope. They got as high as 5,900 feet (1,800 meters) but it wasn’t high enough. By about six thousand years ago there were no more large pack rats present on the east side of Death Valley.

Not all mammal extinctions were due to warming or man. UCLA’s Van Valkenburgh argues that over the last 50 million years, successive groups of large cat-like, wolf-like, and hyena-like mammalian carnivores diversified but then declined and went extinct. At one time the Canidae family (wolf-like carnivores) had three subfamilies. Two of those went extinct. Van Valkenburgh believes that some of this was
caused by what she calls “the meat trap.” In situations where carnivores need more energy, they may switch not only to a pure carnivore diet but also to a diet in which their prey are bigger than they are. Once there, however, they have trouble going back to smaller portions.

All three subfamilies of Canidae reached a peak about 30 million years ago, but only one subfamily survived. That included domestic dogs, wolves, foxes, and coyotes. The other two subfamilies increased in body size by 400 to 600 percent, but when their prey got sparse, they couldn’t switch back to smaller prey. They
had adapted to eating all meat, all of the time, and only from animals larger than themselves. Their diets were simply unsustainable. Still, there were once twenty-five contemporaneous species of canids native to North America as opposed to seven today. Nature has indeed been much richer before. But can it ever return to the diversity it once had? Can we turn back the clock?

For years, the golden era to which environmentalists in North America have often spoken of turning back the clock was before 1492, when the Europeans arrived. However, in the journal
Nature
in 2005, Josh Dolan, a biologist at Cornell University, and a group of prominent scientists expressed their desire to go back even further. They wanted to go back to a time before the Clovis people, the real starting point for human change in the Americas.

Dolan’s group declared that Western scientists had gone into full retreat from the battle to stop biodiversity loss and were now simply struggling to diminish the rate. The team wanted to change the game from just “managing the extinction” to actively “restoring ecological and evolutionary processes.” Their idea was to
restore all the big animals that once stocked North America with surrogates from other continents that could push back the time line to when there were horses, camels, elephants, and even lions stalking the land.

One of the first things the group proposed was to restore the largest tortoise in America, the Bolson tortoise, to areas of the Southwestern United States. I accompanied the late David Morafka, a herpetologist at California State University, Dominguez Hills, to visit the Mapimí Biosphere Reserve, dedicated to the protection of the Bolson tortoise and other unique flora and fauna of the Bolsón de Mapimí, a large inland basin in the Chihuahuan Desert north of Mexico City. The Bolson tortoise, whose range had once extended across the Chihuahuan Desert in northern Mexico and the southern extremes of the US, was making a last stand here. Repatriating the Bolson tortoise to the broader expanse of the Chihuahuan desert tortoise could bring the largest of the continent’s tortoise species back to the US.

Wild horses were another possibility for rewilding. They were introduced by Europeans to North America about five hundred years ago and have since taken up ecological niches that were held more in balance thirteen thousand years ago. Many ranchers look at wild horses and burros as large pests that foul watering holes and compete with cattle, native pronghorn antelope, and native bighorn sheep. To Dolan, the horse is just as native to this land as any other species.

The problem is you
can’t just reintroduce a large herbivore like a horse and not reintroduce predators to keep the animals under control. In 1971, the Wild Free-Roaming Horses and Burros Act made it illegal for anyone to harass, capture, or kill wild horses. Since then, populations of the animals have soared throughout the Great Basin Desert, which lies mostly in Nevada and extends to the fringes of surrounding states. But this is not the case in Montgomery Pass Wild Horse Territory, which straddles the California-Nevada border. There scientists study mountain lions, which are an effective predator control for these animals.

Such a balanced approach could provide a lifeline for Przewalski’s horse, smaller than most domesticated horses and native to the steppes, the vast semiarid grass-covered plains of Central Asia, as well as the Asiatic wild ass, both free-roaming and critically endangered equids. Translocation to the US might save them from extinction and
repatriate horses to their evolutionary home ground. Many scientists say that the trick is to introduce predators to these ranges as well, in order to keep large horse populations in check.

Believe it or not, camels originated in North America. They migrated north from the Arizona desert and crossed the Bering Strait land bridge three to four million years ago. The IUCN currently lists the Bactrian (two-humped) camel as
critically endangered
. There are about 600 Bactrian camels surviving in the wild in China and 450 in Mongolia. It is the only truly wild camel. Dromedary (one-humped) camels, but for some feral animals in Australia, exist only as domestic animals. There were four species of camels and llamas in North America at the end of the last ice age. Today wild Bactrian camels are restricted to the Gobi Desert and their cousins, the llamas, to South America.

In the 1850s, Lt. Edward Beale led the US Camel Corps, mostly dromedaries, from Texas to California, and he was amazed at how camels grazed on creosote and other brush species that now form dense monocultures across much of the Southwest desert. If we brought Bactrian camels back again or released domestic camels into the wild, the landscape of plants could be more diverse. Camels were once a vital part of the ecological community. Australia has well-managed co-grazing programs of cattle and dromedary camels, which could provide meat and milk, and an increase in the mosaic of plant species.

Elephants would be another winner in the west. At Olduvai Gorge, I saw elephants feeding on shrub forests. Despite a plethora of sharp spines and thorns, the elephants cleared away the brush as efficiently as tractors but left the refuse to regenerate the soil. Much of the open grasslands of East African plains owe their existence to the assistance of elephants. Introducing elephants to the juniper forests on the Edwards Plateau in Texas might alleviate the juniper problem.

Another animal that the “rewilders” would like to reintroduce to the American West is the cheetah. Cheetahs were once here.
The American cheetah first appeared perhaps 2.5 million years ago but went extinct about two thousand years ago with the rest of the
megafauna. They are the reason that the American pronghorn antelope is so fast. Pronghorn can travel at a top speed of sixty miles an hour, second only to the cheetah. But whereas the cheetah is a mere sprinter, the pronghorn is an endurance runner. Pronghorn can average forty miles an hour for half an hour or more, galloping across the high prairies of Wyoming. There is no living reason for pronghorn to move that fast. Biologists believe that they evolved to outrun the American cheetah, which was around when pronghorn, mammoths, and giant sloths roamed the North American plains. Returning the cheetah to America could give the pronghorn an impetus to stay fit. Also, the African cheetah, once found throughout Africa and southwestern Asia, has been greatly reduced and is not likely to survive into the next century. Moving them to the North American plains might increase their chances. This wouldn’t be another case of introducing an invasive to North America, as all these species were present long before man showed up. In many ways, we’re the worst of the invasives.

There are currently about a thousand African cheetahs in zoo populations across the world that could act as surrogates for the American cheetah, which is closely related. I watched a cheetah from a safari car in Ngorongoro Crater in Tanzania: the animal was grooming itself in the sun. Behind the cheetah were several antelope, something that attracted the cheetah’s attention as well. The cheetah slowly got up and started to stalk an antelope, when a pair of hyenas jumped up, drawn by the cheetah’s hunting pose. They bared their enormous teeth like laughing clowns, waiting for the action to begin.

The cheetah took a runner’s pose and bolted, leaving a huge cloud of dust behind it. The galloping cheetah quickly caught up with the antelope, knocking it over, while the hyenas danced about, wildly excited over the promise of shared meat.

Such scenes would be great for tourists. Ecotourism has that potential even in North America to raise substantial funds that could benefit the parks that protect these animals as wells as the surrounding communities. About 1.5 million people annually visit the San
Diego Zoo’s Wild Animal Park in California to see large animals. By contrast, only twelve US national parks receive that many visitors.

Rewilding might fill the excitement gap of public and private parks in the US. The reintroduction of wolves to Yellowstone National Park has generated an additional $6 million to $9 million annually at costs of $500,000 to $900,000 to the park. If the chance of seeing a wolf in the wild has generated that much support, how much support might come from the chance to see a cheetah or an elephant?

The California condor thrived throughout North America until the end of the last ice age. They roamed over the Grand Canyon ten thousand years ago, scavenging on large animals that are now extinct. Today, California condors once again soar over the Grand Canyon, but the captive breeding program that promotes this must feed these animals with cattle carcasses. If Pleistocene megafauna were returned to the American West, these scavengers might again flourish.

Today, deer populations in the Northeastern woods of the United States are at historically high levels; so are disease-bearing pests, as we’ve seen with black-legged ticks. The presence of disease is associated with ticks, white-footed mice, and white-tailed deer. Gray wolves once caused deer to avoid heavily wooded areas, where they were more vulnerable to attack. But without gray wolves, white-tailed deer frequent the wooded forests, where ticks and Lyme disease reach their highest incidence. If wolves were to return, a lessening of disease risk, including Lyme disease, hantavirus, monkey pox, typhus, bubonic plague, and hemorrhagic fever might result from a better-balanced ecosystem.

These megafauna proxies proposed for rewilding are not exactly the same species that existed at the time of the Pleistocene extinction, but they could fulfill similar roles, as did the reintroduced birds in the North American peregrine falcon program. That program attempted to restore to North America peregrine falcons, whose eggs had become too brittle for hatching due to the use of DDT, a commonly used pesticide that was banned in 1972 but persisted in the environment for years afterward. The program used large numbers of
captive-bred birds of different subspecies to bolster American falcon populations. In the end, these birds adapted to fulfill the niche left by the Midwestern peregrine population, which disappeared in the 1960s.

Biologists with cautious controls would carefully monitor a Pleistocene rewilding program while staying as true to the fossil record as possible. Private lands would hold the most immediate potential. More than seventy-seven thousand large Asian and African mammals now occupy Texas ranches. Larger tracts of public lands in the Southwestern United States could be brought on board to expand the program.

Bolson tortoises and exotic species of horses might be the first logical step, since they so recently occupied similar lands in North America. Camels and llamas might follow, since these animals could help control invasive plants. The final introductions might be elephants and African lions. The benefit of having elephants and camels for the control of woody vegetation has already been explained. But the benefit of African lions is more controversial. The African lion was once the widest-ranging land mammal of all time. The Asiatic lion is critically endangered, with a single population in India’s Gujarat State. Yet lions have been introduced and managed in African and Indian reserves that are a similar size to some contiguous and private lands in the US.

Establishing a predator population would be a necessity. The central issue, of course, is that lions sometimes attack humans. Such a reality has been growing in acceptance with mountain lions in the US. Attacks don’t precipitate large kills of lions anymore. But African lions would be an upgrade in size and predator status. The African lion is the apex predator of Africa.

The African and Indian reserves that have reintroduced lions have been successful in reestablishing normal behavior and population controls in their prey. But momentous questions would have to be answered before the reintroduction of cheetahs and lions could begin
in the US.

Wolves were introduced in the 1990s to Yellowstone National Park and they have contained burgeoning elk populations there sufficiently to allow a resurgence of the forest. They have also started to take coyotes, not just as prey, but as competitors, which reduces the coyotes’ take of pronghorn antelope fawns and other smaller predators, like raccoons and beavers. Wolves also reduce or scare off hoofed mammals that trample streamside vegetation, and this enhances nesting habitat for migrant birds.

Before man migrated to North America,
there were many more predators and prey in considerably grander and better-balanced ecosystems. The situation that exists now is diminished, impoverished, and unnatural. We have fewer birds, animals, reptiles, and amphibians—fewer of almost everything. “But we are incredibly adaptive, which means we don’t remember the past well,” says UC Berkeley paleobiologist Charles Marshall. “Where I grew up in Australia, the area was just packed with wildlife and all sorts of natural noises. In comparison America is much more impoverished. It has far fewer natural sounds. But I’ve adapted. I don’t notice the relatively silent days anymore. But I sure noticed it when I got here.”