The Kingdom of Rarities (8 page)

In the Foja Mountains, the birds seemed to be common within their narrow range and tame, whereas the mammals appeared neither common nor tame. Perhaps the explanation is that some traits selected for in response to encounters with human hunters had persisted even when such wildlife populations dispersed into new areas. The range of these species of mammals included areas hunters frequented. Some, such as the six-wired bird of paradise, changed, reverting to natural boldness in isolation from humans; others, such as tree kangaroos, which remain shy, seem to have been more resistant to evolving to take advantage of the absence of human predators. Bruce had invoked what scientists call “the ghost of evolution,” that is, in this instance, the “echo” of past influence of New Guinea–wide hunting pressure continuing to resound through time, even in the absence of the original hunting pressure, at least for some of the mammals. “What we are actually observing is natural selection on the local scale in real time, not over thousands of years. Only the stealthy or wary species survive the hunter's bow, snare, or shotgun when wildlife meets humans for the first time. It's why some birds of paradise disappear right away near villages.”

Further analysis of some of the other taxa supported the findings on birds of paradise, bowerbirds, and tree kangaroos. New Guinea is one of the global centers of diversity of palms, with about 145 species plus 5 new ones discovered by the Beehler team. What were the patterns of rarity and abundance among palms or orchids or other vascular plants? Was the pattern here similar to what we expect in other tropical forests: a few abundant tree and understory shrub species and many other species represented by a few individuals? Was this true for butterflies as well? Brother Henk van Mastrigt confirmed that for the groups of butterflies and moths he collected, the pattern held. Many frogs, too, showed the same basic pattern
as the birds and mammals of the Fojas: a few common species with very limited distributions, with a number of other frogs that were range limited and had low population density, in comparison with a few Fojas species that were widely distributed across the northern mountain ranges of New Guinea.

The combined data on mammals, birds, and amphibians led to some important conclusions. First, the Foja range clearly emerged as one of the world's centers of mountain-dwelling species found nowhere else on Earth. Second, its fauna is a wonderful example of localized speciation fashioned by geologic processes. Isolation and speciation, again, are engines of rarity. Of course, the Foja expedition still leaves lots of blank pages to fill in about nature without humans. The costs and logistics of an expedition limit researchers such as Bruce Beehler to short-term visits, even though long-term studies are required to unravel the patterns of rarity. Until permanent research camps are established, insights into patterns of rarity in places without humans will be mined slowly. Thus the paradox of accessibility: if upland forests were more open to biologists, we might know more about rarity and abundance for all the vertebrates, yet if they were more reachable, the vertebrates would likely be gone. Two return visits to the Fojas in 2006 and 2009 by Bruce and colleagues also offered new data. To cite one example, the scientists encountered the golden-mantled tree kangaroo only three times in three trips—that is rare by any measure. On the second trip they never located that species, nor did the Papasena hunternaturalists who went out in search of it. The echidna was not seen on the final two trips—not once.

Places such as the Foja Mountains are already quite rare globally and will remain so. The range covers more than 3,000 square kilometers of untouched old-growth tropical forest sans humans. While such are the places of naturalists' dreams, the Foja natural experiment is impossible to replicate in many places in the twenty-first century. One of the best examples of what might be called “restored isolation,” though, comes from across the island. From
1998 to 2008, Jared Diamond spent time surveying an area in Papua New Guinea's Kikori River valley, where Chevron has built a 171-kilometer pipeline to ship oil from an inland mountain valley to the coast. The pipeline road was gated to keep intruders out of this vast wild landscape. The result was a reverse experiment in recovery of the native fauna. Diamond noted species that had become common again, such as the southern cassowary, hornbills, birds of paradise, some of the giant pigeons, parrots, tree kangaroos, and hundreds of species of the forest interior, all of which normally disappear once hunters gain access. As much as the guns-and-fences approach to conservation is dismissed by so many these days, the Chevron Kikori experiment illustrates how once rare species can recover with strict protection. Restricting whole landscapes, as in Kikori, however, is neither practical nor ethical and certainly is not affordable unless financed and policed by, for example, a major multinational energy company.

In truth, the Foja Mountains are well guarded by the Kwerba and Papasena, who control access. This range is their patrimony and their most important source of wealth—timber, pure water, meat, medicinal plants, even bird of paradise feathers—and they will not be giving it away to outsiders any time soon. After Bruce's helicopter lifted off the lake bed on his second visit to this remote domain, the montane forest would return to its splendid state of isolation. The visitors had gone home. The bowerbirds would continue to dance around their bowers. Nearby, the male six-wired would shake himself into a joyous blur, and the uninhibited displays of other birds in this paradise would resume without a human audience.

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ROPICAL RAIN FORESTS OFFER
stunning exhibitions of animals and plants. Many artists have tried to portray this richness, none better than the French painter Henri Rousseau. His canvases, filled with curious primates and fearsome wild cats, grace the walls of leading museums, and reproductions appear on the covers of ecology textbooks. Despite Rousseau's lack of formal scientific training or travel to equatorial regions, his paintings capture many of the central themes in modern tropical ecology. A biologist wandering through a Rousseau retrospective would marvel at how the Parisian anticipated such key topics as the importance of predation by large cats on large plant-eating mammals, the abundance of plants whose seeds are animal dispersed, and even a visual hint of the rarity of tropical forest dwellers.

To understand rarity in nature, whether as an artist or a biologist, one of the best places to look is in the tropical belt. The Amazon
and Congo basins, Southeast Asia including Sumatra (Indonesia), and New Guinea are the four largest expanses of rain forest; along with some smaller regions, they hold more than 60 percent of the world's known species—crammed into less than 5 percent of Earth's surface. Because these rain forests are incredibly rich in species, they contain unusual numbers of rarities. The Foja Mountains of Papua Province, Indonesia, on the island of New Guinea, serves as a great starter location for understanding how rarity is created through extreme isolation on mountain chains. The Amazon rain forest, the next locale on our journey, is a vast, low-lying region where native tree species and a wide variety of vertebrates that inhabit them—carnivores, monkeys, and macaws, to name a few described here—illustrate another crucial type of rarity to consider: species that occur at a very low density but over a wide range. Three of these great reservoirs are mainland rain forests. They offer an important missing element in the mix of rarities that is absent in the New Guinea fauna—top predators, especially the large cats. These cats stalk their prey on the rain forest floor: jaguars and pumas in the Amazon, leopards in the Congo, tigers and clouded leopards in parts of Indonesia and Indochina.

One of the most cat-rich rain forests on Earth is a nearly unbroken belt of wilderness in the western arc of the Amazon basin. In the secluded Madre de Dios region of Amazonian Peru, we can examine how and why individuals of the wild cat family and other terrestrial organisms inhabit great expanses but are relatively distant from one another. In this remote Amazonian locale, enclaves also exist with no evidence that large cats have ever been hunted. In such a sanctuary, we can see how rare rain forest mammals and birds, such as jaguars and pumas, even at very low densities, influence the species-rich domain over which they rule.

On a sunny morning in August 2009, in the very heart of the Madre de Dios region, I joined the husband-and-wife team of George Powell and Sue Palminteri to survey a stunning rain forest panorama from the top of the canopy-viewing tower in Peru's
Manu Wildlife Center. Some fifty meters above the ground, I wondered what Rousseau would have chosen to portray in the scene before me. Surrounding the tower was perhaps the world's richest natural arboretum, a forest holding one-tenth of all bird species and enough as yet unnamed invertebrates to fill several natural history museums. Acrobatic spider monkeys and their slow-moving relatives, red howlers, appeared below. In a neighboring fig tree, brightly plumed trogons and barbets decorated the branches. Flocks of tricolored scarlet macaws flashed by at eye level, penetrating the forest with their cacophonous squawks. For these canopy residents—monkeys, macaws, and thousands of others—this is the sweet life on the breezy, green roof of the rain forest. The chance to join them in this restorative stratum, even for an hour, is a relief from the claustrophobia of the dark, dank forest floor. For the elevated naturalist, the exhilarating climb to the top serves as a refresher course—a moment to ponder when our ancestors, too, were arboreal.

The tropical rain forest is full of common species such as ants, nematodes, and fungi that contribute heavily to the unseen machinery of an intact rain forest, yet it is a bountiful Kingdom of Rarities as well: Many living things in this landscape, from the tops of emerging giant trees to the thin soils covering their roots, exhibit several forms of scarcity. Some insect species exist only in the canopy of a single tree species, but there they mass in numbers. The giant trees orchestrate life in the Amazon and create a three-dimensional stage for millions of smaller organisms and staggering diversity, too: a single tree may hold more ant species than are found in the entire British Isles. Yet the distribution of these trees is quite different from that in England and western Europe, where a few elms, maples, beeches, or oaks may dominate a large patch of forest. In the Amazon, particular trees, such as mahogany and members of the Brazil nut family, may range eastward across Brazil but be spread out as individuals, occurring maybe only once every few hectares, sometimes even more dispersed. The jaguars and
pumas that wander below their crowns and several of the monkeys that live in them also range widely but are thinly distributed. The macaws that fly across the canopy also appear across much of the lowlands but are locally scarce.

The unusual flash of brightly colored birds in an all-green realm triggered a raft of intriguing questions that had been lingering in my mind for years: Why might such species be rare? And why are rare creatures as different as macaws, monkeys, cats, and rain forest trees so similar in the character of their spacing patterns? Was one single factor the cause, transcending whether an organism was covered in fur, feathers, or leaves? And why do biologists believe that some of the scarcest species exert a tremendous influence on the workings of the rain forest?

Up in the Manu viewing tower, the distant sound of communal throat clearing caught Sue's attention: the hubbub was a troop of capuchin monkeys expressing their displeasure at an intruder lurking nearby. Perhaps a jaguar had walked past and settled along the riverbank or a forest eagle or falcon had passed overhead. “As long as the capuchins stay hidden in the branches, they're generally safe from aerial predators,” Sue related. “But they're scared to death of an opportunistic spotted margay cat that could climb up after them.” At all costs, capuchins and other monkeys avoid the ground, where they would be an easy mark for a jaguar. This largest of South American cats is known by its local name,
yaguara
, which means “to kill with one pounce.”

Consistently locating jaguars was central to George's research project. He sought to answer one of the most pressing questions of tropical biology: How much is enough? He wanted to know how much habitat area was needed to conserve jaguars, pumas, peccaries, tapirs, and other locally rare Amazon species. Up to now, scientists could only guess or shrug in response.

Sue had spent the previous five years searching these forests for wild primates, the little-known saki in particular, so she knew all about the wariness of monkeys. The bald-faced saki, part of an unusual-looking
group of primates, the pithecians, is distinguished by its long, coarse fur, a pelage seemingly out of place in the tropical rain forest but quite useful as camouflage, an important feature for canopy residents that weigh only two kilograms. Their very long, black-and-white mottled hair not only makes these monkeys appear twice their size but also resembles the shape, color, and texture of the branches of their home in the lower canopy. Their unusually bushy tail only adds to the strange silhouette, although it is not prehensile like the tails of larger-bodied New World monkeys. Rather than hang from tree branches as do some other primates, they scamper over canopy limbs like giant squirrels. When they reach a tree laden with unripe fruit, sakis use their massive (for their size) canines to pry, rip, or split open the often hard-coated fruits to reach the soft young seeds. But few primatologists had ever seen bald-faced sakis for very long, let alone studied them. Even their weird vocalizations seemed like part of the “camouflage” adaptation: their birdlike sounds, on top of their secretive behavior, contributed to Sue's own ecological name for this group: stealth monkeys.

Sue and her associates had been the first to acclimatize troops of bald-faced saki monkeys to human presence and watch them every day for hours on end. Eventually, the primates became comfortable enough to act without visible concern about their presence. That allowed her to focus on the contributions of her sakis to the rain forest ecology. Sakis seemed to be everywhere but nowhere at the same time, she noticed. A distribution map of the saki indicates the species is found throughout Madre de Dios, but when one tries to find them, the monkeys' presence seems irregular and unpredictable, what biologists call “patchy.” Why should that be so when all of that forest looks so similar to us?