The Kingdom of Rarities (4 page)

Rarity is all around us, but an excellent starting point for understanding its generation, superior to the Juan Fernández group in its illustrative qualities, is on a large, highly mountainous tropical island. Even better is if such a landmass is far from a major continent and has remained separated from it for eons. In this environment we could seek a rich assemblage of plants and animals illustrating the first condition of rarity—a narrow range. Such an ideal locale sits on the other side of the southern Pacific Ocean from the Juan Fernández Islands: the huge island of New Guinea. Here we can clearly observe how geologic events and evolutionary mechanisms influence rarity; indeed, they help to create it. New Guinea's array of fabled birds of paradise and tree kangaroos illustrates how such episodes and processes lead to the separation of populations and the surfacing of new species, a number of which earn the moniker “rare.”

Geologic events are harbingers of evolution. By this I mean that they often create the conditions that divide previously continuous populations into subpopulations that are isolated from one another, the condition that enables them to evolve separately. In New Guinea, for example, the formation of rugged mountain ranges isolated populations of the same species from one another by distances so great that individuals no longer dispersed between them. Over many generations, through genetic mutation and adaptation to differences in the environments on the isolated ranges, the populations may diverge enough in important characteristics that if members of the divergent groups are reunited, they can no longer interbreed. In
this way new species are born—a process called speciation—with such new species often starting their existence as rare forms with a narrow range and low numbers. For this process to occur for birds and mammals, the isolated populations must persist long enough for the required genetic changes to accumulate. Speciation in birds and mammals does not happen on small islands because distances are not great enough to isolate populations for a long enough time. In contrast, amphibians do speciate on small islands, owing to their reduced mobility. But New Guinea is large enough and rugged enough for its lofty mountain ranges, surrounded by tropical lowlands unsuitable for mountain animals, to have witnessed many bouts of speciation. Although much of the seminal work on speciation used islands as the model, speciation is hardly restricted to islands and occurs on large landmasses as well. So, a critical insight about rarity is that island life per se is not the key to frequent evolution of new species and new rarities; rather, it is isolation, which can be provided by island archipelagoes or large islands.

If all islands are physically isolated from a mainland, are all islands, by the very nature of their limited range, repositories of rarities? Not necessarily, because several factors influence evolutionary processes on islands. Among them are distance from a mainland, length of time the island has been isolated, and size and diversity of habitats on the island. Islands that were once connected to the mainland are called continental islands. Some of them separated from a mainland when the ancient continent of Gondwanaland split up, beginning about 200 million years ago. These include Madagascar, New Zealand, the Seychelles, New Guinea, and New Caledonia, off the northeastern coast of Australia. They are loaded with ancient endemic species, many rare, and most quite different from the closest mainland flora and fauna. Other continental islands separated from adjacent mainland only a few thousand years ago when rising sea levels caused by melting glaciers severed their lowland connections. For example, Sri Lanka was connected to India only a few thousand years ago, and Trinidad was connected to
Venezuela until about 11,000–15,000 years ago. On each of these islands, the flora and fauna are quite similar to those of the continent nearby because insufficient time has elapsed for much evolutionary change to happen.

Other island groups, such as the Hawaiian and Juan Fernández Islands, are oceanic islands formed by volcanic action. They were never connected to a continental landmass. Thus, all organisms living on them must have dispersed across oceanic barriers. This is why the Juan Fernández Islands, although formed 1 to 6 million years ago, have few endemic vertebrates and only a modest number of endemic plants. Also, the few islands in the archipelago are too close to one another to isolate populations. The fauna and flora of nearshore oceanic islands, such as those in the Gulf of California, often tend to look quite similar to those on the mainland. They are within easy reach of mainland species that can fly or raft over on floating vegetation or whose seeds arrive on the winds. Habitat diversity also plays a key role in the amount of speciation that takes place. Like New Guinea, some of the most ecologically diverse islands—such as New Caledonia and Madagascar—are covered in mountain chains or bisected by plateaus. The resulting rain shadow creates wet forests on the island's windward side and dry forests on its leeward side, the different habitats favoring different species.

New Guinea not only embodies areas of exceptional isolation conducive to speciation. Much of the island has another quality that makes it an ideal natural laboratory for the study of rarity and abundance—remote mountain ranges marked by the virtual absence of human interference. Today, natural patterns of rarity and abundance on virtually all equatorial islands have become increasingly obscured by the destructive spread of invasive species—goats, cattle, pigs, cats, dogs, rats, rabbits—and by the logging of native forests, conversion of cutover land to agriculture, and other forms of development and exploitation that have followed the arrival of humans.

A scientist in New Guinea, in contrast, can still observe the interplay of geology, evolution, and rarity in an all but undisturbed venue. The mountain walls, deep gorges, and numerous rivers create barriers that prevent recently arrived species from spreading and swamping the local biota. Some of the high ranges even check the spread of humans. New Guinea is about twice the size of California but remains sparsely populated. With so few people—about 7 million inhabitants—and so much forest and rugged terrain, there may even be places where people have never set foot.

Among wild destinations, New Guinea surpasses all others as an outpost of mysterious dimensions. The lack of roads and few airstrips limit access to its isolated valleys. Flights into the mistcloaked mountains are fraught with danger. In 1991, an up-and-coming field biologist and a colleague, Ian Craven, perished when his single-engine bush plane crashed in the island's far western wilderness. Then there is the famous disappearance of anthropologist Michael Rockefeller about fifty years ago somewhere on the southern coast. Explorers of New Guinea know the risks and the challenges: avoiding deadly strains of malaria; living on tinned mackerel and navy biscuits; not getting lost in the uncharted forest; and not getting eaten. The highlands are known for their fierce mountain clans who wage ritualized war with neighboring groups and occasionally dine on one another.

Then there are the rewards. On my first trip, in 1990, I carried along a copy of
Birds of New Guinea
by Bruce Beehler and Thane Pratt. The pages of the bird guide and Dale Zimmerman's illustrations came to life when I saw and heard my first magnificent riflebird, a bird of paradise, in a park outside the capital. Upon my return, I finally met Bruce, and discovery of our mutual interests in New Guinea's unique flora and fauna led to more frequent contact. I grew envious listening to his stories about what he had observed—the birds of paradise, cassowaries, bowerbirds, giant fruit bats, tree kangaroos—and his biological surveys into the most remote region of the planet.

The island of New Guinea is especially interesting to biologists because so many of its species are found nowhere else. New Guinea itself is politically divided—the western portion is Papua (formerly Irian Jaya), a province of Indonesia, and the eastern half is the sovereign nation of Papua New Guinea, or PNG for short. The political division obscures a common geography, similar rain forests, and shared cultures. No other large tropical island is so mountainous, and the isolation created by its cordilleras, or mountain chains, has had a profound effect not only on the evolution of animal and plant life but also on human communication. Nearly one-fourth of all spoken languages on Earth are known only in New Guinea (about 1,100 true languages, not including dialects), and most are spoken by fewer than 1,000 people. Languages, like birds of paradise or tree kangaroos, can also be labeled as endemic to a place. And perhaps the same forces—geologic, geographic, and evolutionary—that resulted in so many tongues spoken by so few people in this land might be related to why so many species of widely different lineages occupy such narrow ranges: a prime element of rarity.

In the late summer of 2005, I received an excited message from Bruce that he would have to bow out of a birding trip we had planned in Maryland. “I can't believe it,” he wrote. “After twenty-five years of trying, I have just been granted permission to bring a small research team into the Foja Mountains!” More than twenty years of guerilla warfare in Papua Province had prevented any field expeditions in this region. When Papua's political troubles subsided in 2003, Bruce joined herpetologist Stephen Richards of the South Australian Museum to try once more. Two years later, in October 2005, villagers of the Kwerba and Papasena clans granted Bruce and his group permission to enter their homeland. It would turn out to yield a wonderful collection of naturally engendered rarities.

If New Guinea is the ultimate destination for field biologists, within it the Fojas loom as the pinnacles of desire. The Foja Mountains
were reportedly so inaccessible that humans had never settled there. I had come to doubt whether places such as the Fojas still existed, geographic outliers with no history of interlopers—gold miners, oil drillers, religious zealots, or armed guerillas—either seeking their fortune or looking for an escape from modern society.

The purpose of Bruce's expedition was to survey the biota and to find species new to science and others poorly known that he thought might be inhabiting this isolated range. The Fojas sit in the heart of Papua Province, and their summits reach 2,200 meters above sea level. The surrounding 7,500 square kilometers, lightly inhabited by jungle dwellers, lack roads. Taken together, the vast landscape stands as the largest expanse of pristine forest in the tropical Pacific.

The Fojas have a reputation for repelling outsiders. The legendary secretary of the Smithsonian Institution S. Dillon Ripley, for whom Bruce had worked, tried to approach them from the north in 1960. He failed because the rivers were not navigable. In the late 1970s, both Bruce and Jared Diamond, a noted New Guinea bird expert long before penning his best-selling
Guns, Germs, and Steel
, raced to explore them. Diamond, through helicopter and grit, arrived first in 1979. He found a species that had eluded birders for seven decades, the “lost” golden-fronted bowerbird, and returned home to bask in ornithological glory. His find earned extensive press coverage, and his technical paper reporting the rediscovery of the bowerbird enlivened the cover article in
Science
.

Bruce believed that the Fojas might hold many species new to science as well as others that science had forgotten, the so-called lost species. Although they had not been declared extinct, these “lost” species had not been seen in decades, a category of rarity but a half step from oblivion. To help them, Bruce and Steve Richards assembled a team of crack naturalists who specialized in different taxa—birds, mammals, reptiles, amphibians, butterflies, other insects, plants—along with several Papuan biology students. They would be guided by members of the Kwerba and Papasena tribes who lived in the Foja region. The guides were as excited as the
biologists at the prospect of exploring this area. Not only were the Fojas uninhabited, but also—as far as they knew—the mountains had never been part of their clans' hunting territories.

Would new species of apes or monkeys be spotted in the Fojas? Would the researchers need to be vigilant for prowling leopards or tigers? If this were Sumatra, such concerns would be accurate. Tigers, leopards, apes, and monkeys, however, are part of the Indo-Malayan but not the Australian faunal realm. New Guinea sits east of what is known as Wallace's Line; most of the islands west of that demarcation were physically connected to Asia (via a landmass known as the Sunda Shelf) during recent glacial periods when sea levels were much lower than they are today. Asia's large vertebrates had no need to swim across even shallow waters to reach Sumatra, Java, Borneo, and Bali. They simply walked.

Technically, Wallace's Line falls between the islands of Bali and Lombok and divides the Indonesian archipelago in two. Alfred Russel Wallace was the first to identify this natural longitude, so the name celebrates his insight. On the western side of Wallace's Line live animals of largely Asian origin; on the eastern side are those common to Australia, to which New Guinea was at times connected (to the Sahul Shelf) by a land bridge over the Torres Strait prior to about 20,000 years ago. The lack of land bridges spanning Wallace's Line and the presence of deep ocean trenches precluded the mixing of faunas. The simple fact is that most mammals are poor long-distance swimmers, and they can't drink seawater. So even those that managed to hitch rides on floating mats of vegetation—natural rafts—would have died of dehydration before they reached land. In New Guinea, then, birds of paradise and tree kangaroos would be evident, but no orangutans, gibbons, macaques, or leaf monkeys ever arrived there. The range of large terrestrial carnivores also stopped farther west, in Bali (tigers) and Borneo (clouded leopards), because they too could not cross deep water. Absent as well would be the giant herbivores, such as tapirs and wild cattle, that the big cats prey upon.