Untold, Unknown
Encompassing more than 2.5 million square
miles of waterways, rainforest, and a wealth of other natural
resources,
the
Amazon Basin—also known as Amazonia—forms the world’s
most diverse ecosystem. Untold numbers of species—millions
of different kinds of plants and animals—live in
Amazonia, bound in infinitely complex, intimate interrelationships,
the knotted threads of which scientists are just beginning
to unravel.
Through the marvels of modern engineering we have explored distant planets, but remote areas of Amazonia remain unknown, perhaps never to be seen by human eyes.
People in the Picture
Yet Amazonia is not without people.
People have lived off the bounty of Amazonia for perhaps
20,000
years.
When
Europeans found Amazonia 500 years ago, it supported six
million people. Few descendants—only about 250,000—of
these indigenous peoples survive today, but they have been
replaced by 17 million others, largely of European and
African ancestry, who are struggling to survive in an environment
from which many remain alienated. But this is where they
live.
And ultimately it is how these people adapt to Amazonia, how they learn to prosper using river, rainforest, and natural resources without destroying them, that will determine the fate of all the rest of Amazonia’s species.
At the Zoo
The Zoo's exquisite Amazonia habitat exhibit offers us the opportunity to experience a bit of Amazonia, to explore the flow of the river, the otherworldliness of the canopy, the wealth of biological diversity, and the lives of the people who live there.
River of Renown
Fed by 80 to 120 inches of precipitation each year, the Amazon is the world’s greatest river system. The Amazon River discharges more than four times the amount of water as the Zaire (Congo) River, which discharges the next largest amount, and about 11 times what the Mississippi discharges. Seventeen of the Amazon’s 1,000 or so named tributaries are more than 900 miles long, and the system includes about 50,000 miles of navigable waterways.
Flooded Forest
People who live along the Amazon and its tributaries
have learned to adapt to the annual floods that raise water
levels between 20 and 50 feet and inundate the forest
as far as 20 miles on either side of the main river channel.
Seasonally flooded forest make up only about two percent of the basin, but land flooded by silt-laden whitewater rivers known as varsea forests, is far more fertile than terra firma forest or forest flooded by blackwater rivers, known as igapo forest. However, people who farm the alluvial soils of the varzea forest must move to higher ground during the months their land is underwater.
Disappearing Giants
Giant otters (Pteronura brasiliensis) have all but disappeared from the rivers of Amazonia, victims of fur traders and of local people who perceive them as competitors for fish. Giant otters live and travel in noisy, conspicuous groups, and are active during the day. These traits, coupled with the accessibility of their riverside habitat, make giant otters easy to find and kill. They survive today only in a few remote protected areas.
Fishes Abound
More species of fishes inhabit the Amazon and its countless tributaries than inhabit any other of the world’s freshwater ecosystems. Scientists estimate the total number at between 2,500 and 3,000—ten times the number living in the Mississippi.
Most—perhaps 80 percent—of the species belong to one of two groups: characins and catfish. Tetras and piranhas are characins familiar to aquarium hobbyists, but the thousand or so species in Amazonia include three-foot-long “dog tooth” fishes, named for their huge caninelike teeth, and small hatchet fishes that are capable of short flights out of water.
The catfishes are also extremely diverse, ranging in size from tiny three-quarter-inch-long bloodsucking candirus to the six-foot-long 300-pound monsters known as piraiba.
An Immensity of Plants
Temperate zone forests are usually
classified according to the two or three tree species that
predominate:
oak/hickory
forest, for example, or spruce/hemlock. No such classification
is possible for tropical rainforests, where, no single tree domimates.
In the Amazon rainforest, scientists counted 245 species in a 2.5-acre plot in Ecuador, and 283 species in a similar sized plot in Peru.
Buttressing the Forest
“A very remarkable feature in these trees is the growth of buttress-shaped projections round the lower part of their stems. The spaces between the buttresses, which are generally thin walls of wood, form spacious chambers, and may be compared to stalls in a stable: some of them are large enough to hold a half dozen persons.”
—Henry Walter Bates, 1863
Trees in the Amazonian rainforest may grown as tall as 200 feet; above ground buttress roots help prevent these huge, but shallow-rooted trees from toppling over. The roots of rainforest trees are shallow because most of the decaying organic material trees need for food is at the surface and in the first few inches of soil.
Rainforest soils, called oxisols, are old and extremely poor as a result of years of leaching away of nutrients by rainfall. The rainforest topsoil layer is only about four inches deep; in contrast topsoil may be one to two feet deep in temperate deciduous forests.
Up in the Air
“The tropical wet forest is ecologically a desert covered by trees.”
—R.J.A. Goodland and H.S. Irwin, 1975
Although most people imagine the rainforest as a thick
green jungle only to be pushed through with aid of a machete,
the floor of unbroken rainforest is surprisingly open,
even barren. In fact, the “jungle” is all overhead—some 100 to 200 feet above the ground in the
rainforest canopy, where a tangle of woody lianas and a
miniature forest of epiphytes cover and connect the leafy
branches of the trees.
Seen from above, the canopy appears as a vast green meadow, studded with brightly colored wildflowers. And it supports a stunning array of animals, from beetles and butterflies, to monkeys and macaws, to swallows and sloths. The canopy, which captures most of the sunlight, and thus carries out most of the photosynthesis in the rainforest, also feeds terrestrial animals and fish with the fruits, nuts, seeds, and leaves that fall to the ground or river.
Epiphytes A-plenty
The trees of the Amazonian rainforest
are festooned with epiphytes—plants that avoid the
gloom of the forest floor by growing on other plants, usually
in
the canopy.
Among the epiphytes are species of algae, mosses, fungi,
ferns, lichens, and liverworts, and of flowering plants
such as orchids, anthuriums, bromeliads, gesneriads, and
cactus.
Epiphytes, which usually do not take nutrients from their host plants, have evolved a variety of ingenious methods of obtaining nutrients. Some epiphytes enjoy a symbiotic relationship with ants: Ant nests are good germination sites for seeds and provide nutrients, while the roots of the plant provide a substrate and reinforcement for the nests.
Other epiphytes, known as trash basket plants, “collect” organic debris in baskets formed of aerial roots. The debris then breaks down into humus, from which roots can take up nutrients.
Rainforest Riches
“Antibiotics, fungicides, insecticides, viricides, new products, new crops and a vast genetic bank are just part of the intellectual and practical harvest that awaits prudent exploitation of the forest. If we destroy it we will lose forever more information than is contained in all the libraries on our planet.”
—Mike Robinson, former National Zoo director, 1992
The indigenous peoples of Amazonia use an incredible array
of plants for food, fuel, tools, shelter, crafts, and medicines.
By one estimate, as many as 25,000 different species of
plants potentially useful to people grow in the Amazon
Basin. Only a few of these have been widely exploited,
but their products are extremely important: rubber, chocolate,
manioc, curare, and quinine.
Today, many scientists are examining rainforest plants looking for new treatments for cancer and other diseases. Learning how indigenous peoples use various plants for medicinal purposes will greatly aid this effort. Unfortunately, much of this traditional knowledge may already have been lost with the extinction in the last few centuries of hundreds of Amazonia’s ethnic groups.
Fish Food
The waters in many of Amazonia’s rivers are
nutrient-poor. As a result, these blackwaters and clearwaters
lack aquatic
vegetation and plankton for fishes to feed on. Instead,
many species of Amazonian fishes eat fruits, nuts, and
leavers that fall into the water from the trees that overhang
the riverbanks, or that fish can reach themselves when
the forest is flooded, living on fat reserves the rest
of the year. Tambaqui, for instance, live on the seeds
of rubber trees, and thus the survival of this commercially
important food fish depends on the survival of the forest.
Many species of piranhas are also fruit and nut eaters;
in fact, some scientists speculate that their fearsome
teeth evolved primarily to cut fruit, not flesh.
Hidden Wildlife
“We were disappointed also in not meeting with any of the larger animals of the forest. There was no tumultuous movement, or sound of life. We did not see or hear monkeys, and no tapir or jaguar crossed our path. Birds, also, appeared to be exceedingly rare.”
—Henry Walter Bates, 1893
In fact, Amazonia is home to about 800 species of mammals and 2,000 species of birds, but it is true that, aside from insects, visitors to the rainforest see little of the regions incredible diversity of animals. Individuals birds and mammals are usually widely dispersed as well as reluctant to make themselves conspicuous to people. Only one jaguar, for instance, might be found in a 12-square-mile area. Most rainforest birds and mammals are seldom seen; they live high in the canopy and might come down to the ground only occasionally. All of Amazonia’s 36 or so species of monkeys, for example, live in trees, as do all other New World monkeys.
Wild People
“One lives there [in Manu, in Peruvian Amazonia] by the tacit acquiescence of unseen and totally wild human being wild human beings. Now and then, we come upon a trail of footprints, or a makeshift overnight lean-to on a beach. Once a pair of naked figures spring for cover. Nothing more. They are around us, and they know we are there. But we don’t know who they are, where they live, or even what language they speak.”
—John Terborgh, 1983
Only a few “wild people,” not contacted or influenced by Europeans, still live in the rainforest as their ancestors have for millennia, but many indigenous tribe are struggling to preserve their land and culture against the onslaught of settlers, loggers, and others attempting to exploit the forest.
Urban Amazonia
Surrounded by rainforest, the city of Manaus lies at the center of Amazonia, some 2,000 miles up the Amazon at the confluence of the Rio Negro and the Rio Solimoes. With a population of more than one million people, Manaus is the commercial center of the upper Amazon region and a bustling river port that accommodates oceangoing ships.
Founded by the Portuguese in 1669 to protect the slavers who hunted Indians living along the river, Manaus achieved prominence during the rubber boom of the 1800s, when for a few years it was one of the richest cities in the world.
Today, Manaus is a major manufacturing center from which other development activities radiate, activities that are often destructive to the rainforest.
