Amazonia Exhibit Audio Tour Scripts
About the Amazonia Exhibit
Welcome to Amazonia! Before we make our first stop, I'd like to draw your attention to two pieces of artwork near the entrance.
Just above the outside entry door, you will see a circular wooden medallion with a relief carving of a fish inside and a group of ants on the rim. The fish is the arowana, a large freshwater species native to the Amazon. This fish, also known in the Amazon as the “water monkey,” is about three feet long and is best known for its ability to leap twice its own body length out of the water to snatch invertebrates, bats, birds, and other animals from overhanging vegetation.
Just inside the entry door is a ceramic map of South America with a green area depicting the Amazon Basin. Note its size. The lowland basin that surrounds the Amazon River and its territories is about 1.4 million square miles in size and is really a huge watershed that collects about one-fifth of the world's freshwater into a vast network of streams and rivers that eventually empties into the Atlantic Ocean. The Amazon River system is the largest in the world, discharging 12 times more water annually than the Mississippi and as much water in one day as the Thames River in England discharges in an entire year.
Now proceed on through the inner doors to our first stop, which will be the flooded forest on your right.
Welcome to the Amazonia Podcast Tour. This audio tour will guide you through the National Zoo's Amazonia exhibit and will conclude with an introduction to the science resources of the Amazonia Science Gallery.
The Amazonia exhibit is located at the bottom of the Zoo, next to the Kids' Farm and at the lower end of the Beaver Valley Trail. The closest parking is in Lot D, at the bottom of the Zoo, about a five-minute walk from Amazonia.
The Podcast Tour will take about 20 minutes but we encourage you to stay longer and see everything. On the lower level of Amazonia, the Podcast Tour stops will be at the flooded forest and the stingrays; at the giant river fish exhibit, and in front of the freshwater turtles. And on the upper level, the tour will stop at the kapok tree; the river overlook; and the bromeliad forest.
If you find yourself in line waiting to enter Amazonia , you may want to listen to the Podcast Tour episode entitled “About the Amazonia Exhibit.” But if you are ready to enter the exhibit now, please proceed to the first stop on the Amazonia Podcast Tour: the Flooded Forest.
The flooded forest is the first exhibit on your right. It depicts a typical scene in the river's floodplain during the flood season.
In the Amazon, it can rain any day of the year but there are seasons when rainfall is extremely heavy. During these times, the flat relief of the Amazon Basin enables rivers to flood their banks for many miles in all directions. The flooded areas can remain up to 40 feet deep for months, totally submerging some vegetation and completely covering the roots of most trees. About ten percent of the Amazon is subject to these seasonal floods. The remaining 90 percent, known as terra firma, or “firm ground,” occurs on slightly elevated terrain and never floods during the rainy season.
When the rivers overflow, animals normally confined to the main channel spread out into the flooded forest and forage on fruits, leaves, and even animals that fall into the water. The main river channel can be a very poor source of food for fish, so for them, the flood is a time of abundance and many species reproduce and migrate at this time.
There are two distinctly different types of water in the Amazon. White-water, which is relatively fast-flowing and filled with silt eroded from the surrounding landscape, and black-water, which is calm and clear and contains very little sediment. Forests flooded by white-water rivers are known as varzea, and those flooded by black-water rivers are termed igapo. Our flooded forest exhibit depicts a black-water igapo environment.
The most prominent animals in the flooded forest exhibit are the fresh water, or river, stingrays. These graceful creatures spend their lives foraging for crabs, mollusks, and other small invertebrates in steam and river sediments. The vast majority of stingray species live in marine, or salt water, environments and ancestors of these stingrays arrived in the Amazon millions of years ago when it was a huge inland gulf connected to the Pacific Ocean. When the ocean connection was blocked by the rise of the Andes, stingrays and a number of other marine species were trapped in a vast, brackish inland lake and have remained there over the eons gradually adapting to freshwater conditions.
Stingrays are docile animals, but on Amazonia's rivers, they inflict more human injuries each year than any other animal. When resting, the well-camouflaged stingrays settle into the river bottom and can be easily stepped on by unsuspecting fishermen and swimmers. Even the slightest pressure on the back causes the stingray's tail, and the mildly venomous barbed spine near its base, to become upright and perfectly poised to inflict an excruciatingly painful sting to the bottom of the foot.
The next stop on our Podcast Tour is the giant river fish exhibit just ahead on your left.
This stop on the Amazonia Podcast Tour is the giant river fish exhibit, on your left immediately after the flooded forest.
The Amazon Basin contains many aquatic features including rivers, lakes, channels, streams, and the floodplains of seasonally flooded forest. This varied aquatic environment is home to an enormous diversity of life including over 2,500 species of fishes. In fact, the Amazon has the greatest fish diversity of any river system in the world and some of the largest freshwater fish to boot. You see some of these giants here.
When Amazon rivers overflow, water spreads into he surrounding forest for miles, and many fish travel into the forest with it. In remote areas, the floodwater may be very still and contain so much decaying vegetation that oxygen levels are too low to support most fish. The arapaima is an exception and can survive in oxygen-depleted waters because it has the ability to breathe air. In fact, its gills are so small and inadequate that the arapaima must breathe air using a highly modified air bladder as the equivalent of a lung. Watch carefully and you may see an arapaima rise to the surface and take a quick gulp of air.
The flood is a time when many plants reproduce and disperse seeds. Many release diaspores—fruits and seeds with ingenious structural characteristics that allow them to float for a while before sinking. A large percentage of diaspores are consumed by fish, such as the pacu you see here, which has strong, peg-like teeth used for crushing the tough covers of fruits, pods, and the seeds inside. Many seeds are killed in the process, but some survive and are eliminated by the fish some distance away from the parent tree. In this way both plant and animal benefit—the fish by getting a tasty meal and the plant by having its seeds dispersed. When different organisms like this benefit from their relationship it is called is called a mutualism and tropical forests are loaded with mutualistic relationships.
The role of fish as seed dispersers in the Amazon can be quite significant. Some species migrate hundreds of miles during the flood season and as much as 20 miles a day. A few species of catfish even undertake annual migrations from the nutrient rich estuaries at the mouth of the Amazon on the Atlantic coast, to the upper reaches of the river almost 2,000 miles away, where they breed.
The next stop on the Podcast Tour is the giant river turtle exhibit ahead on your left just before the stairs. On your way there, take a look at the mural on the wall to your right, which depicts life on an Amazonian river and in the surrounding forest.
This stop on the Amazonia Podcast Tour is in front of the last exhibit on the lower level, just before the stairs. Here you will see a variety of smaller Amazonian fishes and the giant river turtles, which are the subject of this Podcast episode.
Giant river turtles are the largest species of turtle in the Amazon, with some individuals reaching 200 pounds or more in weight. They are primarily herbivorous, preferring to eat the soft parts of aquatic plants. Like many of the Amazon's other aquatic animals, these turtles venture into the flooded forest during the wet season where they eat flowers, fruits, and seeds.
Giant freshwater turtles breed during the dry season when low water levels expose sandy beaches and sandbars along river courses. They congregate on these sandy spots in large numbers, attracted by the limited number of suitable nesting sites. Mating occurs in the water and about six weeks later females dig holes in suitable sandy locations, each depositing as many as 140 eggs, which hatch about 50 days later.
Early European explorers in the Amazon were amazed by the abundance of turtles along riverbanks and often commented on the importance of turtle eggs and turtle meat in the diet of the local people. The turtles' habit of congregating in large numbers during the breeding season made them easy targets for turtle hunters who, in earlier years, took relatively small and sustainable numbers of the eggs and adults. In recent years, however, many of Amazonia's freshwater turtles have been over-hunted, almost to the point of extinction. Over-exploitation has not only resulted in a decline in numbers but also in a decline in the average size and reproductive rate of the turtles as the larger individuals are hunted out of the population.
The decline in Amazonian freshwater turtles mirrors a similar trend in other tropical countries, especially in southeast Asia, where many species of freshwater turtles are threatened or endangered because of over-exploitation for food and the pet trade.
The next stop on the Amazonia Podcast Tour will be in front of the large kapok tree at the top of the stairs.
This Amazonia Podcast Tour stop is at the top of the stairs in front of the large kapok tree. This stop puts us at the beginning of the forest walk, which winds along the edge of the river that we were just viewing from below.
Stand here for a moment and look around to get a sense of the architecture of a tropical forest: you can imagine a roof—the dense canopy of leaves overhead; and a floor, which is covered with leaf litter and a latticework of exposed roots. There are even interior “rooms”—forest openings filled with tree trunks, ropy lianas, aerial roots, and under story plants.
You will quickly begin to notice some of the other characteristics of wet tropical forests. Even at midday it's rather dim; mostly there's dappled light and occasional flashes of sunlight blinking through the canopy foliage. The air is still and humid, and even standing quietly can make you sweat. There are few animals to be seen, but you hear calls of insects, frogs, birds, and monkeys someplace, but you're not sure exactly where. The under story itself is remarkably open and easy to walk through—it's not the impenetrable “jungle” you might have been expecting.
As you start to focus on details, you can see that many of the trees have buttresses, prop roots, and other supporting structures. Their purpose is to keep the trees upright. Tropical soils are so thin, and competition for nutrients among plants is so great, that most produce roots that penetrate just into the thin nutrient layer, which may be no more than 18 inches or so deep. Buttresses, prop roots, and stilts provide ground- level support in these thin soils. The tallest trees, like the buttressed kapok tree you see here, also gain support from intertwining their branches with those of their neighbors, and from the vast web of lianas (or vines) and aerial roots that snake from tree to tree.
The buttressed tree you see here is a fiberglass casting taken from a kapok tree on Barro Colorado Island in Panama. This island is one of the principle field sites of the Smithsonian Tropical Research Institute, a Smithsonian bureau that studies the biology of tropical forests around the world. The tropical forest of Barro Colorado Island has been under continuous study by Smithsonian scientists for over 75 years and is the best-studied tropical ecosystem in the world.
The area around the kapok tree is a good place to spot the exhibit's titi and Goeldi's monkeys.
The next stop in our Amazonia Podcast Tour is the river overlook just ahead on your right.
This stop on the Amazonia Podcast Tour is the river overlook on the upper level. Proceed from the kapok tree at the top of the stairs to one of the three pull-offs on the right where you can overlook the river. This stop, which looks down on the fish and turtle exhibits you just passed on the lower level, depicts a typical scene along a small river in the Amazon.
As they wind their way through the forest, streams and rivers create openings in what is otherwise a closed canopy. In most tropical forests, only about two percent of the light striking the canopy actually penetrates to the forest floor, making it surprisingly dark and open at ground level. In contrast, river openings are filled with light. Plants along the banks compete fiercely for the sunlight creating an almost impenetrable mass of vegetation. This green wall is an excellent example of what ecologists call “an edge,” a place where two different kinds of habitat meet. Edges are generally biologically very productive, and the abundance of sunlight and water along the rivers edge results in high concentrations of flowers, fruits, and seeds that attract much wildlife.
River clearings also serve as highways for wildlife. Not just for the fish, turtles, otters, and other aquatic animals that live and travel in the water, but also for the insects, birds, and bats that use the openings above the water's surface to move unimpeded through the forest.
Forest openings can also be created anywhere in the forest when one of the large canopy trees falls. Almost instantly the dark forest floor is bathed in sunlight and the environment in the clearing is altered. Plants that had been struggling in the gloom, scramble toward the light in what may be a once in a lifetime opportunity to reach the canopy.
The first plants to take advantage of these opening are low- to medium-growing gap specialists—like the heliconias ahead on the left—that can complete several life-cycles very quickly in the few short months between the time the clearing opens and closes up again. Others, like the seedlings and saplings of forests giants, are in it for the long haul and slowly but surely grow toward the canopy, and will eventually shade out the fast starters below.
The next stop in this Amazonia Podcast Tour is the bromeliad forest ahead on your left, just before the exit.
This stop on the Amazonia Podcast Tour is the bromeliad forest located on your left just before the exit. This stop overlooks bromeliads and other plants growing on the tree branches above the flooded forest exhibit, where we started the tour.
Tropical forest plants have a variety of ways of gaining access to life-giving sunlight. Those that live their entire lives in the understory tend to have very large or dark green leaves, which are efficient at capturing the meager amount of light that filters down to them. On the other hand, giant emergent trees grow tall and strive to thrust their leaves through the canopy and into the sunlight. But many plants have neither large leaves nor the capacity to grow to great heights, and must adopt different approaches to the problem of reaching the light.
The bromeliads you see here belong to a group of plants called epiphytes, a term meaning “air plants.” Epiphytes actually live on other plants and use them as a substrate upon which to grow and reproduce. In this way they gain access to light without having to invest in structures like woody trunks and branches. But while living on another plant helps epiphytes solve one problem—that of access to light—it creates another by placing them far away from the ground soil and the nutrients they need to grow and reproduce.
Epiphytes have evolved an ingenious solution to this problem: They use their leaves and roots to trap water and organic debris, like falling leaves, dust, and even the bodies of dead animals. In the warm, humid environment this detritus rapidly decomposes and provides the nutrients epiphytes need.
This system works so well that some epiphytes, like the bromeliads you see here, contain mini-ecosystems that support many different forms of life. In addition to trapping debris, the bromeliad's spirally arranged leaves can form a water-trapping reservoir, called a tank, in which worms, insects, crabs, snails, and even some vertebrates, like small frogs and lizards, live and reproduce. These animals consume trapped plant matter, and one another, and contribute waste and eventually their own dead bodies to the bromeliad environment. In this way nutrients in the bromeliad environment are recycled in a miniature replica of the vast tropical ecosystem in which they live.
This is the last stop on our Amazonia Podcast Tour. If you would like to learn more about the tropical forest and the work Zoo and Smithsonian scientists are doing in tropical forests around the world, please visit the Amazonia Science Gallery which begins immediately after you leave the forest exhibit.