Biomes: Tropical Rainforest (1989)

[Music] [Music] A biome is a community of living things. vegetation that develops in a certain climate region and the animal life that has become adapted to it. Of the major biomes on Earth, the community with the greatest number of species is the tropical rainforest. Rainforests once covered much of our planet. For millions of years, they provided an optimal environment in which life could grow. In that environment, an astonishing number of species evolved. Today, the rainforests are much reduced. They are confined to areas near the equator to parts of Malaysia, Central America, the Amazon basin of South America, the Congo Basin of Africa, and some tropical islands. But as small as they are, modern rainforests still contain more species of plants and animals than any other biome on Earth. What factors make this abundance of life forms possible? One factor is water. In almost daily thunderstorms, more than 150 in of rain falls every year. That's nearly 400 cm. Life here is adapted to the frequent rains. Leaves tend to be waxy and water repellent. Many leaves have pointed tips which shed excess water. Another factor that makes the rainforest possible is brilliant tropical sunshine. Solar energy provides the power for the rainforest's lush growth. Together, water and sunshine produce the rainforest's yearround growing season that makes the abundance of life forms possible. Thousands of species grow there. Most of their branches grow at the top where leaves compete for sunlight. This makes many trees so topheavy that they require buttress roots to support their weight in the shallow soil. Trees in a rainforest do not grow in stands or large concentrations of single species. Instead, the many species are mixed together. These trees create four distinct layers which are found in every rainforest. These layers help explain the great diversity of life in the rainforest. Each layer provides a great many small separate habitats for plants and animals. The topmost layer is called the emergent layer. Here the crowns of a few tall trees rise above the rest of the forest. These trees are favorite nesting sites for eagles. Each rainforest has its own species of eagle. This is Africa's crowned eagle. The emergent layer is also favored by orapendalus. Their woven nests hang from trees like seed pods. Although life is plentiful in the emergent layer, it is teeming in the layer called the canopy, where treetops form an umbrella over the forest floor. Vines overgrow the treetops, reaching for light. Bromeliads overgrow both trees and vines. Bromeliads are epipites or airplants. Epipites are not parasites. They do not take nourishment from trees. They put out aerial roots which absorb water and dissolved minerals directly from humid air. The roots also collect leaf mold and debris from which they take their nutrients. Promeilads create tiny habitats for other living [Music] things. Small reptiles feed on [Music] them. Tree frogs lay eggs, hatch, mature, and die in tiny pools at the center of bromeilads. In the canopy where bromeilads live, millions of insects also live. Some species are found here and nowhere else on Earth. There are so many different insects in the canopy that as many as 950 species of beetle have been collected from just one tree. Not surprisingly, birds thrive on the insects of the canopy. Onethird of all the world's bird species are found in rainforests. Most live in the canopy. Some, like hummingbirds, drink nectar. Many birds eat fruit that grows on canopy trees. Fruit eating birds help the trees by dispersing their seeds around the [Applause] rainforest. An unusual number of mammals has adapted to life in the treetops. The howler monkey eats tree fruit and flowers. The tree porcupine uses its tail to grip a branch. Troops of mangabay monkeys in Africa range through the canopy in search of food, while a South American sloth may live for weeks in a single tree. [Music] As night falls, other animals hunt for food in the canopy. This Maray, a tree living cat, has caught a [Music] rodent. A second one tries to get it. [Music] [Applause] [Music] The two-toed anteater uses its sticky tongue to lap up ants. The kinkaju feeds mostly on fruits and seeds. Tree frogs thrive in the canopy's high humidity. [Music] [Music] Beneath the canopy is a third layer of the rainforest called the understory. Here the treetops above cast deep shadows which limit plant growth. Much of the vegetation consists of shorter trees. Many different species of insects live in the understory. The lowest layer of this biome is the forest floor. Plant life is sparse here because of the shade cast by trees. Forest floor animals often depend on fruits and seeds that fall from the trees. Rainforest fruits are often quite large, like this seed pod that an Agooti is feeding on. Vegetation is thinner here. The only lush growth on the forest floor is along river banks. Here, sunlight penetrates almost to the ground. Few mammals live on the forest floor. One of the largest is the South American taper. It takes to the water to escape from tropical [Applause] heat. The taper's natural enemy is the jaguar, the largest carnivore in South America. Jaguars prefer to eat other mammals, but when large prey is not available, they catch and eat fish. The most important inhabitants of the forest floor are called decomposers. Decomposers break down the thin layer of forest debris into nutrients. They include tiny molds and fungi and the insects who live among them. Some leaves are harvested by leaf cutter ants before they become debris. The ants cut pieces out of the leaves and then carry them back to their nest. The leaves are not food for the ants. But for fungi, the ants cultivate in their nest and then use for food. The fungi use the nutrients from the decomposing leaves for their growth. So the ants supply the fungi with food and the ants use the fungi for food. Each depends on the other. Termites build elaborate nests on the forest floor. They are also decomposers. As they digest the wood of fallen trees, termites break down the wood's chemical structure and return nutrients to the rainforest. Fungi that grow in close association with living tree roots work with the roots to capture and recycle nutrients released by decay. This is an efficient system that recycles almost all the nutrients released as the bodies of plants and animals break down after death. This recycling process, while it sustains the lush vegetation of the rainforest, leaves few nutrients to enrich the soil. Cleared of trees, the land supports crops for only a few years. But as long as it remains undisturbed, the rainforest provides an irreplaceable genetic bank whose long-term value is incalculable. [Music]