The rainforest canopy
By Rhett A. Butler
April 1, 2019
THE RAINFOREST CANOPY
An estimated 50-90 percent of life in the rainforest exists in the trees, above the shaded forest floor. Primary tropical rainforest is vertically divided into at least five layers: the overstory, the canopy, the understory, the shrub layer, and the forest floor. Each layer has its own unique plant and animal species interacting with the ecosystem around them. The overstory refers to the crowns of emergent trees which soar 20-100 feet above the rest of the canopy. The canopy is the dense ceiling of closely spaced trees and their branches, while the understory is the term for more widely spaced, smaller tree species and juvenile individuals that form a broken layer below the canopy. The shrub layer is characterized by shrubby species and juvenile trees that grow only 5-20 feet off the forest floor. The forest floor is the ground layer of the forest made up of the trunks of trees, fungus, and low-growing vegetation. These layers are not always distinct and can vary from forest to forest, but serve as a good model of the vegetative and mechanical structures of the forest.
The overstory is characterized by scattered emergent trees that tower above the rest of the canopy, the tops of some species exceeding 210 feet (65 m). Below the overstory trees, the canopy stretches for vast distances, seemingly unbroken when observed from an airplane. However, despite overlapping tree branches, canopy trees rarely interlock or even touch. Instead they are separated from one another by a few feet. Why the branches of these trees do not touch is still a mystery, but it is thought that it might serve as protection from infestations from tree-eating caterpillars and tree diseases like leaf blight. To survive, canopy dwellers must have the ability to negotiate these gaps by climbing, leaping, gliding, or flying.
The billions of leaves of the canopy, acting as miniature solar panels, provide the source of power for the forest by converting sunlight to energy through photosynthesis. Photosynthesis is the process by which plants convert atmospheric carbon dioxide and water into oxygen and simple sugars. Since the rate of photosynthesis of canopy trees is so high, these plants have a higher yield of fruits, seeds, flowers, and leaves which attract and support a wide diversity of animal life. Besides attracting a broad array of wildlife, the canopy plays an important role in regulating regional and global climate because it is the principal site of the interchange of heat, water vapor, and atmospheric gases. In addition to collecting solar energy and regulating the climate, the canopy shields the understory from harsh and intense sunlight, drying winds, and heavy rainfall, and retains the moisture of the forest below. Thus the forest interior is a far less volatile environment than the upper parts of the canopy ceiling. The interior region is protected from the extremes of the canopy: temperature fluctuations, damaging solar radiation, and strong winds. Light levels are diffuse and subdued, the humidity is higher and more constant, and there is very little direct sunlight in the lower canopy.
HOW RESEARCHERS STUDY THE CANOPY
Little was known about this rich layer until relatively recently when scientists discovered efficient ways to study the canopy. However, even with modern techniques of study, many species, systems, and relationships of the canopy are still mysterious and much is still left to be discovered.
Early attempts to study the canopy ranged from the ingenious to the bizarre. These included the felling of whole trees, shooting down branches with shotguns, hiring natives to climb trees, and firing ropes up into the trees for climbing. One scientist in Borneo even trained a monkey to climb into trees to bring down samples of epiphytes. The bits and pieces of collected canopy were examined and scientists tried to piece the canopy puzzle together. This process was extremely difficult—assembling a car without instructions, given just a toolbox, random sheet metal, and some nuts and bolts would probably be an easier endeavor.
In the 1970s scientists began to use mountaineering techniques and ropes to access the canopy and platforms for long-term surveillance. This method was far more successful than any previous, but the area of observation was limited to a small area. In addition, the rope climbing was often dangerous, expensive, and had limited potential for eco-tourism.
Today, elaborate methods of canopy exploration have been devised, of which some are clearly more practical and successful than others. In 1990 a balloon-raft was placed on top of the canopy in locations in West Africa and French Guiana. The scientists could access the canopy from above and observe as they sat on the raft. However, this method was expensive and possibly damaging to the forest. Another technique, utilizing a construction crane, is employed by the Smithsonian Tropical Research Institute in Panama (also see the Global Canopy Programme). Canopy walkways are gaining popularity in several rainforests both as a research tool and as a way to attract tourists. Other ways to explore the canopy include using ultra-lite planes, dirigible balloons, ski-lift-style trams, and remote-controlled pulley systems. Often these projects pay for themselves in the number of tourists that come to experience the walkway, but there is always a danger of over-use.
In the 2010s, falling costs of technology, spurred innovation in canopy research, including the use of drones, camera traps, and audio recorders to monitor wildlife interactions in previously difficult-to-access parts of the canopy.
Even with modern techniques of study, much of the biological machinery of the canopy, especially pollination and the relationships between different organisms, still remains unknown. Hence future forest study will most likely continue to be concentrated in the canopy.
THE RAINFOREST OVERSTORY
The overstory consists of giant emergent trees that tower above the surrounding canopy. These trees are huge, at least by tropical standards, some exceeding a height of 213 feet (65 meters) with horizontal limbs that stretch over 100 feet (30 m). These trees live in a different climate from the trees of the canopy. The air is much drier and moderately strong winds blow through their branches. These overstory species have adapted to take advantage of the wind for seed dispersal and typically the seeds of these species are light and equipped with some sort of mechanism to allow the winds to carry the seeds great distances away from the parent tree. The Kapok (Ceiba), or Silk-cotton tree, of South America releases its seeds attached to cotton-like material, which drifts in the wind currents for miles before reaching earth. Before fruiting, the tree sheds all its leaves so breezes pass unimpeded through its branches. In Asia, the seeds of emergent tree species Dipterocarps are equipped with "wings" that cause the spinning seed to slow as it falls and enable it to be carried long distances by the breeze.
These emergent tree species are often covered with epiphytes (non-parasitic plants which take no nutrients from the host plant but use it for support). Over 2,000 epiphytes may be found on a single tree, making up one-third of the tree's total weight and 40 percent of the leaf biomass in some forests. Lianas, too, cling in mass numbers to emergent trees with over 1,500 regularly found on a single tree, making up about 20 percent of the total leaf biomass of the forest.
The most successful and most plentiful predators of vertebrates in the canopy are the birds of prey. Each continental forest region has its own species of giant eagle characterized by short wings, a long tail, and razor-sharp talons. These birds are most abundant in the overstory where they build nests near the top of giant emergent trees and raise single hatchlings. Because these eagles generally nest in the tallest trees, which are often the most valuable timber trees, they are especially threatened by selective logging, which not only destroys their habitat and nesting grounds, but also frightens away their prey. These giant eagles fly through the canopy with great speed and agility as they hunt their prey of primates, parrots, and other large mammals. When their prey is spotted, the eagle dives beneath the canopy and attacks its prey from underneath. The harpy eagle of South and Central America is the largest of these eagles attaining a height of 3 feet (1 m) and a wingspan of 6 feet (1.8 m). Because of its size, one of the harpy eagle's favorite foods is the sloth. From Southeast Asia, although now limited to four islands in the Philippines, comes the highly threatened monkey-eating eagle (100-300 left), while the crowned eagle hails from West Africa.
RAINFOREST CANOPY TREES
The canopy is the richest region of the diverse rainforest, and ranges in thickness from 10-40 feet (3-12 m). Countless species usually thought of as ground dwellers have adapted to life in the canopy—including worms, crabs, frogs, kangaroos, anteaters, and porcupines—where they feed on the abundance of fruits, seeds, and leaves or the numerous animals that are attracted these foods. The plant life of the canopy is nearly as rich due to the variety of epiphytes and lianas.
As a result of the crowded growing conditions, canopy trees only branch near the top of their long, pole-like trunks (which also make them good for timber). Since there is no shortage of sunlight for the uppermost leaves of canopy trees, the exposed leaves are generally small and waxy to retain water. The leaves of the lower canopy branches, shaded from the harsh sun by the upper canopy ceiling, are often a darker blue-green color than the leaves of the upper canopy in order to absorb the red wavelengths necessary for photosynthesis. This red-wavelength light is generally missed by the upper leaves, which have chlorophyll pigment for capturing shorter wavelength light. Due to the lower light levels and differing types of light in the mid-canopy, the plants of this region and below have a greater variety of colors than the uniform sea of green as observed from above. New leaves in the canopy are generally not produced continuously, but instead, like fruits and seeds, often are produced in flushes of new growth. This feature helps protect young, vulnerable leaves by swamping leaf-predators. Sometimes new leaves are red or white in color warning leaf-eaters of the presence of distasteful compounds.
Unlike the overstory trees, the trees of the canopy cannot depend on wind for spreading their seeds, so they rely primarily on animals for dispersal and pollination. Insects are one of the largest groups responsible for flower pollination because many plant and insect species co-evolved together and today play intimate roles in the life cycles of each other. In fact it is estimated that 30 unique species of insect may be dependent on each species of tree. In turn, a tree species may be dependent on a number of species to complete its life cycle: a bat for pollination, and a bird to disperse and process its seeds. If the critical bat or bird is removed from the system, the tree may no longer propagate and the species may die out in the area.
Because there are no true seasons in lowland equatorial rainforest, there is often no predictable flowering or fruiting season where all the trees of the forest may bloom, bear fruit, or shed all leaves. Instead, to outside observers the flowering cycles of lowland canopy trees may seem random and without obvious pattern. Although there must be some trigger for flowering, the mechanisms for most species are still largely unknown. For a few species the mystery been solved. The stimulus that triggers flowering can range from fire to species that flower after an especially rainy year. During a "dipterocarp year" in Southeast Asia, the canopy erupts in color as numerous emergent Dipterocarp trees flower almost simultaneously. These "mast flowerings" at irregular intervals (once or twice per decade) may be a strategy to swamp seed predators with so many of the large, energy-rich seeds (individual trees may have 120,000 fruits) that many seeds escape predation. Additionally the random nature of flowering means no seed predator has the opportunity to specialize on dipterocarp seeds. The principal pollinators of diperocarps—small insects known as thrips—have a short life cycle well adapted to the random flowering cycle of these trees. During the intervals between mast flowering events sparse thrip populations are sustained by feeding on understory flowers. When a mass flowering is triggered (studies show a strong correlation between flowering and droughts/El Nino events) the thirp population increases exponentially to take advantage of the massive number of flowers (about four million flowers per tree).
Since as many as 70-90 percent of canopy tree species depend on animals for pollination and seed dispersal, numerous species are equipped with special mechanisms to ensure the proper species will take and deposit pollen in the proper plant species and disperse seeds in a suitable place. Plants pollinated by certain animals often have certain characteristics. For example, flowers pollinated by birds have brightly colored, cup-shaped flowers, while flowers pollinated by bats are often white nocturnal blooms with copious amounts of nectar. Flowers pollinated by flies often have a rotting or mildew-like smell just as "bee-flowers" have a sweet odor. Butterfly flowers have a mild odor and are red or orange, since butterflies are one of few insects with good color vision. These flowers are most common in light-gap and forest-edge plants species, so butterflies tend to be most abundant in these areas.
Due to the great diversity of flowering plant species in the rainforest, no one species dominates. Therefore it is sometimes difficult for a particular species, say bee species, to sustain itself feeding on the nectar of one species of tree. It may feed on the nectar of several species of tree within the same family. However, by doing this, there is a great risk of hybridization and much wasted pollen. Coevolution—the process where a trait in species A has evolved to a trait in species B, which had previously been affected by a trait in species A—has reduced this problem. The flower of one plant species (call it species A) has structures to deposit pollen on one particular part of the bee, maybe its left back leg. When the bee visits another species (call it species B), the pollen from species A will remain on the bee"s left back leg without being deposited in flower B. In the meantime, species B may plant its pollen on the upper part of the bee"s right wing. As the bee flies away from flower B, it will have pollen from both flower B and the previous flower it visited. When the bee lands in another flower A, the flower picks up the pollen off the beecs left hind leg because it is equipped with an apparatus to do so, and the flower is pollinated.
Bees are one of the major insect groups responsible for pollination of rainforest trees. Plant species are often highly specialized to be pollinated by one unique species of bee. For example, the castanharanas tree, a relative of the Brazil nut tree, have flowers with spring-hood covers which must lifted to get nectar. In the process, the bees are brushed with pollen, so when they visit the next castanharanas flower, the bee pollinates it. Many bees use "buzzing" to get the flower to release pollen. The flower only releases pollen when the bee beats its wings at the right frequency; thus only certain bee species can harvest the pollen of specific plant species. Bees recognize color, odor, and shape, and flowers pollinated by bees are often yellow, white, or blue with a showy shape.
The insects of the order Lepidoptera, better known as butterflies and moths (pictures), contribute to the continuance of canopy trees, among many other plant species. The Lepidoptera order is the second largest order after Coleoptera (the beetles) with over 150,000 member species encompassing about 80 families. Most people think of butterflies (17,500 species over 14 families) as primary pollinators, but moths (130,000 species over 65 families), too, have an important role in pollination. For example, the piranha tree is pollinated by moths, just after the peak of the Amazonian flood season, when the tree loses all of its leaves and new ones appear immediately. The new crop of young leaves is soon completely covered with moth caterpillars. Once a tree is stripped, caterpillars form cocoons which are suspended from the tree branches. The tree produces a second crop of leaves, untouched by the caterpillars, now in the pupal stage of development. The adult moths emerge from the cocoons and pollinate the flowers. Moths, being nocturnal, are attracted to dull white to yellow flowers that open and release odor after sunset.
Flies are important pollinators of forest flowers and are attracted by the rot-like odor produced by some flowers. Small flies (drosophilids) are common pollinators of tiny orchid blooms that have an odor like decaying matter.
Beetles are pollinators with a good sense of smell and are attracted to odors of fermentation, spice, and fruit. Much is still unknown about the significance of beetle pollination in the forest, although with the incredible diversity of beetles—over 400,000 described species making up about 25 percent of all described species on Earth—they probably play an important role. One example is a beetle species that pollinates a species of canopy tree, annona. Annona flowers produce an odor after sundown that attracts beetles and flies which must push through the flower petals. Once the flower is penetrated, pollen is released on the insects. The petals drop off at dawn and the pollen-covered insects fly away to another flower the next evening.
Birds are important pollinators, and the hummingbirds of the New World and their Old World counterparts, the sunbirds, are attracted to flowers with large, cup-like flowers with bright colors and large amounts of sweet nectar. Hummingbirds are able to avoid the problem that afflicts most nectar-feeding birds: finding a suitable perch, by having the ability to beat their wings fast enough to hang in the air. Birds are showered, marked, or even stabbed with pollen when they arrive to feed.
Although most people do not think of mammals as pollinators, they play a crucial role in both pollination and seed dispersal of rainforest trees. Bats are the most important pollinators among mammals in the rainforest. Bats, active at night, are attracted primarily to nocturnal blooms with a strong, musty odor and generous amounts of nectar. Fruit bats of the New World and flying foxes of the Old World are responsible for the pollination and seed dispersal of many canopy trees. Other mammals known to pollinate plants are Australian/Papuan marsupials, rodents, and primates.
There are well over 15,000 epiphytes in the neotropical realm alone, and over 30,000 worldwide as well as numerous uncataloged species. The term epiphyte describes a plant which, like a parasite, grows on a host, but unlike a parasite, takes no nutrients from the tree itself and relies on nutrients from the air, falling rain, and the compost that lies on tree branches. Their epiphytic way of life gives these plants advantages in the rainforest, allowing them access to more direct sunlight, a greater number of canopy animal pollinators, and the possibility of dispersing their seeds via wind. Epiphytes may be familiar to people in temperate climates because many house plants and "air-plants" are actually epiphytes from the rainforest.
Epiphytes are found throughout rainforests, but exist in the greatest abundance in the so-called cloud forests which exist at the fog-laden elevation of 3,300-6,600 feet (1,000-2,000 m). Epiphytes belong to 83 families, of which the majority are ferns and flowering plants. Some of the better-known epiphytes include ferns, lichens, mosses, cacti, bromeliads (over 2,000 species), and orchids.
Orchids are the most diverse group of flowering plants with over 18,000 species, representing about 8 percent of all flowering plants found worldwide. It is estimated that there are another 10,000 to 12,000 species that have yet to be described. Many of these species are endemic to microhabitats like a single Andean valley or a canyon of a tepui in the Guyana Shield and are very rare. Every year, it is likely that hundreds of orchid species go extinct as valley systems, especially those along the Andes, are destroyed. Nonetheless, there is a huge variety of orchids ranging from species that grow on the ground to the 70 percent of orchids which grow as epiphytes.
Orchids are very well-adapted to life in the canopy. They have roots with a large surface area for rapid absorption of nutrients and water. Their secondary stems can hold stores of water so the plant can withstand periods of drying.
One major reason orchids are so successful in the forest is because they produce tiny seeds (measured in microns) that number in the hundreds of thousands. The balloon-like seed coat coupled with the small seed size enables orchid seeds to be dispersed over great areas by wind currents.
Orchids also utilize insects to spread their pollen. Several species from Madagascar release a strong odor to attract sphinx moths, which drink the nectar of the white flower and then carry away pollen with which they fertilize, inadvertently, other orchid plants. One species, the hawkmoth—which superficially resembles a hummingbird—has a tongue that exceeds 14 inches (35 cm.) so only it can penetrate the long trailing spurs of the flower of one orchid species, Angraecum sesquipedale. Numerous orchid species have tiny, almost microscopic, blooms which release a mildew-like odor that attracts small flies for fertilization. Another orchid, the bucket orchid of Central America, is equipped with a small bucket structure behind the flower. The flower produces an oil which drips into the "bucket" and attracts bees with its unique odor. Each bucket orchid species has its own scent, thus each attracts its own species of bee. When the male bee smells the perfume, it goes to the orchid to collect an oily substance which he will use to attract females (he is only attracted to one orchid species scent since he wants to attract only females of the same species). However, often as he is collecting his oil, the bee falls into the bucket. The only way out is through a tube. The bee moves through the tube, getting "tagged" with orchid pollen, so when he visits the next flower he will pollinate it as he passes through its tunnel. Another interesting orchid reproduction strategy is that of the dancing lady orchid of South America. These produce many tiny flowers that are positioned so they "dance" even with the slightest breeze. These flowers are lively enough so that small aggressive bees—thinking they are intruders—attack them and in the process are dusted with pollen.
The cacti of the rainforest are quite different from the cacti of more temperate and desert zones of the world. The cacti found in deserts grow in the soil or sand to get moisture and are outfitted with round, waxy leaves to reduce water loss. These cacti are often protected by sharp spines. However, the majority of cacti from tropical regions grow in the canopy as epiphytes, lack sharp quills, and have elongated leaves for light absorption, not water retention.
Epiphytes add a new dimension to the forest, creating new niches to be exploited by a wide range of species. One of the best examples of a tiny ecosystem based in an epiphyte is the tank bromeliad of South America whose stiff, upturned leaves can hold more than two gallons (8 L) of water. These reservoirs of water not only provide a drinking supply for many canopy animals but also create an entire habitat which species use for shelter and breeding. A multitude of insect larvae exist in these pools and are fed upon by other animals. The water catchments of the tank bromeliad serve as a nursery for poison-arrow frog tadpoles. The female frog lays its eggs on a leaf or in burrows on the forest floor. When the tadpoles hatch, she allows them to climb upon her back and she makes her way up to a bromeliad where she deposits the tadpoles into one of the plant's pools that is free of potential predators. The tadpole feeds on the developing insect larvae of the catchment. Some species of frog employ another strategy; they actually return to the bromeliad every few days to deposit an infertile egg into the water. The tadpole can then feed on the egg yolk. Bromeliads, especially those with interconnecting chambers, are often colonized by stinging ants, which provide the plant with nutrients produced by ant waste and their collection of decaying debris.
Epiphytes are superbly adapted to the often harsh conditions of the canopy: the serious lack of water and the shortage of minerals and nutrients. Many species, like the orchids, have developed structures to conserve water. Some have thick stems that store water; others have leaf hairs that effectively close the plant stomata when it is dry; and the tank bromeliads hold water in their stiff, upturned leaves. To counter the lack of nutrients, plant species have either developed symbiotic relationships with animals or have mechanisms, like a basket shape, for catching fallen debris which decomposes and provides sustenance. A surprisingly high amount of nutrients is provided by falling rain. For example, at a site near Manaus, Brazil, rain brought three kilograms of phosphorus, two kilograms of iron, and ten kilograms of nitrogen per hectare annually. As already mentioned, both tank bromeliads and other epiphytes rely on symbiotic relationships: tank bromeliads use the excrement produced by inhabitants of its water catchments, while other bromeliads, including nest epiphytes and mymecophytes, rely on waste created by resident ant colonies.
Epiphytes produce far more seeds than their grounded counterparts because so many of their seeds fail to reach suitable places to grow. Many epiphytes have wind-dispersed, microscopic seeds equipped with wings, gliding apparatuses, or parachutes. Even epiphytes that offer fleshy fruits may have several thousand seeds in a single berry. Mistletoe, actually an arboreal parasite, is a typical example of an aerial epiphyte-like plant with seeds that are spread in such a way as to ensure continuance of the species. Its berries have a laxative coating so they pass rapidly through the digestive system of the birds that consume them. In addition, the seeds have a sticky coat so when they pass out of the bird, they stick to the tail feathers. Hence, when the bird rubs the seeds on canopy branches, complete with natural fertilizer, the seeds end up in just the right place for growth.
Epiphytes grow most readily in cracks, grooves, crannies, and pockets where organic debris has collected and provides sustenance for initial growth. Surprisingly there is an abundance of canopy compost created by the decay of fallen leaves, wood, and animal waste. The layer of mulch provides moisture and trace minerals for epiphyte growth.
VINES AND LIANAS IN THE RAINFOREST
Creepers, vines, and lianas (woody vines) are abundant in the canopy and make up a significant proportion of the vegetation in tropical rainforests. There are over 2,500 species of vines from about 90 families [liana distribution]. They range from small, indiscrete vines that grow against the tree to giant lianas thick as trees that seemingly hang in the middle of the forest independent of trees. Some of the larger woody lianas may exceed 3,000 feet in length. Rattan, a liana, is well known for its use in furniture and ropes. Rattan also produces large, edible fruits—a favorite of primates.
Lianas are vines that begin life on the ground as small self-supporting shrubs and rely on other plants to reach the light-rich environment of the upper canopy. Because lianas use the architecture of other plants for support, they devote relatively little to structural support and instead allocate more resources to leaf production and stem/root elongation for rapid growth. Since lianas are rooted throughout their lives (unlike other structural parasites like epiphytes and hemiepiphytes), they take nothing from the tree except support.
In a 2002 paper, Schnitzer and Bongers review some of the mechanisms lianas use to ascend to the heights of the canopy. "Lianas have a variety of adaptations for attaching themselves to their host and climb towards the forest canopy," say the scientists. "These adaptations include stem twining, clasping tendrils arising from stem, leaf and branch modifications, thorns and spikes that attach the liana to its host, downward-pointing adhesive hairs, and adhesive, adventitious roots . . . The relative proportion of lianas with different climbing mechanisms might be directly influenced by the successional stage or disturbance regime of the forest."
Upon reaching the canopy, vines and lianas spread from tree to tree, and in some forests their leaves may make up 40 percent of canopy leaves.
Hemiepiphytes rely on a different strategy. These plants start life in the canopy as epiphytes and grow down to the ground. Hemiepiphytes grow extremely slowly due to dry conditions in the canopy but once the roots reach the ground and tap into the nutrients of the leaf litter, growth rates accelerate. One of the best known hemiepiphytes is the Strangler Fig.
Creepers are among the many rainforest species that change their leaf structure as they grow. The plants, especially those of the Araceae family, start as shrubs on the forest floor and gravitate toward dark objects, usually tree trunks. When they reach the tree, the climbers grow vertically up the tree held fast by the triangular flattened leaves. The leaves are positioned to catch reflected light. Once the vine reaches the bright upper regions of the canopy, the leaves are modified to grow away from the tree in order to intercept more direct sunlight.
Lianas are a huge problem for rainforest trees, and numerous species have developed means of discouraging their growth. Many palm and tree ferns regularly drop fronds, while other trees may lose limbs to rid themselves of lianas. Francis Putz, who studied Panamanian lianas, suggested it may be advantageous for trees to sway out of phase from their neighbors because this would tend to snap vine connections and kink lianas, cutting off transport systems. Some lianas have adapted to this mechanism by coiling and bending so they are spring-like and better able to absorb the shock.
Lianas play an important role in forest dynamics "including suppressing tree regeneration, increasing tree mortality, providing a valuable food source for animals, and physically linking trees together, thereby providing canopy-to-canopy access for arboreal animals." Schnitzer and Bongers (2002). Furthermore, lianas contribute to overall plant diversity in tropical forests (especially in and around light gaps and forest edges where lianas are notably abundant due to the increased availability of light). With their high photosynthetic production and sizable biomass, lianas also make a significant contribution to carbon sequestration.
In 2005, researchers made some surprising discoveries about lianas. Using data from 69 tropical forests worldwide, Stefan Schnitzer of the University of Wisconsin—Milwaukee found that liana abundance is correlated negatively with precipitation and positively with seasonality, a pattern precisely the opposite of most other plant types. Schnitzer believes that the deep root and efficient vascular systems of lianas enable them to suffer less water stress during seasonal droughts while many competitors are dormant, giving lianas a competitive advantage during the dry season. The assistant professor of biology at UWM tested his hypothesis in central Panama and found that "lianas grew approximately seven times more in height than did trees during the dry season but only twice as much during the wet season." While this dry-season advantage may allow lianas to increase in abundance in seasonal forests, says Schnitzer, in wet rainforests with year-round rainfall, lianas gain no such advantage because competing plants are rarely limited by water. In a second study, Schnitzer teamed with Mirjam Kuzee and Frans Bongers of Wageningen University in the Netherlands to find that lianas play a substantial role in limiting the growth of saplings in disturbed and secondary tropical forests through below-ground (root) competition and above-ground (light) competition and mechanical stress.
OTHER PLANT AND ANIMAL RELATIONSHIPS
Canopy trees have coexisted with insects for millions of years and many have developed unique relationships beyond pollination. Myrmecophytes or ant-plants are common in the rainforest. For example in South America, the cecropia tree is colonized by azteca ants. The tree is segmented like bamboo, providing compartments for ant colonization. A queen establishes a nest in one of the hollow chambers, while other cells are inhabited by workers until the entire tree becomes a colony. The workers defend the plant from all invaders—including insects and epiphytes—although they do not attack the three-toed sloths which feed exclusively on the leaves of cecropia. The plant entices worker ants to stay and protect it by offering oil and sugars provided through leaf hairs and special structures at the base of the leaf stem.
Another example of ants and plants working together was documented in a 2005 paper by Stanford University researchers. The team found that Cedrela odorata, a species of cedar tree, is aggressively protected by ants (Myrmelachista schumanni) that clear all vegetation from the area surrounding the plant. So effective is the vegetation control around these trees that locals believe evil forest spirits are responsible for the clearings, called "Devil's gardens." The researchers determined that ants, not supernatural beings, kill surrounding plants by injecting a toxin called formic acid into the leaves. A single ant colony with as many as 3 million workers and 15,000 queens may tend a typical garden, which can be older than 800 years, according to calculations by the researchers.
Other plant species have similar relations with ants including some orchid species, bromeliads, Acacia, and Rubiaceae among others.
Many tree species have mechanisms and strategies to prevent burdensome epiphytes, which can add so much weight (especially when full of water after a rainstorm) that they topple the tree. The gumbo limbo tree [Bursera simaruba] of South America and the krystonia tree of Southeast Asia are among several species of tree that have peeling bark that prevents epiphytes and creepers from getting a hold or finding a suitable place to start growth. Other species produce toxins in their bark to ward off infestation by pests and to discourage the growth of epiphytes and lianas.
RAINFOREST CANOPY ANIMALS
The incredible diversity of food sources and unique niches of the canopy trees support a wide variety of animal species. Animals often congregate around a flowering tree, which makes trees in this stage some of the best sites for viewing wildlife. In places like these, where food is abundant, animals set up territories, but since canopy leaf cover affects visual territorial displays, most animals rely on sound signals. Thus some of the loudest animals of the world are canopy dwellers. Many primates emit howls and screams, while birds use song to let other animals know that they are intruding on their space.
Common paths, often leading to fruiting trees, where many animals may pass in the course of the day are well-worn and often free of epiphytes; these form highways in the trees. Similarly, areas in the canopy free of vegetation form flight corridors used by numerous species, especially the birds of prey which often attack their prey from below. These flight paths are embedded in the memory of bats and birds.
Despite the huge abundance of canopy leaves, few mammals are properly equipped to eat them. Cellulose, the material of which cell walls are made, is difficult to digest, so leaf-eating animals must have large stomachs to hold their meal while it is being broken down. A large stomach is often accompanied by a large body which can be detrimental to canopy dwellers who depend on branches to support their weight. Similarly, very few birds specialize in leaf-eating because the extensive digestive system adds weight that hinders flight. Interestingly, more Old World mammal species, especially primates, rely heavily on leaves for the bulk of their diet, but few New World primates have the physiological adaptations to digest fibrous cellulose. Forest canopy mammals outfitted to feed on leaves include sloths, howler monkeys, orangutans, and chimpanzees.NEW WORLD
Sloths (pictures) are unique mammals highly adapted to life in the canopy. They belong to the Endentata (= "without teeth") order, although they do possess cheek teeth, and are endemic to Central and South America. There are six to seven species represented by two distinct groups: the three-toed sloth and the two-toed sloth. Three-toed sloths feed almost exclusively on cecropia leaves, while two-toed sloths live high in the canopy feeding on a wide variety of leaves and fruits. Three-toed sloths range from Honduras to Argentina and are known locally by natives as "Ai" for their shrill call. Two-toed sloths or "unau" inhabit forest areas from Nicaragua to Bolivia and northern Brazil. Both species are predominantly nocturnal. To facilitate water runoff, the hair of both species grows from the stomach to the back since sloths spend most of their time hanging from branches upside down. The slow movement and moist climate of the hair stimulates the growth of green algae in the fur of the sloth, giving it a greenish color which helps it camouflage from predators like the harpy eagle. Sloths are well evolved as a leaf-eating mammal with stomachs divided into many digestive compartments that contain cellulose-digesting bacteria. A low metabolic rate combined with minimum movement and 15 hours of daily sleep help the sloth conserve energy. Leaf-eaters in general must consume large quantities of their food to satisfy their nutritional requirements. Leaves may last up to one month in the sloth's intestines and feces and urine are passed about once a week when the sloth descends to the ground at habitual places.
The sloth's fur is an entire ecosystem of its own: one study found more than 950 beetles on a single sloth, living off the algae growing in its fur. The fur is also home to a certain species of moth which is dependent on the sloth's descent for its life cycle. When the sloth reaches the ground, the moth quickly lays its eggs in the sloth's dung and returns to the sloth's fur. After the eggs hatch and the caterpillars become moths, the moths, in some way or another, claim another sloth.
The routine descent of the sloth raises an interesting question—if sloths are so clumsy and slow on the ground why do they put themselves at risk to terrestrial predators when they could easily defecate from the trees? The answer lies in the intricacy of the rainforest ecosystem. By defecating at the base of their host cecropia tree, the sloth provides the tree with precious fertilizer, a rare but vital commodity in most rainforests.
Howler monkeys (pictures) are another New World canopy animal that relies heavily on leaves. Howler monkeys have earned the distinction of the loudest animal, according to the Guinness Book of World Records, with their raucous howls that can be heard clearly at distances over 10 miles away. This record is quite believable when a troop of noisy howler monkeys approaches. The male howler monkey, closely related to the spider monkey, is equipped with a special voice box which enables it to vocally defend its small territory without physical confrontation. Howler monkeys live in troops of 5-20 animals (average), in which females and juveniles make up the greatest percentage. These stocky, black primates, weighing up to 20 pounds (9 kg), are also known to eat leaves, although this species usually turns to canopy leaves only when fruits are in short supply.OLD WORLD
In the Old World, a few canopy primates turn to leaves. The orangutan, Asia's largest rainforest primate, and the third largest primate in the world, is one of these. The orangutan was once found throughout Asia, but is now limited to northern Borneo (the Borneo orangutan species) and Sumatra (the Sumatra orangutan species). Male specimens of the Sumatran form may reach 5 feet (1.6 m) and 400 pounds (180 kg) with an arm span exceeding 6.5 feet (2 m). The Borneo form is much smaller. Orangutans occupy the mid-strata of the forest canopy where they feed on leaves, fruits, and young shoots, and occasionally may take a bird egg or two. Orangutans are not social animals, but solitary creatures that do not form lasting pairs. Fascinatingly, the unsociable behavior of orangutans is not instinctive but learned. Mothers enforce a regime of strict separation by dragging youngsters away from each other and leaving them alone in the forest. Solitary behavior is of the utmost importance for survival in the rainforest where food trees are widely scattered. A pair or a group of slow-moving orangutans would find little more food than an individual, but have to divide it among more mouths. Orangutans share 98 percent of our genetic makeup and, like humans, participate in prolonged care for their young. Like humans each individual has a distinctive face. From birth, the orangutan undergoes variations in facial structure during the course of its lifetime: at birth its face is bare, juveniles are bearded, and adult males have skin pouches on their cheeks. Orangutans build sleeping nests, 16-80 feet (5-25 m) off the ground, each night and never return to an earlier nest.
Orangutans are highly threatened by the illegal trade in endangered species and widespread deforestation in Indonesia and Malaysia. Scientists estimate that of the remaining 45,000-60,000 orangutans in the wild, more than 1,000 are poached every year as pets or sources of bushmeat.
Chimpanzees (pictures | news), genetically, the closest living relation to man, are also leaf eaters, although they also feed on shoots, seeds, bark, fruits, and (less frequently) insects, fish, reptiles, and small mammals. Chimpanzees are highly threatened in their native West and Central Africa by destruction of habitat and hunting as a source of bush meat. Chimpanzees, up to 5.5 feet (1.7 m) when erect, are strong animals that dwell both arboreally and terrestrially.
CANOPY LOCOMOTION IN THE RAINFOREST
Because significant gaps exist between the branches of the canopy, animals of this zone must be able to negotiate these discontinuities by some means. The majority of canopy species climb, leap, or fly from tree to tree, and are equipped with appropriate mechanisms which enable them to do so successfully. Some species have undergone major adaptations which allow them to glide. The dominant form of canopy locomotion differs in each continental rainforest, a product of forest structure and evolutionary history.
In the Americas, where woody lianas abound, the prehensile tail, acting like a fifth limb, predominates among canopy dwellers. By definition, a prehensile tail is capable of supporting the animal's full weight. In addition to supporting body weight, the prehensile tail (the tip is often hairless) usually acts as a tactile organ.
Primates (pictures | news) are some of the best known mammals outfitted with a prehensile tail and several New World primates have this fifth limb, including howler and spider monkeys. Spider monkeys of Central and South America owe their name to their long, supple limbs which give them impressive agility in tree habitats much like the gibbons of Asia. Although closely related to howler monkeys, spider monkeys have a slender body and exceed 13 pounds (6 kg). This monkey feeds on fruit, shoots, flowers, and occasionally insects and bird eggs.
The largest New World monkey is the muriqui or charcoal monkey, which was once distributed throughout Brazil's Atlantic forests, but is now restricted to a few small patches, since less than 5 percent of its original forest remains. Before the Portuguese arrived in Brazil, the muriqui population probably numbered around 400,000, but a 1987 census found only 386 animals and a 1993 census found 559. Habitat reduction is speculated to be the leading cause the muriqui decline, although extensive hunting has also had a detrimental effect. The muriqui is characterized by light golden gray fur, a dark hairless face, and a prehensile tail. This species has interesting reproductive behavior with several males mating with a single female in the course of a day. The most fit sperm is responsible for fertilization. The muriqui is an exception among primates and other animals in that the females leave the troop when they reach maturity. Usually, in animal populations, the males disperse and add variation to the gene pool.
Several members of the Endentata order have prehensile tails including mammal species that are not usually considered tree dwellers. Two species of anteaters (Myrmecophagidae family) and at least one species of porcupine are tree dwellers, equipped with prehensile tails. Even a carnivore, the nocturnal kinkajou, possesses a prehensile tail.
In Asian rainforests, especially those of the island of Borneo, where taller trees are characteristic, gliding and brachiation are the predominant means of locomotion.
Among those species equipped with mechanisms allowing extended gliding are flying squirrels (several genera), flying lemurs (two species), geckos (two species - pictures), draco lizards (several species - pictures), frogs (several species - pictures), and the chrysopelea snake. Only one mammal species of Southeast Asia, the pangolin, has a prehensile tail; the pangolin is described later under Africa. (The marsupial cuscus of Sulawesi and New Guinea is also equipped with a prehensile tail.)
None of these gliding creatures can actually fly, but instead glide from tree to tree. In order to glide, the animal must climb to the upper regions of a tree and leap and glide at a downward angle to another tree. Many species have evolved a gliding membrane known as a patagium. The patagium consists of a loose flap of skin that is opened when the animal extends its limbs and sometimes its tail. When not in use, this skin hangs loosely on the sides of the animal and often makes for difficult walking and climbing.
The most well known, widely dispersed gliding animal is the flying squirrel. These squirrels are found almost worldwide in tropical, temperate, and even Arctic environments. Rainforest flying squirrels are found only in Southeast Asia, India, and Sri Lanka, where they are most active at night. Flying squirrels have been recorded gliding distances of over 650 feet (200 m). A lesser known glider is the flying lemur (though not actually a lemur) of Southeast Asia.
Surprisingly, at least four species of lizard have developed means for gliding. The two species of flying dragon are found in Sri Lanka, India, and Southeast Asia although the best known, Draco splendens, is from the Philippines, Malaysia, and Indonesia. Flying dragons live in trees all their lives except when they go down to the forest floor to nest, and they feed primarily on tree ants. This lizard can glide up to 325 feet (100 m), but usually not more than 65 to 100 feet (20-30 m) since forest trees tend to be closely spaced. Flying dragons are able to glide thanks to a patagium supported by its elongated ribs. Two species of flying gecko from Southeast Asia have a different style of patagium. Instead of having one large patagium supported by its ribs, the flying gecko has small skin flaps along its limbs, torso, tail, and head.
Even stranger than the gliding lizards is the Malayan flying frog which glides using the membranes between the toes of its limbs, and small membranes located at the heel, the base of the leg, and the forearm. Its color varies, although usually the frog's back is bright green with yellow belly and blue patches on the feet and shoulder. Its eggs are laid like many other canopy frogs, on vegetation overhanging water, so the tadpoles drop into the water when they hatch.
Perhaps the strangest gliding animal is the paradise tree snake from southern Thailand, Malaysia, Borneo, Philippines, and Sulawesi. It has the ability to parachute by stretching out its body sideways by opening its ribs so the belly is concave, and by making lateral slithering movements.
Brachiation is the form of arboreal locomotion characteristic of certain primates—especially the gibbon—where movement is accomplished by swinging by the arms from one branch to another. Such primates are anatomically adapted for this form of movement with their long arms and fingers and their mobile shoulder joints.
In Africa, where the forests are of intermediate height and limited liana growth, neither form of canopy locomotion predominates. The most notable species with a prehensile tail is the pangolin; all of Africa's mammals lack prehensile tails. The pangolin is an odd-looking creature—resembling an Old World cross between the New World armadillos and anteaters—having a body completely covered (except for the belly) with large, thick scales that render it inedible to predators when it curls up into a spiny ball. It has a long muzzle, small protected eyes, and strong arms and legs for digging and tearing. Its prehensile tail, like similar animals of the New World, has a finger-like sensor at the tip. There are about seven species of pangolin distributed in Africa, India, and Asia, of which six are found in rainforest regions. Within the rainforest some pangolins are canopy dwellers, while others prefer the ground. Ground dwelling species live in burrows, while arboreal pangolins live in tree hollows, have prehensile tails, and are good climbers. Regardless of what zone they prefer, all pangolins are excellent swimmers, are nocturnal, and feed on termites, ants, and larvae. Pangolins depend on their well-developed sense of smell to locate termites and ants. With their strong, sharp claws, pangolins tear open ant and termite nests and use their 10-inch long (25 cm.) tongues to capture insects. As they feed, pangolins pick up grit from the nest which is useful later in the stomach for grinding up the insects.
OTHER FORMS OF LOCOMOTION
One of the most common forms of moving through the canopy is simply scurrying along tree limbs using a tail for balance and leaping the small gaps between trees. Many monkeys, squirrels, and lemurs have bushy tails to assist in balancing. Other canopy dwellers, like lorises, sloths, and anteaters, simply use large claws to cling to canopy branches and move slowly in the trees.
BATS IN THE RAINFOREST
The most abundant mammals in the rainforest are not large ground-dwelling creatures, but bats. The tropics have the greatest variety of bats, and accordingly, the most diverse mammalian group of the tropical rainforest is bats, making up over 50 percent of mammal species. Bats range in size from the giant flying foxes, with wingspans of six feet (1.8 m), to the tiny bumblebee bat of Thailand, the world's smallest mammal, weighing less than an American penny. Equally diverse are the feeding habits of tropical bats, which include fruit, nectar, blood, and carnivorous feeders; and the places bats choose for shelter.
Although most bats of the world are insectivores, rainforests have a high percentage of fruit eaters. While insectivorous and other carnivorous bats rely on echolocation to find their prey, fruit-eating bats depend mostly on sight and a sophisticated sense of smell. True fruit-eating bats, the flying foxes of Madagascar, India, Sri Lanka, Southeast Asia, New Guinea, and Australia, did not reach the New World, so their niche was filled by spear-nosed fruit bats which evolved from insect-eating bats. Today, countless canopy plant species depend on bats for pollination or seed dispersal, making bats the best mammalian dispersal agents.
Flying foxes are the fruit bats of the Old World and are limited to the tropics by their need for fruit year round. Visitors to areas frequented by flying foxes are likely to notice trees with hundreds and even thousands of pod-like forms that shriek incessantly. These are likely a colony of flying foxes. The individual flying fox's place in the tree is determined by its stature in the colony which is established by fighting. The most powerful males occupy the highest, safest areas, while the weaker bats occupy lower, more exposed branches. There are places in the well-developed pecking order for sentries, which are posted to warn the colony when danger approaches.
Nectar-feeding bats are important pollinators of tropical rainforest plants. Like fruit-eating bats, nectar-feeding bats rely on sight to locate their primary source of food: flower nectar. Thus flowers targeted by these nocturnal bats are night-blooming and are easily seen in relative darkness with large, white petals. Nectar-feeding bats are equipped with a long, thin tongue, like that of a hummingbird, to reach nectar deep inside the flower.
Vampire bats of the New World are well-known and quite often feared for their feeding on the blood of animals, even humans. Despite the stories of Dracula and Transylvania, vampire bats feed mostly on farm animals in tropical regions. In fact, man has inadvertently increased vampire bat populations by introduction of livestock, mostly cattle, into formerly forested lands. Vampires, which are only active in the darkest hours of the night in order to avoid predators, feed by using their chisel-like incisor teeth to make a small incision in the animal's skin. The bat drinks, not sucks, the blood which freely flows from the wound thanks to an anticoagulant, which incidentally, has been chemically isolated to create a drug for treating heart attack victims. Strangely, vampires prefer to land at a distance from their victim and approach by foot. Animals fed upon by vampires are rarely injured or killed by the feeding. Despite their cruel reputation, vampire bats have been known to adopt and feed orphaned bats.
Besides the best known insectivorous bats—each individual may eat over 3,000 insects a night—several bat species feed on vertebrate animals. One of the most notable bat groups are the fishing bats which have echolocation so sophisticated that they can detect minnows swimming at the water surface. Other bats feed on frogs and are able to distinguish poisonous species from edible species by listening to their calls. These bats associate the bad experience of eating one of these toxic frogs with their call.
Bats are best known for roosting in caves during the day when they are inactive. Where caves exist in the tropics, many bats do roost there and in some areas blacken the sky as they leave the caves at dusk. However, the majority of tropical rainforest regions lack caves, so bat species must look elsewhere for cover. Many species choose the hollows of trees, while flying foxes sleep out in the open. However, some species have adapted interesting, if not bizarre, retreats. The tiny woolly bats of West Africa live in the large webs of colonial spiders, while some bats of Central and South America construct shelters by cutting banana leaves into tent-like structures.
Because so many plant species, including kapok, eucalyptus, durian, mango, clove, banana, guava, avocado, breadfruit, ebony, mahogany, and cashew trees, depend exclusively on bats for pollination and seed dispersal, bats play a monumental role in the health of the rainforest. For example, bats are the dominant pollinators of forests on remote Pacific islands. Since many plant species on such islands co-evolved features to facilitate specific bat pollination, once bats are eliminated there are no other pollinators to fill the niche. Bats also play a crucial role in controlling insects. In several locations, municipal bat roosts have been proposed to stymie malaria-carrying mosquitos.
Bats are particularly subject to extermination by the destruction of their habitat. The reasons include their high concentrations in relatively few areas (especially in their caves), their specialized roles in filling feeding niches, and their relatively small number of young (since extra young add extra weight—a liability to flying). An infant bat weighs one-third of the mother's weight when it is born, essentially the same as a woman giving birth to a 40-pound (18 kg) baby (Bat Conservation International). In addition, bats can be highly sensitive to disturbances. For example, when there is a food shortage, bats may shut down their metabolism until more plentiful times. When a hibernating bat is disturbed, its body temperature spikes upward in preparation for escape, costing as much as a month of stored fat reserve. Baby bats are particularly sensitive to temperature and when disturbed, they frequently move to a slightly cooler area and die of exposure. More than 60 percent of bats do not survive infancy.
Primates (pictures | news) are characteristic of every continental rainforest realm, except for the Australasian realm, and are made up of nearly 200 living species in more than 50 genera. Primates are thought to have originated from their insectivore-like ancestors between 100 million and 65 million years ago. The ancient primates most resembled lemurs and the tarsier of today, and upper primates did not appear until 37 to 23 million years ago. Upper primates include monkeys, apes, chimps, and humans, and the non-human species are generally divided into Old World monkeys and New World monkeys.
Old World and New World monkeys are thought to have diverged from a common ancestor about 55-60 million years ago. Since that time, the two groups have been evolving separately and today have notable differences. For example, Old World monkeys have nostrils that are close together and open downward, while New World monkeys have nostrils that are wide apart and open toward the sides. Old World monkeys sleep in a sitting position, while New World monkeys tend to sleep lying down. While Old World monkeys live in a variety of habitats, all New World monkeys are arboreal. As for body structure, many New World monkeys are equipped with a prehensile tail, a feature that Old World monkeys lack. However, Old World monkeys make up for the absence of a prehensile tail by having fully opposable first digits (thumbs and big toes), meaning that this digit is apart from the others, as in humans. Among New World monkeys, only a few species have partially opposable first digits, while the rest totally lack opposability. Since Old World monkeys lack prehensile tails, some species rely on brachiation for locomotion through the treetops. In addition, Old World monkeys generally tend to show more pronounced sexual differences than New World monkeys.
The African continent is known for its arboreal primates including chimps and Colobus monkeys. However, Africa has some lesser known primates like the insectivorous Pygmy Bushbaby with its large radio-dish-like ears used to pick up insect movement and huge eyes for nocturnal action. Its niche is filled by lorises in Asia and related (same sub-order) lemurs of Madagascar
Madagascar lacks the dominant form of primate distributed worldwide, those of the suborder Haplorhini (monkeys, chimps, gorillas, and Homo sapiens). Instead, their niche has been filled by a more primitive (read as older) group of primates, the lemurs. Lemurs belong to the sub-order Strepsirhini together with bushbabies, lorises, and pottos which, like the original lemurs, are nocturnal, insectivorous primates characterized by a small body, a long nose, and large eyes. Lemurs have an interesting evolutionary history and the only reason they still exist today is because of Madagascar's isolation (actually one species, believed to be introduced, is shared with the Comoros, a set of small islands off the northwestern coast of Madagascar).
Back in the days of the super continent Gondwanaland (formed of Africa, South America, Australia, Antarctica, India, and Madagascar), Madagascar was still part of the African mainland. About 160 million years ago, when Madagascar separated from the African continent, it had no primate life. The first lemur-like primates on the fossil record appeared roughly 60 million years ago, about which time the gap between Madagascar and Africa was still narrow. By rafting or walking during low ocean levels, lemur-like primates reached Madagascar. The island continued to drift eastward and by the time monkeys evolved 23-17 million years ago, the gap was too wide to be bridged and Madagascar missed the arrival of the more competitive, more intelligent primates that descended from the same ancestors as the lemurs. The mainland lemur lineage in Africa, Europe, and North America, which was not isolated from the evolutionary changes of the world, was quickly out-competed by the monkeys and driven to extinction. Only the enclave of lemurs on Madagascar survived, although some Strepsirhines (Bushbabies, lorises, and pottos) managed to pull though by retaining their nocturnal, solitary, and insectivorous traits. Since their arrival, the lemurs of Madagascar have been free to radiate into the large island's many niches without much competition or predation, and some have developed adaptations similar to those of monkeys, including forming social groups, being herbivorous, and being active by day. Today lemurs can be found in virtually all of Madagascar's ecosystems, from the tropical rainforest to the unique spiny desert to the deciduous woodlands. Upper primates did not reach Madagascar until about the time they learned to sail on the high seas. Two thousand years ago man invaded and began to threaten lemurs by destroying their environment. At one time, more than 48 lemur species existed, including giant gorilla-sized species, but today the number has been reduced to about 32 species.
The poster species for lemurs is not a rainforest dweller, but exists in the dry and deciduous parts of Southwestern Madagascar. The ring-tailed Lemur is recognizable by its black-and-white-banded tail much like that of a raccoon. Unlike other lemurs, the ring-tailed lemur spends a good portion of its time on the ground.
The aye-aye is one of the world's most bizarre creatures. This lemur, first classified as a rodent, is superbly adapted to its specific niche as evidenced by its long twig-like middle finger, huge eyes, rat-like teeth, and large bat-like ears. The nocturnal aye-aye uses its long middle finger as a tool for finding insects. After tapping the tree bark, it uses its sensitive hearing to detect the movement of insect larvae. Studies have found that the aye-aye is capable of sensing insect movement at a depth of 12 feet. Sadly this odd creature is endangered by both habitat destruction in northeastern Madagascar and widespread persecution by native Malagasy who consider it a harbinger of bad luck.
The largest living lemur is the Indri (Indri indri) of the montane forests of eastern Madagascar. In coloration, it resembles a giant panda with its black and white fur, but in body shape it is more anthropomorphic with its long neck and arms, and small ears. The Indri feeds on canopy fruits and leaves and is best known for its eerie yet beautiful song, which can carry for more than 1.2 miles (2 km). This diurnal lemur will bark when confronted with danger, and make kissing sounds when affectionate. Despite its large size, the Indri refuses to move along the ground, and will negotiate gaps by leaping, often more than 33 feet (10 m), between tree trunks. Naturally rare due to its low birth rate (one birth every three years) and small population density, today the Indri's numbers are small and dwindling due to habitat loss and hunting. A good portion of the world's remaining Indri population is in the Analamazaotra (Perinet) reserve and surrounding forest, due east of Madagascar's capital, Antananarivo. The Indri will not survive in captivity, a trait that is a major hurdle to possible rehabilitation projects and conservation.
One of the most recently discovered (by Western science) large mammal species is the golden bamboo lemur (Hapalemur aureus), which was found by an expedition searching for the greater bamboo lemur (H. simius), which was believed to be extinct. The last known (at the time) greater bamboo lemur specimen died in captivity in the mid 1970s, and in 1986 an expedition was organized to confirm that the species was extinct. The expedition found a previously undescribed bamboo-eating lemur with reddish gold fur, which was later named the golden bamboo lemur. Interestingly, Madagascar's forests support a third species of bamboo-eating lemur, the gentle bamboo lemur (H. griseus). These three species coexist by having specialized bamboo-feeding habits. The golden bamboo lemur, apparently tolerant of high concentrations of cyanide, eats the cyanide-containing leaf bases, shoots, and piths of new growth giant bamboo. The amount of cyanide consumed daily by this species is enough to kill three men. The greater bamboo lemur eats the mature pith of the same bamboo, while the gentle bamboo lemur eats the leaves of another bamboo species.
Today virtually all lemurs are threatened by habitat destruction. Unfortunately, natives are increasingly turning to lemurs as a source of meat. Many lemurs are particularly easy targets for hunting because evolution has rendered them ecologically naive (a term coined by Quammen in 1996) in that without natural predators over the majority of their existence, evolution has left them without fear of man. Similar behavior has been observed throughout the world in ecosystems (especially islands like the Galapagos) where predators have been historically non-existent.
Asia has more arboreal primate diversity than Africa, but still far less than the New World. One of the best known Asian primates are the Gibbons of Southeast Asia which represent about seven species characterized by long arms (armspan may reach 7 feet—2.1 m) and no tail. These arboreal apes are considered acrobats of the trees for their prowess and agility in the high canopy where their diet includes fruits and leaves, supplemented with eggs and small birds. Gibbons are strongly territorial, but defend only an area large enough to provide food for family sustenance. Gibbons live in family groups of three to six individuals; usually one male, one female, and young. Other Asiatic primates include macaques, langurs, leaf monkeys, and Proboscis monkeys.
South and Central America have the greatest arboreal primate diversity, probably because they evolved as forest dwellers and never descended to fill the terrestrial niches occupied by their Old World counterparts. South America is home to some of the world's smallest monkeys, the marmosets and tamarins, which average between the size of a rat and a squirrel. The largest species reaches 21 ounces (600 g), while the pygmy marmoset reaches its maximum at six inches (15 cm.) and three ounces (80 g). The pygmy marmoset, the smallest monkey in world, has a unique nocturnal feeding habit. It has chisel-like incisor teeth which allow it to gouge holes in bark to start the flow of tree fluids on which it feeds. Interestingly, both human rubber tappers and marmosets must be careful not to over-tap the trees, which would have the effect of killing the trees and destroying a source of sustenance. Other marmosets and tamarins feed on insects, eggs, fruits, and berries and are characterized by a long, bushy, non-prehensile tail. The exceedingly rare gold lion tamarin of the Poco das Anas Biological Reserve in Brazil is famous for its beautiful, long, golden fur and serves as a flagship species for the conservation of Brazil's endangered Atlantic forest. This small tamarin has recently been threatened by fires which burned nearly 1/3 of its reserve.
South America's wide primate diversity also includes: the world's only nocturnal monkey, the douroucouli; the intelligent capuchin monkeys, named for the resemblance of their crown hair to the capuche of French friars; the saki or sloth monkeys, known as flying monkeys for their ability to leap over 30 feet between trees; the variable uakari monkeys including the bald Uakari, a favorite of many tourists with its bald head and bright glowing red face; and many other species.
Carnivores (pictures | news) are found in the canopy where they thrive on the abundance of prey. For example, the coatimundi is a small carnivorous animal related to the raccoon, which feeds on worms, lizards, and grubs. The coatimundi, or coati for short, ranges from the southwest U.S. to South America and is divided into three species over its range. Male coati are solitary, but females and juveniles live in bands of 6-12. Unlike most other arboreal animals, they have reversible ankles which allow them to descend head first.
Cats are found worldwide in the tropics except for Australia and Madagascar. There are numerous small to medium-sized cats of the tropical rainforest including the well-known ocelot (neotropical), the clouded leopard (Asia), the golden cat (Africa), and the margay (neotropical). Old World rainforests have the genet, a cat-like creature of the Central African rainforest, which uses its long tail for balance in the canopy, and the palm civet, another agile climber.
Several marsupials make their home in the canopy including opossums of the new world and tree kangaroos of New Guinea. Tree kangaroos appear to fill the niche left vacant by the absence of monkeys in the Australian realm.
RAINFOREST CANOPY BIRDS
Of the more than 10,000 species of birds in the world, the majority are found in the tropics with 50 percent of all bird species found in the Amazon Basin and Indonesia.
One of the most recognizable bird groups in the world is the parrots (about 315 species) with their bright colors, distinctive loud calls, powerful beaks, and feet with two toes facing forward and two facing rearward. Parrots are most prominent in the rainforest, although they are found in countless other tropical habitats around the world. Parrots feed on seeds, fruits, grass, leaves, and plant shoots and use their strong beaks to crack hard shells, grind their food, and as a third limb for climbing. Parrots come in a range of sizes from the 39-inch (1 m), three-pound (1.4 kg) hyacinthine macaw of Brazil to the pygmy parrot which rarely reaches three and a half inches (9 cm) and weighs only about half an ounce (15 g). Besides size variation, some parrots have very unusual habits, like the Southeast Asian hanging parrots which sleep hanging upside down like bats. Many parrots live in flocks or in life-long partnerships with a single mate. When one member of the pair dies, the other mate either lives out its life in lonely solitude or joins another pair to make a triple. Many parrots show marked sexual dimorphism with males usually more strikingly colored than females. Due to their attractive coloration, many parrots are threatened by over-collecting for the pet trade in addition to threats from loss of habitat.
Each continental region has its own form of giant parrots: Central and South America have macaws, while Australia and Southeast Asia have cockatoos. Macaws are well known throughout the New World for their bright colors, their loud call, and their demeanor as pet birds. In addition, macaws are famous for gathering by the hundreds, even thousands, along the clay cliffs of the Amazon river where they feed on minerals which bind to the seed toxins, rendering the seeds on which they feed less toxic by preventing their absorption. The world's rarest bird is a macaw, Spix's macaw, which is a beautiful bird with a dark blue head, a blue body, and a greenish belly with a black mask and bright yellow eye. It has always been rare, limited to palm groves and river edges in small areas near the center of Brazil, but recent deforestation, importation of Africanized bees—which took their tree hollows—and over collection for hobbyists caused this species' demise. In 1987, four birds remained; now only a single male bird may remain as the species' lone wild representative on Earth. Cockatoos are also widely kept as pets for their attractive plumage and well-developed crests, but are routinely killed in their native lands as menaces to crops.
WORLDWIDE CANOPY BIRDS
Swifts are interesting birds found worldwide, though generally not considered rainforest birds since they may spend 2-3 years in flight, before landing to nest in caves, emergent canopy trees, or buildings. Swifts can only land in locations with altitude because their wing structure,built for extended flight,does not facilitate conventional take-off. Swifts are able stay aloft for such extended periods because of their two-lobed brain which allows for one half to "sleep" while the other performs bodily functions like flying and catching insects in flight. Swifts are well-known in Asia not for their stamina, but for their nests built of their saliva and blood, mixed with twigs. These nests are constructed in large numbers in caves in Southeast Asia and in tall forest trees in Africa. The nests are built upside down and the eggs are glued in with saliva. The nests are popular as a delicacy believed to bring good luck.
Owls are successful nocturnal birds of prey that are found worldwide. They are successful due to their superb adaptations to nocturnal hunting. Despite their immobile eye sockets, owls have incredible vision. Their cornea is highly convex so that their vision up, down, left and right is good, and they have the ability to turn their head up to 270 degrees. The face of an owl is disk-shaped in order to pick up more light and sound waves, much like a satellite dish. The owl's hearing is far superior to that of a human thanks to the placement of the ears: the right ear is located above the left ear and pointed at a different angle so the owl can perceive vertical sound movement in addition to the horizontal sound movement that humans can detect. In addition to sight and hearing, the owl has physiological adaptations to make it nearly silent when it flies. The chest and underwings are soft down feathers and the owl flies with a butterfly-stroke motion to ensure stealth.
Rainforests are home to many other birds of prey like hawks, eagles, and vultures. Vultures are seen virtually everywhere in the tropics because they feed on the remains of other creatures. Vultures may seem ubiquitous, but many birds of prey are threatened by habitat destruction and hunting as pests. One of the best examples is the Mauritius kestrel, the population of which—through habitat fragmentation, introduction of foreign species, and pollution caused by widespread use of pesticides— was down to four wild birds in 1974. However, thanks to the hard work of Carl Jones in Mauritius, by 1996 the number had climbed to about 400 total birds [See Solutions: Restoration of Habitats and Species].
NEW WORLD BIRDS
South America is sometimes called the "bird continent" for its diverse range of birds. This diversity can be partly attributed to the multitude of fruits which provide sustenance for the large number of fruit-eating birds including toucans, oropendulas, parrots, parakeets, tanagers, cotingas, and manakins.
One of the images conjured up when people think of the rainforest is a popular breakfast cereal image, the large, colorful bill of the toucan. About 40 species of toucans are distributed from Mexico to Paraguay and many are marked with bright contrasting colors including yellow, orange, red, blue, and white zones on the upper parts. Toucans are tree dwellers which usually nest at 65-100 feet (20-30 m) and feed on fleshy tropical fruits, and infrequently on insects and birds eggs. Their large bill is hollow, but still impedes flight which essentially consists of a leap from one tree, a few clumsy wing beats, a carefully planned landing, and a bit of luck.
Another beautiful New World bird is the quetzal from Central American forests, which was revered as a god by the Aztecs and Mayas. Quetzals pluck fruit in flight and bring it back to their perch for consumption. This small but voracious bird eats more than half its weight each day in insects, frogs, lizards, and snails. The quetzal is becoming rare with extensive deforestation in Central America.
Hummingbirds are an additional type of colorful bird found only in the New World, although they do have Old World counterparts, the sunbirds. They are the second largest bird family in the New World, with 320 species, and are some of the smallest birds in the world. The smallest species, the bee hummingbird, has a maximum size of two inches, half of which is tail and beak. Because hummingbirds use so much energy, with a heart rate from 450-1300 beats per minute, they must consume several times their body weight in nectar each day. In addition, hummingbirds conserve energy by falling into a comatose-like state at night. Their heart rate falls to 35-50 beats per minute at night and their body temperature approaches the surrounding temperature.
One of the strangest birds in the world is the hoatzin which jumps and climbs about in the canopy of South America. This chicken-sized bird has red eyes surrounded by bright blue skin and a crest of long thin feathers. The hoatzin is a clumsy flier that only flies when it must and then only for short distances. One of the most interesting aspects of hoatzin ecology is that young birds have a pair of claws on the bend of each wing. When confronted with danger, the young birds drop out of the tree into the water. They wait there until the danger has passed and climb back up to their nest with the help of their clawed wings. Adult birds have another means of defense; they can produce on offensive odor that drives enemies away. Hence its other common name, the stink bird.
Although most birds build their nests to conceal them from predators, two New World species, oropendulas and caciques, construct their nests in open areas so predators have to cross open ground, which few are willing to do. The long, hanging, basket-like nests are almost always constructed near a stinging bee, wasp, or ant nest which tends to deter potential predators, along with the parasitic botfly, the larvae of which lives under the skin of the chicks, feeds on its flesh, and can devastate an entire oropendula colony. Botfly larvae can also infest humans, and are an extremely nasty-looking parasite that is difficult to remove.
OLD WORLD BIRDS
The birds of the tropical rainforests of the Old World are nearly as diverse as those of the New World, and contain some stunning species. Among the most striking are the paradise birds of the Australasian realm and the hornbills of Africa, Southeast Asia, and New Guinea. The paradise birds from New Guinea and Australia are colorful birds with fantastic plumage; they were first considered divine creatures from heaven when early skins sent back to Europe had their feet removed and had such brilliant appearances. There are some 40 odd species of paradise birds, most of which are arboreal, live in mountain zones, and eat insects, small vertebrates, and fruit.
Another memorable group of birds are the hornbills, which are large (the helmeted hornbill may reach five feet (1.5 m). These noisy birds are represented by 45 species including the imposing rhinoceros hornbill of Sumatra, Borneo, and Western Java. This species has black plumage with a white tail and an enormous yellow beak with a casque--a horny sheath situated on the crown. The Rhinoceros hornbill has a remarkable nesting behavior in which the female holes up using mud in her tree hollow with her eggs, leaving only a tiny opening. She is entirely dependent on the male to bring her and her young fruits, snakes, lizards, and insects. If something happens to the male bird, she will die unless another, un-mated male comes to her rescue, which does sometimes occur. Like other hornbills, the rhinoceros hornbill is an important seed disperser in the tropical rainforest. Recent research on African hornbills by San Francisco State University suggests that the role of hornbills in forest regeneration is becoming even more important as deforestation spreads. Unlike primates and forest elephants, which will often not cross clearings, hornbills have a large range and will cross logged areas to disperse seeds in forest fragments.
One interesting groups of birds, the honey guides of Sub-Saharan Africa and Southeast Asia, are well-known for their habit of guiding humans and honey badgers to beehives. The bird calls when man or badger approaches, and flies off calling again until the man approaches again. It repeats this process until it is near a hive. Once the man opens the nest and takes the honey, the bird can then eat the wax, bees, and larvae.
REPTILES AND AMPHIBIANS OF THE RAINFOREST CANOPY
Frogs are overwhelmingly the most abundant amphibians (pictures | news) in the rainforest. Unlike temperate frogs that are mostly limited to habitats near water, tropical frogs are most abundant in the trees, and relatively few are found near bodies of water on the forest floor. The reason for this is quite simple: frogs must always keep their skin moist since almost half of their respiration in carried out through the skin. The high humidity of the rainforest and frequent rainstorms gives tropical frogs infinitely more freedom to move into the trees and escape the many predators of rainforest waters.
The differences between temperate and tropical frogs extend beyond their habitat. Whereas nearly all temperate frogs lay their eggs in water, the majority of rainforest species place eggs in vegetation or lay them in the ground. By leaving the water, frogs avoid egg-predators like fish, shrimp, aquatic insects, and insect larvae. Several species of frogs, including the American glass frogs, lay their eggs on vegetation that overhangs water. The humid climate keeps the eggs moist and when the tadpoles hatch they drop into the water below. Glass frogs are also interesting because they are transparent except for their visible organs and the faint yellow spots that some species possess. These yellow spots resemble a cluster of the frog's eggs, enough to fool predators. Other frog species develop fully into froglets within their eggs, and emerge as fully formed frogs, thus by-passing the tadpole stage altogether.
When many people think of the "jungle," they think of huge deadly snakes; but this is not the case in the canopy where very few species pose any threat to humans. The majority of canopy snakes are constrictors or mildly venomous species and are rarely encountered by humans. Even in the canopy, chances are you will not see many snakes, since numerous species camouflage themselves like leaves and vines.
The best known venomous canopy-dwelling snake is the eyelash viper of the New World which exists in several different color forms including yellow, green, olive, and orange. The eyelash viper is so named for the presence of small horned scales above the eye. Also found in the canopy are various constrictors of the Boa family which use their strong muscles to constrict their prey to death.
In addition to snakes, the forest canopy contains lizards. Iguanas are large greenish lizards of the New World, which have the unique ability to drop over 60 feet (18 m) from canopy trees unharmed. Their strong tail is used for balance during the fall and catching branches during the descent to break the impact of the fall. Iguanas often inhabit limbs that overhang rivers so they are able to escape predators by dropping into the river and waiting submerged for over 30 minutes. Iguanas may attain a length of six feet (1.8 m), though they are generally smaller. Iguanas have the ability to undergo a small color change to better blend into their surrounding environment. But the true color-change artists of the forest are the chameleons—of which every forested continent has its own. Chameleons are lizards that have the ability to rapidly change their colors to match their surroundings, although they tend to change more in accordance with their emotions. The Old World or true chameleons of Africa and Madagascar (pictures) have the best color-change ability and will often assume bright orange, purple, and blue coloring to reflect their mood. South America has the anole, a much less spectacular chameleon, while Asia has the agamas.
INVERTEBRATES IN THE RAINFOREST CANOPY
Insects (pictures | news) are the most successful rainforest animals as demonstrated by their tremendous diversity. Insects are so ubiquitous that they have filled many niches usually occupied by other animals. For example, some postulate that in South America the role of the forest elephant is filled by leaf-cutter ants. In the rainforest canopy, insects abound: a study of the rainforest canopy in Peru with 500 cubic meters of foliage (about the size of a two-car garage) found more than 50 species of ants, 1,000 beetle species, 1,700 arthropod species, and more than 100,000 individuals. A rainforest tree alone can have some 1,200 species of beetle, while a single hectare of rich forest canopy is projected to have 12,448 beetle species.
There are many insects and other invertebrates that would not usually be considered arboreal but exist in the rainforest canopy. For example, several species of crabs have been found hundreds of feet above the ground in tank bromeliads of neotropical forests. Similarly, earthworms and giant planarians (flatworms) are also part of the canopy system, with earthworms playing an important role in the processing of canopy soils and mulch that supports epiphytic growth. Even leeches are found in the canopy where they may surprise first-time visitors to the Asian forest canopy. Mosquitoes, too, are abundant in the canopy, though on the ground there are generally few puddles for breeding and no pronounced seasonal changes to stimulate massive mosquito-breeding frenzy. In the canopy, mosquitoes lay their eggs in the up-turned leaves of epiphytes like tank bromeliads. Therefore, you may be more likely to get mosquito bites in the canopy than on the forest floor.
Many insects like stick insects, katydids, leaf hoppers, and mantids have developed incredible behavior, body structure, and color to mimic their surroundings. These insects, which mimic dead and living leaves, half-eaten leaves, sticks, bark, bird droppings, and flower parts, avoid detection by predators and prey as they hunt and rest.
- Where does the rainforest derive its energy?
- Where do the majority of rainforest species live?
- Why is most rainforest life found in the canopy?
- How do rainforest canopy trees disperse their seeds?
- What are common pollinators in the rainforest?
- What are epiphytes?
- True or false—Orchids can be a type of epiphyte.
- What is a liana?
- How does ants and some tree species mutually benefit from their symbiotic relationship?
- What are three types of mimicry?
- Why is completely important?
- How do animals communicate in the canopy?
- Why do relatively few animals eat leaves as the staple of their diet?
- Where does the orangutan live and why is it endangered?
- What are some ways that animals move through the canopy?
- What is a prehensile tail?
- What is a flying fox and what does it eat?
- Why are important for an ecosystem?
- Are vampire bats real?
- What are lemurs and where are they found?
- Generally, how are New World monkeys different from Old World monkeys?
- How many bird species are there in the world?
- What do parrots eat?
- What continent has the most species of birds?
- What is the most abundant type of amphibian in the rainforest?
- What is the most diverse group of creatures in the rainforest?
- Where does the rainforest derive its energy?
- Where do the majority of rainforest species live?