The Liquid Forest

FLOATING MEADOWS IN THE RAINFOREST

Floating plants have advantages over submerged plants in that they always have access to sunlight and can readily use the nutrients of whitewater rivers. Submerged plants have difficulty capturing enough sunlight in the muddy waters to carry out sufficient photosynthesis.

In some areas giant floating meadows form unique ecosystems colonized by small trees, shrubs, and vines. Such meadows may exceed a square mile in area and are home to a multitude of vertebrate and invertebrate species. One of the most famous floating-meadow dwellers is the world's largest rodent, the cabybara. The cabybara, resembling a 50-kg guinea pig, is most commonly seen grazing grasses on floating meadows and along rivers. Although it looks nothing like a swimmer, the cabybara is a strong swimmer using its webbed feet. Cabybaras live in herds of 10 to 15 individuals and are most active at night. Their numbers have been somewhat reduced due to intense hunting by locals for their good-tasting meat, but their reproductive rates are high and the species is now being used in sustainable development schemes.

Another mammal found in the quiet waters surrounding floating meadows is the manatee. The manatee, thought to be descended from elephants, is a source for the legendary mermaids of ancient times. Although more than 15 feet long and stocky, their form was often mistaken by sailors for that of a beautiful maiden, half fish, half human. The manatee is found both in marine systems and freshwater habitats from Florida to the Orinoco to the Amazon Basin. The manatee is a slow, peaceful creature that spends most of its time sleeping and consuming huge quantities of grasses and aquatic vegetation. During the flood season, when aquatic plants and grasses are easily accessible, the manatee gorges itself with over 110 pounds (50 kg) every day. When the water drops, and food is scarce, the manatee depends on its fat reserves with help from its slow metabolic rate. Interestingly, the manatee has a well-developed system of tooth replacement because its teeth are rapidly worn down by the large quantities of silica in the vegetation on which it feeds. Because of their size, adult manatees have no natural predators, but nonetheless they are highly endangered today by hunting, habitat loss, boat traffic, and other human activities.

Found throughout the Amazon and other tropical waters are giant water lilies, which in clusters form a sort of miniature floating meadow. The most magnificent water lily is Victoria amazonica, the Amazon water lily. Measuring up to four feet in diameter, it is capable of supporting the weight of a small child. The Amazon water lily has a remarkable pollination cycle. Giant white flowers, some the size of a plate, open at dusk with a speed readily seen. The flowers generate a strong butterscotch odor and trigger a stimulus that causes the temperature of the central blossom to rise 11¡ above that of the surroundings. The fragrance combined with the heat attracts scarab beetles, which gather at the flower's center. As night falls the flowers close, trapping the beetles. By dawn the flowers have turned pink and the beetles are gorging themselves on the inner parts of the flower. By the late afternoon the flowers, which have turned a deep reddish purple, open and the beetles, coated in pollen, fly off to find another lily flower. In doing so, they carry the pollen of the first flower and fertilize the second.

A common avian resident of the water-lily meadows are jacanas, which have the ability to run on the water surface or on floating vegetation using their extremely long toes, which distribute their weight sufficiently so they do not sink. Jacanas make nests in floating vegetation, and when the eggs or young are threatened, adult birds feign broken wings, pretending that they cannot fly in order to distract predators.

Both during high and low water the emerged and submerged parts of floating plants provide food and breeding habitats for many vertebrate and invertebrate species. The submerged root zone of one square meter of floating meadow will support over 50,000 invertebrate individuals. These include insects (especially larvae), mollusks worms, arachnids, and crustaceans.

Review questions:

• What is the capybara?

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Continued / Next: Life by the River