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Capybara leaving water with a bird on its back. (Photo by R. Butler)
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FLOATING MEADOWS
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.
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Amazonian Water Lilies, Brazil 1999. (Photo by R. Butler).
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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.
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Continued: Life by the River
This article was written by Rhett A. Butler [bibliographic citation for this page] and was last updated on the most recent date listed in the column on the right side.
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