Biology Reference
In-Depth Information
the region. Glycine max , as it is known to science, might have been more aptly named Gly-
cine“min” until a few years ago, when crop and soil scientists figured out that the addition of
lime to reduce soil acidity enabled the conversion of pasture and cattle ranching to soybean
cultivation. As a consequence, the nitrogen-fixing legume began to prosper in areas where it
could not grow before.
Brazilian farming practices changed almost overnight. Brazil has become the second-
largest exporter of soy, after the United States. Much of it is exported as soybean oil, the
most widely used cooking oil, or soybean meal, which has many uses but largely is fed to
cattle. Producing high yields requires extensive use of fungicides, which are applied every
few days. The corn grown in the next pasture was subjected to heavy doses of Roundup to
control weeds. Pesticide use was rampant. White-tailed hawks and some kestrels flew by, but
raptors and other birds were few. The agrotoxins may have already thinned their numbers.
Perhaps a rumored decline in the bird fauna here, however anecdotal, is an early warning sig-
nal as to what lies ahead for surviving Cerrado wildlife.
That night at dinner with Leandro Silveira, Anah, and their team of researchers, the con-
versation focused on big mammals, beginning with rhinos and elephants in Asia and Africa.
“Our biggest herbivore in Brazil is now the tapir,” Leandro noted, “small by megaherbivore
standards.” A tapir is about the size of a large pony, with a pig-shaped body. Leandro was
pointing out one of the great anomalies of nature. Even though there are more mammal spe-
cies in South America than anywhere else, large mammals are even rarer here than in other
parts of the world. In truth, most South American mammals can fit inside a shoe box. Of
course, there are important exceptions that are considerably bigger—the larger primates, pec-
caries, capybaras and other large rodents, deer, and larger predators—all of which are well
documented as having a major impact on their surroundings.
It was not always so. Paleontologists tell us that we are simply several million years too
late to witness the South American Serengeti. Back in the Pliocene epoch, about 5.3 to 2.6
million years before the present, a rich megafauna filled South American forests, savan-
nas, and pampas. Giant ground sloths rose up on their hind legs like giraffes to browse tree
branches. Swamp mammals the size of hippos and rhinos crashed through the canebrakes.
Across the grasslands galloped camel-like creatures. Around the waterholes lurked long-
fanged marsupials that shared a common ancestor with opossums but bore a remarkable re-
semblance to saber-toothed cats.
The large mammals were basically done for before humans arrived, likely as a result of cli-
mate change. During most of the Age of Mammals—when the class Mammalia first evolved
about 60 million years ago, after the ebb of the dinosaurs—South America was a continental
island, and its unusual mammalian fauna evolved in isolation from the fauna of other contin-
ents. The first and probably greatest wave of extinctions occurred during the Great American
Interchange about 4 million years ago, when the Isthmus of Panama rose above sea level, and
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