The Flight of the Iguana by David Quammen Read Free Book Online Page B

mammal—and perhaps, as we’ll see, surprisingly well suited to another function too.
    I tell this whole story because several matters of science underlie it—the least interesting of which is that piranha, as advertised, can be dangerous little creatures with an eclectic palate for meat. I knew that before seeing it so vividly demonstrated, and youknow it too. More fascinating, and more significant, is the network of ecological relations connecting four separate elements of this vignette. That network of improbable connections has only lately been discovered by science. The four elements are: certain piranha species found in blackwater rivers like the Zabalo, subsistence fishermen like Lorenzo, certain tree species of the lowland jungle, and floodplain development projects like the one at Lago Agrio.
    The forest and the fishes turn out to be more intimately related, in parts of Amazonia, than biologists had realized.
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    For a long period each year the lowland forest throughout much of the Amazon basin is covered by floodwater, in some places up to forty feet deep. Depending upon the area, the water may remain there from two to ten months. This cycle of drastic but regular flooding is the result of geologic and meteorological conditions that are not duplicated on any other continent. The ecological consequences of that flood cycle, which has repeated itself annually over millions of years, seem also to be unique on the planet.
    To begin with, a large portion of the Amazon basin is extremely flat. From the Peruvian border to the Atlantic, the river drops only about 250 feet. (In the northern Rockies, for comparison, a whitewater river might drop as far within four miles.) There are exceptions to that overall Amazon flatness, of course—most notably the Andes. North of the main trunk of the river rises another formation, a modestly elevated area known as the Guianan Shield, and to the south is a similar uplift called the Brazilian Shield. Lying in among these three zones of high ground is the great Amazon floodplain. Rainfall is prodigious throughout the entire drainage, ranging between about sixty and one hundred and twenty inches per year. In consequence, the Amazon river system contains one fifth of the total amount of river water on Earth. So much water in a rush to the sea, somuch flatness, and the ineluctable result is flooding. Every year, during the wet season, roughly 30,000 square miles of the Brazilian Amazon are covered with standing water.
    This land is known to ecologists as the flooded forest, and to rural Brazilians as igapó. Brazilian fishermen, in particular, have good reason to be familiar with igapó.
    Over the epochs the plant species of the flooded forest have had to adapt themselves to this regularly recurrent inundation. They now live semiaquatic lives. Seedlings, saplings, and shrubs must—and do—survive being totally submerged for months of every year. Full-grown trees resist drowning despite having their roots and lower trunks covered; some species have developed special respiratory roots that top out above the flood level, like cypress knees in a Georgia swamp. But coping with floodwater itself is not the only problem those trees face. They must also cope with seed-eating fish.
    During every wet season fish in great number and variety invade the flooded forest, searching for food. They come chiefly from nutrient-poor blackwater rivers, like the Zabalo, and from other streams so impoverished of minerals and small aquatic organisms that no real food chain can be supported; they come, hungry and desperate, to feed on the seeds and fruit that fall from those igapó trees. Feasting voraciously, they build up fat reserves to help carry them through the rest of the year. In some fish species the seeds and fruit taken during flood time may account for almost their total annual sustenance. And of course these fish, like the trees, have