Biology Reference
In-Depth Information
an eastern direction in search of food. Finally, no longer able to proceed on
land, he ordered that a boat be built . . . at the confl uence of the 'Rio de los
Omáguas,' now the Rio Napo, with the Rio Aguárico. By the end of 1541
he had embarked on it, together with 55 Spanish soldiers and two Fratres,
one of whom, Frey Gaspar de Carvajal, became the chronicler of the voyage.
Instead of fi nding either El Dorado or cinnamon, Orellana discovered the
mightiest river on earth, the 'Rio de las Amazonas,' fi rst given the name
'Rio de Orellana.' The boat followed the current of the river down into the
unknown until it came out at the mouth into the Atlantic on August 26,
1542.
Only a few sections of Father Carvajal's report are interesting from a
natural sciences' standpoint. One of the most worthwhile is the paragraph,
“On the same day . . . we saw the mouth of another big river, on the left side,
which entered that one in which we navigated, and of water as black as ink,
and therefore we gave it the name Rio Negro.” In these laconic words the
greatest tropical blackwater river was made known for the fi rst time in his-
tory to European civilization.” (Sioli 1984, 1-2)
A popular misconception about the Amazon Basin is that it has a uni-
form topography and climate that supports a continuous cover of rain for-
est. It is true that the relief is mostly less than 900 m, and rain forest is the
prominent vegetation, but over the expanse of the basin there is consider-
able variation. A moderate dry season extends from June to August when
“popcorn” clouds form over the forest but not the rivers (see fi g. 2.47 be-
low). Salt and brackish water is carried 650 km upstream by rapidly fl owing
tides. Its tumultuous meeting with the onrushing fresh water of the river
is called the pororoca, and it produces waves up to 6 m high. There are
lake and river communities, inundated fl oodplains called várzeas, and lands
beyond the fl oodplains called terra fi rme. Different microhabitats exist on
the trunks of the giant forest trees that extend from damp, dimly lit ground
cover to full sunlight 60-70 m above ground. Along the way there are vari-
ous species of bromeliads, which store water in overlapping, funnel-shaped
leaves in which live bacteria, algae, aquatic fungi, protozoans, small crus-
taceans, snails, spiders, and mosquito larvae, on which frogs live, that are
in turn eaten by a variety of small snakes—altogether 250 species may live
on the trunk of a single rain forest tree. There are topographic and edaphic
variations within the basin that support patches of grassland, savanna, and
dry forest on promontories and sandy soil, and the surrounding cerrado
and caatingas extend into the basin varying distances from the surrounding
margins (fi g. 2.45). These different habitats and their biota are important
