The Flight of the Iguana (7 page)

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, so
much 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 in the passing of time adapted themselves especially to this way of life. A delicate and mutually satisfactory balance seems to have developed.

An ecologist named Michael Goulding, after two years of fieldwork along the Rio Madeira, a major Amazon tributary in western Brazil, has produced the first broad study
(The Fishes and the Forest: Explorations in Amazonian Natural History)
of this interrelationship in the flooded forest. The featured players in Goulding's
study are a group of fish known as the characins, a highly diversified and successful clan that numbers up to a thousand species in Amazon waters. Included among the seed-eating characins is a species called the
tambaqui,
one of the largest fish found in the Amazon and possibly the single most important source of protein for the region's human population. Also included, unexpectedly, are some of the piranhas.

Tambaqui are seed predators of huge appetite. They migrate into the flooded forest and gather in crowds beneath their favorite food-furnishing species, the rubber tree
Hevea spruceana.
Like most tree species in the Amazon,
H. spruceana
grows not in clusters or groves but as widely separated individuals, surrounded by other tree species yet with a large distance between each
spruceana.
Consequently, a whole gang of tambaqui may simultaneously address themselves to a single
spruceana
tree. They could conceivably eat every seed that it drops. To crush the hard nut walls of those seeds, tambaqui have evolved large jaws and strong, broad, molar-like teeth. They crunch up the
spruceana
seeds (which are about as tough as Brazil nuts) and swallow the nut shells as well as the seed tissue—though only the seed tissue gives them any nutrition. A single gorged tambaqui, weighing thirty pounds, might carry two pounds of ground-up seeds in its stomach. That's like you or I tucking away twelve pounds of peanuts, shells and all, in the course of an afternoon ball game.

The seed-eating piranhas are a bit more fastidious, and it seems to be precisely those pointed, razor-edge teeth that make such fastidiousness possible.

Even the most notorious flesh-eating piranhas—for instance, that large species commonly known as the black piranha—evidently move up into the flooded forest on a seasonal search for food. They aren't necessarily there for the seeds. In the
igapó
these flesh-eaters continue to function as secondary consumers, preying upon other fish, insects, occasionally a bird or a mammal
or any other animal that might inhabit the forest waters or be so unlucky as to fall in. Black piranha do seem to be omnivorous rather than strictly carnivorous, opportunistic enough to make seeds and fruit a small fraction of their diet when those foods are easily available. But the piranhas that specialize in seed-eating, though closely related, are distinct.

Michael Goulding has identified at least two species of piranha
—Serrasalmus serrulatus
and
Serrasalmus striolatus
—that live mainly on a diet of seeds. Each of these species retains jaw and tooth structures almost identical to those seen in its infamous, flesh-eating cousins.
Serrulatus
and
striolatus
merely put those structures to different use. According to Goulding: “Piranhas shell the nuts they eat and ingest only the soft seed contents. . . . After the nut wall is broken, the endosperm contents are removed and the shell is discarded. By doing this the piranha does not fill its stomach and intestines with material that cannot be digested but that will take up space. The sharp teeth of piranhas allow them to masticate the soft seed contents into small bits that are usually of nearly equal size.” By slicing through the nut wall and rejecting it, eating only the seed tissue itself (and ignoring also the fleshy fruits in which some
igapó
trees wrap their seeds), the piranha maximize their nutritional benefit from each belly-load of food. It is a delicacy of appetite that, during the lean times when no seeds are falling, when the fish must live off stored fat, could make the difference for survival.

•   •   •

Take away those floodplain trees, though, and survival becomes far more problematic.

Timbering, slash-and-burn agriculture, clearing away floodplain forests with the notion of pasturing cattle or planting rice or for other development projects intended to make the jungle “productive” or “habitable” by our civilized standards—all these represent attacks not only on the lowland tree communities but also on the fish species that feed among them. And by Michael
Goulding's estimate, those seed- and fruit-eating species account for something like seventy-five percent of all the fish sold at markets in Manaus and other cities of the basin. Since fish are the primary source of animal protein for the human population there—not just for canny fishermen like Lorenzo, not just for tribes like the Cofan, but throughout both backcountry and urban Amazonia—this whole chain of interdependence is crucial by any standard.

Remove the trees, and you can expect the fish to disappear. Kill off the fish, and likewise some of those tree species (the ones that depend on fish for dispersing their seeds) may not survive. Contrary to common misconception, the soils from which grow the Amazon jungle are very poor, and the rivers draining those soils are also therefore infertile. So the fish that spend half their lives in those rivers depend utterly on the manna that falls in the forest, and on the floods that carry them to it.

It's just another demonstration of what we already know. The great jungle ecosystems of Amazonia are not a
symptom
of the region's richness. They
are
that richness. Wreck them, and you wreck everything.

The Fragile Truce Between Man and Scorpion

Allow me to confess an invidious personal bias: I don't trust any animal with more than six legs and more than two eyes. No rational explanation for this, it's just a cringe reflex from the murkiest subconscious, but there you are. Six and two. I go queasy with terror and disgust whenever confronted with a beast who flouts those magic limits. Six and two. Octopuses are suspect but acceptable. Insects, however bizarre, are fine. Snakes are among my favorite living things—beautiful, sleek, unadorned, binocular. A dizzying wave of repulsion passes over me, on the other hand, at the mere glimpse of a color photograph of a tarantula. One, two, three, four, five, six, seven, gack, eight—and
then
the legs. Am I alone or does anyone else experience this neurosis? Have you ever looked a black widow spider in the face? Poison isn't the problem; a rattlesnake has poison, yet a rattlesnake is merely handsome and dangerous. Hideousness is the problem. I know it's subjective, I know it's unfair. But a creature with that many legs and eyes, Judas, you just never know what it might be getting ready to do. One on one, it already has you outnumbered. Spiders are bad enough. Consider, though, the scorpion.

My own heartfelt conviction is that scorpions are perhaps the most drastically, irredeemably repulsive group of animals on the
face of the Earth, even including toy poodles. Maybe that's part of what makes them so interesting.

Scorpions violate the six-and-two rule flagrantly: four pairs of walking legs, one pair of pincers, one pair of leg-like appendages modified to serve as jaws, another pair that are hidden beneath the abdomen like landing gear and perform some still-mysterious sensory function—which makes fourteen limbs altogether—plus anywhere from zero to twelve eyes, yipe, in most species eight, arranged in three widely spaced clusters like Cinerama cameras. The mere listing makes me sweat. And as if that weren't enough, they also carry a nasty hypodermic stinger hanging overhead on the end of a long tail. Scorpions are more cluttered with obnoxiously useful hardware than a Swiss Army knife.

They travel under cover of darkness. They prey on insects and spiders, as well as the occasional small lizard or mouse. They kill people too—surprisingly many in some countries—though only while defending themselves, or by mistake. A scorpion drops from the thatched roof of a house into a baby's crib, a young child runs barefoot through a garden, an adult carelessly picks up a piece of firewood, and whammo. In Mexico, at least until recently, more than a thousand humans died each year from scorpion stings. Most of those victims were kids. Another 69,000 Mexicans annually survive a sting that is at least bad enough to report. In Brazil the death rate for young children stung by scorpions is almost one in five, and a single Brazilian city recorded a hundred fatalities in a year. Algeria is another zone of high jeopardy, as are Egypt, Jordan, Turkey, and Trinidad. Scorpions can be found nearly everywhere in the warm latitudes, jungle and mountain terrain as well as desert, but among different species there is wide variation in the potency of the venom.

Some venoms merely cause local swelling and pain. Others attack the nervous system, resulting in high pulse rate, irregular breathing, feelings of fright or excitement, impaired vision, vomiting, and a range of other symptoms of which the final, if it
comes to that, is complete respiratory failure. Death by suffocation, out there under the clear equatorial sky.

J. L. Cloudsley-Thompson, a British zoologist who spent part of his career as a museum keeper in the Sudan, described the whole baleful sequence: “First, a feeling of tightness develops in the throat so that the victim tries to clear his throat of an imaginary phlegm. The tongue develops a feeling of thickness and speech becomes difficult. The victim next becomes restless and there may be slight, involuntary twitching of the muscles. Small children at this stage will not be still: Some attempt to climb up the wall or the sides of their cot. A series of sneezing spasms is accompanied by a continuous flow of fluid from nose and mouth which may form a copious froth. Occasionally the rate of heartbeat is considerably increased. Convulsions follow, the arms are flailed about and the extremities become quite blue before death occurs.” This progression of symptoms, he says, closely resembles poisoning with strychnine.

Cloudsley-Thompson might be talking about a sting from
Androtonus australis,
the fearsome North African species said to have venom as toxic as a cobra's—but he isn't. He's talking about an American scorpion called
Centruroides sculpturatus.
Most infamous of the forty species found in the southern United States, C.
sculpturatus
is familiarly known as the bark scorpion, from its habit of hiding beneath loose and fallen pieces of tree bark. During one twenty-year period it accounted for sixty-four deaths in just the state of Arizona.