THE HIDDEN AMAZON COMES TO LIGHT
The not-so-hidden-any-longer Amazon
by William W. Lamar
Species, species, and more species...
A cornucopia of unrivaled biological diversity, the Upper Amazon Basin boasts the highest number of plant and animal species in the world, with even more than the Lower Amazon Basin in Brazil. Area surveys of the Upper Amazon have demonstrated the world’s greatest variety of trees. A hectare of land (2.5 acres) can have 40 to 300 tree species compared with 4 to 25 in North American forests. The greatest numbers of monkey species are to be found in this region; 17 kinds have been recorded in one small area. The Amazon proper indisputably contains the highest number of fish species in the world, with over 2,000 known and another 2,000 species likely. It also is believed to hold 95% of the world’s 350,000 kinds of beetles and, in one tree alone in the Upper Amazon, over 1,500 species were taken! Peru has over 400 species of butterflies. GreenTracks’ long-term natural history inventories in this region have produced the greatest number of amphibian and reptile species for any single locality on earth. Bird life in the countries comprising the Upper Amazon Basin is staggeringly rich, representing over a fifth of all the species found throughout the world.
Why so many kinds of living things?
There are several theories, among them changing habitat, river barriers to dispersal, and topography.
Forest to grassland and back....
We know from the study of fossil pollen that the Amazon Basin has changed dramatically several times owing to fluctuating relative humidity during glacial and inter-glacial periods through the Pleistocene era. Much of the forested region we see today has, in fact, been grassland at different times, and this leads some to think the expanding and contracting forest fragments have effectively served as “islands” and thus have allowed for plants and animals to speciate extensively.
Rivers as prisons...
Nearly 150 years ago, the famed naturalist Alfred Russell Wallace noted that range boundaries for a number of animal species in the Amazonian rainforest seemed to coincide with the region's many rivers. That observation marked the origin of one of the leading hypotheses for why the Amazon harbors such extraordinary biodiversity for its size. In its modern form, this "riverine barrier hypothesis" posits that the Amazon's major rivers functioned as natural barriers to gene flow between populations. As a result, the populations ultimately diverged. This model has received a certain amount of support from molecular studies in recent years.
Hills and valleys...
Recent investigations along the Jurua River, one of the Amazon’s largest tributaries, point to a different explanation. The pattern of diversity in frog and small mammal communities along the Jurua does not fit with predictions based on riverbank affiliation. Rather the composition of these communities is best predicted by geographic distance and habitat type. What’s more, the distributions of small mammals terminate perpendicular to the river and parallel to the Andes Mountains, which suggests that the topography of the Amazonian lowlands may generate the biodiversity. Thus far only a single river has been studied, but it is believed that the results can be extended to all large meandering rivers in the region as a working hypothesis.
Going, going, gone...
So, much remains to be studied, and the Amazon Basin stands today as the single most complex, daunting, tantalizing, and stimulating place on the planet. And it is slipping away at an alarming rate. Scientists estimate that tropical forests cover only 6 percent of the planet, less than half of what they recently occupied. The Association for Tropical Biology and Conservation, founded to foster the exchange of ideas among scientists working in tropical environments, notes unprecedented changes, with 1.2 percent of the remaining area disappearing every year.
Until recently, the forests and rivers of the Upper Amazon Basin were accessible only to intrepid explorers willing to brave hardship, disease, hostilities, and, perhaps worst of all, their own fears of the great unknown. Thanks to advances in medicine and travel it is now possible to see this great tropical wilderness first-hand. Diseases are easily avoided through vaccines and air and boat travel make access simple. The region is still filled with mystery, but we know so much now that was regrettably unavailable to the early explorers. And knowledge has allowed us to see things once considered to be repugnant as beautiful and interesting. Simply tracing the steps of those who first entered the Amazonian region, seeing everything from piranhas to gigantic capybaras and manatees (largest mammal on the continent), and doing so in relative ease and comfort, is a remarkable privilege.
Recently, GreenTracks has designed new Natural History Programs in the Upper Amazon Basin, some of them featuring riverboat cruises and others featuring rainforest lodges, both of which provide excursions by small boat and hiking to observe the flora and fauna. Programs on local culture and archeology are also available. For those who share with us the desire to simply BE THERE, this is an excellent opportunity to fulfill that dream.