Since the end of the Miocene (about 25 Mya) the Amazon Basin follows a unique geo-morphological history. During this geological era lowland pre-Amazon Amazonia, basically forming one almost continental inland sea, saw its salty water turn into fresh water after having been brackish for millions of years. Then, the landscape turned into a predominantly black-water swamp with gradually more islands of never inundated dry-land (terra firme) which were drained by streams that discharged into large rivers such as the proto-Amazon and proto-Orinoco, which in turn flowed into the Pacific Ocean. A riparian forest type evolved adapting to annual black-water flooding which shows how ancient extant black-water flooded forest called igapó is that forms the floodplain along black-water streams and lakes. Throughout these geological times a number of typically marine animals adapted gradually to fresh water, among which molluscs (e.g., shells, oysters and mussels), shrimps, crabs, fish (e.g., stingrays, sharks), terrapins (turtles), caymans, manatees and dolphins.
The rise of the Andes, about 12-15 Mya, drastically changed the drainage of the proto-Amazon Basin reversing the course of the main rivers. The Amazon River began to flow into the Atlantic Ocean and the Orinoco River into the Caribbean Sea. A number of rivers draining the eastern flanks of the Andes carried and deposited on their way to the Atlantic Ocean enormous amounts of silt forthcoming the erosion of the young volcanic Andean mountain range. A second type of floodplain forest consequently originated adapting to annual flooding by muddy, silt-laden, café-au-lait coloured water rich in all kinds of nutrients, called várzea.
Three major types of water are found in the Amazon each with its own clarity and acidity (pH). Black-water and clear-water are the most ancient water types. Black-water rivers drain mostly forest and savannah areas on extremely poor sandy soils (i.e., Rio Negro and many rivers in the central Amazon Basin draining relatively small interfluves with sandy soils) having coca-cola coloured water stained with folic acids causing pH values as low as 3-4. Clear-water rivers drain predominantly pre-Cambrian rocky areas of the Brazilian Shield (i.e., Tapajós, Xingú and Aripuana Rivers) and Guayanan Shield (i.e., Marauiá, Padauarí, Demeni and Branco Rivers, and all rivers in the Guianas flowing south-northwards into the Caribbean Sea). Clear-water rivers have crystal-clear water most of the year and account for pH values of around 7. White-water rivers always drain regions with fertile soils of volcanic origin (Amazonas Solimões, Madeira, Purús, Juruá and Javarí Rivers) and carry fertile silt that makes the water light brown muddy and silty accounting for pH values of 7-8.
The entire lowland Amazon is drained by more than one thousand rivers. Most rivers inundate their floodplains on an annual base ("the annual tide"), the peak of the flooding coinciding with the end of the rainy season. The flooded forests fringing the rivers and lakes over tens to hundreds of kilometers fall dry during the dry season lasting on average 5-6 months. The riparian forest inundates over 6-8 months and the maximum flood reaches levels of 7-13 metres. The various types of floodplain forest along rivers and lakes can be associated with its water type. Both clear-water and black-water floodplain forests are called igapó . Although they share quite a few components they are basically different in plant composition. White-water floodplain forest is called várzea and its composition does not vary much along the course of a white-water river. Most floodplain plant species attune their fruiting season to the highest tide during the second half of the flood season. The majority of fruits and seeds from inundated forests are either dispersed by water through floating, or dispersed by fish or other animals. White-water floodplain (várzea) harbours partly or fully folivorous (leaf-eating) and insect-eating animals throughout the year, whereas the igapó offers living conditions to predominantly fruit- and seed-consuming animals (frugivores) only during the second half of the flood season. Plants of the igapó, in general, have their leaves protected by highly toxic secondary compounds, whereas the leaves of várzea trees and lianas often can be consumed by leaf-eaters such as hoatzins, iguanas, and howling monkeys. The extremely important phenomenon of seasonal lateral migration by all kinds of fruit- and/or seed-eating animals (frugivores) coming from the far high dry-land forests and spending about three months in the igapós of rivers and lakes is hitherto not mentioned in the specific literature. This phenomenon takes place everywhere in lowland Amazonia towards the second half of the flood season and lasts 2-3 months, there where extensive floodplain bodies can be reached from the nearby high dry-land (terra firme) hinterland. Fruit and seed production in the igapós is highly synchronized (typical igapó plants show a phenology adapted to seed dispersal by water and animals, including fish) and peaks at the time that fruit supply in terra firme forest drops dramatically, near the end of the rainy season. In the far hinterland this causes food scarcity or even famine to specialized frugivores, animals living mainly on a fruit and/or seed diet. The frugivore communities in terra firme areas up to 10 km away from extensive black-water and clear-water floodplains, which perform seasonal lateral migration, tend to show up to tenfold higher biomass and individual densities than those from the terra firme forests too far away for the local frugivores to know about the existence of igapós as better feeding grounds. Mortality caused by food shortage or famine every now and then could well explain for the overall up to tenfold lower densities in remote terra firme ecosystems.
In his account on the “Monkeys of the Amazon” (1854), Alfred Russel Wallace based his evolutionary ideas on observations made during his long stay in the Upper Amazon. In his river barrier hypothesis he considered the Amazon Basin a huge freshwater archipelago with the main rivers acting as barriers provoking as such speciation through isolation. On my travels through Amazonia to study biodiversity in the Amazon I noticed how right Wallace was and how well his river barrier hypothesis applies to the evolution and demography of species in the Amazon. It explains well for the extremely high biodiversity of the Amazon, by far the highest on the planet, in particular when we look at animals that do not fly. Island biogeography as defined for oceanic archipelagos can be perfectly applied to the interfluves of major Amazonian rivers including their floodplains. When flying for hours over the never ending sea of tree crowns most people tend to think that the Amazon rain forest is just “sea of broccoli”. The 50,000 (or rather 100,000) species of plant as well as the millions of animal species (including the insects) are not evenly spread over the entire Amazon. If so, it would not contain the highest biodiversity of life on earth. The extremely high biodiversity of the Amazon can be well explained by the tropical climate, the extremely poor soils it grows on, the unique geological history, the complex mosaic of vegetation types, and the insulation caused by hundreds of rivers of different water types that act as geographical barriers for animals and plants to cross over from one interfluvial island to the other.
When a baby dwarf marmoset, later baptized Callibella humilis, was delivered to my doorstep back in 1996, a series of discoveries of unique, hitherto unidentified fauna and flora was triggered. The indisputable existence of this creature somewhere out there in the vast Amazon Basin took away the scepsis from the scientist in me, convinced as I was before that finding new primate species at the end of the 20th century would be impossible. Describing new species of megafauna is widely considered a privilege reserved to the great naturalists of the 18th and 19th centuries. My odyssey in search of the land of the Callibella revealed an entire river basin never visited before by naturalists or scientists teeming with hitherto undescribed plant and animal species. A biological "terra incognita" that turned into a naturalist’s “el dorado”, Then followed first encounters with a number of new megafauna species in the canopy, on the forest floor and even in the water. I was confronted with the difficulties in laying one’s hand on biological material without having to kill the animal. Other obstacles lay on my path such as collecting and transporting holotype material and DNA samples of new plant and animal species and having genome DNA analysis run in foreign laboratories in order to publish them.
Publications on the web and in high profile scientific journals will attract national and international public awareness and draw attention to some of the most special and poorest known regions in the Amazon that include the highest biodiversity on earth, such as the Rio Aripuana Basin. Since publication in peer-reviewed scientific print journals is a slow and time-consuming process, we decided to first make them available on the internet. This way the AAPN intends to use the discoveries of large terrestrial and aquatic mammal species as a quick and effective tool to get significant parts of the Amazon preserved. Full treatments including interesting anecdotes soon will become available about the following animals: the giant peccary, the white-socked white-lipped peccary, the dwarf peccary, the dwarf tapir, the orange pair-bond coatimundi, the black agouti, the red agouti, the tree-dwelling giant armadillo, the white brocket deer, the white-throated black jaguar or “onca-cangucú”, the purple-grey river dolphin or “boto roxo”, the dwarf manatee, the giant paca, the black giant riverotter, and a number of primates such as the black woolly monkey, the orange woolly monkey, the silvery woolly monkey, the long-membered spider monkey, the eastern Rio Purús spider monkey, the bare-faced grey saki, the grey squirrel monkey, the Pauiní white uacari, another collared titi monkey, another tamarin belonging to the fuscicollis Group, and the Upper Xingú black bearded saki.
If we wish to preserve the biodiversity of the Amazon for the future, a significant and representative part of each specific ecosystem in each interfluve should be fully preserved including all species endemic to the area. This could be done by way of natural world heritage sites or national parks that could be effectively protected when surrounded by sustainably managed forest and water reserves. These fully protected reserves should be created and designed taking into account the annual phenomenon of seasonal lateral migration of the entire frugivore community to nearby floodplains (igapós). This migration of entire fruit-and seed-eating communities from the high dry-land (terra firme) to the nearest black-water and clear-water igapós along rivers and lakes is a phenomenon at present not even known to the scientific and conservation community. It should be urgently included in the design of protected areas in the Amazon. By use of Landsat pictures fully protected areas could be designed along the long axis of larger rivers including large black-water and clear-water floodplains together with at least 10 km of terra firme rain forest behind the floodplain. As such, all species endemic to the particular interfluve will be included and, most importantly, up to ten times higher numbers of these species will be protected.
All this, and much more will be described in detail in Dr. Marc van Roosmalen’s forthcoming book entitled “Barefoot through the Amazon: On the Track of Evolution”