The South American continent separated from the ancient southern landmass of Gondwanaland about 100 mya (million years ago) and moved westward until hitting the Nazca plate about 65 mya.  At this point, the Andes were created through the volcanic activity associated with the subduction of the more western plate.  Several orders of animals evolved in situ on the island of South America, such as sloths and armadillos.  Other orders presumably migrated from the Old World while the Southern Atlantic Ocean was still not large enough to pose as a complete barrier (e.g., primates, marsupials, and some rodents such as capybaras).

As the Andes rose, erosion of the eastern portion of the mountains began to fill an inland sea -- a vast area that now forms the Amazon basin -- with sediment.  The major soils found in Yasuní  -- clay and sandstone -- were deposited in this region between 18 and 12 mya.  By 8 mya, with the continued rising of the Andes and filling of the sea, the Amazon river drainage formed which for the first time pushed Andean sediments to the Atlantic.

About 3.5 mya, when the Ithmus of Panama rose above sea level, South America was joined to the North American continent.  This event led to an exchange of orders of animals that had long been separated.  Primates, armadillos, sloths, possums, and some rodents migrated north while carnivores, squirrels, deer, peccaries and other types rodents moved south.  Many orders of animals endemic to South America went extinct over time.

The effect of humans on the prehistorical environment of Yasuní and the Amazon is unknown.  Given that most of the Amazon basin -- that further from major rivers -- did not lend itself to a sedentary lifestyle with intensive farming, it is difficult to assess past human population levels.  Currently, there is some evidence for maize horticulture between 6000 and 7000 years ago in eastern Ecuador.  Patricia Netherly, an archaeologist who surveyed the Pompeya Sur-Iro road corridor, found evidence of settlement near major rivers and hypothesizes that population density by rivers was large in comparison to further inland.  However, Netherly found it difficult to date material culture found.  Spanish historical records from the 1500s (Francisco de Orellana's "discovery" of the Amazon) indicate that many human populations lived along the length of the Napo and Amazon Rivers.   Consequently, there is a possibility that humans shaped some of the biotic patterns observed today, although direct evidence is not readily available.

Given the complexity of geological and biotic factors that have led to present day Yasuní National Park, it is not surprising that sections of land within the park vary considerably from each other -- to the point where the variation is visible on satellite images.  Sections of Yasuní are composed of knife ridges and ravines, such as those found at the Proyecto Primates field site, while others are low seasonal floodplains, swamps, or gently sloping hills and terraces.  The soils that make up these areas  vary in the proportion of clay or sand, in the percentage of pebbles, and in mineral content.  Furthermore, variation in hydrology -- localized rainfall, nearness to large, seasonally flooding rivers -- counteracts with landform to change soils available for the biotic system that they contribute to.

The climate of the Proyecto Primates field site -- and of eastern Ecuador in general -- is wet, warm, and mildly seasonal.  Data collected at the site and across the region show a mean annual temperature in the shade of ~26°C and a mean annual rainfall of ~3,200 mm.  No month receives less than 100 mm of rain, but there are two seasonally dry periods, one in August and the other in December-February, during which some canopy and emergent trees drop their leaves.  Temperature is stable throughout the year.  Seasonal variation in day length is small in Yasuní, and there are roughly 12 hours of daylight year-round.

Seasonal fluctuation in rainfall and temperature does affect the reproductive effort and species composition of the forest.  For example, the "drier" season  is exemplified by a change in availability of ripe fruit (less) and flowers (more).  This change in available food items brings a shift in, for example, the woolly monkey diet (Di Fiore) -- flowers become a larger portion of the diet, and insects and fruit compose less of the diet than in wet months.   After rain increases during November, the forest produces a large quantity of new leaves, which in turn increases the biomass of insects.  Woolly monkeys respond by foraging more regularly for insect prey.   See Research for further details on forest phenology.

In general, forest in the Amazon basin is considered tropical moist.  Forests in tropical areas are richer in species diversity and are more productive than forests in other parts of the world.  First, the forest in Yasuní National Park has roughly 200 more species of trees per hectare than forests in temperate zones.   Nigel Pitman, researching  29 one-hectare botanical plots throughout the Park, found that the number of species per hectare ranges between 307 and 114 for 10cm dbh trees (dbh: a standardized method of measuring tree trunk size) -- the highest woody plant diversity in the world.  Pitman estimates that the total number of species of trees and shrubs may be as high as 3141 (1500 for trees with 10cm dbh).  Second, the high rate of productivity is exemplified by a study that found tropical forests three times as productive as temperate forests, a fact explained in part by the longer, year-round growing season.  Given that plants photosynthesize, this translates into a higher rate of oxygen production.   (Although note that it is forest in tropical areas is what is more productive.  In general, tropical forests produce five times as much as grasslands, so it can be assumed that disturbed areas are not as productive.)

Several forest types are found throughout Yasuní: terra firme, flooded and swamp.  According to Pitman, 90% of Yasuní is terra firme with an average of 239 species of 10cm dbh trees per hectare and a density of over 600 trees (10cm dbh) per hectare .  Flooded forest was once thought to be dissimilar to terra firme in forest composition.   However, Pitman's study revealed that only 17% of the 520 total species found in floodable forest were not found in terra firme.  In both forest types, species composition of adjacent botanical plots are widely different in composition and density.  Flooded forests, however, tend to be less dense as a whole than terra firme and individual plots tend to be less diverse (permanently flooded swamps are even less diverse in the number of species).  Finally, disturbed or successional forest is found in areas of oil or human development (e.g., camps, road corridor, helipads). Cecropia sciadophylla and Ochroma pyramidale, two fast-growing, weedy trees, dominate these areas, but other tree and understory species have begun to replace them over time.  This pattern is seen on a smaller scale in forest cleared by treefalls due to wind and rain.

Plant composition of the forest in Yasuní is either woody (trees, lianas, shrubs) or to a lesser degree not (epiphytes, herbs).  Most plants are evergreens.  The canopy height is roughly 30 meters, although a few emergent trees, such as the Ceiba, can reach 50 meters in height.  Pitman notes that the most common woody plant families include Fabaceae, Arecaceae, Rubiaceae, Melastomataceae Lauraceae, Annonaceae, Moraceae, and Sapotaceae -- families similar to forests throughout the Amazon.  To date, botanists have discovered a few new tree species, for example Pentaplaris huaoranica (Tiliaceae), Inga sarayacuensis (Fabaceae: Mimosoideae), and Acanthosyris annonagustata (Santalaceae).

The All Species Foundation will attempt to inventory all species on earth.

It is well known that a large percentage of the earth's species reside in the tropics, the tropics encompassing a small portion (about 6%) of the earth (Conservation and links within that section addresses numbers of species lost per day). In the tropics, about half of the world's vertebrates and potentially up to 90% of invertebrates are found, and new species of both are discovered often.

Surveys in the neotropics and in Yasuní National Park have demonstrated the high diversity of species. For example, 60,000 species of insects are estimated to exist in a hectare of forest at Yasuní (Terry Erwin in Morell 1999). Furthermore, 84 species of amphibians and 77 species of reptiles have been recorded around the Estación Cientifíca Yasuní  (S. Ron).    (For information on the declining amphibian populations worldwide, contact Declining Amphibian Population Task Force.) Fish are also numerous in species: more than 2400 species of fish have been recorded for the Amazon (Photos of fish; information on neotropical fish: Neodat; discovery of new catfish: Amazon Conservation). And of the nearly 4000 species of birds of the neotropics, Robert Ridgley et al. recorded over 600 species in Yasuní. Finally, roughly 550 species of mammals have been found in the neotropics, and, of those, bats are the most common making up about 40% of the species in a neotropical community. New mammals are discovered even today:Marc van Roosmalen found two new primates (National Geographic article).

Although humans have lived in Amazonia for centuries, only during the past 50 years has deforestation become a serious threat to the region.  For example, between 1978 and 1996, 12.5% of the Amazon was deforested (CNN press release).  Ecuadorian Amazonia has so far suffered less from deforestation than some other regions.  According to a map prepared by R. Sierra (1999: Vegetacíon remanante del Ecuador continental c.1996;  Proyecto INEFAN/GEF/WCS), Ecuador lost 16% of its Amazon forest by 1996 (although rates have increased: Myers 1989 estimates a 4% yearly loss in "Deforestation Rates in Tropical Forests and Their Climatic Implications").  Most destruction is in the north central portion of Ecuador's Amazon and linked with the recent development of towns, roads and petroleum fields.   Yasuní National Park encompasses a good portion of remaining primary forest, although the threats to this Park are not small (e.g., oil development, hunting, farming noted throughout this website). See map and information from the World Resources Institute.

The causes of deforestation are multiple.  Much of it stems from the ever-increasing pressure of an ever-increasing human population.   Ecuador, a country of over 12 million, has one of the world's highest population growth rates at 2.04%.  Ecuador has thus been designated a global "hot spot", an area with high species diversity that is particularly environmentally threatened by human activity (Myers et al 2000).

Human population levels impact tropical forest and the species therein through several avenues.    First, habitat destruction for the purpose of agriculture or ranching leads to the local extinction of species that cannot adapt to disturbed areas.  For example, many primates are arboreal and primarily frugivorous, making it difficult for them to adapt to sparsely treed grasslands.  Also, slash and burn, rather than intensive agriculture, is the norm in this region of the world, primarily because burning releases minerals found in the plants (most minerals in the Amazon are stored in plants, not soils). Burning is especially damaging in regions of high rain in that the  minerals gained by  burning are rapidly leeched out of the system and farm productivity reduces each year.  Second, hunting for subsistence or sale (the latter for either the pet trade or as food) alters species composition, particularly affecting larger, group-living animals and fish that are more easily hunted.  Modern hunting technologies drastically affect the rate of animal depletion (dynamite and shotguns can kill many in a short period of time).  The maturation and reproductive rates of a species also affects the ability to adapt to hunting pressure.  Primates, for example, are especially slow at reproduction and are often one of the first species to go locally extinct.   Finally, the introduction of exotic species also affects the ability of local  animals and plants -- especially if the exotic species do not have natural predators and are able to out compete natives.  Grasses and other plants were introduced into Yasuní by the oil companies, and most indigenous families have domestic pets.  Their future effects are currently unknown. 

A major cause of deforestation in the Amazon is activity by companies seeking profits through resource extraction  (e.g., of oil, minerals, timber) and the demand for these resources in other parts of the world.   In Ecuador, oil exploration since the 1960s has been the catalyst for much of the deforestation in the Amazon region.  According to Judith Kimmerling's 1993 book (Amazon Crude), Ecuador’s initial profits from oil extraction have been distributed very unequally.  Furthermore, since oil extraction began the national debt has grown, and the amount of poverty has increased.  However, roughly 40% (recent estimates state more) of Ecuador's national budget comes from oil extraction, so it is difficult to imagine the country refraining from exploiting this resource.  (Kimmerling notes that the entire oil production in the Cuyabeno Wildlife Reserve by Texaco, a company that began oil  development in Ecuador, was 1.4 billion gallons, an amount consumed in less than 80 days in the United States.  This extraction left a huge environmental disaster in oil spills and livelihood destruction of indigenous people.  Reuters press release.)   Further information about oil in Yasuní.

Infrastructure development for oil extraction also leads to numerous problems in the rainforest.  Roads allow hunters access to animal populations that can be exploited and sold in markets great distances away.  Roads fragment tracks of land into islands, making it impossible for some animals to disperse. These "islands" can thus become devoid of large mammals and birds, can have fewer species of plants because of seed dispersion problems, and can also have drastically altered "gene pools" of those remaining plant and animal species.Finally, road building and development leads to an influx of colonists that cause further damage by clearing land along roads and rivers for subsistence.  As these farms spread and local populations increase, official protected status of these lands often becomes irrelevant.

The impacts of tropical deforestation are tremendous.   Since most of the Earth’s animal and plant species live in rainforests, the loss of world-wide species diversity is huge.  Most scientists now believe that the earth is beginning a human-initiated mass species extinction event similar to the meteor-caused extinction of the dinosaurs.  There are many estimates of current world-wide extinction rates (e.g., E.O. Wilson: 137 species per day) that highlight the seriousness of human impact on the environment (see fact sheets/news releases from RAN and IUCN).  Deforestation can also increase desertificaiton the tropics, change global weather patterns (dryer in tropics, wetter away from tropics) and contribute to greenhouse effect by increasing greenhouse gases and by reducing carbon-fixing plant growth.

Yasuní’s plant and animal species diversity is among the highest on Earth (Myers et al 2000).   Conserving these forests is therefore one of the most effective ways to conserve the highest numbers of species per acre.  Yasuní also has relatively rich soils and high animal population densities. Forest preserved in Yasuní can thus more effectively conserve animal and plant populations threatened by hunting and fragmentation than would the protection of less diverse and less productive lands elsewhere (Peres 2000).  A gem among gems, Yasuní National Park is an area whose protection more effectively conserves species than almost any other region in the world.