But they still debate on what other factors have influenced it. Others propose that geographic barriers such as rivers are responsible for isolating populations and causing different species to evolve. The rising of mountains 2-5 million years ago may also have isolated populations causing them to evolve into different species. So many different species can coexist in the rain forest because there is a high degree of specialization. Some species are adapted to life on the forest floor, while others are specialized for life in the understory, or the treetop.
Some species are active during the day, while others are active during the night.
The limiting factor for the number of animals in the rain forests is the amount of food available. In some areas of the forest there is a lean period when only a few tree species bear fruit. Because they are essential to sustain frugivorous animals these trees are called keystone species. If greenhouse emissions continue to increase at the current rate, the entire Amazon rain forest will disappear by the end of the next century, along with many of the World's forests, according to a three-year study by the Hadley Center of Britain's Meteorological Office. An Introduction to Tropical Rain Forests.