Why are so many types of plants and organisms in the rainforest

Why are so many types of plants and organisms in the rainforest

 A tropical greenhouse

More than two thirds of the world's plant species are found in the tropical rainforests: plants that provide shelter and food for rainforest animals as well as taking part in the gas exchanges which provide much of the world's oxygen supply.

Rainforest plants live in a warm humid environment that allows an enormous variation rare in more temperate climates: some like the orchids have beautiful flowers adapted to attract the profusion of forest insects.

Competition at ground level for light and food has lead to evolution of plants  which live on the branches of other plants, or even strangle large trees to fight for survival.

The aerial plants often gather nourishment from the air itself using so-called 'air roots';. The humidity of the rainforest encourages such adaptations which would be impossible in most temperate forests with their much drier conditions.

Bromeliads     Buttress Roots     Carniverous Plants
Epiphytes     Lianas     Orchids
Saprophytes     Stilt/Prop Roots     Strangler Fig

Why is so much of the flora and fauna of the earth concentrated in only 6% of the land surface? The answer is at least partially historical. For the first three billion years of life on earth, there was little increase in the number of species, but later diversification became explosive. Species and other taxonomic groups arose and disappeared, with an average duration for a species of probably less than 10 million years. But, during the Permian period, about 240 million years ago, between 77% and 96% of the marine fauna became extinct (Wilson, 1989; see also Gibbs, 2001).

Land organisms were also significantly affected, if not to the same extent. In the late Cretaceous period there was another massive extinction (65 million years ago) of approximately 50% of existing species, and other lesser extinction events have followed. These extinctions opened the field for the radiation and development of many new species (Raup, 1988

As mentioned, changes in land masses over geological time have provided the impetus for the evolution of a great variety of taxonomic groups. As the original continent Pangaea split into Laurasia and Gondwana and as these land masses became sundered, organisms were separated from each other, thereafter following different evolutionary paths (but note the conservatism at higher taxonomic level in tropical forests, mentioned above). It is generally thought that one of the major mechanisms of the evolution of new species is natural selection following geographical isolation of groups within the same species. After a long period of time, the separated groups – should they remain apart – may diverge sufficiently to be considered separate species. But the number of different taxonomic groups increases disproportionately in tropical regions. Why