The unsolved mysteries of the rainforest are formless and seductive. They are like unnamed islands hidden in the blank spaces of old maps, like dark shapes glimpsed descending the far wall of a reef into the abyss. They draw us forward and stir strange apprehensions. The unknown and prodigious are drugs to the scientific imagination, stirring insatiable hunger with a single taste. In our hearts we hope we will never discover everything. The rainforest in its richness is one of the last repositories on earth of that timeless dream.
Edward O. Wilson, The Diversity of Life
It is difficult not to be puzzled by the diversity of life forms within our biosphere. Some well-known ecosystems, such as coral reefs and tropical rainforests (Figure 7.1), show extraordinarily high diversity. This is what the ecologist Ramön Margalef called "the baroque of nature," meaning that ecosystems contain many more species than would be necessary if biological efficiency were the criterion for their organization.
Rainforests contain a great fraction of our planet's biodiversity, 1 including, according to a Robert May 1990 estimate, over 50,000 tree species worldwide. But the coexistence of such a great number of species in relatively small local areas is not well understood. Rich ecosystems have at least two common peculiarities. First, environmental variables such as temperature and humidity are often relatively uniform in space and time throughout the system, and second, numbers of individuals