Travel Reference
In-Depth Information
Tropical ecologists who came after Wallace were puzzled by this spe-
cies diversity. How can so many dif erent species of tree live packed so
closely together in what seems at fi rst blush to be an ordinary, rather uni-
form, wet tropical environment? It is immediately obvious that there are
tall trees, medium-sized trees, and short trees in a rainforest, each adapted
to dif erent amounts of sunlight. But dif erences in sunlight account for
only a small number of ecological niches. How can a rainforest possibly
encompass hundreds or thousands of dif erent ecological niches, when it
is clear that all the plants that form the base of the food chain have access
to at least the necessities of life?
Although I had no background in tropical forest ecology I began to won-
der whether I could apply principles of population genetics to the problem.
And it was at that point that I embarked on the research project that eventu-
ally provided some answers to these questions.
The origin of the rainforests
To understand rainforests, we must begin with their history. A mature rain-
forest of the present day consists of an understory of small and young plants,
a dense midstory of medium-sized trees, and a towering canopy of a few
giant trees that have managed to break through into the open sunlight high
above.
Rainforests of the past had a similar overall structure but a dif erent mix
of plants. At successive times they were dominated by seed ferns, cycads, and
evergreens. One of the great events in evolution has been the recent transfor-
mation of forests throughout much of the world as they were taken over by
fl owering plants.
Trees and other plants that reproduce using fl owers have a more sophis-
ticated reproductive system than the cycads and evergreens that domi-
nated forests in the distant past. Flowering plants can attract a wide variety
of pollinators, which help to ensure fertilization of their eggs. But perhaps
more importantly, the fl owering plants use a trick called double fertilization
to provide stored food only to the eggs that are fertilized. They do not waste
