from plant to plant, animals disperse pollen, making
cross- pollination efficient and ensuring reproduction
of the plants. This relationship is mutualistic— both
plant and pollinating animal benefit.
Animal pollination is widespread throughout tropical
ecosystems, particularly forests. As mentioned earlier,
in contrast to temperate forests, where wind pollination
is common, rain forests are sufficiently dense that
wind pollination would tend to be ineffective, except
perhaps among emergent trees. It is not surprising that
grasses, sedges, pines, and other species of open areas
such as savannas are the only tropical plant groups
characterized by wind pollination.
Insects and vertebrates are major pollinators
throughout the tropics. Among insects, pollination is
accomplished by numerous species of bees, flies, beetles,
butterflies, and moths (plate 10- 27). Among vertebrates
in the Neotropics, hummingbirds (Trochilidae, about
350 species) feed most heavily on nectar, but otherspecies including tanagers and orioles also utilize nectar
and may act as cross- pollinators.
Hummingbird- pollinated flowers take many shapes,
but some have long tubes and are red, orange, purple, or
yellow. In contrast, bat- pollinated flowers are often white
(easy to locate in the dark) and may have a musky odor, an
attractant to the bats. Many flowers are visited by a variety
of vertebrates and insects that are all potential pollinators.
Pollinators that fly long distances are most
advantageous to plants, as such behavior helps ensure
effective cross- pollination between widely separated
plants. Euglossine bees (plate 10- 28) are long- distance
fliers, and the males pollinate certain widely separated
orchids. Compounds in the orchid flower that are
absorbed by the male bees contribute to the longevity
of the insects. Daniel Janzen documented that male
euglossine bees live up to six months, a long life for a
bee, adding to the likelihood of numerous long flights
that result in successful pollination.Plate 10- 27. Bees are attracted to the flowers opening on
this Kapok Tree (Ceiba pentandra; chapter 7). Many species
from bees to bats aid in cross- pollination of Kapoks. Photo by
Dennis Paulson.Plate 10- 28. This Eulaema polychroma is a “long- distance”
euglossine bee, shown here stocking up on pollen (note the
pollen bulge beneath the abdomen). Photo by Dennis Paulson.Darwin, Pollination, and Coevolution
Charles Darwin, in On the Origin of Species, wrote about the coevolved relationship between bees and the clover they
pollinate: “The tubes of the corollas of the common red and incarnate clovers (Trifolium pratense and incarnatum)
do not on a hasty glance appear to differ in length; yet the hive- bee can easily suck the nectar out of the incarnate
clover, but not out of the common red clover, which is visited by humble- bees alone.” Darwin discussed pollination
and coevolution further in a monograph, On the various contrivances by which British and foreign orchids are fertilized by
insects, and on the good effects of intercrossing, published in 1862.Darwin’s clear understanding of the interdependency between various plants and their specific pollinators and of
how the behaviors of the insects, as well as the morphologies of both insects and plants, have evolved from the
exertion of mutual selection pressures makes him the person who discovered coevolution.chapter 10 tropical intimacy: mutualism and coevolution 171