a few studies of herbivory in particular species (e.g.,
Peck, "Agroecology of Prosapia," pp. 409-410), even
basic surveys remain to be done. Monteverde provides
an excellent location for comparative studies of plant-
animal interactions over an elevational gradient.
In this chapter, we focus on work conducted in
Monteverde and make comparisons to other sites.
Introductions to plant-animal interactions are in
Thompson (1982, 1994), Boucher (1985), Howe and
Westley (1988), and Abrahamson (1989). Feinsinger
(1983), Real (1983), and Jones and Little (1983) pro-
vide introductions to pollination biology, as do Howe
and Smallwood (1982). Murray (1986) describes
frugivory and seed dispersal, and Gilbert and Raven
(1975), Nitecki (1983), and Futuyma and Slatkin
(1983) provide a general treatment of coevolution.
8.1. Plant Pollinator Interactions
8.1.1. Who Pollinates What
To reproduce sexually, flowering plants must import
and export pollen. Pollen is transported abiotically
(by wind or water) or biotically (by invertebrate or
vertebrate animals who visit flowers to collect nec-
tar, pollen, or other floral rewards). The vast major-
ity of pollinating animals are insects, including thrips,
leafhoppers, flies, beetles, butterflies, moths, bees,
and wasps (Proctor et al. 1996). Hummingbirds and
other birds pollinate plants as they forage for nectar.
Mammals such as bats, rodents, marsupials, and pri-
mates also visit flowers, but pollination by mammals
other than bats is rare.
Flowers pollinated by animals are remarkably di-
verse in color, scent, nectar composition and produc-
tion rate, phenology, shape, symmetry, and design of
floral display. Floral traits are thought to reflect co-
evolution between plants and the animals that polli-
nate them (Faegri and van der Pijl 1979), because
traits of flowers and their pollinator mutualists
broadly match. For example, flowers whose pollen is
transported on the bills and heads of hummingbirds
tend to be red and tubular (matching the visual acu-
ity and bill shape of the birds), whereas moth-visited
flowers often have white petals and sweet nocturnal
scents (matching the nocturnal habits and visual and
olfactory orientation of moths). Naturalists call these
patterns "pollination syndromes" (Faegri and van der
Pijl 1979) or "pollination systems" (Kress and Beach
1994). Although pollination systems are a useful tool
for exploring mechanisms of pollination (Proctor et al.
1996), their assumptions (e.g., that particular plants
and their pollinators have coevolved) and predictions
(e.g., that the most effective pollinator has had the
largest selective impact on floral traits) can limit the
questions we pursue (Herrera 1996). The systems
approach has not traditionally been linked to studies
of plants' mating and population structures (Harder and
Barrett 1996), a link that is critical for conservation.
The complementarity between traits of pollen-
transporting animals and flowers is one of several
plant-pollinator correspondences. Three others are
discussed in this section. First is the relationship
between floral sexuality (the distribution of male and
female structures and functions within and between
plants) and pollination systems. For example, many
beetle-pollinated plant species have unisexual flow-
ers. Second is the correspondence between pollina-
tion systems and plant life-forms (Table 8.1); for ex-
ample, tropical trees are more likely to be pollinated
by bees than by birds or small moths, but pollination
by birds is frequent among herbaceous plants. Third,
elevation influences the relative frequencies of pol-
lination systems because flight in cool, cloudy con-
ditions is easier for some animals than for others
(Cruden 1972). For example, hummingbird pollina-
tion is especially conspicuous and frequent in Monte-
verde, particularly for the rich vascular epiphyte flora.
The 13 pollination systems discussed here are very
broad categories (Baker et al. 1983, Wyatt 1983, Bawa
1990) that allow comparison to other tropical sites
(Bawa et al. 1985, Kress and Beach 1994). Our infor-
mation on pollination systems for Monteverde comes
primarily from two sources. First, William Haber and
colleagues (e.g., Koptur et al. 1988) documented
floral characteristics (and flower visitors in many
cases) and assigned likely pollination systems to
Monteverde's flowering plants. Haber's list (Appen-
dix 1) is the major reference for this section's sum-
mary (Table 8.1) of pollination system patterns in the
Monteverde flora. The second source was the set of
studies that document pollinators or details of pol-
lination for various taxa (Koptur 1984b, Cane 1993).
Pollination by hummingbirds has been studied in
detail (Feinsinger 1978, Feinsinger et al. 1986,1987,
1988b). For the majority of plant species at Monte-
verde, however, few details of reproductive biology
are known.Large flying animals. Flowers adapted for pollination
by bats, hummingbirds, and hawkmoths are conspicu-
ous because they are big, bright, or strongly scented.
These large fliers pollinate nearly 15% of Monte-
verde's flowering plants (Table 8.1), and may be espe-
cially important to montane plant mutualists because
they are strong fliers in cool misty conditions. Because
some are able to fly long distances relative to smaller
pollinators, they may occasionally effect long-dis-
tance pollen movement and gene flow (Janzen 1983).246 Plant-Animal Interactions