seed passage rate is now known from two studies. The
possibility that secondary chemicals in fruits might
have other pharmacological effects (e.g., antiparasitic)
has not been investigated.
There is still a great need for general comparisons
of Monteverde plant-frugivore communities to those
at other sites to identify similarities or differences
between communities derived from their climate,
evolutionary history, or anthropogenic manipula-
tions. Studies that integrate the areas of pollination
and seed dispersal will be particularly useful. Un-
derstanding these interactions is critical for their
management in an increasingly fragmented land-
scape. Of equal importance are plant-animal inter-
actions other than pollination and seed dispersal
mutualisms, areas which are virtually unexplored in
Monteverde. One very common type of mutualism
in tropical habitats occurs between plants and ants;
ants protect the plants from herbivores and receive
food and sometimes shelter in return (Schupp and
Feener 1991, Rico-Gray 1993, Fonseca and Ganade
1996; see Longino, "Myrmecophytes," pp. 291-293).
Little work has been conducted on ant-plant mutualisms
in Monteverde or on herbivory, seed predation, and
other antagonistic plant-animal interactions (see
the following essays by Koptur, Weiss, Wenny, and
Longino). These interactions have demographic and
genetic consequences for plant and animal popu-
lations at the population, community, and regional
level.HUMMINGBIRD POLLINATION OF EPIPHYTIC ERICACEAE
IN THE CLOUD FOREST CANOPY
William H. Busbyn Monteverde, members of the Ericaceae (blue-
berry family) are conspicuous epiphytes, with
their shrublike growth form, abundant displays
of showy flowers, and fleshy, bird-dispersed fruits.
Most of the 15-20 species in Monteverde occur in the
wet, upper elevation forests of the MCFP. I studied
the pollination ecology of nine species of canopy-
dwelling Ericaceae in the preserve to determine flo-
ral biology, nectar secretion and sugar ratios, and
flower visitors. As part of a larger project (Feinsinger
et al. 1987), my colleagues and I examined humming-
birds captured in mist nets to determine which types
of pollen were carried by birds.
The floral biology of all but one species indicated
adaptations for pollination by hummingbirds (Table
8.2). Most flowers have red, purple, and white tubu-
lar corollas oriented at a downward angle. Nectar of
moderate concentration (14-22% sugar) is produced
during the day. As with most species adapted for
hummingbird pollination (Baker and Baker 1979), the
dominant sugar in the nectar is sucrose. The excep-
tion is Vaccinium poasanum, which has greenish
white, bell-shaped flowers displayed in pendant clus-
ters that produce nectar composed largely of glucose
and fructose. This species was occasionally visited
by short-billed hummingbirds, but the most frequent
visitors (and presumed pollinators) were bumblebees
(Bombus spp.).
Seven species of ericads with short tubular corol-
las were visited by three species of hummingbirds
with short bills: Coppery-headed Emerald (very short,
slightly decurved bill), Purple-throated Mountain-
gem (short, straight bill), and Fiery-throated Hum-
mingbird (short, straight bill). The Coppery-headed
Emerald, a seasonal short-billed visitor that forages
in the canopy, visited only the two ericads with the
shortest corollas, Cavendishia complectans and C.
capitulata. In contrast, the Purple-throated Mountain-
gem, the most conspicuous hummingbird in the MCFP
and a year-round resident, was the most frequent visi-
tor to short-corolla flowers and was observed visiting
all but one of the short-corolla species. The Fiery-
throated Hummingbird is found at higher elevations
in the preserve, where it defends rich floral resources
(three of the seven species) in the canopy. The Purple-
throated Mountain-gem and Fiery-throated Hum-
mingbird are probably able to extract nectar from
all short-corolla ericads. However, some species of
ericads and hummingbirds occupy narrow elevational
and environmental ranges, and not all ericads over-
lap with all hummingbird species.
The long flowers of Psammisia ramiflora were vis-
ited by a different set of hummingbirds. The principal
flower visitor was the Green-fronted Lancebill, a hum-
mingbird with a long (34.4 mm) straight bill. Psam-
misia ramiflora has long pendent corollas that require
pollinators to hover beneath the flowers, probing ver-
tically upward to reach the nectary. Other humming-
birds, particularly the Green Hermit, occasionally
visit Psammisia ramiflora flowers and may pollinate
them, but only the Green-fronted Lancebill appears
able to extract nectar efficiently. Analysis of pollen
on the bills and heads of five hummingbird species
revealed that all frequently carry ericad pollen. Pol-267 Plant-Animal InteractionsI