feeding behavior characteristics. The feeding records
for Monteverde (Wheelwright et al. 1984, Bronstein
and Hoffman 1987, Wheelwright 1988a, Nadkarni and
Matelson 1989) provide an example of how diffuse the
interactions among plants and their dispersers are.
Very few cases exist in which a plant has only one
known disperser, or in which a particular bird spe-
cies feeds on only one species of fruit (Jordano 1987).
In contrast to the "specialization-generalization"
paradigm, Wheelwright (1985b) predicted that diet
breadth in Monteverde birds would be proportional
to gape width, because all birds could feed on smaller
fruits whereas only large birds would have access to
larger ones. Larger fruit-eating birds tend to feed on
many different fruits (Wheelwright et al. 1984). The
"winner" in terms of diet breadth is the Emerald Tou-
canet (gape 26 mm), with 95 food plants in the Monte-
verde area. The other large well-studied frugivores,
Resplendent Quetzals (21 mm), Three-wattled Bell-
birds (25 mm), and Black Guans (31 mm), ate 38, 29,
and 26 species, respectively. Several smaller birds,
including Long-tailed Manakins (8.5 mm), Mountain
Robins (12 mm) and Black-faced Solitaires (11 mm),
also have exceedingly broad diets, however (37, 44,
and 51 species, respectively), so the positive correla-
tion between bird size and number of fruit species
eaten has many exceptions.
Counts of the number of fruit species eaten are
inadequate estimators of the relative importance of
different bird species in the community because they
do not take into account the number of other birds that
also provide dispersal service to particular plants.
Black-faced Solitaires, for example, which consume
many fruits that are also eaten by a wide variety of
other species, are usually thought to be less impor-
tant for maintaining the Monteverde plant community
than are Resplendent Quetzals, whose (typically large-
seeded) food plants probably support fewer alterna-
tive dispersers. However, small frugivores such as
solitaires may be more important than some of the
larger frugivores, due to their high abundance and
broad diet (see Murray, "Importance," pp. 294-295).Fruit size and shape. Research on large fruits and their
dispersers provides evidence of the effects of disperser
morphology and behavior on the shape and upper size
limit of seeds (Howe and Richter 1982, Wheelwright
1993). Although they can eat large fruits, quetzals,
bellbirds, toucanets, and manakins are often unable
to swallow the largest fruits that they pluck from
plants (Wheelwright 1985a;Fig. 8.4). Birds often drop
the largest fruits from a plant on the ground after try-
ing unsuccessfully to swallow them. Presumably, the
negative consequences of large fruit size and seed sizeFigure 8.4. Skull of Resplendent Quetzal next to a fruit (above) and seed (below) of Beilschmeidio
brenesii, one of the large-fruited species of Lauraceae that birds are able to swallow. Photograph by
Nathaniel Wheelwright.260 Plant-Animal Interactions