no obligate agaonine wasps associated with it (Ramirez
1970). Differences also exist among populations of in-
dividual species; for example, in northern Mexico,
F. pertusa lacks the tight within-tree flowering syn-
chrony of Monteverde and Panama (Bronstein 1988a,
Smith and Bronstein 1996, A. Herre, pers. comm.).
A breakdown in within-tree synchrony is another pho-
nological trait that stabilizes fig wasp population dy-
namics in models, but it is not found across the spe-
cies' entire range.
The unusual phenology of figs has important im-
plications for their interactions with seed dispersers.
At the population level, fig trees flower year-round.
They also fruit year-round, so they are a reliable food
source for vertebrates at times of year when little else
is available. Nearly all vertebrates in tropical forests
are believed to feed on figs at some time in their lives
(Janzen 1979). Figs have thus been termed "keystone
resources" in tropical forests. Their loss would pose
serious threats to maintaining vertebrate popula-
tions, even though they make up a relatively small
proportion of the biomass of the forest (Terborgh
1986).
Figs can be divided into two widely recognized
"fruit syndromes." The first group of species includes
those dispersed primarily by mammals, particularly
fruit bats. These figs ripen at night and are green,
spongy, and fragrant when ripe. Bats feed on four of
the five Monteverde fig species: F. tuerkheimii (whose
fruits are also eaten by large birds), F. crassiuscula,
F. velutina, and F. yoponensis (Dinerstein 1983). The
second group consists of species whose figs ripen dur-
ing the day and are red, juicy, and odorless when ripe;
they appeal particularly to birds. Ficus pertusa is a
bird-dispersed species in Monteverde. Twenty-six
species of birds from 10 families fed in F. pertusa
pasture trees over a 5-month period (Bronstein and
Hoffman 1987).
Although figs have community-level importance
because of their broad acceptability and availability in
times of need, they are not a preferred food. They are
nutritionally poor in comparison to other tropical fruits
(Dinerstein 1983) and are abandoned when better foods
become available. The greatest numbers and diversity
of bird visitors (resident and migrant) to F. pertusa trees
occurred between February and April, when few
other Monteverde species were in fruit (Bronstein
and Hoffman 1987). This was followed by a dramatic
drop in visitation by all species in late April, a time of
relatively high fruit abundance in Monteverde (Wheel-
wright 1983). There is also striking spatial variation in
the identities of birds feeding at F. pertusa trees, both
among different pastures (Bronstein and Hoffman 1987)
and between pastures and the upper forested regions of
Monteverde 1 km away (Wheelwright et al. 1984). Re-
gional comparisons will provide insights into the ecol-
ogy and evolution of these interactions. For example,
on Barro Colorado Island, F. pertusa fruits are green
when ripe and are taken by bats (Kalko et al. 1996); in
Monteverde, bats consistently reject the red-ripe fruits
(J. Rieger and E. Jakob, unpubl. data).
Mutualism is the most poorly understood form
of interspecific interaction (Bronstein 1994). Stud-
ies comparing different types of mutualism (e.g.,
F. pertusa's specialized pollination mutualism and
generalized seed dispersal mutualism), similar mu-
tualisms involving different species pairs (e.g., the
five fig-pollinator combinations in Monteverde), and
the same mutualism in different regions (e.g., the F.
pertusa-P. silvestrii mutualism in Monteverde and
Mexico) hold great promise for understanding these
fascinating interactions.THE REPRODUCTIVE BIOLOGY Qf'BIAKEA
AND TOPOBEA (MELASTQMATACEAE)
Cecile turnerlakea and Topobea (Melastomataceae) are two
closely related genera of hemiepiphytes (plants
germinating on trees but sending roots to the
ground as adults). These genera are identical except
for the shape of their anthers (Gleason 1945). Blakea
has squat wedge-shaped anthers (Fig. 8.10); the
anthers of Topobea are longer and narrower (Fig.
8,11). Five species of Blakea occur in Monteverde
(B. anomala, B. chlorantha, B. gracilis, B. grand i-
flora, and B. tuberculata). Topobea is represented bythree species (T. brenesii, T. durandiana, and T. pit-
tieri}. Blakea chlorantha, B. grandiflora, B. tuber-
culata, and T. pittieri grow in the MCFP; B. gracilis
and T. brenesii are common in open disturbed areas
just below the MCFP. Blakea anomala grows at the
edge of the MCFP and in the wet montane forest just
below it. Topobea durandiana occurs only at lower
elevations in the Monteverde community. These spe-
cies are large sun-loving hemiepiphytes that grow at
various levels in the canopy. They also grow in open273 Plant-Animal InteractionsB