number of plant species is disproportionately impor-
tant to Monteverde frugivores (Fig. 8.26), parallel to
the first result. A high correlation exists between
the index values for particular plant species and a
simple count of the number of bird species known
to feed on them. This pattern is difficult to interpret
because the seven plant species with the highest im-
portance values (Acnistis arborescens [Solanaceae],
Sapium glandulosum [Euphorbiaceae], Citharexylum
costaricensis [Verbenaceae], Hampea appendiculata
[Malvaceae], Trema micrantha [Ulmaceae], Rubus
roseafolia [Rosaceae], and Conostegia oerstediana
[Melastomataceae]) are pioneers that occur in un-
naturally high densities in the pasture-second-growth
forest mosaic of the Monteverde community where
many of the feeding records were recorded (Wheel-
wright et al. 1984). Such pioneer species cannot be
omitted from the analysis because they occur natu-
rally in small-scale disturbances such as treefalls
and are fed on by a large number of forest frugivores.
Other species, for example, the mistletoes Struthan-
thus oerstedii (Loranthaceae) and Phoradendron
robaloense (Viscaceae), have high values because they
serve as important food sources for birds (primarily
euphonias) that are mistletoe specialists. Our general
conclusions are that some plant species are dispro-
portionately important (i.e., are keystone resources)
to Monteverde frugivores. We must monitor popula-
tions of all keystone mutualists at Monteverde, not just
the large frugivores and dominant forest trees that
largely determine the physical structure of the forest.
The huge variety of epiphytes that make cloud forests
unique may depend on smaller, less conspicuous ani-
mals such as Black-faced Solitaires, and our conserva-
tion efforts and priorities must be directed toward these
elements of the community.Figure 8.26. Importance values (see equation 1) for the
15 bird-dispersed plant species with the highest indices
at Monteverde. Names of plant species, and numbers
of bird species known to consume fruits of each are
(from left to right) Acnistus arborescens (44), Sapium
glandulosum (formerly 5. oligoneuron, 23), Citharexylum
costaricensis (formerly C integerrimum, 23), Hampea
appendiculata (22), Trema micrantha (22), Rubus
roseafolia (10), Conostegia oerstediana (formerly C.
bernouliana, 17), Ocotea tonduzii (18), Miconia "species A"
(9), Struthanthus oerstedii (7), Myrsine coriacea (formerly
Rapanea myricoides, 13), Cecropia obtu si folia (11),
Ficus tuerckheimii (21), Ossaea micrantha (6), and
Phoradendron robaloense (4). See text for sources.Literature CitedAbrahamson, W. G. 1989. Plant-animal interactions.
McGraw-Hill, New York.
Agren, J., and D. W. Schemske. 1991. Pollination by deceit
in a neotropical monoecious herb, Begonia involucrata.
Biotropica 23:235-241.. 1993. Outcrossing rate and inbreeding depression in
two annual monoecious herbs, Begonia hirsuta and B.
semiovata. Evolution 47:125-135.
AH, S. A. 1931. The role of the sunbirds and the flowerpeckers
in the propagation and the distribution of the tree para-
site Loranthus longiflorus Desr. in the Konkan (W. In-
dia). Journal of the Bombay Natural History Society
75:943-945.
Anstett, M. C., G. Michaloud, and F. Kjellberg. 1995. Criti-
cal population size for fig/wasp mutualism in a seasonal
environment: effect and evolution of the duration of
receptivity. Oecologia 103:453-461.
Anstett, M. C., F. Kjellberg, and J. L. Bronstein. 1996. Wait-
ing for wasps: consequences for the pollination dynam-
ics of Ficus pertusa L. Journal of Biogeography 23:459-
466.
Appanah, S. 1990. Plant-pollinator interactions in Malay-
sian rain forests. Pages 85-101 in K. S. Bawa and M.
Hadley, editors. Reproductive ecology of tropical for-
est plants. Parthenon, Carnforth, UK, and UNESCO,
Paris.
Augspurger, C. K. 1983a. Offspring recruitment around
tropical trees: changes in cohort distance with time.
Oikos 40:189-196.. 1983b. Seed dispersal of the tropical tree Platypodium
elegans, and the escape of its seedlings from fungal
pathogens. Journal of Ecology 71: 759-771.
Ayala, F. J., J. K. Wetterer, J. T. Longino, and D. L. Hartl. 1996.
Molecular phylogeny of Azteca ants (Hymenoptera:
Formicidae) and the colonization of Cecropia trees.
Molecular Phylogenetics and Evolution 5:423-428.
295 Plant-Animal Interactions