The term “plant-animal interactions” includes a diverse array of biologically important relationships. Plant-herbivore relationships (in which an animal feeds on whole plants or parts of them) are examples of exploitation, because one species benefits from the interaction while the other suffers. Plant-pollinator and plant-seed disperser relationships (in which animals disperse pollen or seeds, usually in return for a food reward) are examples of mutualisms because they are beneficial to both parties. Another class of plant-animal mutualisms involves plants that provide nesting sites and/or food rewards to ants, which often protect the plant from herbivores or competing plants. Plantpollinator and plant-seed disperser mutualisms probably originated as cases of exploitation of plants by animals (Thompson 1982, Crepet 1983, Tiffney 1986). Many of the distinctive plant structures associated with animal-mediated pollen and seed dispersal (e.g., flowers, nectaries, attractive odors, fleshy fruit pulp, and thickened seed coats) presumably evolved to attract consumers of floral or seed resources while preventing them from digesting the pollen or seeds. mutualisms in structuring ecological communities. Competition and predator-prey interactions were more common subjects. Botanists had described the characteristics of the plant and animal players in pollination and seed dispersal mutualisms (Knuth 1906, 1908, 1909, Ridley 1930, van der Pijl 1969, Faegri and van der Pijl 1979), but these descriptive works did not fully examine plant-animal mutualisms in the context of communities. The opportunity to work in the neotropics, facilitated by the Organization for Tropical Studies (OTS), the Smithsonian Tropical Research Institute (STRI), and other institutions, attracted the attention of temperate-zone ecologists to the mutualisms that are much more conspicuous components of tropical systems than of temperate ones (Wheelwright 1988b). Plant-pollinator interactions have attracted more attention in Monteverde than plant-frugivore interactions, and plant-herbivore interactions remain conspicuously understudied. This imbalance probably reflects the interests of those who first worked at Monteverde and later returned with their own students, rather than differences in the significance of the interactions at Monteverde or elsewhere. Aside from a few studies of herbivory in particular species (e.g., Peck, “Agroecology of Prosapia,”), even basic surveys remain to be done.
A continuum of specialists and generalists in empirical communities