Anti-Pollinators for Mass-Flowering Plants?

Abstract

Mass-flowering species of woody tropical plants frequently attract a large and diverse array of pollinating insects together with insectivorous birds. It is proposed that the attraction of such pollinator predators or anti-pollinators is an integral part of the mass-flowering adaptive strategy. An insect-pollinated mass-flowering plant may expend energy resources in order to attract a surplus of pollinators which then draws insectivorous birds; which in turn facilitate cross-pollination by interacting with and dispersing pollinators between individual plants. MUCH ATtENTION has been given in recent years to phenomena associated with mass-flowering in woody tropical plants. The individuals of such plant species bloom profusely and synchronously during a short time interval which is often correlated with the dry season (Janzen 1967) and generally attract a large and diverse spectrum of potential pollinators, especially bes (e.g., Gentry 1974a, 1974b; Frankie 1975, 1976; Frankie and Baker 1975). From the plant's viewpoint, one of the major drawbacks to mass-flowering is the tendency of insect visitors to move from flower to flower on a single plant rather than between widely spaced plants. In return for the energy invested, the plant would receive from such intra-plant movements only the low reproductive return of geitonogamy, which is genetically no better than self ing, or, in the common case of self-incompatible species (Bawa 1975, Kalin 1976), no pollination at all. A strategy which has been suggested as a mechanism for increasing the rate of inter-plant visits by pollinators is low nectar production, forcing pollinators constantly to seek new nectar sources (Heinrich and Raven 1972). In intrinsically high-nectarproducing mass-flowering species this result may be achieved indirectly through depletion of the nectar supply by robbers (Heinrich and Raven 1972). In the case of mass-flowering Bignoniaceae, for example, such robbers are very prevalent and are mostly xylocopids and hummingbirds which perforate the base of the tubular corolla without contacting anthers or stigma (Gentry 1974b). An opposite strategy to increase inter-plant pollinator movements has been postulated by Frankie (1975, 1976) who noted the high frequency of aggressive interacticns between the numerous individuals of territorial or group-foraging bee species at prolific mass-flowering plant species like Pterocarpus rohrii Vahl, Andira inermis (Wright) DC., Piscidia carthaginensis Jacq., Tabebuia rosea (Bertol.) DC., and Caesalpinia eriastachya Benth. By increasing its nectar production, a mass-flowering species might attract more potential pollinators, in turn increase aggressive interactions among them and thus potentially increase their frequency of inter-plant move-