Many animals derive their food energy from the nectar of flowers, and the flowers may also provide them with the materials for growth and reproduction. To the plants, in turn, the animals are the vehicle for the transport of male gametes for fertilization. As a consequence, there is a mutual interdependence involving a set of evolved games where the pollinators try to get the most for their foraging effort, while flowers provide the least reward possible. The flowers must provide enough reward to attract the pollinators and keep them from visiting competitor species, but the rewards must be sufficiently small to keep them moving from one plant to another (Heinrich & Raven, 1972). Interesting complications arise in this simple scheme in male vs. female functions of flowers, when manyflowered vs. fewor single-flowered plants are considered, and when any one plant's most potent competitors are other individuals of the same rather than other species. The latter aspects have been little explored. In order for the pollination system to work requires several conditions. First, there must be advertisement of the rewards. Secondly, flower morphology must be appropriate for the pollinator to become dusted with pollen without dusting the pistil, and to transfer this pollen to a receptive pistil of another flower. The morphological features of the flower act to manipulate the close-in behavior of the pollinator to increase the percentage of cross-pollination events per given food reward provided, or per given forager-flower encounter (Macior, 1974). It is probably a safe working hypothesis that the foragers have selected, by those visits that have resulted in fertilization, most of the flowers that we know today. They have been the agents of flower horticulture in nature, and if we want to observe the selective pressures that have shaped or are shaping flower evolution, we must look to the foraging behavior of the flower visitors. The third major consideration is that the foragers must not only be appropriately manipulated at the flowers, they must also be caused to move between them (Heinrich & Raven, 1972). This involves energetics. And when one looks from the standpoint of energetics, it becomes necessary to consider the environment and the other plants relative to whom the pollinator's choices are made. Most pollinators are inherently promiscuous; they visit flowers for the rewards they contain, regardless of the shape or color of the flower's exterior. But to the plant, to whom flower constancy is important for cross-pollination, fidelity can be bought by providing large food rewards. But this purchase may be at a high price. In the immediate, ecological, sense, too strict a fidelity will hinder the contribution of male gametes to other flowers. A bee, for example, will return repeatedly to a single blossom, visiting no others, provided this blossom is sufficiently rewarding, conspicuous and isolated (McGregor et al., 1959). A second cost, one that may not be apparent unless measured against an evolutionary time
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Jul 1, 1983
Remi Quirion + 1
Open Access