POLLINATION ECOLOGY OF THE SPRING WILDFLOWER COMMUNITY IN THE DECIDUOUS FORESTS OF PIEDMONT NORTH CAROLINA (HEPATICA, ERYTHRONIUM, CLAYTONIA)

Inadequate pollination seems likely in the spring wildflower community of mesic deciduous forests for several reasons. The blooming season is short with considerable overlap in flowering phenologies, many species share pollinators (predominantly flies and solitary bees), and inclement weather frequently interrupts insect acitivity. I used an experimental approach to determine (a) whether seed-set in the community was pollinator-limited, (b) what plant characteristics promoted full pollination, and (c) how competition for pollination affected reproductive success. Supplemental hand-pollination significantly improved fecundity in only 3 of 12 species, all pollinated by queen bumblebees. Detailed studies were made on Hepatica americana, Erythronium umbilicatum, and Claytonia virginica to learn how floral biology traits of these typical species contributed to pollination success. Hepatica has nectarless flowers, blooms very early, and attracts few visitors; experiments with emasculated flowers indicated that without autogamy its seed-set would be markedly depressed. In Erythronium and Claytonia, extended perianth persistence allows flowers to remain receptive through periods of pollinator scarcity. Most spring wildflowers can be pollinated by various visitor types in 1-2 visits, as demonstrated by counting the number of seeds or pollen tubes resulting from a controlled number of visits. Both honeybees and the smaller, native andrenids effectively pollinate Erythronium. The most common visitors to Claytonia, a specialist andrenid bee and a generalist bee-fly, Bombylius major, pollinate this species nearly equally well. Additional measurements of pollinator effectiveness and of visitation rates indicated that visitors with several floral hosts account for much of the pollination in the community and confirmed that most spring wildflowers are adequately pollinated. Competition for pollination through interspecific pollinator movements is likely but does not significantly depress seed-set. It may affect seed quality. Competition probably has little effect on species diversity or composition but may help maintain the distinctive characteristics of spring wildflowers: autogamy, extended receptivity, and pollination by various shared pollinators. These traits can be interpreted as adaptations to infrequent or inefficient pollination. The lack of well-defined examples of specialization or character displacement in the spring wildflower community represents a different response to potentially inadequate pollinator service than observed in most previously described communities dominated by bumblebees or hummingbirds.