For many species of conservation significance, multiple factors limit reproduction. This research examines the contributions of pollinator attraction, successful pollen receipt, and granivory as limiting factors to reproduction in the White Lady’s Slipper Orchid, Cypripedium candidum Muhl ex Willd. Cypripedium spp. typically require the presence of a suitable pollinator as the relatively complex floral anatomy prevents intra-flower selfing. In addition, C. candidum produces a variable number of single-flowered stems per plant. Increased floral display size can serve to attract additional pollinators at the expense of increased granivore attraction. Pollen limitation, granivory and reproductive trade-offs were examined in a field experiment in an unusually large population (n > 6000). Pairs of plants were matched by number of flowering stems (1-6) and either received supplemental hand or natural pollination (n=36). Capsule maturation, mass of seeds, and granivory rates were scored.
Results/Conclusions
Pollen supplementation significantly (p<0.0001) increased the percent of flowers setting mature fruit, with 87% fruit set for flowers receiving supplemental pollen compared to only 46% for those only receiving natural pollinator service. In a logistic regression of height, number of flowers and number of leaves, only height significantly explained (p<0.0089) variation in fruit set. Seed predation played a significant role in total seed set with 73% of the capsules produced being preyed upon. In initial analysis, no variables measured (height, number of flowers and leaf size) significantly explained granivory.