Temporal Patterns of Nectar and Pollen Production in Aralia Hispida: Implications for Reproductive Success

Large plants of Aralia hispida present their pollen and nectar in hundreds of small flowers than open sequentially over 2—3 wk in a pattern of synchronized protandry that alternates male and female phases. The primary pollinators, bumble bees, are able to discover individual plants with elevated levels of either nectar or pollen, and to return to them more often than to less rewarding plants. Both pollen and nectar are presented gradually over time in such a way as to favor traplining behavior by the bees, with many, frequent visits. In controlled environments, lifetime sugar production per flower varies among plants, among umbel orders within plants and between male and female phases of bloom within umbel orders; there are further interactions among these sources of variation, which complicate any consideration of differential male—phase vs. female—phase nectar production. After draining, floral nectar is rapidly replenished, rendering umbels attractive to bees again within 15 min. Pollen production per flower and pollen grain size vary among umbel orders, increasing toward the end of bloom: grain size (but not production) varies among plants as well. Given the high visitation rate by bees, the gradual presentation of pollen should result in more efficient dispersal than simultaneous presentation would.