Summary1. Plants that display many open flowers usually receive higher pollinator visitation rates, but it is unclear whether pollinators select plants to visit based on the size of floral display (apparent size) or the value of the floral rewards (reward size). To examine how pollinators respond to apparent size and reward size, we observed bumble bees foraging among arrays of artificial plants. 2. We constructed two kinds of artificial flower: (i) rewarding flowers that produced nectar constantly; and (ii) unrewarding flowers that produced only water. Thus, we could construct plants that varied both in numbers of flowers (apparent size) and in numbers of rewarding flowers (reward size). 3. At the beginning of the experiments, bees made more visits to the plants with the most flowers, irrespective of the rewards they contained. However, after several hours of foraging, bees returned selectively to plants with the greater number of rewarding flowers, irrespective of the number of flowers the plant presented. After we replaced rewarding plants with non-rewarding plants, bees continued visiting plants at formerlyprofitable locations for a while. 4. Our results demonstrate that bees initially showed preferences for plants with larger floral displays, but eventually bees were able to discriminate between rewarding and less-rewarding plants of equal display size by associating a plant's location with its reward size. Our results suggest that plants with many flowers can achieve higher visitation rates from pollinators in two ways: (i) by attracting inexperienced pollinators with large displays; and (ii) by encouraging experienced pollinators to return with the promise of greater rewards.

To explain the general tendency of large mothers to produce large offspring, we developed two models in which either the rate at which each single offspring extracts resources from the mother or the rate at which the mother supplies resources to all the offspring is limited (terminal- or upper-stream-limitation on resource transport, respectively). We also reanalyzed the data of Erythronium japonicum to test the models. The terminal-stream-limitation model predicted that the optimal offspring size that maximizes the fitness of the mother increases with an increase in the maximum rate of resource extraction by each single offspring. Thus, large mothers produce large offspring if the maximum resource extraction rate is high in those mothers. The upper-stream-limitation model predicted that the optimal offspring size decreases with an increase in the maximum rate of resource supply by the mother to all the offspring. In E. japonicum, the maximum growth rate of a seed was independent of the number of seeds of a plant, suggesting that the resource extraction rate is limited at the individual seed level. The maximum growth rate was high in large plants and had a strong positive effect on final seed mass. Thus, the results were consistent with the terminal-stream-limitation model.

Summary 1.Most pollination biologists have used the collective pollinator visits to a plant as the measure of its pollinator attraction. However, we know very little about how many returns by the same individuals compose these visits, and how far each visitor travels after leaving the plant. Such behavioural aspects of individual pollinators are essential to understand the patterns of pollen flow among plants. 2. We observed plant visits by tagged bumble bees Bombus diversus in a field population of Cirsium purpuratum. By dissecting the collective visitation data into visits made by individual foragers, we addressed how 'visitor density' (number of individuals that visited a plant per 2 h) and 'individual visitation rate' (number of visits made by each individual per 2 h) are related to floral display size (number of flowering heads on a plant) and local flower density (number of flowering heads on neighbouring plants). We also tracked individual bees to determine how display size and local flower density of a plant influences its relative position in a bee's foraging area. Plants attracted both regular visitors (bees that visited a plant more than three times per 2 h) and occasional visitors (bees that visited a plant fewer than four times per 2 h).Densities of both types of visitors increased with floral display size, whereas only occasional visitor's density increased with local flower density. 4. Individual bees preferred to visit central plants within their own foraging areas, plants with larger displays, and plants with lower local flower density. However, these preferences were independent from one another. Plants with large displays were not necessarily chosen by a bee as the centre of its own foraging area. On the other hand, plants with high local flower density were often located near the centre of a bee's foraging area. 5. The observed pollinator movements have implications for pollen flow in the plant population. Plants with larger displays probably experience greater mate diversity by attracting more occasional visitors, but they also assure matings with particular plants by increasing returns from regular visitors.

Summary 1.We analysed how male and female success affects the floral longevity in Erythronium japonicum . We found that flower senescence is advanced by deposition of pollen grains on the stigma but that there exists a minimum longevity (13·64 days in 1996 and 12·20 days in 1997) during which the flower never abscises, even if it is pollinated with a sufficient number of pollen grains. 2. We suggest that this floral longevity does not exist to benefit the female function, because the time needed for corolla abscission reacting to ovule fertilization was not so long and the female function was completed within about 3 days. 3. Flowers of E. japonicum do not react to pollen removal, as shown by the fact that anther removal experiments did not affect floral longevity. However, it would be advantageous to have some duration of longevity which benefits male success such that most of pollen grains can be expected to be exported. The duration needed to disperse most pollen grains of a flower was about 12 days, very close to the minimum floral longevity. 4. We conclude that a minimum longevity may exist for male functions and that floral longevity may be influenced differently by the male and the female functions of flowers.

No abstract