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We studied nectar characteristics in 12 species of Neotropical hummingbird-pollinated plants: Aphelandra golfodulcensis, A. sinclairiana, A. storkii, Justicia aurea (Acanthaceae); Heliconia irrasa, H. latispatha, H. mathiasii (Heliconiaceae); Pavonia dasypetala (Malvaceae); Isertia haenkeana, Palicourea guianense, Pentagonia macrophylla (Rubiaceae); and Renealmia cernua (Zingiberaceae). The diurnal patterns in sugar content and cumulative volume of nectar were documented in flowers that were protected from flower visitors. Sugar content in these species (mean of all flowers sampled per species ranged from 16 to 28%) was comparable to those reported for other hummingbird-pollinated species. Mean nectar volume per flower spanned an order of magnitude (i.e., 8.8 [Palicourea]–72.7 μl [H. latispatha]), indicating that hummingbirds visited flowers with a wide range of reward. We observed low intraspecific variation in sugar content but high variation in nectar volume. Among species, 10–50 percent of th...

We documented the diurnal pattern of nectar volumes in flowers of seven Neotropical hummingbird-pollinated plant species that were open to flower visitors and compared these standing crop data to nectar volumes in flowers protected from visitors. Standing crop of nectar bore little relationship to nectar in bagged flowers either in terms of volume or temporal pattern of availability. There was almost no nectar in open flowers except in those collected at dawn and those of Aphelandra sinclairiana; these were apparently too abundant to be depleted by visitors. Nectar volumes in open flowers were even more variable than in bagged flowers. We argue that understanding the evolution of plant– pollinator interactions requires understanding the relationship between nectar production and standing crop, as well as the impact of high variability on decisions by foraging animals. We conducted experiments to determine the effect of nectar removal on nectar production. Nectar removal via simulated legitimate v...

Counts of pollen grains on the stigmas of individual flowers of Trichanthera gigantea in Central Panama were related to seed set. At least eight grains were necessary for fruit set in this species and mean seed set per fruit was less than one (of a maximum of eight). Less than 50 percent of the flowers (108 of 277) received eight or more pollen grains and, of these, only 5 1 set fruit. These results suggest that pollination limits seed production by this species at this site.