Nectar in hummingbird-pollinated neotropical plants I: Patterns of production and variability in 12 species

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 mul [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 the variation in nectar volume was explained by time of day. For a subset of four species (A. sinclairiana, Isertia, Palicourea, and Pentagonia), we studied variation among individuals in nectar volume. With time of day controlled, individual explained as much as 70 percent of the variation in nectar volume (A. sinclairiana) and as little as 20 percent (Pentagonia). We suggest that nectar volume likely has a genetic component in these species, but also that variation may itself be a trait, especially in Palicourea and Pentagonia. In three of the four species for which we had data from individuals, mean nectar volume and standard deviation were not correlated, suggesting that these traits may vary independently (Pentagonia was the exception with mean and standard deviation positively correlated). For two species (Isertia and Palicourea), we found evidence of seasonal variation in nectar production, with more nectar per flower produced early in the flowering season than later.