Use and pollination of a hawkmoth plant, Nicotiana attenuata, by migrant hummingbirds

摘要

Nicotiana attenuata, an herbaceous annual plant of disturbed sites in cold deserts Of Western North America, has traits that suggest adaptation for hawkmoth (Sphingidae, e.g., Hyles lineata or Manduca spp.) pollination, The tubular flowers are white and open fully at night and twilight, often closing by midday. Nectar is produced between dusk and clawn, and if not harvested is resorbed between clawn and midday. At our study site in northern Arizona, hawkmoths were absent or scarce during September and early October 1994, but migrating female and juvenile Selasphorus hummingbirds (rufous and broad-tailed hummingbirds) visited flowers regularly during morning or evening and briefly, defended territories centered on plants. Most of these hummingbirds disappeared from the patch at midday, We found only weak evidence that hummingbirds have acted as agents of,election on floral traits of N. attenuata. Nectar production was low (ca. 1.15 mul/floweright, containing 0.43 mg sugar) relative to most hummingbird flowers of the western United States. and although hummingbirds obtained a short-term profit from attenuata in the morning and early evening when nectar standing crop was high, most birds could not meet their daily energy requirements h foraging exclusively On its flowers. Hummingbird pollination had no impact on female Fitness of N. attenuata, because seed production was not affected 13 provision of self or outcross pollen. Hummingbirds may have affected plant fitness through pollen export. Our results demonstrate the opportunism of migrant hummingbirds and suggest the potential for evolution of floral traits to proceed from such an opportunistic use of a plant in the absence of its syndrome pollinator [References: 40]