Columnar cacti can be pollinated by various insect and vertebrate species, often showing either close adaptations to a single pollinator group, or a mixed pollination syndrome, depending on a variety of different animals for pollination. As pollination data for columnar cacti in South America are scarce, we investigated the spectrum, frequency, and behavior of floral visitors in Echinopsis atacamensis subsp. pasacana. We compared two habitats with differences in mean annual precipitation and human impact, finding considerably higher activity and diversity of flower visitors in the population with higher humidity. Bees, wasps, and the giant hummingbird (Patagona gigas) were shown to visit cactus flowers during the day to gather nectar or pollen. We found marked differences in the spectrum of floral visitors between both populations. In one study site, the introduced honeybee Apis mellifera removed large quantities of pollen, but seemed to be a comparatively inefficient pollinator. Additionally, first evidence for visits by nocturnal hawkmoths is provided. These results demonstrate an unspecialized floral syndrome for Echinopsis atacamensis subsp. pasacana, with both diurnal and nocturnal pollinators. Such a mixed floral syndrome is fairly widespread among columnar cacti in the northern hemisphere but was hitherto only shown for one South American species, Weberbauerocereus weberbaueri.
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Vol. 2005 • No. 11