Pollination ecology of the cactus Arrojadoa rhodantha in a seasonal hiper-xerophilous tropical forest

Abstract

Arrojadoa rhodantha is a widely distributed species in the Caatinga. Due to deforestation, however, their populations have suffered considerable reduction both in terms of distribution and abundance. We study the reproductive phenology, floral biology and pollination mechanism of A. rhodantha to provide information about the pollination ecology of this species. The study was conducted between August 2010 and July 2011, in a caatinga area, municipality of Petrolina, Permanbuco State, Brazil, with 15 individuals of A. rhodantha and a sampling effort of 35 h observing floral visitors. Stages of flowering and fruiting occurred throughout the year, with greater production of flowers and fruits in the rainy season. The flowers are magenta, opening at around 4:00 a.m. and closing at 11:00 p.m. They were visited by hummingbirds (3 species), bees (3), flies (1) and butterflies (1). Trigona spinipes, Friseomelitta doederleini and a Halictidae were the most common floral visitors (93.16% of total visits). The hummingbirds are considered potential pollinators of this cactus, but accounted for only 6.18% of total visits, and Eupetomena macroura was the most frequent species. Bees, flies and the butterflies Phoebis philea were classified as nectar/pollen thieves or pollen robbers. Arrojadoa rhodantha produced fruits only in natural conditions (55%) and by xenogamy (35.3%). Because of the continuous flowering and fruiting, this species can be considered as an important source of food for the fauna from the Caatinga, where there is seasonality in the availability of food sources.