FLORAL ECOLOGY OF PUYA CTENORHYNCHA (BROMELIACEAE) AN ENDEMIC PLANT OF BOLIVIA

Background: The terrestrial bromeliad Puya ctenorhyncha is a near-threatened endemic species that grows between 2,500-4,050 m asl. Hypotheses: Hummingbirds are the most important visitors of this plant given its morphological and floral traits. Study site: The study was carried out along the “Death Road”, located in the Yungas montane cloud forest, La Paz, Bolivia. Methods: We monitored an average of 216 individuals monthly for two years (2018-2019). Besides we conducted direct observations of focal plants to quantify the visits of animals. Results: The reproductive season lasted from April to August in the first year and from May to June in the second. The mean nectar volume was 8.09 ± 1.59 μL per flower and its composition included fructose, glucose, and 86 % of water. With 341 hours of observations, we determined that Coeligena torquata (Trochilidae) is the main visitor and putative pollinator, followed by C. violifer. Males of both species were more frequent visitors than females. Coeligena torquata showed the highest activity during the afternoon while C. violifer was more active in the morning. Conclusions: Floral phenology seems to be annual and unimodal. Although the main pollinators seem to be hummingbirds, the nectar concentration and composition is more similar to bromeliad species of other genera which are pollinated by bats or passerine birds. It is important to evaluate, in future studies, the dependence of both hummingbirds and their behavioural response towards the plant.