Plant fitness is reduced by pollen limitation when the amount and quality of pollen deposited on stigmas is restricted. Pollen limitation has direct implications in mating system and floral evolution, and negatively affects population dynamics. We assessed pollen limitation in the cactus Ariocarpus kotschoubeyanus from the western Chihuahuan Desert. We performed a supplementary pollen treatment then compared outcomes with naturally pollinated flowers using generalized linear models (GLM) and a pollen limitation index (L). Floral aperture was compared between days of anthesis using a single ANOVA, whereas nectar production was contrasted between covered/uncovered flowers and days of anthesis using a factorial ANOVA. Results of both GLM and L show that seed set proportion decreases 0.22 as a result of pollen limitation in natural pollinated flowers contrasted with pollen-supplemented flowers. Most flowers opened two days, and floral aperture between the first and second day varied slightly. Nectar volume was higher in covered flowers, showing that floral visitors consume this reward. However, high variances in nectar volumes obscured potential differences between treatments. Competition for pollinators among flowers as a result of its synchronous flowering and patchy distribution, as well as limited bee abundance generated by anthropogenic disturbance, are the more plausible causes of pollen limitation in A. kotschoubeyanus.
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Vol. 2016 • No. 22