Pollen limitation and spatial variation of reproductive success in the insect-pollinated shrub Chuquiraga opposotifolia (Asteraceae) in the Chilian Andes

Abstract

Low temperatures, short growing seasons, and strong winds, which constrain the abundance and activity of insect pollinators, characterize alpine ecosystems. In northern hemisphere alpine environments, the reproductive output of several insect-pollinated plants has been reported to be pollen-limited. Using a supplemental hand-pollination experiment, we assessed the magnitude of pollen limitation (PL) in the obligate outcrossing insect-pollinated shrub Chuquiraga oppositifolia in the lower alpine scrub vegetation belt in the central Chilean Andes. We also assessed spatial variation in its reproductive success by comparing seed production among three additional sites. Hand-pollination resulted in a two- to three-fold increase in seed output above natural levels, thus demonstrating PL in this species. Nevertheless, percentage seed output remained low, increasing from 2.0 to 5.7%. Seed weight was reduced by 15% in hand-pollinated plants. Seed output was also low in the three additional site