Successful sexual reproduction in flowering plants is determined by the quantity and quality of pollen available for pollination. Flower pollen donor interactions, in particular competition between genetically distinct pollen grains, have been shown to play an important role in plant population dynamics by determining genetic diversity and offspring performance. We measured the variation in conspecific pollen donor quantity and reproductive synchrony on individual reproductive success in the self-incompatible cactus Opuntia cantabrigiensis. We found that 1) increasing pollen donor quantity through hand pollination experiments significantly increased fruit and seed production in this species, 2) flowering is highly synchronous and may favor exogenous conspecific pollen flow. Our results indicate that reproductive success of self-incompatible species increases with pollen donor abundance and pollen flow between genetically distinct individuals, thus disruption of pollination services and/or reduced abundance of compatible reproductive individuals may lead to increased pollen limitation and reduced fecundity in a local plant system, together these factors may limit population recruitment and alter long-term population dynamics.